Refrigeration device and container for transportation

Abstract

A refrigerant circuit (30) of a refrigeration apparatus (10) has a defrosting pipe (32) and a fourth expansion valve (EV4). The refrigeration apparatus (10) performs a defrosting operation to melt the frost on an inner heat exchanger (57). In the defrosting operation, a refrigerant discharged by a compressor (50) flows in the defrosting pipe (32), is then decompressed when passing through the fourth expansion valve (EV4), and then flows into the inner heat exchanger (57). A controller (90) controls the opening degree of the fourth expansion valve (EV4) based on one or both of the pressure and the temperature of the refrigerant discharged by the compressor (50) in the defrosting operation.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a refrigeration apparatus and a transportation container.BACKGROUND ART

[0002] Patent Document 1 discloses a heat pump device that performs a refrigeration cycle. The heat pump device includes a refrigerant circuit provided with a high-pressure-side defrosting circuit. The high-pressure-side defrosting circuit is a passage in which a refrigerant flows while bypassing a heat-dissipating heat exchanger and a decompression unit. In a defrosting operation to melt the frost on an atmospheric heat exchanger, the refrigerant discharged from a compressor is supplied to the atmospheric heat exchanger through the high-pressure-side defrosting circuit, and the frost on the atmospheric heat exchanger is warmed and melted by the refrigerant.

[0003] In the defrosting operation performed by the heat pump device of Patent Document 1, the refrigerant circulates between the compressor and the atmospheric heat exchanger through the high-pressure-side defrosting circuit. The defrosting operation is an operation to melt the frost on the atmospheric heat exchanger by using the heat applied to the refrigerant in the compressor.CITATION LISTPATENT DOCUMENT

[0004] Patent Document 1: Japanese Unexamined Patent Publication No. 2004-347185SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0005] In the defrosting operation performed by the heat pump device of Patent Document 1, the refrigerant discharged from the compressor flows into the atmospheric heat exchanger substantially without being decompressed. For this reason, the difference between the pressure of the refrigerant sucked into the compressor and the pressure of the refrigerant discharged by the compressor may decrease, and thus the amount of heat applied to the refrigerant by the compressor may decrease. If the amount of heat applied to the refrigerant by the compressor in the defrosting operation is small, the amount of heat used to melt the frost on the atmospheric heat exchanger is smaller, and thus the time to defrost may be longer.

[0006] An object of the present disclosure is to provide a refrigeration apparatus that performs a refrigeration cycle, where the time to defrost a heat exchanger is shorter.SOLUTION TO THE PROBLEM

[0007] A first aspect of the present disclosure is directed to a refrigeration apparatus (10) which includes a refrigerant circuit (30) having a compressor (50), a heat-source-side heat exchanger (56), an expansion valve (65), and a utilization-side heat exchanger (57), and which is configured to condition air in a target space (5), wherein the refrigerant circuit (30) has a bypass passage (32) configured to send a refrigerant discharged by the compressor (50) to the utilization-side heat exchanger (57) while bypassing the heat-source-side heat exchanger (56) and the expansion valve (65), and a decompression valve (EV4) of which an opening degree is variable and which is configured to decompress a refrigerant flowing in the bypass passage (32), the refrigeration apparatus (10) performs a cooling operation to perform a refrigeration cycle in which the heat-source-side heat exchanger (56) functions as a radiator and the utilization-side heat exchanger (57) functions as an evaporator, and to blow air cooled in the utilization-side heat exchanger (57) into the target space (5), and a defrosting operation to melt frost on the utilization-side heat exchanger (57) by supplying the refrigerant discharged by the compressor (50) to the utilization-side heat exchanger (57) through the bypass passage (32), and the refrigeration apparatus (10) includes a controller (90) configured to control the opening degree of the decompression valve (EV4) based on one or both of a pressure and a temperature of the refrigerant discharged by the compressor (50) in the defrosting operation.

[0008] In the first aspect, the refrigeration apparatus (10) performs the defrosting operation. During the defrosting operation, the controller (90) controls the opening degree of the decompression valve (EV4). In the defrosting operation, the refrigerant supplied to the utilization-side heat exchanger (57) through the bypass passage (32) is decompressed when passing through the decompression valve (EV4). Thus, the difference between the pressure of the refrigerant sucked by the compressor (50) (the suction pressure) and the pressure of the refrigerant discharged by the compressor (50) (the discharge pressure) is larger than when the refrigerant discharged by the compressor (50) is supplied to the utilization-side heat exchanger (57) without being decompressed. When the difference between the suction pressure and the discharge pressure is larger, the amount of heat applied to the refrigerant in the course of the compressor (50) compressing the refrigerant increases. Thus, according to this aspect, the amount of heat used to melt the frost on the utilization-side heat exchanger (57) is larger and the time to defrost the utilization-side heat exchanger (57) is shorter than when the refrigerant discharged by the compressor (50) is supplied to the utilization-side heat exchanger (57) without being decompressed.

[0009] A second aspect of the present disclosure is an embodiment of the first aspect. In the second aspect, the refrigerant circuit (30) has a receiver (62) disposed between the heat-source-side heat exchanger (56) and the utilization-side heat exchanger (57), and in the defrosting operation, the refrigeration apparatus (10) performs a normal operation to circulate a refrigerant between the compressor (50) and the utilization-side heat exchanger (57) in a state in which an inflow of a refrigerant to the receiver (62) and an outflow of a refrigerant from the receiver (62) are blocked, an outflow operation to allow a refrigerant to flow out from the receiver (62) to decrease an amount of refrigerant stored in the receiver (62), and an inflow operation to allow a refrigerant to flow into the receiver (62) to increase an amount of refrigerant stored in the receiver (62).

[0010] In the defrosting operation, the refrigeration apparatus (10) of the second aspect performs the normal operation, the outflow operation, and the inflow operation. The outflow operation and the inflow operation are operations to adjust the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) in the defrosting operation. In the outflow operation, the amount of refrigerant stored in the receiver (62) decreases, and the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) increases. In the inflow operation, the amount of refrigerant stored in the receiver (62) increases, and the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) decreases.

[0011] A third aspect of the present disclosure is an embodiment of the second aspect. In the third aspect, the refrigeration apparatus starts the outflow operation if a temperature of the refrigerant discharged by the compressor (50) becomes higher during the normal operation than a reference temperature.

[0012] If the temperature of the refrigerant discharged from the compressor (50) becomes higher during the normal operation, it is estimated that the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) is insufficient. Thus, the refrigeration apparatus (10) of the third aspect ends the normal operation and starts the outflow operation if the temperature of the refrigerant discharged from the compressor (50) becomes higher during the normal operation than the reference temperature.

[0013] A fourth aspect of the present disclosure is an embodiment of the second or third aspect. In the fourth aspect, the refrigeration apparatus starts the normal operation if a degree of superheat of a refrigerant having flowed out from the utilization-side heat exchanger (57) becomes lower during the outflow operation than a reference degree of superheat.

[0014] If the degree of superheat of the refrigerant having discharged from the utilization-side heat exchanger (57) becomes lower during the outflow operation, it is estimated that the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) is appropriate. Thus, the refrigeration apparatus (10) of the fourth aspect ends the outflow operation and starts the normal operation if the degree of superheat of the refrigerant having discharged from the utilization-side heat exchanger (57) becomes lower during the outflow operation than the reference degree of superheat.

[0015] A fifth aspect of the present disclosure is an embodiment of any one of the second to fourth aspects. In the fifth aspect, the outflow operation includes a gas outflow operation to allow a gas refrigerant to flow out from the receiver (62), and a liquid outflow operation to allow a liquid refrigerant to flow out from the receiver (62).

[0016] The refrigeration apparatus (10) of the fifth aspect performs the gas outflow operation or the liquid outflow operation as the outflow operation.

[0017] A sixth aspect of the present disclosure is an embodiment of any one of the second to fourth aspects. In the sixth aspect, in the outflow operation, a refrigerant having flowed out from the receiver (62) is sucked by the compressor (50).

[0018] In the outflow operation performed by the refrigeration apparatus (10) of the sixth aspect, the refrigerant having discharged from the receiver (62) is sucked by the compressor (50). As a result, the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) in the defrosting operation increases.

[0019] A seventh aspect of the present disclosure is an embodiment of the sixth aspect. In the seventh aspect, the outflow operation includes a first outflow operation in which the compressor (50) sucks a refrigerant from both the receiver (62) and the utilization-side heat exchanger (57), and a second outflow operation in which the compressor (50) sucks a refrigerant from the receiver (62) and does not suck a refrigerant from the utilization-side heat exchanger (57).

[0020] The refrigeration apparatus (10) of the seventh aspect performs the first outflow operation or the second outflow operation as the outflow operation. In the first outflow operation, the compressor (50) sucks the refrigerant having flowed out from the receiver (62) and the refrigerant having flowed out from the utilization-side heat exchanger (57). In the second outflow operation, the compressor (50) sucks the refrigerant having flowed out from the receiver (62) and does not suck the refrigerant having flowed out from the utilization-side heat exchanger (57).

[0021] An eighth aspect of the present disclosure is an embodiment of any one of the second to seventh aspects. In the eighth aspect, the refrigeration apparatus starts the inflow operation if a pressure of the refrigerant discharged from the compressor (50) becomes higher during the normal operation than a reference pressure.

[0022] If the pressure of the refrigerant discharged from the compressor (50) becomes higher during the normal operation, it is estimated that the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) is excessive. Thus, the refrigeration apparatus (10) of the eighth aspect ends the normal operation and starts the inflow operation if the pressure of the refrigerant discharged from the compressor (50) becomes higher during the normal operation than the reference pressure.

[0023] A ninth aspect of the present disclosure is an embodiment of any one of the second to eighth aspects. In the ninth aspect, in the inflow operation, part of the refrigerant discharged from the compressor (50) flows into the receiver (62) through the heat-source-side heat exchanger (56), and a rest of the refrigerant discharged from the compressor (50) is supplied to the utilization-side heat exchanger (57) through the bypass passage (32).

[0024] In the inflow operation performed by the refrigeration apparatus (10) of the ninth aspect, part of the refrigerant discharged from the compressor (50) flows into the receiver (62), and the amount of refrigerant stored in the receiver (62) increases. Further, in the inflow operation, the rest of the refrigerant discharged from the compressor (50) is supplied to the utilization-side heat exchanger (57) through the bypass passage (32), and the frost on the utilization-side heat exchanger (57) is melted.

[0025] A tenth aspect of the present disclosure is an embodiment of any one of the first to ninth aspects. In the tenth aspect, the refrigerant circuit (30) has a path changing mechanism (67) that changes a flow path of a refrigerant in the refrigerant circuit (30), and the controller (90) controls the path changing mechanism (67) to switch between the cooling operation and the defrosting operation.

[0026] In the tenth aspect, the controller (90) controls the path changing mechanism (67). The path changing mechanism (67) changes the flow path of a refrigerant to switch between the cooling operation and the defrosting operation.

[0027] An eleventh aspect of the present disclosure is an embodiment of any one of the second to ninth aspects. In the eleventh aspect, the refrigerant circuit (30) has a path changing mechanism (67) that changes a flow path of a refrigerant in the refrigerant circuit (30), and the controller (90) controls the path changing mechanism (67) to switch between the cooling operation and the defrosting operation, and also to switch between the normal operation, the outflow operation, and the inflow operation in the defrosting operation.

[0028] In the eleventh aspect, the controller (90) controls the path changing mechanism (67). The path changing mechanism (67) changes the flow path of a refrigerant to switch between the cooling operation and the defrosting operation. Further, the path changing mechanism (67) changes the flow path of a refrigerant during the defrosting operation to switch between the normal operation, the outflow operation, and the inflow operation.

[0029] A twelfth aspect of the present disclosure is an embodiment of the tenth or eleventh aspect. In the twelfth aspect, the path changing mechanism (67) has a plurality of control valves controlled by the controller (90).

[0030] In the twelfth aspect, the controller (90) controls the plurality of control valves of the path changing mechanism (67).

[0031] A thirteenth aspect of the present disclosure is an embodiment of any one of the first to twelfth aspects. In the thirteenth aspect, the decompression valve includes a first decompression valve (EV4-1) and a second decompression valve (EV4-2) which are connected in parallel.

[0032] In the bypass passage (32) of the refrigeration apparatus (10) of the thirteenth aspect, the first decompression valve (EV4-1) and the second decompression valve (EV4-2) are connected in parallel.

[0033] A fourteenth aspect of the present disclosure is an embodiment of any one of the first to thirteenth aspects. In the fourteenth aspect, the refrigeration apparatus performs a heating operation to supply the refrigerant discharged by the compressor (50) to the utilization-side heat exchanger (57) through the bypass passage (32) and to blow the air heated in the utilization-side heat exchanger (57) into the target space (5).

[0034] In the fourteenth aspect, the refrigeration apparatus (10) performs the heating operation. In the heating operation, the refrigerant discharged by the compressor (50) is supplied to the utilization-side heat exchanger (57) through the bypass passage (32), and exchanges heat with the air passing through the utilization-side heat exchanger (57). The air heated in the utilization-side heat exchanger (57) is blown into the target space (5).

[0035] A fifteenth aspect of the present disclosure is an embodiment of any one of the first to fourteenth aspects. In the fifteenth aspect, the refrigerant circuit (30) has a reheating heat exchanger (58) disposed upstream of the decompression valve (EV4) in the bypass passage (32) and configured to exchange heat between air having passed through the utilization-side heat exchanger (57) and a refrigerant.

[0036] In the fifteenth aspect, the refrigerant circuit (30) is provided with the reheating heat exchanger (58). The reheating heat exchanger (58) exchanges heat between the refrigerant supplied through the bypass passage (32) and the air having passed through the utilization-side heat exchanger (57). The refrigerant having passed through the reheating heat exchanger (58) is sent to the utilization-side heat exchanger (57) after passing through the decompression valve (EV4).

[0037] A sixteenth aspect of the present disclosure is an embodiment of any one of the first to fifteenth aspects. In the sixteenth aspect, the refrigerant circuit (30) is filled with carbon dioxide as a refrigerant.

[0038] The refrigerant circuit (30) of the sixteenth aspect circulates carbon dioxide as the refrigerant to perform the refrigeration cycle.

[0039] A seventeenth aspect of the present disclosure is directed to a transportation container (1) including: the refrigeration apparatus (10) of any one of the first to sixteenth aspects, and a container body (2) forming the target space (5) in which the air is conditioned by the refrigeration apparatus (10).

[0040] The transportation container (1) of the seventeenth aspect includes the refrigeration apparatus (10) and the container body (2). The container body (2) forms the target space (5). The refrigeration apparatus (10) conditions the air in the target space (5).BRIEF DESCRIPTION OF THE DRAWINGS

[0041] [FIG. 1] FIG. 1 is a schematic perspective view of a refrigeration apparatus of a first embodiment. [FIG. 2] FIG. 2 is a schematic sectional view of a transportation container of the first embodiment. [FIG. 3] FIG. 3 is a piping diagram which shows the configuration of the refrigeration apparatus of the first embodiment. [FIG. 4] FIG. 4 is a block diagram which shows the configuration of a controller of the first embodiment. [FIG. 5] FIG. 5 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in a cooling operation. [FIG. 6] FIG. 6 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in a dehumidifying operation. [FIG. 7] FIG. 7 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in a heating operation and a normal operation of a defrosting operation. [FIG. 8] FIG. 8 is a Mollier diagram (a pressure-enthalpy diagram) which shows the change in the state of a refrigerant in a refrigerant circuit during the defrosting operation. [FIG. 9] FIG. 9 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in an inflow operation. [FIG. 10] FIG. 10 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in a gas outflow operation of a first outflow operation. [FIG. 11] FIG. 11 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in a liquid outflow operation of the first outflow operation. [FIG. 12] FIG. 12 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in a gas outflow operation of a second outflow operation. [FIG. 13] FIG. 13 is a state transition diagram which shows operation of a controller in the defrosting operation. [FIG. 14] FIG. 14 is a piping diagram which shows the configuration of a refrigeration apparatus of a second embodiment. [FIG. 15] FIG. 15 is a piping diagram which shows the configuration of a refrigeration apparatus of a third embodiment. [FIG. 16] FIG. 16 is a flowchart which shows operation performed by a controller during a defrosting operation of a refrigeration apparatus of a fourth embodiment. [FIG. 17] FIG. 17 is a piping diagram which shows the configuration of a refrigeration apparatus of a first variation of other embodiments. [FIG. 18] FIG. 18 is a piping diagram which shows the configuration of a refrigeration apparatus of a second variation of the other embodiments. DESCRIPTION OF EMBODIMENTS<<First Embodiment>>

[0042] The first embodiment will be described. This embodiment is a transportation container (1) including a refrigeration apparatus (10).-Transportation Container-

[0043] As shown in FIG. 1, the transportation container (1) includes a container body (2) and the refrigeration apparatus (10). The transportation container (1) is a reefer container capable of controlling a temperature in the container.

[0044] The transportation container (1) of this embodiment is used mainly for marine transportation. The transportation container (1) is loaded onto a ship or the like and transported. Usage of the transportation container (1) is not limited to marine transportation. The transportation container (1) may be used for land transportation. In this case, the transportation container (1) is transported by an automobile such as a truck or by rail.-Container Body-

[0045] As shown in FIG. 2, the container body (2) is formed in a hollow box shape. The container body (2) is horizontally long. The container body (2) has an opening at one end in the longitudinal direction. The opening of the container body (2) is blocked by the refrigeration apparatus (10). The container body (2) forms an internal space (5) for housing cargos. The internal space (5) is a target space in which the air is conditioned by the refrigeration apparatus.-Refrigeration Apparatus-

[0046] As shown in FIG. 2, the refrigeration apparatus (10) is attached to the opening of the container body (2). The refrigeration apparatus (10) of this embodiment is a refrigeration apparatus for transportation. The refrigeration apparatus (10) includes a casing (11), a refrigerant circuit (30), and a controller (80). The refrigeration apparatus (10) adjusts the temperature of the air (the inside air) in the internal space (5).<Casing>

[0047] The casing (11) includes a division wall (12) and a partition plate (15).

[0048] An internal flow path (20) is formed inside the division wall (12). An external chamber (23) is formed outside the division wall (12). The internal flow path (20) and the external chamber (23) are partitioned by the division wall (12).

[0049] The division wall (12) includes an external wall (13) and an internal wall (14). The external wall (13) is located outside the container body (2). The internal wall (14) is located inside the container body (2).

[0050] The external wall (13) closes the opening of the container body (2). The external wall (13) is attached to a peripheral edge portion of the opening of the container body (2). A lower part of the external wall (13) bulges toward the inside of the container body (2). The external chamber (23) is formed by the lower part of the external wall (13).

[0051] The internal wall (14) faces the external wall (13). The internal wall (14) has a shape conforming to the external wall (13). The internal wall (14) is spaced apart from the external wall (13). A thermal insulator (16) is provided between the internal wall (14) and the external wall (13).

[0052] The partition plate (15) is disposed further inward of the container body (2) than the internal wall (14). The internal flow path (20) is formed between the division wall (12) and the partition plate (15). An air inlet port (21) is formed between the upper end of the partition plate (15) and a top panel of the container body (2). An air outlet port (22) is formed between the lower end of the partition plate (15) and the lower end of the division wall (12). The internal flow path (20) is formed from the air inlet port (21) to the air outlet port (22).<Refrigerant Circuit>

[0053] The refrigerant circuit (30) is a closed circuit filled with a refrigerant. The refrigerant circuit (30) circulates a refrigerant to perform a vapor compression refrigeration cycle. The refrigerant circuit (30) includes an outer heat exchanger (56), an inner heat exchanger (57), and a reheating heat exchanger (58). The refrigerant circuit (30) will be described in detail later.

[0054] Each of the outer heat exchanger (56), the inner heat exchanger (57), and the reheating heat exchanger (58) is a fin-and-tube heat exchanger that exchanges heat between a refrigerant and air.

[0055] The outer heat exchanger (56) is disposed in an upper part of the external chamber (23). The outer heat exchanger (56) is a heat-source-side heat exchanger that exchanges heat between a refrigerant and outside air. The outer heat exchanger (56) has a generally rectangular tubular shape.

[0056] The inner heat exchanger (57) is disposed in the internal flow path (20). The inner heat exchanger (57) is a utilization-side heat exchanger that exchanges heat between a refrigerant and inside air.

[0057] The reheating heat exchanger (58) is disposed downstream of the inner heat exchanger (57) in the internal flow path (20). The reheating heat exchanger (58) is a heat exchanger that exchanges heat between a refrigerant and inside air.

[0058] Although not shown, a drain pan is provided below the inner heat exchanger (57). The drain pan receives drain water generated in the inner heat exchanger (57). The drain water having dropped into the drain pan is discharged to the outside of the container.<External Fan>

[0059] The refrigeration apparatus (10) includes an external fan (26). The external fan (26) is a propeller fan. The external fan (26) is disposed in the external chamber (23). The external fan (26) is disposed inside the outer heat exchanger (56) having a tubular shape. The external fan (26) sends the outside air to the outer heat exchanger (56).<Internal Fan>

[0060] The refrigeration apparatus (10) includes an internal fan (27). The internal fan (27) is a propeller fan. The internal fan (27) is disposed in the internal flow path (20). The internal fan (27) is disposed above the inner heat exchanger (57). The internal fan (27) sends the inside air to the inner heat exchanger (57).<Sensor>

[0061] The refrigeration apparatus (10) includes a first air temperature sensor (86), a second air temperature sensor (87), and a humidity sensor (88).

[0062] The first air temperature sensor (86) is disposed upstream of the internal fan (27) in the internal flow path (20). The first air temperature sensor (86) measures the temperature of the air having flowed into the internal flow path (20) through the air inlet port (21).

[0063] The second air temperature sensor (87) and the humidity sensor (88) are disposed downstream of the reheating heat exchanger (58) in the internal flow path (20). The second air temperature sensor (87) measures the temperature of the air having passed through the reheating heat exchanger (58). The humidity sensor (88) measures the relative humidity of the air having passed through the reheating heat exchanger (58).<Electric Component Box>

[0064] As shown in FIG. 1, the refrigeration apparatus (10) includes an electric component box (28). The electric component box (28) is disposed in an upper part in the external chamber (23). The electric component box (28) houses electric components such as an inverter board and a control board.-Refrigerant Circuit-

[0065] As shown in FIG. 3, the refrigerant circuit (30) is a closed circuit filled with a refrigerant. The refrigerant in the refrigerant circuit (30) of this embodiment is carbon dioxide.

[0066] The refrigerant circuit (30) includes a main circuit (31), a defrosting pipe (32), and a reheating pipe (33). The refrigerant circuit (30) includes a gas-side connection pipe (41), a liquid-side connection pipe (42), an intermediate connection pipe (43), a low-stage connection pipe (44), and a high-stage connection pipe (45).<Main Circuit>

[0067] The main circuit (31) includes a low-stage compressor (51), a high-stage compressor (52), the outer heat exchanger (56), a receiver (62), and the inner heat exchanger (57). In the main circuit (31), the low-stage compressor (51), the high-stage compressor (52), the outer heat exchanger (56), the receiver (62), and the inner heat exchanger (57) are connected in sequence through pipes.

[0068] A discharge pipe of the low-stage compressor (51) is connected to a suction pipe of the high-stage compressor (52). A pipe that connects the discharge pipe of the low-stage compressor (51) and the suction pipe of the high-stage compressor (52) is provided with a first check valve (CV1) and a first electric valve (MV1). The first electric valve (MV1) is disposed downstream of the first check valve (CV1). The first check valve (CV1) allows a refrigerant to flow in the direction in which a refrigerant flows out from the low-stage compressor (51), and prevents a refrigerant from flowing in the opposite direction.

[0069] A discharge pipe of the high-stage compressor (52) is connected to one end of the outer heat exchanger (56). A pipe that connects the discharge pipe of the high-stage compressor (52) and one end of the outer heat exchanger (56) is provided with a second check valve (CV2) and a second electric valve (MV2). The second electric valve (MV2) is disposed downstream of the second check valve (CV2). The second check valve (CV2) allows a refrigerant to flow in the direction in which a refrigerant flows out from the high-stage compressor (52), and prevents a refrigerant from flowing in the opposite direction.

[0070] The other end of the outer heat exchanger (56) is connected to an inflow port of the receiver (62). A pipe that connects the other end of the outer heat exchanger (56) and the inflow port of the receiver (62) is provided with a first flow path (61a) of an internal heat exchanger (61) and a first expansion valve (EV1). The first expansion valve (EV1) is disposed downstream of the internal heat exchanger (61).

[0071] A liquid outflow port of the receiver (62) is connected to one end of the inner heat exchanger (57). A pipe that connects the liquid outflow port of the receiver (62) and one end of the inner heat exchanger (57) is provided with a first electromagnetic valve (SV1) and a second expansion valve (EV2). The second expansion valve (EV2) is disposed downstream of the first electromagnetic valve (SV1).

[0072] The other end of the inner heat exchanger (57) is connected to a suction pipe of the low-stage compressor (51).

[0073] In the main circuit (31), the first expansion valve (EV1) is disposed upstream of the receiver (62), and the second expansion valve (EV2) is disposed downstream of the receiver (62). The first expansion valve (EV1) and the second expansion valve (EV2) are the expansion valves (65) of the refrigerant circuit (30).<Gas-Side Connection Pipe>

[0074] One end of the gas-side connection pipe (41) is connected to a gas outflow port of the receiver (62). The other end of the gas-side connection pipe (41) is connected to one end of the intermediate connection pipe (43). The gas-side connection pipe (41) is provided with a second electromagnetic valve (SV2) and a second flow path (61b) of the internal heat exchanger (61). The second flow path (61b) of the internal heat exchanger (61) is disposed downstream of the second electromagnetic valve (SV2).<Liquid-Side Connection Pipe>

[0075] One end of the liquid-side connection pipe (42) is connected to part of the main circuit (31) that is between the first electromagnetic valve (SV1) and the second expansion valve (EV2). The other end of the liquid-side connection pipe (42) is connected to one end of the intermediate connection pipe (43). The liquid-side connection pipe (42) is provided with a third expansion valve (EV3).<Intermediate Connection Pipe>

[0076] As described above, one end of the intermediate connection pipe (43) is connected with the other end of the gas-side connection pipe (41) and the other end of the liquid-side connection pipe (42). The other end of the intermediate connection pipe (43) is connected to part of the main circuit (31) that is between the first electric valve (MV1) and the high-stage compressor (52). The intermediate connection pipe (43) is provided with a third check valve (CV3). The third check valve (CV3) allows a refrigerant to flow from one end to the other end of the intermediate connection pipe (43), and prevents a refrigerant from flowing in the opposite direction.<Low-Stage Connection Pipe>

[0077] The low-stage connection pipe (44) is a pipe that allows a refrigerant to flow while bypassing the low-stage compressor (51). One end of the low-stage connection pipe (44) is connected to part of the main circuit (31) that is between the suction pipe of the low-stage compressor (51) and the inner heat exchanger (57). The other end of the low-stage connection pipe (44) is connected to part of the main circuit (31) that is between the first check valve (CV1) and the first electric valve (MV1). The low-stage connection pipe (44) is provided with a fourth check valve (CV4). The fourth check valve (CV4) allows a refrigerant to flow from one end to the other end of the low-stage connection pipe (44), and prevents a refrigerant from flowing in the opposite direction.<High-Stage Connection Pipe>

[0078] The high-stage connection pipe (45) is a pipe that allows a refrigerant to flow while bypassing the high-stage compressor (52). One end of the high-stage connection pipe (45) is connected to part of the main circuit (31) that is between the first check valve (CV1) and the first electric valve (MV1). The other end of the high-stage connection pipe (45) is connected to part of the main circuit (31) that is between the second check valve (CV2) and the second electric valve (MV2). The high-stage connection pipe (45) is provided with a fifth check valve (CV5). The fifth check valve (CV5) allows a refrigerant to flow from one end to the other end of the high-stage connection pipe (45), and prevents a refrigerant from flowing in the opposite direction.<Defrosting Pipe>

[0079] One end of the defrosting pipe (32) is connected to part of the main circuit (31) that is between the second check valve (CV2) and the second electric valve (MV2). In the main circuit (31), one end of the defrosting pipe (32) is located downstream of the other end of the high-stage connection pipe (45). The other end of the defrosting pipe (32) is connected to part of the main circuit (31) that is between the second expansion valve (EV2) and the inner heat exchanger (57). The defrosting pipe (32) forms a bypass passage that sends the refrigerant discharged by the high-stage compressor (52) to the inner heat exchanger (57) while bypassing the outer heat exchanger (56), the first expansion valve (EV1), and the second expansion valve (EV2).

[0080] The defrosting pipe (32) is provided with a fourth expansion valve (EV4). The fourth expansion valve (EV4) is a decompression valve of which the opening degree is variable and which decompresses the refrigerant flowing in the defrosting pipe (32).<Reheating Pipe>

[0081] One end of the reheating pipe (33) is connected to part of the main circuit (31) that is between the second check valve (CV2) and the second electric valve (MV2). In the main circuit (31), one end of the reheating pipe (33) is located downstream of the other end of the high-stage connection pipe (45). The other end of the reheating pipe (33) is connected to part of the main circuit (31) that is between the second expansion valve (EV2) and the inner heat exchanger (57).

[0082] The reheating pipe (33) is provided with a third electromagnetic valve (SV3), the reheating heat exchanger (58), and a fifth expansion valve (EV5). The reheating heat exchanger (58) is disposed downstream of the third electromagnetic valve (SV3). The fifth expansion valve (EV5) is disposed downstream of the reheating heat exchanger (58).<Expansion Valve>

[0083] Each of the first expansion valve (EV1), the second expansion valve (EV2), the third expansion valve (EV3), the fourth expansion valve (EV4), and the fifth expansion valve (EV5) is a so-called electronic expansion valve. Each of the expansion valves (EV1 to EV5) includes a valve body and a stepping motor that drives the valve body. When the valve body is moved by the stepping motor, the opening degree of the expansion valve (EV1 to EV5) changes continuously.<Electric Valve>

[0084] Each of the first electric valve (MV1) and the second electric valve (MV2) is a valve of which the opening degree is variable. Each of the electric valves (MV1, MV2) includes a valve body and a stepping motor that drives the valve body. When the valve body is moved by the stepping motor, the opening degree of the electric valve (MV1, MV2) changes continuously.<Electromagnetic Valve>

[0085] Each of the first electromagnetic valve (SV1), the second electromagnetic valve (SV2), and the third electromagnetic valve (SV3) is an on-off valve. Each of the electromagnetic valves (SV1 to SV3) includes a valve body and a solenoid that drives the valve body. When the valve body is moved by the solenoid, the electromagnetic valve (SV1 to SV3) is turned on or off.<Path Changing Mechanism>

[0086] The second expansion valve (EV2), the third expansion valve (EV3), the fourth expansion valve (EV4), the second electric valve (MV2), the first electromagnetic valve (SV1), the second electromagnetic valve (SV2), and the third electromagnetic valve (SV3) form a path changing mechanism (67). The path changing mechanism (67) is a mechanism that changes the flow path of a refrigerant in the refrigerant circuit (30).

[0087] The second expansion valve (EV2), the third expansion valve (EV3), the fourth expansion valve (EV4), the second electric valve (MV2), the first electromagnetic valve (SV1), the second electromagnetic valve (SV2), and the third electromagnetic valve (SV3) that form the path changing mechanism (67) are the control valves controlled by a controller (90). When the state of one or more of these valves that form the path changing mechanism (67) is changed by the controller (90), the flow path of a refrigerant in the refrigerant circuit (30) changes, and as a result, the operating state of the refrigeration apparatus (10) changes.<Low-Stage Compressor and High-Stage Compressor>

[0088] Each of the low-stage compressor (51) and the high-stage compressor (52) is a hermetic scroll compressor. Although not shown, each of the low-stage compressor (51) and the high-stage compressor (52) includes a compression mechanism, an electric motor that drives the compression mechanism, and a casing that houses the compression mechanism and the electric motor. The compression mechanism is a scroll type fluid machine, and sucks and compresses a refrigerant.

[0089] The suction pipe of the low-stage compressor (51) is provided with an accumulator (51a). The suction pipe of the high-stage compressor (52) is provided with an accumulator (52a). Each of the low-stage compressor (51) and the high-stage compressor (52) compresses the refrigerant sucked from the suction pipe, and discharges the compressed refrigerant from the discharge pipe. The low-stage compressor (51) and the high-stage compressor (52) are the compressors (50) provided in the refrigerant circuit (30).

[0090] Each of the low-stage compressor (51) and the high-stage compressor (52) is not limited to a scroll compressor. Each of the low-stage compressor (51) and the high-stage compressor (52) may be, for example, a rotary compressor or may be a reciprocating compressor.<Outer Heat Exchanger and Inner Heat Exchanger>

[0091] As described above, each of the outer heat exchanger (56), the inner heat exchanger (57), and the reheating heat exchanger (58) is a fin-and-tube heat exchanger that exchanges heat between a refrigerant and air. The outer heat exchanger (56) exchanges heat between a refrigerant and outside air (external air). Each of the inner heat exchanger (57) and the reheating heat exchanger (58) exchanges heat between a refrigerant and inside air.<Internal Heat Exchanger>

[0092] The internal heat exchanger (61) is a heat exchanger that exchanges heat between a refrigerant and a refrigerant. The internal heat exchanger (61) of this embodiment is a plate-type heat exchanger. The internal heat exchanger (61) has the first flow path (61a) and the second flow path (61b). The first flow path (61a) of the internal heat exchanger (61) is disposed in part of the main circuit (31) that is between the outer heat exchanger (56) and the first expansion valve (EV1). The second flow path (61b) of the internal heat exchanger (61) is disposed downstream of the second electromagnetic valve (SV2) in the gas-side connection pipe (41). The internal heat exchanger (61) exchanges heat between the refrigerant flowing in the first flow path (61a) and the refrigerant flowing in the second flow path (61b).<Receiver>

[0093] The receiver (62) is a container member that stores a refrigerant. The receiver (62) also functions as a gas-liquid separator. The receiver (62) separates the refrigerant in a gas-liquid two-phase state having flowed from the inflow port into a liquid refrigerant and a gas refrigerant. In the receiver (62), the liquid refrigerant is accumulated in a lower part in the receiver (62), and then flows out through the liquid outflow port formed in a bottom part of the receiver (62). In the receiver (62), the gas refrigerant is accumulated in an upper part in the receiver (62), and then flows out through the gas outflow port formed in an upper part of the receiver (62).<Sensors for Low-Stage Compressor>

[0094] In the main circuit (31), a pipe connected to the suction pipe of the low-stage compressor (51) is provided with a low-stage suction temperature sensor (70) and a low-stage suction pressure sensor (75). The low-stage suction temperature sensor (70) measures the temperature of the refrigerant sucked by the low-stage compressor (51). The low-stage suction pressure sensor (75) measures the pressure of the refrigerant sucked by the low-stage compressor (51).

[0095] In the main circuit (31), a pipe between the discharge pipe of the low-stage compressor (51) and the first check valve (CV1) is provided with a low-stage discharge temperature sensor (71) and a low-stage discharge pressure sensor (76). The low-stage discharge temperature sensor (71) measures the temperature of the refrigerant discharged by the low-stage compressor (51). The low-stage discharge pressure sensor (76) measures the pressure of the refrigerant discharged by the low-stage compressor (51).<Sensors for High-Stage Compressor>

[0096] In the main circuit (31), a pipe between the suction pipe of the high-stage compressor (52) and the first electric valve (MV1) is provided with a high-stage suction temperature sensor (72) and a high-stage suction pressure sensor (77). The high-stage suction temperature sensor (72) measures the temperature of the refrigerant sucked by the high-stage compressor (52). The high-stage suction pressure sensor (77) measures the pressure of the refrigerant sucked by the high-stage compressor (52).

[0097] In the main circuit (31), a pipe between the discharge pipe of the high-stage compressor (52) and the second check valve (CV2) is provided with a high-stage discharge temperature sensor (73) and a high-stage discharge pressure sensor (78). The high-stage discharge temperature sensor (73) measures the temperature of the refrigerant discharged by the high-stage compressor (52). The high-stage discharge pressure sensor (78) measures the pressure of the refrigerant discharged by the high-stage compressor (52).<Other Sensors>

[0098] The refrigerant circuit (30) is provided with a receiver pressure sensor (79), first to fourth refrigerant temperature sensors (81 to 84), and a heat exchanger temperature sensor (85).

[0099] The receiver pressure sensor (79) is connected to part of the gas-side connection pipe (41) that is between the receiver (62) and the second electromagnetic valve (SV2). The receiver pressure sensor (79) measures the pressure of the refrigerant stored in the receiver (62).

[0100] The first refrigerant temperature sensor (81) is provided in a pipe of the main circuit (31) that is between the outer heat exchanger (56) and the internal heat exchanger (61). The first refrigerant temperature sensor (81) measures the temperature of the refrigerant flowing into the first flow path (61a) of the internal heat exchanger (61).

[0101] The second refrigerant temperature sensor (82) is provided in a pipe of the main circuit (31) that is between the receiver (62) and the first electromagnetic valve (SV1). The second refrigerant temperature sensor (82) measures the temperature of the refrigerant having flowed out from the liquid outflow port of the receiver (62).

[0102] The third refrigerant temperature sensor (83) is provided in a pipe of the main circuit (31) that is between the second expansion valve (EV2) and the inner heat exchanger (57). The third refrigerant temperature sensor (83) is disposed near one end of the inner heat exchanger (57). The third refrigerant temperature sensor (83) measures the temperature of the refrigerant at the inlet of the inner heat exchanger (57).

[0103] The fourth refrigerant temperature sensor (84) is provided in a pipe of the main circuit (31) that is between the inner heat exchanger (57) and the low-stage compressor (51). The fourth refrigerant temperature sensor (84) is disposed near the other end of the inner heat exchanger (57). The fourth refrigerant temperature sensor (84) measures the temperature of the refrigerant at the outlet of the inner heat exchanger (57).

[0104] The heat exchanger temperature sensor (85) is attached to the inner heat exchanger (57). The heat exchanger temperature sensor (85) measures the temperature of the inner heat exchanger (57).-Controller-

[0105] As shown in FIG. 4, the controller (90) includes a microcomputer (91) and a memory device (92). The memory device (92) is a semiconductor memory. The memory device (92) stores software for operating the microcomputer (91). The controller (90) is housed in the electric component box (28).

[0106] The controller (90) receives measurement values of the sensors provided in the refrigeration apparatus (10). The controller (90) controls the devices provided in the refrigeration apparatus (10) based on the received measurement values of the sensors. For example, the controller (90) controls the rotational speed of the low-stage compressor (51), the rotational speed of the high-stage compressor (52), the opening degrees of the first to fifth expansion valves (EV1 to EV5), the opening degrees of the first and second electric valves (MV1, MV2), the rotational speed of the external fan (26), the rotational speed of the internal fan (27), and the like.-Operation of Refrigeration Apparatus-

[0107] The operation of the refrigeration apparatus (10) will be described. The refrigeration apparatus (10) performs a cooling operation, a dehumidifying operation, a heating operation, and a defrosting operation. Switching between the cooling operation, the dehumidifying operation, the heating operation, and the defrosting operation is performed by the controller (90) controlling the plurality of valves that form the path changing mechanism (67).<Cooling Operation>

[0108] The cooling operation is an operation to cool the inside air. In the cooling operation, the refrigeration apparatus (10) blows the air cooled in the inner heat exchanger (57) into the internal space (5).

[0109] When the refrigeration apparatus (10) performs the cooling operation, the refrigerant circuit (30) performs a refrigeration cycle. In the cooling operation, the refrigerant circulates in the main circuit (31) of the refrigerant circuit (30), the outer heat exchanger (56) functions as a radiator, and the inner heat exchanger (57) functions as an evaporator. The inner heat exchanger (57) cools the air flowing in the internal flow path (20). In the cooling operation, the refrigerant flows in the gas-side connection pipe (41) and the intermediate connection pipe (43).

[0110] When the refrigeration apparatus (10) performs the cooling operation, the controller (90) operates the external fan (26) and the internal fan (27). In the transportation container (1), the air circulates between the internal flow path (20) of the refrigeration apparatus (10) and the internal space (5) of the container body (2). The inside air of the internal space (5) flows into the internal flow path (20) through the air inlet port (21). The inside air flowing in the internal flow path (20) is cooled by the inner heat exchanger (57). The inside air cooled by the inner heat exchanger (57) is supplied to the internal space (5) through the air outlet port (22).

[0111] In the cooling operation, the controller (90) controls the rotational speeds of the low-stage compressor (51) and the high-stage compressor (52) and the like so that the temperature of the air blown into the internal space (5) through the air outlet port (22) (specifically, the measurement value of the second air temperature sensor (87)) can reach a set temperature.

[0112] The cooling operation will be described with reference to FIG. 5.

[0113] In the cooling operation, the controller (90) controls the rotational speeds of the low-stage compressor (51) and the high-stage compressor (52). Further, the controller (90) controls the opening degrees of the first expansion valve (EV1) and the second expansion valve (EV2), and holds the third expansion valve (EV3), the fourth expansion valve (EV4), and the fifth expansion valve (EV5) in a fully-closed state. Further, the controller (90) holds the first electric valve (MV1) and the second electric valve (MV2) in a fully-open state, holds the first electromagnetic valve (SV1) and the second electromagnetic valve (SV2) in an open state, and holds third electromagnetic valve (SV3) in a closed state.

[0114] The high-stage compressor (52) compresses the sucked refrigerant to a pressure higher than the critical pressure of the refrigerant and discharges the compressed refrigerant. The refrigerant having discharged from the high-stage compressor (52) exchanges heat with the external air in the outer heat exchanger (56), and dissipates heat to the external air. The refrigerant having passed through the outer heat exchanger (56) flows into the first flow path (61a) of the internal heat exchanger (61), and is cooled by exchanging heat with the refrigerant flowing in the second flow path (61b) of the internal heat exchanger (61). The refrigerant having passed through the first flow path (61a) of the internal heat exchanger (61) is decompressed when passing through the first expansion valve (EV1) and is brought into a gas-liquid two-phase state. Then, the refrigerant flows into the receiver (62), and is separated into a liquid refrigerant and a gas refrigerant.

[0115] The liquid refrigerant having flowed out from the receiver (62) is decompressed when passing through the second expansion valve (EV2), and then flows into the inner heat exchanger (57). The refrigerant having flowed into the inner heat exchanger (57) absorbs heat from the air passing through the inner heat exchanger (57) and then is evaporated. The refrigerant having flowed out from the inner heat exchanger (57) is sucked into the low-stage compressor (51). The low-stage compressor (51) compresses and discharges the sucked refrigerant. The refrigerant having discharged from the low-stage compressor (51) is sucked into the high-stage compressor (52).

[0116] The gas refrigerant having flowed out from the receiver (62) flows in the gas-side connection pipe (41), then flows into the second flow path (61b) of the internal heat exchanger (61), and then absorbs heat from the refrigerant flowing in the first flow path (61a) of the internal heat exchanger (61). The refrigerant having flowed out from the second flow path (61b) of the internal heat exchanger (61) passes through the intermediate connection pipe (43), and is sucked into the high-stage compressor (52) together with the refrigerant having discharged from the low-stage compressor (51).<Dehumidifying Operation>

[0117] The dehumidifying operation is an operation to dehumidify the inside air while maintaining the temperature of the air in the internal space (5). In the dehumidifying operation, the refrigeration apparatus (10) blows the air dehumidified in the inner heat exchanger (57) and then heated in the reheating heat exchanger (58) into the internal space (5).

[0118] In the dehumidifying operation of the refrigeration apparatus (10), similarly to the cooling operation, the controller (90) operates the external fan (26) and the internal fan (27). In the transportation container (1), the air circulates between the internal flow path (20) of the refrigeration apparatus (10) and the internal space (5) of the container body (2). The inside air of the internal space (5) flows into the internal flow path (20) through the air inlet port (21). The inside air flowing in the internal flow path (20) passes through the inner heat exchanger (57) and the reheating heat exchanger (58) in sequence, and then is supplied to the internal space (5) through the air outlet port (22).

[0119] The dehumidifying operation will be described with reference to FIG. 6.

[0120] In the dehumidifying operation, the controller (90) controls the rotational speeds of the low-stage compressor (51) and the high-stage compressor (52). Further, the controller (90) controls the opening degrees of the first expansion valve (EV1), the second expansion valve (EV2), and the fifth expansion valve (EV5), and holds the third expansion valve (EV3) and the fourth expansion valve (EV4) in a fully-closed state. Further, the controller (90) holds the first electric valve (MV1) and the second electric valve (MV2) in a fully-open state, and holds the first electromagnetic valve (SV1), the second electromagnetic valve (SV2), and the third electromagnetic valve (SV3) in an open state.

[0121] The dehumidifying operation is different from the cooling operation in that the controller (90) controls the opening degree of the fifth expansion valve (EV5) and holds the third electromagnetic valve (SV3) in an open state. Further, the dehumidifying operation is different from the cooling operation in that the refrigerant flows in the reheating pipe (33) as well as the main circuit (31), the gas-side connection pipe (41), and the intermediate connection pipe (43).

[0122] When the refrigeration apparatus (10) performs the dehumidifying operation, the refrigerant circuit (30) performs a refrigeration cycle. In the dehumidifying operation, similarly to the cooling operation, the refrigerant circulates in the main circuit (31) of the refrigerant circuit (30), the outer heat exchanger (56) functions as a radiator, and the inner heat exchanger (57) functions as an evaporator. The inner heat exchanger (57) cools the air flowing in the internal flow path (20).

[0123] In the dehumidifying operation, the evaporation temperature of the refrigerant in the inner heat exchanger (57) is set to a value lower than the dew point temperature of the air flowing into the inner heat exchanger (57). Thus, in the inner heat exchanger (57), the moisture contained in the air is condensed into drain water. The drain water generated in the inner heat exchanger (57) flows down into the drain pan, and then is discharged to the outside of the container. Thus, each of the temperature and absolute humidity of the air flowing in the internal flow path (20) is reduced when the air passes through the inner heat exchanger (57).

[0124] In the dehumidifying operation, similarly to the cooling operation, the refrigerant flows in the gas-side connection pipe (41) and the intermediate connection pipe (43). The gas refrigerant having flowed out from the receiver (62) passes through the gas-side connection pipe (41) and the intermediate connection pipe (43) in sequence, and then is sucked into the high-stage compressor (52) together with the refrigerant having discharged from the low-stage compressor (51).

[0125] In the dehumidifying operation, part of the refrigerant having discharged from the high-stage compressor (52) is supplied to the reheating heat exchanger (58) through the reheating pipe (33). In the reheating heat exchanger (58), the air having passed through the inner heat exchanger (57) is heated by the refrigerant. The refrigerant having dissipated heat in the reheating heat exchanger (58) is decompressed when passing through the fifth expansion valve (EV5). The refrigerant having passed through the fifth expansion valve (EV5) flows into the main circuit (31), and then flows into the inner heat exchanger (57) together with the refrigerant having passed through the second expansion valve (EV2).

[0126] In the dehumidifying operation, the controller (90) controls the rotational speed of the low-stage compressor (51) so that the humidity of the air having passed through the reheating heat exchanger (58) can reach a target humidity. Specifically, the controller (90) controls the rotational speed of the low-stage compressor (51) so that the measurement value of the humidity sensor (88) can reach a set humidity. If the measurement value of the humidity sensor (88) is higher than the set humidity, the controller (90) increases the rotational speed of the low-stage compressor (51) in order to decrease the evaporation temperature of the refrigerant in the inner heat exchanger (57). If the measurement value of the humidity sensor (88) is lower than the set humidity, the controller (90) decreases the rotational speed of the low-stage compressor (51) in order to increase the evaporation temperature of the refrigerant in the inner heat exchanger (57).

[0127] In the dehumidifying operation, the controller (90) controls the opening degree of the fifth expansion valve (EV5) so that the temperature of the air having passed through the reheating heat exchanger (58) can reach a set temperature. Specifically, the controller (90) controls the opening degree of the fifth expansion valve (EV5) so that the measurement value of the second air temperature sensor (87) can reach the set temperature. If the measurement value of the second air temperature sensor (87) is higher than the set temperature, the controller (90) reduces the opening degree of the fifth expansion valve (EV5) in order to decrease the flow rate of the refrigerant in the reheating heat exchanger (58). If the measurement value of the second air temperature sensor (87) is lower than the set temperature, the controller (90) expands the opening degree of the fifth expansion valve (EV5) in order to increase the flow rate of the refrigerant in the reheating heat exchanger (58).

[0128] In the dehumidifying operation, the temperature and absolute humidity of the air flowing in the internal flow path (20) decrease in the course of passing through the inner heat exchanger (57), and the temperature of the air increases in the course of passing through the reheating heat exchanger (58). Thus, by the refrigeration apparatus (10) performing the dehumidifying operation, it is possible to decrease the humidity of the inside air while maintaining the temperature of the air in the internal space (5).<Heating Operation>

[0129] The heating operation is an operation to heat the inside air. In the heating operation, the refrigeration apparatus (10) blows the air heated in the inner heat exchanger (57) into the internal space (5). The heating operation is performed to hold the temperature of the air in the internal space (5) at a set temperature if the external air temperature is lower than the set temperature of the internal space (5), for example.

[0130] When the refrigeration apparatus (10) performs the heating operation, the controller (90) holds the external fan (26) in a stop state, and operates the internal fan (27). In the transportation container (1), the air circulates between the internal flow path (20) of the refrigeration apparatus (10) and the internal space (5) of the container body (2). The inside air of the internal space (5) flows into the internal flow path (20) through the air inlet port (21). The inside air flowing in the internal flow path (20) passes through the inner heat exchanger (57), and then is supplied to the internal space (5) through the air outlet port (22).

[0131] The heating operation will be described with reference to FIG. 7.

[0132] In the heating operation, the controller (90) holds the low-stage compressor (51) in the stop state, and controls the rotational speed of the high-stage compressor (52). Further, the controller (90) holds the first expansion valve (EV1) in an open state, holds the second expansion valve (EV2), the third expansion valve (EV3), and the fifth expansion valve (EV5) in a closed state, and controls the opening degree of the fourth expansion valve (EV4). Further, the controller (90) holds the first electric valve (MV1) in a fully-open state, holds the second electric valve (MV2) in a fully-closed state, and holds the first electromagnetic valve (SV1), the second electromagnetic valve (SV2), and the third electromagnetic valve (SV3) in a closed state.

[0133] In the refrigerant circuit (30) that is performing the heating operation, the refrigerant circulates between the high-stage compressor (52) and the inner heat exchanger (57) without passing through the outer heat exchanger (56). The refrigerant having discharged from the high-stage compressor (52) flows in the defrosting pipe (32), and then is decompressed when passing through the fourth expansion valve (EV4). The refrigerant having passed through the fourth expansion valve (EV4) flows into the inner heat exchanger (57), and then dissipates heat to the air passing through the inner heat exchanger (57). The refrigerant having flowed out from the inner heat exchanger (57) is sucked into the high-stage compressor (52) through the low-stage connection pipe (44). The high-stage compressor (52) compresses and discharges the sucked refrigerant.

[0134] In the heating operation, the controller (90) controls the opening degree of the fourth expansion valve (EV4) so that the temperature of the air having passed through the inner heat exchanger (57) can reach a set temperature. Specifically, the controller (90) controls the opening degree of the fourth expansion valve (EV4) so that the measurement value of the second air temperature sensor (87) can reach the set temperature. If the measurement value of the second air temperature sensor (87) is higher than the set temperature, the controller (90) reduces the opening degree of the fourth expansion valve (EV4) in order to decrease the flow rate of the refrigerant in the inner heat exchanger (57). If the measurement value of the second air temperature sensor (87) is lower than the set temperature, the controller (90) expands the opening degree of the fourth expansion valve (EV4) in order to increase the flow rate of the refrigerant in the inner heat exchanger (57).-Defrosting Operation of Refrigeration Apparatus-

[0135] The defrosting operation is an operation to melt the frost on the inner heat exchanger (57) in the cooling operation.

[0136] In the cooling operation, the evaporation temperature of the refrigerant in the inner heat exchanger (57) may be lower than 0°C. In this case, the moisture in the air is frozen into frost, and the frost adheres to the inner heat exchanger (57). When the frost adheres to the inner heat exchanger (57), the frost blocks the flow of the air passing through the inner heat exchanger (57), and blocks heat exchange between the refrigerant and the air.

[0137] Thus, if the defrosting start condition is satisfied during the cooling operation, the refrigeration apparatus (10) temporarily stops the cooling operation and performs the defrosting operation. For example, the defrosting start condition is the condition that "the cumulative value of the execution time of the cooling operation in which the evaporation temperature of the refrigerant in the internal heat exchanger is lower than 0°C has reached a predetermined time (for example, 2 hours)".

[0138] If the defrosting end condition is satisfied during the defrosting operation, the refrigeration apparatus (10) ends the defrosting operation, and restarts the cooling operation. For example, the defrosting end condition is the condition that "the temperature of the inner heat exchanger (57) (specifically, the measurement value of the heat exchanger temperature sensor (85)) has reached a predetermined temperature (for example, 10°C)".

[0139] In the defrosting operation, the refrigeration apparatus (10) mainly performs a normal operation. If the mass of the refrigerant that circulates between the high-stage compressor (52) and the inner heat exchanger (57) becomes too large during the normal operation, the refrigeration apparatus (10) temporarily stops the normal operation and performs an inflow operation. If the mass of the refrigerant that circulates between the high-stage compressor (52) and the inner heat exchanger (57) becomes too small during the normal operation, the refrigeration apparatus (10) temporarily stops the normal operation and performs an outflow operation. Switching between the normal operation, the inflow operation, and the outflow operation is performed by the controller (90) controlling the plurality of valves that form the path changing mechanism (67).

[0140] In each of the normal operation, the inflow operation, and the outflow operation, the controller (90) holds the internal fan (27) in a stop state. Thus, no air flows in the internal flow path (20). Further, in each of the normal operation, the inflow operation, and the outflow operation, the controller (90) holds the low-stage compressor (51) in a stop state, and operates the high-stage compressor (52).<Normal Operation>

[0141] The normal operation of the defrosting operation will be described with reference to FIG. 7.

[0142] In the normal operation, the controller (90) holds the external fan (26) and the internal fan (27) in a stop state. Further, the controller (90) holds the low-stage compressor (51) in a stop state, and controls the rotational speed of the high-stage compressor (52). Further, the controller (90) holds the first expansion valve (EV1) in an open state, holds the second expansion valve (EV2), the third expansion valve (EV3), and the fifth expansion valve (EV5) in a closed state, and controls the opening degree of the fourth expansion valve (EV4). Further, the controller (90) holds the first electric valve (MV1) in a fully-open state, holds the second electric valve (MV2) in a fully-closed state, and holds the first electromagnetic valve (SV1), the second electromagnetic valve (SV2), and the third electromagnetic valve (SV3) in a closed state.

[0143] In the refrigerant circuit (30) operating in the normal operation, the refrigerant flows as in the heating operation. In the refrigerant circuit (30) operating in the normal operation, the refrigerant circulates between the high-stage compressor (52) and the inner heat exchanger (57) in a state in which the inflow of a refrigerant to and the outflow of a refrigerant from the receiver (62) are blocked.

[0144] The state of the refrigerant in the refrigerant circuit (30) operating in the normal operation will be described with reference to a Mollier diagram (a pressure-enthalpy diagram) of FIG. 8.

[0145] In the refrigerant circuit (30), the refrigerant in the state of the point A is sucked into the high-stage compressor (52), and is compressed into the state of the point B by the high-stage compressor (52). In the course of the refrigerant being compressed by the high-stage compressor (52), the pressure of the refrigerant increases, and the enthalpy of the refrigerant increases.

[0146] The refrigerant having discharged from the high-stage compressor (52) flows into the fourth expansion valve (EV4) through the defrosting pipe (32). In the course of flowing from the high-stage compressor (52) to the fourth expansion valve (EV4), the refrigerant dissipates some heat, and thus the state of the refrigerant changes from the point B to the point C. The refrigerant in the state of the point C is decompressed in the course of passing through the fourth expansion valve (EV4) and is brought into the state of the point D.

[0147] The refrigerant in the state of the point D flows into the inner heat exchanger (57) and dissipates heat. In the inner heat exchanger (57), the frost on the inner heat exchanger (57) is warmed and melted by the refrigerant. Further, in the inner heat exchanger (57), the pressure of the refrigerant decreases due to a pressure loss in the course of the refrigerant passing through the inner heat exchanger (57). Thus, the refrigerant is brought into the state of the point E at the outlet of the inner heat exchanger (57). The refrigerant having flowed out from the inner heat exchanger (57) dissipates some heat in the course of flowing toward the high-stage compressor (52) and is brought into the state of the point A.<Inflow Operation>

[0148] The inflow operation is an operation to allow the refrigerant to flow into the receiver (62) in order to increase the mass of the refrigerant stored in the receiver (62). The refrigeration apparatus (10) performs the inflow operation to decrease the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57).

[0149] The inflow operation of the defrosting operation will be described with reference to FIG. 9.

[0150] In the inflow operation, the controller (90) operates the external fan (26), and brings the second electric valve (MV2) into an open state. The differences between the inflow operation and the normal operation are that the external fan (26) is operated and that the second electric valve (MV2) is brought into an open state. Further, in the inflow operation, the controller (90) controls the opening degree of the first expansion valve (EV1) as necessary.

[0151] In the inflow operation, similarly to the normal operation, the refrigerant circulates between the high-stage compressor (52) and the inner heat exchanger (57). In the inflow operation, part of the refrigerant having discharged from the high-stage compressor (52) flows into the outer heat exchanger (56). The refrigerant having flowed into the outer heat exchanger (56) dissipates heat to the external air, and then flows into the receiver (62) through the first expansion valve (EV1).

[0152] In the inflow operation, since the first electromagnetic valve (SV1) and the second electromagnetic valve (SV2) are in a closed state, no refrigerant flows out from the receiver (62). Thus, in the inflow operation, the mass of the refrigerant stored in the receiver (62) increases, and as a result, the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) decreases.

[0153] If the pressure of the refrigerant discharged by the high-stage compressor (52) during the inflow operation is higher than to equal to the critical pressure of the refrigerant, the controller (90) controls the opening degree of the first expansion valve (EV1) so that the pressure of the refrigerant flowing into the receiver (62) is lower than the critical pressure of the refrigerant.<Outflow Operation>

[0154] The outflow operation is an operation to allow the refrigerant to flow out from the receiver (62) in order to decrease the mass of the refrigerant stored in the receiver (62). The refrigeration apparatus (10) performs the outflow operation to increase the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57).

[0155] The refrigeration apparatus (10) performs a first outflow operation or a second outflow operation as the outflow operation. In each of the first outflow operation and the second outflow operation, the refrigeration apparatus (10) performs a gas outflow operation or a liquid outflow operation.<First Outflow Operation / Gas Outflow Operation>

[0156] The gas outflow operation of the first outflow operation will be described with reference to FIG. 10.

[0157] In the gas outflow operation of the first outflow operation, the controller (90) brings the second electromagnetic valve (SV2) into an open state. The difference between the gas outflow operation of the first outflow operation and the normal operation is that the second electromagnetic valve (SV2) is brought into an open state.

[0158] In the gas outflow operation of the first outflow operation, similarly to the normal operation, the refrigerant circulates between the high-stage compressor (52) and the inner heat exchanger (57). In the gas outflow operation of the first outflow operation, the gas refrigerant in the receiver (62) flows into the gas-side connection pipe (41). The gas refrigerant having flowed into the gas-side connection pipe (41) passes through the intermediate connection pipe (43), and is sucked into the high-stage compressor (52) together with the refrigerant having flowed out from the inner heat exchanger (57).

[0159] In the gas outflow operation of the first outflow operation, since the second electric valve (MV2) is in a closed state, no refrigerant flows into the receiver (62). Thus, in the gas outflow operation of the first outflow operation, the mass of the refrigerant stored in the receiver (62) decreases, and as a result, the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) increases.<First Outflow Operation / Liquid Outflow Operation>

[0160] For example, if the external air temperature is relatively low, the pressure of the refrigerant in the receiver (62) is relatively low; and thus the difference between the pressure of the refrigerant in the receiver (62) and the pressure of the refrigerant in the inner heat exchanger (57) may be small during the outflow operation. If the gas outflow operation is performed in this case, the flow rate of the gas refrigerant flowing out from the receiver (62) decreases, and thus it may take a long time to increase the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57). For this reason, in such a case, the refrigeration apparatus (10) performs the liquid outflow operation instead of the gas outflow operation.

[0161] The liquid outflow operation of the first outflow operation will be described with reference to FIG. 11.

[0162] In the liquid outflow operation of the first outflow operation, the controller (90) brings the first electromagnetic valve (SV1) into an open state, brings the second electromagnetic valve (SV2) into a closed state, and brings the third expansion valve (EV3) into an open state. The differences between the liquid outflow operation and the gas outflow operation of the first outflow operation are that the second electromagnetic valve (SV2) is brought into a closed state and that the first electromagnetic valve (SV1) and the third expansion valve (EV3) are brought into an open state.

[0163] In the liquid outflow operation of the first outflow operation, similarly to the gas outflow operation of the first outflow operation, the refrigerant circulates between the high-stage compressor (52) and the inner heat exchanger (57). In the liquid outflow operation of the first outflow operation, the liquid refrigerant in the receiver (62) flows into the liquid-side connection pipe (42). The liquid refrigerant having flowed into the liquid-side connection pipe (42) passes through the intermediate connection pipe (43), and is sucked into the high-stage compressor (52) together with the refrigerant having flowed out from the inner heat exchanger (57).

[0164] In the liquid outflow operation of the first outflow operation, since the second electric valve (MV2) is in a closed state, no refrigerant flows into the receiver (62). Thus, in the liquid outflow operation of the first outflow operation, the mass of the refrigerant stored in the receiver (62) decreases, and as a result, the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) increases.

[0165] The liquid refrigerant in the receiver (62) has a higher density than the gas refrigerant in the receiver (62). Thus, even if the difference between the pressure of the refrigerant in the receiver (62) and the pressure of the refrigerant in the inner heat exchanger (57) is small, the mass flow rate of the refrigerant flowing out from the receiver (62) can be ensured, and the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) can be sufficiently increased in a relatively short time.<Second Outflow Operation>

[0166] For example, if the external air temperature is extremely low, the pressure of the refrigerant in the receiver (62) may be lower during the outflow operation than the pressure of the refrigerant in the inner heat exchanger (57). On the other hand, in the first outflow operation, the pressure of the refrigerant sucked into the high-stage compressor (52) is substantially equal to the pressure of the refrigerant in the inner heat exchanger (57). Thus, even if the first outflow operation is performed in such a case, the refrigerant is not allowed to flow out from the receiver (62). For this reason, in such a case, the refrigeration apparatus (10) performs the second outflow operation instead of the first outflow operation.

[0167] The gas outflow operation of the second outflow operation will be described with reference to FIG. 12.

[0168] In the gas outflow operation of the second outflow operation, the controller (90) brings the first electric valve (MV1) into a closed state. The difference between the gas outflow operation of the second outflow operation and the gas outflow operation of the first outflow operation is that the first electric valve (MV1) is brought into a closed state.

[0169] In the gas outflow operation of the second outflow operation, the first electric valve (MV1) is in a closed state, and a portion between the high-stage compressor (52) and the inner heat exchanger (57) is blocked by the first electric valve (MV1). Thus, the high-stage compressor (52) sucks the refrigerant from the receiver (62) alone out of the receiver (62) and the inner heat exchanger (57).

[0170] Similarly to the gas outflow operation of the first outflow operation, the gas refrigerant having flowed out from the gas outflow port of the receiver (62) passes through the gas-side connection pipe (41) and the intermediate connection pipe (43), and then is sucked into the high-stage compressor (52). Thus, in the gas outflow operation of the second outflow operation, the mass of the refrigerant stored in the receiver (62) decreases, and as a result, the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) increases when the normal operation is restarted.

[0171] The liquid outflow operation of the second outflow operation will be described.

[0172] In the liquid outflow operation of the second outflow operation, the controller (90) brings the first electric valve (MV1) into a closed state. The difference between the liquid outflow operation of the second outflow operation and the liquid outflow operation of the first outflow operation is that the first electric valve (MV1) is brought into a closed state.

[0173] In the liquid outflow operation of the second outflow operation, the first electric valve (MV1) is in a closed state, and a portion between the high-stage compressor (52) and the inner heat exchanger (57) is blocked by the first electric valve (MV1). Thus, the high-stage compressor (52) sucks the refrigerant from the receiver (62) alone out of the receiver (62) and the inner heat exchanger (57).

[0174] Similarly to the liquid outflow operation of the first outflow operation, the liquid refrigerant having flowed out from the liquid outflow port of the receiver (62) passes through the liquid-side connection pipe (42) and the intermediate connection pipe (43), and then is sucked into the high-stage compressor (52). Thus, in the liquid outflow operation of the second outflow operation, the mass of the refrigerant stored in the receiver (62) decreases, and as a result, the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) increases when the normal operation is restarted.-Operation of Controller in Defrosting Operation-

[0175] The operation performed by the controller (90) in the defrosting operation will be described with reference to FIG. 13.

[0176] In the defrosting operation, the controller (90) controls the refrigeration apparatus (10) so that the amount of heat applied to the internal heat exchanger to melt frost (hereinafter referred to as the "defrosting heat amount") can reach a target heat amount.

[0177] As an index of the dehumidification heat amount, the controller (90) of this embodiment uses the current supplied to the electric motor of the high-stage compressor (52) (hereinafter referred to as the "input current"). As the target current, the controller (90) stores the value of the input current at which the defrosting heat amount can reach the target heat amount. The controller (90) of this embodiment instructs the refrigeration apparatus (10) to selectively execute the normal operation, the inflow operation, or the outflow operation so that the input current of the high-stage compressor (52) can reach the target current.<Control in Normal Operation>

[0178] In the normal operation, the controller (90) controls the rotational speed of the high-stage compressor (52) and the opening degree of the fourth expansion valve (EV4). The controller (90) controls the rotational speed of the high-stage compressor (52) prior to controlling the opening degree of the fourth expansion valve (EV4).

[0179] When the normal operation is started, the controller (90) sets the opening degree of the fourth expansion valve (EV4) to an initial opening degree, and controls the rotational speed of the high-stage compressor (52) based on the input current. The controller (90) controls the rotational speed of the high-stage compressor (52) so that the input current can reach the target current. If the input current is lower than the target current, the controller (90) increases the rotational speed of the high-stage compressor (52). If the input current is higher than the target current, the controller (90) decreases the rotational speed of the high-stage compressor (52).

[0180] When the rotational speed of the high-stage compressor (52) reaches a reference speed (for example, the upper speed limit) but the input current is lower than the target current, the defrosting heat amount is insufficient, but the defrosting heat amount cannot be increased by the control of the rotational speed of the high-stage compressor (52). For this reason, in this case, the controller (90) controls the opening degree of the fourth expansion valve (EV4).

[0181] The controller (90) controls the opening degree of the fourth expansion valve (EV4) based on the pressure of the refrigerant discharged by the high-stage compressor (52) (specifically, the measurement value of the high-stage discharge pressure sensor (78)). The controller (90) decreases the opening degree of the fourth expansion valve (EV4) as much as possible within a range in which the measurement value of the high-stage discharge pressure sensor (78) is held lower than or equal to the reference pressure.

[0182] Specifically, the controller (90) controls the opening degree of the fourth expansion valve (EV4) so that the measurement value of the high-stage discharge pressure sensor (78) falls within a reference pressure range. The reference pressure range is a pressure range including the reference pressure. The maximum value of the reference pressure range is the reference pressure.

[0183] If the measurement value of the high-stage discharge pressure sensor (78) is lower than the minimum value of the reference pressure range, the controller (90) reduces the opening degree of the fourth expansion valve (EV4). If the measurement value of the high-stage discharge pressure sensor (78) is higher than the maximum value of the reference pressure range (= the reference pressure), the controller (90) expands the opening degree of the fourth expansion valve (EV4). If the measurement value of the high-stage discharge pressure sensor (78) falls within the reference pressure range, the controller (90) maintains the opening degree of the fourth expansion valve (EV4).

[0184] When the opening degree of the fourth expansion valve (EV4) reaches a reference opening degree but the input current is higher than the target current, the defrosting heat amount is excessive, but the defrosting heat amount cannot be decreased by the control of the opening degree of the fourth expansion valve (EV4). For this reason, in this case, the controller (90) controls the rotational speed of the high-stage compressor (52) again.<Switching between Normal Operation and Inflow Operation>

[0185] If the inflow start condition is satisfied during the normal operation, the controller (90) switches the operation executed by the refrigeration apparatus (10) from the normal operation to the inflow operation.

[0186] The inflow start condition is the condition indicating that the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) is excessive. The inflow start condition of this embodiment is the condition that "the pressure of the refrigerant discharged by the high-stage compressor (52) (specifically, the measurement value of the high-stage discharge pressure sensor (78)) is higher than or equal to the upper limit pressure". In the controller (90), the upper limit pressure is set to a value slightly lower than the maximum pressure that the refrigerant circuit (30) can withstand.

[0187] When the refrigeration apparatus (10) starts the inflow operation, part of the refrigerant discharged from the high-stage compressor (52) flows into the receiver (62), and the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) decreases.

[0188] If the inflow end condition is satisfied during the inflow operation, the controller (90) switches the operation executed by the refrigeration apparatus (10) from the inflow operation to the normal operation.

[0189] The inflow end condition is the condition indicating that the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) is appropriate. The inflow end condition of this embodiment is the condition that "the pressure of the refrigerant discharged by the high-stage compressor (52) (specifically, the measurement value of the high-stage discharge pressure sensor (78)) is lower than the upper limit pressure". If the inflow end condition is satisfied, the refrigeration apparatus (10) ends the inflow operation and restarts the normal operation.

[0190] The inflow end condition may be the condition that "the duration time of the inflow operation has reached a predetermined time (for example, five seconds)".<Switching between Normal Operation and Outflow Operation>

[0191] If the outflow start condition is satisfied during the normal operation, the controller (90) switches the operation executed by the refrigeration apparatus (10) from the normal operation to the outflow operation.

[0192] The outflow start condition is the condition indicating that the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) is insufficient. The outflow start condition of this embodiment is the condition that "the temperature of the refrigerant discharged by the high-stage compressor (52) (specifically, the measurement value of the high-stage discharge temperature sensor (73)) is higher than or equal to the upper limit temperature".

[0193] When the refrigeration apparatus (10) starts the outflow operation, the refrigerant having flowed out from the receiver (62) is sucked into the high-stage compressor (52), and the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) increases.

[0194] If the outflow end condition is satisfied during the outflow operation, the controller (90) switches the operation executed by the refrigeration apparatus (10) from the outflow operation to the normal operation. The outflow end condition is the condition that "the duration time of the outflow operation has reached a predetermined time (for example, one minute)".

[0195] The outflow end condition may be the condition that "the degree of superheat of the refrigerant at the outlet of the inner heat exchanger (57) is lower than a reference degree of superheat". In this case, by using the measurement value of the fourth refrigerant temperature sensor (84) and the measurement value of the low-stage suction pressure sensor (75), the controller (90) calculates the degree of superheat of the refrigerant at the outlet of the inner heat exchanger (57).<Control in Outflow Operation>

[0196] The controller (90) instructs the refrigeration apparatus (10) to execute one of the first outflow operation or the second outflow operation as the outflow operation.

[0197] The controller (90) selects one of the first outflow operation or the second outflow operation based on the difference (Pr-Ps) between the pressure of the refrigerant in the receiver (62) (specifically, the measurement value Pr of the receiver pressure sensor (79)) and the pressure of the refrigerant sucked into the high-stage compressor (52) (specifically, the measurement value Ps of the high-stage suction pressure sensor (77)).

[0198] If the pressure difference (Pr-Ps) is more than or equal to a reference value, "the pressure of the refrigerant in the receiver (62)" is higher to some extent than "the pressure of the refrigerant sucked into the high-stage compressor (52)". In this case, the high-stage compressor (52) can suck the refrigerant from both the receiver (62) and the inner heat exchanger (57). Thus, in this case, the controller (90) instructs the refrigeration apparatus (10) to execute the first outflow operation.

[0199] If the pressure difference (Pr-Ps) is less than the reference value, "the pressure of the refrigerant in the receiver (62)" is close to "the pressure of the refrigerant sucked into the high-stage compressor (52)", or that "the pressure of the refrigerant in the receiver (62)" is lower than "the pressure of the refrigerant sucked into the high-stage compressor (52)". In this case, the high-stage compressor (52) cannot suck the refrigerant from both the receiver (62) and the inner heat exchanger (57). Thus, in this case, the controller (90) instructs the refrigeration apparatus (10) to execute the second outflow operation so that the high-stage compressor (52) can suck the refrigerant from the receiver (62) alone.

[0200] In the outflow operation for the first time, the controller (90) instructs the refrigeration apparatus (10) to execute the gas outflow operation. If the outflow start condition is satisfied again in the normal operation performed by the refrigeration apparatus (10) after the outflow operation for the first time ends, it can be determined that the mass of the refrigerant having flowed out from the receiver (62) in the outflow operation for the first time is small. Thus, in the outflow operation for the second time, the controller (90) instructs the refrigeration apparatus (10) to perform the liquid outflow operation to increase the mass of the refrigerant flowing out from the receiver (62).-Feature (1) of First Embodiment-

[0201] In the refrigeration apparatus (10) of this embodiment, the controller (90) controls the opening degree of the fourth expansion valve (EV4) as the decompression valve during the defrosting operation. In the defrosting operation, the refrigerant discharged from the high-stage compressor (52) (the point B in FIG. 8) is decompressed when passing through the fourth expansion valve (EV4), and the decompressed refrigerant (the point D in FIG. 8) is supplied to the inner heat exchanger (57). Thus, the pressure of the refrigerant flowing out from the inner heat exchanger (57) (the point E in FIG. 8) is lower than when the refrigerant discharged by the high-stage compressor (52) is supplied to the inner heat exchanger (57) without being decompressed, and as a result, the pressure difference between the refrigerant sucked by the high-stage compressor (52) (the point A in FIG. 8) and the refrigerant discharged by the high-stage compressor (52) (the point B in FIG. 8) increases.

[0202] When the pressure difference between the refrigerant sucked by the high-stage compressor (52) and the refrigerant discharged by the high-stage compressor (52) increases, the amount of heat applied to the refrigerant in the course of the high-stage compressor (52) compressing the refrigerant increases. Thus, according to this embodiment, the amount of heat which can be used to melt the frost on the inner heat exchanger (57) can be more increased than when the refrigerant discharged by the high-stage compressor (52) is supplied to the inner heat exchanger (57) without being decompressed, and as a result, the time to defrost the inner heat exchanger (57) can be shortened.-Feature (2) of First Embodiment-

[0203] In the defrosting operation, the refrigeration apparatus (10) of this embodiment performs the normal operation, the outflow operation, and the inflow operation. In the outflow operation, the mass of the refrigerant stored in the receiver (62) decreases, and the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) increases. In the inflow operation, the mass of the refrigerant stored in the receiver (62) increases, and the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) decreases.

[0204] By performing the inflow operation and the outflow operation, the refrigeration apparatus (10) of this embodiment can adjust the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) during the defrosting operation. Thus, the defrosting operation can be continuously performed while the pressure and temperature of the refrigerant discharged by the high-stage compressor (52) are held at appropriate values, and the frost on the inner heat exchanger (57) can be reliably melted by the defrosting operation.-Feature (3) of First Embodiment-

[0205] The refrigeration apparatus (10) of this embodiment performs the first outflow operation or the second outflow operation as the outflow operation. In the first outflow operation, the high-stage compressor (52) sucks the refrigerant having flowed out from the receiver (62) and the refrigerant having flowed out from the inner heat exchanger (57). In the second outflow operation, the high-stage compressor (52) sucks the refrigerant having flowed out from the receiver (62) and does not suck the refrigerant having flowed out from the inner heat exchanger (57).

[0206] Here, for example, when the external air has an extremely low temperature (for example, about -20°C to -30°C), the pressure of the refrigerant in the receiver (62) may be lower than the pressure of the refrigerant in the inner heat exchanger (57). If the pressure of the refrigerant in the receiver (62) is lower than the pressure of the refrigerant in the inner heat exchanger (57), the high-stage compressor (52) cannot suck the refrigerant from the receiver (62), and thus the refrigerant is not allowed to flow out from the receiver (62) by the first outflow operation.

[0207] On the other hand, in the second outflow operation, the refrigerant in the receiver (62) can be sucked into the high-stage compressor (52) regardless of the pressure of the refrigerant in the inner heat exchanger (57). Thus, even if the pressure of the refrigerant in the receiver (62) is lower than the pressure of the refrigerant in the inner heat exchanger (57), the refrigerant is allowed to flow out from the receiver (62) and the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) can be increased.

[0208] Thus, according to this embodiment, the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) during the defrosting operation can be increased by the outflow operation regardless of the pressure of the refrigerant in the receiver (62).-Feature (4) of First Embodiment-

[0209] The refrigeration apparatus (10) of this embodiment performs the gas outflow operation or the liquid outflow operation as the outflow operation. In the gas outflow operation, the gas refrigerant having flowed out from the receiver (62) is sucked into the high-stage compressor (52). In the liquid outflow operation, the liquid refrigerant having flowed out from the receiver (62) is sucked into the high-stage compressor (52).

[0210] For example, if the external air temperature is relatively low, the pressure of the refrigerant in the receiver (62) is relatively low, and the difference between the pressure of the refrigerant in the receiver (62) and the pressure of the refrigerant in the inner heat exchanger (57) may be small during the outflow operation. If the gas outflow operation is performed in this case, the flow rate of the gas refrigerant flowing out from the receiver (62) decreases, and it may take a long time to increase the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57).

[0211] In such a case, the refrigeration apparatus (10) of this embodiment performs the liquid outflow operation instead of the gas outflow operation. In the liquid outflow operation, the liquid refrigerant having flowed out from the receiver (62) is sucked into the high-stage compressor (52). The density of the liquid refrigerant is significantly higher than the density of the gas refrigerant. Thus, according to the refrigeration apparatus (10) of this embodiment that performs the liquid outflow operation, even if the difference between the pressure of the refrigerant in the receiver (62) and the pressure of the refrigerant in the inner heat exchanger (57) is relatively small, the mass flow rate of the refrigerant flowing out from the receiver (62) can be held high, and as a result, the time to increase the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) can be held short.

[0212] Here, if a relatively large amount of liquid refrigerant flows into the compression mechanism of the high-stage compressor (52), the compression mechanism may be damaged. On the other hand, in the refrigeration apparatus (10) of this embodiment, the refrigerant sucked into the high-stage compressor (52) passes through the accumulator (52a), and then flows into the compression mechanism of the high-stage compressor (52). Thus, in the liquid outflow operation, the liquid refrigerant having flowed out from the receiver (62) flows into the accumulator (52a), and the refrigerant having vaporized in the accumulator (52a) is sucked into the compression mechanism of the high-stage compressor (52). Thus, in the refrigeration apparatus (10) of this embodiment, even in the liquid outflow operation, the compression mechanism of the high-stage compressor (52) is not damaged even when sucking a relatively large amount of liquid refrigerant.<<Second Embodiment>>

[0213] The second embodiment will be described. The transportation container (1) of this embodiment is the transportation container (1) of the first embodiment that includes a modified version of the refrigeration apparatus (10).

[0214] The refrigeration apparatus (10) of this embodiment is different in the configuration of the refrigerant circuit (30) from the refrigeration apparatus (10) of the first embodiment. Here, regarding the refrigerant circuit (30) of this embodiment, the differences from the refrigerant circuit (30) of the first embodiment will be described.

[0215] As shown in FIG. 14, in the refrigerant circuit (30) of this embodiment, the defrosting pipe (32) is provided with a drain pan heater (63). In the defrosting pipe (32), the drain pan heater (63) is disposed downstream of the fourth expansion valve (EV4). The drain pan heater (63) is a pipe attached to the drain pan. The drain pan heater (63) heats the drain pan by the refrigerant flowing therein.-Defrosting Operation of Refrigeration Apparatus-

[0216] In the defrosting operation performed by the refrigeration apparatus (10) of this embodiment, similarly to the defrosting operation performed by the refrigeration apparatus (10) of the first embodiment, the refrigerant discharged from the high-stage compressor (52) flows into the defrosting pipe (32). In the defrosting operation performed by the refrigeration apparatus (10) of this embodiment, the refrigerant having flowed into the defrosting pipe (32) dissipates heat to the drain pan while passing through the drain pan heater (63), and then flows into the inner heat exchanger (57).

[0217] During the defrosting operation, the frost separated from the inner heat exchanger (57) may drop into the drain pan. In the defrosting operation performed by the refrigeration apparatus (10) of this embodiment, the drain pan is warmed by the refrigerant flowing in the drain pan heater (63). Thus, the frost having dropped from the inner heat exchanger (57) to the drain pan is warmed and melted by the drain pan, and then is discharged as drain water to the external space.<<Third Embodiment>>

[0218] The third embodiment will be described. The transportation container (1) of this embodiment is the transportation container (1) of the second embodiment that includes a modified version of the refrigeration apparatus (10).

[0219] The refrigeration apparatus (10) of this embodiment is different in the configuration of the refrigerant circuit (30) from the refrigeration apparatus (10) of the second embodiment. Here, regarding the refrigerant circuit (30) of this embodiment, the differences from the refrigerant circuit (30) of the second embodiment will be described.

[0220] As shown in FIG. 15, in the refrigerant circuit (30) of this embodiment, the defrosting pipe (32) is provided with the reheating heat exchanger (58) and the third electromagnetic valve (SV3), and not provided with the reheating pipe (33) and the fifth expansion valve (EV5). In the refrigerant circuit (30) of this embodiment, the defrosting pipe (32) also serves as the reheating pipe (33) for sending the refrigerant to the reheating heat exchanger (58). In the defrosting pipe (32) of this embodiment, the reheating heat exchanger (58) is disposed upstream of the fourth expansion valve (EV4), the drain pan heater (63) is disposed upstream of the reheating heat exchanger (58), and the third electromagnetic valve (SV3) is disposed upstream of the drain pan heater (63). The path changing mechanism (67) of this embodiment does not include the fourth expansion valve (EV4).-Operation of Controller-

[0221] In the refrigeration apparatus of this embodiment, the controller (90) controls the opening degree of the fourth expansion valve (EV4) in both the defrosting operation and the dehumidifying operation. In the defrosting operation, the controller (90) of this embodiment controls the opening degree of the fourth expansion valve (EV4) similarly to the controllers (90) of the first and second embodiments. In the dehumidifying operation, the controller (90) of this embodiment controls the opening degree of the fourth expansion valve (EV4) in the way the controllers (90) of the first and second embodiments control the opening degree of the fifth expansion valve (EV5). That is, in the dehumidifying operation, the controller (90) of this embodiment controls the opening degree of the fourth expansion valve (EV4) so that the temperature of the air having passed through the reheating heat exchanger (58) (specifically, the measurement value of the second air temperature sensor (87)) can reach the set temperature.<<Fourth Embodiment>>

[0222] The fourth embodiment will be described. In the refrigeration apparatus (10) of this embodiment, the controller (90) performs substantially the same operation as the controller (90) of the first embodiment when the refrigeration apparatus (10) is doing the defrosting operation. Here, the operation performed by the controller (90) of this embodiment when the refrigeration apparatus (10) is doing the defrosting operation will be described with reference to FIG. 16.

[0223] As described above, if the defrosting start condition is satisfied during the cooling operation, the refrigeration apparatus (10) temporarily stops the cooling operation and performs the defrosting operation. When the refrigeration apparatus (10) starts the normal operation of the defrosting operation, the controller (90) starts with the process of step ST1.<Step ST1>

[0224] In the process of step ST1, the controller (90) sets the opening degree of the fourth expansion valve (EV4) to the initial opening degree. After ending the process of step ST1, the controller (90) conducts the process of step ST2.<Step ST2>

[0225] In the process of step ST2, the controller (90) controls the rotational speed of the high-stage compressor (52) based on the input current. The controller (90) controls the rotational speed of the high-stage compressor (52) so that the input current can reach the target current. This operation of the controller (90) is the same as the operation of the controller (90) of the first embodiment to control the rotational speed of the high-stage compressor (52) based on the input current. After ending the process of step ST2, the controller (90) conducts the process of step ST3.<Step ST3>

[0226] In the process of step ST3, the controller (90) determines whether the defrosting end condition is satisfied. If the defrosting end condition is satisfied, the controller (90) ends the defrosting operation of the refrigeration apparatus (10), and restarts the cooling operation of the refrigeration apparatus (10). On the other hand, if the defrosting end condition is not satisfied, the controller (90) conducts the process of step ST4.<Step ST4>

[0227] In the process of step ST4, the controller (90) compares the measurement value Pdh of the high-stage discharge pressure sensor (78) with the upper limit pressure. If the condition that "the measurement value Pdh of the high-stage discharge pressure sensor (78) is higher than or equal to the upper limit pressure" is satisfied, the controller (90) conducts the process of step ST9. On the other hand, if this condition is not satisfied, the controller (90) conducts the process of step ST5.<Step ST5>

[0228] In the process of step ST5, the controller (90) compares the measurement value Tdh of the high-stage discharge temperature sensor with the upper limit temperature. If the condition that "the measurement value Tdh of the high-stage discharge temperature sensor is higher than or equal to the upper limit temperature" is satisfied, the controller (90) conducts the process of step ST11. On the other hand, if this condition is not satisfied, the controller (90) conducts the process of step ST6.<Step ST6>

[0229] In the process of step ST6, the controller (90) compares the input current of the high-stage compressor (52) with the target current, and compares the rotational speed RSh of the high-stage compressor (52) with the reference speed. If at least one of the condition that "the input current of the high-stage compressor (52) is higher than or equal to the target current" or the condition that "the rotational speed RSh of the high-stage compressor (52) is lower than the reference speed" is satisfied, the controller (90) conducts the process of step ST2. On the other hand, if both of the two conditions are not satisfied, the controller (90) conducts the process of step ST7.<Step ST7>

[0230] In the process of step ST7, the controller (90) compares the opening degree of the fourth expansion valve (EV4) with the reference opening degree. If the condition that "the opening degree of the fourth expansion valve (EV4) is lower than or equal to the reference opening degree" is satisfied, the controller (90) conducts the process of step ST11. On the other hand, if this condition is not satisfied, the controller (90) conducts the process of step ST8.<Step ST8>

[0231] In the process of step ST8, the controller (90) controls the opening degree of the fourth expansion valve (EV4) so that the measurement value Pdh of the high-stage discharge pressure sensor (78) falls within the reference pressure range. This operation of the controller (90) is the same as the operation of the controller (90) of the first embodiment to control the opening degree of the fourth expansion valve (EV4) based on the measurement value Pdh of the high-stage discharge pressure sensor (78). After ending the process of step ST8, the controller (90) conducts the process of step ST2.<Step ST9>

[0232] The condition in the process of step ST4 that "the measurement value Pdh of the high-stage discharge pressure sensor (78) is higher than or equal to the upper limit pressure" is the inflow start condition. As described in the first embodiment, the inflow start condition is the condition indicating that the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) is excessive.

[0233] Thus, in the process of step ST9, the controller (90) switches the operation executed by the refrigeration apparatus (10) from the normal operation to the inflow operation. Then, the controller (90) conducts the process of step ST10.<Step ST10>

[0234] In the process of step ST10, the controller (90) determines whether the condition that "the measurement value Pdh of the high-stage discharge pressure sensor (78) is lower than the upper limit pressure" is satisfied. This condition is the inflow end condition. As described in the first embodiment, the inflow end condition is the condition indicating that the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) is appropriate.

[0235] If the inflow end condition is satisfied, the controller (90) conducts the process of step ST2. On the other hand, if the inflow end condition is not satisfied, the controller (90) instructs the refrigeration apparatus (10) to continue the inflow operation.<Step ST11>

[0236] The condition in the process of step ST5 that "the measurement value Tdh of the high-stage discharge temperature sensor is higher than or equal to the upper limit temperature" is the outflow start condition. As described in the first embodiment, the outflow start condition is the condition indicating that the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) is insufficient.

[0237] Thus, in the process of step ST11, the controller (90) switches the operation executed by the refrigeration apparatus (10) from the normal operation to the outflow operation. Then, the controller (90) conducts the process of step ST12.<Step ST12>

[0238] In the process of step ST12, the controller (90) determines whether the condition that "the duration time of the outflow operation has reached a predetermined time" is satisfied. This condition is the outflow end condition. As described in the first embodiment, the outflow end condition is the condition for ending the outflow operation of the refrigeration apparatus (10).

[0239] If the outflow end condition is satisfied, the controller (90) conducts the process of step ST2. On the other hand, if the outflow end condition is not satisfied, the controller (90) instructs the refrigeration apparatus (10) to continue the outflow operation.<<Other Embodiments>>

[0240] The refrigeration apparatuses (10) of the above embodiments may be modified as follows. The following variations may be combined or replaced as necessary only if the functions of the refrigeration apparatus (10) are not impaired.-First Variation-

[0241] The refrigerant circuit (30) of the refrigeration apparatus (10) of each of the first to fourth embodiments may be provided with a plurality of fourth expansion valves (EV4-1, EV4-2). Here, regarding this variation applied to the refrigeration apparatus (10) of the first embodiment, the differences from the refrigeration apparatus (10) of the first embodiment will be described.

[0242] As shown in FIG. 17, in the refrigerant circuit (30) of this variation, the defrosting pipe (32) is provided with two fourth expansion valves (EV4-1, EV4-2). In the defrosting pipe (32), the two fourth expansion valves (EV4-1, EV4-2) are connected in parallel. The fourth expansion valve (EV4-1), one of the two fourth expansion valves, is a first decompression valve. The fourth expansion valve (EV4-2), the other one of the two fourth expansion valves, is a second decompression valve. In the defrosting pipe (32) of this variation, three or more fourth expansion valves may be connected in parallel.

[0243] In the refrigeration apparatus (10) of this variation, the controller (90) sets each of the fourth expansion valves (EV4-1, EV4-2) to the same opening degree. When changing the opening degrees of the fourth expansion valves (EV4-1, EV4-2), the controller (90) expands or reduces the opening degree of each of the fourth expansion valves (EV4-1, EV4-2) by the same amount. However, the controller (90) may be configured to individually control the opening degree of each of the fourth expansion valves (EV4-1, EV4-2).-Second Variation-

[0244] The refrigeration apparatus (10) of each of the first to fourth embodiments may be configured to perform only a single-stage compression refrigeration cycle. Here, regarding this variation applied to the refrigeration apparatus (10) of the third embodiment, the differences from the refrigeration apparatus (10) of the third embodiment will be described.

[0245] As shown in FIG. 18, the refrigerant circuit (30) of the refrigeration apparatus (10) of this variation is not provided with the low-stage compressor (51), the low-stage connection pipe (44), and the high-stage connection pipe (45). The refrigerant circuit (30) of this variation is provided with one compressor (52) that corresponds to the high-stage compressor of the refrigerant circuit (30) of the third embodiment.

[0246] In the main circuit (31) of the refrigerant circuit (30) of this variation, the other end of the inner heat exchanger (57) is connected to the suction pipe of the compressor (52). The first electric valve (MV1) is provided in part of the main circuit (31) that is between the inner heat exchanger (57) and the suction pipe of the compressor (52). The other end of the intermediate connection pipe (43) is connected to part of the main circuit (31) that is between the first electric valve (MV1) and the compressor (52).

[0247] In the cooling operation of the refrigeration apparatus (10) of this variation, the refrigerant circuit (30) performs the single-stage compression refrigeration cycle. In the refrigerant circuit (30), the compressor (52) operates to circulate the refrigerant in the main circuit (31). The refrigerant discharged by the compressor (52) dissipates heat to the external air in the outer heat exchanger (56). The refrigerant having flowed out from the outer heat exchanger (56) passes through the first flow path (61a) of the internal heat exchanger (61), the first expansion valve (EV1), the receiver (62), the first electromagnetic valve (SV1), and the second expansion valve (EV2) in sequence, and then flows into the inner heat exchanger (57). The refrigerant having flowed into the inner heat exchanger (57) absorbs heat from the air flowing in the internal flow path (20) and then evaporates. The refrigerant having evaporated in the inner heat exchanger (57) is sucked into the compressor (52). The compressor (52) compresses and discharges the sucked refrigerant.-Third Variation-

[0248] In the normal operation of the defrosting operation, the controller (90) of the refrigeration apparatus (10) of each of the first to fourth embodiments may control the opening degree of the fourth expansion valve (EV4) based on the temperature of the refrigerant discharged by the high-stage compressor (52) (specifically, the measurement value of the high-stage discharge temperature sensor (73)). The controller (90) decreases the opening degree of the fourth expansion valve (EV4) as much as possible within a range in which the measurement value of the high-stage discharge temperature sensor (73) is held lower than or equal to the reference temperature.

[0249] Specifically, the controller (90) controls the opening degree of the fourth expansion valve (EV4) so that the measurement value of the high-stage discharge temperature sensor (73) falls within a reference temperature range. The reference temperature range is a temperature range including the reference temperature. The maximum value of the reference temperature range is the reference temperature.

[0250] If the measurement value of the high-stage discharge temperature sensor (73) is lower than the minimum value of the reference temperature range, the controller (90) reduces the opening degree of the fourth expansion valve (EV4). If the measurement value of the high-stage discharge temperature sensor (73) is higher than the maximum value of the reference temperature range (= the reference temperature), the controller (90) expands the opening degree of the fourth expansion valve (EV4). If the measurement value of the high-stage discharge temperature sensor (73) falls within the reference temperature range, the controller (90) maintains the opening degree of the fourth expansion valve (EV4).

[0251] In the normal operation of the defrosting operation, the controller (90) of this variation may control the opening degree of the fourth expansion valve (EV4) based on both the temperature and the pressure of the refrigerant discharged by the high-stage compressor (52). In this case, the controller (90) decreases the opening degree of the fourth expansion valve (EV4) as much as possible within a range in which the measurement value of the high-stage discharge pressure sensor (78) is held lower than or equal to the reference pressure and the measurement value of the high-stage discharge temperature sensor (73) is held lower than or equal to the reference temperature.-Fourth Variation-

[0252] In the first outflow operation of the defrosting operation, the controller (90) of the refrigeration apparatus (10) of each of the first to fourth embodiments may select one of the gas outflow operation or the liquid outflow operation based on the external air temperature.

[0253] If the external air temperature is relatively low, the pressure of the refrigerant in the receiver (62) is relatively low. If the gas outflow operation is performed in this situation, the flow rate of the gas refrigerant flowing out from the receiver (62) decreases, and it may take a long time to increase the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57). Thus, the controller (90) of this variation instructs the refrigeration apparatus (10) to execute the gas outflow operation if the external air temperature is higher than or equal to the reference external air temperature, and instructs the refrigeration apparatus (10) to execute the liquid outflow operation if the external air temperature is lower than the reference external air temperature.-Fifth Variation-

[0254] The refrigeration apparatus (10) of each of the first and second embodiments may not be provided with the reheating heat exchanger (58) and the reheating pipe (33). The refrigeration apparatus (10) of this variation is not provided with the third electromagnetic valve (SV3) and the fifth expansion valve (EV5), both provided in the reheating pipe (33). Thus, the path changing mechanism (67) of this variation does not include the third electromagnetic valve (SV3).-Sixth Variation-

[0255] The refrigeration apparatus (10) of each of the first and second embodiments may not be provided with the first electromagnetic valve (SV1). When the first electromagnetic valve (SV1) in the refrigeration apparatus (10) of each of the first and second embodiments is held in a closed state, the second expansion valve (EV2) in the refrigeration apparatus (10) of this variation is held in a fully-closed state. The path changing mechanism (67) of this variation does not include the first electromagnetic valve (SV1).-Seventh Variation-

[0256] Usage of the refrigeration apparatus (10) of each of the first to fourth embodiments is not limited to the air conditioning of the internal space (5) of the transportation container (1). The refrigeration apparatus (10) of each of the first to fourth embodiments may be used for air conditioning of an internal space of a stationary refrigerator or a cold storage warehouse, for example.

[0257] While the embodiments and variations thereof have been described above, it will be understood that various changes in form and details may be made without departing from the spirit and scope of the claims. The elements according to the embodiments, the variations thereof, and the other embodiments may be combined and replaced with each other. In addition, the expressions of "first", "second", "third", . . . , in the specification and claims are used to distinguish the terms to which these expressions are given, and do not limit the number and order of the terms.INDUSTRIAL APPLICABILITY

[0258] As described above, the present disclosure is useful for a refrigeration apparatus and a transportation container.DESCRIPTION OF REFERENCE CHARACTERS

[0259] 1Transportation Container 2Container Body 5Internal Space (Target Space) 10Refrigeration Apparatus 30Refrigerant Circuit 32Defrosting Pipe (Bypass Passage) 50Compressor 56Outer Heat Exchanger (Heat-Source-Side Heat Exchanger) 57Inner Heat Exchanger (Utilization-Side Heat Exchanger) 58Reheating Heat Exchanger 62Receiver 65Expansion Valve 67Path Changing Mechanism 90Controller EV4Fourth Expansion Valve (Decompression Valve) EV4-1Fourth Expansion Valve (First Decompression Valve) EV4-2Fourth Expansion Valve (Second Decompression Valve)

Examples

first embodiment

[0042]The first embodiment will be described. This embodiment is a transportation container (1) including a refrigeration apparatus (10).

-Transportation Container-

[0043]As shown in FIG. 1, the transportation container (1) includes a container body (2) and the refrigeration apparatus (10). The transportation container (1) is a reefer container capable of controlling a temperature in the container.

[0044]The transportation container (1) of this embodiment is used mainly for marine transportation. The transportation container (1) is loaded onto a ship or the like and transported. Usage of the transportation container (1) is not limited to marine transportation. The transportation container (1) may be used for land transportation. In this case, the transportation container (1) is transported by an automobile such as a truck or by rail.

-Container Body-

[0045]As shown in FIG. 2, the container body (2) is formed in a hollow box shape. The container body (2) is horizontally long. The containe...

third embodiment

[0245]As shown in FIG. 18, the refrigerant circuit (30) of the refrigeration apparatus (10) of this variation is not provided with the low-stage compressor (51), the low-stage connection pipe (44), and the high-stage connection pipe (45). The refrigerant circuit (30) of this variation is provided with one compressor (52) that corresponds to the high-stage compressor of the refrigerant circuit (30) of the

[0246]In the main circuit (31) of the refrigerant circuit (30) of this variation, the other end of the inner heat exchanger (57) is connected to the suction pipe of the compressor (52). The first electric valve (MV1) is provided in part of the main circuit (31) that is between the inner heat exchanger (57) and the suction pipe of the compressor (52). The other end of the intermediate connection pipe (43) is connected to part of the main circuit (31) that is between the first electric valve (MV1) and the compressor (52).

[0247]In the cooling operation of the refrigeration apparatus (10...

TECHNICAL FIELD

[0001] The present disclosure relates to a refrigeration apparatus and a transportation container.BACKGROUND ART

[0002] Patent Document 1 discloses a heat pump device that performs a refrigeration cycle. The heat pump device includes a refrigerant circuit provided with a high-pressure-side defrosting circuit. The high-pressure-side defrosting circuit is a passage in which a refrigerant flows while bypassing a heat-dissipating heat exchanger and a decompression unit. In a defrosting operation to melt the frost on an atmospheric heat exchanger, the refrigerant discharged from a compressor is supplied to the atmospheric heat exchanger through the high-pressure-side defrosting circuit, and the frost on the atmospheric heat exchanger is warmed and melted by the refrigerant.

[0003] In the defrosting operation performed by the heat pump device of Patent Document 1, the refrigerant circulates between the compressor and the atmospheric heat exchanger through the high-pressure-side defrosting circuit. The defrosting operation is an operation to melt the frost on the atmospheric heat exchanger by using the heat applied to the refrigerant in the compressor.CITATION LISTPATENT DOCUMENT

[0004] Patent Document 1: Japanese Unexamined Patent Publication No. 2004-347185SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0005] In the defrosting operation performed by the heat pump device of Patent Document 1, the refrigerant discharged from the compressor flows into the atmospheric heat exchanger substantially without being decompressed. For this reason, the difference between the pressure of the refrigerant sucked into the compressor and the pressure of the refrigerant discharged by the compressor may decrease, and thus the amount of heat applied to the refrigerant by the compressor may decrease. If the amount of heat applied to the refrigerant by the compressor in the defrosting operation is small, the amount of heat used to melt the frost on the atmospheric heat exchanger is smaller, and thus the time to defrost may be longer.

[0006] An object of the present disclosure is to provide a refrigeration apparatus that performs a refrigeration cycle, where the time to defrost a heat exchanger is shorter.SOLUTION TO THE PROBLEM

[0007] A first aspect of the present disclosure is directed to a refrigeration apparatus (10) which includes a refrigerant circuit (30) having a compressor (50), a heat-source-side heat exchanger (56), an expansion valve (65), and a utilization-side heat exchanger (57), and which is configured to condition air in a target space (5), wherein the refrigerant circuit (30) has a bypass passage (32) configured to send a refrigerant discharged by the compressor (50) to the utilization-side heat exchanger (57) while bypassing the heat-source-side heat exchanger (56) and the expansion valve (65), and a decompression valve (EV4) of which an opening degree is variable and which is configured to decompress a refrigerant flowing in the bypass passage (32), the refrigeration apparatus (10) performs a cooling operation to perform a refrigeration cycle in which the heat-source-side heat exchanger (56) functions as a radiator and the utilization-side heat exchanger (57) functions as an evaporator, and to blow air cooled in the utilization-side heat exchanger (57) into the target space (5), and a defrosting operation to melt frost on the utilization-side heat exchanger (57) by supplying the refrigerant discharged by the compressor (50) to the utilization-side heat exchanger (57) through the bypass passage (32), and the refrigeration apparatus (10) includes a controller (90) configured to control the opening degree of the decompression valve (EV4) based on one or both of a pressure and a temperature of the refrigerant discharged by the compressor (50) in the defrosting operation.

[0008] In the first aspect, the refrigeration apparatus (10) performs the defrosting operation. During the defrosting operation, the controller (90) controls the opening degree of the decompression valve (EV4). In the defrosting operation, the refrigerant supplied to the utilization-side heat exchanger (57) through the bypass passage (32) is decompressed when passing through the decompression valve (EV4). Thus, the difference between the pressure of the refrigerant sucked by the compressor (50) (the suction pressure) and the pressure of the refrigerant discharged by the compressor (50) (the discharge pressure) is larger than when the refrigerant discharged by the compressor (50) is supplied to the utilization-side heat exchanger (57) without being decompressed. When the difference between the suction pressure and the discharge pressure is larger, the amount of heat applied to the refrigerant in the course of the compressor (50) compressing the refrigerant increases. Thus, according to this aspect, the amount of heat used to melt the frost on the utilization-side heat exchanger (57) is larger and the time to defrost the utilization-side heat exchanger (57) is shorter than when the refrigerant discharged by the compressor (50) is supplied to the utilization-side heat exchanger (57) without being decompressed.

[0009] A second aspect of the present disclosure is an embodiment of the first aspect. In the second aspect, the refrigerant circuit (30) has a receiver (62) disposed between the heat-source-side heat exchanger (56) and the utilization-side heat exchanger (57), and in the defrosting operation, the refrigeration apparatus (10) performs a normal operation to circulate a refrigerant between the compressor (50) and the utilization-side heat exchanger (57) in a state in which an inflow of a refrigerant to the receiver (62) and an outflow of a refrigerant from the receiver (62) are blocked, an outflow operation to allow a refrigerant to flow out from the receiver (62) to decrease an amount of refrigerant stored in the receiver (62), and an inflow operation to allow a refrigerant to flow into the receiver (62) to increase an amount of refrigerant stored in the receiver (62).

[0010] In the defrosting operation, the refrigeration apparatus (10) of the second aspect performs the normal operation, the outflow operation, and the inflow operation. The outflow operation and the inflow operation are operations to adjust the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) in the defrosting operation. In the outflow operation, the amount of refrigerant stored in the receiver (62) decreases, and the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) increases. In the inflow operation, the amount of refrigerant stored in the receiver (62) increases, and the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) decreases.

[0011] A third aspect of the present disclosure is an embodiment of the second aspect. In the third aspect, the refrigeration apparatus starts the outflow operation if a temperature of the refrigerant discharged by the compressor (50) becomes higher during the normal operation than a reference temperature.

[0012] If the temperature of the refrigerant discharged from the compressor (50) becomes higher during the normal operation, it is estimated that the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) is insufficient. Thus, the refrigeration apparatus (10) of the third aspect ends the normal operation and starts the outflow operation if the temperature of the refrigerant discharged from the compressor (50) becomes higher during the normal operation than the reference temperature.

[0013] A fourth aspect of the present disclosure is an embodiment of the second or third aspect. In the fourth aspect, the refrigeration apparatus starts the normal operation if a degree of superheat of a refrigerant having flowed out from the utilization-side heat exchanger (57) becomes lower during the outflow operation than a reference degree of superheat.

[0014] If the degree of superheat of the refrigerant having discharged from the utilization-side heat exchanger (57) becomes lower during the outflow operation, it is estimated that the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) is appropriate. Thus, the refrigeration apparatus (10) of the fourth aspect ends the outflow operation and starts the normal operation if the degree of superheat of the refrigerant having discharged from the utilization-side heat exchanger (57) becomes lower during the outflow operation than the reference degree of superheat.

[0015] A fifth aspect of the present disclosure is an embodiment of any one of the second to fourth aspects. In the fifth aspect, the outflow operation includes a gas outflow operation to allow a gas refrigerant to flow out from the receiver (62), and a liquid outflow operation to allow a liquid refrigerant to flow out from the receiver (62).

[0016] The refrigeration apparatus (10) of the fifth aspect performs the gas outflow operation or the liquid outflow operation as the outflow operation.

[0017] A sixth aspect of the present disclosure is an embodiment of any one of the second to fourth aspects. In the sixth aspect, in the outflow operation, a refrigerant having flowed out from the receiver (62) is sucked by the compressor (50).

[0018] In the outflow operation performed by the refrigeration apparatus (10) of the sixth aspect, the refrigerant having discharged from the receiver (62) is sucked by the compressor (50). As a result, the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) in the defrosting operation increases.

[0019] A seventh aspect of the present disclosure is an embodiment of the sixth aspect. In the seventh aspect, the outflow operation includes a first outflow operation in which the compressor (50) sucks a refrigerant from both the receiver (62) and the utilization-side heat exchanger (57), and a second outflow operation in which the compressor (50) sucks a refrigerant from the receiver (62) and does not suck a refrigerant from the utilization-side heat exchanger (57).

[0020] The refrigeration apparatus (10) of the seventh aspect performs the first outflow operation or the second outflow operation as the outflow operation. In the first outflow operation, the compressor (50) sucks the refrigerant having flowed out from the receiver (62) and the refrigerant having flowed out from the utilization-side heat exchanger (57). In the second outflow operation, the compressor (50) sucks the refrigerant having flowed out from the receiver (62) and does not suck the refrigerant having flowed out from the utilization-side heat exchanger (57).

[0021] An eighth aspect of the present disclosure is an embodiment of any one of the second to seventh aspects. In the eighth aspect, the refrigeration apparatus starts the inflow operation if a pressure of the refrigerant discharged from the compressor (50) becomes higher during the normal operation than a reference pressure.

[0022] If the pressure of the refrigerant discharged from the compressor (50) becomes higher during the normal operation, it is estimated that the amount of refrigerant circulating between the compressor (50) and the utilization-side heat exchanger (57) is excessive. Thus, the refrigeration apparatus (10) of the eighth aspect ends the normal operation and starts the inflow operation if the pressure of the refrigerant discharged from the compressor (50) becomes higher during the normal operation than the reference pressure.

[0023] A ninth aspect of the present disclosure is an embodiment of any one of the second to eighth aspects. In the ninth aspect, in the inflow operation, part of the refrigerant discharged from the compressor (50) flows into the receiver (62) through the heat-source-side heat exchanger (56), and a rest of the refrigerant discharged from the compressor (50) is supplied to the utilization-side heat exchanger (57) through the bypass passage (32).

[0024] In the inflow operation performed by the refrigeration apparatus (10) of the ninth aspect, part of the refrigerant discharged from the compressor (50) flows into the receiver (62), and the amount of refrigerant stored in the receiver (62) increases. Further, in the inflow operation, the rest of the refrigerant discharged from the compressor (50) is supplied to the utilization-side heat exchanger (57) through the bypass passage (32), and the frost on the utilization-side heat exchanger (57) is melted.

[0025] A tenth aspect of the present disclosure is an embodiment of any one of the first to ninth aspects. In the tenth aspect, the refrigerant circuit (30) has a path changing mechanism (67) that changes a flow path of a refrigerant in the refrigerant circuit (30), and the controller (90) controls the path changing mechanism (67) to switch between the cooling operation and the defrosting operation.

[0026] In the tenth aspect, the controller (90) controls the path changing mechanism (67). The path changing mechanism (67) changes the flow path of a refrigerant to switch between the cooling operation and the defrosting operation.

[0027] An eleventh aspect of the present disclosure is an embodiment of any one of the second to ninth aspects. In the eleventh aspect, the refrigerant circuit (30) has a path changing mechanism (67) that changes a flow path of a refrigerant in the refrigerant circuit (30), and the controller (90) controls the path changing mechanism (67) to switch between the cooling operation and the defrosting operation, and also to switch between the normal operation, the outflow operation, and the inflow operation in the defrosting operation.

[0028] In the eleventh aspect, the controller (90) controls the path changing mechanism (67). The path changing mechanism (67) changes the flow path of a refrigerant to switch between the cooling operation and the defrosting operation. Further, the path changing mechanism (67) changes the flow path of a refrigerant during the defrosting operation to switch between the normal operation, the outflow operation, and the inflow operation.

[0029] A twelfth aspect of the present disclosure is an embodiment of the tenth or eleventh aspect. In the twelfth aspect, the path changing mechanism (67) has a plurality of control valves controlled by the controller (90).

[0030] In the twelfth aspect, the controller (90) controls the plurality of control valves of the path changing mechanism (67).

[0031] A thirteenth aspect of the present disclosure is an embodiment of any one of the first to twelfth aspects. In the thirteenth aspect, the decompression valve includes a first decompression valve (EV4-1) and a second decompression valve (EV4-2) which are connected in parallel.

[0032] In the bypass passage (32) of the refrigeration apparatus (10) of the thirteenth aspect, the first decompression valve (EV4-1) and the second decompression valve (EV4-2) are connected in parallel.

[0033] A fourteenth aspect of the present disclosure is an embodiment of any one of the first to thirteenth aspects. In the fourteenth aspect, the refrigeration apparatus performs a heating operation to supply the refrigerant discharged by the compressor (50) to the utilization-side heat exchanger (57) through the bypass passage (32) and to blow the air heated in the utilization-side heat exchanger (57) into the target space (5).

[0034] In the fourteenth aspect, the refrigeration apparatus (10) performs the heating operation. In the heating operation, the refrigerant discharged by the compressor (50) is supplied to the utilization-side heat exchanger (57) through the bypass passage (32), and exchanges heat with the air passing through the utilization-side heat exchanger (57). The air heated in the utilization-side heat exchanger (57) is blown into the target space (5).

[0035] A fifteenth aspect of the present disclosure is an embodiment of any one of the first to fourteenth aspects. In the fifteenth aspect, the refrigerant circuit (30) has a reheating heat exchanger (58) disposed upstream of the decompression valve (EV4) in the bypass passage (32) and configured to exchange heat between air having passed through the utilization-side heat exchanger (57) and a refrigerant.

[0036] In the fifteenth aspect, the refrigerant circuit (30) is provided with the reheating heat exchanger (58). The reheating heat exchanger (58) exchanges heat between the refrigerant supplied through the bypass passage (32) and the air having passed through the utilization-side heat exchanger (57). The refrigerant having passed through the reheating heat exchanger (58) is sent to the utilization-side heat exchanger (57) after passing through the decompression valve (EV4).

[0037] A sixteenth aspect of the present disclosure is an embodiment of any one of the first to fifteenth aspects. In the sixteenth aspect, the refrigerant circuit (30) is filled with carbon dioxide as a refrigerant.

[0038] The refrigerant circuit (30) of the sixteenth aspect circulates carbon dioxide as the refrigerant to perform the refrigeration cycle.

[0039] A seventeenth aspect of the present disclosure is directed to a transportation container (1) including: the refrigeration apparatus (10) of any one of the first to sixteenth aspects, and a container body (2) forming the target space (5) in which the air is conditioned by the refrigeration apparatus (10).

[0040] The transportation container (1) of the seventeenth aspect includes the refrigeration apparatus (10) and the container body (2). The container body (2) forms the target space (5). The refrigeration apparatus (10) conditions the air in the target space (5).BRIEF DESCRIPTION OF THE DRAWINGS

[0041] [FIG. 1] FIG. 1 is a schematic perspective view of a refrigeration apparatus of a first embodiment. [FIG. 2] FIG. 2 is a schematic sectional view of a transportation container of the first embodiment. [FIG. 3] FIG. 3 is a piping diagram which shows the configuration of the refrigeration apparatus of the first embodiment. [FIG. 4] FIG. 4 is a block diagram which shows the configuration of a controller of the first embodiment. [FIG. 5] FIG. 5 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in a cooling operation. [FIG. 6] FIG. 6 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in a dehumidifying operation. [FIG. 7] FIG. 7 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in a heating operation and a normal operation of a defrosting operation. [FIG. 8] FIG. 8 is a Mollier diagram (a pressure-enthalpy diagram) which shows the change in the state of a refrigerant in a refrigerant circuit during the defrosting operation. [FIG. 9] FIG. 9 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in an inflow operation. [FIG. 10] FIG. 10 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in a gas outflow operation of a first outflow operation. [FIG. 11] FIG. 11 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in a liquid outflow operation of the first outflow operation. [FIG. 12] FIG. 12 is a piping diagram which corresponds to FIG. 3 and which shows the flow of a refrigerant in a gas outflow operation of a second outflow operation. [FIG. 13] FIG. 13 is a state transition diagram which shows operation of a controller in the defrosting operation. [FIG. 14] FIG. 14 is a piping diagram which shows the configuration of a refrigeration apparatus of a second embodiment. [FIG. 15] FIG. 15 is a piping diagram which shows the configuration of a refrigeration apparatus of a third embodiment. [FIG. 16] FIG. 16 is a flowchart which shows operation performed by a controller during a defrosting operation of a refrigeration apparatus of a fourth embodiment. [FIG. 17] FIG. 17 is a piping diagram which shows the configuration of a refrigeration apparatus of a first variation of other embodiments. [FIG. 18] FIG. 18 is a piping diagram which shows the configuration of a refrigeration apparatus of a second variation of the other embodiments. DESCRIPTION OF EMBODIMENTS<<First Embodiment>>

[0042] The first embodiment will be described. This embodiment is a transportation container (1) including a refrigeration apparatus (10).-Transportation Container-

[0043] As shown in FIG. 1, the transportation container (1) includes a container body (2) and the refrigeration apparatus (10). The transportation container (1) is a reefer container capable of controlling a temperature in the container.

[0044] The transportation container (1) of this embodiment is used mainly for marine transportation. The transportation container (1) is loaded onto a ship or the like and transported. Usage of the transportation container (1) is not limited to marine transportation. The transportation container (1) may be used for land transportation. In this case, the transportation container (1) is transported by an automobile such as a truck or by rail.-Container Body-

[0045] As shown in FIG. 2, the container body (2) is formed in a hollow box shape. The container body (2) is horizontally long. The container body (2) has an opening at one end in the longitudinal direction. The opening of the container body (2) is blocked by the refrigeration apparatus (10). The container body (2) forms an internal space (5) for housing cargos. The internal space (5) is a target space in which the air is conditioned by the refrigeration apparatus.-Refrigeration Apparatus-

[0046] As shown in FIG. 2, the refrigeration apparatus (10) is attached to the opening of the container body (2). The refrigeration apparatus (10) of this embodiment is a refrigeration apparatus for transportation. The refrigeration apparatus (10) includes a casing (11), a refrigerant circuit (30), and a controller (80). The refrigeration apparatus (10) adjusts the temperature of the air (the inside air) in the internal space (5).<Casing>

[0047] The casing (11) includes a division wall (12) and a partition plate (15).

[0048] An internal flow path (20) is formed inside the division wall (12). An external chamber (23) is formed outside the division wall (12). The internal flow path (20) and the external chamber (23) are partitioned by the division wall (12).

[0049] The division wall (12) includes an external wall (13) and an internal wall (14). The external wall (13) is located outside the container body (2). The internal wall (14) is located inside the container body (2).

[0050] The external wall (13) closes the opening of the container body (2). The external wall (13) is attached to a peripheral edge portion of the opening of the container body (2). A lower part of the external wall (13) bulges toward the inside of the container body (2). The external chamber (23) is formed by the lower part of the external wall (13).

[0051] The internal wall (14) faces the external wall (13). The internal wall (14) has a shape conforming to the external wall (13). The internal wall (14) is spaced apart from the external wall (13). A thermal insulator (16) is provided between the internal wall (14) and the external wall (13).

[0052] The partition plate (15) is disposed further inward of the container body (2) than the internal wall (14). The internal flow path (20) is formed between the division wall (12) and the partition plate (15). An air inlet port (21) is formed between the upper end of the partition plate (15) and a top panel of the container body (2). An air outlet port (22) is formed between the lower end of the partition plate (15) and the lower end of the division wall (12). The internal flow path (20) is formed from the air inlet port (21) to the air outlet port (22).<Refrigerant Circuit>

[0053] The refrigerant circuit (30) is a closed circuit filled with a refrigerant. The refrigerant circuit (30) circulates a refrigerant to perform a vapor compression refrigeration cycle. The refrigerant circuit (30) includes an outer heat exchanger (56), an inner heat exchanger (57), and a reheating heat exchanger (58). The refrigerant circuit (30) will be described in detail later.

[0054] Each of the outer heat exchanger (56), the inner heat exchanger (57), and the reheating heat exchanger (58) is a fin-and-tube heat exchanger that exchanges heat between a refrigerant and air.

[0055] The outer heat exchanger (56) is disposed in an upper part of the external chamber (23). The outer heat exchanger (56) is a heat-source-side heat exchanger that exchanges heat between a refrigerant and outside air. The outer heat exchanger (56) has a generally rectangular tubular shape.

[0056] The inner heat exchanger (57) is disposed in the internal flow path (20). The inner heat exchanger (57) is a utilization-side heat exchanger that exchanges heat between a refrigerant and inside air.

[0057] The reheating heat exchanger (58) is disposed downstream of the inner heat exchanger (57) in the internal flow path (20). The reheating heat exchanger (58) is a heat exchanger that exchanges heat between a refrigerant and inside air.

[0058] Although not shown, a drain pan is provided below the inner heat exchanger (57). The drain pan receives drain water generated in the inner heat exchanger (57). The drain water having dropped into the drain pan is discharged to the outside of the container.<External Fan>

[0059] The refrigeration apparatus (10) includes an external fan (26). The external fan (26) is a propeller fan. The external fan (26) is disposed in the external chamber (23). The external fan (26) is disposed inside the outer heat exchanger (56) having a tubular shape. The external fan (26) sends the outside air to the outer heat exchanger (56).<Internal Fan>

[0060] The refrigeration apparatus (10) includes an internal fan (27). The internal fan (27) is a propeller fan. The internal fan (27) is disposed in the internal flow path (20). The internal fan (27) is disposed above the inner heat exchanger (57). The internal fan (27) sends the inside air to the inner heat exchanger (57).<Sensor>

[0061] The refrigeration apparatus (10) includes a first air temperature sensor (86), a second air temperature sensor (87), and a humidity sensor (88).

[0062] The first air temperature sensor (86) is disposed upstream of the internal fan (27) in the internal flow path (20). The first air temperature sensor (86) measures the temperature of the air having flowed into the internal flow path (20) through the air inlet port (21).

[0063] The second air temperature sensor (87) and the humidity sensor (88) are disposed downstream of the reheating heat exchanger (58) in the internal flow path (20). The second air temperature sensor (87) measures the temperature of the air having passed through the reheating heat exchanger (58). The humidity sensor (88) measures the relative humidity of the air having passed through the reheating heat exchanger (58).<Electric Component Box>

[0064] As shown in FIG. 1, the refrigeration apparatus (10) includes an electric component box (28). The electric component box (28) is disposed in an upper part in the external chamber (23). The electric component box (28) houses electric components such as an inverter board and a control board.-Refrigerant Circuit-

[0065] As shown in FIG. 3, the refrigerant circuit (30) is a closed circuit filled with a refrigerant. The refrigerant in the refrigerant circuit (30) of this embodiment is carbon dioxide.

[0066] The refrigerant circuit (30) includes a main circuit (31), a defrosting pipe (32), and a reheating pipe (33). The refrigerant circuit (30) includes a gas-side connection pipe (41), a liquid-side connection pipe (42), an intermediate connection pipe (43), a low-stage connection pipe (44), and a high-stage connection pipe (45).<Main Circuit>

[0067] The main circuit (31) includes a low-stage compressor (51), a high-stage compressor (52), the outer heat exchanger (56), a receiver (62), and the inner heat exchanger (57). In the main circuit (31), the low-stage compressor (51), the high-stage compressor (52), the outer heat exchanger (56), the receiver (62), and the inner heat exchanger (57) are connected in sequence through pipes.

[0068] A discharge pipe of the low-stage compressor (51) is connected to a suction pipe of the high-stage compressor (52). A pipe that connects the discharge pipe of the low-stage compressor (51) and the suction pipe of the high-stage compressor (52) is provided with a first check valve (CV1) and a first electric valve (MV1). The first electric valve (MV1) is disposed downstream of the first check valve (CV1). The first check valve (CV1) allows a refrigerant to flow in the direction in which a refrigerant flows out from the low-stage compressor (51), and prevents a refrigerant from flowing in the opposite direction.

[0069] A discharge pipe of the high-stage compressor (52) is connected to one end of the outer heat exchanger (56). A pipe that connects the discharge pipe of the high-stage compressor (52) and one end of the outer heat exchanger (56) is provided with a second check valve (CV2) and a second electric valve (MV2). The second electric valve (MV2) is disposed downstream of the second check valve (CV2). The second check valve (CV2) allows a refrigerant to flow in the direction in which a refrigerant flows out from the high-stage compressor (52), and prevents a refrigerant from flowing in the opposite direction.

[0070] The other end of the outer heat exchanger (56) is connected to an inflow port of the receiver (62). A pipe that connects the other end of the outer heat exchanger (56) and the inflow port of the receiver (62) is provided with a first flow path (61a) of an internal heat exchanger (61) and a first expansion valve (EV1). The first expansion valve (EV1) is disposed downstream of the internal heat exchanger (61).

[0071] A liquid outflow port of the receiver (62) is connected to one end of the inner heat exchanger (57). A pipe that connects the liquid outflow port of the receiver (62) and one end of the inner heat exchanger (57) is provided with a first electromagnetic valve (SV1) and a second expansion valve (EV2). The second expansion valve (EV2) is disposed downstream of the first electromagnetic valve (SV1).

[0072] The other end of the inner heat exchanger (57) is connected to a suction pipe of the low-stage compressor (51).

[0073] In the main circuit (31), the first expansion valve (EV1) is disposed upstream of the receiver (62), and the second expansion valve (EV2) is disposed downstream of the receiver (62). The first expansion valve (EV1) and the second expansion valve (EV2) are the expansion valves (65) of the refrigerant circuit (30).<Gas-Side Connection Pipe>

[0074] One end of the gas-side connection pipe (41) is connected to a gas outflow port of the receiver (62). The other end of the gas-side connection pipe (41) is connected to one end of the intermediate connection pipe (43). The gas-side connection pipe (41) is provided with a second electromagnetic valve (SV2) and a second flow path (61b) of the internal heat exchanger (61). The second flow path (61b) of the internal heat exchanger (61) is disposed downstream of the second electromagnetic valve (SV2).<Liquid-Side Connection Pipe>

[0075] One end of the liquid-side connection pipe (42) is connected to part of the main circuit (31) that is between the first electromagnetic valve (SV1) and the second expansion valve (EV2). The other end of the liquid-side connection pipe (42) is connected to one end of the intermediate connection pipe (43). The liquid-side connection pipe (42) is provided with a third expansion valve (EV3).<Intermediate Connection Pipe>

[0076] As described above, one end of the intermediate connection pipe (43) is connected with the other end of the gas-side connection pipe (41) and the other end of the liquid-side connection pipe (42). The other end of the intermediate connection pipe (43) is connected to part of the main circuit (31) that is between the first electric valve (MV1) and the high-stage compressor (52). The intermediate connection pipe (43) is provided with a third check valve (CV3). The third check valve (CV3) allows a refrigerant to flow from one end to the other end of the intermediate connection pipe (43), and prevents a refrigerant from flowing in the opposite direction.<Low-Stage Connection Pipe>

[0077] The low-stage connection pipe (44) is a pipe that allows a refrigerant to flow while bypassing the low-stage compressor (51). One end of the low-stage connection pipe (44) is connected to part of the main circuit (31) that is between the suction pipe of the low-stage compressor (51) and the inner heat exchanger (57). The other end of the low-stage connection pipe (44) is connected to part of the main circuit (31) that is between the first check valve (CV1) and the first electric valve (MV1). The low-stage connection pipe (44) is provided with a fourth check valve (CV4). The fourth check valve (CV4) allows a refrigerant to flow from one end to the other end of the low-stage connection pipe (44), and prevents a refrigerant from flowing in the opposite direction.<High-Stage Connection Pipe>

[0078] The high-stage connection pipe (45) is a pipe that allows a refrigerant to flow while bypassing the high-stage compressor (52). One end of the high-stage connection pipe (45) is connected to part of the main circuit (31) that is between the first check valve (CV1) and the first electric valve (MV1). The other end of the high-stage connection pipe (45) is connected to part of the main circuit (31) that is between the second check valve (CV2) and the second electric valve (MV2). The high-stage connection pipe (45) is provided with a fifth check valve (CV5). The fifth check valve (CV5) allows a refrigerant to flow from one end to the other end of the high-stage connection pipe (45), and prevents a refrigerant from flowing in the opposite direction.<Defrosting Pipe>

[0079] One end of the defrosting pipe (32) is connected to part of the main circuit (31) that is between the second check valve (CV2) and the second electric valve (MV2). In the main circuit (31), one end of the defrosting pipe (32) is located downstream of the other end of the high-stage connection pipe (45). The other end of the defrosting pipe (32) is connected to part of the main circuit (31) that is between the second expansion valve (EV2) and the inner heat exchanger (57). The defrosting pipe (32) forms a bypass passage that sends the refrigerant discharged by the high-stage compressor (52) to the inner heat exchanger (57) while bypassing the outer heat exchanger (56), the first expansion valve (EV1), and the second expansion valve (EV2).

[0080] The defrosting pipe (32) is provided with a fourth expansion valve (EV4). The fourth expansion valve (EV4) is a decompression valve of which the opening degree is variable and which decompresses the refrigerant flowing in the defrosting pipe (32).<Reheating Pipe>

[0081] One end of the reheating pipe (33) is connected to part of the main circuit (31) that is between the second check valve (CV2) and the second electric valve (MV2). In the main circuit (31), one end of the reheating pipe (33) is located downstream of the other end of the high-stage connection pipe (45). The other end of the reheating pipe (33) is connected to part of the main circuit (31) that is between the second expansion valve (EV2) and the inner heat exchanger (57).

[0082] The reheating pipe (33) is provided with a third electromagnetic valve (SV3), the reheating heat exchanger (58), and a fifth expansion valve (EV5). The reheating heat exchanger (58) is disposed downstream of the third electromagnetic valve (SV3). The fifth expansion valve (EV5) is disposed downstream of the reheating heat exchanger (58).<Expansion Valve>

[0083] Each of the first expansion valve (EV1), the second expansion valve (EV2), the third expansion valve (EV3), the fourth expansion valve (EV4), and the fifth expansion valve (EV5) is a so-called electronic expansion valve. Each of the expansion valves (EV1 to EV5) includes a valve body and a stepping motor that drives the valve body. When the valve body is moved by the stepping motor, the opening degree of the expansion valve (EV1 to EV5) changes continuously.<Electric Valve>

[0084] Each of the first electric valve (MV1) and the second electric valve (MV2) is a valve of which the opening degree is variable. Each of the electric valves (MV1, MV2) includes a valve body and a stepping motor that drives the valve body. When the valve body is moved by the stepping motor, the opening degree of the electric valve (MV1, MV2) changes continuously.<Electromagnetic Valve>

[0085] Each of the first electromagnetic valve (SV1), the second electromagnetic valve (SV2), and the third electromagnetic valve (SV3) is an on-off valve. Each of the electromagnetic valves (SV1 to SV3) includes a valve body and a solenoid that drives the valve body. When the valve body is moved by the solenoid, the electromagnetic valve (SV1 to SV3) is turned on or off.<Path Changing Mechanism>

[0086] The second expansion valve (EV2), the third expansion valve (EV3), the fourth expansion valve (EV4), the second electric valve (MV2), the first electromagnetic valve (SV1), the second electromagnetic valve (SV2), and the third electromagnetic valve (SV3) form a path changing mechanism (67). The path changing mechanism (67) is a mechanism that changes the flow path of a refrigerant in the refrigerant circuit (30).

[0087] The second expansion valve (EV2), the third expansion valve (EV3), the fourth expansion valve (EV4), the second electric valve (MV2), the first electromagnetic valve (SV1), the second electromagnetic valve (SV2), and the third electromagnetic valve (SV3) that form the path changing mechanism (67) are the control valves controlled by a controller (90). When the state of one or more of these valves that form the path changing mechanism (67) is changed by the controller (90), the flow path of a refrigerant in the refrigerant circuit (30) changes, and as a result, the operating state of the refrigeration apparatus (10) changes.<Low-Stage Compressor and High-Stage Compressor>

[0088] Each of the low-stage compressor (51) and the high-stage compressor (52) is a hermetic scroll compressor. Although not shown, each of the low-stage compressor (51) and the high-stage compressor (52) includes a compression mechanism, an electric motor that drives the compression mechanism, and a casing that houses the compression mechanism and the electric motor. The compression mechanism is a scroll type fluid machine, and sucks and compresses a refrigerant.

[0089] The suction pipe of the low-stage compressor (51) is provided with an accumulator (51a). The suction pipe of the high-stage compressor (52) is provided with an accumulator (52a). Each of the low-stage compressor (51) and the high-stage compressor (52) compresses the refrigerant sucked from the suction pipe, and discharges the compressed refrigerant from the discharge pipe. The low-stage compressor (51) and the high-stage compressor (52) are the compressors (50) provided in the refrigerant circuit (30).

[0090] Each of the low-stage compressor (51) and the high-stage compressor (52) is not limited to a scroll compressor. Each of the low-stage compressor (51) and the high-stage compressor (52) may be, for example, a rotary compressor or may be a reciprocating compressor.<Outer Heat Exchanger and Inner Heat Exchanger>

[0091] As described above, each of the outer heat exchanger (56), the inner heat exchanger (57), and the reheating heat exchanger (58) is a fin-and-tube heat exchanger that exchanges heat between a refrigerant and air. The outer heat exchanger (56) exchanges heat between a refrigerant and outside air (external air). Each of the inner heat exchanger (57) and the reheating heat exchanger (58) exchanges heat between a refrigerant and inside air.<Internal Heat Exchanger>

[0092] The internal heat exchanger (61) is a heat exchanger that exchanges heat between a refrigerant and a refrigerant. The internal heat exchanger (61) of this embodiment is a plate-type heat exchanger. The internal heat exchanger (61) has the first flow path (61a) and the second flow path (61b). The first flow path (61a) of the internal heat exchanger (61) is disposed in part of the main circuit (31) that is between the outer heat exchanger (56) and the first expansion valve (EV1). The second flow path (61b) of the internal heat exchanger (61) is disposed downstream of the second electromagnetic valve (SV2) in the gas-side connection pipe (41). The internal heat exchanger (61) exchanges heat between the refrigerant flowing in the first flow path (61a) and the refrigerant flowing in the second flow path (61b).<Receiver>

[0093] The receiver (62) is a container member that stores a refrigerant. The receiver (62) also functions as a gas-liquid separator. The receiver (62) separates the refrigerant in a gas-liquid two-phase state having flowed from the inflow port into a liquid refrigerant and a gas refrigerant. In the receiver (62), the liquid refrigerant is accumulated in a lower part in the receiver (62), and then flows out through the liquid outflow port formed in a bottom part of the receiver (62). In the receiver (62), the gas refrigerant is accumulated in an upper part in the receiver (62), and then flows out through the gas outflow port formed in an upper part of the receiver (62).<Sensors for Low-Stage Compressor>

[0094] In the main circuit (31), a pipe connected to the suction pipe of the low-stage compressor (51) is provided with a low-stage suction temperature sensor (70) and a low-stage suction pressure sensor (75). The low-stage suction temperature sensor (70) measures the temperature of the refrigerant sucked by the low-stage compressor (51). The low-stage suction pressure sensor (75) measures the pressure of the refrigerant sucked by the low-stage compressor (51).

[0095] In the main circuit (31), a pipe between the discharge pipe of the low-stage compressor (51) and the first check valve (CV1) is provided with a low-stage discharge temperature sensor (71) and a low-stage discharge pressure sensor (76). The low-stage discharge temperature sensor (71) measures the temperature of the refrigerant discharged by the low-stage compressor (51). The low-stage discharge pressure sensor (76) measures the pressure of the refrigerant discharged by the low-stage compressor (51).<Sensors for High-Stage Compressor>

[0096] In the main circuit (31), a pipe between the suction pipe of the high-stage compressor (52) and the first electric valve (MV1) is provided with a high-stage suction temperature sensor (72) and a high-stage suction pressure sensor (77). The high-stage suction temperature sensor (72) measures the temperature of the refrigerant sucked by the high-stage compressor (52). The high-stage suction pressure sensor (77) measures the pressure of the refrigerant sucked by the high-stage compressor (52).

[0097] In the main circuit (31), a pipe between the discharge pipe of the high-stage compressor (52) and the second check valve (CV2) is provided with a high-stage discharge temperature sensor (73) and a high-stage discharge pressure sensor (78). The high-stage discharge temperature sensor (73) measures the temperature of the refrigerant discharged by the high-stage compressor (52). The high-stage discharge pressure sensor (78) measures the pressure of the refrigerant discharged by the high-stage compressor (52).<Other Sensors>

[0098] The refrigerant circuit (30) is provided with a receiver pressure sensor (79), first to fourth refrigerant temperature sensors (81 to 84), and a heat exchanger temperature sensor (85).

[0099] The receiver pressure sensor (79) is connected to part of the gas-side connection pipe (41) that is between the receiver (62) and the second electromagnetic valve (SV2). The receiver pressure sensor (79) measures the pressure of the refrigerant stored in the receiver (62).

[0100] The first refrigerant temperature sensor (81) is provided in a pipe of the main circuit (31) that is between the outer heat exchanger (56) and the internal heat exchanger (61). The first refrigerant temperature sensor (81) measures the temperature of the refrigerant flowing into the first flow path (61a) of the internal heat exchanger (61).

[0101] The second refrigerant temperature sensor (82) is provided in a pipe of the main circuit (31) that is between the receiver (62) and the first electromagnetic valve (SV1). The second refrigerant temperature sensor (82) measures the temperature of the refrigerant having flowed out from the liquid outflow port of the receiver (62).

[0102] The third refrigerant temperature sensor (83) is provided in a pipe of the main circuit (31) that is between the second expansion valve (EV2) and the inner heat exchanger (57). The third refrigerant temperature sensor (83) is disposed near one end of the inner heat exchanger (57). The third refrigerant temperature sensor (83) measures the temperature of the refrigerant at the inlet of the inner heat exchanger (57).

[0103] The fourth refrigerant temperature sensor (84) is provided in a pipe of the main circuit (31) that is between the inner heat exchanger (57) and the low-stage compressor (51). The fourth refrigerant temperature sensor (84) is disposed near the other end of the inner heat exchanger (57). The fourth refrigerant temperature sensor (84) measures the temperature of the refrigerant at the outlet of the inner heat exchanger (57).

[0104] The heat exchanger temperature sensor (85) is attached to the inner heat exchanger (57). The heat exchanger temperature sensor (85) measures the temperature of the inner heat exchanger (57).-Controller-

[0105] As shown in FIG. 4, the controller (90) includes a microcomputer (91) and a memory device (92). The memory device (92) is a semiconductor memory. The memory device (92) stores software for operating the microcomputer (91). The controller (90) is housed in the electric component box (28).

[0106] The controller (90) receives measurement values of the sensors provided in the refrigeration apparatus (10). The controller (90) controls the devices provided in the refrigeration apparatus (10) based on the received measurement values of the sensors. For example, the controller (90) controls the rotational speed of the low-stage compressor (51), the rotational speed of the high-stage compressor (52), the opening degrees of the first to fifth expansion valves (EV1 to EV5), the opening degrees of the first and second electric valves (MV1, MV2), the rotational speed of the external fan (26), the rotational speed of the internal fan (27), and the like.-Operation of Refrigeration Apparatus-

[0107] The operation of the refrigeration apparatus (10) will be described. The refrigeration apparatus (10) performs a cooling operation, a dehumidifying operation, a heating operation, and a defrosting operation. Switching between the cooling operation, the dehumidifying operation, the heating operation, and the defrosting operation is performed by the controller (90) controlling the plurality of valves that form the path changing mechanism (67).<Cooling Operation>

[0108] The cooling operation is an operation to cool the inside air. In the cooling operation, the refrigeration apparatus (10) blows the air cooled in the inner heat exchanger (57) into the internal space (5).

[0109] When the refrigeration apparatus (10) performs the cooling operation, the refrigerant circuit (30) performs a refrigeration cycle. In the cooling operation, the refrigerant circulates in the main circuit (31) of the refrigerant circuit (30), the outer heat exchanger (56) functions as a radiator, and the inner heat exchanger (57) functions as an evaporator. The inner heat exchanger (57) cools the air flowing in the internal flow path (20). In the cooling operation, the refrigerant flows in the gas-side connection pipe (41) and the intermediate connection pipe (43).

[0110] When the refrigeration apparatus (10) performs the cooling operation, the controller (90) operates the external fan (26) and the internal fan (27). In the transportation container (1), the air circulates between the internal flow path (20) of the refrigeration apparatus (10) and the internal space (5) of the container body (2). The inside air of the internal space (5) flows into the internal flow path (20) through the air inlet port (21). The inside air flowing in the internal flow path (20) is cooled by the inner heat exchanger (57). The inside air cooled by the inner heat exchanger (57) is supplied to the internal space (5) through the air outlet port (22).

[0111] In the cooling operation, the controller (90) controls the rotational speeds of the low-stage compressor (51) and the high-stage compressor (52) and the like so that the temperature of the air blown into the internal space (5) through the air outlet port (22) (specifically, the measurement value of the second air temperature sensor (87)) can reach a set temperature.

[0112] The cooling operation will be described with reference to FIG. 5.

[0113] In the cooling operation, the controller (90) controls the rotational speeds of the low-stage compressor (51) and the high-stage compressor (52). Further, the controller (90) controls the opening degrees of the first expansion valve (EV1) and the second expansion valve (EV2), and holds the third expansion valve (EV3), the fourth expansion valve (EV4), and the fifth expansion valve (EV5) in a fully-closed state. Further, the controller (90) holds the first electric valve (MV1) and the second electric valve (MV2) in a fully-open state, holds the first electromagnetic valve (SV1) and the second electromagnetic valve (SV2) in an open state, and holds third electromagnetic valve (SV3) in a closed state.

[0114] The high-stage compressor (52) compresses the sucked refrigerant to a pressure higher than the critical pressure of the refrigerant and discharges the compressed refrigerant. The refrigerant having discharged from the high-stage compressor (52) exchanges heat with the external air in the outer heat exchanger (56), and dissipates heat to the external air. The refrigerant having passed through the outer heat exchanger (56) flows into the first flow path (61a) of the internal heat exchanger (61), and is cooled by exchanging heat with the refrigerant flowing in the second flow path (61b) of the internal heat exchanger (61). The refrigerant having passed through the first flow path (61a) of the internal heat exchanger (61) is decompressed when passing through the first expansion valve (EV1) and is brought into a gas-liquid two-phase state. Then, the refrigerant flows into the receiver (62), and is separated into a liquid refrigerant and a gas refrigerant.

[0115] The liquid refrigerant having flowed out from the receiver (62) is decompressed when passing through the second expansion valve (EV2), and then flows into the inner heat exchanger (57). The refrigerant having flowed into the inner heat exchanger (57) absorbs heat from the air passing through the inner heat exchanger (57) and then is evaporated. The refrigerant having flowed out from the inner heat exchanger (57) is sucked into the low-stage compressor (51). The low-stage compressor (51) compresses and discharges the sucked refrigerant. The refrigerant having discharged from the low-stage compressor (51) is sucked into the high-stage compressor (52).

[0116] The gas refrigerant having flowed out from the receiver (62) flows in the gas-side connection pipe (41), then flows into the second flow path (61b) of the internal heat exchanger (61), and then absorbs heat from the refrigerant flowing in the first flow path (61a) of the internal heat exchanger (61). The refrigerant having flowed out from the second flow path (61b) of the internal heat exchanger (61) passes through the intermediate connection pipe (43), and is sucked into the high-stage compressor (52) together with the refrigerant having discharged from the low-stage compressor (51).<Dehumidifying Operation>

[0117] The dehumidifying operation is an operation to dehumidify the inside air while maintaining the temperature of the air in the internal space (5). In the dehumidifying operation, the refrigeration apparatus (10) blows the air dehumidified in the inner heat exchanger (57) and then heated in the reheating heat exchanger (58) into the internal space (5).

[0118] In the dehumidifying operation of the refrigeration apparatus (10), similarly to the cooling operation, the controller (90) operates the external fan (26) and the internal fan (27). In the transportation container (1), the air circulates between the internal flow path (20) of the refrigeration apparatus (10) and the internal space (5) of the container body (2). The inside air of the internal space (5) flows into the internal flow path (20) through the air inlet port (21). The inside air flowing in the internal flow path (20) passes through the inner heat exchanger (57) and the reheating heat exchanger (58) in sequence, and then is supplied to the internal space (5) through the air outlet port (22).

[0119] The dehumidifying operation will be described with reference to FIG. 6.

[0120] In the dehumidifying operation, the controller (90) controls the rotational speeds of the low-stage compressor (51) and the high-stage compressor (52). Further, the controller (90) controls the opening degrees of the first expansion valve (EV1), the second expansion valve (EV2), and the fifth expansion valve (EV5), and holds the third expansion valve (EV3) and the fourth expansion valve (EV4) in a fully-closed state. Further, the controller (90) holds the first electric valve (MV1) and the second electric valve (MV2) in a fully-open state, and holds the first electromagnetic valve (SV1), the second electromagnetic valve (SV2), and the third electromagnetic valve (SV3) in an open state.

[0121] The dehumidifying operation is different from the cooling operation in that the controller (90) controls the opening degree of the fifth expansion valve (EV5) and holds the third electromagnetic valve (SV3) in an open state. Further, the dehumidifying operation is different from the cooling operation in that the refrigerant flows in the reheating pipe (33) as well as the main circuit (31), the gas-side connection pipe (41), and the intermediate connection pipe (43).

[0122] When the refrigeration apparatus (10) performs the dehumidifying operation, the refrigerant circuit (30) performs a refrigeration cycle. In the dehumidifying operation, similarly to the cooling operation, the refrigerant circulates in the main circuit (31) of the refrigerant circuit (30), the outer heat exchanger (56) functions as a radiator, and the inner heat exchanger (57) functions as an evaporator. The inner heat exchanger (57) cools the air flowing in the internal flow path (20).

[0123] In the dehumidifying operation, the evaporation temperature of the refrigerant in the inner heat exchanger (57) is set to a value lower than the dew point temperature of the air flowing into the inner heat exchanger (57). Thus, in the inner heat exchanger (57), the moisture contained in the air is condensed into drain water. The drain water generated in the inner heat exchanger (57) flows down into the drain pan, and then is discharged to the outside of the container. Thus, each of the temperature and absolute humidity of the air flowing in the internal flow path (20) is reduced when the air passes through the inner heat exchanger (57).

[0124] In the dehumidifying operation, similarly to the cooling operation, the refrigerant flows in the gas-side connection pipe (41) and the intermediate connection pipe (43). The gas refrigerant having flowed out from the receiver (62) passes through the gas-side connection pipe (41) and the intermediate connection pipe (43) in sequence, and then is sucked into the high-stage compressor (52) together with the refrigerant having discharged from the low-stage compressor (51).

[0125] In the dehumidifying operation, part of the refrigerant having discharged from the high-stage compressor (52) is supplied to the reheating heat exchanger (58) through the reheating pipe (33). In the reheating heat exchanger (58), the air having passed through the inner heat exchanger (57) is heated by the refrigerant. The refrigerant having dissipated heat in the reheating heat exchanger (58) is decompressed when passing through the fifth expansion valve (EV5). The refrigerant having passed through the fifth expansion valve (EV5) flows into the main circuit (31), and then flows into the inner heat exchanger (57) together with the refrigerant having passed through the second expansion valve (EV2).

[0126] In the dehumidifying operation, the controller (90) controls the rotational speed of the low-stage compressor (51) so that the humidity of the air having passed through the reheating heat exchanger (58) can reach a target humidity. Specifically, the controller (90) controls the rotational speed of the low-stage compressor (51) so that the measurement value of the humidity sensor (88) can reach a set humidity. If the measurement value of the humidity sensor (88) is higher than the set humidity, the controller (90) increases the rotational speed of the low-stage compressor (51) in order to decrease the evaporation temperature of the refrigerant in the inner heat exchanger (57). If the measurement value of the humidity sensor (88) is lower than the set humidity, the controller (90) decreases the rotational speed of the low-stage compressor (51) in order to increase the evaporation temperature of the refrigerant in the inner heat exchanger (57).

[0127] In the dehumidifying operation, the controller (90) controls the opening degree of the fifth expansion valve (EV5) so that the temperature of the air having passed through the reheating heat exchanger (58) can reach a set temperature. Specifically, the controller (90) controls the opening degree of the fifth expansion valve (EV5) so that the measurement value of the second air temperature sensor (87) can reach the set temperature. If the measurement value of the second air temperature sensor (87) is higher than the set temperature, the controller (90) reduces the opening degree of the fifth expansion valve (EV5) in order to decrease the flow rate of the refrigerant in the reheating heat exchanger (58). If the measurement value of the second air temperature sensor (87) is lower than the set temperature, the controller (90) expands the opening degree of the fifth expansion valve (EV5) in order to increase the flow rate of the refrigerant in the reheating heat exchanger (58).

[0128] In the dehumidifying operation, the temperature and absolute humidity of the air flowing in the internal flow path (20) decrease in the course of passing through the inner heat exchanger (57), and the temperature of the air increases in the course of passing through the reheating heat exchanger (58). Thus, by the refrigeration apparatus (10) performing the dehumidifying operation, it is possible to decrease the humidity of the inside air while maintaining the temperature of the air in the internal space (5).<Heating Operation>

[0129] The heating operation is an operation to heat the inside air. In the heating operation, the refrigeration apparatus (10) blows the air heated in the inner heat exchanger (57) into the internal space (5). The heating operation is performed to hold the temperature of the air in the internal space (5) at a set temperature if the external air temperature is lower than the set temperature of the internal space (5), for example.

[0130] When the refrigeration apparatus (10) performs the heating operation, the controller (90) holds the external fan (26) in a stop state, and operates the internal fan (27). In the transportation container (1), the air circulates between the internal flow path (20) of the refrigeration apparatus (10) and the internal space (5) of the container body (2). The inside air of the internal space (5) flows into the internal flow path (20) through the air inlet port (21). The inside air flowing in the internal flow path (20) passes through the inner heat exchanger (57), and then is supplied to the internal space (5) through the air outlet port (22).

[0131] The heating operation will be described with reference to FIG. 7.

[0132] In the heating operation, the controller (90) holds the low-stage compressor (51) in the stop state, and controls the rotational speed of the high-stage compressor (52). Further, the controller (90) holds the first expansion valve (EV1) in an open state, holds the second expansion valve (EV2), the third expansion valve (EV3), and the fifth expansion valve (EV5) in a closed state, and controls the opening degree of the fourth expansion valve (EV4). Further, the controller (90) holds the first electric valve (MV1) in a fully-open state, holds the second electric valve (MV2) in a fully-closed state, and holds the first electromagnetic valve (SV1), the second electromagnetic valve (SV2), and the third electromagnetic valve (SV3) in a closed state.

[0133] In the refrigerant circuit (30) that is performing the heating operation, the refrigerant circulates between the high-stage compressor (52) and the inner heat exchanger (57) without passing through the outer heat exchanger (56). The refrigerant having discharged from the high-stage compressor (52) flows in the defrosting pipe (32), and then is decompressed when passing through the fourth expansion valve (EV4). The refrigerant having passed through the fourth expansion valve (EV4) flows into the inner heat exchanger (57), and then dissipates heat to the air passing through the inner heat exchanger (57). The refrigerant having flowed out from the inner heat exchanger (57) is sucked into the high-stage compressor (52) through the low-stage connection pipe (44). The high-stage compressor (52) compresses and discharges the sucked refrigerant.

[0134] In the heating operation, the controller (90) controls the opening degree of the fourth expansion valve (EV4) so that the temperature of the air having passed through the inner heat exchanger (57) can reach a set temperature. Specifically, the controller (90) controls the opening degree of the fourth expansion valve (EV4) so that the measurement value of the second air temperature sensor (87) can reach the set temperature. If the measurement value of the second air temperature sensor (87) is higher than the set temperature, the controller (90) reduces the opening degree of the fourth expansion valve (EV4) in order to decrease the flow rate of the refrigerant in the inner heat exchanger (57). If the measurement value of the second air temperature sensor (87) is lower than the set temperature, the controller (90) expands the opening degree of the fourth expansion valve (EV4) in order to increase the flow rate of the refrigerant in the inner heat exchanger (57).-Defrosting Operation of Refrigeration Apparatus-

[0135] The defrosting operation is an operation to melt the frost on the inner heat exchanger (57) in the cooling operation.

[0136] In the cooling operation, the evaporation temperature of the refrigerant in the inner heat exchanger (57) may be lower than 0°C. In this case, the moisture in the air is frozen into frost, and the frost adheres to the inner heat exchanger (57). When the frost adheres to the inner heat exchanger (57), the frost blocks the flow of the air passing through the inner heat exchanger (57), and blocks heat exchange between the refrigerant and the air.

[0137] Thus, if the defrosting start condition is satisfied during the cooling operation, the refrigeration apparatus (10) temporarily stops the cooling operation and performs the defrosting operation. For example, the defrosting start condition is the condition that "the cumulative value of the execution time of the cooling operation in which the evaporation temperature of the refrigerant in the internal heat exchanger is lower than 0°C has reached a predetermined time (for example, 2 hours)".

[0138] If the defrosting end condition is satisfied during the defrosting operation, the refrigeration apparatus (10) ends the defrosting operation, and restarts the cooling operation. For example, the defrosting end condition is the condition that "the temperature of the inner heat exchanger (57) (specifically, the measurement value of the heat exchanger temperature sensor (85)) has reached a predetermined temperature (for example, 10°C)".

[0139] In the defrosting operation, the refrigeration apparatus (10) mainly performs a normal operation. If the mass of the refrigerant that circulates between the high-stage compressor (52) and the inner heat exchanger (57) becomes too large during the normal operation, the refrigeration apparatus (10) temporarily stops the normal operation and performs an inflow operation. If the mass of the refrigerant that circulates between the high-stage compressor (52) and the inner heat exchanger (57) becomes too small during the normal operation, the refrigeration apparatus (10) temporarily stops the normal operation and performs an outflow operation. Switching between the normal operation, the inflow operation, and the outflow operation is performed by the controller (90) controlling the plurality of valves that form the path changing mechanism (67).

[0140] In each of the normal operation, the inflow operation, and the outflow operation, the controller (90) holds the internal fan (27) in a stop state. Thus, no air flows in the internal flow path (20). Further, in each of the normal operation, the inflow operation, and the outflow operation, the controller (90) holds the low-stage compressor (51) in a stop state, and operates the high-stage compressor (52).<Normal Operation>

[0141] The normal operation of the defrosting operation will be described with reference to FIG. 7.

[0142] In the normal operation, the controller (90) holds the external fan (26) and the internal fan (27) in a stop state. Further, the controller (90) holds the low-stage compressor (51) in a stop state, and controls the rotational speed of the high-stage compressor (52). Further, the controller (90) holds the first expansion valve (EV1) in an open state, holds the second expansion valve (EV2), the third expansion valve (EV3), and the fifth expansion valve (EV5) in a closed state, and controls the opening degree of the fourth expansion valve (EV4). Further, the controller (90) holds the first electric valve (MV1) in a fully-open state, holds the second electric valve (MV2) in a fully-closed state, and holds the first electromagnetic valve (SV1), the second electromagnetic valve (SV2), and the third electromagnetic valve (SV3) in a closed state.

[0143] In the refrigerant circuit (30) operating in the normal operation, the refrigerant flows as in the heating operation. In the refrigerant circuit (30) operating in the normal operation, the refrigerant circulates between the high-stage compressor (52) and the inner heat exchanger (57) in a state in which the inflow of a refrigerant to and the outflow of a refrigerant from the receiver (62) are blocked.

[0144] The state of the refrigerant in the refrigerant circuit (30) operating in the normal operation will be described with reference to a Mollier diagram (a pressure-enthalpy diagram) of FIG. 8.

[0145] In the refrigerant circuit (30), the refrigerant in the state of the point A is sucked into the high-stage compressor (52), and is compressed into the state of the point B by the high-stage compressor (52). In the course of the refrigerant being compressed by the high-stage compressor (52), the pressure of the refrigerant increases, and the enthalpy of the refrigerant increases.

[0146] The refrigerant having discharged from the high-stage compressor (52) flows into the fourth expansion valve (EV4) through the defrosting pipe (32). In the course of flowing from the high-stage compressor (52) to the fourth expansion valve (EV4), the refrigerant dissipates some heat, and thus the state of the refrigerant changes from the point B to the point C. The refrigerant in the state of the point C is decompressed in the course of passing through the fourth expansion valve (EV4) and is brought into the state of the point D.

[0147] The refrigerant in the state of the point D flows into the inner heat exchanger (57) and dissipates heat. In the inner heat exchanger (57), the frost on the inner heat exchanger (57) is warmed and melted by the refrigerant. Further, in the inner heat exchanger (57), the pressure of the refrigerant decreases due to a pressure loss in the course of the refrigerant passing through the inner heat exchanger (57). Thus, the refrigerant is brought into the state of the point E at the outlet of the inner heat exchanger (57). The refrigerant having flowed out from the inner heat exchanger (57) dissipates some heat in the course of flowing toward the high-stage compressor (52) and is brought into the state of the point A.<Inflow Operation>

[0148] The inflow operation is an operation to allow the refrigerant to flow into the receiver (62) in order to increase the mass of the refrigerant stored in the receiver (62). The refrigeration apparatus (10) performs the inflow operation to decrease the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57).

[0149] The inflow operation of the defrosting operation will be described with reference to FIG. 9.

[0150] In the inflow operation, the controller (90) operates the external fan (26), and brings the second electric valve (MV2) into an open state. The differences between the inflow operation and the normal operation are that the external fan (26) is operated and that the second electric valve (MV2) is brought into an open state. Further, in the inflow operation, the controller (90) controls the opening degree of the first expansion valve (EV1) as necessary.

[0151] In the inflow operation, similarly to the normal operation, the refrigerant circulates between the high-stage compressor (52) and the inner heat exchanger (57). In the inflow operation, part of the refrigerant having discharged from the high-stage compressor (52) flows into the outer heat exchanger (56). The refrigerant having flowed into the outer heat exchanger (56) dissipates heat to the external air, and then flows into the receiver (62) through the first expansion valve (EV1).

[0152] In the inflow operation, since the first electromagnetic valve (SV1) and the second electromagnetic valve (SV2) are in a closed state, no refrigerant flows out from the receiver (62). Thus, in the inflow operation, the mass of the refrigerant stored in the receiver (62) increases, and as a result, the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) decreases.

[0153] If the pressure of the refrigerant discharged by the high-stage compressor (52) during the inflow operation is higher than to equal to the critical pressure of the refrigerant, the controller (90) controls the opening degree of the first expansion valve (EV1) so that the pressure of the refrigerant flowing into the receiver (62) is lower than the critical pressure of the refrigerant.<Outflow Operation>

[0154] The outflow operation is an operation to allow the refrigerant to flow out from the receiver (62) in order to decrease the mass of the refrigerant stored in the receiver (62). The refrigeration apparatus (10) performs the outflow operation to increase the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57).

[0155] The refrigeration apparatus (10) performs a first outflow operation or a second outflow operation as the outflow operation. In each of the first outflow operation and the second outflow operation, the refrigeration apparatus (10) performs a gas outflow operation or a liquid outflow operation.<First Outflow Operation / Gas Outflow Operation>

[0156] The gas outflow operation of the first outflow operation will be described with reference to FIG. 10.

[0157] In the gas outflow operation of the first outflow operation, the controller (90) brings the second electromagnetic valve (SV2) into an open state. The difference between the gas outflow operation of the first outflow operation and the normal operation is that the second electromagnetic valve (SV2) is brought into an open state.

[0158] In the gas outflow operation of the first outflow operation, similarly to the normal operation, the refrigerant circulates between the high-stage compressor (52) and the inner heat exchanger (57). In the gas outflow operation of the first outflow operation, the gas refrigerant in the receiver (62) flows into the gas-side connection pipe (41). The gas refrigerant having flowed into the gas-side connection pipe (41) passes through the intermediate connection pipe (43), and is sucked into the high-stage compressor (52) together with the refrigerant having flowed out from the inner heat exchanger (57).

[0159] In the gas outflow operation of the first outflow operation, since the second electric valve (MV2) is in a closed state, no refrigerant flows into the receiver (62). Thus, in the gas outflow operation of the first outflow operation, the mass of the refrigerant stored in the receiver (62) decreases, and as a result, the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) increases.<First Outflow Operation / Liquid Outflow Operation>

[0160] For example, if the external air temperature is relatively low, the pressure of the refrigerant in the receiver (62) is relatively low; and thus the difference between the pressure of the refrigerant in the receiver (62) and the pressure of the refrigerant in the inner heat exchanger (57) may be small during the outflow operation. If the gas outflow operation is performed in this case, the flow rate of the gas refrigerant flowing out from the receiver (62) decreases, and thus it may take a long time to increase the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57). For this reason, in such a case, the refrigeration apparatus (10) performs the liquid outflow operation instead of the gas outflow operation.

[0161] The liquid outflow operation of the first outflow operation will be described with reference to FIG. 11.

[0162] In the liquid outflow operation of the first outflow operation, the controller (90) brings the first electromagnetic valve (SV1) into an open state, brings the second electromagnetic valve (SV2) into a closed state, and brings the third expansion valve (EV3) into an open state. The differences between the liquid outflow operation and the gas outflow operation of the first outflow operation are that the second electromagnetic valve (SV2) is brought into a closed state and that the first electromagnetic valve (SV1) and the third expansion valve (EV3) are brought into an open state.

[0163] In the liquid outflow operation of the first outflow operation, similarly to the gas outflow operation of the first outflow operation, the refrigerant circulates between the high-stage compressor (52) and the inner heat exchanger (57). In the liquid outflow operation of the first outflow operation, the liquid refrigerant in the receiver (62) flows into the liquid-side connection pipe (42). The liquid refrigerant having flowed into the liquid-side connection pipe (42) passes through the intermediate connection pipe (43), and is sucked into the high-stage compressor (52) together with the refrigerant having flowed out from the inner heat exchanger (57).

[0164] In the liquid outflow operation of the first outflow operation, since the second electric valve (MV2) is in a closed state, no refrigerant flows into the receiver (62). Thus, in the liquid outflow operation of the first outflow operation, the mass of the refrigerant stored in the receiver (62) decreases, and as a result, the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) increases.

[0165] The liquid refrigerant in the receiver (62) has a higher density than the gas refrigerant in the receiver (62). Thus, even if the difference between the pressure of the refrigerant in the receiver (62) and the pressure of the refrigerant in the inner heat exchanger (57) is small, the mass flow rate of the refrigerant flowing out from the receiver (62) can be ensured, and the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) can be sufficiently increased in a relatively short time.<Second Outflow Operation>

[0166] For example, if the external air temperature is extremely low, the pressure of the refrigerant in the receiver (62) may be lower during the outflow operation than the pressure of the refrigerant in the inner heat exchanger (57). On the other hand, in the first outflow operation, the pressure of the refrigerant sucked into the high-stage compressor (52) is substantially equal to the pressure of the refrigerant in the inner heat exchanger (57). Thus, even if the first outflow operation is performed in such a case, the refrigerant is not allowed to flow out from the receiver (62). For this reason, in such a case, the refrigeration apparatus (10) performs the second outflow operation instead of the first outflow operation.

[0167] The gas outflow operation of the second outflow operation will be described with reference to FIG. 12.

[0168] In the gas outflow operation of the second outflow operation, the controller (90) brings the first electric valve (MV1) into a closed state. The difference between the gas outflow operation of the second outflow operation and the gas outflow operation of the first outflow operation is that the first electric valve (MV1) is brought into a closed state.

[0169] In the gas outflow operation of the second outflow operation, the first electric valve (MV1) is in a closed state, and a portion between the high-stage compressor (52) and the inner heat exchanger (57) is blocked by the first electric valve (MV1). Thus, the high-stage compressor (52) sucks the refrigerant from the receiver (62) alone out of the receiver (62) and the inner heat exchanger (57).

[0170] Similarly to the gas outflow operation of the first outflow operation, the gas refrigerant having flowed out from the gas outflow port of the receiver (62) passes through the gas-side connection pipe (41) and the intermediate connection pipe (43), and then is sucked into the high-stage compressor (52). Thus, in the gas outflow operation of the second outflow operation, the mass of the refrigerant stored in the receiver (62) decreases, and as a result, the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) increases when the normal operation is restarted.

[0171] The liquid outflow operation of the second outflow operation will be described.

[0172] In the liquid outflow operation of the second outflow operation, the controller (90) brings the first electric valve (MV1) into a closed state. The difference between the liquid outflow operation of the second outflow operation and the liquid outflow operation of the first outflow operation is that the first electric valve (MV1) is brought into a closed state.

[0173] In the liquid outflow operation of the second outflow operation, the first electric valve (MV1) is in a closed state, and a portion between the high-stage compressor (52) and the inner heat exchanger (57) is blocked by the first electric valve (MV1). Thus, the high-stage compressor (52) sucks the refrigerant from the receiver (62) alone out of the receiver (62) and the inner heat exchanger (57).

[0174] Similarly to the liquid outflow operation of the first outflow operation, the liquid refrigerant having flowed out from the liquid outflow port of the receiver (62) passes through the liquid-side connection pipe (42) and the intermediate connection pipe (43), and then is sucked into the high-stage compressor (52). Thus, in the liquid outflow operation of the second outflow operation, the mass of the refrigerant stored in the receiver (62) decreases, and as a result, the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) increases when the normal operation is restarted.-Operation of Controller in Defrosting Operation-

[0175] The operation performed by the controller (90) in the defrosting operation will be described with reference to FIG. 13.

[0176] In the defrosting operation, the controller (90) controls the refrigeration apparatus (10) so that the amount of heat applied to the internal heat exchanger to melt frost (hereinafter referred to as the "defrosting heat amount") can reach a target heat amount.

[0177] As an index of the dehumidification heat amount, the controller (90) of this embodiment uses the current supplied to the electric motor of the high-stage compressor (52) (hereinafter referred to as the "input current"). As the target current, the controller (90) stores the value of the input current at which the defrosting heat amount can reach the target heat amount. The controller (90) of this embodiment instructs the refrigeration apparatus (10) to selectively execute the normal operation, the inflow operation, or the outflow operation so that the input current of the high-stage compressor (52) can reach the target current.<Control in Normal Operation>

[0178] In the normal operation, the controller (90) controls the rotational speed of the high-stage compressor (52) and the opening degree of the fourth expansion valve (EV4). The controller (90) controls the rotational speed of the high-stage compressor (52) prior to controlling the opening degree of the fourth expansion valve (EV4).

[0179] When the normal operation is started, the controller (90) sets the opening degree of the fourth expansion valve (EV4) to an initial opening degree, and controls the rotational speed of the high-stage compressor (52) based on the input current. The controller (90) controls the rotational speed of the high-stage compressor (52) so that the input current can reach the target current. If the input current is lower than the target current, the controller (90) increases the rotational speed of the high-stage compressor (52). If the input current is higher than the target current, the controller (90) decreases the rotational speed of the high-stage compressor (52).

[0180] When the rotational speed of the high-stage compressor (52) reaches a reference speed (for example, the upper speed limit) but the input current is lower than the target current, the defrosting heat amount is insufficient, but the defrosting heat amount cannot be increased by the control of the rotational speed of the high-stage compressor (52). For this reason, in this case, the controller (90) controls the opening degree of the fourth expansion valve (EV4).

[0181] The controller (90) controls the opening degree of the fourth expansion valve (EV4) based on the pressure of the refrigerant discharged by the high-stage compressor (52) (specifically, the measurement value of the high-stage discharge pressure sensor (78)). The controller (90) decreases the opening degree of the fourth expansion valve (EV4) as much as possible within a range in which the measurement value of the high-stage discharge pressure sensor (78) is held lower than or equal to the reference pressure.

[0182] Specifically, the controller (90) controls the opening degree of the fourth expansion valve (EV4) so that the measurement value of the high-stage discharge pressure sensor (78) falls within a reference pressure range. The reference pressure range is a pressure range including the reference pressure. The maximum value of the reference pressure range is the reference pressure.

[0183] If the measurement value of the high-stage discharge pressure sensor (78) is lower than the minimum value of the reference pressure range, the controller (90) reduces the opening degree of the fourth expansion valve (EV4). If the measurement value of the high-stage discharge pressure sensor (78) is higher than the maximum value of the reference pressure range (= the reference pressure), the controller (90) expands the opening degree of the fourth expansion valve (EV4). If the measurement value of the high-stage discharge pressure sensor (78) falls within the reference pressure range, the controller (90) maintains the opening degree of the fourth expansion valve (EV4).

[0184] When the opening degree of the fourth expansion valve (EV4) reaches a reference opening degree but the input current is higher than the target current, the defrosting heat amount is excessive, but the defrosting heat amount cannot be decreased by the control of the opening degree of the fourth expansion valve (EV4). For this reason, in this case, the controller (90) controls the rotational speed of the high-stage compressor (52) again.<Switching between Normal Operation and Inflow Operation>

[0185] If the inflow start condition is satisfied during the normal operation, the controller (90) switches the operation executed by the refrigeration apparatus (10) from the normal operation to the inflow operation.

[0186] The inflow start condition is the condition indicating that the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) is excessive. The inflow start condition of this embodiment is the condition that "the pressure of the refrigerant discharged by the high-stage compressor (52) (specifically, the measurement value of the high-stage discharge pressure sensor (78)) is higher than or equal to the upper limit pressure". In the controller (90), the upper limit pressure is set to a value slightly lower than the maximum pressure that the refrigerant circuit (30) can withstand.

[0187] When the refrigeration apparatus (10) starts the inflow operation, part of the refrigerant discharged from the high-stage compressor (52) flows into the receiver (62), and the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) decreases.

[0188] If the inflow end condition is satisfied during the inflow operation, the controller (90) switches the operation executed by the refrigeration apparatus (10) from the inflow operation to the normal operation.

[0189] The inflow end condition is the condition indicating that the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) is appropriate. The inflow end condition of this embodiment is the condition that "the pressure of the refrigerant discharged by the high-stage compressor (52) (specifically, the measurement value of the high-stage discharge pressure sensor (78)) is lower than the upper limit pressure". If the inflow end condition is satisfied, the refrigeration apparatus (10) ends the inflow operation and restarts the normal operation.

[0190] The inflow end condition may be the condition that "the duration time of the inflow operation has reached a predetermined time (for example, five seconds)".<Switching between Normal Operation and Outflow Operation>

[0191] If the outflow start condition is satisfied during the normal operation, the controller (90) switches the operation executed by the refrigeration apparatus (10) from the normal operation to the outflow operation.

[0192] The outflow start condition is the condition indicating that the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) is insufficient. The outflow start condition of this embodiment is the condition that "the temperature of the refrigerant discharged by the high-stage compressor (52) (specifically, the measurement value of the high-stage discharge temperature sensor (73)) is higher than or equal to the upper limit temperature".

[0193] When the refrigeration apparatus (10) starts the outflow operation, the refrigerant having flowed out from the receiver (62) is sucked into the high-stage compressor (52), and the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) increases.

[0194] If the outflow end condition is satisfied during the outflow operation, the controller (90) switches the operation executed by the refrigeration apparatus (10) from the outflow operation to the normal operation. The outflow end condition is the condition that "the duration time of the outflow operation has reached a predetermined time (for example, one minute)".

[0195] The outflow end condition may be the condition that "the degree of superheat of the refrigerant at the outlet of the inner heat exchanger (57) is lower than a reference degree of superheat". In this case, by using the measurement value of the fourth refrigerant temperature sensor (84) and the measurement value of the low-stage suction pressure sensor (75), the controller (90) calculates the degree of superheat of the refrigerant at the outlet of the inner heat exchanger (57).<Control in Outflow Operation>

[0196] The controller (90) instructs the refrigeration apparatus (10) to execute one of the first outflow operation or the second outflow operation as the outflow operation.

[0197] The controller (90) selects one of the first outflow operation or the second outflow operation based on the difference (Pr-Ps) between the pressure of the refrigerant in the receiver (62) (specifically, the measurement value Pr of the receiver pressure sensor (79)) and the pressure of the refrigerant sucked into the high-stage compressor (52) (specifically, the measurement value Ps of the high-stage suction pressure sensor (77)).

[0198] If the pressure difference (Pr-Ps) is more than or equal to a reference value, "the pressure of the refrigerant in the receiver (62)" is higher to some extent than "the pressure of the refrigerant sucked into the high-stage compressor (52)". In this case, the high-stage compressor (52) can suck the refrigerant from both the receiver (62) and the inner heat exchanger (57). Thus, in this case, the controller (90) instructs the refrigeration apparatus (10) to execute the first outflow operation.

[0199] If the pressure difference (Pr-Ps) is less than the reference value, "the pressure of the refrigerant in the receiver (62)" is close to "the pressure of the refrigerant sucked into the high-stage compressor (52)", or that "the pressure of the refrigerant in the receiver (62)" is lower than "the pressure of the refrigerant sucked into the high-stage compressor (52)". In this case, the high-stage compressor (52) cannot suck the refrigerant from both the receiver (62) and the inner heat exchanger (57). Thus, in this case, the controller (90) instructs the refrigeration apparatus (10) to execute the second outflow operation so that the high-stage compressor (52) can suck the refrigerant from the receiver (62) alone.

[0200] In the outflow operation for the first time, the controller (90) instructs the refrigeration apparatus (10) to execute the gas outflow operation. If the outflow start condition is satisfied again in the normal operation performed by the refrigeration apparatus (10) after the outflow operation for the first time ends, it can be determined that the mass of the refrigerant having flowed out from the receiver (62) in the outflow operation for the first time is small. Thus, in the outflow operation for the second time, the controller (90) instructs the refrigeration apparatus (10) to perform the liquid outflow operation to increase the mass of the refrigerant flowing out from the receiver (62).-Feature (1) of First Embodiment-

[0201] In the refrigeration apparatus (10) of this embodiment, the controller (90) controls the opening degree of the fourth expansion valve (EV4) as the decompression valve during the defrosting operation. In the defrosting operation, the refrigerant discharged from the high-stage compressor (52) (the point B in FIG. 8) is decompressed when passing through the fourth expansion valve (EV4), and the decompressed refrigerant (the point D in FIG. 8) is supplied to the inner heat exchanger (57). Thus, the pressure of the refrigerant flowing out from the inner heat exchanger (57) (the point E in FIG. 8) is lower than when the refrigerant discharged by the high-stage compressor (52) is supplied to the inner heat exchanger (57) without being decompressed, and as a result, the pressure difference between the refrigerant sucked by the high-stage compressor (52) (the point A in FIG. 8) and the refrigerant discharged by the high-stage compressor (52) (the point B in FIG. 8) increases.

[0202] When the pressure difference between the refrigerant sucked by the high-stage compressor (52) and the refrigerant discharged by the high-stage compressor (52) increases, the amount of heat applied to the refrigerant in the course of the high-stage compressor (52) compressing the refrigerant increases. Thus, according to this embodiment, the amount of heat which can be used to melt the frost on the inner heat exchanger (57) can be more increased than when the refrigerant discharged by the high-stage compressor (52) is supplied to the inner heat exchanger (57) without being decompressed, and as a result, the time to defrost the inner heat exchanger (57) can be shortened.-Feature (2) of First Embodiment-

[0203] In the defrosting operation, the refrigeration apparatus (10) of this embodiment performs the normal operation, the outflow operation, and the inflow operation. In the outflow operation, the mass of the refrigerant stored in the receiver (62) decreases, and the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) increases. In the inflow operation, the mass of the refrigerant stored in the receiver (62) increases, and the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) decreases.

[0204] By performing the inflow operation and the outflow operation, the refrigeration apparatus (10) of this embodiment can adjust the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) during the defrosting operation. Thus, the defrosting operation can be continuously performed while the pressure and temperature of the refrigerant discharged by the high-stage compressor (52) are held at appropriate values, and the frost on the inner heat exchanger (57) can be reliably melted by the defrosting operation.-Feature (3) of First Embodiment-

[0205] The refrigeration apparatus (10) of this embodiment performs the first outflow operation or the second outflow operation as the outflow operation. In the first outflow operation, the high-stage compressor (52) sucks the refrigerant having flowed out from the receiver (62) and the refrigerant having flowed out from the inner heat exchanger (57). In the second outflow operation, the high-stage compressor (52) sucks the refrigerant having flowed out from the receiver (62) and does not suck the refrigerant having flowed out from the inner heat exchanger (57).

[0206] Here, for example, when the external air has an extremely low temperature (for example, about -20°C to -30°C), the pressure of the refrigerant in the receiver (62) may be lower than the pressure of the refrigerant in the inner heat exchanger (57). If the pressure of the refrigerant in the receiver (62) is lower than the pressure of the refrigerant in the inner heat exchanger (57), the high-stage compressor (52) cannot suck the refrigerant from the receiver (62), and thus the refrigerant is not allowed to flow out from the receiver (62) by the first outflow operation.

[0207] On the other hand, in the second outflow operation, the refrigerant in the receiver (62) can be sucked into the high-stage compressor (52) regardless of the pressure of the refrigerant in the inner heat exchanger (57). Thus, even if the pressure of the refrigerant in the receiver (62) is lower than the pressure of the refrigerant in the inner heat exchanger (57), the refrigerant is allowed to flow out from the receiver (62) and the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) can be increased.

[0208] Thus, according to this embodiment, the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) during the defrosting operation can be increased by the outflow operation regardless of the pressure of the refrigerant in the receiver (62).-Feature (4) of First Embodiment-

[0209] The refrigeration apparatus (10) of this embodiment performs the gas outflow operation or the liquid outflow operation as the outflow operation. In the gas outflow operation, the gas refrigerant having flowed out from the receiver (62) is sucked into the high-stage compressor (52). In the liquid outflow operation, the liquid refrigerant having flowed out from the receiver (62) is sucked into the high-stage compressor (52).

[0210] For example, if the external air temperature is relatively low, the pressure of the refrigerant in the receiver (62) is relatively low, and the difference between the pressure of the refrigerant in the receiver (62) and the pressure of the refrigerant in the inner heat exchanger (57) may be small during the outflow operation. If the gas outflow operation is performed in this case, the flow rate of the gas refrigerant flowing out from the receiver (62) decreases, and it may take a long time to increase the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57).

[0211] In such a case, the refrigeration apparatus (10) of this embodiment performs the liquid outflow operation instead of the gas outflow operation. In the liquid outflow operation, the liquid refrigerant having flowed out from the receiver (62) is sucked into the high-stage compressor (52). The density of the liquid refrigerant is significantly higher than the density of the gas refrigerant. Thus, according to the refrigeration apparatus (10) of this embodiment that performs the liquid outflow operation, even if the difference between the pressure of the refrigerant in the receiver (62) and the pressure of the refrigerant in the inner heat exchanger (57) is relatively small, the mass flow rate of the refrigerant flowing out from the receiver (62) can be held high, and as a result, the time to increase the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) can be held short.

[0212] Here, if a relatively large amount of liquid refrigerant flows into the compression mechanism of the high-stage compressor (52), the compression mechanism may be damaged. On the other hand, in the refrigeration apparatus (10) of this embodiment, the refrigerant sucked into the high-stage compressor (52) passes through the accumulator (52a), and then flows into the compression mechanism of the high-stage compressor (52). Thus, in the liquid outflow operation, the liquid refrigerant having flowed out from the receiver (62) flows into the accumulator (52a), and the refrigerant having vaporized in the accumulator (52a) is sucked into the compression mechanism of the high-stage compressor (52). Thus, in the refrigeration apparatus (10) of this embodiment, even in the liquid outflow operation, the compression mechanism of the high-stage compressor (52) is not damaged even when sucking a relatively large amount of liquid refrigerant.<<Second Embodiment>>

[0213] The second embodiment will be described. The transportation container (1) of this embodiment is the transportation container (1) of the first embodiment that includes a modified version of the refrigeration apparatus (10).

[0214] The refrigeration apparatus (10) of this embodiment is different in the configuration of the refrigerant circuit (30) from the refrigeration apparatus (10) of the first embodiment. Here, regarding the refrigerant circuit (30) of this embodiment, the differences from the refrigerant circuit (30) of the first embodiment will be described.

[0215] As shown in FIG. 14, in the refrigerant circuit (30) of this embodiment, the defrosting pipe (32) is provided with a drain pan heater (63). In the defrosting pipe (32), the drain pan heater (63) is disposed downstream of the fourth expansion valve (EV4). The drain pan heater (63) is a pipe attached to the drain pan. The drain pan heater (63) heats the drain pan by the refrigerant flowing therein.-Defrosting Operation of Refrigeration Apparatus-

[0216] In the defrosting operation performed by the refrigeration apparatus (10) of this embodiment, similarly to the defrosting operation performed by the refrigeration apparatus (10) of the first embodiment, the refrigerant discharged from the high-stage compressor (52) flows into the defrosting pipe (32). In the defrosting operation performed by the refrigeration apparatus (10) of this embodiment, the refrigerant having flowed into the defrosting pipe (32) dissipates heat to the drain pan while passing through the drain pan heater (63), and then flows into the inner heat exchanger (57).

[0217] During the defrosting operation, the frost separated from the inner heat exchanger (57) may drop into the drain pan. In the defrosting operation performed by the refrigeration apparatus (10) of this embodiment, the drain pan is warmed by the refrigerant flowing in the drain pan heater (63). Thus, the frost having dropped from the inner heat exchanger (57) to the drain pan is warmed and melted by the drain pan, and then is discharged as drain water to the external space.<<Third Embodiment>>

[0218] The third embodiment will be described. The transportation container (1) of this embodiment is the transportation container (1) of the second embodiment that includes a modified version of the refrigeration apparatus (10).

[0219] The refrigeration apparatus (10) of this embodiment is different in the configuration of the refrigerant circuit (30) from the refrigeration apparatus (10) of the second embodiment. Here, regarding the refrigerant circuit (30) of this embodiment, the differences from the refrigerant circuit (30) of the second embodiment will be described.

[0220] As shown in FIG. 15, in the refrigerant circuit (30) of this embodiment, the defrosting pipe (32) is provided with the reheating heat exchanger (58) and the third electromagnetic valve (SV3), and not provided with the reheating pipe (33) and the fifth expansion valve (EV5). In the refrigerant circuit (30) of this embodiment, the defrosting pipe (32) also serves as the reheating pipe (33) for sending the refrigerant to the reheating heat exchanger (58). In the defrosting pipe (32) of this embodiment, the reheating heat exchanger (58) is disposed upstream of the fourth expansion valve (EV4), the drain pan heater (63) is disposed upstream of the reheating heat exchanger (58), and the third electromagnetic valve (SV3) is disposed upstream of the drain pan heater (63). The path changing mechanism (67) of this embodiment does not include the fourth expansion valve (EV4).-Operation of Controller-

[0221] In the refrigeration apparatus of this embodiment, the controller (90) controls the opening degree of the fourth expansion valve (EV4) in both the defrosting operation and the dehumidifying operation. In the defrosting operation, the controller (90) of this embodiment controls the opening degree of the fourth expansion valve (EV4) similarly to the controllers (90) of the first and second embodiments. In the dehumidifying operation, the controller (90) of this embodiment controls the opening degree of the fourth expansion valve (EV4) in the way the controllers (90) of the first and second embodiments control the opening degree of the fifth expansion valve (EV5). That is, in the dehumidifying operation, the controller (90) of this embodiment controls the opening degree of the fourth expansion valve (EV4) so that the temperature of the air having passed through the reheating heat exchanger (58) (specifically, the measurement value of the second air temperature sensor (87)) can reach the set temperature.<<Fourth Embodiment>>

[0222] The fourth embodiment will be described. In the refrigeration apparatus (10) of this embodiment, the controller (90) performs substantially the same operation as the controller (90) of the first embodiment when the refrigeration apparatus (10) is doing the defrosting operation. Here, the operation performed by the controller (90) of this embodiment when the refrigeration apparatus (10) is doing the defrosting operation will be described with reference to FIG. 16.

[0223] As described above, if the defrosting start condition is satisfied during the cooling operation, the refrigeration apparatus (10) temporarily stops the cooling operation and performs the defrosting operation. When the refrigeration apparatus (10) starts the normal operation of the defrosting operation, the controller (90) starts with the process of step ST1.<Step ST1>

[0224] In the process of step ST1, the controller (90) sets the opening degree of the fourth expansion valve (EV4) to the initial opening degree. After ending the process of step ST1, the controller (90) conducts the process of step ST2.<Step ST2>

[0225] In the process of step ST2, the controller (90) controls the rotational speed of the high-stage compressor (52) based on the input current. The controller (90) controls the rotational speed of the high-stage compressor (52) so that the input current can reach the target current. This operation of the controller (90) is the same as the operation of the controller (90) of the first embodiment to control the rotational speed of the high-stage compressor (52) based on the input current. After ending the process of step ST2, the controller (90) conducts the process of step ST3.<Step ST3>

[0226] In the process of step ST3, the controller (90) determines whether the defrosting end condition is satisfied. If the defrosting end condition is satisfied, the controller (90) ends the defrosting operation of the refrigeration apparatus (10), and restarts the cooling operation of the refrigeration apparatus (10). On the other hand, if the defrosting end condition is not satisfied, the controller (90) conducts the process of step ST4.<Step ST4>

[0227] In the process of step ST4, the controller (90) compares the measurement value Pdh of the high-stage discharge pressure sensor (78) with the upper limit pressure. If the condition that "the measurement value Pdh of the high-stage discharge pressure sensor (78) is higher than or equal to the upper limit pressure" is satisfied, the controller (90) conducts the process of step ST9. On the other hand, if this condition is not satisfied, the controller (90) conducts the process of step ST5.<Step ST5>

[0228] In the process of step ST5, the controller (90) compares the measurement value Tdh of the high-stage discharge temperature sensor with the upper limit temperature. If the condition that "the measurement value Tdh of the high-stage discharge temperature sensor is higher than or equal to the upper limit temperature" is satisfied, the controller (90) conducts the process of step ST11. On the other hand, if this condition is not satisfied, the controller (90) conducts the process of step ST6.<Step ST6>

[0229] In the process of step ST6, the controller (90) compares the input current of the high-stage compressor (52) with the target current, and compares the rotational speed RSh of the high-stage compressor (52) with the reference speed. If at least one of the condition that "the input current of the high-stage compressor (52) is higher than or equal to the target current" or the condition that "the rotational speed RSh of the high-stage compressor (52) is lower than the reference speed" is satisfied, the controller (90) conducts the process of step ST2. On the other hand, if both of the two conditions are not satisfied, the controller (90) conducts the process of step ST7.<Step ST7>

[0230] In the process of step ST7, the controller (90) compares the opening degree of the fourth expansion valve (EV4) with the reference opening degree. If the condition that "the opening degree of the fourth expansion valve (EV4) is lower than or equal to the reference opening degree" is satisfied, the controller (90) conducts the process of step ST11. On the other hand, if this condition is not satisfied, the controller (90) conducts the process of step ST8.<Step ST8>

[0231] In the process of step ST8, the controller (90) controls the opening degree of the fourth expansion valve (EV4) so that the measurement value Pdh of the high-stage discharge pressure sensor (78) falls within the reference pressure range. This operation of the controller (90) is the same as the operation of the controller (90) of the first embodiment to control the opening degree of the fourth expansion valve (EV4) based on the measurement value Pdh of the high-stage discharge pressure sensor (78). After ending the process of step ST8, the controller (90) conducts the process of step ST2.<Step ST9>

[0232] The condition in the process of step ST4 that "the measurement value Pdh of the high-stage discharge pressure sensor (78) is higher than or equal to the upper limit pressure" is the inflow start condition. As described in the first embodiment, the inflow start condition is the condition indicating that the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) is excessive.

[0233] Thus, in the process of step ST9, the controller (90) switches the operation executed by the refrigeration apparatus (10) from the normal operation to the inflow operation. Then, the controller (90) conducts the process of step ST10.<Step ST10>

[0234] In the process of step ST10, the controller (90) determines whether the condition that "the measurement value Pdh of the high-stage discharge pressure sensor (78) is lower than the upper limit pressure" is satisfied. This condition is the inflow end condition. As described in the first embodiment, the inflow end condition is the condition indicating that the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) is appropriate.

[0235] If the inflow end condition is satisfied, the controller (90) conducts the process of step ST2. On the other hand, if the inflow end condition is not satisfied, the controller (90) instructs the refrigeration apparatus (10) to continue the inflow operation.<Step ST11>

[0236] The condition in the process of step ST5 that "the measurement value Tdh of the high-stage discharge temperature sensor is higher than or equal to the upper limit temperature" is the outflow start condition. As described in the first embodiment, the outflow start condition is the condition indicating that the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57) is insufficient.

[0237] Thus, in the process of step ST11, the controller (90) switches the operation executed by the refrigeration apparatus (10) from the normal operation to the outflow operation. Then, the controller (90) conducts the process of step ST12.<Step ST12>

[0238] In the process of step ST12, the controller (90) determines whether the condition that "the duration time of the outflow operation has reached a predetermined time" is satisfied. This condition is the outflow end condition. As described in the first embodiment, the outflow end condition is the condition for ending the outflow operation of the refrigeration apparatus (10).

[0239] If the outflow end condition is satisfied, the controller (90) conducts the process of step ST2. On the other hand, if the outflow end condition is not satisfied, the controller (90) instructs the refrigeration apparatus (10) to continue the outflow operation.<<Other Embodiments>>

[0240] The refrigeration apparatuses (10) of the above embodiments may be modified as follows. The following variations may be combined or replaced as necessary only if the functions of the refrigeration apparatus (10) are not impaired.-First Variation-

[0241] The refrigerant circuit (30) of the refrigeration apparatus (10) of each of the first to fourth embodiments may be provided with a plurality of fourth expansion valves (EV4-1, EV4-2). Here, regarding this variation applied to the refrigeration apparatus (10) of the first embodiment, the differences from the refrigeration apparatus (10) of the first embodiment will be described.

[0242] As shown in FIG. 17, in the refrigerant circuit (30) of this variation, the defrosting pipe (32) is provided with two fourth expansion valves (EV4-1, EV4-2). In the defrosting pipe (32), the two fourth expansion valves (EV4-1, EV4-2) are connected in parallel. The fourth expansion valve (EV4-1), one of the two fourth expansion valves, is a first decompression valve. The fourth expansion valve (EV4-2), the other one of the two fourth expansion valves, is a second decompression valve. In the defrosting pipe (32) of this variation, three or more fourth expansion valves may be connected in parallel.

[0243] In the refrigeration apparatus (10) of this variation, the controller (90) sets each of the fourth expansion valves (EV4-1, EV4-2) to the same opening degree. When changing the opening degrees of the fourth expansion valves (EV4-1, EV4-2), the controller (90) expands or reduces the opening degree of each of the fourth expansion valves (EV4-1, EV4-2) by the same amount. However, the controller (90) may be configured to individually control the opening degree of each of the fourth expansion valves (EV4-1, EV4-2).-Second Variation-

[0244] The refrigeration apparatus (10) of each of the first to fourth embodiments may be configured to perform only a single-stage compression refrigeration cycle. Here, regarding this variation applied to the refrigeration apparatus (10) of the third embodiment, the differences from the refrigeration apparatus (10) of the third embodiment will be described.

[0245] As shown in FIG. 18, the refrigerant circuit (30) of the refrigeration apparatus (10) of this variation is not provided with the low-stage compressor (51), the low-stage connection pipe (44), and the high-stage connection pipe (45). The refrigerant circuit (30) of this variation is provided with one compressor (52) that corresponds to the high-stage compressor of the refrigerant circuit (30) of the third embodiment.

[0246] In the main circuit (31) of the refrigerant circuit (30) of this variation, the other end of the inner heat exchanger (57) is connected to the suction pipe of the compressor (52). The first electric valve (MV1) is provided in part of the main circuit (31) that is between the inner heat exchanger (57) and the suction pipe of the compressor (52). The other end of the intermediate connection pipe (43) is connected to part of the main circuit (31) that is between the first electric valve (MV1) and the compressor (52).

[0247] In the cooling operation of the refrigeration apparatus (10) of this variation, the refrigerant circuit (30) performs the single-stage compression refrigeration cycle. In the refrigerant circuit (30), the compressor (52) operates to circulate the refrigerant in the main circuit (31). The refrigerant discharged by the compressor (52) dissipates heat to the external air in the outer heat exchanger (56). The refrigerant having flowed out from the outer heat exchanger (56) passes through the first flow path (61a) of the internal heat exchanger (61), the first expansion valve (EV1), the receiver (62), the first electromagnetic valve (SV1), and the second expansion valve (EV2) in sequence, and then flows into the inner heat exchanger (57). The refrigerant having flowed into the inner heat exchanger (57) absorbs heat from the air flowing in the internal flow path (20) and then evaporates. The refrigerant having evaporated in the inner heat exchanger (57) is sucked into the compressor (52). The compressor (52) compresses and discharges the sucked refrigerant.-Third Variation-

[0248] In the normal operation of the defrosting operation, the controller (90) of the refrigeration apparatus (10) of each of the first to fourth embodiments may control the opening degree of the fourth expansion valve (EV4) based on the temperature of the refrigerant discharged by the high-stage compressor (52) (specifically, the measurement value of the high-stage discharge temperature sensor (73)). The controller (90) decreases the opening degree of the fourth expansion valve (EV4) as much as possible within a range in which the measurement value of the high-stage discharge temperature sensor (73) is held lower than or equal to the reference temperature.

[0249] Specifically, the controller (90) controls the opening degree of the fourth expansion valve (EV4) so that the measurement value of the high-stage discharge temperature sensor (73) falls within a reference temperature range. The reference temperature range is a temperature range including the reference temperature. The maximum value of the reference temperature range is the reference temperature.

[0250] If the measurement value of the high-stage discharge temperature sensor (73) is lower than the minimum value of the reference temperature range, the controller (90) reduces the opening degree of the fourth expansion valve (EV4). If the measurement value of the high-stage discharge temperature sensor (73) is higher than the maximum value of the reference temperature range (= the reference temperature), the controller (90) expands the opening degree of the fourth expansion valve (EV4). If the measurement value of the high-stage discharge temperature sensor (73) falls within the reference temperature range, the controller (90) maintains the opening degree of the fourth expansion valve (EV4).

[0251] In the normal operation of the defrosting operation, the controller (90) of this variation may control the opening degree of the fourth expansion valve (EV4) based on both the temperature and the pressure of the refrigerant discharged by the high-stage compressor (52). In this case, the controller (90) decreases the opening degree of the fourth expansion valve (EV4) as much as possible within a range in which the measurement value of the high-stage discharge pressure sensor (78) is held lower than or equal to the reference pressure and the measurement value of the high-stage discharge temperature sensor (73) is held lower than or equal to the reference temperature.-Fourth Variation-

[0252] In the first outflow operation of the defrosting operation, the controller (90) of the refrigeration apparatus (10) of each of the first to fourth embodiments may select one of the gas outflow operation or the liquid outflow operation based on the external air temperature.

[0253] If the external air temperature is relatively low, the pressure of the refrigerant in the receiver (62) is relatively low. If the gas outflow operation is performed in this situation, the flow rate of the gas refrigerant flowing out from the receiver (62) decreases, and it may take a long time to increase the mass of the refrigerant circulating between the high-stage compressor (52) and the inner heat exchanger (57). Thus, the controller (90) of this variation instructs the refrigeration apparatus (10) to execute the gas outflow operation if the external air temperature is higher than or equal to the reference external air temperature, and instructs the refrigeration apparatus (10) to execute the liquid outflow operation if the external air temperature is lower than the reference external air temperature.-Fifth Variation-

[0254] The refrigeration apparatus (10) of each of the first and second embodiments may not be provided with the reheating heat exchanger (58) and the reheating pipe (33). The refrigeration apparatus (10) of this variation is not provided with the third electromagnetic valve (SV3) and the fifth expansion valve (EV5), both provided in the reheating pipe (33). Thus, the path changing mechanism (67) of this variation does not include the third electromagnetic valve (SV3).-Sixth Variation-

[0255] The refrigeration apparatus (10) of each of the first and second embodiments may not be provided with the first electromagnetic valve (SV1). When the first electromagnetic valve (SV1) in the refrigeration apparatus (10) of each of the first and second embodiments is held in a closed state, the second expansion valve (EV2) in the refrigeration apparatus (10) of this variation is held in a fully-closed state. The path changing mechanism (67) of this variation does not include the first electromagnetic valve (SV1).-Seventh Variation-

[0256] Usage of the refrigeration apparatus (10) of each of the first to fourth embodiments is not limited to the air conditioning of the internal space (5) of the transportation container (1). The refrigeration apparatus (10) of each of the first to fourth embodiments may be used for air conditioning of an internal space of a stationary refrigerator or a cold storage warehouse, for example.

[0257] While the embodiments and variations thereof have been described above, it will be understood that various changes in form and details may be made without departing from the spirit and scope of the claims. The elements according to the embodiments, the variations thereof, and the other embodiments may be combined and replaced with each other. In addition, the expressions of "first", "second", "third", . . . , in the specification and claims are used to distinguish the terms to which these expressions are given, and do not limit the number and order of the terms.INDUSTRIAL APPLICABILITY

[0258] As described above, the present disclosure is useful for a refrigeration apparatus and a transportation container.DESCRIPTION OF REFERENCE CHARACTERS

[0259] 1Transportation Container 2Container Body 5Internal Space (Target Space) 10Refrigeration Apparatus 30Refrigerant Circuit 32Defrosting Pipe (Bypass Passage) 50Compressor 56Outer Heat Exchanger (Heat-Source-Side Heat Exchanger) 57Inner Heat Exchanger (Utilization-Side Heat Exchanger) 58Reheating Heat Exchanger 62Receiver 65Expansion Valve 67Path Changing Mechanism 90Controller EV4Fourth Expansion Valve (Decompression Valve) EV4-1Fourth Expansion Valve (First Decompression Valve) EV4-2Fourth Expansion Valve (Second Decompression Valve)

Examples

first embodiment

[0042]The first embodiment will be described. This embodiment is a transportation container (1) including a refrigeration apparatus (10).

-Transportation Container-

[0043]As shown in FIG. 1, the transportation container (1) includes a container body (2) and the refrigeration apparatus (10). The transportation container (1) is a reefer container capable of controlling a temperature in the container.

[0044]The transportation container (1) of this embodiment is used mainly for marine transportation. The transportation container (1) is loaded onto a ship or the like and transported. Usage of the transportation container (1) is not limited to marine transportation. The transportation container (1) may be used for land transportation. In this case, the transportation container (1) is transported by an automobile such as a truck or by rail.

-Container Body-

[0045]As shown in FIG. 2, the container body (2) is formed in a hollow box shape. The container body (2) is horizontally long. The containe...

third embodiment

[0245]As shown in FIG. 18, the refrigerant circuit (30) of the refrigeration apparatus (10) of this variation is not provided with the low-stage compressor (51), the low-stage connection pipe (44), and the high-stage connection pipe (45). The refrigerant circuit (30) of this variation is provided with one compressor (52) that corresponds to the high-stage compressor of the refrigerant circuit (30) of the

[0246]In the main circuit (31) of the refrigerant circuit (30) of this variation, the other end of the inner heat exchanger (57) is connected to the suction pipe of the compressor (52). The first electric valve (MV1) is provided in part of the main circuit (31) that is between the inner heat exchanger (57) and the suction pipe of the compressor (52). The other end of the intermediate connection pipe (43) is connected to part of the main circuit (31) that is between the first electric valve (MV1) and the compressor (52).

[0247]In the cooling operation of the refrigeration apparatus (10...

Claims

1. A refrigeration apparatus (10) which includes a refrigerant circuit (30) having a compressor (50), a heat-source-side heat exchanger (56), an expansion valve (65), and a utilization-side heat exchanger (57), and which is configured to condition air in a target space (5), wherein the refrigerant circuit (30) has a bypass passage (32) configured to send a refrigerant discharged by the compressor (50) to the utilization-side heat exchanger (57) while bypassing the heat-source-side heat exchanger (56) and the expansion valve (65), and a decompression valve (EV4) of which an opening degree is variable and which is configured to decompress a refrigerant flowing in the bypass passage (32), the refrigeration apparatus (10) performs a cooling operation to perform a refrigeration cycle in which the heat-source-side heat exchanger (56) functions as a radiator and the utilization-side heat exchanger (57) functions as an evaporator, and to blow air cooled in the utilization-side heat exchanger (57) into the target space (5), and a defrosting operation to melt frost on the utilization-side heat exchanger (57) by supplying the refrigerant discharged by the compressor (50) to the utilization-side heat exchanger (57) through the bypass passage (32), and the refrigeration apparatus (10) includes a controller (90) configured to control the opening degree of the decompression valve (EV4) based on one or both of a pressure and a temperature of the refrigerant discharged by the compressor (50) in the defrosting operation.

2. The refrigeration apparatus of claim 1, wherein the refrigerant circuit (30) has a receiver (62) disposed between the heat-source-side heat exchanger (56) and the utilization-side heat exchanger (57), and in the defrosting operation, the refrigeration apparatus (10) performs a normal operation to circulate a refrigerant between the compressor (50) and the utilization-side heat exchanger (57) in a state in which an inflow of a refrigerant to the receiver (62) and an outflow of a refrigerant from the receiver (62) are blocked, an outflow operation to allow a refrigerant to flow out from the receiver (62) to decrease an amount of refrigerant stored in the receiver (62), and an inflow operation to allow a refrigerant to flow into the receiver (62) to increase an amount of refrigerant stored in the receiver (62).

3. The refrigeration apparatus of claim 2, wherein the refrigeration apparatus starts the outflow operation if a temperature of the refrigerant discharged by the compressor (50) becomes higher during the normal operation than a reference temperature.

4. The refrigeration apparatus of claim 2 or 3, wherein the refrigeration apparatus starts the normal operation if a degree of superheat of a refrigerant having flowed out from the utilization-side heat exchanger (57) becomes lower during the outflow operation than a reference degree of superheat.

5. The refrigeration apparatus of any one of claims 2 to 4, wherein the outflow operation includes a gas outflow operation to allow a gas refrigerant to flow out from the receiver (62), and a liquid outflow operation to allow a liquid refrigerant to flow out from the receiver (62).

6. The refrigeration apparatus of any one of claims 2 to 4, wherein in the outflow operation, a refrigerant having flowed out from the receiver (62) is sucked by the compressor (50).

7. The refrigeration apparatus of claim 6, wherein the outflow operation includes a first outflow operation in which the compressor (50) sucks a refrigerant from both the receiver (62) and the utilization-side heat exchanger (57), and a second outflow operation in which the compressor (50) sucks a refrigerant from the receiver (62) and does not suck a refrigerant from the utilization-side heat exchanger (57).

8. The refrigeration apparatus of any one of claims 2 to 7, wherein the refrigeration apparatus starts the inflow operation if a pressure of the refrigerant discharged from the compressor (50) becomes higher during the normal operation than a reference pressure.

9. The refrigeration apparatus of any one of claims 2 to 8, wherein in the inflow operation, part of the refrigerant discharged from the compressor (50) flows into the receiver (62) through the heat-source-side heat exchanger (56), and a rest of the refrigerant discharged from the compressor (50) is supplied to the utilization-side heat exchanger (57) through the bypass passage (32).

10. The refrigeration apparatus of any one of claims 1 to 9, wherein the refrigerant circuit (30) has a path changing mechanism (67) that changes a flow path of a refrigerant in the refrigerant circuit (30), and the controller (90) controls the path changing mechanism (67) to switch between the cooling operation and the defrosting operation.

11. The refrigeration apparatus of any one of claims 2 to 9, wherein the refrigerant circuit (30) has a path changing mechanism (67) that changes a flow path of a refrigerant in the refrigerant circuit (30), and the controller (90) controls the path changing mechanism (67) to switch between the cooling operation and the defrosting operation, and also to switch between the normal operation, the outflow operation, and the inflow operation in the defrosting operation.

12. The refrigeration apparatus of claim 10 or 11, wherein the path changing mechanism (67) has a plurality of control valves controlled by the controller (90).

13. The refrigeration apparatus of any one of claims 1 to 12, wherein the decompression valve includes a first decompression valve (EV4-1) and a second decompression valve (EV4-2) which are connected in parallel.

14. The refrigeration apparatus of any one of claims 1 to 13, wherein the refrigeration apparatus performs a heating operation to supply the refrigerant discharged by the compressor (50) to the utilization-side heat exchanger (57) through the bypass passage (32) and to blow the air heated in the utilization-side heat exchanger (57) into the target space (5).

15. The refrigeration apparatus of any one of claims 1 to 14, wherein the refrigerant circuit (30) has a reheating heat exchanger (58) disposed upstream of the decompression valve (EV4) in the bypass passage (32) and configured to exchange heat between air having passed through the utilization-side heat exchanger (57) and a refrigerant.

16. The refrigeration apparatus of any one of claims 1 to 15, wherein the refrigerant circuit (30) is filled with carbon dioxide as a refrigerant.

17. A transportation container comprising: the refrigeration apparatus (10) of any one of claims 1 to 16; and a container body (2) forming the target space (5) in which air is conditioned by the refrigeration apparatus (10).

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