Freezer device and container for transportation

Abstract

A freezer device (10) is provided with a refrigerant circuit (20), and performs a two-stage compression operation and a single-stage compression operation. The refrigerant circuit (20) has a first upstream pipe (41), a second upstream pipe (51), and a first pipe (61). The first upstream pipe (41) connects a first compressor (31a) and a first radiator (32a). The second upstream pipe (51) connects a second compressor (31b) and a second radiator (32b). The first pipe (61) connects the first upstream pipe (41) and the second upstream pipe (51). The first pipe (61) is provided with a first valve (71).

Description

Refrigeration device and transport container

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

[0002] Patent Document 1 discloses a refrigeration device. This refrigeration device selectively performs a two-stage compression refrigeration cycle and a single-stage compression refrigeration cycle. In the two-stage compression refrigeration cycle, the first compressor and the second compressor are arranged in series, and the refrigerant passes through the first compressor, the intercooler, the second compressor, and the gas cooler in this order. In the single-stage compression refrigeration cycle, the first compressor and the second compressor are arranged in parallel, the refrigerant discharged from the first compressor flows into the intercooler, and the refrigerant discharged from the second compressor flows into the gas cooler.

[0003] International Publication No. 2012 / 145156

[0004] Normally, in a refrigeration device that performs a two-stage compression refrigeration cycle, the heat exchanger that functions as an intercooler has a smaller capacity than the heat exchanger that functions as a gas cooler. On the other hand, in the refrigeration device of Patent Document 1, in the single-stage compression refrigeration cycle, the refrigerant discharged from the first compressor flows into the intercooler, and the refrigerant discharged from the second compressor flows into the gas cooler. Therefore, the capacity of the heat exchanger does not match the flow rate of the refrigerant flowing through the heat exchanger, and as a result, the efficiency of the refrigeration cycle may be reduced.

[0005] An object of the present disclosure is to improve the operating efficiency of a refrigeration device that performs a two-stage compression refrigeration cycle and a single-stage compression refrigeration cycle.

[0006] A first aspect of this disclosure is a refrigeration system (10) comprising a refrigerant circuit (20) having a first compressor (31a), a second compressor (31b), a first radiator (32a), a second radiator (32b), an expansion valve (33), and an evaporator (35), wherein the refrigerant circuit (20) performs a two-stage compression operation in which it performs a two-stage compression refrigeration cycle, and a single-stage compression operation in which it performs a single-stage compression refrigeration cycle. During the execution of the two-stage compression operation, the refrigerant circuit (20) has the first compressor (31a) draw in refrigerant flowing out from the evaporator (35), and the refrigerant discharged from the first compressor (31a) flows sequentially through the first radiator (32a), the second compressor (31b), and the second radiator (32b). During the execution of the single-stage compression operation described above, in the refrigerant circuit (20), both the first compressor (31a) and the second compressor (31b) draw in the refrigerant flowing out from the evaporator (35), and the refrigerant discharged from the first compressor (31a) and the refrigerant discharged from the second compressor (31b) flow through one or both of the first radiator (32a) and the second radiator (32b). The refrigerant circuit (20) includes a first upstream pipe (41) connecting the discharge port of the first compressor (31a) to the inlet of the first radiator (32a), a second upstream pipe (51) connecting the discharge port of the second compressor (31b) to the inlet of the second radiator (32b), a first pipe (61) with one end connected to the first upstream pipe (41) and the other end connected to the second upstream pipe (51), and a first valve (71) provided in the first pipe (61).

[0007] In the first embodiment, the refrigeration system (10) performs two-stage compression operation and single-stage compression operation. When the first valve (71) is open, the first upstream piping (41) and the second upstream piping (51) are connected via the first piping (61), and the refrigerant flows through the first piping (61). Therefore, in single-stage compression operation, it is possible to balance the flow rate of the refrigerant flowing through the first radiator (32a) with the capacity of the first radiator (32a), and to balance the flow rate of the refrigerant flowing through the second radiator (32b) with the capacity of the second radiator (32b). Consequently, in this embodiment, it is possible to improve the operating efficiency of the refrigeration system (10) in single-stage compression operation.

[0008] A second aspect of the present disclosure, in the first aspect described above, includes a controller (90) that closes the first valve (71) during the two-stage compression operation and opens the first valve (71) during the single-stage compression operation.

[0009] In the second embodiment, the controller (90) controls the first valve (71).

[0010] A third aspect of this disclosure is that, in the first aspect described above, during the execution of the single-stage compression operation, in the refrigerant circuit (20), the refrigerant flowing out from the first heat sink (32a) and the refrigerant flowing out from the second heat sink (32b) merge before flowing into the expansion valve (33).

[0011] In the third embodiment, during single-stage compression operation, the refrigerant that has passed through the first radiator (32a) and the refrigerant that has passed through the second radiator (32b) merge and then pass through the expansion valve (33).

[0012] A fourth aspect of the present disclosure is the third aspect described above, wherein the refrigerant circuit (20) is provided upstream or downstream of the first heat sink (32a) and includes a first flow control valve (45) for adjusting the flow rate of the refrigerant flowing through the first heat sink (32a).

[0013] In the fourth embodiment, the refrigerant circuit (20) has a first flow control valve (45). When the opening of the first flow control valve (45) changes, the flow rate of the refrigerant flowing through the first heat sink (32a) changes.

[0014] A fifth aspect of the present disclosure, in the fourth aspect, includes a controller (90) which closes the first valve (71) during the execution of the two-stage compression operation and opens the first valve (71) during the execution of the single-stage compression operation, and controls the opening degree of the first flow control valve (45) based on a first indicator that shows the state of the refrigerant at the outlet of the first heat sink (32a).

[0015] In the fifth embodiment, during two-stage compression operation, the controller (90) closes the first valve (71). During two-stage compression operation, no refrigerant flows through the first piping (61). On the other hand, during single-stage compression operation, the controller (90) opens the first valve (71) and controls the opening degree of the first flow control valve (45). When the opening degree of the first flow control valve (45) changes, the flow rate of refrigerant flowing through the first piping (61) from one of the first upstream piping (41) to the other of the second upstream piping (51) changes. As a result, the flow rate of refrigerant flowing through the first radiator (32a) and the flow rate of refrigerant flowing through the second radiator (32b) change.

[0016] A sixth aspect of the present disclosure is, in the third or fourth aspect described above, the refrigerant circuit (20) is provided upstream or downstream of the second heat sink (32b) and includes a second flow control valve (55) for adjusting the flow rate of the refrigerant flowing through the second heat sink (32b).

[0017] In the sixth embodiment, the refrigerant circuit (20) has a second flow control valve (55). When the opening of the second flow control valve (55) changes, the flow rate of the refrigerant flowing through the second heat sink (32b) changes.

[0018] A seventh aspect of the present disclosure, in the sixth aspect, includes a controller (90) which closes the first valve (71) during the execution of the two-stage compression operation and opens the first valve (71) during the execution of the single-stage compression operation, and controls the opening degree of the second flow control valve (55) based on a second indicator that shows the state of the refrigerant at the outlet of the second heat sink (32b).

[0019] In the seventh embodiment, during two-stage compression operation, the controller (90) closes the first valve (71). During two-stage compression operation, no refrigerant flows through the first piping (61). On the other hand, during single-stage compression operation, the controller (90) opens the first valve (71) and controls the opening degree of the second flow control valve (55). When the opening degree of the second flow control valve (55) changes, the flow rate of refrigerant flowing through the first piping (61) from one of the first upstream piping (41) to the other of the second upstream piping (51) changes. As a result, the flow rate of refrigerant flowing through the first radiator (32a) and the flow rate of refrigerant flowing through the second radiator (32b) change.

[0020] An eighth aspect of the present disclosure is, in the first aspect described above, during the execution of the single-stage compression operation, in the refrigerant circuit (20), the refrigerant discharged from the first compressor (31a) flows into the second radiator (32b), the refrigerant discharged from the second compressor (31b) flows into the first radiator (32a), and the refrigerant that has flowed out of the first radiator (32a) and the refrigerant that has flowed out of the second radiator (32b) merge and then flow into the expansion valve (33).

[0021] In the eighth embodiment, during single-stage compression operation, the refrigerant discharged from the first compressor (31a) flows into the expansion valve (33) after passing through the second heat sink (32b), and the refrigerant discharged from the second compressor (31b) flows into the expansion valve (33) after passing through the first heat sink (32a).

[0022] A ninth aspect of the present disclosure, in the first aspect described above, the refrigerant circuit (20) includes a first upstream valve (46) provided between one end of the first pipe (61) in the first upstream piping (41) and the first compressor (31a), a second upstream valve (56) provided between the other end of the first pipe (61) in the second upstream piping (51) and the second radiator (32b), a second pipe (62) with one end connected between the first upstream valve (46) and the first compressor (31a) in the first upstream piping (41) and the other end connected between the second upstream valve (56) and the second radiator (32b) in the second upstream piping (51), and a second valve (72) provided in the second pipe (62).

[0023] The refrigerant circuit (20) of the ninth embodiment includes a first upstream valve (46), a second upstream valve (56), a second pipe (62), and a second valve (72).

[0024] A tenth aspect of the present disclosure, in the ninth aspect, includes a controller (90) which, during the execution of the two-stage compression operation, opens the first upstream valve (46) and the second upstream valve (56) and closes the first valve (71) and the second valve (72); and during the execution of the single-stage compression operation, opens the first valve (71) and the second valve (72) and closes the first upstream valve (46) and the second upstream valve (56).

[0025] In the tenth embodiment, the controller (90) controls the first upstream valve (46), the second upstream valve (56), the first valve (71), and the second valve (72).

[0026] In the 10th embodiment, the controller (90) opens the first upstream valve (46) and the second upstream valve (56) and closes the first valve (71) and the second valve (72) during two-stage compression operation. During two-stage compression operation, the refrigerant discharged from the first compressor (31a) flows into the first radiator (32a), and the refrigerant discharged from the second compressor (31b) flows into the second radiator (32b).

[0027] In the 10th embodiment, the controller (90) opens the first valve (71) and the second valve (72) and closes the first upstream valve (46) and the second upstream valve (56) during single-stage compression operation. During single-stage compression operation, the refrigerant discharged from the first compressor (31a) flows into the second radiator (32b) through the second piping (62), and the refrigerant discharged from the second compressor (31b) flows into the first radiator (32a) through the first piping (61).

[0028] An eleventh aspect of the present disclosure is, in the tenth aspect, the controller (90) opens the first valve (71) and the second valve (72) and then closes the first upstream valve (46) and the second upstream valve (56) when switching the operation performed by the refrigeration system (10) from the two-stage compression operation to the single-stage compression operation, and opens the first upstream valve (46) and the second upstream valve (56) and then closes the first valve (71) and the second valve (72) when switching the operation performed by the refrigeration system (10) from the single-stage compression operation to the two-stage compression operation.

[0029] In the eleventh embodiment, the controller (90) switches the operation performed by the refrigeration system (10) from two-stage compression operation to single-stage compression operation, first opening a valve that switches from a closed state to an open state, and then closing a valve that switches from an open state to a closed state. As a result, the refrigerant circuit (20) can be kept in a state where refrigerant flows while the operation performed by the refrigeration system (10) is being switched, and damage to the refrigerant circuit (20) can be avoided.

[0030] A twelfth aspect of the present disclosure, in the ninth aspect, includes a controller (90) which, during the execution of the two-stage compression operation, opens the first upstream valve (46) and the second upstream valve (56) and closes the first valve (71) and the second valve (72); during the execution of the single-stage compression operation, opens the first valve (71) and the second valve (72), controls the opening degree of one of the first upstream valve (46) and the second upstream valve (56) based on a first indicator indicating the state of the refrigerant at the outlet of the first radiator (32a) and a second indicator indicating the state of the refrigerant at the outlet of the second radiator (32b), and closes the other of the first upstream valve (46) and the second upstream valve (56).

[0031] In the twelfth embodiment, the controller (90) controls the first upstream valve (46), the second upstream valve (56), the first valve (71), and the second valve (72).

[0032] In the twelfth embodiment, the controller (90) opens the first upstream valve (46) and the second upstream valve (56) and closes the first valve (71) and the second valve (72) during two-stage compression operation. During two-stage compression operation, the refrigerant discharged from the first compressor (31a) flows into the first radiator (32a), and the refrigerant discharged from the second compressor (31b) flows into the second radiator (32b).

[0033] In the twelfth embodiment, the controller (90) opens the first valve (71) and the second valve (72) during single-stage compression operation, and controls the opening degree of one of the first upstream valve (46) and the second upstream valve (56) to close the other. When the opening degree of the first upstream valve (46) changes while the second upstream valve (56) is closed, the ratio of the refrigerant discharged from the first compressor (31a) that flows into the second radiator (32b) through the second piping (62) and the refrigerant that flows into the first radiator (32a) through the first upstream valve (46) changes. Furthermore, when the opening of the second upstream valve (56) changes while the first upstream valve (46) is closed, the ratio of the refrigerant discharged from the second compressor (31b) that flows through the first piping (61) to the first radiator (32a) and the refrigerant that flows through the second upstream valve (56) to the second radiator (32b) changes. Therefore, in single-stage compression operation, the flow rate of the refrigerant flowing through the first radiator (32a) and the flow rate of the refrigerant flowing through the second radiator (32b) are adjusted by the operation of the controller (90).

[0034] A thirteenth aspect of the present disclosure is that, in the first aspect described above, during the execution of the single-stage compression operation, in the refrigerant circuit (20), the refrigerant discharged from the first compressor (31a) and the refrigerant discharged from the second compressor (31b) merge and then flow sequentially through the second heat sink (32b) and the first heat sink (32a).

[0035] In the 13th embodiment, during single-stage compression operation, the refrigerant discharged from the first compressor (31a) and the refrigerant discharged from the second compressor (31b) merge, and the merged refrigerant passes through the second radiator (32b) and the first radiator (32a) in sequence.

[0036] A fourteenth aspect of the present disclosure is the refrigerant circuit (20) in the first aspect, comprising: a first downstream pipe (42) connecting the outlet of the first radiator (32a) to the inlet of the second compressor (31b); a first downstream valve (47) provided in the first downstream pipe (42); a second downstream pipe (52) connecting the outlet of the second radiator (32b) to the expansion valve (33); a second downstream valve (57) provided in the second downstream pipe (52); a first upstream valve (46) provided between one end of the first pipe (61) and the first radiator (32a) in the first upstream pipe (41); and one end of the first upstream pipe ( 41) has a third pipe (63) connected between the first upstream valve (46) and the first radiator (32a) in the above-mentioned pipe (41), with the other end connected between the second radiator (32b) and the second downstream valve (57) in the above-mentioned second downstream pipe (52), a third valve (73) provided on the third pipe (63), a fourth pipe (64) with one end connected between the first radiator (32a) and the first downstream valve (47) in the above-mentioned first downstream pipe (42), with the other end connected between the second downstream valve (57) and the expansion valve (33) in the above-mentioned second downstream pipe (52), and a fourth valve (74) provided on the fourth pipe (64).

[0037] The refrigerant circuit (20) of the 14th embodiment includes a first downstream pipe (42), a first downstream valve (47), a second downstream pipe (52), a second downstream valve (57), a first upstream valve (46), a third pipe (63), a third valve (73), a fourth pipe (64), and a fourth valve (74).

[0038] A fifteenth aspect of the present disclosure is, in the fourteenth aspect, the fourth valve (74) is a check valve that allows the flow of refrigerant from one end of the fourth pipe (64) to the other end and prevents the flow of refrigerant from the other end of the fourth pipe (64) to the one end, and comprises a controller (90) which, during the execution of the two-stage compression operation, opens the first upstream valve (46) and the second downstream valve (57) and closes the first valve (71) and the third valve (73), and during the execution of the single-stage compression operation, opens the first valve (71) and the third valve (73) and closes the first upstream valve (46) and the second downstream valve (57).

[0039] In the 15th embodiment, the controller (90) controls the first upstream valve (46), the second downstream valve (57), the first valve (71), and the third valve (73).

[0040] In the 15th embodiment, the controller (90) opens the first upstream valve (46) and the second downstream valve (57) and closes the first valve (71) and the third valve (73) during two-stage compression operation. During two-stage compression operation, the refrigerant discharged from the first compressor (31a) flows into the first radiator (32a), and the refrigerant discharged from the second compressor (31b) flows into the second radiator (32b).

[0041] In the 15th embodiment, the controller (90) opens the first valve (71) and the third valve (73) and closes the first upstream valve (46) and the second downstream valve (57) during single-stage compression operation. During single-stage compression operation, the refrigerant discharged from the first compressor (31a) flows through the first piping (61) and merges with the refrigerant discharged from the second compressor (31b). The merged refrigerant then passes through the second radiator (32b), the third piping (63), and the first radiator (32a) in order, and then flows through the fourth piping (64) to the expansion valve (33).

[0042] A sixteenth aspect of the present disclosure is, in the fifteenth aspect, the controller (90) opens the first valve (71) and the third valve (73) and then closes the first upstream valve (46) and the second downstream valve (57) when switching the operation performed by the refrigeration device (10) from the two-stage compression operation to the single-stage compression operation, and opens the first upstream valve (46) and the second downstream valve (57) and then closes the first valve (71) and the third valve (73) when switching the operation performed by the refrigeration device (10) from the single-stage compression operation to the two-stage compression operation.

[0043] In the 16th embodiment, the controller (90) switches the operation performed by the refrigeration system (10) from two-stage compression operation to single-stage compression operation, first opening a valve that switches from a closed state to an open state, and then closing a valve that switches from an open state to a closed state. Therefore, the refrigerant circuit (20) can be kept in a state where refrigerant flows while the operation performed by the refrigeration system (10) is being switched, and damage to the refrigerant circuit (20) can be avoided.

[0044] In the seventeenth aspect of the present disclosure, in any one of the first to sixteenth aspects, the refrigerant filled in the refrigerant circuit (20) is carbon dioxide.

[0045] In the seventeenth aspect, carbon dioxide is filled as a refrigerant in the refrigerant circuit (20).

[0046] The eighteenth aspect of the present disclosure is a transport container (1) including the refrigeration apparatus (10) according to any one of the first to seventeenth aspects and a container body (2) that forms a target space (5) in which air conditioning is performed by the refrigeration apparatus (10).

[0047] The transport container (1) according to the eighteenth aspect includes the refrigeration apparatus (10) according to any one of the first to seventeenth aspects and the container body (2). The refrigeration apparatus (10) performs air conditioning of the target space (5) formed by the container body (2).

[0048] FIG. 1 is a perspective view of a transport container equipped with the refrigeration device of Embodiment 1. FIG. 2 is a piping diagram showing the refrigerant circuit of the refrigeration device of Embodiment 1. FIG. 3 is a block diagram showing the controller of the refrigeration device of Embodiment 1. FIG. 4 is a piping diagram corresponding to FIG. 2, showing the flow path of the refrigerant in the two-stage compression operation of the refrigeration device of Embodiment 1. FIG. 5 is a piping diagram corresponding to FIG. 2, showing the flow path of the refrigerant in the first single-stage compression operation of the refrigeration device of Embodiment 1. FIG. 6 is a piping diagram corresponding to FIG. 2, showing the flow path of the refrigerant in the second single-stage compression operation of the refrigeration device of Embodiment 1. FIG. 7 is a piping diagram showing the refrigerant circuit of the refrigeration device of Embodiment 2. FIG. 8 is a piping diagram corresponding to FIG. 7, showing the flow path of the refrigerant in the two-stage compression operation of the refrigeration device of Embodiment 2. FIG. 9 is a piping diagram corresponding to FIG. 7, showing the flow path of the refrigerant in the first single-stage compression operation of the refrigeration device of Embodiment 2. FIG. 10 is a piping diagram corresponding to FIG. 7, showing the flow path of the refrigerant in the second single-stage compression operation of the refrigeration device of Embodiment 2. FIG. 11 is a piping diagram showing the refrigerant circuit of the refrigeration device of Embodiment 3. FIG. 12 is a piping diagram corresponding to FIG. 11, showing the flow path of the refrigerant in the two-stage compression operation of the refrigeration device of Embodiment 3. FIG. 13 is a piping diagram corresponding to FIG. 11, showing the flow path of the refrigerant in the first single-stage compression operation of the refrigeration device of Embodiment 3. FIG. 14 is a piping diagram corresponding to FIG. 11, showing the flow path of the refrigerant in the second single-stage compression operation of the refrigeration device of Embodiment 3.

[0049] <<Embodiment 1>> Embodiment 1 will be described. This embodiment is a transport container (1) equipped with a refrigeration device (10).

[0050] -Transport Container- As shown in FIG. 1, the transport container (1) includes a container body (2) and a refrigeration device (10). The transport container (1) is a reefer container capable of temperature control inside the container.

[0051] 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.

[0052] -Container body- 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.

[0053] -Refrigeration device- The refrigeration device (10) is installed in the opening of the container body (2). The refrigeration device (10) in this embodiment is a transport refrigeration device. The refrigeration device (10) adjusts the temperature of the air (internal air) in the internal space (5).

[0054] As shown in Figures 2 and 3, the refrigeration system (10) comprises a refrigerant circuit (20), an external fan (16), an internal fan (17), and a controller (90). The evaporator (35) of the refrigerant circuit (20) and the internal fan (17) are arranged in an air passage that communicates with the internal space (5). The internal fan (17) supplies internal air to the evaporator (35) of the refrigerant circuit (20). The components of the refrigerant circuit (20) other than the evaporator (35), the external fan (16), and the controller (90) are arranged in the space outside the refrigerant circuit. The external fan (16) supplies outside air (outside air) to the first radiator (32a) and the second radiator (32b) of the refrigerant circuit (20).

[0055] -Refrigerant Circuit- As shown in Figure 2, the refrigerant circuit (20) comprises a main circuit (21), a first pipe (61), a fourth pipe (64), a fifth pipe (65), and a sixth pipe (66). The refrigerant circuit (20) also comprises a first compressor (31a), a second compressor (31b), a first radiator (32a), a second radiator (32b), an evaporator (35), an expansion valve (33), and a receiver (34). The expansion valve (33) includes a first expansion valve (33a) and a second expansion valve (33b).

[0056] <Main Circuit> In the main circuit (21), the first compressor (31a), the first heat sink (32a), the second compressor (31b), the second heat sink (32b), the first expansion valve (33a), the receiver (34), the second expansion valve (33b), and the evaporator (35) are arranged in that order.

[0057] The main circuit (21) includes a first upstream pipe (41) and a first downstream pipe (42). One end of the first upstream pipe (41) is connected to the discharge port of the first compressor (31a). The other end of the first upstream pipe (41) is connected to the inlet of the first radiator (32a). One end of the first downstream pipe (42) is connected to the outlet of the first radiator (32a). The other end of the first downstream pipe (42) is connected to the suction port of the second compressor (31b).

[0058] A first downstream valve (47) is provided in the first downstream piping (42). The first downstream valve (47) is an on / off valve consisting of a solenoid valve.

[0059] The main circuit (21) includes a second upstream pipe (51) and a second downstream pipe (52). One end of the second upstream pipe (51) is connected to the discharge port of the second compressor (31b). The other end of the second upstream pipe (51) is connected to the inlet of the second radiator (32b). One end of the second downstream pipe (52) is connected to the outlet of the second radiator (32b). The other end of the second upstream pipe (51) is connected to the inlet of the first expansion valve (33a).

[0060] <First Compressor, Second Compressor> The first compressor (31a) and the second compressor (31b) are both fully enclosed scroll compressors. Note that the first compressor (31a) and the second compressor (31b) can be any positive displacement compressor, and are not limited to scroll compressors.

[0061] In this embodiment, the displacement volume of the second compressor (31b) is smaller than the displacement volume of the first compressor (31a). However, the displacement volume of the second compressor (31b) may be equal to the displacement volume of the first compressor (31a).

[0062] <First radiator, second radiator> The first radiator (32a) and the second radiator (32b) are both fin-and-tube type air heat exchangers. The first radiator (32a) and the second radiator (32b) exchange heat between the refrigerant and the outside air. The capacity (heat exchange capacity) of the first radiator (32a) is smaller than the capacity (heat exchange capacity) of the second radiator (32b).

[0063] <First Expansion Valve, Second Expansion Valve> The first expansion valve (33a) and the second expansion valve (33b) are so-called electronic expansion valves. Each of the first expansion valve (33a) and the second expansion valve (33b) comprises a valve body and a stepping motor that drives the valve body. The opening degree of each of the first expansion valve (33a) and the second expansion valve (33b) is changed by the stepping motor moving the valve body.

[0064] <Receiver> The receiver (34) is a hollow container-shaped component. The receiver (34) stores the refrigerant filled in the refrigerant circuit (20). The top of the receiver (34) is connected via piping to the outlet of the first expansion valve (33a). The bottom of the receiver (34) is connected via piping to the inlet of the second expansion valve (33b).

[0065] <Evaporator> The evaporator (35) is a fin-and-tube type air heat exchanger. The evaporator (35) exchanges heat between the refrigerant and the air inside the chamber.

[0066] <First flow control valve, second flow control valve> A first flow control valve (45) is provided in the first downstream piping (42). The first flow control valve (45) is positioned between the first radiator (32a) and the first downstream valve (47) in the first downstream piping (42). In the main circuit (21) of the refrigerant circuit (20), the first flow control valve (45) is positioned downstream of the first radiator (32a).

[0067] A second flow control valve (55) is provided in the second downstream piping (52). In the main circuit (21) of the refrigerant circuit (20), the second flow control valve (55) is located downstream of the second radiator (32b).

[0068] The first flow control valve (45) and the second flow control valve (55) are both electrically operated valves with a variable opening. Each of the first flow control valve (45) and the second flow control valve (55) comprises a valve body and a stepping motor that drives the valve body. The opening degree of each of the first flow control valve (45) and the second flow control valve (55) is changed by the stepping motor moving the valve body.

[0069] <First Piping> One end of the first piping (61) is connected to the first upstream piping (41). The other end of the first piping (61) is connected to the second upstream piping (51). The first piping (61) is equipped with a first valve (71). The first valve (71) is an on / off valve consisting of a solenoid valve.

[0070] <Fourth Piping> One end of the fourth piping (64) is connected between the first flow control valve (45) and the first downstream valve (47) in the first downstream piping (42). The other end of the fourth piping (64) is connected between the second flow control valve (55) and the first expansion valve (33a) in the second downstream piping (52). A fourth valve (74) is provided in the fourth piping (64). The fourth valve (74) is a check valve. The fourth valve (74) allows the flow of refrigerant from one end of the fourth piping (64) to the other end, and blocks the flow of refrigerant in the reverse direction.

[0071] <Fifth Piping> One end of the fifth piping (65) is connected to the piping that connects the outlet of the evaporator (35) and the inlet of the first compressor (31a). The other end of the fifth piping (65) is connected between the first downstream valve (47) and the second compressor (31b) in the first downstream piping (42). The fifth valve (75) is provided in the fifth piping (65). The fifth valve (75) is an on / off valve consisting of a solenoid valve.

[0072] <Sixth Piping> One end of the sixth piping (66) is connected to the top of the receiver (34). The other end of the sixth piping (66) is connected between the first downstream valve (47) and the second compressor (31b) in the first downstream piping (42). The sixth piping (66) is provided with a sixth valve (76) and a sixth check valve (77) in order from one end to the other. The sixth valve (76) is an on / off valve consisting of a solenoid valve. The sixth check valve (77) allows the flow of refrigerant from one end to the other of the sixth piping (66) and blocks the flow of refrigerant in the reverse direction.

[0073] <Sensors> The refrigerant circuit (20) is provided with a first pressure sensor (81), a second pressure sensor (82), a first temperature sensor (86), and a second temperature sensor (87).

[0074] The first pressure sensor (81) and the first temperature sensor (86) are positioned between the first radiator (32a) and the first flow control valve (45) in the first downstream piping (42). The first pressure sensor (81) measures the pressure of the refrigerant at the outlet of the first radiator (32a). The first temperature sensor (86) measures the temperature of the refrigerant at the outlet of the first radiator (32a).

[0075] The second pressure sensor (82) and the second temperature sensor (87) are positioned between the second radiator (32b) and the second flow control valve (55) in the second downstream piping (52). The second pressure sensor (82) measures the refrigerant pressure at the outlet of the second radiator (32b). The second temperature sensor (87) measures the refrigerant temperature at the outlet of the second radiator (32b).

[0076] -Controller- As shown in Figure 3, 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 the software necessary to operate the microcomputer (91).

[0077] The controller (90) receives the measured values ​​from the first pressure sensor (81), the second pressure sensor (82), the first temperature sensor (86), and the second temperature sensor (87). The controller (90) controls the equipment installed in the refrigeration unit (10). For example, the controller (90) controls the rotational speed of the first compressor (31a) and the second compressor (31b), the opening degree of the first expansion valve (33a) and the second expansion valve (33b), the opening degree of the first flow control valve (45) and the second flow control valve (55), the state of the first valve (71), the fifth valve (75), and the sixth valve (76), and the rotational speed of the external fan (16) and the internal fan (17).

[0078] - Refrigeration System Operation - The refrigeration system (10) selectively performs two-stage compression operation, first single-stage compression operation, and second single-stage compression operation.

[0079] <Two-stage compression operation> In the two-stage compression operation of the refrigeration system (10), the refrigerant circuit (20) performs a two-stage compression refrigeration cycle. In the two-stage compression operation, the first radiator (32a) functions as an intercooler, and the second radiator (32b) functions as a gas cooler.

[0080] In two-stage compression operation, the controller (90) controls the opening of the first expansion valve (33a) and the second expansion valve (33b), keeps the first flow control valve (45) and the second flow control valve (55) fully open, keeps the first downstream valve (47) open, and keeps the first valve (71) and the fifth valve (75) closed. The controller (90) also opens and closes the sixth valve (76) as needed.

[0081] The refrigerant flow path in the refrigerant circuit (20) will be explained with reference to Figure 4. Here, the refrigerant flow path when the sixth valve (76) is closed will be explained.

[0082] The refrigerant discharged from the first compressor (31a) flows into the first radiator (32a) and dissipates heat into the outside air. The refrigerant that has passed through the first radiator (32a) is drawn into the second compressor (31b) and compressed. The second compressor (31b) compresses the drawn-in refrigerant to a pressure higher than the critical pressure of the refrigerant (carbon dioxide in this embodiment). The refrigerant discharged from the second compressor (31b) flows into the second radiator (32b) and dissipates heat into the outside air.

[0083] The refrigerant that has passed through the second heat exchanger (32b) is depressurized as it passes through the first expansion valve (33a) and then flows into the receiver (34). The pressure of the refrigerant that has passed through the first expansion valve (33a) is lower than the critical pressure of the refrigerant. The refrigerant flowing into the receiver (34) is in a gas-liquid two-phase state. The refrigerant that has flowed out of the receiver (34) is depressurized as it passes through the second expansion valve (33b) and then flows into the evaporator (35).

[0084] The refrigerant flowing into the evaporator (35) absorbs heat from the air inside the storage compartment and evaporates. The air cooled in the evaporator (35) is blown out from the refrigeration unit (10) into the storage compartment space (5). The refrigerant that has passed through the evaporator (35) is drawn into the first compressor (31a). The first compressor (31a) compresses the drawn-in refrigerant and discharges it.

[0085] <First Single-Stage Compression Operation> In the first single-stage compression operation of the refrigeration system (10), the refrigerant circuit (20) performs a single-stage compression refrigeration cycle. In the first single-stage compression operation, both the first compressor (31a) and the second compressor (31b) draw in the refrigerant that has passed through the evaporator (35). Also, in the first single-stage compression operation, both the first radiator (32a) and the second radiator (32b) function as condensers.

[0086] In the first single-stage compression operation, the controller (90) controls the opening of the first expansion valve (33a) and the second expansion valve (33b), controls the opening of the first flow control valve (45) and the second flow control valve (55), keeps the first valve (71) and the fifth valve (75) in the open state, and keeps the first downstream valve (47) and the sixth valve (76) in the closed state.

[0087] The refrigerant flow path in the refrigerant circuit (20) will be explained with reference to Figure 5.

[0088] The refrigerant discharged from the first compressor (31a) flows into the first radiator (32a) through the first upstream piping (41). Meanwhile, the refrigerant discharged from the second compressor (31b) flows into the second radiator (32b) through the second upstream piping (51). The pressure of the refrigerant discharged from the first compressor (31a) and the pressure of the refrigerant discharged from the second compressor (31b) are both lower than the critical pressure of the refrigerant.

[0089] As described above, in the refrigeration system (10) of this embodiment, the displacement volume of the second compressor (31b) is smaller than the displacement volume of the first compressor (31a). Also, in the first single-stage compression operation, the opening of the first flow control valve (45) and the second flow control valve (55) is controlled by the controller (90). Therefore, a portion of the refrigerant discharged from the first compressor (31a) flows through the first piping (61) into the second upstream piping (51) and flows into the second heat exchanger (32b) together with the refrigerant discharged from the second compressor (31b).

[0090] The refrigerant that has passed through the first radiator (32a) flows through the first downstream piping (42), passes through the first flow control valve (45), and then flows through the fourth piping (64) into the second downstream piping (52). The refrigerant that has passed through the second radiator (32b) flows through the second downstream piping (52), passes through the second flow control valve (55), and merges with the refrigerant that has flowed in from the fourth piping (64) (i.e., the refrigerant that has passed through the first radiator (32a)). The refrigerant after the merge is depressurized as it passes through the first expansion valve (33a) and then flows into the receiver (34). The refrigerant that has flowed out of the receiver (34) is depressurized as it passes through the second expansion valve (33b) and then flows into the evaporator (35).

[0091] The refrigerant flowing into the evaporator (35) absorbs heat from the air inside the storage compartment and evaporates. The air cooled in the evaporator (35) is blown out from the refrigeration unit (10) into the storage compartment space (5). A portion of the refrigerant that has passed through the evaporator (35) is drawn into the first compressor (31a), and the remainder is drawn into the second compressor (31b) through the fifth pipe (65). The first compressor (31a) and the second compressor (31b) each compress the drawn-in refrigerant and discharge it.

[0092] <Second Single-Stage Compression Operation> In the second single-stage compression operation of the refrigeration system (10), the refrigerant circuit (20) performs a single-stage compression refrigeration cycle. In the second single-stage compression operation, the first compressor (31a) draws in the refrigerant that has passed through the evaporator (35), and the second compressor (31b) draws in the gaseous refrigerant that has flowed out from the receiver (34). In addition, in the second single-stage compression operation, both the first radiator (32a) and the second radiator (32b) function as condensers.

[0093] In the second single-stage compression operation, the controller (90) controls the opening of the first expansion valve (33a) and the second expansion valve (33b), controls the opening of the first flow control valve (45) and the second flow control valve (55), keeps the first valve (71) and the sixth valve (76) in the open state, and keeps the first downstream valve (47) and the fifth valve (75) in the closed state.

[0094] The refrigerant flow path in the refrigerant circuit (20) will be explained with reference to Figure 6. Here, we will explain the differences between the refrigerant flow path in the refrigerant circuit (20) during the second single-stage compression operation and the refrigerant flow path in the refrigerant circuit (20) during the first single-stage compression operation.

[0095] All of the refrigerant that has passed through the evaporator (35) is drawn into the first compressor (31a). The gaseous refrigerant in the receiver (34) flows through the sixth pipe (66) into the first downstream pipe (42), and is then drawn into the second compressor (31b). The refrigerant flow path in the refrigerant circuit (20) during second single-stage compression operation is the same as the refrigerant flow path in the refrigerant circuit (20) during first single-stage compression operation, except for the two points mentioned above.

[0096] -Controller Operation- As described above, in the first single-stage compression operation and the second single-stage compression operation, the controller (90) controls the opening degree of the first flow control valve (45) and the second flow control valve (55). Here, we will explain the operation in which the controller (90) controls the opening degree of the first flow control valve (45) and the second flow control valve (55).

[0097] The controller (90) controls the opening of the first flow control valve (45) and the second flow control valve (55) based on the first and second indicators.

[0098] The first indicator is an indicator showing the state of the refrigerant at the outlet of the first heat sink (32a). In this embodiment, the first indicator is the specific enthalpy h1 of the refrigerant at the outlet of the first heat sink (32a). The controller (90) calculates the specific enthalpy h1 of the refrigerant at the outlet of the first heat sink (32a) using the measured value of the first pressure sensor (81) and the measured value of the first temperature sensor (86).

[0099] The second indicator is an indicator showing the state of the refrigerant at the outlet of the second heat sink (32b). In this embodiment, the second indicator is the specific enthalpy h2 of the refrigerant at the outlet of the second heat sink (32b). The controller (90) calculates the specific enthalpy h2 of the refrigerant at the outlet of the second heat sink (32b) using the measurement value of the second pressure sensor (82) and the measurement value of the second temperature sensor (87).

[0100] The controller (90) controls the opening degrees of the first flow control valve (45) and the second flow control valve (55) so that the first index and the second index have the same value. Specifically, the controller (90) sets the opening degree of the second flow control valve (55) to a predetermined opening degree (for example, 100% opening) and controls the opening degree of the first flow control valve (45) so that the first index (specific enthalpy h1) and the second index (specific enthalpy h2) have the same value.

[0101] If the first indicator is lower than the second indicator, the controller (90) increases the opening of the first flow control valve (45). When the opening of the first flow control valve (45) increases, the flow rate of the refrigerant discharged from the first compressor (31a) that flows into the first piping (61) decreases. As a result, the flow rate of refrigerant flowing into the first radiator (32a) increases, and the flow rate of refrigerant flowing into the second radiator (32b) decreases. Consequently, the specific enthalpy h1 of the refrigerant at the outlet of the first radiator (32a) increases, and the specific enthalpy h2 of the refrigerant at the outlet of the second radiator (32b) decreases.

[0102] If the first indicator is higher than the second indicator, the controller (90) reduces the opening of the first flow control valve (45). When the opening of the first flow control valve (45) is reduced, the flow rate of the refrigerant discharged from the first compressor (31a) that flows into the first piping (61) increases. As a result, the flow rate of refrigerant flowing into the first radiator (32a) decreases, and the flow rate of refrigerant flowing into the second radiator (32b) increases. Consequently, the specific enthalpy h1 of the refrigerant at the outlet of the first radiator (32a) decreases, and the specific enthalpy h2 of the refrigerant at the outlet of the second radiator (32b) increases.

[0103] If the first indicator matches the second indicator, the controller (90) maintains the opening of the first flow control valve (45) without changing it.

[0104] -Features of Embodiment 1- The refrigeration system (10) of this embodiment performs two-stage compression operation and first and second single-stage compression operation. In the first and second single-stage compression operation, the controller (90) opens the first valve (71) and controls the opening of the first flow control valve (45) and the second flow control valve (55).

[0105] When the opening of the first flow control valve (45) changes, the flow rate of refrigerant flowing from the first upstream pipe (41) to the second upstream pipe (51) through the first pipe (61) changes. As a result, the flow rate of refrigerant flowing through the first radiator (32a) and the flow rate of refrigerant flowing through the second radiator (32b) change.

[0106] In the refrigeration system (10) of this embodiment, during the first and second single-stage compression operation, it is possible to balance the flow rate of refrigerant flowing through the first heat sink (32a) with the capacity of the first heat sink (32a), and to balance the flow rate of refrigerant flowing through the second heat sink (32b) with the capacity of the second heat sink (32b). Therefore, in this embodiment, it is possible to improve the operating efficiency of the refrigeration system (10) during the first and second single-stage compression operation.

[0107] -Modification 1 of Embodiment 1- The refrigeration device (10) of this embodiment may be equipped with only the first flow control valve (45) among the first flow control valve (45) and the second flow control valve (55). In this modified refrigeration device (10), the controller (90) controls the opening degree of the first flow control valve (45) using a first index (specific enthalpy h1) and a second index (specific enthalpy h2).

[0108] Specifically, the controller (90) in this modified example controls the opening degree of the first flow control valve (45) so that the first index and the second index are the same value. If the first index is lower than the second index, the controller (90) increases the opening degree of the first flow control valve (45). If the first index is higher than the second index, the controller (90) decreases the opening degree of the first flow control valve (45). If the first index is equal to the second index, the controller (90) maintains the opening degree of the first flow control valve (45) without changing it.

[0109] -Modification 2 of Embodiment 1- The refrigeration device (10) of this embodiment may be equipped with only the second flow control valve (55) among the first flow control valve (45) and the second flow control valve (55). In this modified refrigeration device (10), the controller (90) controls the opening degree of the second flow control valve (55) using the first index (specific enthalpy h1) and the second index (specific enthalpy h2).

[0110] Specifically, the controller (90) in this modified example controls the opening of the second flow control valve (55) so that the first index and the second index have the same value. If the first index is lower than the second index, the controller (90) reduces the opening of the second flow control valve (55). If the first index is higher than the second index, the controller (90) increases the opening of the second flow control valve (55). If the first index matches the second index, the controller (90) maintains the opening of the second flow control valve (55) without changing it.

[0111] -Modification 3 of Embodiment 1- In the refrigeration device (10) of this embodiment, the controller (90) may use the temperature of the refrigerant at the outlet of the first heat sink (32a) as the first indicator, and the temperature of the refrigerant at the outlet of the second heat sink (32b) as the second indicator. In this modified example, the controller (90) uses the measurement value of the first temperature sensor (86) as the first indicator, and the measurement value of the second temperature sensor (87) as the second indicator.

[0112] If the first indicator is lower than the second indicator, the controller (90) increases the opening of the first flow control valve (45). If the first indicator is higher than the second indicator, the controller (90) decreases the opening of the first flow control valve (45). If the first indicator is equal to the second indicator, the controller (90) maintains the opening of the first flow control valve (45) without changing it.

[0113] -Modification 4 of Embodiment 1- In the refrigeration device (10) of this embodiment, the first flow control valve (45) may be located upstream of the first radiator (32a) in the refrigerant circuit (20). In this case, the first flow control valve (45) is provided between one end of the first pipe (61) in the first upstream piping (41) and the first radiator (32a).

[0114] -Modification 5 of Embodiment 1- In the refrigeration device (10) of this embodiment, the second flow control valve (55) may be located upstream of the second heat radiator (32b) in the refrigerant circuit (20). In this case, the second flow control valve (55) is provided between the other end of the first pipe (61) and the second heat radiator (32b) in the second upstream piping (51).

[0115] 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).

[0116] The refrigeration system (10) of this embodiment differs from the refrigeration system (10) of Embodiment 1 in the configuration of the refrigerant circuit (20) and the controller (90). Here, we will mainly explain the differences between the refrigerant circuit (20) and the controller (90) of this embodiment and those of Embodiment 1.

[0117] -Refrigerant Circuit- As shown in Figure 7, the refrigerant circuit (20) of this embodiment includes a first upstream valve (46), a second upstream valve (56), and a second pipe (62). On the other hand, in the refrigerant circuit (20) of this embodiment, the first flow control valve (45) and the second flow control valve (55) are omitted.

[0118] <First upstream valve, second upstream valve> The first upstream valve (46) is positioned between one end of the first pipe (61) in the first upstream piping (41) and the first compressor (31a). The second upstream valve (56) is positioned between the other end of the first pipe (61) in the second upstream piping (51) and the second radiator (32b).

[0119] The first upstream valve (46) and the second upstream valve (56) are both electrically operated valves with variable opening. Each of the first upstream valve (46) and the second upstream valve (56) comprises a valve body and a stepping motor that drives the valve body. The opening degree of each of the first upstream valve (46) and the second upstream valve (56) is changed by the stepping motor moving the valve body.

[0120] <Second Piping> One end of the second piping (62) is connected between the first upstream valve (46) and the first compressor (31a) in the first upstream piping (41). The other end of the second piping (62) is connected between the second upstream valve (56) and the second radiator (32b) in the second upstream piping (51). The second piping (62) is provided with a second valve (72). The second valve (72) is an on / off valve consisting of a solenoid valve.

[0121] - Refrigeration System Operation - The refrigeration system (10) of this embodiment, like the refrigeration system (10) of Embodiment 1, selectively performs two-stage compression operation, first single-stage compression operation, and second single-stage compression operation.

[0122] <Two-stage compression operation> In the two-stage compression operation of the refrigeration system (10), the refrigerant circuit (20) performs a two-stage compression refrigeration cycle. In the two-stage compression operation, the first radiator (32a) functions as an intercooler, and the second radiator (32b) functions as a gas cooler.

[0123] In two-stage compression operation, the controller (90) controls the opening of the first expansion valve (33a) and the second expansion valve (33b), keeps the first upstream valve (46) and the second upstream valve (56) fully open, keeps the first downstream valve (47) open, and keeps the first valve (71), the second valve (72), and the fifth valve (75) closed. The controller (90) also opens and closes the sixth valve (76) as needed.

[0124] The refrigerant flow path in the refrigerant circuit (20) will now be explained. As shown in Figure 8, the refrigerant flow path in the refrigerant circuit (20) of this embodiment is the same as the refrigerant flow path in the refrigerant circuit (20) of Embodiment 1 shown in Figure 4. The refrigerant that has passed through the evaporator (35) is compressed in the first compressor (31a), releases heat in the first heat sink (32a), is compressed in the second compressor (31b), releases heat in the second heat sink (32b), and absorbs heat in the evaporator (35).

[0125] <First Single-Stage Compression Operation> In the first single-stage compression operation of the refrigeration system (10), the refrigerant circuit (20) performs a single-stage compression refrigeration cycle. In the first single-stage compression operation, both the first compressor (31a) and the second compressor (31b) draw in the refrigerant that has passed through the evaporator (35). Also, in the first single-stage compression operation, both the first radiator (32a) and the second radiator (32b) function as condensers.

[0126] In the first single-stage compression operation, the controller (90) controls the opening degree of the first expansion valve (33a) and the second expansion valve (33b), controls the opening degree of the first upstream valve (46), keeps the first valve (71), the second valve (72), and the fifth valve (75) in the open state, and keeps the first downstream valve (47), the second upstream valve (56), and the sixth valve (76) in the closed state.

[0127] The refrigerant flow path in the refrigerant circuit (20) will be explained with reference to Figure 9. Here, the refrigerant flow path when the first upstream valve (46) is closed will be explained.

[0128] The refrigerant discharged from the first compressor (31a) flows through the second piping (62) into the second upstream piping (51), and then into the second radiator (32b). On the other hand, the refrigerant discharged from the second compressor (31b) flows through the first piping (61) into the first upstream piping (41), and then into the first radiator (32a). The pressure of the refrigerant discharged from the first compressor (31a) and the pressure of the refrigerant discharged from the second compressor (31b) are both lower than the critical pressure of the refrigerant.

[0129] As described above, in the refrigeration system (10) of this embodiment, the displacement volume of the second compressor (31b) is smaller than that of the first compressor (31a). Also, in the refrigeration system (10) of this embodiment, the capacity of the first radiator (32a) is smaller than that of the second radiator (32b). In the first single-stage compression operation of this embodiment, the refrigerant discharged from the second compressor (31b), which has a relatively small displacement volume, flows into the first radiator (32a), which has a relatively small capacity. Also, the refrigerant discharged from the first compressor (31a), which has a relatively large displacement volume, flows into the second radiator (32b), which has a relatively large capacity.

[0130] The refrigerant flowing into the first radiator (32a) releases heat into the outside air, and then flows through the fourth pipe (64) into the second downstream pipe (52). The refrigerant flowing into the second radiator (32b) releases heat into the outside air. The refrigerant that has passed through the second radiator (32b) flows through the second downstream pipe (52) and, together with the refrigerant that has flowed in from the fourth pipe (64) (i.e., the refrigerant that has flowed out from the first radiator (32a)), flows into the first expansion valve (33a). The refrigerant that has flowed into the first expansion valve (33a) expands as it passes through the first expansion valve (33a), and then flows into the receiver (34). The refrigerant that has flowed out from the receiver (34) is depressurized as it passes through the second expansion valve (33b), and then flows into the evaporator (35).

[0131] The refrigerant flowing into the evaporator (35) absorbs heat from the air inside the storage compartment and evaporates. The air cooled in the evaporator (35) is blown out from the refrigeration unit (10) into the storage compartment space (5). A portion of the refrigerant that has passed through the evaporator (35) is drawn into the first compressor (31a), and the remainder is drawn into the second compressor (31b) through the fifth pipe (65). The first compressor (31a) and the second compressor (31b) each compress the drawn-in refrigerant and discharge it.

[0132] <Second Single-Stage Compression Operation> In the second single-stage compression operation of the refrigeration system (10), the refrigerant circuit (20) performs a single-stage compression refrigeration cycle. In the second single-stage compression operation, the first compressor (31a) draws in the refrigerant that has passed through the evaporator (35), and the second compressor (31b) draws in the gaseous refrigerant that has flowed out from the receiver (34). In addition, in the second single-stage compression operation, both the first radiator (32a) and the second radiator (32b) function as condensers.

[0133] In the second single-stage compression operation, the controller (90) controls the opening degree of the first expansion valve (33a) and the second expansion valve (33b), controls the opening degree of the first upstream valve (46), keeps the first valve (71), the second valve (72), and the sixth valve (76) in the open state, and keeps the first downstream valve (47), the second upstream valve (56), and the fifth valve (75) in the closed state.

[0134] The refrigerant flow path in the refrigerant circuit (20) will be explained with reference to Figure 10. Here, we will explain the differences between the refrigerant flow path in the refrigerant circuit (20) during the second single-stage compression operation and the refrigerant flow path in the refrigerant circuit (20) during the first single-stage compression operation.

[0135] All of the refrigerant that has passed through the evaporator (35) is drawn into the first compressor (31a). The gaseous refrigerant in the receiver (34) flows through the sixth pipe (66) into the first downstream pipe (42), and is then drawn into the second compressor (31b). The refrigerant flow path in the refrigerant circuit (20) during second single-stage compression operation is the same as the refrigerant flow path in the refrigerant circuit (20) during first single-stage compression operation, except for the two points mentioned above.

[0136] -Controller Operation- The control operation performed by the controller (90) is described below.

[0137] <Control operation in single-stage compression operation> As described above, in the first single-stage compression operation and the second single-stage compression operation, the controller (90) controls the opening degree of the first upstream valve (46). Here, we will explain the operation in which the controller (90) controls the opening degree of the first upstream valve (46).

[0138] The controller (90) controls the opening degree of the first upstream valve (46) based on a first indicator and a second indicator. Similar to Embodiment 1, the first indicator is the specific enthalpy h1 of the refrigerant at the outlet of the first radiator (32a), and the second indicator is the specific enthalpy h2 of the refrigerant at the outlet of the second radiator (32b).

[0139] The controller (90) controls the opening degree of the first upstream valve (46) so that the first index and the second index have the same value.

[0140] If the first indicator is lower than the second indicator, the controller (90) opens the first upstream valve (46) or increases the opening of the first upstream valve (46). When the first upstream valve (46) is open, a portion of the refrigerant discharged from the first compressor (31a) passes through the first upstream valve (46) and merges with the refrigerant flowing from the first piping (61) into the first upstream piping (41) (i.e., the refrigerant discharged from the second compressor (31b)). As a result, the flow rate of refrigerant flowing into the first radiator (32a) increases, and the flow rate of refrigerant flowing into the second radiator (32b) decreases. Consequently, the specific enthalpy h1 of the refrigerant at the outlet of the first radiator (32a) increases, and the specific enthalpy h2 of the refrigerant at the outlet of the second radiator (32b) decreases.

[0141] If the first indicator is higher than the second indicator, the controller (90) reduces the opening of the first upstream valve (46) or closes the first upstream valve (46). When the opening of the first upstream valve (46) is reduced, the flow rate of the refrigerant discharged from the first compressor (31a) that passes through the first upstream valve (46) decreases. As a result, the flow rate of refrigerant flowing into the first radiator (32a) decreases, and the flow rate of refrigerant flowing into the second radiator (32b) increases. Consequently, the specific enthalpy h1 of the refrigerant at the outlet of the first radiator (32a) decreases, and the specific enthalpy h2 of the refrigerant at the outlet of the second radiator (32b) increases.

[0142] If the first indicator matches the second indicator, the controller (90) maintains the opening of the first flow control valve (45) without changing it.

[0143] <Switching between two-stage compression operation and single-stage compression operation> First, the control operation when the controller (90) switches the operating state of the refrigeration system (10) from two-stage compression operation to first single-stage compression operation or second single-stage compression operation will be explained. In this case, the controller (90) closes the first upstream valve (46), which was open in the two-stage compression operation, and then controls the opening degree of the first upstream valve (46). Also in this case, the controller (90) opens the first valve (71), the second valve (72), and the fifth valve (75), which were closed in the two-stage compression operation, and then closes the first upstream valve (46), the first downstream valve (47), and the second upstream valve (56), which were open in the two-stage compression operation.

[0144] Next, the control operation when the controller (90) switches the operating state of the refrigeration system (10) from first single-stage compression operation or second single-stage compression operation to two-stage compression operation will be described. In this case, the controller (90) opens the first upstream valve (46), the first downstream valve (47), and the second upstream valve (56), which were closed in the first or second single-stage compression operation, and then closes the first valve (71), the second valve (72), and the fifth valve (75), which were open in the first or second single-stage compression operation.

[0145] Thus, when the controller (90) switches the operation performed by the refrigeration system (10) from two-stage compression operation to single-stage compression operation, it first opens a valve that switches from a closed state to an open state, and then closes a valve that switches from an open state to a closed state.

[0146] -Features of Embodiment 2 (1)- In the first and second single-stage compression operation performed by the refrigeration system (10) of this embodiment, the refrigerant discharged from the second compressor (31b), which has a relatively small displacement volume, flows into the first radiator (32a), which has a relatively small capacity. Also, the refrigerant discharged from the first compressor (31a), which has a relatively large displacement volume, flows into the second radiator (32b), which has a relatively large capacity.

[0147] Therefore, in the refrigeration system (10) of this embodiment, in the first and second single-stage compression operation, it is possible to balance the flow rate of refrigerant flowing through the first heat sink (32a) with the capacity of the first heat sink (32a), and to balance the flow rate of refrigerant flowing through the second heat sink (32b) with the capacity of the second heat sink (32b). Accordingly, in this embodiment, it is possible to improve the operating efficiency of the refrigeration system (10) in the first and second single-stage compression operation.

[0148] -Features of Embodiment 2 (2)- In this embodiment, when the refrigeration device (10) switches the operation performed by the refrigeration device (10) from one to the other, the controller (90) first opens a valve that switches from a closed state to an open state, and then closes a valve that switches from an open state to a closed state. As a result, the refrigerant circuit (20) can be kept in a state where refrigerant flows while the operation performed by the refrigeration device (10) is being switched. As a result, a sudden rise in local pressure in the refrigerant circuit (20) can be prevented, and damage to the refrigerant circuit (20) can be avoided.

[0149] -Modification 1 of Embodiment 2- In the refrigerant circuit (20) of this embodiment, the second upstream valve (56) may be an on / off valve consisting of a solenoid valve.

[0150] -Modification 2 of Embodiment 2- In this embodiment, the controller may keep the first upstream valve (46) closed and control the opening degree of the second upstream valve (56) during the first single-stage compression operation and the second single-stage compression operation.

[0151] The controller (90) of this modified example controls the opening degree of the second upstream valve (56) so that the first index (specific enthalpy h1) and the second index (specific enthalpy h2) have the same value.

[0152] If the first indicator is higher than the second indicator, the controller (90) opens the second upstream valve (56) or increases the opening of the second upstream valve (56). When the second upstream valve (56) is open, a portion of the refrigerant discharged from the second compressor (31b) passes through the second upstream valve (56) and merges with the refrigerant flowing from the second piping (62) into the second upstream piping (51) (i.e., the refrigerant discharged from the first compressor (31a)). As a result, the flow rate of refrigerant flowing into the first radiator (32a) decreases, and the flow rate of refrigerant flowing into the second radiator (32b) increases. Consequently, the specific enthalpy h1 of the refrigerant at the outlet of the first radiator (32a) decreases, and the specific enthalpy h2 of the refrigerant at the outlet of the second radiator (32b) increases.

[0153] If the first indicator is lower than the second indicator, the controller (90) reduces the opening of the second upstream valve (56) or closes the second upstream valve (56). When the opening of the second upstream valve (56) is reduced, the flow rate of the refrigerant discharged from the second compressor (31b) that passes through the second upstream valve (56) decreases. As a result, the flow rate of refrigerant flowing into the first radiator (32a) increases, and the flow rate of refrigerant flowing into the second radiator (32b) decreases. Consequently, the specific enthalpy h1 of the refrigerant at the outlet of the first radiator (32a) increases, and the specific enthalpy h2 of the refrigerant at the outlet of the second radiator (32b) decreases.

[0154] If the first indicator matches the second indicator, the controller (90) maintains the opening of the first flow control valve (45) without changing it.

[0155] In the modified refrigeration device (10), the first upstream valve (46) may be an on / off valve consisting of a solenoid valve.

[0156] -Modification 3 of Embodiment 2- In the refrigeration device (10) of this embodiment, the controller (90) may use the temperature of the refrigerant at the outlet of the first heat sink (32a) as the first indicator and the temperature of the refrigerant at the outlet of the second heat sink (32b) as the second indicator. In this modified example, the controller (90) uses the measurement value of the first temperature sensor (86) as the first indicator and the measurement value of the second temperature sensor (87) as the second indicator.

[0157] Embodiment 3 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).

[0158] The refrigeration system (10) of this embodiment differs from the refrigeration system (10) of Embodiment 1 in the configuration of the refrigerant circuit (20) and the controller (90). Here, we will mainly explain the differences between the refrigerant circuit (20) and the controller (90) of this embodiment and those of Embodiment 1.

[0159] -Refrigerant Circuit- As shown in Figure 11, the refrigerant circuit (20) of this embodiment includes a first upstream valve (46), a second downstream valve (57), and a third pipe (63). On the other hand, in the refrigerant circuit (20) of this embodiment, the first flow control valve (45) and the second flow control valve (55) are omitted.

[0160] <First upstream valve, second downstream valve> The first upstream valve (46) is positioned between one end of the first pipe (61) in the first upstream piping (41) and the first radiator (32a). The second downstream valve (57) is positioned between the other end of the fourth pipe (64) in the second downstream piping (52) and the second radiator (32b). Both the first upstream valve (46) and the second downstream valve (57) are on-off valves made of solenoid valves.

[0161] <Third Piping> One end of the third piping (63) is connected between the first upstream valve (46) and the first radiator (32a) in the first upstream piping (41). The other end of the third piping (63) is connected between the second downstream valve (57) and the second radiator (32b) in the second downstream piping (52). A third valve (73) is provided in the third piping (63). The third valve (73) is an on / off valve consisting of a solenoid valve.

[0162] - Refrigeration System Operation - The refrigeration system (10) of this embodiment, like the refrigeration system (10) of Embodiment 1, selectively performs two-stage compression operation, first single-stage compression operation, and second single-stage compression operation.

[0163] <Two-stage compression operation> In the two-stage compression operation of the refrigeration system (10), the refrigerant circuit (20) performs a two-stage compression refrigeration cycle. In the two-stage compression operation, the first radiator (32a) functions as an intercooler, and the second radiator (32b) functions as a gas cooler.

[0164] In two-stage compression operation, the controller (90) controls the opening of the first expansion valve (33a) and the second expansion valve (33b), keeps the first upstream valve (46), the first downstream valve (47), and the second downstream valve (57) open, and keeps the first valve (71), the third valve (73), and the fifth valve (75) closed. The controller (90) also opens and closes the sixth valve (76) as needed.

[0165] The refrigerant flow path in the refrigerant circuit (20) will now be explained. As shown in Figure 12, the refrigerant flow path in the refrigerant circuit (20) of this embodiment is the same as the refrigerant flow path in the refrigerant circuit (20) of Embodiment 1 shown in Figure 4. The refrigerant that has passed through the evaporator (35) is compressed in the first compressor (31a), releases heat in the first heat sink (32a), is compressed in the second compressor (31b), releases heat in the second heat sink (32b), and absorbs heat in the evaporator (35).

[0166] <First Single-Stage Compression Operation> In the first single-stage compression operation of the refrigeration system (10), the refrigerant circuit (20) performs a single-stage compression refrigeration cycle. In the first single-stage compression operation, both the first compressor (31a) and the second compressor (31b) draw in the refrigerant that has passed through the evaporator (35). Also, in the first single-stage compression operation, both the first radiator (32a) and the second radiator (32b) function as condensers.

[0167] In the first single-stage compression operation, the controller (90) controls the opening of the first expansion valve (33a) and the second expansion valve (33b), keeps the first valve (71), the third valve (73), and the fifth valve (75) in the open state, and keeps the first upstream valve (46), the first downstream valve (47), the second downstream valve (57), and the sixth valve (76) in the closed state.

[0168] The refrigerant flow path in the refrigerant circuit (20) will be explained with reference to Figure 13.

[0169] The refrigerant discharged from the first compressor (31a) flows through the first piping (61) into the second upstream piping (51). The refrigerant discharged from the second compressor (31b) flows through the second upstream piping (51) and merges with the refrigerant flowing in from the first piping (61). In this way, in the first single-stage compression operation, the refrigerant discharged from the first compressor (31a) and the refrigerant discharged from the second compressor (31b) merge. The merged refrigerant then flows into the second radiator (32b).

[0170] The refrigerant flowing into the second radiator (32b) releases heat into the outside air. The refrigerant that has passed through the second radiator (32b) flows through the third pipe (63) into the first radiator (32a) and releases heat into the outside air. The refrigerant that has passed through the first radiator (32a) flows through the fourth pipe (64) into the second downstream pipe (52), and then into the first expansion valve (33a). The refrigerant that has flowed into the first expansion valve (33a) expands as it passes through the first expansion valve (33a), and then flows into the receiver (34). The refrigerant that has flowed out of the receiver (34) is depressurized as it passes through the second expansion valve (33b), and then flows into the evaporator (35).

[0171] The refrigerant flowing into the evaporator (35) absorbs heat from the air inside the storage compartment and evaporates. The air cooled in the evaporator (35) is blown out from the refrigeration unit (10) into the storage compartment space (5). A portion of the refrigerant that has passed through the evaporator (35) is drawn into the first compressor (31a), and the remainder is drawn into the second compressor (31b) through the fifth pipe (65). The first compressor (31a) and the second compressor (31b) each compress the drawn-in refrigerant and discharge it.

[0172] <Second Single-Stage Compression Operation> In the second single-stage compression operation of the refrigeration system (10), the refrigerant circuit (20) performs a single-stage compression refrigeration cycle. In the second single-stage compression operation, the first compressor (31a) draws in the refrigerant that has passed through the evaporator (35), and the second compressor (31b) draws in the gaseous refrigerant that has flowed out from the receiver (34). In addition, in the second single-stage compression operation, both the first radiator (32a) and the second radiator (32b) function as condensers.

[0173] In the second single-stage compression operation, the controller (90) controls the opening of the first expansion valve (33a) and the second expansion valve (33b), keeps the first valve (71), the third valve (73), and the sixth valve (76) in the open state, and keeps the first upstream valve (46), the first downstream valve (47), the second downstream valve (57), and the fifth valve (75) in the closed state.

[0174] The refrigerant flow path in the refrigerant circuit (20) will be explained with reference to Figure 14. Here, we will explain the differences between the refrigerant flow path in the refrigerant circuit (20) during the second single-stage compression operation and the refrigerant flow path in the refrigerant circuit (20) during the first single-stage compression operation.

[0175] All of the refrigerant that has passed through the evaporator (35) is drawn into the first compressor (31a). The gaseous refrigerant in the receiver (34) flows through the sixth pipe (66) into the first downstream pipe (42), and is then drawn into the second compressor (31b). The refrigerant flow path in the refrigerant circuit (20) during second single-stage compression operation is the same as the refrigerant flow path in the refrigerant circuit (20) during first single-stage compression operation, except for the two points mentioned above.

[0176] -Controller Operation- The control operation performed by the controller (90) is described below.

[0177] First, the control operation when the controller (90) switches the operating state of the refrigeration system (10) from two-stage compression operation to first single-stage compression operation or second single-stage compression operation will be explained. In this case, the controller (90) opens the first valve (71), third valve (73), and fifth valve (75), which were closed in the two-stage compression operation, and then closes the first upstream valve (46), first downstream valve (47), and second downstream valve (57), which were open in the two-stage compression operation.

[0178] Next, the control operation when the controller (90) switches the operating state of the refrigeration system (10) from first single-stage compression operation or second single-stage compression operation to two-stage compression operation will be described. In this case, the controller (90) opens the first upstream valve (46), the first downstream valve (47), and the second downstream valve (57), which were closed in the first or second single-stage compression operation, and then closes the first valve (71), the third valve (73), and the fifth valve (75), which were open in the first or second single-stage compression operation.

[0179] Thus, when the controller (90) switches the operation performed by the refrigeration system (10) from two-stage compression operation to single-stage compression operation, it first opens a valve that switches from a closed state to an open state, and then closes a valve that switches from an open state to a closed state.

[0180] -Features of Embodiment 3 (1)- In the first and second single-stage compression operation performed by the refrigeration system (10) of this embodiment, the refrigerant discharged from the first compressor (31a) and the refrigerant discharged from the second compressor (31b) merge. The merged refrigerant dissipates heat in the second heat exchanger (32b) and then flows into the first heat exchanger (32a).

[0181] Thus, in the first and second single-stage compression operations of this embodiment, the refrigerant dissipates heat in the second heat sink (32b), which has a relatively larger capacity, and becomes denser before flowing into the first heat sink (32a), which has a relatively smaller capacity. Therefore, the flow velocity of the refrigerant in the first heat sink (32a) is lower than when the refrigerant flows sequentially through the first heat sink (32a) and the second heat sink (32b).

[0182] Accordingly, according to this embodiment, even when both the refrigerant discharged from the first compressor (31a) and the refrigerant discharged from the second compressor (31b) flow through the first radiator (32a) during the first and second single-stage compression operation, the pressure loss of the refrigerant in the first radiator (32a) can be kept low. As a result, it is possible to improve the operating efficiency of the refrigeration system (10) during the first and second single-stage compression operation.

[0183] -Features of Embodiment 3 (2)- In this embodiment, when the refrigeration device (10) switches the operation performed by the refrigeration device (10) from one to the other, the controller (90) first opens a valve that switches from a closed state to an open state, and then closes a valve that switches from an open state to a closed state. As a result, the refrigerant circuit (20) can be kept in a state where refrigerant flows while the operation performed by the refrigeration device (10) is being switched. As a result, a sudden rise in local pressure in the refrigerant circuit (20) can be prevented, and damage to the refrigerant circuit (20) can be avoided.

[0184] 《Other Embodiments》 The following modifications may be applied to the refrigeration apparatus of the above embodiment. The following modifications may be combined or substituted as appropriate, as long as they do not impair the function of the refrigeration apparatus.

[0185] -First Modification- The use of the refrigeration device (10) in each of the above embodiments is not limited to a transport refrigeration device installed in a transport container (1). The refrigeration device (10) in each of the above embodiments may be used to cool the air inside a refrigerator or cold storage warehouse. Furthermore, the refrigeration device (10) in each of the above embodiments may be used as an air conditioner to conditioned the air in indoor spaces such as buildings.

[0186] -Second Modification- In the refrigeration apparatus (10) of each of the above embodiments, the refrigerant filled into the refrigerant circuit (20) is not limited to carbon dioxide. The refrigerant filled into the refrigerant circuit (20) may be a fluorocarbon refrigerant such as R22, R23, R32, R404A, R410A, for example.

[0187] -Third Modification- The refrigeration device (10) of each of the above embodiments may include a first external fan that sends outside air (outside air) to a first heat sink (32a), and a second external fan that sends outside air (outside air) to a second heat sink (32b). In this modified refrigeration device (10), when the first external fan is activated, outside air passes through the first heat sink (32a), and when the second external fan is activated, outside air passes through the second heat sink (32b).

[0188] While embodiments and modifications have been described above, it should 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.

[0189] As described above, this disclosure is useful for refrigeration equipment and transport containers.

[0190] 1. Transport container 2. Container body 5. Interior space (target space) 10. Refrigeration system 20. Refrigerant circuit 31a. First compressor 31b. Second compressor 32a. First radiator 32b. Second radiator 33. Expansion valve 35. Evaporator 41. First upstream piping 42. First downstream piping 45. First flow control valve 46. First upstream valve 47. First downstream valve 51. Second upstream piping 52. Second downstream piping 55. Second flow control valve 56. Second upstream valve 57. Second downstream valve 61. First piping 62. Second piping 63. Third piping 64. Fourth piping 71. First valve 72. Second valve 73. Third valve 74. Fourth valve 90. Controller

Claims

1. A refrigeration system (10) comprising a refrigerant circuit (20) having a first compressor (31a), a second compressor (31b), a first radiator (32a), a second radiator (32b), an expansion valve (33), and an evaporator (35), wherein the refrigerant circuit (20) performs a two-stage compression operation in which it performs a two-stage compression refrigeration cycle, and a single-stage compression operation in which it performs a single-stage compression refrigeration cycle, wherein during the execution of the two-stage compression operation, the refrigerant circuit (20) has the first compressor (31a) suck in the refrigerant flowing out from the evaporator (35), and the refrigerant discharged from the first compressor (31a) flows sequentially through the first radiator (32a), the second compressor (31b), and the second radiator (32b), During the execution of the above single-stage compression operation, in the refrigerant circuit (20), both the first compressor (31a) and the second compressor (31b) draw in the refrigerant flowing out from the evaporator (35), and the refrigerant discharged from the first compressor (31a) and the refrigerant discharged from the second compressor (31b) flow through one or both of the first radiator (32a) and the second radiator (32b), and the refrigerant circuit (20) includes: a first upstream pipe (41) connecting the discharge port of the first compressor (31a) to the inlet of the first radiator (32a), a second upstream pipe (51) connecting the discharge port of the second compressor (31b) to the inlet of the second radiator (32b), and a first pipe (61) with one end connected to the first upstream pipe (41) and the other end connected to the second upstream pipe (51), A refrigeration apparatus having a first valve (71) provided in the first pipe (61) described above.

2. The refrigeration apparatus according to claim 1, further comprising a controller (90) that closes the first valve (71) during the two-stage compression operation and opens the first valve (71) during the single-stage compression operation.

3. The refrigeration apparatus according to claim 1, wherein, during the execution of the single-stage compression operation described above, the refrigerant discharged from the first heat exchanger (32a) and the refrigerant discharged from the second heat exchanger (32b) in the refrigerant circuit (20) merge and then flow into the expansion valve (33).

4. The refrigeration apparatus according to claim 3, wherein the refrigerant circuit (20) is provided upstream or downstream of the first heat exchanger (32a) and includes a first flow control valve (45) for adjusting the flow rate of the refrigerant flowing through the first heat exchanger (32a).

5. The refrigeration apparatus according to claim 4, comprising a controller (90), wherein the controller (90) closes the first valve (71) during the execution of the two-stage compression operation, opens the first valve (71) during the execution of the single-stage compression operation, and controls the opening degree of the first flow control valve (45) based on a first indicator that shows the state of the refrigerant at the outlet of the first heat exchanger (32a).

6. The refrigeration apparatus according to claim 3 or 4, wherein the refrigerant circuit (20) is provided upstream or downstream of the second heat exchanger (32b) and includes a second flow control valve (55) for adjusting the flow rate of the refrigerant flowing through the second heat exchanger (32b).

7. The refrigeration apparatus according to claim 6, comprising a controller (90), wherein the controller (90) closes the first valve (71) during the execution of the two-stage compression operation, opens the first valve (71) during the execution of the single-stage compression operation, and controls the opening degree of the second flow control valve (55) based on a second indicator that shows the state of the refrigerant at the outlet of the second heat exchanger (32b).

8. The refrigeration apparatus according to claim 1, wherein, during the execution of the single-stage compression operation described above, in the refrigerant circuit (20), the refrigerant discharged from the first compressor (31a) flows into the second heat sink (32b), the refrigerant discharged from the second compressor (31b) flows into the first heat sink (32a), and the refrigerant discharged from the first heat sink (32a) and the refrigerant discharged from the second heat sink (32b) merge and then flow into the expansion valve (33).

9. The refrigeration apparatus according to claim 1, wherein the refrigerant circuit (20) comprises: a first upstream valve (46) provided between one end of the first pipe (61) in the first upstream piping (41) and the first compressor (31a); a second upstream valve (56) provided between the other end of the first pipe (61) in the second upstream piping (51) and the second radiator (32b); a second pipe (62) having one end connected between the first upstream valve (46) and the first compressor (31a) in the first upstream piping (41) and the other end connected between the second upstream valve (56) and the second radiator (32b) in the second upstream piping (51); and a second valve (72) provided in the second pipe (62).

10. The refrigeration apparatus according to claim 9, comprising a controller (90), wherein the controller (90) opens the first upstream valve (46) and the second upstream valve (56) and closes the first valve (71) and the second valve (72) during the execution of the two-stage compression operation, and opens the first valve (71) and the second valve (72) and closes the first upstream valve (46) and the second upstream valve (56) during the execution of the single-stage compression operation.

11. The refrigeration apparatus according to claim 10, wherein the controller (90) opens the first valve (71) and the second valve (72) when switching the operation performed by the refrigeration apparatus (10) from the two-stage compression operation to the single-stage compression operation, and then closes the first upstream valve (46) and the second upstream valve (56), and opens the first upstream valve (46) and the second upstream valve (56) when switching the operation performed by the refrigeration apparatus (10) from the single-stage compression operation to the two-stage compression operation, and then closes the first valve (71) and the second valve (72).

12. The refrigeration apparatus according to claim 9, comprising a controller (90), wherein the controller (90) opens the first upstream valve (46) and the second upstream valve (56) and closes the first valve (71) and the second valve (72) during the execution of the two-stage compression operation, and opens the first valve (71) and the second valve (72) during the execution of the single-stage compression operation, controls the opening degree of one of the first upstream valve (46) and the second upstream valve (56) based on a first indicator indicating the state of the refrigerant at the outlet of the first radiator (32a) and a second indicator indicating the state of the refrigerant at the outlet of the second radiator (32b), and closes the other of the first upstream valve (46) and the second upstream valve (56).

13. The refrigeration apparatus according to claim 1, wherein, during the execution of the single-stage compression operation described above, the refrigerant discharged from the first compressor (31a) and the refrigerant discharged from the second compressor (31b) merge in the refrigerant circuit (20) and then flow sequentially through the second heat exchanger (32b) and the first heat exchanger (32a).

14. The above refrigerant circuit (20) includes: a first downstream pipe (42) connecting the outlet of the first radiator (32a) to the inlet of the second compressor (31b); a first downstream valve (47) provided in the first downstream pipe (42); a second downstream pipe (52) connecting the outlet of the second radiator (32b) to the expansion valve (33); a second downstream valve (57) provided in the second downstream pipe (52); and a first upstream valve (46) provided between one end of the first pipe (61) and the first radiator (32a) in the first upstream pipe (41). A refrigeration apparatus according to claim 1, comprising: a third pipe (63) having one end connected between the first upstream valve (46) and the first radiator (32a) in the first upstream pipe (41), and the other end connected between the second radiator (32b) and the second downstream valve (57) in the second downstream pipe (52); a third valve (73) provided in the third pipe (63); a fourth pipe (64) having one end connected between the first radiator (32a) and the first downstream valve (47) in the first downstream pipe (42), and the other end connected between the second downstream valve (57) and the expansion valve (33) in the second downstream pipe (52); and a fourth valve (74) provided in the fourth pipe (64).

15. The refrigeration apparatus according to claim 14, wherein the fourth valve (74) is a check valve that allows the flow of refrigerant from one end of the fourth pipe (64) to the other end and prevents the flow of refrigerant from the other end of the fourth pipe (64) to the one end, and comprises a controller (90), the controller (90) opens the first upstream valve (46) and the second downstream valve (57) and closes the first valve (71) and the third valve (73) during the execution of the two-stage compression operation, and opens the first valve (71) and the third valve (73) and closes the first upstream valve (46) and the second downstream valve (57) during the execution of the single-stage compression operation.

16. The refrigeration apparatus according to claim 15, wherein the controller (90) opens the first valve (71) and the third valve (73) when switching the operation performed by the refrigeration apparatus (10) from the two-stage compression operation to the single-stage compression operation, and then closes the first upstream valve (46) and the second downstream valve (57), and opens the first upstream valve (46) and the second downstream valve (57) when switching the operation performed by the refrigeration apparatus (10) from the single-stage compression operation to the two-stage compression operation, and then closes the first valve (71) and the third valve (73).

17. The refrigeration apparatus according to any one of claims 1 to 16, wherein the refrigerant filled in the refrigerant circuit (20) is carbon dioxide.

18. A transport container comprising a refrigeration device (10) according to any one of claims 1 to 17, and a container body (2) that forms a target space (5) where air conditioning is performed by the refrigeration device (10).

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