Refrigeration equipment and transport containers

Abstract

During dehumidification operation, the temperature of the air blown out by the refrigeration unit is appropriately adjusted. [Solution] In the reheat piping (33) of the refrigerant circuit (30), a fifth expansion valve (EV5) is provided downstream of the reheat heat exchanger (58). During dehumidification operation, the internal heat exchanger (57) cools and dehumidifies the air. During dehumidification operation, the refrigerant discharged from the compressor (50) is supplied to the reheat heat exchanger (58). The reheat heat exchanger (58) heats the air that has been dehumidified in the internal heat exchanger (57). When the controller (90) changes the opening of the fifth expansion valve (EV5), the flow rate of the refrigerant in the reheat heat exchanger (58) changes, and the temperature of the air that has passed through the reheat heat exchanger (58) changes.

Description

Technical Field

[0001] The present disclosure relates to a refrigeration device and a transport container.

Background Art

[0002] Patent Document 1 discloses a refrigeration device for a container, which is a type of refrigeration device. This refrigeration device for a container includes an evaporator and a reheat heat exchanger (reheat exchanger), and performs a dehumidification operation.

[0003] In the dehumidification operation, the air is cooled and dehumidified by the evaporator. Also, in the dehumidification operation, the refrigerant discharged from the compressor is supplied to the reheat heat exchanger through the reheat circuit. In the reheat heat exchanger, the air that has been cooled and dehumidified when passing through the evaporator is heated by the refrigerant.

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

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the reheat circuit of the container refrigeration system described in 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, it was not possible to properly adjust the flow rate of the refrigerant in the reheat heat exchanger during dehumidification operation, and there was a risk that the temperature of the air blown out into the interior space after passing through the reheat heat exchanger could not be properly controlled.

[0007] The purpose of this disclosure is to appropriately adjust the temperature of the air blown out by a refrigeration system during dehumidification operation of the refrigeration system. [Means for solving the problem]

[0008] A first aspect of this disclosure is a refrigeration system (10) that provides air conditioning for 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). The refrigerant circuit (30) includes a reheat heat exchanger (58) that exchanges heat between the air that has passed through the utilization side heat exchanger (57) and the refrigerant, a reheat passage (33) that sends the refrigerant discharged by the compressor (50) to the reheat heat exchanger (58), and a variable-opening control valve (EV5) provided downstream of the reheat heat exchanger (58) in the reheat passage (33). The above-mentioned refrigeration device (10) performs a refrigeration cycle in which the heat source side heat exchanger (56) functions as a heat radiator and the utilization side heat exchanger (57) functions as an evaporator, cools and dehumidifies the 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 performs a dehumidification operation in which the heated air in the reheat heat exchanger (58) is blown out to the target space (5), and includes a controller (90) that controls the opening degree of the control valve (EV5) during the dehumidification operation.

[0009] The refrigeration device (10) of the first embodiment performs a dehumidification operation. In the dehumidification operation, the utilization-side heat exchanger (57), which functions as an evaporator, cools and dehumidifies the air. In the dehumidification operation, the 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 that has been dehumidified in the utilization-side heat exchanger (57) with the refrigerant. In the dehumidification operation, the air that has been dehumidified in the utilization-side heat exchanger (57) and then heated in the reheat heat exchanger (58) is blown out into the target space (5).

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

[0011] A second aspect of this disclosure is that, in the first aspect described above, during the dehumidification operation, the pressure of the refrigerant supplied to the reheat heat exchanger (58) through the reheat passage (33) is equal to or greater than the critical pressure of the refrigerant.

[0012] In the defrosting operation performed by the refrigeration system (10) of the second embodiment, the refrigerant at a pressure above critical pressure exchanges heat with the air in the reheat heat exchanger (58). The refrigerant at a pressure above critical pressure undergoes a change in sensible heat during the heat dissipation process. Therefore, in the defrosting operation performed by the refrigeration system (10) of this embodiment, the refrigerant dissipates heat at a roughly constant rate throughout the reheat heat exchanger (58). As a result, the temperature of the air blown out by the refrigeration system (10) during dehumidification operation becomes uniform.

[0013] A third aspect of the present disclosure is, in the second aspect described above, the controller (90) controls the opening of the expansion valve (65) in the dehumidification operation such that the pressure of the refrigerant discharged by the compressor (50) is equal to or greater than the critical pressure of the refrigerant.

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

[0015] A fourth aspect of the present disclosure is that, in any one of the first to third embodiments, the controller (90) controls the opening degree 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.

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

[0017] A fifth aspect of the present disclosure is that, in any one of the first to third embodiments described above, the controller (90) controls the opening degree of the control valve (EV5) based on the temperature of the refrigerant discharged from the reheat heat exchanger (58) during the dehumidification operation.

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

[0019] A sixth aspect of the present disclosure is that, in any one of the first to fifth aspects, the controller (90) controls the rotational speed of the compressor (50) in the dehumidification operation such 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] During dehumidification operation, a change in the rotational speed of the compressor (50) alters the evaporation temperature of the refrigerant in the utilization-side heat exchanger (57). Therefore, the controller (90) of the sixth embodiment controls the rotational 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) becomes a control target value.

[0021] A seventh aspect of the present disclosure, in any one of the first to fifth aspects, the refrigerant circuit (30) has a receiver (62) located 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) located between the heat source side heat exchanger (56) and the receiver (62), and a second expansion valve (EV2) located between the receiver (62) and the utilization side heat exchanger (57). The controller (90) controls the opening of the first expansion valve (EV1) in the dehumidification operation so that the pressure of the refrigerant discharged by the compressor (50) is equal to or greater than the critical pressure of the refrigerant, and controls the opening 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] The controller (90) of the seventh embodiment controls the opening of the first expansion valve (EV1) and the opening of the second expansion valve (EV2) during dehumidification operation. When the opening of the first expansion valve (EV1) changes, the pressure of the refrigerant discharged by the compressor (50) changes. Therefore, the controller (90) controls the opening of the first expansion valve (EV1) so that the pressure of the refrigerant discharged by the compressor (50) is equal to or greater than the critical pressure of the refrigerant. When the opening of the second expansion valve (EV2) changes, the evaporation temperature of the refrigerant in the utilization-side heat exchanger (57) changes. Therefore, the controller (90) controls the opening 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.

[0023] In the eighth aspect of the present disclosure, in the sixth or seventh aspect described above, in the dehumidification operation, the controller (90) sets the control target value based on the humidity of the air flowing from the target space (5) to the utilization-side heat exchanger (57) or the humidity of the air blown into the target space (5).

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

[0025] In the ninth aspect of the present disclosure, in any one of the first to eighth aspects described above, the compressor (50) includes a low-stage compressor (51) that sucks in the refrigerant that has passed through the utilization-side heat exchanger (57), and a high-stage compressor (52) that sucks in the refrigerant discharged from the low-stage compressor (51). In the dehumidification operation, the refrigeration device (10) selectively performs 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 stopped, and a two-stage compression operation in which both the low-stage compressor (51) and the high-stage compressor (52) operate.

[0026] In the dehumidification operation, the refrigeration device (10) of the ninth aspect selectively performs a single-stage compression operation and a two-stage compression operation.

[0027] In the tenth aspect of the present disclosure, in any one of the first to ninth aspects described above, in the dehumidification operation, when a temperature unevenness condition indicating that the temperature of the air passing through the reheater (58) is uneven is satisfied, the controller (90) increases the opening degree of the regulating valve (EV5).

[0028] The controller (90) of the tenth embodiment determines whether the temperature unevenness condition is met. When the temperature unevenness condition is met, there is a high probability that the temperature of the air that has passed through the reheat heat exchanger (58) is uneven. The main reason why the temperature of the air that has passed through the reheat heat exchanger (58) is uneven is that the amount of heating to the air in each part of the reheat heat exchanger (58) is uneven. Therefore, when the temperature unevenness condition is met, the controller (90) increases the opening of the control valve (EV5). When the opening 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 to the air in each part of the reheat heat exchanger (58) becomes uniform.

[0029] An eleventh aspect of this disclosure is that, in any one of the first to tenth aspects described above, 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 11th embodiment of the refrigeration apparatus (10), the refrigerant that has passed through the reheat heat exchanger (58) during dehumidification operation flows into the utilization-side heat exchanger (57) after passing through the control valve (EV5).

[0031] A twelfth aspect of this disclosure is that, in any one of the first to eleventh aspects described above, the refrigerant circuit (30) is filled with carbon dioxide as a refrigerant.

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

[0033] A thirteenth aspect of this disclosure is a transport container (1) comprising a refrigeration device (10) according to any one of the first to twelfth aspects described above, and a container body (2) that forms the target space (5) where air conditioning is performed by the refrigeration device (10).

[0034] A transport container (1) of the 13th embodiment comprises a refrigeration unit (10) and a container body (2). The container body (2) forms a target space (5). The refrigeration unit (10) provides air conditioning for the target space (5). [Brief explanation of the drawing]

[0035] [Figure 1] Figure 1 is a schematic perspective view of the refrigeration apparatus of Embodiment 1. [Figure 2] Figure 2 is a schematic cross-sectional view of the transport container according to Embodiment 1. [Figure 3] Figure 3 is a piping diagram showing the configuration of the refrigeration system of Embodiment 1. [Figure 4] Figure 4 is a block diagram showing the configuration of the controller in Embodiment 1. [Figure 5] Figure 5 is a piping diagram corresponding to Figure 3, showing the flow of refrigerant during cooling operation. [Figure 6] Figure 6 is a piping diagram corresponding to Figure 3, showing the refrigerant flow during the two-stage compression operation of the dehumidification process. [Figure 7] Figure 7 is a piping diagram corresponding to Figure 3, showing the refrigerant flow during the single-stage compression operation of the dehumidification function. [Figure 8] Figure 8 is a piping diagram corresponding to Figure 3, showing the flow of refrigerant during defrosting operation. [Figure 9] Figure 9 is a state transition diagram showing the operation of the controller during dehumidification. [Figure 10] Figure 10 is a flowchart showing the humidity control operation of the controller. [Figure 11] Figure 11 is a flowchart illustrating the temperature control operation of the controller. [Figure 12] Figure 12 is a flowchart showing the high-voltage control operation of the controller. [Figure 13] Figure 13 is a piping diagram showing the configuration of the refrigeration system of Embodiment 2. [Figure 14] Figure 14 is a piping diagram showing the configuration of the refrigeration system of Embodiment 3. [Figure 15] Figure 15 is a piping diagram showing the configuration of a refrigeration system in a first modified example of another embodiment. [Modes for carrying out the invention]

[0036] Embodiment 1 Embodiment 1 will now be described. This embodiment is a transport container (1) equipped with a refrigeration device (10).

[0037] -Shipping container- As shown in Figure 1, the transport container (1) comprises a container body (2) and a refrigeration unit (10). The transport container (1) is a reefer container that allows for temperature control inside the container.

[0038] The transport container (1) of this embodiment is mainly used for maritime transport. This transport container (1) is transported loaded onto ships or the like. However, the use of the transport container (1) is not limited to maritime transport. The transport container (1) may also be used for land transport. In this case, the transport container (1) is transported by automobiles such as trucks 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 in a horizontal shape. An opening is formed at one end of the container body (2) in the longitudinal direction. The opening of the container body (2) is closed by the refrigeration unit (10). The container body (2) forms an internal space (5) for storing cargo. The internal space (5) is the space to be air-conditioned by the refrigeration unit.

[0040] -Refrigeration equipment- As shown in Figure 2, the refrigeration unit (10) is attached to the opening of the container body (2). The refrigeration unit (10) in this embodiment is a transport refrigeration unit. The refrigeration unit (10) comprises a casing (11), a refrigerant circuit (30), and a controller (80). The refrigeration unit (10) adjusts the temperature of the air (internal air) in the internal space (5).

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

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

[0043] The bulkhead (12) comprises an outer wall (13) and an inner wall (14). The outer wall (13) is located on the outside of the container body (2). The inner wall (14) is located on the inside of the container body (2).

[0044] The outer wall (13) closes the opening of the container body (2). The outer wall (13) is attached to the periphery of the opening of the container body (2). The lower part of the outer wall (13) bulges inward toward the inside of the container body (2). The outer chamber (23) is formed by the lower part of the outer 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 positioned at a distance from the exterior wall (13). An insulating material (16) is provided between the interior wall (14) and the exterior wall (13).

[0046] The partition plate (15) is positioned inside the container body (2) relative to the interior wall (14). An internal airflow channel (20) is formed between the partition wall (12) and the partition plate (15). An air intake (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 airflow channel (20) extends from the air intake (21) to the air outlet (22).

[0047] <Refrigerant Circuit> The refrigerant circuit (30) is a closed circuit filled with refrigerant. The refrigerant circuit (30) circulates the refrigerant to perform a vapor compression type 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 explained in more detail later.

[0048] Each of the external heat exchanger (56), internal heat exchanger (57), and 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 located at the top 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 outside air. The external heat exchanger (56) is generally rectangular in shape.

[0050] The internal heat exchanger (57) is located in the internal flow path (20). The internal heat exchanger (57) is a user-side heat exchanger that exchanges heat between the refrigerant and the air inside the chamber.

[0051] The reheat heat exchanger (58) is located 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 in the diagram, a drain pan is provided below the internal heat exchanger (57). The drain pan receives the condensate water generated in the internal heat exchanger (57). The condensate water that falls into the drain pan is discharged outside the chamber.

[0053] <External fan> The refrigeration unit (10) is equipped with an external fan (26). The external fan (26) is a propeller fan. The external fan (26) is located in the external chamber (23). The external fan (26) is also located inside the cylindrical external heat exchanger (56). The external fan (26) sends external air to the external heat exchanger (56).

[0054] <Interior fan> The refrigeration unit (10) is equipped with an internal fan (27). The internal fan (27) is a propeller fan. The internal fan (27) is positioned in the internal airflow path (20). The internal fan (27) is also positioned above the internal heat exchanger (57). The internal fan (27) sends internal air to the internal heat exchanger (57).

[0055] <Sensor> The refrigeration device (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 positioned upstream of the internal fan (27) in the internal flow path (20). The first air temperature sensor (86) measures the temperature of the air that flows into the internal flow path (20) through the air intake (21).

[0057] The second air temperature sensor (87) and humidity sensor (88) are positioned 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 Figure 1, the refrigeration unit (10) has an electrical component box (28). The electrical component box (28) is located at the top of the outer compartment (23). Electrical components such as an inverter board and a control board are housed inside the electrical component box (28).

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

[0060] The refrigerant circuit (30) comprises a main circuit (31), defrosting piping (32), and reheating piping (33). The refrigerant circuit (30) also comprises 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 order by piping.

[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 motorized 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 motorized valve (MV1) is positioned downstream of the first check valve (CV1). The first check valve (CV1) allows the flow of refrigerant in the direction of outflow from the low-stage compressor (51) and blocks the flow of refrigerant in the reverse direction.

[0063] The 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 motorized valve (MV2) are provided in the piping connecting the discharge pipe of the high-stage compressor (52) and one end of the external heat exchanger (56). The second motorized valve (MV2) is positioned downstream of the second check valve (CV2). The second check valve (CV2) allows the flow of refrigerant in the direction of outflow from the high-stage compressor (52) and prevents the flow of refrigerant in the reverse direction.

[0064] The other end of the external heat exchanger (56) is connected to the inlet of the receiver (62). The piping connecting the other end of the external heat exchanger (56) and the inlet of the receiver (62) is provided with the first flow path (61a) of the internal heat exchanger (61) and the first expansion valve (EV1). The first expansion valve (EV1) is located downstream of the internal heat exchanger (61).

[0065] The 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 the piping connecting the liquid outlet of the receiver (62) and one end of the internal heat exchanger (57). The second expansion valve (EV2) is located 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), the first expansion valve (EV1) is located upstream of the receiver (62), and the second expansion valve (EV2) is located downstream of the receiver (62). The first expansion valve (EV1) and the second expansion valve (EV2) are the expansion valves (65) of the refrigerant circuit (30).

[0068] <Gas side connection pipe> One end of the gas-side connecting pipe (41) is connected to the 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 located downstream of the second solenoid valve (SV2).

[0069] <Liquid-side connecting pipe> One end of the liquid-side connecting pipe (42) is connected 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). A third expansion valve (EV3) is provided in the liquid-side connecting pipe (42).

[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 between the first electric valve (MV1) and the high-stage compressor (52) in the main circuit (31). A third check valve (CV3) is provided in the intermediate connecting pipe (43). The third check valve (CV3) allows the flow of refrigerant from one end of the intermediate connecting pipe (43) to the other end, and prevents the flow of refrigerant in the reverse direction.

[0071] <Low-stage connecting pipe> The low-stage connecting pipe (44) is a pipe that bypasses the low-stage compressor (51) and allows refrigerant to flow. One end of the low-stage connecting pipe (44) is connected between the suction pipe of the low-stage compressor (51) and the internal heat exchanger (57) in the main circuit (31). The other end of the low-stage connecting pipe (44) is connected between the first check valve (CV1) and the first motorized valve (MV1) in the main circuit (31). A fourth check valve (CV4) is provided in the low-stage connecting pipe (44). The fourth check valve (CV4) allows the flow of refrigerant from one end of the low-stage connecting pipe (44) to the other end, and prevents the flow of refrigerant in the reverse direction.

[0072] <High-stage connecting pipe> The high-stage connecting pipe (45) is a pipe that bypasses the high-stage compressor (52) and allows refrigerant to flow. One end of the high-stage connecting pipe (45) is connected between the first check valve (CV1) and the first motorized valve (MV1) in the main circuit (31). The other end of the high-stage connecting pipe (45) is connected between the second check valve (CV2) and the second motorized valve (MV2) in the main circuit (31). A fifth check valve (CV5) is provided in the high-stage connecting pipe (45). The fifth check valve (CV5) allows the flow of refrigerant from one end of the high-stage connecting pipe (45) to the other end, and prevents the flow of refrigerant in the reverse direction.

[0073] <Defrost piping> One end of the defrosting pipe (32) is connected between the second check valve (CV2) and the second electric valve (MV2) in the main circuit (31). 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 between the second expansion valve (EV2) and the internal heat exchanger (57) in the main circuit (31).

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

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

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

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

[0078] <Electric valve> The first electric valve (MV1) and the second electric valve (MV2) are both variable-opening valves. Each electric valve (MV1, MV2) comprises a valve body and a stepping motor that drives the valve body. When the valve body is moved by the stepping motor, the opening degree of the electric valves (MV1, MV2) changes continuously.

[0079] <Solenoid valve> The first solenoid valve (SV1), the second solenoid valve (SV2), and the third solenoid valve (SV3) are each on-off valves. Each solenoid valve (SV1 to SV3) comprises a valve body and a solenoid that drives the valve body. When the valve body is moved by the solenoid, the solenoid valves (SV1 to SV3) open and close.

[0080] <Low-stage compressor, high-stage compressor> The low-stage compressor (51) and the high-stage compressor (52) are both fully enclosed scroll compressors. Although not shown in the diagram, each of the low-stage compressor (51) and the high-stage compressor (52) comprises 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 a refrigerant and compresses it.

[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). The low-stage compressor (51) and the high-stage compressor (52) each compress the refrigerant drawn in from the suction pipe and discharge the compressed refrigerant from the discharge pipe. The low-stage compressor (51) and the high-stage compressor (52) are compressors (50) provided in the refrigerant circuit (30).

[0082] Note that the low-stage compressor (51) and the high-stage compressor (52) are not limited to scroll compressors. 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, the external heat exchanger (56), the internal heat exchanger (57), and the reheat heat exchanger (58) are each fin-and-tube heat exchangers that exchange heat between the refrigerant and the air. The external heat exchanger (56) exchanges heat between the refrigerant and the outside air (outside air). The internal heat exchanger (57) and the reheat heat exchanger (58) each exchange heat between the refrigerant and the inside 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) has a first flow path (61a) and a second flow path (61b). The first flow path (61a) of the internal heat exchanger (61) is located 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 located 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-shaped component for storing the refrigerant. The receiver (62) also functions as a gas-liquid separator. The receiver (62) separates the gas-liquid two-phase refrigerant flowing in from the inlet into liquid refrigerant and gaseous refrigerant. In the receiver (62), the liquid refrigerant accumulates at the bottom of the receiver (62) and flows out through a liquid outlet formed at the bottom of the receiver (62). In the receiver (62), the gaseous refrigerant accumulates at the top of the receiver (62) and flows out through a gas outlet formed at the top of the receiver (62).

[0086] <Sensors related to low-stage compressors> In the main circuit (31), a low-stage suction temperature sensor (70) and a low-stage suction pressure sensor (75) are provided in the piping connected to the suction pipe of the low-stage compressor (51). The low-stage suction temperature sensor (70) measures the temperature of the refrigerant suctioned by the low-stage compressor (51). The low-stage suction pressure sensor (75) measures the pressure of the refrigerant suctioned by 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 the 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 by the low-stage compressor (51). The low-stage discharge pressure sensor (76) measures the pressure of the refrigerant discharged by the low-stage compressor (51).

[0088] <Sensors related to high-stage compressors> 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 electric valve (MV1). The high-stage suction temperature sensor (72) measures the temperature of the refrigerant suctioned by the high-stage compressor (52). The high-stage suction pressure sensor (77) measures the pressure of the refrigerant suctioned by 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 the 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 by the high-stage compressor (52). The high-stage discharge pressure sensor (78) measures the pressure of the refrigerant discharged by the high-stage compressor (52).

[0090] <Other sensors> The refrigerant circuit (30) is equipped 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 between the receiver (62) and the second solenoid valve (SV2) in the gas-side connecting pipe (41). The receiver pressure sensor (79) measures the pressure of the refrigerant stored in the receiver (62).

[0092] The first refrigerant temperature sensor (81) is installed in the piping between the external heat exchanger (56) and the internal heat exchanger (61) in the main circuit (31). 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 installed in the piping 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 that has flowed out from the liquid outlet of the receiver (62).

[0094] The third refrigerant temperature sensor (83) is installed in the piping between the second expansion valve (EV2) and the internal heat exchanger (57) in the main circuit (31). The third refrigerant temperature sensor (83) is positioned near 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 installed in the piping between the internal heat exchanger (57) and the low-stage compressor (51) in the main circuit (31). The fourth refrigerant temperature sensor (84) is positioned 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). The heat exchanger temperature sensor (85) measures the temperature of the internal heat exchanger (57).

[0097] -Controller- As shown in Figure 4, the controller (90) comprises 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 an electrical components box (28).

[0098] The controller (90) receives the measured values ​​from sensors installed in the refrigeration unit (10). Based on the measured values ​​from the sensors that are input, the controller (90) controls the equipment installed in the refrigeration unit (10). For example, the controller (90) controls the rotational speed of the low-stage compressor (51), the rotational speed of the high-stage compressor (52), the opening degree of the first to fifth expansion valves (EV1 to EV5), the opening degree of the first to second electric valves (MV1, MV2), the rotational speed of the external fan (26), the rotational speed of the internal fan (27), and so on.

[0099] - Refrigeration System Operation - The operation of the refrigeration unit (10) will be explained. The refrigeration unit (10) performs cooling, dehumidifying, and defrosting operations.

[0100] <Cooling operation> Cooling operation is an operation to cool the air inside the storage chamber. During cooling operation, the refrigeration unit (10) blows the air cooled by the internal heat exchanger (57) into the storage chamber space (5).

[0101] During the cooling operation of the refrigeration unit (10), the refrigerant circuit (30) performs the refrigeration cycle. During the cooling operation, the refrigerant circulates in the main circuit (31) of the refrigerant circuit (30), the external heat exchanger (56) functions as a heat 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). Also during the cooling operation, the refrigerant flows through the gas-side connecting pipe (41) and the intermediate connecting pipe (43).

[0102] During 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 airflow channel (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 airflow channel (20) through the air intake (21). The internal air flowing through the internal airflow channel (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] During cooling operation, the controller (90) controls the rotational speed of the compressor (50) and other parameters so that the temperature of the air blown out into the interior space (5) through the air outlet (22) (specifically, the value measured by the second air temperature sensor (87)) reaches the set temperature.

[0104] During cooling operation, the refrigeration system (10) selectively performs two-stage compression operation and single-stage compression operation. In 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 single-stage compression operation, the low-stage compressor (51) stops and the high-stage compressor (52) operates, and a single-stage compression refrigeration cycle is performed in the refrigerant circuit (30). During cooling operation, the refrigeration system (10) performs two-stage compression operation when the difference between high and low pressure 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 during cooling) The two-stage compression operation of the cooling process will be explained with reference to Figure 5.

[0106] In the two-stage compression operation of the cooling operation, the controller (90) controls the rotational speed of the low-stage compressor (51) and the high-stage compressor (52). The controller (90) also controls the opening degree of the first expansion valve (EV1) and the second expansion valve (EV2), and holds the third expansion valve (EV3), the fourth expansion valve (EV4), and the fifth expansion valve (EV5) in a fully closed state. Furthermore, the controller (90) holds the first motor valve (MV1) and the second motor valve (MV2) in a fully open state, holds the first solenoid valve (SV1) and the second solenoid valve (SV2) in an open state, and holds the third solenoid valve (SV3) in a closed state.

[0107] The high-stage compressor (52) compresses the inhaled refrigerant to a pressure higher than the critical pressure of the refrigerant and discharges it. The refrigerant discharged from the high-stage compressor (52) exchanges heat with the 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 exchanging heat with the refrigerant flowing in 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 depressurized as it passes through the first expansion valve (EV1) and becomes a gas-liquid two-phase state. After that, the refrigerant flows into the receiver (62) and is separated into liquid refrigerant and gaseous refrigerant.

[0108] The liquid refrigerant flowing out of the receiver (62) is depressurized as it passes 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 drawn into the low-stage compressor (51). The low-stage compressor (51) compresses the drawn-in refrigerant and discharges it. The refrigerant discharged from the low-stage compressor (51) is drawn into the high-stage compressor (52).

[0109] The gaseous refrigerant flowing out of the receiver (62) flows through the gas-side connecting pipe (41) and into the second flow path (61b) of the internal heat exchanger (61), absorbing 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 drawn into the high-stage compressor (52) together with the refrigerant discharged from the low-stage compressor (51).

[0110] (Single-stage compression operation during cooling) This section describes the single-stage compression operation during cooling.

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

[0112] In the refrigerant circuit (30), the refrigerant flowing out from the internal heat exchanger (57) is drawn 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 single-stage compression operation is the same as the refrigerant flow path in the refrigerant circuit (30) during two-stage compression operation.

[0113] <Dehumidification operation> Dehumidification operation is performed to dehumidify the air inside the storage compartment (5) while maintaining the temperature inside the compartment. During dehumidification operation, the refrigeration unit (10) blows air that has been dehumidified in the internal heat exchanger (57) and then heated in the reheat heat exchanger (58) into the storage compartment (5).

[0114] The refrigeration unit (10) performs defrosting when the temperature inside the storage space (5) is stable. Specifically, the controller (90) of the refrigeration unit (10) determines whether the temperature stabilization condition has been met. The temperature stabilization condition is a condition that indicates the temperature inside the storage space (5) is stable. An example of a temperature stabilization condition is that "the measurement value of the second air temperature sensor (87) remains within the range of ±0.5℃ of the set temperature for 5 minutes." When the controller (90) determines that the temperature stabilization condition has been met, it instructs the refrigeration unit (10) to perform dehumidification.

[0115] In the dehumidification operation of the refrigeration unit (10), the controller (90) operates the external fan (26) and the internal fan (27), similar to the cooling operation. 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 intake (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 order, and is then supplied to the internal space (5) through the air outlet (22).

[0116] Similar to the cooling operation, the refrigeration unit (10) selectively performs two-stage compression operation and single-stage compression operation during dehumidification operation. In 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 single-stage compression operation, the low-stage compressor (51) stops and the high-stage compressor (52) operates, and a single-stage compression refrigeration cycle is performed in the refrigerant circuit (30). During dehumidification operation, the refrigeration unit (10) performs two-stage compression operation when the difference between high and low pressure 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 during dehumidification) The two-stage compression operation of the dehumidification process will be explained with reference to Figure 6.

[0118] In the two-stage compression operation of the dehumidification operation, the controller (90) controls the rotational speed of the low-stage compressor (51) and the high-stage compressor (52). The controller (90) also controls the opening degree of the first expansion valve (EV1), the second expansion valve (EV2), and the fifth expansion valve (EV5), and holds the third expansion valve (EV3) and the fourth expansion valve (EV4) in a fully closed state. Furthermore, the controller (90) holds the first electric valve (MV1) and the second electric valve (MV2) in a fully open state, and holds 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 dehumidification differs from cooling operation in that the controller (90) controls the opening of the fifth expansion valve (EV5) and holds the third solenoid valve (SV3) in the open position. Furthermore, the two-stage compression operation in dehumidification differs from 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 piping (33).

[0120] In the two-stage compression operation of the dehumidification operation of the refrigeration unit (10), the refrigerant circuit (30) performs the refrigeration cycle. In the two-stage compression operation of the dehumidification operation, similar to the cooling operation, the refrigerant circulates in the main circuit (31) of the refrigerant circuit (30), the external heat exchanger (56) functions as a heat 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] During dehumidification 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). As a result, moisture in the air condenses in the internal heat exchanger (57) to form condensate. The condensate generated in the internal heat exchanger (57) flows into the drain pan and is discharged outside the unit. Consequently, the temperature and absolute humidity of the air flowing through the internal flow path (20) decrease as it passes through the internal heat exchanger (57).

[0122] In dehumidification operation, the refrigerant flows through the gas-side connecting pipe (41) and the intermediate connecting pipe (43), similar to cooling operation. The gaseous refrigerant flowing out from the receiver (62) passes through the gas-side connecting pipe (41) and the intermediate connecting pipe (43) in sequence and is drawn into the high-stage compressor (52) together with the refrigerant discharged by the low-stage compressor (51).

[0123] During dehumidification, a portion of the refrigerant discharged from the high-stage compressor (52) is supplied to the reheat heat exchanger (58) through the reheat piping (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 released heat in the reheat heat exchanger (58) is depressurized as it passes through the fifth expansion valve (EV5). The refrigerant that has passed through the fifth expansion valve (EV5) flows into the main circuit (31) and, together with the refrigerant that has passed through the second expansion valve (EV2), flows into the internal heat exchanger (57).

[0124] (Single-stage compression operation during dehumidification) The single-stage compression operation of the dehumidification process will be explained with reference to Figure 7.

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

[0126] In the refrigerant circuit (30), the refrigerant flowing out from the internal heat exchanger (57) is drawn 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 single-stage compression operation is the same as the refrigerant flow path in the refrigerant circuit (30) during two-stage compression operation.

[0127] <Defrosting operation> Defrosting is performed to melt the frost that has accumulated on the internal heat exchanger (57) during cooling operation.

[0128] During 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 condenses as frost on the internal heat exchanger (57). When frost accumulates on the internal heat exchanger (57), it obstructs the airflow through the internal heat exchanger (57) and hinders heat exchange between the refrigerant and the air.

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

[0130] Furthermore, if the defrosting termination condition is met during the defrosting operation, the refrigeration unit (10) terminates the defrosting operation and resumes the cooling operation. The defrosting 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 explained with reference to Figure 8.

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

[0133] During defrosting operation, the refrigerant circuit (30) 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 piping (32) and is depressurized as it passes 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 and melted by the refrigerant. The refrigerant that has flowed out of the internal heat exchanger (57) is drawn into the high-stage compressor (52) through the low-stage connecting pipe (44). The high-stage compressor (52) compresses the drawn-in refrigerant and discharges it.

[0134] -Controller operation during dehumidification- The operation performed by the controller (90) during dehumidification will be explained below.

[0135] As shown in Figure 9, during dehumidification operation, the controller (90) repeatedly performs humidity control, temperature control, and high-pressure control operations in sequence. The controller (90) also switches between performing humidity control, temperature control, and high-pressure control operations at regular intervals (for example, every 5 seconds). Note that the order in which the humidity control, temperature control, and high-pressure control operations are performed is not limited to the order shown in Figure 9. The order shown in Figure 9 is merely an example.

[0136] <Humidity control operation> The humidity control operation will be explained with reference to Figure 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) by the refrigeration unit (10) during dehumidification operation becomes the 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 uses the set target evaporation temperature to control the rotational speed of the compressor (50) and the opening degree of the second expansion valve (EV2).

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

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

[0139] In step ST11, the controller (90) compares the measured value RH from the humidity sensor (88) with the highest value in the set humidity range. If the condition that "the measured value RH from the humidity sensor (88) is higher than the highest value in the set humidity range" is met, the controller (90) proceeds to step ST12. In step ST12, the controller (90) lowers the target evaporation temperature. If this condition is not met, the controller (90) proceeds to step ST13.

[0140] In step ST13, the controller (90) compares the measured value RH from the humidity sensor (88) with the lowest value of the set humidity range. If the condition that "the measured value RH from the humidity sensor (88) is lower than the lowest value of the set humidity range" is met, the controller proceeds to step ST14. In step ST14, the controller (90) lowers the target evaporation temperature. If this condition is not met, the controller (90) proceeds to step ST15.

[0141] If the conditions in step ST13 are not met, the measured value RH from the humidity sensor (88) is within the set humidity range. Therefore, the controller (90) maintains the target evaporation temperature without changing it in step ST15. After the processing in steps ST12, ST14, or ST15 is completed, the controller (90) performs the processing in step ST16.

[0142] (Control of the compressor and the second expansion valve) The controller (90) controls the rotational speed of the compressor (50) and the opening degree of the second expansion valve (EV2) so that the measured value Tr3 from the third refrigerant temperature sensor (83) falls within the target evaporation temperature range (for example, within the range of target evaporation temperature ±0.5℃).

[0143] The third refrigerant temperature sensor (83) measures the temperature of the refrigerant flowing into the internal heat exchanger (57) after passing through the second expansion valve (EV2). The refrigerant that has passed 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). Thus, 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 the controlled object) The controller (90) selectively controls the rotational speed of the compressor (50) and the opening degree of the second expansion valve (EV2).

[0145] The process in step ST16 of Figure 10 is for selecting the control target. In the process of step ST16, the controller (90) determines whether the selection conditions are met.

[0146] The selection criteria are that "the first condition is met, and at least one of the second and third conditions is met." The first condition is that "the target superheat level is the lower limit superheat level." The lower limit superheat level is the lowest value in the range of values ​​that can be set as the target superheat level. The second condition is that "the rotational 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] In step ST16, if the selection condition is met, the controller (90) performs the process in step ST17 to start controlling the rotational speed of the compressor (50). On the other hand, if the selection condition is not met, the controller (90) performs the process in step ST22 to start controlling the opening degree of the second expansion valve (EV2).

[0148] (Control of the compressor's rotational speed) The control of the rotational speed of the compressor (50) by the controller (90) will be explained.

[0149] The controller (90) controls the rotational speed of the compressor (50), which draws in the refrigerant that has leaked out of the internal heat exchanger (57) during dehumidification operation, based on the measurement value of the third refrigerant temperature sensor (83). In the two-stage compression operation of dehumidification, the controller (90) controls the rotational speed of the lower-stage compressor (51) based on the measurement value of the third refrigerant temperature sensor (83). In the single-stage compression operation of dehumidification, the controller (90) controls the rotational speed of the upper-stage compressor (52) based on the measurement value of the third refrigerant temperature sensor (83).

[0150] The controller (90) performs the processes from step ST17 to step ST21 in Figure 10 as an operation to control the rotational speed of the compressor (50). The controller (90) compares the measured value Tr3 from the third refrigerant temperature sensor (83) with the target evaporation temperature range and controls the rotational speed of the compressor (50) based on the result.

[0151] In step ST17, the controller (90) compares the measured value Tr3 from the third refrigerant temperature sensor (83) with the highest value in the target evaporation temperature range. If the condition that "the measured value Tr3 from the third refrigerant temperature sensor (83) is higher than the highest value in the target evaporation temperature range" is met, the controller (90) proceeds to step ST18. In step ST18, the controller (90) increases the rotational speed of the compressor (50). If this condition is not met, the controller (90) proceeds to step ST19.

[0152] In step ST19, the controller (90) compares the measured value Tr3 from the third refrigerant temperature sensor (83) with the lowest value of the target evaporation temperature range. If the condition that "the measured value Tr3 from the third refrigerant temperature sensor (83) is lower than the lowest value of the target evaporation temperature range" is met, the controller (90) proceeds to step ST20. In step ST20, the controller (90) reduces the rotational speed of the compressor (50). If this condition is not met, the controller (90) proceeds to step ST21.

[0153] If the conditions in step ST19 are not met, the measured value Tr3 from the third refrigerant temperature sensor (83) is within the target evaporation temperature range. Therefore, the controller (90) maintains the rotational speed of the compressor (50) without changing it during the process of step ST21. After the processing of steps ST18, ST20, or 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 rotational 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 rotational 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 the opening degree of the second expansion valve) The control of the opening degree of the second expansion valve (EV2) by the controller (90) will be explained.

[0156] The controller (90) controls the opening of the second expansion valve (EV2) based on the degree of superheating 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 in the internal heat exchanger (57) changes, the degree of superheating of the refrigerant at the outlet of the internal heat exchanger (57) changes. Therefore, the degree of superheating 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 in the internal heat exchanger (57).

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

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

[0159] In step ST22, the controller (90) compares the measured value Tr3 from the third refrigerant temperature sensor (83) with the highest value in the target evaporation temperature range. If the condition that "the measured value Tr3 from the third refrigerant temperature sensor (83) is higher than the highest value in the target evaporation temperature range" is met, the controller (90) proceeds to step ST23. In step ST23, the controller (90) increases the target superheat level. When the target superheat level increases, the controller (90) reduces the opening of the second expansion valve (EV2) in order to increase the superheat level 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) proceeds to step ST24.

[0160] In step ST24, the controller (90) compares the measured value Tr3 from the third refrigerant temperature sensor (83) with the lowest value of the target evaporation temperature range. If the condition that "the measured value Tr3 from the third refrigerant temperature sensor (83) is lower than the lowest value of the target evaporation temperature range" is met, the controller (90) proceeds to step ST25. In step ST25, the controller (90) lowers the target superheat. When the target superheat is lowered, the controller (90) increases the opening of the second expansion valve (EV2) to reduce the superheat SH of the refrigerant at the outlet of the internal heat exchanger (57). If this condition is not met, the controller (90) proceeds to step ST26.

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

[0162] <Temperature control operation> The temperature control operation will be explained with reference to Figure 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) by the refrigeration unit (10) during dehumidification operation reaches the 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 degree 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 degree of the fifth expansion valve (EV5) so that the measurement value of the second air temperature sensor (87) falls within the set air temperature range (for example, within the range of set air temperature ± 0.5°C).

[0164] In step ST31, the controller (90) compares the measured value Ta2 from the second air temperature sensor (87) with the highest value in the set air temperature range. If the condition that "the measured value Ta2 from the second air temperature sensor (87) is higher than the highest value in the set air temperature range" is met, the controller (90) proceeds to step ST32. In step ST32, the controller (90) reduces the opening of the fifth expansion valve (EV5) in order to decrease the flow rate of the refrigerant in the reheat heat exchanger (58). If this condition is not met, the controller (90) proceeds to step ST33.

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

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

[0167] <High-voltage control operation> The high-pressure control operation will be explained with reference to Figure 12. In high-pressure control operation, the controller (90) controls the opening of the first expansion valve (EV1) so that the pressure of the refrigerant supplied to the reheat heat exchanger (58) during dehumidification operation is maintained at a relatively high pressure. The controller (90) controls the opening 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 by the high-stage compressor (52).

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

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

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

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

[0172] The refrigerant filled into the refrigerant circuit (30) of 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 between 8 MPa and 15 MPa. Therefore, the controller (90) of this embodiment controls the opening of the first expansion valve (EV1) so that the pressure of the refrigerant discharged by the high-stage compressor (52) is equal to or greater than the critical pressure of the refrigerant (carbon dioxide).

[0173] -Features of Embodiment 1 (1)- The refrigeration device (10) of this embodiment performs a dehumidification operation. During the dehumidification operation, the air flowing through the internal passage (20) experiences a decrease in temperature and absolute humidity as it passes through the internal heat exchanger (57), and a rise in temperature as it passes through the reheat heat exchanger (58). Therefore, by performing a dehumidification operation, the refrigeration device (10) can maintain the temperature of the internal space (5) while lowering the humidity of the internal air.

[0174] During dehumidification operation, the controller (90) of this embodiment controls the opening degree of the control valve (EV5). When the opening degree of the control valve (EV5) changes, the flow rate of the refrigerant in the reheat heat exchanger (58) changes, and the amount of heat supplied to the air in the reheat heat exchanger (58) changes. As a result, the temperature of the air blown out into the storage space (5) after passing through the reheat heat exchanger (58) changes. Therefore, by controlling the opening degree of the fifth expansion valve (EV5) with the controller (90), it is possible to control the temperature of the air blown out into the storage space (5) by the refrigeration device (10) during dehumidification operation.

[0175] -Features of Embodiment 1 (2)- In the two-stage compression operation of the defrosting operation performed by the refrigeration device (10) of this embodiment, the refrigerant at a pressure above critical pressure exchanges heat with air in the reheat heat exchanger (58). The refrigerant at a pressure above critical pressure undergoes a sensible heat change without condensing during the heat dissipation process.

[0176] When a refrigerant at a pressure above critical pressure flows through the reheat heat exchanger (58), the heat transfer coefficient between the refrigerant and the air becomes approximately constant throughout the reheat heat exchanger (58). Therefore, in the two-stage compression operation of the defrosting operation performed by the refrigeration device (10) of this embodiment, the refrigerant dissipates heat at approximately a constant rate throughout the reheat heat exchanger (58), and as a result, the temperature of the air blown out from the air outlet (22) by the refrigeration device (10) during dehumidification operation becomes uniform.

[0177] -Features of Embodiment 1 (3)- In the refrigeration apparatus (10) of this embodiment, the controller (90) performs humidity control and temperature control operations.

[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 rotational speed of the compressor (50) that sucks in the refrigerant that has flowed out from the internal heat exchanger (57) during dehumidification operation, based on the target evaporation temperature. Therefore, in the refrigeration system (10) of this embodiment, the humidity of the air that the refrigeration system (10) blows out into the internal space (5) during dehumidification operation can be appropriately controlled.

[0179] In the temperature control operation, the controller (90) controls the opening degree 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 this embodiment, the temperature of the air blown out into the interior space (5) by the refrigeration system (10) during dehumidification operation can be appropriately controlled.

[0180] Embodiment 2 Embodiment 2 will now be described. This embodiment is a modified version of Embodiment 1 in which the configuration of the refrigeration device (10) is changed in the transport container (1).

[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, we will explain the differences between the refrigerant circuit (30) of this embodiment and the refrigerant circuit (30) of Embodiment 1.

[0182] As shown in Figure 13, in the refrigerant circuit (30) of this embodiment, a drain pan heater (63) is provided in the defrosting piping (32). In the defrosting piping (32), the drain pan heater (63) is located 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 through it.

[0183] -Defrosting operation of the refrigeration system- In the defrosting operation performed by the refrigeration system (10) of this embodiment, a portion of the refrigerant discharged from the high-stage compressor (52) flows into the defrosting piping (32), similar to the defrosting operation performed by the refrigeration system (10) of Embodiment 1. In the defrosting operation performed by the refrigeration system (10) of this embodiment, the refrigerant that flows into the defrosting piping (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 defrosting, frost that has detached 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 from the internal heat exchanger (57) into the drain pan is heated by the drain pan, melts, and is discharged to the outside space as drain water.

[0185] Embodiment 3 Embodiment 3 will now be described. This embodiment is a modified version of Embodiment 2 in which the configuration of the refrigeration device (10) is changed in the transport container (1).

[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, we will explain the differences between the refrigerant circuit (30) of this embodiment and the refrigerant circuit (30) of Embodiment 2.

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

[0188] -Controller operation- In the refrigeration system of this embodiment, the controller (90) controls the opening degree of the fifth expansion valve (EV5) in both defrosting and dehumidification operations. In defrosting operations, the controller (90) of this embodiment performs the same opening degree control on the fifth expansion valve (EV5) as the controller (90) of embodiments 1 and 2 performs on the fourth expansion valve (EV4). In dehumidification operations, the controller (90) of this embodiment controls the opening degree of the fifth expansion valve (EV5) in the same manner as the controller (90) of embodiments 1 and 2.

[0189] Other embodiments The following modifications may be applied to the refrigeration device (10) of the above embodiment. These modifications may be combined or substituted as appropriate, as long as they do not impair the function of the refrigeration device (10).

[0190] -First variation- The refrigeration apparatus (10) in the above embodiments 1 to 3 may be configured to perform only a single-stage compression refrigeration cycle. Here, we will explain the differences between this modified example and the refrigeration apparatus (10) of embodiment 3, which is applied to the refrigeration apparatus (10) of embodiment 3.

[0191] As shown in Figure 15, in the refrigerant circuit (30) of this modified refrigeration device (10), the low-stage compressor (51), the low-stage connecting pipe (44), and the high-stage connecting pipe (45) are omitted. The refrigerant circuit (30) of this modified version is provided with one compressor (52) which corresponds to the high-stage compressor of the refrigerant circuit (30) of Embodiment 3.

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

[0193] In the cooling operation of the refrigeration system (10) of this modified example, the refrigerant circuit (30) performs a single-stage compression refrigeration cycle. In the refrigerant circuit (30), the compressor (52) operates and the refrigerant circulates in the main circuit (31). The refrigerant discharged by 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 in order 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) of the internal heat exchanger (61), and then flows into the internal heat exchanger (57). The refrigerant that flows into the internal heat exchanger (57) absorbs heat from the air flowing through the internal flow path (20) and evaporates. The refrigerant evaporated in the internal heat exchanger (57) is drawn into the compressor (52). The compressor (52) compresses the refrigerant it has drawn in and discharges it.

[0194] -Second variation- In the humidity control operation of the refrigeration system (10) in embodiments 1 to 3 described above, the controller (90) 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 rotational speed of the compressor (50) and the opening degree of the second expansion valve (EV2).

[0195] In contrast, the controller (90) in Embodiments 1 to 3 may use the refrigerant saturation temperature corresponding to the measurement value of the low-stage suction pressure sensor (75) as the refrigerant evaporation temperature in the internal heat exchanger (57). In this case, the controller (90) calculates the refrigerant saturation temperature corresponding to the measurement value of the low-stage suction pressure sensor (75) and controls the rotational speed of the compressor (50) and the opening degree of the second expansion valve (EV2) so that the calculated saturation temperature falls within the target evaporation temperature range.

[0196] Furthermore, the controller (90) in Embodiments 1 to 3 may set a target evaporation pressure range corresponding to the target evaporation temperature range and control the rotational speed of the compressor (50) and the opening degree of the second expansion valve (EV2) so that the measured 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 refrigerant pressure in the suction pipe of the low-stage compressor (51). The refrigerant pressure in the suction pipe of the low-stage compressor (51) is substantially equal to the pressure of the refrigerant flowing out of the internal heat exchanger (57). Furthermore, the pressure of the refrigerant flowing out of the internal heat exchanger (57) is practically 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 refrigerant pressure in the suction pipe of the low-stage compressor (51) is a physical quantity correlated with the evaporation temperature of the refrigerant in the internal heat exchanger (57).

[0198] -Third variation- In the dehumidification operation of the refrigeration device (10), the controller (90) of the above embodiments 1 to 3 may control the opening degree of the fifth expansion valve according to whether the temperature unevenness condition is met. The temperature unevenness condition is a condition that indicates that the temperature of the air that has passed through the reheat heat exchanger (58) is uneven in location. Examples of the temperature unevenness condition include the following first temperature unevenness condition and second temperature unevenness condition. The controller (90) of this modified example may determine whether only one of the first temperature unevenness condition and the second temperature unevenness condition is met, or it may determine whether both are met.

[0199] <Condition 1: Temperature unevenness> The first temperature unevenness condition is 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 met, it is highly likely that the amount of heating in the region upstream of the second air temperature sensor (87) in the reheat heat exchanger (58) is greater than the amount of heating in other regions. When the amount of heating is uneven in each part of the reheat heat exchanger (58), the temperature of the air that has passed through the reheat heat exchanger (58) will be uneven in location. In this explanation, "amount of heating" refers to the amount of heat that the reheat heat exchanger (58) transfers to the air.

[0201] Therefore, the controller (90) of this modified example increases the opening of the fifth expansion valve (EV5) when the first temperature unevenness condition is met. When the opening of the fifth expansion valve (EV5) increases, the flow rate of the refrigerant in the reheat heat exchanger (58) increases. When the flow rate of the refrigerant in the reheat heat exchanger (58) increases when the refrigerant is at a pressure above critical pressure, the amount of temperature drop of the refrigerant as it passes through the reheat heat exchanger (58) decreases. As a result, the amount of heating in each part of the reheat heat exchanger (58) becomes uniform, and as a result, the temperature of the air that has passed through the reheat heat exchanger (58) becomes uniform in terms of location.

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

[0203] In a heat exchanger functioning as an evaporator, the system is divided into a gas-liquid two-phase region where the refrigerant in a gas-liquid two-phase state exchanges heat with air, and a superheated region where the refrigerant in a gas-single-phase 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 gas-liquid two-phase 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 gas-liquid two-phase region.

[0204] When the second temperature unevenness condition is met, the superheated region is likely to be relatively large in the internal heat exchanger (57) which functions as an evaporator. Therefore, the temperature of the air that has passed through the internal heat exchanger (57) is likely to be unevenly distributed. When the temperature of the air that has passed through the internal heat exchanger (57) is unevenly distributed, the temperature of the air flowing into the reheat heat exchanger (58) is also unevenly distributed, and as a result, the temperature of the air that has passed through the reheat heat exchanger (58) is also unevenly distributed.

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

[0206] -Fourth variation- In the refrigeration system (10) of the above embodiments 1 to 3, the controller (90) may, in temperature control operation, 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 this modified refrigeration system (10), a fifth refrigerant temperature sensor is provided in the piping between the reheat heat exchanger (58) and the fifth expansion valve (EV5) in the reheat piping (33). 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) in this modified system controls the opening degree 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 opening of the fifth expansion valve (EV5) based on the temperature of the refrigerant at the outlet of the reheat heat exchanger (58), the temperature of the air that has passed through the reheat heat exchanger (58) can be brought within the target temperature range.

[0209] -Fifth variation- In the refrigeration apparatus (10) of the above embodiments 1 to 3, the humidity sensor (88) may be provided upstream of the internal heat exchanger (57) in the internal flow path (20). In this modified example, the humidity sensor (88) 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) in this modified example performs humidity control operations using the measured value of the humidity sensor (88) located upstream of the internal heat exchanger (57).

[0210] -Sixth variation- The applications of the refrigeration devices (10) in embodiments 1 to 3 described above are not limited to air conditioning the interior space (5) of a transport container (1). The refrigeration devices (10) in embodiments 1 to 3 may, for example, be used to air condition the interior space of a stationary refrigerator or cold storage warehouse.

[0211] While embodiments and modifications have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims. Furthermore, elements of the embodiments, modifications, and other embodiments described above may be combined or substituted as appropriate. In addition, the designations "first," "second," "third," etc. in the specification and claims are used to distinguish the phrases to which these designations are given, and do not limit the number or order of such phrases. [Industrial applicability]

[0212] As described above, this disclosure is useful for refrigeration equipment and transport containers. [Explanation of symbols]

[0213] 1. Shipping container 2 Container body 5. Interior space (target space) 10 Refrigeration equipment 30 Refrigerant Circuit 33 Reheat piping (reheat passage) 50 Compressors 51 Low-stage compressor 52 High-stage compressor 56 External heat exchanger (heat source side heat exchanger) 57 Internal heat exchanger (user side heat exchanger) 58 Reheat heat exchanger 62 Receivers 65 Expansion valve 90 Controllers 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) is provided, 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), The above refrigerant circuit (30) is, A reheat heat exchanger (58) that exchanges heat between the refrigerant and the air that has passed through the above-mentioned utilization-side heat exchanger (57), A reheat passage (33) that sends the refrigerant discharged by the compressor (50) to the reheat heat exchanger (58), The reheat passage (33) has a variable-opening control valve (EV5) located downstream of the reheat heat exchanger (58), The above-mentioned refrigeration device (10) is A refrigeration cycle is performed in which the heat source side heat exchanger (56) functions as a heat radiator and the utilization side heat exchanger (57) functions as an evaporator, the utilization side heat exchanger (57) cools and dehumidifies the air, the air that has passed through the utilization side heat exchanger (57) is heated in the reheat heat exchanger (58), and the heated air in the reheat heat exchanger (58) is blown out to the target space (5) in a dehumidification operation. The dehumidification operation described above includes a controller (90) that controls the opening degree of the control valve (EV5). Refrigeration equipment.

2. In the above dehumidification operation, the pressure of the refrigerant supplied to the reheat heat exchanger (58) through the reheat passage (33) is equal to or greater than the critical pressure of the refrigerant. The refrigeration apparatus according to claim 1.

3. The controller (90) controls the opening of the expansion valve (65) so that, during the dehumidification operation, the pressure of the refrigerant discharged by the compressor (50) is equal to or greater than the critical pressure of the refrigerant. The refrigeration apparatus according to claim 2.

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

5. The controller (90) controls the opening degree of the control valve (EV5) during the dehumidification operation based on the temperature of the refrigerant discharged from the reheat heat exchanger (58). A refrigeration apparatus according to any one of claims 1 to 3.

6. The controller (90) controls the rotational speed of the compressor (50) during the dehumidification operation so that a physical quantity correlated with the evaporation temperature of the refrigerant in the heat exchanger (57) on the user side becomes a control target value. A refrigeration apparatus according to any one of claims 1 to 3.

7. The above-mentioned refrigerant circuit (30) has a receiver (62) positioned between the heat source side heat exchanger (56) and the utilization side heat exchanger (57), The above expansion valve (65) is, A first expansion valve (EV1) is positioned between the heat source side heat exchanger (56) and the receiver (62), It includes a second expansion valve (EV2) positioned between the receiver (62) and the user-side heat exchanger (57), The above-mentioned controller (90) operates during the above-mentioned dehumidification operation. The opening degree of the first expansion valve (EV1) is controlled so that the pressure of the refrigerant discharged by the compressor (50) is equal to or greater than the critical pressure of the refrigerant. The opening degree of the second expansion valve (EV2) is controlled so that a physical quantity correlated with the evaporation temperature of the refrigerant in the above-mentioned heat exchanger (57) on the user side becomes the control target value. A refrigeration apparatus according to any one of claims 1 to 3.

8. The controller (90) sets the control target value in the dehumidification operation based on the humidity of the air flowing from the target space (5) to the user-side heat exchanger (57), or the humidity of the air blown out to the target space (5). The refrigeration apparatus according to claim 6.

9. The above compressor (50) is A low-stage compressor (51) that draws in the refrigerant that has passed through the above-mentioned heat exchanger on the user side (57), The above-mentioned low-stage compressor (51) includes a high-stage compressor (52) that draws in the refrigerant discharged by the low-stage compressor (51), The above-mentioned refrigeration device (10) operates in the above-mentioned dehumidification operation, In a single-stage compression operation in which one of the above-mentioned low-stage compressor (51) and the above-mentioned high-stage compressor (52) operates while the other remains inactive, The system selectively performs a two-stage compression operation in which both the lower-stage compressor (51) and the upper-stage compressor (52) are in operation. A refrigeration apparatus according to any one of claims 1 to 3.

10. The controller (90) increases the opening of the control valve (EV5) when a temperature unevenness condition is met during the dehumidification operation, indicating that the temperature of the air that has passed through the reheat heat exchanger (58) is uneven. A refrigeration apparatus according to any one of claims 1 to 3.

11. The reheat passage (33) above sends the refrigerant that has passed through the reheat heat exchanger (58) to the utilization-side heat exchanger (57). A refrigeration apparatus according to any one of claims 1 to 3.

12. The above refrigerant circuit (30) is filled with carbon dioxide as a refrigerant. A refrigeration apparatus according to any one of claims 1 to 3.

13. A refrigeration apparatus (10) according to any one of claims 1 to 3, The system comprises a container body (2) that forms the target space (5) where air conditioning is performed by the above-mentioned refrigeration device (10), and a container body (2). Shipping container.

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