Refrigeration cycle device

Abstract

To suppress a liquefied refrigerant flowing into a compressor.SOLUTION: A refrigeration cycle device (1) includes a first circuit (10), a second circuit (20), and a control part (6). The first circuit (10) includes a first compressor (11), a first heat exchanger (12), a first expansion mechanism (13), and a cascade heat exchanger (30). In the first circuit (10), a first refrigerant circulates. The second circuit (20) includes a second compressor (21), a second heat exchanger (23), the cascade heat exchanger (30), a second expansion mechanism (24) and a third heat exchanger (25). In the second circuit (20), a second refrigerant circulates. The control part (6) performs stop control for collecting the first refrigerant in the first heat exchanger (12) before stopping the operation of the first circuit (10).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This relates to a refrigeration cycle device. [Background technology]

[0002] Patent document 1 (Patent No. 5430604) discloses that in a dual-stage refrigeration system equipped with a low-stage refrigeration cycle using carbon dioxide refrigerant and a high-stage refrigeration cycle that assists in heat dissipation from the low-stage refrigeration cycle, the evaporator of the high-stage refrigeration cycle and the condenser of the low-stage refrigeration cycle exchange heat using a cascade condenser. Summary of the Invention [Problem to be solved by the invention]

[0003] However, the present inventors have focused on a problem in the cascade refrigeration system of Patent Document 1, that is, there is a risk of liquid refrigerant flowing into the compressor. [Means for solving the problem]

[0004] The inventors discovered that the above problem is caused by the fact that when the high-temperature refrigeration cycle is stopped, the evaporator of the high-temperature refrigeration cycle in the cascade condenser is cooled and the refrigerant liquefies. If the high-temperature refrigeration cycle is operated in this state, the liquefied refrigerant will flow into the compressor.

[0005] Therefore, a refrigeration cycle device according to a first aspect includes a first circuit, a second circuit, and a control unit. The first circuit includes a first compressor, a first heat exchanger, a first expansion mechanism, and a cascade heat exchanger. A first refrigerant circulates through the first circuit. The second circuit includes a second compressor, a second heat exchanger, the cascade heat exchanger, a second expansion mechanism, and a third heat exchanger. A second refrigerant circulates through the second circuit. The control unit performs stop control to collect the first refrigerant in the first heat exchanger before stopping operation of the first circuit.

[0006] In the refrigeration cycle apparatus of the first aspect, the control unit performs stop control to collect the first refrigerant in the first heat exchanger before stopping the operation of the first circuit, so that the first refrigerant collected in the cascade heat exchanger can be reduced. Therefore, the first refrigerant in the cascade heat exchanger can be prevented from liquefying while the first circuit is stopped. Since the first circuit is operated in this state, it is possible to prevent the liquefied first refrigerant from flowing into the first compressor.

[0007] A refrigeration cycle apparatus according to a second aspect is the refrigeration cycle apparatus according to the first aspect, wherein the control unit operates the second circuit prior to the first circuit during cooling operation.

[0008] In the refrigeration cycle apparatus of the second aspect, by operating the second circuit before the first circuit, when the second refrigerant passes through the cascade heat exchanger after passing through the second heat exchanger of the second circuit, heat can be imparted to the first refrigerant collected in the cascade heat exchanger. This heat can heat the first refrigerant, making it possible to further suppress the liquefied first refrigerant from flowing into the first compressor.

[0009] A refrigeration cycle apparatus according to a third aspect is the refrigeration cycle apparatus according to the second aspect, in which the operation of the first circuit is started when the difference between the inlet temperature and the outlet temperature of the cascade heat exchanger in the second circuit becomes equal to or less than a certain value.

[0010] In the refrigeration cycle apparatus of the third aspect, when the difference between the inlet temperature and the outlet temperature of the cascade heat exchanger in the second circuit becomes equal to or smaller than a certain value, it is determined that the heat of the second refrigerant is transferred to the first refrigerant in the cascade heat exchanger and the first refrigerant is vaporized. Since the first circuit is operated in this state, it is possible to further suppress the liquefied first refrigerant from flowing into the first compressor.

[0011] A refrigeration cycle apparatus according to a fourth aspect is the refrigeration cycle apparatus according to the second aspect, wherein the control unit starts the operation of the first circuit after a predetermined time has elapsed since the start of the operation of the second circuit.

[0012] In the refrigeration cycle apparatus of the fourth aspect, when a predetermined time has elapsed since the second circuit began operating, it is determined that heat from the second refrigerant has been transferred to the first refrigerant in the cascade heat exchanger, causing the first refrigerant to evaporate. Since the first circuit is operated in this state, it is possible to further prevent the liquefied first refrigerant from flowing into the first compressor.

[0013] A refrigeration cycle apparatus according to a fifth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the fourth aspect, in which the opening degree of the first expansion mechanism is increased after the first compressor is started.

[0014] In the refrigeration cycle apparatus of the fifth aspect, since the opening degree of the first expansion mechanism is not increased when the first compressor is started, the first refrigerant in the first circuit can be prevented from flowing directly into the first compressor, thereby making it possible to further prevent the liquefied first refrigerant from flowing into the first compressor.

[0015] A refrigeration cycle apparatus of a sixth aspect is the refrigeration cycle apparatus of the fifth aspect, wherein the control unit starts the second compressor, then increases the opening degree of the second expansion mechanism, then starts the first compressor, and then increases the opening degree of the first expansion mechanism.

[0016] As in the refrigeration cycle apparatus of the sixth aspect, by controlling the second compressor, the second expansion mechanism, the first compressor and the first expansion mechanism in that order, it is possible to operate the first circuit and the second circuit while suppressing the flow of liquefied first refrigerant into the first compressor.

[0017] A refrigeration cycle apparatus according to a seventh aspect is the refrigeration cycle apparatus according to any one of the first aspect to the sixth aspect, wherein the control unit controls an operation of the first circuit and an operation of the second circuit.

[0018] As in the refrigeration cycle apparatus of the seventh aspect, the control section of the second circuit may control the first circuit.

[0019] A refrigeration cycle apparatus according to an eighth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the seventh aspect, wherein the first heat exchanger is a flat multi-hole tube.

[0020] In the refrigeration cycle apparatus of the eighth aspect, the flat multi-hole tube as the first heat exchanger can be made small in volume, so that the amount of the first refrigerant can be reduced, and therefore the amount of the first refrigerant collected in the cascade heat exchanger can be reduced.

[0021] A refrigeration cycle apparatus according to a ninth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the eighth aspect, further comprising a fan that sends outdoor air to the first heat exchanger and the second heat exchanger.

[0022] In the refrigeration cycle device of the ninth aspect, since a fan that sends outdoor air to the first heat exchanger and the second heat exchanger is common, outdoor air flows into the first heat exchanger when the second circuit is operating even if the first circuit is stopped. Therefore, the first refrigerant collected in the first heat exchanger exchanges heat with the outdoor air, making it easier to collect the liquefied first refrigerant in the first heat exchanger. This makes it possible to further suppress the liquefied first refrigerant from flowing into the first compressor.

[0023] A refrigeration cycle apparatus according to a tenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the ninth aspect, wherein the first circuit further includes an accumulator.

[0024] In the refrigeration cycle apparatus of the tenth aspect, the liquefied first refrigerant can be stored in the accumulator, and therefore the liquefied first refrigerant can be further prevented from flowing into the first compressor.

[0025] A refrigeration cycle apparatus of an eleventh aspect is the refrigeration cycle apparatus of any one of the first aspect to the tenth aspect, in which the control unit fully closes the first expansion mechanism while the second circuit is in operation and the first circuit is stopped.

[0026] When the second circuit is operating and the first circuit is stopped, the first refrigerant is likely to be cooled in the cascade heat exchanger. In this case, in the refrigeration cycle device of the eleventh aspect, the first expansion mechanism is fully closed, thereby reducing the first refrigerant flowing into the cascade heat exchanger. This makes it possible to further suppress the liquefied first refrigerant from flowing into the first compressor.

[0027] A refrigeration cycle apparatus according to a twelfth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the eleventh aspect, wherein the control unit performs a heating operation and a cooling operation.

[0028] In the refrigeration cycle apparatus of the twelfth aspect, by stopping the operation of the first circuit during heating operation, the first refrigerant collected in the cascade heat exchanger is likely to liquefy, which can easily cause a problem that the liquefied first refrigerant flows into the first compressor. Even in a case where this problem is likely to occur, by performing stop control, it is possible to prevent the liquefied first refrigerant from flowing into the first compressor.

[0029] A refrigeration cycle apparatus according to a thirteenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the twelfth aspect, wherein the first refrigerant is flammable, toxic, or has a GWP (global warming potential) of more than 500.

[0030] As in the refrigeration cycle apparatus of the thirteenth aspect, a first refrigerant that is flammable, toxic, or has a GWP exceeding 500 may be used. [Brief description of the drawings]

[0031] [Figure 1] 1 is a schematic configuration diagram of a refrigeration cycle device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the outdoor unit. [Diagram 3] FIG. 2 is a schematic perspective view of a first heat exchanger. [Figure 4] FIG. 2 is a control block diagram of the refrigeration cycle device. [Diagram 5] FIG. 4 is a diagram showing the operation of the refrigeration cycle device in a heating operation. [Figure 6] FIG. 4 is a diagram showing the operation of the refrigeration cycle device in cooling operation. [Figure 7] 4 is a flowchart of a stop control. [Figure 8] 4 is a flowchart of start control. [Figure 9]13 is a flowchart of start control of Modification 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] (1) Overall structure As shown in FIG. 1, a refrigeration cycle apparatus 1 according to an embodiment of the present disclosure is an apparatus used for cooling and heating a room in a building or the like by performing a vapor compression refrigeration cycle operation.

[0033] The refrigeration cycle device 1 includes a first circuit 10, a second circuit 20, and a control unit 6. The refrigeration cycle device 1 of the present embodiment has a binary refrigerant circuit consisting of a vapor compression type first circuit 10 and a vapor compression type second circuit 20, and performs a binary refrigeration cycle.

[0034] A first refrigerant circulates through the first circuit 10. A second refrigerant circulates through the second circuit 20. The first circuit 10 and the second circuit 20 are thermally connected via a cascade heat exchanger 30.

[0035] The refrigeration cycle apparatus 1 includes an outdoor unit 2 and an indoor unit 3. The refrigeration cycle apparatus 1 is configured such that the outdoor unit 2 and the indoor unit 3 are connected to each other via communication pipes 4 and 5.

[0036] Before stopping the operation of the first circuit 10, the control unit 6 performs a stop control to collect the first refrigerant in the first heat exchanger 12.

[0037] (2) Detailed configuration (2-1) 1st circuit The first refrigerant flowing through the first circuit 10 is not particularly limited, but here, is flammable, toxic, or has a GWP exceeding 500. The first refrigerant is, for example, a hydrocarbon refrigerant such as R1234yf, R1234ze, or R32, and is R290 in this embodiment.

[0038] The first circuit 10 constitutes a subcooling circuit during cooling operation. The first circuit is an assist circuit that assists the capacity of the second circuit 20 during cooling operation.

[0039] The first circuit 10 includes a first compressor 11, a first heat exchanger 12, a first expansion mechanism 13, a first accumulator 14, and a cascade heat exchanger 30.

[0040] The first compressor 11 is a device for compressing the first refrigerant, and is, for example, a positive displacement compressor such as a scroll type compressor whose operating capacity can be varied by inverter controlling the compressor motor.

[0041] The first heat exchanger 12 is a device for exchanging heat between the first refrigerant and the outdoor air. In the first heat exchanger 12, the first refrigerant obtains cold or hot heat from the outdoor air. The first heat exchanger 12 is, for example, a flat multi-hole tube as shown in FIG. 3.

[0042] The first expansion mechanism 13 is a device that reduces the pressure of the first refrigerant, and is, for example, an electric expansion valve.

[0043] The first accumulator 14 is provided in the middle of a suction flow passage that connects the cascade heat exchanger 30 and the suction side of the first compressor 11. The first accumulator 14 separates the flowing refrigerant into liquid refrigerant and gas refrigerant, and allows only the gas refrigerant to flow to the suction side of the first compressor 11.

[0044] In this embodiment, a normal accumulator is omitted, and the first accumulator 14 is a sub-accumulator that accompanies a normal accumulator. Specifically, the volume of the first accumulator 14 is half or less of the volume of the second accumulator 26 of the second circuit 20 described later.

[0045] The cascade heat exchanger 30 is a device for performing heat exchange between a first refrigerant and a second refrigerant without mixing them. The cascade heat exchanger 30 is, for example, a plate-type heat exchanger. The cascade heat exchanger 30 has a first flow path 31 belonging to the first circuit 10 and a second flow path 32 belonging to the second circuit 20. The first flow path 31 is connected on the gas side to the first compressor 11 and on the liquid side to the first expansion mechanism 13.

[0046] When the first heat exchanger 12 is used as a radiator and the second heat exchanger 23 of the second circuit 20 described later is used as a radiator, the cascade heat exchanger 30 has the purpose of supercooling the second refrigerant cooled in the second heat exchanger 23, and plays the role of assisting the second circuit 20.

[0047] (2-2) Second circuit The second refrigerant flowing through the second circuit 20 is not particularly limited and may be the same as the first refrigerant or may be different from the first refrigerant. Here, the second refrigerant is non-flammable, non-toxic, or has a GWP of 500 or less. The second refrigerant is, for example, a natural refrigerant, and in this embodiment, is carbon dioxide.

[0048] The second circuit 20 is a main circuit configured to heat or cool indoor air with a second refrigerant.

[0049] The second circuit 20 includes a second compressor 21, a switching mechanism 22, a second heat exchanger 23, a cascade heat exchanger 30, a second expansion mechanism 24, a third heat exchanger 25, and a second accumulator 26.

[0050] The second compressor 21 is a device for compressing the second refrigerant, and is, for example, a positive displacement compressor such as a scroll type compressor whose operating capacity can be varied by inverter controlling the compressor motor.

[0051] The switching mechanism 22 is a device that switches between a first state (see the solid line of the switching mechanism 22 in FIG. 1) in which the second heat exchanger 23 functions as a radiator of the second refrigerant and the third heat exchanger 25 functions as an evaporator of the second refrigerant, and a second state (see the dashed line of the switching mechanism 22 in FIG. 1) in which the second heat exchanger 23 functions as an evaporator of the second refrigerant and the third heat exchanger 25 functions as a radiator of the second refrigerant. The switching mechanism 22 is, for example, a four-way switching valve. In the first state, the switching mechanism 22 connects the discharge side of the second compressor 21 to the gas side of the second heat exchanger 23, and connects the suction side of the second compressor 21 to the gas side of the third heat exchanger 25. In addition, in the second state, the switching mechanism 22 connects the discharge side of the second compressor 21 to the gas side of the third heat exchanger 25, and also connects the suction side of the second compressor 21 to the gas side of the second heat exchanger 23.

[0052] The second heat exchanger 23 is a device for exchanging heat between the second refrigerant and the outdoor air. In the second heat exchanger 23, the second refrigerant obtains cold or hot heat from the outdoor air. The second heat exchanger 23 is, for example, a cross fin tube type heat exchanger.

[0053] The second circuit 20 has a second flow path 32 of a cascade heat exchanger 30. In the second state, the second flow path 32 is connected on its gas side to the second heat exchanger 23 and on its liquid side to the third heat exchanger 25.

[0054] The second expansion mechanism 24 is a device that reduces the pressure of the second refrigerant, and is, for example, an electric expansion valve.

[0055] The third heat exchanger 25 is a device for exchanging heat between the second refrigerant and the indoor air, and is, for example, a fin-and-tube heat exchanger.

[0056] The second accumulator 26 is provided in the middle of the suction flow path that connects the switching mechanism 22 and the suction side of the second compressor 21. The second accumulator 26 separates the flowing refrigerant into liquid refrigerant and gas refrigerant, and allows only the gas refrigerant to flow to the suction side of the second compressor 21.

[0057] (2-3) Outdoor unit In the following description, expressions indicating directions such as "up", "down", and "front" are used as appropriate, and these indicate the directions when the outdoor unit 2 is installed outdoors and in normal use. In this embodiment, the up and down direction is the vertical direction.

[0058] The outdoor unit 2 is disposed in a space different from the space in which the indoor unit 3 is disposed. Here, the outdoor unit 2 is installed outdoors (on the roof of a building, near the exterior wall surface of a building, etc.).

[0059] The outdoor unit 2 has the above-mentioned first circuit 10, a part of the second circuit 20, a casing 41, an electrical equipment unit 42, a fan 43, a partition plate 44, a separation plate 45, and various sensors. Specifically, the outdoor unit 2 has the first compressor 11, the first heat exchanger 12, the first expansion mechanism 13, the second compressor 21, the switching mechanism 22, the second heat exchanger 23, the second expansion mechanism 24, the second accumulator 26, the cascade heat exchanger 30, an inlet temperature sensor 46, an outlet temperature sensor 47, the casing 41, the electrical equipment unit 42, the fan 43, the partition plate 44, and the separation plate 45 shown in FIG.

[0060] The casing 41 houses the first compressor 11, the first heat exchanger 12, the first expansion mechanism 13, the second compressor 21, the switching mechanism 22, the second heat exchanger 23, the second expansion mechanism 24, the second accumulator 26, the cascade heat exchanger 30, an electrical equipment unit 42, a fan 43, a partition plate 44, a separation plate 45, and various sensors.

[0061] 2 has a substantially rectangular parallelepiped shape. Specifically, the casing 41 includes a front plate 411, a top plate 412, a bottom plate 413, and side plates 414.

[0062] The front plate 411 is a plate-like member that constitutes the front surface of the casing 41. An air outlet is formed in the front plate 411. The air outlet is an opening for blowing out the outdoor air taken in from the outside of the casing 41 to the inside of the casing 41 to the outside of the casing 41.

[0063] The top plate 412 is a plate-like member that forms the upper surface of the casing 41. The bottom plate 413 is a plate-like member that forms the lower surface of the casing 41. The top plate 412 and the bottom plate 413 face each other.

[0064] The side plate 414 is a plate-like member that constitutes the side surface of the casing 41. The lower portion of the side plate 414 is fixed to the bottom plate 413.

[0065] The electrical equipment unit 42 has electrical equipment mounted on a board. The electrical equipment controls controlled objects such as the first compressor 11, the second compressor 21, the first expansion mechanism 13, the switching mechanism 22, the second expansion mechanism 24, etc.

[0066] The fan 43 causes air to flow through the first heat exchanger 12 and the second heat exchanger 23. In this embodiment, the fan 43 causes outdoor air to flow through both the first heat exchanger 12 and the second heat exchanger 23. Here, the fan 43 generates an air flow in which the outdoor air is guided to the first heat exchanger 12 and the second heat exchanger 23, where it is heat exchanged with the first refrigerant in the first heat exchanger 12 and with the second refrigerant in the second heat exchanger 23, and then discharged to the outside. In FIG. 2, the fan 43 overlaps the first heat exchanger 12 and the second heat exchanger 23 when viewed from the front. The fan 43 is driven by a fan motor.

[0067] Note that a fan for blowing air through the first heat exchanger 12 and a fan for blowing air through the second heat exchanger 23 may be provided separately.

[0068] The partition plate 44 is a plate-like member extending in the vertical direction. A lower portion of the partition plate 44 is fixed to the bottom plate 413 of the casing 41.

[0069] The partition plate 44 divides the inside of the casing 41 into a first chamber S1 and a second chamber S2. Each of the first chamber S1 and the second chamber S2 is a space defined by the partition plate 44 and a front plate 411, a top plate 412, a bottom plate 413, and a side plate 414 of the casing 41.

[0070] Here, the first chamber S1 is an air blowing chamber and an air guide passage through which air drawn in from an inlet of the outdoor unit 2 flows to an outlet. In this embodiment, the first heat exchanger 12, the second heat exchanger 23, the fan 43, and the like are disposed in the first chamber S1.

[0071] The second chamber S2 is a machine chamber in which the first compressor 11, the second compressor 21, the switching mechanism 22, the first expansion mechanism 13, the second expansion mechanism 24, the second accumulator 26, the cascade heat exchanger 30, the electrical equipment unit 42, etc. are disposed.

[0072] The separation plate 45 divides the second chamber S2 into a first machine chamber S21 constituting the first circuit 10 and a second machine chamber S22 constituting the second circuit 20. The separation plate 45 is a plate-shaped member extending in the vertical direction. The lower part of the separation plate 45 is fixed to the bottom plate 413 of the casing 41. Here, the first compressor 11, the first expansion mechanism 13, the cascade heat exchanger 30, etc. are arranged in the first machine chamber S21 divided by the front plate 411, the top plate 412, the bottom plate 413, the side plate 414, and the separation plate 45. The second compressor 21, the switching mechanism 22, the second expansion mechanism 24, the second accumulator 26, the electrical equipment unit 42, etc. are arranged in the second machine chamber S22 divided by the front plate 411, the top plate 412, the bottom plate 413, the partition plate 44, and the separation plate 45.

[0073] During cooling operation, the inlet temperature sensor 46 detects the temperature of the second refrigerant before it flows into the cascade heat exchanger 30. During cooling operation, the outlet temperature sensor 47 detects the temperature of the second refrigerant after it has passed through the cascade heat exchanger 30.

[0074] (2-4) Indoor unit The indoor unit 3 is installed indoors (inside the building). As described above, the indoor unit 3 is connected to the outdoor unit 2 via the connection pipes 4 and 5, and constitutes a part of the second circuit 20.

[0075] As shown in Fig. 1, the indoor unit 3 has a third heat exchanger 25. Here, the indoor unit 3 is installed by embedding or hanging from a ceiling in a room of a building or the like, or by hanging from a wall surface in the room.

[0076] (2-5) Connecting piping The connecting pipes 4, 5 are refrigerant pipes that are installed on-site when the refrigeration cycle apparatus 1 is installed in an installation location such as a building. One end of the liquid side connecting pipe 4 is connected to a liquid side end of the outdoor unit 2, and the other end of the connecting pipe 4 is connected to a liquid side end of the third heat exchanger 25 of the indoor unit 3. One end of the gas side connecting pipe 5 is connected to a gas side end of the outdoor unit 2, and the other end of the connecting pipe 5 is connected to a gas side end of the third heat exchanger 25 of the indoor unit 3.

[0077] (2-6) Control section (2-6-1) Overview The components of the outdoor unit 2 and the indoor unit 3 are controlled by a control unit 6. The control unit 6 is configured by communication connection with an electrical equipment unit 42 and the like provided in the outdoor unit 2 and a control board and the like (not shown) provided in the indoor unit 3.

[0078] As shown in Fig. 4, the control unit 6 controls the components of the refrigeration cycle apparatus 1 (here, the outdoor unit 2 and the indoor unit 3). In other words, the control unit 6 controls the operation of the entire refrigeration cycle apparatus 1. For this reason, the control unit 6 in this embodiment controls the operation of the first circuit 10 and the operation of the second circuit 20. Here, the control unit 6 is provided in a unit constituting the second circuit 20 (the second machine room S22 in Fig. 2), and starts the operation of the first circuit 10 based on the start of operation of the second circuit 20.

[0079] The control unit 6 is realized by a computer. The control unit 6 includes a control arithmetic device and a storage device. The control arithmetic device can be a processor such as a CPU or a GPU. The control arithmetic device reads out a program stored in the storage device, and performs predetermined image processing and arithmetic processing according to the program. Furthermore, the control arithmetic device can write the results of the calculations to the storage device and read out information stored in the storage device according to the program.

[0080] (2-6-2) Stop control The control unit 6 performs stop control to collect the first refrigerant in the first heat exchanger 12 before stopping the operation of the first circuit 10. The stop control is a control in which, when the control unit 6 receives a command to stop the first compressor 11, the control unit 6 operates the first compressor 11 so as to push the first refrigerant in the first circuit 10 into the first heat exchanger 12, and then stops the first compressor 11. Therefore, even when the control unit 6 receives a command to stop the first compressor 11, the control unit 6 does not immediately stop the first compressor 11, but continues the operation of the first compressor 11 for a while so as to push the first refrigerant into the first heat exchanger 12, and then stops the first compressor 11.

[0081] In addition, the timing to stop operation of the first compressor 11 during the stop control is, for example, when a predetermined time has elapsed since a command to stop operation of the first circuit 10, and the pressure or pressure equivalent temperature on the high pressure side is equal to or higher than a predetermined value, or the pressure or pressure equivalent temperature on the low pressure side is equal to or lower than a predetermined value.

[0082] Furthermore, in this embodiment, the control unit 6 fully closes the first expansion mechanism 13 while the second circuit 20 is in heating operation and the first circuit 10 is stopped.

[0083] (2-6-3) Start control During cooling operation, the control unit 6 performs start control to operate the second circuit 20 prior to the first circuit 10. When the control unit 6 receives a command to start the first circuit 10, the start control starts the second compressor 21 before starting the first compressor 11.

[0084] Specifically, the control unit 6 starts the operation of the first circuit 10 when the difference between the inlet temperature and the outlet temperature of the cascade heat exchanger 30 in the second circuit 20 becomes equal to or less than a certain value. Here, the control unit 6 acquires the temperature of the second refrigerant before flowing into the cascade heat exchanger 30 from the inlet temperature sensor 46, and the temperature of the second refrigerant after flowing out of the cascade heat exchanger 30 from the outlet temperature sensor 47. Then, the control unit 6 calculates the temperature difference between the acquired inlet temperature and outlet temperature of the second refrigerant in the cascade heat exchanger 30, and judges whether the temperature difference is equal to or less than a certain value. The temperature difference is, for example, 5°C or less, and preferably 2°C or less. When the control unit 6 judges that the calculated temperature difference is equal to or less than a certain value, it starts the first compressor 11. On the other hand, when the control unit 6 judges that the calculated temperature difference is not equal to or less than a certain value, it does not start the first compressor 11.

[0085] The control unit 6 increases the opening degree of the first expansion mechanism 13 after starting up the first compressor 11. Here, in order to prevent the first refrigerant accumulated in the first flow path 31 of the cascade heat exchanger 30 from flowing out all at once and the liquefied first refrigerant from entering the first compressor 11, the control unit 6 keeps the first expansion mechanism 13 slightly open, which is smaller than the opening degree during cooling operation. After the first refrigerant starts circulating, the control unit 6 controls the opening degree of the first expansion mechanism 13 according to the load.

[0086] In this embodiment, the control unit 6 starts the second compressor 21, then increases the opening degree of the second expansion mechanism 24, then starts the first compressor 11, and then increases the opening degree of the first expansion mechanism 13. At this time, the opening degree of the first expansion mechanism 13 is smaller than the opening degree of the second expansion mechanism 24.

[0087] (3) Operation The operation of the refrigeration cycle apparatus 1 will be described with reference to Fig. 1 to Fig. 8. The refrigeration cycle apparatus 1 is capable of performing a heating operation for heating indoor air and a cooling operation for cooling indoor air for air conditioning. In the heating operation and the cooling operation, the operation of the refrigeration cycle apparatus 1 is controlled by a control unit 6.

[0088] (3-1) Heating operation 5, during heating operation, the switching mechanism 22 is switched to the second state (the state in which the switching mechanism 22 is in the dashed line state) so that the second heat exchanger 23 functions as an evaporator of the second refrigerant and the third heat exchanger 25 functions as a radiator of the second refrigerant. Furthermore, during heating operation, the first compressor 11 is not started and the first refrigerant is not circulated in the first circuit 10. Here, the first expansion mechanism 13 is fully closed.

[0089] In the second circuit 20, the second refrigerant discharged from the second compressor 21 flows out of the outdoor unit 2 through the switching mechanism 22.

[0090] The refrigerant flowing out of the outdoor unit 2 flows into the indoor unit 3 via the gas side connecting pipe 5. In the indoor unit 3, the second refrigerant is sent to the third heat exchanger 25. The second refrigerant sent to the third heat exchanger 25 is cooled by exchanging heat with the indoor air, thereby releasing heat. The second refrigerant that has released heat in the third heat exchanger 25 flows out of the indoor unit 3.

[0091] The second refrigerant flowing out of the indoor unit 3 flows into the outdoor unit 2 via the liquid side connection pipe 4. In the outdoor unit 2, the second refrigerant is sent to the second heat exchanger 23 through the second expansion mechanism 24 and the second flow path 32 of the cascade heat exchanger 30. The second refrigerant sent to the second heat exchanger 23 is heated through heat exchange with outdoor air supplied by the fan 43 and evaporates. The second refrigerant evaporated in the second heat exchanger 23 is sucked back into the second compressor 21 through the switching mechanism 22 and the second accumulator 26.

[0092] (3-2) Cooling operation As shown in FIG. 6, during cooling operation, the switching mechanism 22 is switched to the first state (the state in which the switching mechanism 22 is indicated by the solid line) so that the second heat exchanger 23 functions as a radiator for the second refrigerant and the third heat exchanger 25 functions as an evaporator for the second refrigerant.

[0093] In the second circuit 20, the second refrigerant discharged from the second compressor 21 is sent to the second heat exchanger 23 through the switching mechanism 22. The second refrigerant sent to the second heat exchanger 23 is cooled by exchanging heat with the outdoor air supplied by the fan 43, thereby dissipating heat. The second refrigerant that has dissipated heat in the second heat exchanger 23 is sent to the second flow path 32 of the cascade heat exchanger 30. The second refrigerant sent to the second flow path 32 is further cooled in the cascade heat exchanger 30 by exchanging heat with the first refrigerant flowing through the first flow path 31. The second refrigerant that has been further cooled in the cascade heat exchanger 30 is depressurized by the second expansion mechanism 24 and then flows out of the outdoor unit 2.

[0094] The second refrigerant that flows out of the outdoor unit 2 flows into the indoor unit 3 via the liquid side connecting pipe 4. In the indoor unit 3, the second refrigerant is sent to the third heat exchanger 25. The second refrigerant sent to the third heat exchanger 25 is heated through heat exchange with the indoor air and evaporates. The second refrigerant that has evaporated in the third heat exchanger 25 flows out of the indoor unit 3.

[0095] The second refrigerant that flows out of the indoor unit 3 passes through the gas side communication pipe 5 and flows into the outdoor unit 2. In the outdoor unit 2, the second refrigerant passes through the switching mechanism 22 and the second accumulator 26 and is sucked into the second compressor 21 again.

[0096] In the first circuit 10, the first refrigerant discharged from the first compressor 11 is sent to the first heat exchanger 12. The first refrigerant sent to the first heat exchanger 12 is cooled by heat exchange with the outdoor air supplied by the fan 43, and dissipates heat. The first refrigerant that has dissipated heat in the first heat exchanger 12 is depressurized by the first expansion mechanism 13, and then sent to the first flow path 31 of the cascade heat exchanger 30. The first refrigerant sent to the first flow path 31 is heated by heat exchange with the second refrigerant flowing through the second flow path 32 in the cascade heat exchanger 30, and thereby evaporates. The first refrigerant that has evaporated in the cascade heat exchanger 30 is sucked back into the first compressor 11 through the first accumulator 14.

[0097] (3-3) Shutdown of the 1st circuit When a command to stop the cooling operation is given from a remote control or the like, the control unit 6 stops the operation of the first circuit 10 and the operation of the second circuit 20.

[0098] Specifically, the control unit 6 that receives the command stops the second compressor 21, but continues to operate the first compressor 11 (step S101), as shown in Fig. 7. This allows the first refrigerant to be collected in the first heat exchanger 12.

[0099] Furthermore, the control unit 6 reduces the opening degree of the first expansion mechanism 13 (step S102). Here, the first expansion mechanism 13 is fully closed.

[0100] Then, when the control unit 6 determines that the first refrigerant has been collected in the first heat exchanger 12, the first compressor 11 is stopped (step S103). This allows the operation of the first circuit 10 to be stopped.

[0101] After the first compressor 11 is stopped, the opening degree of the first expansion mechanism 13, which is in a fully closed state, may be slightly opened.

[0102] (3-4) Start of operation of the first circuit When a command to start cooling operation is given from a remote control or the like, the control unit 6 starts operation of the second circuit 20 prior to operation of the first circuit 10.

[0103] Specifically, the control unit 6 that has received the command starts the second compressor 21 (step S111), as shown in Fig. 8. Next, the opening degree of the second expansion mechanism 24 is increased (step S112). By circulating the second refrigerant through the second circuit 20 through steps S111 and S112, the second refrigerant heats the liquefied first refrigerant in the cascade heat exchanger 30.

[0104] Next, the control unit 6 determines whether the difference between the inlet temperature and the outlet temperature of the cascade heat exchanger 30 in the second circuit 20 has become equal to or smaller than a certain value (step S113). In this step S103, the determination is made based on the temperature difference between the inlet temperature detected by the inlet temperature sensor 46 and the outlet temperature detected by the outlet temperature sensor 47.

[0105] In step S113, when it is determined that the temperature difference is not equal to or less than a certain level, it is determined that the first refrigerant in the cascade heat exchanger 30 is liquefied, and the operation of the first circuit 10 is not started, and the operation of the second circuit 20 is continued.

[0106] On the other hand, if it is determined in step S113 that the temperature difference is equal to or less than a certain level, it is determined that the first refrigerant in the cascade heat exchanger 30 is gasified, and the operation of the first circuit 10 is started. To start the operation of the first circuit 10, first, the control unit 6 starts up the first compressor 11 (step S114). Next, the opening degree of the first expansion mechanism 13 is increased (step S115).

[0107] (4) Features (4-1) The refrigeration cycle device 1 according to this embodiment includes a first circuit 10, a second circuit 20, and a control unit 6. The first circuit 10 includes a first compressor 11, a first heat exchanger 12, a first expansion mechanism 13, and a cascade heat exchanger 30. A first refrigerant circulates through the first circuit 10. The second circuit 20 includes a second compressor 21, a second heat exchanger 23, the cascade heat exchanger 30, a second expansion mechanism 24, and a third heat exchanger 25. A second refrigerant circulates through the second circuit 20. Before stopping the operation of the first circuit 10, the control unit 6 performs stop control to collect the first refrigerant in the first heat exchanger 12.

[0108] In the refrigeration cycle device 1 of this embodiment, the control unit 6 performs stop control to collect the first refrigerant in the first heat exchanger 12 before stopping the operation of the first circuit 10, so that the first refrigerant collected in the cascade heat exchanger 30 can be reduced. Therefore, while the first circuit 10 is stopped, the first refrigerant in the cascade heat exchanger 30 is cooled, so that liquefaction can be suppressed. Since the first circuit 10 is operated in this state, it is possible to suppress the liquefied first refrigerant from flowing into the first compressor 11. Therefore, it is possible to suppress the first compressor 11 from compressing the liquefied first refrigerant (liquid compression), so that the failure of the first compressor 11 can be reduced.

[0109] (4-2) The refrigeration cycle apparatus 1 according to this embodiment is the refrigeration cycle apparatus 1 described above in (4-1), and the control unit 6 operates the second circuit 20 prior to the first circuit 10 during cooling operation.

[0110] Here, by operating the second circuit 20 prior to the first circuit 10, when the high-pressure second refrigerant passes through the cascade heat exchanger 30 after passing through the second heat exchanger 23 of the second circuit 20, heat can be imparted to the first refrigerant collected in the cascade heat exchanger 30. This heat can heat the first refrigerant, so that the liquefied first refrigerant can be vaporized. Therefore, the liquefied first refrigerant can be further prevented from flowing into the first compressor 11.

[0111] In particular, it is preferable that the control unit 6 operates the second circuit 20 prior to the first circuit 10 during the first cooling operation after the heating operation. The reason for this will be explained.

[0112] During heating operation, when the second circuit 20 is operated without operating the first circuit 10, the cooled second refrigerant flows through the second flow path 32 belonging to the second circuit 20 of the cascade heat exchanger 30, and if the first refrigerant is stored in the first flow path 31 belonging to the first circuit 10 of the cascade heat exchanger 30, the first refrigerant is cooled and liquefied. In this state, when the operation of the first circuit 10 is started during the first cooling operation after the heating operation, the liquefied first refrigerant in the first flow path 31 of the cascade heat exchanger 30 flows into the first compressor 11. However, when the second circuit 20 is operated prior to the first circuit 10 during the first cooling operation after the heating operation, the liquefied first refrigerant in the first flow path 31 of the cascade heat exchanger 30 can be vaporized when the high-pressure second refrigerant that has passed through the second heat exchanger 23 passes through the second flow path 32 of the cascade heat exchanger 30.

[0113] (4-3) The refrigeration cycle apparatus 1 of this embodiment is the refrigeration cycle apparatus 1 described above in (4-2), and when the difference between the inlet temperature and the outlet temperature of the cascade heat exchanger 30 in the second circuit 20 becomes equal to or less than a certain value, the operation of the first circuit 10 is started.

[0114] Here, when the difference between the inlet temperature and the outlet temperature of the cascade heat exchanger 30 in the second circuit 20 becomes equal to or less than a certain value, it is determined that heat of the second refrigerant is transferred to the first refrigerant in the cascade heat exchanger 30, and the first refrigerant is vaporized. Since the first circuit 10 is operated in this state, it is possible to further suppress the liquefied first refrigerant from flowing into the first compressor 11.

[0115] (4-4) The refrigeration cycle apparatus according to this embodiment is any one of the above refrigeration cycle apparatuses (4-1) to (4-3), in which the opening degree of the first expansion mechanism 13 is increased after the first compressor 11 is started.

[0116] Here, when the first compressor 11 is started, the opening degree of the first expansion mechanism 13 is slightly open or fully closed, so that it is possible to prevent the first refrigerant in the first circuit 10 from flowing directly into the first compressor 11. Therefore, it is possible to further prevent the liquefied first refrigerant from flowing into the first compressor 11.

[0117] (4-5) The refrigeration cycle apparatus 1 of this embodiment is the refrigeration cycle apparatus 1 of (4-4) above, in which the control unit 6 starts the second compressor 21, then increases the opening degree of the second expansion mechanism 24, then starts the first compressor 11, and then increases the opening degree of the first expansion mechanism 13.

[0118] In this manner, by controlling the second compressor 21, the second expansion mechanism 24, the first compressor 11, and the first expansion mechanism 13 in that order, the first circuit 10 and the second circuit 20 can be operated while preventing the liquefied first refrigerant from flowing into the first compressor 11.

[0119] (4-6) The refrigeration cycle apparatus 1 according to this embodiment is any one of the refrigeration cycle apparatuses 1 described above in (4-1) to (4-5), in which the control unit 6 controls the operation of the first circuit 10 and the operation of the second circuit 20.

[0120] In this manner, in the refrigeration cycle apparatus 1 of the present disclosure, the control unit of the second circuit 20 may control the first circuit 10.

[0121] (4-7) The refrigeration cycle apparatus 1 according to this embodiment is any one of the refrigeration cycle apparatuses 1 described above in (4-1) to (4-6), and the first heat exchanger 12 is a flat multi-hole tube.

[0122] Here, the flat multi-hole tube serving as the first heat exchanger 12 can have a small volume, so the amount of the first refrigerant can be reduced. Therefore, the amount of the first refrigerant collected in the cascade heat exchanger 30 can be reduced.

[0123] (4-8) The refrigeration cycle apparatus 1 according to this embodiment is any one of the refrigeration cycle apparatuses 1 described above in (4-1) to (4-7), and further includes a fan 43 that sends outdoor air to the first heat exchanger 12 and the second heat exchanger 23.

[0124] Here, the fan 43 that sends outdoor air to the first heat exchanger 12 and the second heat exchanger 23 is common, so even if the first circuit 10 is stopped, outdoor air flows into the first heat exchanger 12 if the second circuit 20 is operating. Therefore, heat is exchanged between the first refrigerant collected in the first heat exchanger 12 and the outdoor air, making it easier to collect the liquefied first refrigerant in the first heat exchanger 12. This makes it possible to further prevent the liquefied first refrigerant from flowing into the first compressor 11.

[0125] (4-9) The refrigeration cycle apparatus 1 according to this embodiment is any one of the refrigeration cycle apparatuses 1 described above in (4-1) to (4-8), in which the first circuit 10 further includes a first accumulator 14.

[0126] Here, since the liquefied first refrigerant can be stored in the first accumulator 14, the liquefied first refrigerant can be further prevented from flowing into the first compressor 11.

[0127] Incidentally, even if the first accumulator 14 is provided in the first circuit 10, it is not possible to completely prevent liquid refrigerant from flowing into the first compressor 11. Therefore, the stop control of this embodiment has the effect of suppressing liquid compression.

[0128] (4-10) The refrigeration cycle apparatus 1 of this embodiment is any one of the refrigeration cycle apparatuses 1 described above in (4-1) to (4-9), and the control unit 6 fully closes the first expansion mechanism 13 when the second circuit 20 is in heating operation and the first circuit 10 is stopped.

[0129] When the second circuit 20 is in heating operation, a low-pressure second refrigerant passes through the second flow path 32 of the cascade heat exchanger 30. Therefore, when the second circuit 20 is in heating operation and the first circuit 10 is stopped, the first refrigerant collected in the first flow path 31 of the cascade heat exchanger 30 is cooled and easily liquefied. In this case, by fully closing the first expansion mechanism 13, the first refrigerant that flows into the cascade heat exchanger 30 and liquefies can be reduced. Therefore, the liquefied first refrigerant can be further prevented from flowing into the first compressor 11.

[0130] (4-11) The refrigeration cycle apparatus 1 according to this embodiment is any one of the refrigeration cycle apparatuses 1 described above in (4-1) to (4-10), and the control unit 6 performs heating operation and cooling operation.

[0131] Here, by stopping the operation of the first circuit 10 during heating operation, the first refrigerant collected in the cascade heat exchanger 30 is likely to liquefy, which can easily cause a problem that the liquefied first refrigerant flows into the first compressor 11. Even in cases where this problem is likely to occur, it is possible to prevent the liquefied first refrigerant from flowing into the first compressor 11 by performing stop control.

[0132] (4-12) The refrigeration cycle apparatus 1 according to this embodiment is any one of the refrigeration cycle apparatuses 1 described above in (4-1) to (4-11), in which the first refrigerant is flammable, toxic, or has a GWP of over 500.

[0133] Thus, a first refrigerant that is flammable, toxic, or has a GWP greater than 500 may be used.

[0134] (4-13) The refrigeration cycle apparatus 1 according to this embodiment is the refrigeration cycle apparatus 1 described above in (4-12), in which the first refrigerant is R290 and the second refrigerant is carbon dioxide.

[0135] Carbon dioxide refrigerant has a low GWP and can contribute to reducing global warming, but it is difficult to achieve high capacity during cooling operation at high outdoor temperatures. In contrast, the refrigeration cycle device 1 of this embodiment is equipped with the first circuit 10, in which R290 circulates, as a subcooling circuit, and can therefore increase capacity.

[0136] (5) Variations (5-1) Variation 1 (5-1-1) Start control In the above embodiment, as the start control during cooling operation, the control unit 6 starts the operation of the first circuit 10 when the difference between the inlet temperature and the outlet temperature of the cascade heat exchanger 30 in the second circuit 20 becomes equal to or less than a certain value, but this is not limited to this. In this modification, the control unit 6 starts the operation of the first circuit 10 after a predetermined time has elapsed since the start of operation of the second circuit 20. The predetermined time is, for example, 3 minutes or more, and preferably 10 minutes or more.

[0137] 9, the control unit 6 determines whether or not a predetermined time has elapsed since the second compressor 21 was started (step S116). If the control unit 6 determines that the predetermined time has elapsed, it starts the first compressor 11 (step S114). On the other hand, if the control unit 6 determines that the predetermined time has not elapsed, it does not start the first compressor 11.

[0138] (5-1-2) Features The refrigeration cycle apparatus according to this modification is the refrigeration cycle apparatus (4-2) described above, in which the control unit 6 starts the operation of the first circuit 10 after a predetermined time has elapsed since the start of the operation of the second circuit 20.

[0139] Here, when a predetermined time has elapsed since the operation of the second circuit 20, it is determined that the heat of the second refrigerant is transferred to the first refrigerant in the cascade heat exchanger 30, and the first refrigerant is vaporized. Since the first circuit 10 is operated in this state, it is possible to further suppress the liquefied first refrigerant from flowing into the first compressor 11.

[0140] (5-2) Variation 2 In the above embodiment, the control to fully close the first expansion mechanism 13 when the second circuit 20 is in heating operation and the first circuit 10 is stopped has been described as an example, but the present invention is not limited to this. The first expansion mechanism 13 may be fully closed even when the first circuit 10 is stopped because the second circuit 20 is in cooling operation.

[0141] In this manner, in this modified example, the control unit 6 fully closes the first expansion mechanism 13 while the second circuit 20 is in operation and the first circuit 10 is stopped.

[0142] When the second circuit 20 is in operation and the first circuit 10 is stopped, the first refrigerant is likely to be cooled in the cascade heat exchanger 30. In this case, in the refrigeration cycle device of this modified example, the first expansion mechanism 13 is fully closed, thereby reducing the first refrigerant flowing into the cascade heat exchanger 30. This makes it possible to further suppress the liquefied first refrigerant from flowing into the first compressor 11.

[0143] (5-3) Variation 3 In the above embodiment, an example was given of performing start control and stop control when starting and stopping cooling operation, but the start control and stop control may also be applied when stopping and starting the operation of the first circuit 10 during cooling operation.

[0144] Specifically, the control unit 6 may control the operation of the first circuit 10 according to the load during cooling operation. Specifically, when the load during cooling operation is low, the control unit 6 does not operate the first circuit 10, and when the load during cooling operation is high, the control unit 6 operates the first circuit 10. In this case, when the load increases during cooling operation and the first circuit 10 is operated, the control unit 6 performs the above-mentioned start control. Also, when the load decreases during cooling operation and the operation of the first circuit 10 is stopped, the control unit 6 performs the above-mentioned stop control.

[0145] (5-4) Variation 4 In the above embodiment, the control unit 6 is provided in the second machine room S22 of the second circuit 20, and an example is given in which the operation of the first circuit 10 is started based on the start of operation of the second circuit 20, but this is not limited to the above.

[0146] In this modified example, the control unit includes a first control unit that controls the operation of the first circuit 10 and a second control unit that controls the operation of the second circuit 20, and the first control unit starts operation of the first circuit 10 based on instructions from the second control unit.

[0147] (5-5) Variation 5 In the above embodiment, the first circuit 10 includes the first accumulator 14, but is not limited to this. The first circuit of the present disclosure may include an accumulator and a sub-accumulator.

[0148] The first circuit of this modification does not have both the accumulator and the sub-accumulator. Therefore, the amount of the first refrigerant charged in the first circuit 10 can be further reduced. Therefore, the refrigeration cycle device 1 is very useful when using a highly flammable (A3) refrigerant such as R290.

[0149] (5-6) Variation 6 In the above embodiment, an example has been described in which the common fan 43 sends outdoor air to the first heat exchanger 12 and the second heat exchanger 23, but this is not limiting. The refrigeration cycle device of this modified example has a first fan that sends outdoor air to the first heat exchanger 12 and a second fan that sends outdoor air to the second heat exchanger 23, and the first fan and the second fan are different.

[0150] (5-7) Variation 7 In the above embodiment, the refrigeration cycle apparatus 1 in which one indoor unit 3 is connected to one outdoor unit 2 has been described as an example, but is not limited thereto. In the refrigeration cycle apparatus of this modified example, multiple indoor units are connected to one outdoor unit.

[0151] (5-8) Variation 8 In the above embodiment, the refrigeration cycle device 1 performing the cooling operation and the heating operation has been described as an example, but is not limited thereto. The refrigeration cycle device of the present disclosure may further perform a dehumidification operation. During the dehumidification operation, stop control and start control are performed in the same manner as during the cooling operation of the above embodiment. Furthermore, the refrigeration cycle device of the present disclosure may be an air conditioner dedicated to cooling.

[0152] Although the embodiments of the present disclosure have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the present disclosure described in the claims. [Explanation of symbols]

[0153] 1: Refrigeration cycle device 6: Control section 10:1st circuit 11: First compressor 12: 1st heat exchanger 13: First expansion mechanism 14: First accumulator (accumulator) 20: 2nd circuit 21: Second compressor 23:Second heat exchanger 24: Second expansion mechanism 25:Third heat exchanger 30: Cascade heat exchanger 43: Fan [Prior art documents] [Patent documents]

[0154] [Patent Document 1] Patent No. 5430604

Claims

1. a first circuit (10) including a first compressor (11), a first heat exchanger (12), a first expansion mechanism (13), and a cascade heat exchanger (30), in which a first refrigerant circulates; a second circuit (20) including a second compressor (21), a second heat exchanger (23), the cascade heat exchanger (30), a second expansion mechanism (24), and a third heat exchanger (25), in which a second refrigerant circulates; a control unit (6) that performs stop control to collect the first refrigerant in the first heat exchanger before stopping the operation of the first circuit; A refrigeration cycle device (1).

2. The control unit operates the second circuit prior to the first circuit during cooling operation. The refrigeration cycle device according to claim 1.

3. The control unit starts the operation of the first circuit when a difference between an inlet temperature and an outlet temperature of the cascade heat exchanger in the second circuit becomes equal to or smaller than a certain value. The refrigeration cycle device according to claim 2.

4. The control unit starts the operation of the first circuit after a predetermined time has elapsed since the operation of the second circuit has started. The refrigeration cycle device according to claim 2.

5. The control unit increases the opening degree of the first expansion mechanism after the first compressor is started. The refrigeration cycle device according to any one of claims 1 to 4.

6. The control unit starts the second compressor, then increases the opening degree of the second expansion mechanism, then starts the first compressor, and then increases the opening degree of the first expansion mechanism. The refrigeration cycle device according to claim 5.

7. The control unit controls an operation of the first circuit and an operation of the second circuit. The refrigeration cycle device according to any one of claims 1 to 4.

8. The first heat exchanger is a flat multi-hole tube. The refrigeration cycle device according to any one of claims 1 to 4.

9. The air conditioner further includes a fan (43) for sending outdoor air to the first heat exchanger and the second heat exchanger. The refrigeration cycle device according to any one of claims 1 to 4.

10. The first circuit further includes an accumulator (14). The refrigeration cycle device according to any one of claims 1 to 4.

11. The control unit fully closes the first expansion mechanism while the second circuit is in operation and the first circuit is stopped. The refrigeration cycle device according to any one of claims 1 to 4.

12. The control unit performs heating operation and cooling operation. The refrigeration cycle device according to any one of claims 1 to 4.

13. The first refrigerant is flammable, toxic, or has a GWP greater than 500; The refrigeration cycle device according to any one of claims 1 to 4.

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