Refrigeration device and container for transportation

Abstract

In a reheating pipe (33) of a refrigerant circuit (30), a fifth expansion valve (EV5) is provided downstream of a reheating heat exchanger (58). During a dehumidification operation, an internal heat exchanger (57) cools and dehumidifies air. During the dehumidification operation, refrigerant discharged from a compressor (50) is supplied to the reheating heat exchanger (58). The reheating heat exchanger (58) heats the air dehumidified in the internal heat exchanger (57). When a controller (90) changes the aperture of the fifth expansion valve (EV5), the flow rate of the refrigerant in the reheating heat exchanger (58) changes, and the temperature of the air that has passed through the reheating heat exchanger (58) changes.

Description

Refrigeration units and shipping containers

[0001] The present disclosure relates to refrigeration devices and shipping containers.

[0002] Patent Document 1 discloses a container refrigeration unit, which is a type of refrigeration unit. This container refrigeration unit includes an evaporator and a reheat heat exchanger, and performs a dehumidifying operation.

[0003] In dehumidifying operation, the evaporator cools and dehumidifies the air. In dehumidifying operation, the refrigerant discharged from the compressor is supplied to the reheat heat exchanger through a reheat circuit. In the reheat heat exchanger, the air, which has been cooled and dehumidified as it passes through the evaporator, is heated by the refrigerant.

[0004] In the dehumidification operation performed by the container refrigeration unit of Patent Document 1, air cooled and dehumidified in the evaporator is heated in the reheat heat exchanger and then supplied to the interior space. In this way, the container refrigeration unit of Patent Document 1 reduces the humidity of the interior air while suppressing a decrease in the temperature of the interior air.

[0005] JP 2013-122333 A

[0006] In the reheat circuit of the container refrigeration unit of Patent Document 1, an on-off valve is provided upstream of the reheat heat exchanger and a capillary tube is provided downstream of the reheat heat exchanger. As a result, the flow rate of the refrigerant in the reheat heat exchanger cannot be appropriately adjusted during dehumidification operation, and there is a risk that the temperature of the air that passes through the reheat heat exchanger and is blown into the compartment space cannot be appropriately controlled.

[0007] An object of the present disclosure is to appropriately adjust the temperature of air blown out from a refrigeration device during dehumidification operation of the refrigeration device.

[0008] A first aspect of the present disclosure is a refrigeration system (10) for air-conditioning a target space (5), comprising a refrigerant circuit (30) having a compressor (50), a heat source heat exchanger (56), an expansion valve (65), and a utilization heat exchanger (57). The refrigerant circuit (30) includes a reheat heat exchanger (58) that exchanges heat between the air that has passed through the utilization heat exchanger (57) and a refrigerant, a reheat passage (33) that sends the refrigerant discharged from the compressor (50) to the reheat heat exchanger (58), and a variable opening control valve (EV5) that is provided in the reheat passage (33) downstream of the reheat heat exchanger (58). The refrigeration system (10) performs 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, performs a dehumidification operation in which air is cooled and dehumidified in the utilization side heat exchanger (57), the air that has passed through the utilization side heat exchanger (57) is heated in the reheat heat exchanger (58), and the air heated in the reheat heat exchanger (58) is blown into the target space (5), and is provided with a controller (90) that controls the opening of the control valve (EV5) during the dehumidification operation.

[0009] The refrigeration system (10) of the first aspect performs a dehumidifying operation. In the dehumidifying operation, the utilization-side heat exchanger (57) functioning as an evaporator cools and dehumidifies air. In the dehumidifying operation, refrigerant discharged from the compressor (50) is sent to the reheat heat exchanger (58) through the reheat passage (33). The reheat heat exchanger (58) heats the air dehumidified in the utilization-side heat exchanger (57) with the refrigerant. In the dehumidifying operation, the air dehumidified in the utilization-side heat exchanger (57) and then heated in the reheat heat exchanger (58) is blown into the target space (5).

[0010] The controller (90) of the first aspect controls the aperture of the control valve (EV5) during the dehumidification operation. When the aperture of the control valve (EV5) changes, the flow rate of the refrigerant in the reheat heat exchanger (58) changes, and the amount of heat imparted to the air in the reheat heat exchanger (58) changes. As a result, the temperature of the air blown into the target space (5) after passing through the reheat heat exchanger (58) changes. Therefore, by controlling the aperture of the control valve (EV5) by the controller (90), it becomes possible to control the temperature of the air blown into the target space (5) by the refrigeration device (10) during the dehumidification operation.

[0011] A second aspect of the present disclosure is the first aspect, wherein, in the dehumidifying operation, the pressure of the refrigerant supplied to the reheat heat exchanger (58) through the reheat passage (33) is equal to or higher than the critical pressure of the refrigerant.

[0012] In the defrosting operation performed by the refrigeration system (10) of the second embodiment, refrigerant at or above its critical pressure exchanges heat with air in the reheat heat exchanger (58). The refrigerant at or above its critical pressure undergoes sensible heat change in the process of releasing heat. Therefore, in the defrosting operation performed by the refrigeration system (10) of this embodiment, the refrigerant releases heat at a substantially constant rate throughout the reheat heat exchanger (58). As a result, the temperature of the air blown out from the refrigeration system (10) in the dehumidifying operation is made uniform.

[0013] A third aspect of the present disclosure is the second aspect, wherein the controller (90) controls the opening of the expansion valve (65) during the dehumidifying operation so that the pressure of the refrigerant discharged from the compressor (50) is equal to or higher than the critical pressure of the refrigerant.

[0014] In the refrigeration system (10) of the third aspect, the controller (90) controls the opening of the expansion valve (65), so that the pressure of the refrigerant discharged from the compressor (50) becomes equal to or higher than the critical pressure of the refrigerant.

[0015] A fourth aspect of the present disclosure is any one of the first to third aspects, wherein the controller (90) controls the opening of the control valve (EV5) based on the temperature of air that has passed through the reheat heat exchanger (58) during the dehumidification operation.

[0016] The controller (90) of the fourth aspect controls the opening of the control valve (EV5) based on the temperature of the air that has passed through the reheat heat exchanger (58) during the dehumidification operation.

[0017] A fifth aspect of the present disclosure is any one of the first to third aspects, wherein the controller (90) controls the opening degree of the adjustment valve (EV5) based on the temperature of the refrigerant flowing out of the reheat heat exchanger (58) during the dehumidification operation.

[0018] The controller (90) of the fifth aspect controls the opening of the control valve (EV5) based on the temperature of the refrigerant that has passed through the reheat heat exchanger (58) during the dehumidification operation.

[0019] A sixth aspect of the present disclosure is any one of the first to fifth aspects, wherein the controller (90) controls the rotation speed of the compressor (50) during the dehumidifying operation so that a physical quantity correlated with the evaporation temperature of the refrigerant in the utilization side heat exchanger (57) becomes a control target value.

[0020] In the dehumidification operation, a change in the rotation speed of the compressor (50) changes the evaporation temperature of the refrigerant in the utilization side heat exchanger (57). Therefore, the controller (90) of the sixth aspect controls the rotation speed of the compressor (50) so that a physical quantity correlated with the evaporation temperature of the refrigerant in the utilization side heat exchanger (57) reaches a control target value.

[0021] A seventh aspect of the present disclosure is related to any one of the first to fifth aspects, wherein the refrigerant circuit (30) includes a receiver (62) arranged between the heat source side heat exchanger (56) and the utilization side heat exchanger (57). The expansion valve (65) includes a first expansion valve (EV1) arranged between the heat source side heat exchanger (56) and the receiver (62) and a second expansion valve (EV2) arranged between the receiver (62) and the utilization side heat exchanger (57). In the dehumidification operation, the controller (90) controls the aperture of the first expansion valve (EV1) so that the pressure of the refrigerant discharged from the compressor (50) becomes equal to or higher than the critical pressure of the refrigerant, and controls the aperture of the second expansion valve (EV2) so that a physical quantity correlated with the evaporation temperature of the refrigerant in the utilization side heat exchanger (57) becomes a control target value.

[0022] A controller (90) of the seventh aspect controls the aperture of the first expansion valve (EV1) and the aperture of the second expansion valve (EV2) during dehumidification operation. A change in the aperture of the first expansion valve (EV1) changes the pressure of the refrigerant discharged from the compressor (50). Therefore, the controller (90) controls the aperture of the first expansion valve (EV1) so that the pressure of the refrigerant discharged from the compressor (50) is equal to or higher than the critical pressure of the refrigerant. A change in the aperture of the second expansion valve (EV2) changes the evaporation temperature of the refrigerant in the utilization side heat exchanger (57). Therefore, the controller (90) controls the aperture of the second expansion valve (EV2) so that a physical quantity correlated with the evaporation temperature of the refrigerant in the utilization side heat exchanger (57) reaches a control target value.

[0023] An eighth aspect of the present disclosure is the sixth or seventh aspect, wherein the controller (90) sets the control target value based on the humidity of air flowing from the target space (5) into the utilization side heat exchanger (57) or the humidity of air blown into the target space (5) during the dehumidification operation.

[0024] In the eighth aspect, the controller (90) sets a control target value during dehumidification operation based on the humidity of the air flowing from the target space (5) into the utilization side heat exchanger (57) or the humidity of the air blown into the target space (5).

[0025] A ninth aspect of the present disclosure is any one of the first to eighth aspects, wherein the compressor (50) includes a low-stage compressor (51) that sucks in refrigerant that has passed through the utilization side heat exchanger (57) and a high-stage compressor (52) that sucks in refrigerant discharged from the low-stage compressor (51), and the refrigeration system (10) selectively performs, during the dehumidification operation, a single-stage compression operation in which one of the low-stage compressor (51) and the high-stage compressor (52) operates and the other is at rest, and a two-stage compression operation in which both the low-stage compressor (51) and the high-stage compressor (52) operate.

[0026] The refrigeration system (10) of the ninth aspect selectively performs a single-stage compression mode and a two-stage compression mode during dehumidifying operation.

[0027] A tenth aspect of the present disclosure is any one of the first to ninth aspects, wherein the controller (90) increases the opening of the control valve (EV5) when a temperature unevenness condition is established during the dehumidification operation, the temperature unevenness condition indicating that the temperature of the air that has passed through the reheat heat exchanger (58) is uneven.

[0028] The controller (90) of the tenth aspect determines whether the temperature unevenness condition is satisfied. When the temperature unevenness condition is satisfied, there is a high possibility that the temperature of the air passing through the reheat heat exchanger (58) is uneven. The main cause of the uneven temperature of the air passing through the reheat heat exchanger (58) is uneven heating of the air in different parts of the reheat heat exchanger (58). Therefore, when the temperature unevenness condition is satisfied, the controller (90) increases the aperture of the control valve (EV5). When the aperture of the control valve (EV5) is increased, the flow rate of the refrigerant in the reheat heat exchanger (58) increases, and the amount of heating of the air in different parts of the reheat heat exchanger (58) becomes uniform.

[0029] An eleventh aspect of the present disclosure is any one of the first to tenth aspects, wherein the reheat passage (33) sends the refrigerant that has passed through the reheat heat exchanger (58) to the utilization side heat exchanger (57).

[0030] In the refrigeration system (10) of the eleventh aspect, the refrigerant that has passed through the reheat heat exchanger (58) during the dehumidifying operation passes through the control valve (EV5) and then flows into the utilization side heat exchanger (57).

[0031] A twelfth aspect of the present disclosure is any one of the first to eleventh aspects, wherein the refrigerant circuit (30) is filled with carbon dioxide as the refrigerant.

[0032] The refrigerant circuit (30) of the twelfth aspect performs a refrigeration cycle by circulating carbon dioxide filled as a refrigerant.

[0033] A thirteenth aspect of the present disclosure is a transport container (1) including the refrigeration system (10) of any one of the first to twelfth aspects and a container body (2) that forms the target space (5) that is air-conditioned by the refrigeration system (10).

[0034] A transport container (1) according to a thirteenth aspect includes a refrigeration unit (10) and a container body (2). The container body (2) defines a target space (5). The refrigeration unit (10) conditions the air in the target space (5).

[0035] FIG. 1 is a schematic perspective view of a refrigeration apparatus of embodiment 1. FIG. 2 is a schematic cross-sectional view of a transport container of embodiment 1. FIG. 3 is a piping diagram showing the configuration of the refrigeration apparatus of embodiment 1. FIG. 4 is a block diagram showing the configuration of a controller of embodiment 1. FIG. 5 is a piping diagram corresponding to FIG. 3 showing the flow of refrigerant in cooling operation. FIG. 6 is a piping diagram corresponding to FIG. 3 showing the flow of refrigerant in two-stage compression operation of dehumidifying operation. FIG. 7 is a piping diagram corresponding to FIG. 3 showing the flow of refrigerant in single-stage compression operation of dehumidifying operation. FIG. 8 is a piping diagram corresponding to FIG. 3 showing the flow of refrigerant in defrosting operation. FIG. 9 is a state transition diagram showing the operation of the controller in dehumidifying operation. FIG. 10 is a flow chart showing the humidity control operation of the controller. FIG. 11 is a flow chart showing the temperature control operation of the controller. FIG. 12 is a flow chart showing the high-pressure control operation of the controller. FIG. 13 is a piping diagram showing the configuration of a refrigeration apparatus of embodiment 2. FIG. 14 is a piping diagram showing the configuration of a refrigeration apparatus of embodiment 3. FIG. 15 is a piping diagram showing the configuration of a refrigeration apparatus of a first modified example of another embodiment.

[0036] First Embodiment A first embodiment will be described. This embodiment is a transport container (1) equipped with a refrigeration unit (10).

[0037] 1, the transport container 1 includes a container body 2 and a refrigeration unit 10. The transport container 1 is a reefer container capable of controlling the temperature inside.

[0038] The transport container (1) of this embodiment is mainly used for marine transportation. This transport container (1) is loaded onto a ship or the like for transport. However, the use of the transport container (1) is not limited to marine transportation. The transport container (1) may also be used for land transportation. In this case, the transport container (1) is transported by automobile such as a truck, or by rail.

[0039] - Container Body - As shown in Figure 2, the container body (2) is formed in the shape of a hollow box. The container body (2) is formed horizontally long. An opening is formed at one longitudinal end of the container body (2). The opening of the container body (2) is closed by a refrigeration unit (10). The container body (2) forms an interior space (5) for storing cargo. The interior space (5) is a target space that is air-conditioned by the refrigeration unit.

[0040] 2, the refrigeration unit (10) is attached to the opening of the container body (2). The refrigeration unit (10) of this embodiment is a refrigeration unit for transport. The refrigeration unit (10) includes a casing (11), a refrigerant circuit (30), and a controller (80). The refrigeration unit (10) adjusts the temperature of the air in the interior space (5) (interior air).

[0041] <Casing> The casing (11) includes a partition wall (12) and a partition plate (15).

[0042] An internal flow path (20) is formed inside the partition wall (12). An external chamber (23) is formed outside the partition wall (12). The internal flow path (20) and the external chamber (23) are separated by the partition wall (12).

[0043] The partition wall (12) includes an outer wall (13) and an inner wall (14). The outer wall (13) is located outside the container body (2). The inner wall (14) is located inside the container body (2).

[0044] The exterior wall (13) closes the opening of the container body (2). The exterior wall (13) is attached to the periphery of the opening of the container body (2). The lower part of the exterior wall (13) bulges outward toward the inside of the container body (2). The exterior chamber (23) is formed by the lower part of the exterior wall (13).

[0045] The interior wall (14) faces the exterior wall (13). The interior wall (14) has a shape that conforms to the exterior wall (13). The interior wall (14) is disposed at a distance from the exterior wall (13). A heat insulating material (16) is provided between the interior wall (14) and the exterior wall (13).

[0046] The partition plate (15) is disposed inside the container body (2) relative to the interior wall (14). An internal flow path (20) is formed between the partition wall (12) and the partition plate (15). An air suction port (21) is formed between the upper end of the partition plate (15) and the top plate of the container body (2). An air outlet (22) is formed between the lower end of the partition plate (15) and the lower end of the partition wall (12). The internal flow path (20) is formed from the air suction port (21) to the air outlet (22).

[0047] <Refrigerant Circuit> The refrigerant circuit (30) is a closed circuit filled with a refrigerant. The refrigerant circuit (30) circulates the refrigerant to perform a vapor compression refrigeration cycle. The refrigerant circuit (30) includes an external heat exchanger (56), an internal heat exchanger (57), and a reheat heat exchanger (58). The refrigerant circuit (30) will be described in detail later.

[0048] Each of the external heat exchanger (56), the internal heat exchanger (57), and the reheat heat exchanger (58) is a fin-and-tube heat exchanger that exchanges heat between the refrigerant and air.

[0049] The external heat exchanger (56) is disposed in an upper portion of the external chamber (23). The external heat exchanger (56) is a heat source side heat exchanger that exchanges heat between the refrigerant and the external air. The external heat exchanger (56) has a generally rectangular cylindrical shape.

[0050] The internal heat exchanger (57) is arranged in the internal flow path (20). The internal heat exchanger (57) is a utilization side heat exchanger that exchanges heat between the refrigerant and the internal air.

[0051] The reheat heat exchanger (58) is arranged downstream of the internal heat exchanger (57) in the internal flow path (20). The reheat heat exchanger (58) is a heat exchanger that exchanges heat between the refrigerant and the internal air.

[0052] Although not shown, a drain pan is provided below the internal heat exchanger (57). The drain pan receives drain water generated in the internal heat exchanger (57). The drain water that falls into the drain pan is discharged to the outside of the container.

[0053] <External Fan> The refrigeration system (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 an external heat exchanger (56) formed in a cylindrical shape. The external fan (26) sends external air to the external heat exchanger (56).

[0054] <In-compartment fan> The refrigeration system (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 internal heat exchanger (57). The internal fan (27) sends internal air to the internal heat exchanger (57).

[0055] <Sensors> The refrigeration system (10) includes a first air temperature sensor (86), a second air temperature sensor (87), and a humidity sensor (88).

[0056] The first air temperature sensor (86) is arranged in the internal flow path (20) upstream of the internal fan (27). The first air temperature sensor (86) measures the temperature of the air that has flowed into the internal flow path (20) through the air inlet (21).

[0057] The second air temperature sensor (87) and the humidity sensor (88) are arranged downstream of the reheat heat exchanger (58) in the internal flow path (20). The second air temperature sensor (87) measures the temperature of the air that has passed through the reheat heat exchanger (58). The humidity sensor (88) measures the relative humidity of the air that has passed through the reheat heat exchanger (58).

[0058] <Electrical Component Box> As shown in Fig. 1 , the refrigeration system (10) has an electrical component box (28). The electrical component box (28) is disposed in an upper portion of the exterior chamber (23). Electrical components such as an inverter board and a control board are accommodated inside the electrical component box (28).

[0059] Refrigerant Circuit As shown in Fig. 3, the refrigerant circuit (30) is a closed circuit filled with a refrigerant. The refrigerant filled in the refrigerant circuit (30) of this embodiment is carbon dioxide.

[0060] The refrigerant circuit (30) includes a main circuit (31), a defrosting pipe (32), and a reheating pipe (33). The refrigerant circuit (30) also includes a gas side connecting pipe (41), a liquid side connecting pipe (42), an intermediate connecting pipe (43), a low stage connecting pipe (44), and a high stage connecting pipe (45).

[0061] <Main Circuit> The main circuit (31) includes a low-stage compressor (51), a high-stage compressor (52), an external heat exchanger (56), a receiver (62), and an internal heat exchanger (57). In the main circuit (31), the low-stage compressor (51), the high-stage compressor (52), the external heat exchanger (56), the receiver (62), and the internal heat exchanger (57) are connected in this order by pipes.

[0062] The discharge pipe of the low-stage compressor (51) is connected to the suction pipe of the high-stage compressor (52). A first check valve (CV1) and a first motor-operated valve (MV1) are provided in the piping connecting the discharge pipe of the low-stage compressor (51) and the suction pipe of the high-stage compressor (52). The first motor-operated valve (MV1) is disposed downstream of the first check valve (CV1). The first check valve (CV1) allows the flow of refrigerant in the direction outflowing from the low-stage compressor (51) and prevents the flow of refrigerant in the opposite direction.

[0063] A discharge pipe of the high-stage compressor (52) is connected to one end of the external heat exchanger (56). A second check valve (CV2) and a second motor-operated valve (MV2) are provided in a pipe connecting the discharge pipe of the high-stage compressor (52) and one end of the external heat exchanger (56). The second motor-operated valve (MV2) is disposed downstream of the second check valve (CV2). The second check valve (CV2) allows the refrigerant to flow in the direction outflowing from the high-stage compressor (52) and prevents the refrigerant from flowing in the opposite direction.

[0064] The other end of the external heat exchanger (56) is connected to an inlet of the receiver (62). A first flow path (61a) of the internal heat exchanger (61) and a first expansion valve (EV1) are provided in a pipe connecting the other end of the external heat exchanger (56) and the inlet of the receiver (62). The first expansion valve (EV1) is disposed downstream of the internal heat exchanger (61).

[0065] A liquid outlet of the receiver (62) is connected to one end of the internal heat exchanger (57). A first solenoid valve (SV1) and a second expansion valve (EV2) are provided in a pipe connecting the liquid outlet of the receiver (62) and one end of the internal heat exchanger (57). The second expansion valve (EV2) is arranged downstream of the first solenoid valve (SV1).

[0066] The other end of the internal heat exchanger (57) is connected to the suction pipe of the low stage compressor (51).

[0067] In the main circuit (31), a first expansion valve (EV1) is arranged upstream of the receiver (62), and a second expansion valve (EV2) is arranged downstream of the receiver (62). The first expansion valve (EV1) and the second expansion valve (EV2) are expansion valves (65) of the refrigerant circuit (30).

[0068] <Gas Side Connecting Pipe> One end of the gas side connecting pipe (41) is connected to a gas outlet of the receiver (62). The other end of the gas side connecting pipe (41) is connected to one end of the intermediate connecting pipe (43). The gas side connecting pipe (41) is provided with a second solenoid 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 solenoid valve (SV2).

[0069] <Liquid Side Connecting Pipe> One end of the liquid side connecting pipe (42) is connected to a position between the first solenoid valve (SV1) and the second expansion valve (EV2) in the main circuit (31). The other end of the liquid side connecting pipe (42) is connected to one end of the intermediate connecting pipe (43). The liquid side connecting pipe (42) is provided with a third expansion valve (EV3).

[0070] <Intermediate Connecting Pipe> As described above, one end of the intermediate connecting pipe (43) is connected to the other end of the gas side connecting pipe (41) and the other end of the liquid side connecting pipe (42). The other end of the intermediate connecting pipe (43) is connected to a position in the main circuit (31) between the first electric valve (MV1) and the high-stage compressor (52). The intermediate connecting pipe (43) is provided with a third check valve (CV3). The third check valve (CV3) allows refrigerant to flow from one end of the intermediate connecting pipe (43) to the other end and prevents refrigerant from flowing in the opposite direction.

[0071] <Low-stage connecting pipe> The low-stage connecting pipe (44) is a pipe through which refrigerant flows, bypassing the low-stage compressor (51). One end of the low-stage connecting pipe (44) is connected to the main circuit (31) between the suction pipe of the low-stage compressor (51) and the in-compartment heat exchanger (57). The other end of the low-stage connecting pipe (44) is connected to the main circuit (31) between the first check valve (CV1) and the first motor-operated valve (MV1). The low-stage connecting pipe (44) is provided with a fourth check valve (CV4). The fourth check valve (CV4) allows refrigerant to flow from one end of the low-stage connecting pipe (44) to the other end and prevents refrigerant from flowing in the opposite direction.

[0072] <High-stage connecting pipe> The high-stage connecting pipe (45) is a pipe through which refrigerant flows, bypassing the high-stage compressor (52). One end of the high-stage connecting pipe (45) is connected to a portion between the first check valve (CV1) and the first electric valve (MV1) in the main circuit (31). The other end of the high-stage connecting pipe (45) is connected to a portion between the second check valve (CV2) and the second electric valve (MV2) in the main circuit (31). The high-stage connecting pipe (45) is provided with a fifth check valve (CV5). The fifth check valve (CV5) allows refrigerant to flow from one end of the high-stage connecting pipe (45) to the other end and prevents refrigerant from flowing in the opposite direction.

[0073] <Defrosting Pipe> One end of the defrosting pipe (32) is connected to the main circuit (31) between the second check valve (CV2) and the second motor-operated 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 connecting pipe (45). The other end of the defrosting pipe (32) is connected to the main circuit (31) between the second expansion valve (EV2) and the in-compartment heat exchanger (57).

[0074] The defrosting pipe (32) is provided with a fourth expansion valve (EV4). The fourth expansion valve (EV4) is a pressure reducing valve with a variable opening that reduces the pressure of the refrigerant flowing through the defrosting pipe (32).

[0075] <Reheat Pipe> One end of the reheat pipe (33) is connected to the main circuit (31) between the second check valve (CV2) and the second motor-operated valve (MV2). In the main circuit (31), one end of the reheat pipe (33) is located downstream of the other end of the high-stage connecting pipe (45). The other end of the reheat pipe (33) is connected to the main circuit (31) between the second expansion valve (EV2) and the internal heat exchanger (57). The reheat pipe (33) forms a reheat passage. The reheat pipe (33) sends the refrigerant discharged from the compressor (50) to the internal heat exchanger (57) bypassing the external heat exchanger (56) and the expansion valve (65).

[0076] The reheat pipe (33) is provided with a third solenoid valve (SV3), a reheat heat exchanger (58), and a fifth expansion valve (EV5). The reheat heat exchanger (58) is disposed downstream of the third solenoid valve (SV3). The fifth expansion valve (EV5) is disposed downstream of the reheat heat exchanger (58).

[0077] <Expansion Valves> The first expansion valve (EV1), second expansion valve (EV2), third expansion valve (EV3), fourth expansion valve (EV4), and fifth expansion valve (EV5) are each so-called electronic expansion valves. Each expansion valve (EV1 to EV5) includes a valve disc and a stepping motor that drives the valve disc. When the valve disc is moved by the stepping motor, the opening of the expansion valve (EV1 to EV5) changes continuously.

[0078] <Motor-operated valve> The first motor-operated valve (MV1) and the second motor-operated valve (MV2) are each variable-opening valves. Each motor-operated valve (MV1, MV2) includes a valve element and a stepping motor that drives the valve element. When the valve element is moved by the stepping motor, the opening of the motor-operated valve (MV1, MV2) changes continuously.

[0079] <Solenoid valves> The first solenoid valve (SV1), the second solenoid valve (SV2), and the third solenoid valve (SV3) are each an on-off valve. Each solenoid valve (SV1 to SV3) has a valve element and a solenoid that drives the valve element. When the valve element is moved by the solenoid, the solenoid valve (SV1 to SV3) opens or closes.

[0080] <Low-stage compressor, high-stage compressor> The low-stage compressor (51) and the high-stage compressor (52) are each 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 that draws in and compresses refrigerant.

[0081] An accumulator (51a) is provided in the suction pipe of the low-stage compressor (51). An accumulator (52a) is provided in the suction pipe of the high-stage compressor (52). Each of the low-stage compressor (51) and the high-stage compressor (52) compresses the refrigerant sucked through the suction pipe and discharges the compressed refrigerant from a discharge pipe. The low-stage compressor (51) and the high-stage compressor (52) are compressors (50) provided in the refrigerant circuit (30).

[0082] It should be noted that each of the low-stage compressor (51) and the high-stage compressor (52) is not limited to a scroll compressor, and each of the low-stage compressor (51) and the high-stage compressor (52) may be, for example, a rotary compressor or a reciprocating compressor.

[0083] <External Heat Exchanger, Internal Heat Exchanger> As described above, each of the external heat exchanger (56), the internal heat exchanger (57), and the reheat heat exchanger (58) is a fin-and-tube heat exchanger that exchanges heat between the refrigerant and air. The external heat exchanger (56) exchanges heat between the refrigerant and external air (outside air). The internal heat exchanger (57) and the reheat heat exchanger (58) exchange heat between the refrigerant and internal air.

[0084] <Internal Heat Exchanger> The internal heat exchanger (61) is a heat exchanger that exchanges heat between refrigerants. In this embodiment, the internal heat exchanger (61) is a plate-type heat exchanger. The internal heat exchanger (61) is formed with a first flow path (61a) and a second flow path (61b). The first flow path (61a) of the internal heat exchanger (61) is disposed between the external heat exchanger (56) and the first expansion valve (EV1) in the main circuit (31). The second flow path (61b) of the internal heat exchanger (61) is disposed downstream of the second solenoid valve (SV2) in the gas side connecting pipe (41). The internal heat exchanger (61) exchanges heat between the refrigerant flowing through the first flow path (61a) and the refrigerant flowing through the second flow path (61b).

[0085] <Receiver> The receiver (62) is a container-like member for storing refrigerant. The receiver (62) also functions as a gas-liquid separator. The receiver (62) separates the gas-liquid two-phase refrigerant that has flowed in through the inlet into a liquid refrigerant and a gas refrigerant. In the receiver (62), the liquid refrigerant accumulates in the lower part of the receiver (62) and flows out through a liquid outlet formed in the bottom of the receiver (62). In the receiver (62), the gas refrigerant accumulates in the upper part of the receiver (62) and flows out through a gas outlet formed in the upper part of the receiver (62).

[0086] <Sensors Related to Low-Stage Compressor> In the main circuit (31), a low-stage suction temperature sensor (70) and a low-stage suction pressure sensor (75) are provided in a pipe connected to a suction pipe of the low-stage compressor (51). The low-stage suction temperature sensor (70) measures the temperature of the refrigerant sucked into the low-stage compressor (51). The low-stage suction pressure sensor (75) measures the pressure of the refrigerant sucked into the low-stage compressor (51).

[0087] In the main circuit (31), a low-stage discharge temperature sensor (71) and a low-stage discharge pressure sensor (76) are provided in a piping between the discharge pipe of the low-stage compressor (51) and the first check valve (CV1). The low-stage discharge temperature sensor (71) measures the temperature of the refrigerant discharged from the low-stage compressor (51). The low-stage discharge pressure sensor (76) measures the pressure of the refrigerant discharged from the low-stage compressor (51).

[0088] <Sensors Related to High-Stage Compressor> In the main circuit (31), a high-stage suction temperature sensor (72) and a high-stage suction pressure sensor (77) are provided in the piping between the suction pipe of the high-stage compressor (52) and the first motor-operated valve (MV1). The high-stage suction temperature sensor (72) measures the temperature of the refrigerant sucked into the high-stage compressor (52). The high-stage suction pressure sensor (77) measures the pressure of the refrigerant sucked into the high-stage compressor (52).

[0089] In the main circuit (31), a high-stage discharge temperature sensor (73) and a high-stage discharge pressure sensor (78) are provided in a piping between the discharge pipe of the high-stage compressor (52) and the second check valve (CV2). The high-stage discharge temperature sensor (73) measures the temperature of the refrigerant discharged from the high-stage compressor (52). The high-stage discharge pressure sensor (78) measures the pressure of the refrigerant discharged from the high-stage compressor (52).

[0090] <Other Sensors> 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).

[0091] The receiver pressure sensor (79) is connected to the gas side connecting pipe (41) between the receiver (62) and the second solenoid valve (SV2). The receiver pressure sensor (79) measures the pressure of the refrigerant stored in the receiver (62).

[0092] The first refrigerant temperature sensor (81) is provided on a pipe in the main circuit (31) between the external 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).

[0093] The second refrigerant temperature sensor (82) is provided in a pipe between the receiver (62) and the first solenoid valve (SV1) in the main circuit (31). The second refrigerant temperature sensor (82) measures the temperature of the refrigerant flowing out from the liquid outlet of the receiver (62).

[0094] The third refrigerant temperature sensor (83) is provided on a pipe in the main circuit (31) between the second expansion valve (EV2) and the internal heat exchanger (57). The third refrigerant temperature sensor (83) is disposed in the vicinity of one end of the internal heat exchanger (57). The third refrigerant temperature sensor (83) measures the temperature of the refrigerant at the inlet of the internal heat exchanger (57).

[0095] The fourth refrigerant temperature sensor (84) is provided in a pipe in the main circuit (31) between the internal heat exchanger (57) and the low-stage compressor (51). The fourth refrigerant temperature sensor (84) is disposed near the other end of the internal heat exchanger (57). The fourth refrigerant temperature sensor (84) measures the temperature of the refrigerant at the outlet of the internal heat exchanger (57).

[0096] The heat exchanger temperature sensor (85) is attached to the internal heat exchanger (57) and measures the temperature of the internal heat exchanger (57).

[0097] -Controller- 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 electrical component box (28).

[0098] The controller (90) receives measurement values ​​of sensors provided in the refrigeration system (10). The controller (90) controls devices provided in the refrigeration system (10) based on the received measurement values ​​of the sensors. For example, the controller (90) controls the rotation speed of the low-stage compressor (51), the rotation speed of the high-stage compressor (52), the apertures of the first to fifth expansion valves (EV1 to EV5), the apertures of the first to second motor-operated valves (MV1, MV2), the rotation speed of the external fan (26), the rotation speed of the internal fan (27), etc.

[0099] --Operation of the Refrigeration System-- The operation of the refrigeration system (10) will be described below. The refrigeration system (10) performs a cooling operation, a dehumidifying operation, and a defrosting operation.

[0100] <Cooling Operation> The cooling operation is an operation for cooling the internal air. In the cooling operation, the refrigeration system (10) blows the air cooled in the internal heat exchanger (57) into the internal space (5).

[0101] In the cooling operation of the refrigeration system (10), 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 external heat exchanger (56) functions as a radiator, and the internal heat exchanger (57) functions as an evaporator. The internal heat exchanger (57) cools the air flowing through the internal flow path (20). In the cooling operation, the refrigerant flows through the gas side connecting pipe (41) and the intermediate connecting pipe (43).

[0102] In the cooling operation of the refrigeration unit (10), the controller (90) operates the external fan (26) and the internal fan (27). In the transport container (1), air circulates between the internal flow path (20) of the refrigeration unit (10) and the internal space (5) of the container body (2). The internal air in the internal space (5) flows into the internal flow path (20) through the air inlet (21). The internal air flowing through the internal flow path (20) is cooled by the internal heat exchanger (57). The internal air cooled by the internal heat exchanger (57) is supplied to the internal space (5) through the air outlet (22).

[0103] In the cooling operation, the controller (90) controls the rotation speed of the compressor (50) and the like so that the temperature of the air blown out through the air outlet (22) into the interior space (5) (specifically, the measured value of the second air temperature sensor (87)) becomes the set temperature.

[0104] In the cooling operation, the refrigeration system (10) selectively performs two-stage compression operation and single-stage compression operation. In the two-stage compression operation, both the low-stage compressor (51) and the high-stage compressor (52) operate, and a two-stage compression refrigeration cycle is performed in the refrigerant circuit (30). In the single-stage compression operation, the low-stage compressor (51) is stopped, and the high-stage compressor (52) operates, and a single-stage compression refrigeration cycle is performed in the refrigerant circuit (30). In the cooling operation, the refrigeration system (10) performs two-stage compression operation when the difference between high and low pressures in the refrigeration cycle performed by the refrigerant circuit (30) is relatively large, and performs single-stage compression operation when the difference is relatively small.

[0105] (Two-stage compression operation in cooling operation) The two-stage compression operation in cooling operation will be described with reference to FIG.

[0106] In the two-stage compression operation of the cooling operation, the controller (90) controls the rotation speeds of the low-stage compressor (51) and the high-stage compressor (52). The controller (90) also controls the openings of the first expansion valve (EV1) and the second expansion valve (EV2) to keep the third expansion valve (EV3), the fourth expansion valve (EV4), and the fifth expansion valve (EV5) in fully closed states. The controller (90) also keeps the first electric valve (MV1) and the second electric valve (MV2) in fully open states, keeps the first solenoid valve (SV1) and the second solenoid valve (SV2) in open states, and keeps the third solenoid valve (SV3) in closed states.

[0107] The high-stage compressor (52) compresses the refrigerant it draws in to a pressure higher than the critical pressure of the refrigerant and discharges the refrigerant. The refrigerant discharged from the high-stage compressor (52) exchanges heat with outside air in the external heat exchanger (56) and dissipates heat to the outside air. The refrigerant that has passed through the external heat exchanger (56) flows into the first flow path (61a) of the internal heat exchanger (61) and is cooled by heat exchange with refrigerant flowing through the second flow path (61b) of the internal heat exchanger (61). The refrigerant that has passed through the first flow path (61a) of the internal heat exchanger (61) is reduced in pressure as it passes through the first expansion valve (EV1) and becomes a gas-liquid two-phase state. Thereafter, the refrigerant flows into the receiver (62) and is separated into liquid refrigerant and gas refrigerant.

[0108] The liquid refrigerant flowing out of the receiver (62) is reduced in pressure when passing through the second expansion valve (EV2) and then flows into the internal heat exchanger (57). The refrigerant flowing into the internal heat exchanger (57) absorbs heat from the air passing through the internal heat exchanger (57) and evaporates. The refrigerant flowing out of the internal heat exchanger (57) is sucked into the low-stage compressor (51). The low-stage compressor (51) compresses and discharges the sucked refrigerant. The refrigerant discharged from the low-stage compressor (51) is sucked into the high-stage compressor (52).

[0109] The gas refrigerant flowing out of the receiver (62) flows through the gas side connecting pipe (41), enters the second flow path (61b) of the internal heat exchanger (61), and absorbs heat from the refrigerant flowing through the first flow path (61a) of the internal heat exchanger (61). The refrigerant flowing out of the second flow path (61b) of the internal heat exchanger (61) passes through the intermediate connecting pipe (43), and is sucked into the high-stage compressor (52) together with the refrigerant discharged from the low-stage compressor (51).

[0110] (Single-stage compression operation in cooling operation) The single-stage compression operation in cooling operation will be described.

[0111] In the single-stage compression mode of the cooling operation, the controller (90) keeps the low-stage compressor (51) stopped. The difference between the single-stage compression mode and the two-stage compression mode of the cooling operation is that the low-stage compressor (51) is kept stopped.

[0112] In the refrigerant circuit (30), the refrigerant flowing out from the internal heat exchanger (57) is sucked into the high-stage compressor (52) through the low-stage connecting pipe (44). In this single-stage compression operation, the refrigerant flowing through the refrigerant circuit (30) bypasses the low-stage compressor (51) and is compressed only by the high-stage compressor (52). Except for the fact that the refrigerant flowing out from the internal heat exchanger (57) flows through the low-stage connecting pipe (44), the refrigerant flow path in the refrigerant circuit (30) during the single-stage compression operation is the same as the refrigerant flow path in the refrigerant circuit (30) during the two-stage compression operation.

[0113] <Dehumidifying Operation> The dehumidifying operation is an operation for dehumidifying the air inside the refrigerator while maintaining the temperature of the refrigerator space (5). In the dehumidifying operation, the refrigeration system (10) blows air that has been dehumidified in the refrigerator heat exchanger (57) and then heated in the reheat heat exchanger (58) into the refrigerator space (5).

[0114] The refrigeration system (10) performs a defrosting operation when the temperature of the interior space (5) is stable. Specifically, in the refrigeration system (10), the controller (90) determines whether a temperature stability condition is met. The temperature stability condition is a condition indicating that the temperature of the interior space (5) is stable. An example of the temperature stability condition is a condition in which the measurement value of the second air temperature sensor (87) remains within a range of ±0.5°C of the set temperature for five minutes. When the controller (90) determines that the temperature stability condition is met, it causes the refrigeration system (10) to perform a dehumidifying operation.

[0115] In the dehumidifying operation of the refrigeration system (10), the controller (90) operates the external fan (26) and the internal fan (27), similarly to the cooling operation. In the transport container (1), air circulates between the internal flow path (20) of the refrigeration system (10) and the internal space (5) of the container body (2). The internal air in the internal space (5) flows into the internal flow path (20) through the air inlet (21). The internal air flowing through the internal flow path (20) passes through the internal heat exchanger (57) and the reheat heat exchanger (58) in this order, and is then supplied to the internal space (5) through the air outlet (22).

[0116] As in the cooling operation, in the dehumidifying operation, the refrigeration system (10) selectively performs two-stage compression operation and single-stage compression operation. In the two-stage compression operation, both the low-stage compressor (51) and the high-stage compressor (52) operate, and a two-stage compression refrigeration cycle is performed in the refrigerant circuit (30). In the single-stage compression operation, the low-stage compressor (51) is stopped, and the high-stage compressor (52) operates, and a single-stage compression refrigeration cycle is performed in the refrigerant circuit (30). In the dehumidifying operation, the refrigeration system (10) performs two-stage compression operation when the difference between high and low pressures in the refrigeration cycle performed by the refrigerant circuit (30) is relatively large, and performs single-stage compression operation when the difference is relatively small.

[0117] (Two-stage compression operation in dehumidifying operation) The two-stage compression operation in dehumidifying operation will be described with reference to FIG.

[0118] In the two-stage compression operation of the dehumidification operation, the controller (90) controls the rotation speeds of the low-stage compressor (51) and the high-stage compressor (52). The controller (90) also controls the apertures of the first expansion valve (EV1), the second expansion valve (EV2), and the fifth expansion valve (EV5), and keeps the third expansion valve (EV3) and the fourth expansion valve (EV4) in a fully closed state. The controller (90) also keeps the first electric valve (MV1) and the second electric valve (MV2) in a fully open state, and keeps the first solenoid valve (SV1), the second solenoid valve (SV2), and the third solenoid valve (SV3) in an open state.

[0119] The two-stage compression operation in the dehumidifying operation differs from the cooling operation in that the controller (90) controls the aperture of the fifth expansion valve (EV5) and keeps the third solenoid valve (SV3) open. The two-stage compression operation in the dehumidifying operation also differs from the cooling operation in that the refrigerant flows not only through the main circuit (31), the gas side connecting pipe (41), and the intermediate connecting pipe (43) but also through the reheat pipe (33).

[0120] In the two-stage compression operation of the dehumidification operation of the refrigeration system (10), the refrigerant circuit (30) performs a refrigeration cycle. In the two-stage compression operation of the dehumidification operation, as in the cooling operation, the refrigerant circulates in the main circuit (31) of the refrigerant circuit (30), the external heat exchanger (56) functions as a radiator, and the internal heat exchanger (57) functions as an evaporator. The internal heat exchanger (57) cools the air flowing through the internal flow path (20).

[0121] In the dehumidifying operation, the evaporation temperature of the refrigerant in the internal heat exchanger (57) is set to a value lower than the dew point temperature of the air flowing into the internal heat exchanger (57). Therefore, in the internal heat exchanger (57), moisture contained in the air condenses to form drain water. The drain water generated in the internal heat exchanger (57) flows down into a drain pan and is discharged to the outside of the cabinet. Therefore, the temperature and absolute humidity of the air flowing through the internal flow path (20) decrease while passing through the internal heat exchanger (57).

[0122] In the dehumidifying operation, as in the cooling operation, the refrigerant flows through the gas side connecting pipe (41) and the intermediate connecting pipe (43). The gas refrigerant flowing out of the receiver (62) passes through the gas side connecting pipe (41) and the intermediate connecting pipe (43) in this order, and is sucked into the high-stage compressor (52) together with the refrigerant discharged from the low-stage compressor (51).

[0123] In the dehumidifying operation, a portion of the refrigerant discharged from the high-stage compressor (52) is supplied to the reheat heat exchanger (58) through the reheat pipe (33). In the reheat heat exchanger (58), the air that has passed through the internal heat exchanger (57) is heated by the refrigerant. The refrigerant that has dissipated heat in the reheat heat exchanger (58) is reduced in pressure when passing through the fifth expansion valve (EV5). The refrigerant that has passed through the fifth expansion valve (EV5) flows into the main circuit (31) and then flows into the internal heat exchanger (57) together with the refrigerant that has passed through the second expansion valve (EV2).

[0124] (Single-Stage Compression Operation in Dehumidifying Operation) The single-stage compression operation in dehumidifying operation will be described with reference to FIG.

[0125] In the single-stage compression mode of the dehumidification operation, the controller (90) keeps the low-stage compressor (51) stopped. The difference between the single-stage compression mode and the two-stage compression mode of the dehumidification operation is that the low-stage compressor (51) is kept stopped.

[0126] In the refrigerant circuit (30), the refrigerant flowing out from the internal heat exchanger (57) is sucked into the high-stage compressor (52) through the low-stage connecting pipe (44). In this single-stage compression operation, the refrigerant flowing through the refrigerant circuit (30) bypasses the low-stage compressor (51) and is compressed only by the high-stage compressor (52). Except for the fact that the refrigerant flowing out from the internal heat exchanger (57) flows through the low-stage connecting pipe (44), the refrigerant flow path in the refrigerant circuit (30) during the single-stage compression operation is the same as the refrigerant flow path in the refrigerant circuit (30) during the two-stage compression operation.

[0127] <Defrosting Operation> The defrosting operation is an operation for melting the frost that has formed on the internal heat exchanger (57) during the cooling operation.

[0128] In the cooling operation, the evaporation temperature of the refrigerant in the internal heat exchanger (57) may fall below 0° C. In this case, moisture in the air freezes and turns into frost, which adheres to the internal heat exchanger (57). When frost adheres to the internal heat exchanger (57), the frost obstructs the flow of air passing through the internal heat exchanger (57) and also obstructs heat exchange between the refrigerant and the air.

[0129] Therefore, when a defrosting start condition is satisfied during the cooling operation, the refrigeration system (10) temporarily suspends the cooling operation and performs the defrosting operation. The defrosting start condition is, for example, a condition that "the cumulative value of the execution time of the cooling operation during which the evaporation temperature of the refrigerant in the internal heat exchanger is lower than 0°C reaches a predetermined time (for example, 2 hours)."

[0130] Furthermore, when a defrost termination condition is satisfied during the defrosting operation, the refrigeration system (10) terminates the defrosting operation and resumes the cooling operation. The defrost termination condition is, for example, that the temperature of the internal heat exchanger (57) (specifically, the value measured by the heat exchanger temperature sensor (85)) reaches a predetermined temperature (for example, 10°C).

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

[0132] In the defrosting operation, the controller (90) keeps the external fan (26) and the internal fan (27) stopped. The controller (90) also keeps the low-stage compressor (51) stopped and controls the rotation speed of the high-stage compressor (52). The controller (90) also keeps the first expansion valve (EV1) open, the second expansion valve (EV2), the third expansion valve (EV3), and the fifth expansion valve (EV5) closed, and controls the opening of the fourth expansion valve (EV4). The controller (90) also keeps the first motor-operated valve (MV1) fully open, the second motor-operated valve (MV2) fully closed, and the first solenoid valve (SV1), the second solenoid valve (SV2), and the third solenoid valve (SV3) closed.

[0133] In the refrigerant circuit (30) during the defrosting operation, the refrigerant circulates between the high-stage compressor (52) and the internal heat exchanger (57) without passing through the external heat exchanger (56). The refrigerant discharged from the high-stage compressor (52) flows through the defrosting pipe (32) and is reduced in pressure when passing through the fourth expansion valve (EV4). The refrigerant that has passed through the fourth expansion valve (EV4) flows into the internal heat exchanger (57). In the internal heat exchanger (57), the frost is heated by the refrigerant and melts. The refrigerant that flows out from the internal heat exchanger (57) passes through the low-stage connecting pipe (44) and is drawn into the high-stage compressor (52). The high-stage compressor (52) compresses the drawn refrigerant and discharges it.

[0134] --Operation of the Controller in Dehumidifying Operation-- The operation performed by the controller (90) in the dehumidifying operation will be described.

[0135] As shown in Fig. 9 , in the dehumidification operation, the controller (90) sequentially repeats a humidity control operation, a temperature control operation, and a high-pressure control operation. The controller (90) alternates between the humidity control operation, the temperature control operation, and the high-pressure control operation at regular intervals (e.g., every five seconds). The order in which the humidity control operation, the temperature control operation, and the high-pressure control operation are performed is not limited to the order shown in Fig. 9 . The order shown in Fig. 9 is merely an example.

[0136] <Humidity Control Operation> The humidity control operation will be described with reference to Fig. 10. In the humidity control operation, the controller (90) controls the evaporation temperature of the refrigerant in the internal heat exchanger (57) so that the humidity of the air blown out from the air outlet (22) of the refrigeration system (10) during dehumidification operation becomes a set humidity. In order to control the evaporation temperature of the refrigerant in the internal heat exchanger (57), the controller (90) sets a target evaporation temperature and controls the rotation speed of the compressor (50) and the aperture of the second expansion valve (EV2) using the set target evaporation temperature.

[0137] (Setting of target evaporation temperature) The controller (90) sets a target evaporation temperature based on the measurement value of the humidity sensor (88) and a set value (set humidity) of the humidity of the interior air in the interior space (5). The target evaporation temperature is a target value for the evaporation temperature of the refrigerant in the interior heat exchanger (57).

[0138] As an operation for setting the target evaporation temperature, the controller (90) performs the processes of steps ST11 to ST15 in Fig. 10. The controller (90) compares the measured value RH of the humidity sensor (88) with a set humidity range including the set humidity (for example, a range of the set humidity ±5%), and sets the target evaporation temperature based on the result of the comparison.

[0139] In the process of step ST11, the controller (90) compares the measured value RH of the humidity sensor (88) with the maximum value of the set humidity range. If the condition that "the measured value RH of the humidity sensor (88) is higher than the maximum value of the set humidity range" is met, the controller (90) performs the process of step ST12. In the process of step ST12, the controller (90) lowers the target evaporation temperature. On the other hand, if this condition is not met, the controller (90) performs the process of step ST13.

[0140] In the process of step ST13, the controller (90) compares the measured value RH of the humidity sensor (88) with the minimum value of the set humidity range. If the condition that "the measured value RH of the humidity sensor (88) is lower than the minimum value of the set humidity range" is met, the controller (90) performs the process of step ST14. In the process of step ST14, the controller (90) reduces the target evaporation temperature. On the other hand, if this condition is not met, the controller (90) performs the process of step ST15.

[0141] If the condition for the process of step ST13 is not satisfied, the measured value RH of the humidity sensor (88) is within the set humidity range. Therefore, the controller (90) maintains the target evaporation temperature unchanged in the process of step ST15. After the process of step ST12, step ST14, or step ST15 is completed, the controller (90) performs the process of step ST16.

[0142] (Control of compressor and second expansion valve) The controller (90) controls the rotation speed of the compressor (50) and the opening of the second expansion valve (EV2) so that the measurement value Tr3 of the third refrigerant temperature sensor (83) falls within a target evaporation temperature range including the target evaporation temperature (for example, a range of the target evaporation temperature ±0.5°C).

[0143] The third refrigerant temperature sensor (83) measures the temperature of the refrigerant passing through the second expansion valve (EV2) and flowing into the internal heat exchanger (57). The refrigerant passing through the second expansion valve (EV2) is in a gas-liquid two-phase state. Therefore, the temperature of the refrigerant flowing into the internal heat exchanger (57) is substantially equal to the evaporation temperature of the refrigerant in the internal heat exchanger (57). Therefore, the temperature of the refrigerant flowing into the internal heat exchanger (57) is a physical quantity that correlates with the evaporation temperature of the refrigerant in the internal heat exchanger (57).

[0144] (Selection of Control Target) The controller (90) selectively controls the rotation speed of the compressor (50) and the opening degree of the second expansion valve (EV2).

[0145] The process of step ST16 in Fig. 10 is a process for selecting a control target. In the process of step ST16, the controller (90) determines whether or not a selection condition is met.

[0146] The selection conditions are that "the first condition is satisfied, and at least one of the second and third conditions is satisfied." The first condition is that "the target degree of superheat is the lower limit superheat." The lower limit superheat is the lowest value in the range of values ​​that can be set as the target degree of superheat. The second condition is that "the rotation speed of the compressor (50) is lower than the reference speed." The third condition is that "the measured value Tr3 of the third refrigerant temperature sensor (83) is lower than the lowest value in the target evaporation temperature range."

[0147] If the selection condition is met in the process of step ST16, the controller (90) performs the process of step ST17 to start controlling the rotation speed of the compressor (50). On the other hand, if the selection condition is not met, the controller (90) performs the process of step ST22 to start controlling the opening degree of the second expansion valve (EV2).

[0148] (Control of Rotational Speed ​​of Compressor) Control of the rotational speed of the compressor (50) by the controller (90) will be described.

[0149] The controller (90) controls the rotation speed of the compressor (50) that sucks the refrigerant flowing out from the internal heat exchanger (57) during the dehumidifying operation based on the measurement value of the third refrigerant temperature sensor (83). In the two-stage compression mode of the dehumidifying operation, the controller (90) controls the rotation speed of the low-stage compressor (51) based on the measurement value of the third refrigerant temperature sensor (83). In the single-stage compression mode of the dehumidifying operation, the controller (90) controls the rotation speed of the high-stage compressor (52) based on the measurement value of the third refrigerant temperature sensor (83).

[0150] The controller (90) performs the processes of steps ST17 to ST21 in Fig. 10 as an operation for controlling the rotation speed of the compressor (50). The controller (90) compares the measurement value Tr3 of the third refrigerant temperature sensor (83) with the target evaporation temperature range, and controls the rotation speed of the compressor (50) based on the result of the comparison.

[0151] In the process of step ST17, the controller (90) compares the measurement value Tr3 of the third refrigerant temperature sensor (83) with the maximum value of the target evaporation temperature range. If the condition that "the measurement value Tr3 of the third refrigerant temperature sensor (83) is higher than the maximum value of the target evaporation temperature range" is met, the controller (90) performs the process of step ST18. In the process of step ST18, the controller (90) increases the rotation speed of the compressor (50). On the other hand, if this condition is not met, the controller (90) performs the process of step ST19.

[0152] In the process of step ST19, the controller (90) compares the measurement value Tr3 of the third refrigerant temperature sensor (83) with the minimum value of the target evaporation temperature range. If the condition that "the measurement value Tr3 of the third refrigerant temperature sensor (83) is lower than the minimum value of the target evaporation temperature range" is met, the controller (90) performs the process of step ST20. In the process of step ST20, the controller (90) reduces the rotation speed of the compressor (50). On the other hand, if this condition is not met, the controller (90) performs the process of step ST21.

[0153] If the condition for the process of step ST19 is not satisfied, the measured value Tr3 of the third refrigerant temperature sensor (83) is within the target evaporation temperature range. Therefore, in the process of step ST21, the controller (90) maintains the rotation speed of the compressor (50) unchanged. After the process of step ST18, step ST20, or step ST21 is completed, the controller (90) terminates the humidity control operation.

[0154] In the two-stage compression operation of the dehumidification operation, the controller (90) controls the rotation speed of the high-stage compressor (52) based on the measurement value of the high-stage suction pressure sensor (77). The controller (90) controls the rotation speed of the high-stage compressor (52) so that the measurement value of the high-stage suction pressure sensor (77) becomes the target intermediate pressure. The controller (90) sets the target intermediate pressure based on the low pressure of the refrigeration cycle (specifically, the measurement value of the low-stage suction pressure sensor (75)) and the high pressure of the refrigeration cycle (specifically, the measurement value of the high-stage discharge pressure sensor (78)).

[0155] (Control of Opening Degree of Second Expansion Valve) Control of the opening degree of the second expansion valve (EV2) by the controller (90) will be described.

[0156] The controller (90) controls the opening degree of the second expansion valve (EV2) based on the degree of superheat of the refrigerant at the outlet of the internal heat exchanger (57). When the evaporation temperature (in other words, the saturation temperature) of the refrigerant at the internal heat exchanger (57) changes, the degree of superheat of the refrigerant at the outlet of the internal heat exchanger (57) changes. Therefore, the degree of superheat of the refrigerant at the outlet of the internal heat exchanger (57) is a physical quantity that correlates with the evaporation temperature of the refrigerant at the internal heat exchanger (57).

[0157] The controller (90) controls the opening of the second expansion valve (EV2) so that the degree of superheat SH of the refrigerant at the outlet of the internal heat exchanger (57) falls within a target superheat range including the target degree of superheat (for example, a range of the target degree of superheat ±1° C.). The controller (90) determines the degree of superheat SH of the refrigerant at the outlet of the internal heat exchanger (57) to be the value obtained by subtracting the measurement value Tr3 of the third refrigerant temperature sensor (83) from the measurement value Tr4 of the fourth refrigerant temperature sensor (84) (SH=Tr4−Tr3).

[0158] The controller (90) performs the processes of steps ST22 to ST26 in Fig. 10 as an operation for controlling the opening degree of the second expansion valve (EV2). The controller (90) adjusts the target degree of superheat based on the evaporation temperature of the refrigerant in the internal heat exchanger (57). Specifically, the controller (90) adjusts the target degree of superheat based on the measurement value of the third refrigerant temperature sensor (83) and the target evaporation temperature range. When the target degree of superheat is changed, the opening degree of the second expansion valve (EV2) changes accordingly.

[0159] In the process of step ST22, the controller (90) compares the measurement value Tr3 of the third refrigerant temperature sensor (83) with the maximum value of the target evaporation temperature range. If the condition that "the measurement value Tr3 of the third refrigerant temperature sensor (83) is higher than the maximum value of the target evaporation temperature range" is met, the controller (90) performs the process of step ST23. In the process of step ST23, the controller (90) increases the target degree of superheat. When the target degree of superheat increases, the controller (90) reduces the opening of the second expansion valve (EV2) to increase the degree of superheat SH of the refrigerant at the outlet of the internal heat exchanger (57). On the other hand, if this condition is not met, the controller (90) performs the process of step ST24.

[0160] In the process of step ST24, the controller (90) compares the measurement value Tr3 of the third refrigerant temperature sensor (83) with the minimum value of the target evaporation temperature range. If the condition that “the measurement value Tr3 of the third refrigerant temperature sensor (83) is lower than the minimum value of the target evaporation temperature range” is met, the controller (90) performs the process of step ST25. In the process of step ST25, the controller (90) decreases the target degree of superheat. When the target degree of superheat decreases, the controller (90) increases the opening of the second expansion valve (EV2) to decrease the degree of superheat SH of the refrigerant at the outlet of the internal heat exchanger (57). On the other hand, if this condition is not met, the controller (90) performs the process of step ST26.

[0161] If the condition in the process of step ST24 is not satisfied, the measured value Tr3 of the third refrigerant temperature sensor (83) is within the target evaporation temperature range. Therefore, in the process of step ST26, the controller (90) maintains the target degree of superheat without changing it. If the target degree of superheat does not change, the controller (90) maintains the opening degree of the second expansion valve (EV2) without changing it. After the process of step ST23, step ST25, or step ST26 is completed, the controller (90) terminates the humidity control operation.

[0162] <Temperature Control Operation> The temperature control operation will be described with reference to Fig. 11. In the temperature control operation, the controller (90) controls the flow rate of the refrigerant in the reheat heat exchanger (58) so that the temperature of the air blown out from the air outlet (22) of the refrigeration system (10) during the dehumidification operation becomes a set air temperature. In order to control the flow rate of the refrigerant in the reheat heat exchanger (58), the controller (90) controls the opening of the fifth expansion valve (EV5) based on the measurement value of the second air temperature sensor (87).

[0163] The controller (90) controls the opening of the fifth expansion valve (EV5) so that the measurement value of the second air temperature sensor (87) falls within a set air temperature range including the set air temperature (for example, a range of the set air temperature ±0.5°C).

[0164] In the process of step ST31, the controller (90) compares the measurement value Ta2 of the second air temperature sensor (87) with the maximum value of the set air temperature range. If the condition that "the measurement value Ta2 of the second air temperature sensor (87) is higher than the maximum value of the set air temperature range" is met, the controller (90) performs the process of step ST32. In the process of step ST32, the controller (90) reduces the opening of the fifth expansion valve (EV5) to reduce the flow rate of refrigerant in the reheat heat exchanger (58). On the other hand, if this condition is not met, the controller (90) performs the process of step ST33.

[0165] In the process of step ST33, the controller (90) compares the measurement value Ta2 of the second air temperature sensor (87) with the minimum value of the set air temperature range. If the condition that "the measurement value Ta2 of the second air temperature sensor (87) is lower than the minimum value of the set air temperature range" is met, the controller (90) performs the process of step ST34. In the process of step ST34, the controller (90) increases the opening of the fifth expansion valve (EV5) to increase the flow rate of refrigerant in the reheat heat exchanger (58). On the other hand, if this condition is not met, the controller (90) performs the process of step ST35.

[0166] If the condition in the process of step ST33 is not satisfied, the measured value Ta2 of the second air temperature sensor (87) is within the set air temperature range. Therefore, in the process of step ST35, the controller (90) maintains the opening degree of the fifth expansion valve (EV5) without changing it. After the process of step ST32, step ST34, or step ST35 is completed, the controller (90) ends the temperature control operation.

[0167] <High-Pressure Control Operation> The high-pressure control operation will be described with reference to Fig. 12. In the high-pressure control operation, the controller (90) controls the aperture of the first expansion valve (EV1) so that the pressure of the refrigerant supplied to the reheat heat exchanger (58) during the dehumidification operation is maintained at a relatively high pressure. The controller (90) controls the aperture of the first expansion valve (EV1) based on the measurement value of the high-stage discharge pressure sensor (78) in order to control the pressure of the refrigerant discharged from the high-stage compressor (52).

[0168] The controller (90) controls the opening of the first expansion valve (EV1) so that the measurement value of the high-stage discharge pressure sensor (78) falls within a target pressure range (for example, a range of 10±1 MPa). In the controller (90) of this embodiment, the minimum value of the target pressure range is 8 MPa or more, and the maximum value of the target pressure range is 15 MPa or less.

[0169] In the process of step ST41, the controller (90) compares the measured value Pdh of the high-stage discharge pressure sensor (78) with the maximum value of the target pressure range. If the condition that "the measured value Pdh of the high-stage discharge pressure sensor (78) is higher than the maximum value of the target pressure range" is met, the controller (90) performs the process of step ST42. In the process of step ST42, the controller (90) increases the opening of the first expansion valve (EV1) to reduce the pressure of the refrigerant discharged from the high-stage compressor (52). On the other hand, if this condition is not met, the controller (90) performs the process of step ST43.

[0170] In the process of step ST43, the controller (90) compares the measured value Pdh of the high-stage discharge pressure sensor (78) with the minimum value of the target pressure range. If the condition that "the measured value Pdh of the high-stage discharge pressure sensor (78) is lower than the minimum value of the target pressure range" is met, the controller (90) performs the process of step ST44. In the process of step ST44, the controller (90) reduces the opening of the first expansion valve (EV1) to increase the pressure of the refrigerant discharged from the high-stage compressor (52). On the other hand, if this condition is not met, the controller (90) performs the process of step ST45.

[0171] If the condition for the process of step ST45 is not satisfied, the measured value Pdh of the high-stage discharge pressure sensor (78) is within the target pressure range. Therefore, in the process of step ST45, the controller (90) maintains the opening degree of the first expansion valve (EV1) without changing it. After the process of step ST42, step ST44, or step ST45 is completed, the controller (90) terminates the high-pressure control operation.

[0172] The refrigerant filled in the refrigerant circuit (30) in this embodiment is carbon dioxide. The critical pressure of carbon dioxide is 7.38 MPa. On the other hand, the target pressure range in this embodiment is within the range of 8 MPa to 15 MPa. Therefore, the controller (90) in this embodiment controls the aperture of the first expansion valve (EV1) so that the pressure of the refrigerant discharged from the high-stage compressor (52) is equal to or higher than the critical pressure of the refrigerant (carbon dioxide).

[0173] Feature (1) of First Embodiment The refrigeration system (10) of this embodiment performs a dehumidifying operation. In the dehumidifying operation, the temperature and absolute humidity of the air flowing through the internal flow path (20) decrease as the air passes through the internal heat exchanger (57), and the temperature increases as the air passes through the reheat heat exchanger (58). Therefore, by performing the dehumidifying operation of the refrigeration system (10), it is possible to reduce the humidity of the internal air while maintaining the temperature of the internal space (5).

[0174] In the dehumidifying operation, the controller (90) of this embodiment controls the aperture of the regulating valve (EV5). When the aperture of the regulating valve (EV5) changes, the flow rate of the refrigerant in the reheat heat exchanger (58) changes, and the amount of heat imparted to the air in the reheat heat exchanger (58) changes. As a result, the temperature of the air blown into the internal space (5) after passing through the reheat heat exchanger (58) changes. Therefore, by controlling the aperture of the fifth expansion valve (EV5) by the controller (90), it becomes possible to control the temperature of the air blown into the internal space (5) by the refrigeration device (10) in the dehumidifying operation.

[0175] Feature (2) of First Embodiment In the two-stage compression operation of the defrosting operation performed by the refrigeration system (10) of this embodiment, refrigerant at a pressure equal to or higher than the critical pressure exchanges heat with air in the reheat heat exchanger (58). In the process of releasing heat, the refrigerant at a pressure equal to or higher than the critical pressure undergoes sensible heat conversion without condensation.

[0176] When refrigerant at or above the critical pressure flows through the reheat heat exchanger (58), the heat transfer coefficient between the refrigerant and air is substantially constant throughout the reheat heat exchanger (58). Therefore, in the two-stage compression mode of the defrosting operation performed by the refrigeration system (10) of this embodiment, the refrigerant releases heat at a substantially constant rate throughout the reheat heat exchanger (58). As a result, the temperature of the air blown out of the air outlet (22) by the refrigeration system (10) during the dehumidifying operation is uniform.

[0177] -Feature (3) of First Embodiment- In the refrigeration system (10) of this embodiment, the controller (90) performs humidity control operation and temperature control operation.

[0178] In the humidity control operation, the controller (90) sets a target evaporation temperature based on the measurement value of the humidity sensor (88) and controls the rotation speed of the compressor (50) that sucks the refrigerant flowing out from the internal heat exchanger (57) during the dehumidification operation based on the target evaporation temperature. Therefore, in the refrigeration system (10) of this embodiment, the humidity of the air blown out from the refrigeration system (10) into the internal space (5) during the dehumidification operation can be appropriately controlled.

[0179] In the temperature control operation, the controller (90) controls the opening of the fifth expansion valve (EV5) based on the measurement value of the second air temperature sensor (87). Therefore, in the refrigeration system (10) of the present embodiment, the temperature of the air blown out from the refrigeration system (10) into the internal space (5) during the dehumidification operation can be appropriately controlled.

[0180] Second Embodiment A second embodiment will be described. In this embodiment, the transport container (1) of the first embodiment has a modified configuration of the refrigeration unit (10).

[0181] The refrigeration system (10) of this embodiment differs from the refrigeration system (10) of embodiment 1 in the configuration of the refrigerant circuit (30). Here, the refrigerant circuit (30) of this embodiment differs from the refrigerant circuit (30) of embodiment 1 in the following points.

[0182] As shown in Figure 13, in the refrigerant circuit (30) of this embodiment, a drain pan heater (63) is provided in the defrosting pipe (32). In the defrosting pipe (32), the drain pan heater (63) is arranged 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 with the refrigerant flowing therethrough.

[0183] - Defrosting Operation of Refrigeration Unit - In the defrosting operation performed by the refrigeration unit (10) of this embodiment, a portion of the refrigerant discharged from the high-stage compressor (52) flows into the defrosting pipe (32), similar to the defrosting operation performed by the refrigeration unit (10) of embodiment 1. In the defrosting operation performed by the refrigeration unit (10) of this embodiment, the refrigerant that has 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 internal heat exchanger (57).

[0184] During the defrosting operation, frost peeled off from the internal heat exchanger (57) may fall into the drain pan. In the defrosting operation performed by the refrigeration system (10) of this embodiment, the drain pan is heated by the refrigerant flowing through the drain pan heater (63). Therefore, the frost that has fallen into the drain pan from the internal heat exchanger (57) is heated and melted by the drain pan, and is discharged as drain water to the space outside the compartment.

[0185] Third Embodiment A third embodiment will be described. In this embodiment, the transport container (1) of the second embodiment is modified in terms of the configuration of the refrigeration unit (10).

[0186] The refrigeration system (10) of this embodiment differs from the refrigeration system (10) of embodiment 2 in the configuration of the refrigerant circuit (30). Here, the refrigerant circuit (30) of this embodiment differs from the refrigerant circuit (30) of embodiment 2 in the following points.

[0187] 14 , in the refrigerant circuit (30) of this embodiment, a drain pan heater (63) is provided in the reheat pipe (33), and the defrost pipe (32) and the fourth expansion valve (EV4) are omitted. In the refrigerant circuit (30) of this embodiment, the reheat pipe (33) also serves as the defrost pipe (32) that sends refrigerant to the internal heat exchanger in the defrosting operation. In the reheat pipe (33) of this embodiment, the drain pan heater (63) is disposed between the third solenoid valve (SV3) and the reheat heat exchanger (58).

[0188] —Operation of Controller— In the refrigeration system of the present embodiment, the controller (90) controls the opening degree of the fifth expansion valve (EV5) in both the defrosting operation and the dehumidifying operation. In the defrosting operation, the controller (90) of the present embodiment controls the opening degree of the fifth expansion valve (EV5) in the same manner as the controller (90) of the first and second embodiments controls the opening degree of the fourth expansion valve (EV4). In the dehumidifying operation, the controller (90) of the present embodiment controls the opening degree of the fifth expansion valve (EV5) in the same manner as the controller (90) of the first and second embodiments.

[0189] Other Embodiments The refrigeration system (10) of the above embodiment may be modified as follows: The following modifications may be combined or substituted as appropriate, as long as the functionality of the refrigeration system (10) is not impaired.

[0190] First Modification The refrigeration system (10) of any of the first to third embodiments may be configured to perform only a single-stage compression refrigeration cycle. Here, the differences between the refrigeration system (10) of the third embodiment and the refrigeration system (10) of the first to third embodiments will be described.

[0191] 15, the refrigerant circuit (30) of the refrigeration system (10) of this modified example does not include the low-stage compressor (51), the low-stage connecting pipe (44), and the high-stage connecting pipe (45). The refrigerant circuit (30) of this modified example is provided with one compressor (52) that corresponds to the high-stage compressor of the refrigerant circuit (30) of the third embodiment.

[0192] In the main circuit (31) of the refrigerant circuit (30) of this modified example, the other end of the internal heat exchanger (57) is connected to the suction pipe of the compressor (52). The first motor-operated valve (MV1) is provided in the main circuit (31) between the internal heat exchanger (57) and the suction pipe of the compressor (52). The other end of the intermediate connecting pipe (43) is connected to the main circuit (31) between the first motor-operated valve (MV1) and the compressor (52).

[0193] In the cooling operation of the refrigeration system (10) of this modified example, the refrigerant circuit (30) operates in a single-stage compression refrigeration cycle. In the refrigerant circuit (30), the compressor (52) is activated, and refrigerant circulates in the main circuit (31). The refrigerant discharged from the compressor (52) dissipates heat to the outside air in the external heat exchanger (56). The refrigerant flowing out of the external 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 solenoid valve (SV1), and the second expansion valve (EV2), in that order, and then flows into the internal heat exchanger (57). The refrigerant flowing into the internal heat exchanger (57) absorbs heat from the air flowing through the internal flow path (20) and evaporates. The evaporated refrigerant in the internal heat exchanger (57) is drawn into the compressor (52). The compressor (52) compresses the sucked refrigerant and discharges it.

[0194] -Second Modification- In the humidity control operation, the controller (90) of the refrigeration system (10) of any of the first to third embodiments uses the measurement value of the third refrigerant temperature sensor (83) as the evaporation temperature of the refrigerant in the internal heat exchanger (57) to control the rotation speed of the compressor (50) and the opening of the second expansion valve (EV2).

[0195] In contrast to this, the controller (90) of the first to third embodiments may use the saturation temperature of the refrigerant corresponding to the measurement value of the low-stage suction pressure sensor (75) as the evaporation temperature of the refrigerant in the internal heat exchanger (57). In this case, the controller (90) calculates the saturation temperature of the refrigerant corresponding to the measurement value of the low-stage suction pressure sensor (75), and controls the rotation speed of the compressor (50) and the aperture of the second expansion valve (EV2) so that the calculated saturation temperature falls within a target evaporation temperature range.

[0196] In addition, the controller (90) of the first to third embodiments may set a target evaporation pressure range corresponding to the target evaporation temperature range, and control the rotation speed of the compressor (50) and the aperture of the second expansion valve (EV2) so that the measurement value of the low-stage suction pressure sensor (75) falls within the target evaporation pressure range. The minimum value of the target evaporation pressure range is the saturation pressure of the refrigerant corresponding to the minimum value of the target evaporation temperature range. The maximum value of the target evaporation pressure range is the saturation pressure of the refrigerant corresponding to the maximum value of the target evaporation temperature range.

[0197] The low-stage suction pressure sensor (75) measures the pressure of the refrigerant in the suction pipe of the low-stage compressor (51). The pressure of the refrigerant in the suction pipe of the low-stage compressor (51) is substantially equal to the pressure of the refrigerant flowing out from the internal heat exchanger (57). Furthermore, the pressure of the refrigerant flowing out from the internal heat exchanger (57) is substantially equal to the evaporation pressure of the refrigerant in the internal heat exchanger (57). The evaporation temperature of the refrigerant is the saturation temperature corresponding to the evaporation pressure of the refrigerant. Therefore, the pressure of the refrigerant in the suction pipe of the low-stage compressor (51) is a physical quantity that correlates with the evaporation temperature of the refrigerant in the internal heat exchanger (57).

[0198] -Third Modification- In a dehumidifying operation of the refrigeration system (10), the controller (90) of any of the first to third embodiments may control the aperture of the fifth expansion valve (EV5) depending on whether a temperature unevenness condition is met. The temperature unevenness condition is a condition indicating that the temperature of air passing through the reheat heat exchanger (58) is uneven from place to place. Examples of the temperature unevenness condition include a first temperature unevenness condition and a second temperature unevenness condition described below. The controller (90) of this modification may determine whether only one of the first temperature unevenness condition and the second temperature unevenness condition is met, or may determine whether both are met.

[0199] <First Temperature Unevenness Condition> The first temperature unevenness condition is a condition that "the measurement value of the second air temperature sensor (87) is higher than the measurement value of the first air temperature sensor (86)."

[0200] When the first temperature unevenness condition is satisfied, it is highly likely that the amount of heat applied to the region upstream of the second air temperature sensor (87) in the reheat heat exchanger (58) is greater than the amount of heat applied to other regions. When the amount of heat applied to each portion of the reheat heat exchanger (58) is uneven, the temperature of the air that has passed through the reheat heat exchanger (58) becomes uneven from place to place. In this description, the "amount of heat applied" refers to the amount of heat applied to the air by the reheat heat exchanger (58).

[0201] Therefore, the controller (90) of this modified example increases the aperture of the fifth expansion valve (EV5) when the first temperature unevenness condition is satisfied. Increasing the aperture of the fifth expansion valve (EV5) increases the flow rate of refrigerant in the reheat heat exchanger (58). When refrigerant at or above the critical pressure flows through the reheat heat exchanger (58), increasing the flow rate of refrigerant in the reheat heat exchanger (58) reduces the amount of temperature decrease of the refrigerant passing through the reheat heat exchanger (58). This uniformizes the amount of heating in each portion of the reheat heat exchanger (58), thereby uniformizing the temperature of the air passing through the reheat heat exchanger (58).

[0202] <Second Temperature Unevenness Condition> The second temperature unevenness condition is a condition that "the degree of superheat of the refrigerant at the outlet of the internal heat exchanger (57) is higher than a reference value (for example, 10° C.)".

[0203] Here, a heat exchanger functioning as an evaporator is divided into a two-phase region where the refrigerant in a two-phase gas-liquid state exchanges heat with air, and a superheated region where the refrigerant in a single-phase gas state exchanges heat with air. The heat transfer coefficient between the refrigerant and air in the superheated region is lower than the heat transfer coefficient between the refrigerant and air in the two-phase gas-liquid region. Therefore, in a heat exchanger functioning as an evaporator, the temperature of the air that has passed through the superheated region is likely to be higher than the temperature of the air that has passed through the two-phase gas-liquid region.

[0204] When the second temperature unevenness condition is satisfied, it is highly likely that the internal heat exchanger (57) functioning as an evaporator has a relatively large overheated region. Therefore, it is highly likely that the temperature of the air that has passed through the internal heat exchanger (57) is locally non-uniform. When the temperature of the air that has passed through the internal heat exchanger (57) is locally non-uniform, the temperature of the air flowing into the reheat heat exchanger (58) becomes locally non-uniform, and as a result, the temperature of the air that has passed through the reheat heat exchanger (58) becomes locally non-uniform.

[0205] Therefore, the controller (90) of this modified example increases the aperture of the fifth expansion valve (EV5) when the second temperature unevenness condition is satisfied. When the aperture of the fifth expansion valve (EV5) is increased, the flow rate of the refrigerant in the reheat pipe (33) increases, and as a result, the flow rate of the refrigerant in the internal heat exchanger (57) increases. When the flow rate of the refrigerant in the internal heat exchanger (57) increases, the superheated region of the internal heat exchanger (57) decreases, and the temperature of the air that has passed through the internal heat exchanger (57) becomes locally uniform. As a result, the temperature of the air that has passed through the reheat heat exchanger (58) becomes locally uniform.

[0206] -Fourth Modification- In the temperature control operation, the controller (90) of the refrigeration system (10) of any of the first to third embodiments may control the opening degree of the fifth expansion valve (EV5) based on the temperature of the refrigerant at the outlet of the reheat heat exchanger (58).

[0207] In the refrigeration system (10) of this modified example, a fifth refrigerant temperature sensor is provided in the reheat pipe (33) between the reheat heat exchanger (58) and the fifth expansion valve (EV5). The fifth refrigerant temperature sensor is provided near the other end of the reheat heat exchanger (58) and measures the temperature of the refrigerant at the outlet of the reheat heat exchanger (58). The controller (90) of this modified example controls the opening of the fifth expansion valve (EV5) based on the measurement value of the fifth refrigerant temperature sensor.

[0208] The temperature of the refrigerant at the outlet of the reheat heat exchanger (58) correlates with the temperature of the air that has passed through the reheat heat exchanger (58). Therefore, by controlling the aperture of the fifth expansion valve (EV5) based on the temperature of the refrigerant at the outlet of the reheat heat exchanger (58), it is possible to bring the temperature of the air that has passed through the reheat heat exchanger (58) into a target temperature range.

[0209] Fifth Modification In the refrigeration system (10) of any of the first to third embodiments, the humidity sensor (88) may be provided upstream of the internal heat exchanger (57) in the internal flow path (20). The humidity sensor (88) of this modification measures the relative humidity of the air flowing from the internal space (5) into the internal flow path (20) upstream of the internal heat exchanger (57). The controller (90) of this modification performs humidity control operation using the measurement value of the humidity sensor (88) located upstream of the internal heat exchanger (57).

[0210] -Sixth Modification- The use of the refrigeration system (10) of the first to third embodiments is not limited to air conditioning the interior space (5) of the transport container (1). The refrigeration system (10) of the first to third embodiments may be used to air condition the interior space of a stationary refrigerator or a freezer warehouse, for example.

[0211] Although the embodiments and modifications have been described above, it will be understood that various modifications in form and detail are possible without departing from the spirit and scope of the claims. Furthermore, elements of the above embodiments, modifications, and other embodiments may be combined or substituted as appropriate. Furthermore, the terms "first," "second," "third," etc. in the specification and claims are used to distinguish between terms to which these terms are attached, and do not limit the number or order of those terms.

[0212] As described above, the present disclosure is useful for refrigeration devices and shipping containers.

[0213] 1 Shipping container 2 Container body 5 Internal space (target space) 10 Refrigeration unit 30 Refrigerant circuit 33 Reheat piping (reheat passage) 50 Compressor 51 Low-stage compressor 52 High-stage compressor 56 External heat exchanger (heat source side heat exchanger) 57 Internal heat exchanger (use side heat exchanger) 58 Reheat heat exchanger 62 Receiver 65 Expansion valve 90 Controller EV1 First expansion valve EV2 Second expansion valve EV5 Fifth expansion valve (control valve)

Claims

1. A refrigeration system (10) for air-conditioning a target space (5), comprising 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), wherein the refrigerant circuit (30) comprises: a reheat heat exchanger (58) for exchanging heat between the air that has passed through the utilization side heat exchanger (57) and a refrigerant; a reheat passage (33) for sending the refrigerant discharged from the compressor (50) to the reheat heat exchanger (58); and a variable opening control valve (EV5) provided in the reheat passage (33) downstream of the reheat heat exchanger (58), wherein the refrigeration system (10) comprises: The refrigeration system performs 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, cools and dehumidifies air in the utilization side heat exchanger (57), heats the air that has passed through the utilization side heat exchanger (57) in the reheat heat exchanger (58), and blows the heated air in the reheat heat exchanger (58) into the target space (5), and the refrigeration system includes a controller (90) that controls the opening of the control valve (EV5) during the dehumidification operation.

2. The refrigeration system according to claim 1, wherein, in the dehumidifying operation, the pressure of the refrigerant supplied to the reheat heat exchanger (58) through the reheat passage (33) is equal to or higher than the critical pressure of the refrigerant.

3. The refrigeration system according to claim 2, wherein the controller (90) controls the opening of the expansion valve (65) so that the pressure of the refrigerant discharged from the compressor (50) is equal to or higher than the critical pressure of the refrigerant during the dehumidifying operation.

4. A refrigeration system according to any one of claims 1 to 3, wherein the controller (90) controls the opening of the control valve (EV5) based on the temperature of the air that has passed through the reheat heat exchanger (58) during the dehumidification operation.

5. A refrigeration system according to any one of claims 1 to 3, wherein the controller (90) controls the opening of the control valve (EV5) based on the temperature of the refrigerant flowing out of the reheat heat exchanger (58) during the dehumidification operation.

6. A refrigeration system as described in any one of claims 1 to 5, wherein the controller (90) controls the rotational speed of the compressor (50) during the dehumidifying operation so that a physical quantity correlated with the evaporation temperature of the refrigerant in the utilization side heat exchanger (57) reaches a control target value.

7. The refrigeration system according to any one of claims 1 to 5, wherein the refrigerant circuit (30) has a receiver (62) arranged between the heat source side heat exchanger (56) and the utilization side heat exchanger (57), and the expansion valve (65) includes a first expansion valve (EV1) arranged between the heat source side heat exchanger (56) and the receiver (62), and a second expansion valve (EV2) arranged between the receiver (62) and the utilization side heat exchanger (57), and the controller (90) controls, in the dehumidifying operation, the aperture of the first expansion valve (EV1) so that the pressure of the refrigerant discharged from the compressor (50) becomes equal to or higher than the critical pressure of the refrigerant, and controls the aperture of the second expansion valve (EV2) so that a physical quantity correlated to the evaporation temperature of the refrigerant in the utilization side heat exchanger (57) becomes a control target value.

8. A refrigeration system as described in claim 6 or 7, wherein the controller (90) sets the control target value based on the humidity of the air flowing from the target space (5) into the utilization side heat exchanger (57) or the humidity of the air blown into the target space (5) during the dehumidification operation.

9. The refrigeration system according to any one of claims 1 to 8, wherein the compressor (50) includes a low-stage compressor (51) that sucks in refrigerant that has passed through the utilization-side heat exchanger (57), and a high-stage compressor (52) that sucks in refrigerant discharged by the low-stage compressor (51), and wherein the refrigeration system (10) selectively performs, during the dehumidification operation, a single-stage compression operation in which one of the low-stage compressor (51) and the high-stage compressor (52) is operating and the other is at rest, and a two-stage compression operation in which both the low-stage compressor (51) and the high-stage compressor (52) are operating.

10. A refrigeration system as described in any one of claims 1 to 9, wherein the controller (90) increases the opening of the control valve (EV5) when a temperature unevenness condition is established during the dehumidification operation, which indicates that the temperature of the air that has passed through the reheat heat exchanger (58) is uneven.

11. The refrigeration system according to any one of claims 1 to 10, wherein the reheat passage (33) sends the refrigerant that has passed through the reheat heat exchanger (58) to the utilization side heat exchanger (57).

12. The refrigeration system according to any one of claims 1 to 11, wherein the refrigerant circuit (30) is filled with carbon dioxide as a refrigerant.

13. A transport container comprising: a refrigeration unit (10) according to any one of claims 1 to 12; and a container body (2) that forms the target space (5) that is air-conditioned by the refrigeration unit (10).

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