Refrigeration cycle device

Abstract

A refrigeration cycle device (1) comprises 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 in the first circuit (10). The second circuit (20) includes a second compressor (21), a second heat exchanger (23), a cascade heat exchanger (30), a second expansion mechanism (24), and a third heat exchanger (25). A second refrigerant circulates in the second circuit (20). The control unit (6) performs stop control for collecting the first refrigerant in the first heat exchanger (12) before stopping the operation of the first circuit (10).

Description

Refrigeration Cycle Equipment

[0001] This relates to a refrigeration cycle device.

[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 the heat dissipation of 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.

[0003] However, the present inventors have focused on a problem that the cascade refrigeration system of Patent Document 1 has, that is, there is a risk that liquid refrigerant may flow into the compressor.

[0004] The inventors discovered that the above problem occurs when the high-temperature refrigeration cycle is stopped, and the evaporator of the high-temperature refrigeration cycle in the cascade condenser is cooled, causing the refrigerant to liquefy. If the high-temperature refrigeration cycle is operated under this condition, the liquefied refrigerant will flow into the compressor.

[0005] Therefore, a refrigeration cycle apparatus 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 operation of the first circuit, thereby reducing the amount of first refrigerant collected in the cascade heat exchanger. This prevents the first refrigerant in the cascade heat exchanger 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 second heat exchanger of the second circuit and then passes through the cascade heat exchanger, heat can be imparted to the first refrigerant collected in the cascade heat exchanger. This heat can heat the first refrigerant, thereby further preventing 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, wherein 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 less than a certain value, it is determined that heat of the second refrigerant has been transferred to the first refrigerant in the cascade heat exchanger and the first refrigerant has vaporized. 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.

[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 operation of the first circuit after a predetermined time has elapsed since the start of operation of the second circuit.

[0012] In the refrigeration cycle apparatus of the fourth aspect, after a predetermined time has elapsed since the second circuit began operation, 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, wherein the opening degree of the first expansion mechanism is increased after the first compressor is started.

[0014] In the refrigeration cycle apparatus according to the fifth aspect, the opening degree of the first expansion mechanism is not increased when the first compressor is started, so that the first refrigerant in the first circuit is prevented from flowing directly into the first compressor, thereby further preventing the liquefied first refrigerant from flowing into the first compressor.

[0015] A refrigeration cycle device of a sixth aspect is the refrigeration cycle device of the fifth aspect, in which 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 device of the sixth aspect, by controlling the second compressor, the second expansion mechanism, the first compressor, and the first expansion mechanism in that order, the first circuit and the second circuit can be operated while preventing the liquefied first refrigerant from flowing 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 the operation of the first circuit and the 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 pipe.

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

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

[0022] In the refrigeration cycle apparatus of the ninth aspect, a common fan is used to send outdoor air to the first heat exchanger and the second heat exchanger. Therefore, even if the first circuit is stopped, outdoor air flows through the first heat exchanger as long as the second circuit is operating. Therefore, heat exchange occurs between the first refrigerant collected in the first heat exchanger and the outdoor air, making it easier for the liquefied first refrigerant to be collected in the first heat exchanger. This further reduces the risk of the liquefied first refrigerant 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 device of an eleventh aspect is a refrigeration cycle device of any one of the first aspect to the tenth aspect, wherein the control unit fully closes the first expansion mechanism while the second circuit is operating 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 apparatus of the eleventh aspect, by fully closing the first expansion mechanism, the first refrigerant flowing into the cascade heat exchanger can be reduced. This further reduces the amount of liquefied first refrigerant 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 to eleventh aspects, 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 of the liquefied first refrigerant flowing into the first compressor. Even when 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 greater 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.

[0031] It is a schematic configuration diagram of a refrigeration cycle device according to an embodiment of the present disclosure. It is a cross-sectional schematic diagram of an outdoor unit. It is a schematic perspective view of a first heat exchanger. It is a control block diagram of the refrigeration cycle device. It is a diagram showing the operation of the refrigeration cycle device in heating operation. It is a diagram showing the operation of the refrigeration cycle device in cooling operation. It is a flowchart of stop control. It is a flowchart of start control. It is a flowchart of start control of modified example 1.

[0032] (1) Overall Configuration As shown in FIG. 1 , a refrigeration cycle device 1 according to one embodiment of the present disclosure is a device used for heating and cooling the interior of 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 this embodiment has a binary refrigerant circuit consisting of the vapor compression first circuit 10 and the vapor compression 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 stop control to collect the first refrigerant in the first heat exchanger 12 .

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

[0038] The first circuit 10 constitutes a subcooling circuit during cooling operation, and 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 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 acquires cold or hot heat from the outdoor air. The first heat exchanger 12 is, for example, a flat multi-hole pipe as shown in FIG. 3 .

[0042] The first expansion mechanism 13 is a device that decompresses the first refrigerant and is, for example, an electric expansion valve. The first expansion mechanism 13 is disposed between the first heat exchanger 12 and the cascade heat exchanger 30.

[0043] The first accumulator 14 is provided in the middle of the suction flow path that connects the cascade heat exchanger 30 and the suction side of the first compressor 11. The first accumulator 14 separates the refrigerant that has flowed into it 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 attached to the 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, which will be described later.

[0045] The cascade heat exchanger 30 is a device for exchanging heat 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 has a gas side connected to the first compressor 11 and a liquid side connected 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 is intended to supercool the second refrigerant cooled by 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 or 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 the 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 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 for the second refrigerant and the third heat exchanger 25 functions as an evaporator for 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 for the second refrigerant and the third heat exchanger 25 functions as a radiator for 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 acquires 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 the 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 decompresses 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 refrigerant that has flowed in 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, but these refer to 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 of a building, etc.).

[0059] The outdoor unit 2 includes the first circuit 10, a portion of the second circuit 20, a casing 41, an electrical component unit 42, a fan 43, a partition plate 44, a separation plate 45, and various sensors. Specifically, the outdoor unit 2 includes 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, and the casing 41, the electrical component unit 42, the fan 43, the partition plate 44, and the separation plate 45 shown in FIG. 1 .

[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, the electrical equipment unit 42, the fan 43, the partition plate 44, the separation plate 45, and various sensors.

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

[0062] The front plate 411 is a plate-like member that forms 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 outside air that has been taken into the casing 41 from the outside 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 plates 414 are plate-like members that form the side surfaces of the casing 41. The lower portions of the side plates 414 are fixed to the bottom plate 413.

[0065] The electrical component unit 42 has electrical components mounted on a circuit board. The electrical components control the first compressor 11, the second compressor 21, the first expansion mechanism 13, the switching mechanism 22, the second expansion mechanism 24, and other controlled objects.

[0066] The fan 43 causes air to flow through the first heat exchanger 12 and the second heat exchanger 23. In the present 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 exchanges heat with the first refrigerant in the first heat exchanger 12 and 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] The fan that blows air through the first heat exchanger 12 and the fan that blows air through the second heat exchanger 23 may be provided separately.

[0068] The partition plate 44 is a plate-like member that extends in the vertical direction. The 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 the front plate 411, the top plate 412, the bottom plate 413, and the side plates 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 the air inlet of the outdoor unit 2 flows to the air outlet. In this embodiment, the first chamber S1 is equipped with the first heat exchanger 12, the second heat exchanger 23, the fan 43, and the like.

[0071] The second chamber S2 is a machinery chamber and contains 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 component unit 42, and the like.

[0072] The separator plate 45 divides the second chamber S2 into a first machine chamber S21 that constitutes the first circuit 10 and a second machine chamber S22 that constitutes the second circuit 20. The separator plate 45 is a plate-shaped member extending in the vertical direction. A lower portion of the separator 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 disposed in the first machine chamber S21 that is divided by the front plate 411, the top plate 412, the bottom plate 413, the side plate 414, and the separator plate 45. The second compressor 21, the switching mechanism 22, the second expansion mechanism 24, the second accumulator 26, the electrical component unit 42, etc. are disposed in the second machine chamber S22 that is divided by the front plate 411, the top plate 412, the bottom plate 413, the partition plate 44, and the separator 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 connecting pipes 4 and 5, and constitutes part of the second circuit 20.

[0075] 1, the indoor unit 3 has a third heat exchanger 25. Here, the indoor unit 3 is installed by being embedded in or suspended from the ceiling of a room in a building or the like, or by being wall-mounted on a wall surface of the room.

[0076] (2-5) Connecting Pipes 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 the liquid-side end of the outdoor unit 2, and the other end of the connecting pipe 4 is connected to the 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 the gas-side end of the outdoor unit 2, and the other end of the connecting pipe 5 is connected to the gas-side end of the third heat exchanger 25 of the indoor unit 3.

[0077] (2-6) Control Unit (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 the 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 that constitutes 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 and arithmetic unit and a storage device. The control and arithmetic unit can be a processor such as a CPU or a GPU. The control and arithmetic unit reads a program stored in the storage device and performs predetermined image processing and arithmetic processing in accordance with the program. Furthermore, the control and arithmetic unit can write the results of calculations to the storage device and read information stored in the storage device in accordance with 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 rather continues operation of the first compressor 11 for a short time 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 for stopping operation of the first compressor 11 during stop control is, for example, when a predetermined time has elapsed since the command to stop operation of the first circuit 10, and the pressure or pressure-equivalent temperature on the high-pressure side is above a predetermined value, or when the pressure or pressure-equivalent temperature on the low-pressure side is below a predetermined value.

[0082] In addition, 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 before 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 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 level. 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. The control unit 6 then calculates the temperature difference between the acquired inlet and outlet temperatures of the second refrigerant in the cascade heat exchanger 30 and determines whether the temperature difference is equal to or less than a certain level. The temperature difference is, for example, 5°C or less, preferably 2°C or less. If the control unit 6 determines that the calculated temperature difference is equal to or less than the certain level, it starts the first compressor 11. On the other hand, if the control unit 6 determines that the calculated temperature difference is not equal to or less than the certain level, it does not start the first compressor 11.

[0085] After starting the first compressor 11, the control unit 6 increases the opening degree of the first expansion mechanism 13. Here, 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 liquefying the first refrigerant into 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 Figures 1 to 8. The refrigeration cycle apparatus 1 is capable of performing a heating operation to heat indoor air and a cooling operation to cool indoor air for indoor air conditioning. In the heating operation and the cooling operation, the operation of the refrigeration cycle apparatus 1 is controlled by the control unit 6.

[0088] (3-1) Heating Operation As shown in Fig. 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) 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 passes through the gas-side connecting pipe 5 and flows into the indoor unit 3. 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 via 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 and evaporated by heat exchange with outdoor air supplied by the fan 43. The second refrigerant evaporated in the second heat exchanger 23 is sucked back into the second compressor 21 via 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 in the solid line) so that 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.

[0093] In the second circuit 20, the second refrigerant discharged from the second compressor 21 is sent to the second heat exchanger 23 via the switching mechanism 22. The second refrigerant sent to the second heat exchanger 23 is cooled by exchanging heat with 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. In the cascade heat exchanger 30, the second refrigerant is further cooled 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 decompressed 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 connection 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 connecting 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 again sucked into the second compressor 21.

[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 outdoor air supplied by the fan 43, thereby dissipating heat. The first refrigerant that has dissipated heat in the first heat exchanger 12 is decompressed 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 and evaporated in the cascade heat exchanger 30 by heat exchange with the second refrigerant flowing through the second flow path 32. The first refrigerant that has evaporated in the cascade heat exchanger 30 is drawn back into the first compressor 11 via the first accumulator 14.

[0097] (3-3) Stopping Operation of First Circuit When a command to stop the cooling operation is received from a remote controller 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 receives the command and 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] 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), thereby stopping the operation of the first circuit 10.

[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 First Circuit When a command to start cooling operation is given from a remote controller or the like, the control unit 6 starts operation of the second circuit 20 before operation of the first circuit 10 .

[0103] Specifically, as shown in Fig. 8 , the control unit 6 receives the command and starts the second compressor 21 (step S111). Next, the opening degree of the second expansion mechanism 24 is increased (step S112). By performing steps S111 and S112, the second refrigerant circulates through the second circuit 20, and 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 is equal to or less than a certain value (step S113). In step S113, this 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, if it is determined that the temperature difference is not below a certain level, it is determined that the first refrigerant in the cascade heat exchanger 30 is liquefied, and operation of the second circuit 20 is continued without starting operation of the first circuit 10.

[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 has gasified, and operation of the first circuit 10 is started. To start operation of the first circuit 10, the control unit 6 first starts 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 apparatus 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 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 apparatus 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, thereby reducing the amount of first refrigerant collected in the cascade heat exchanger 30. As a result, while the first circuit 10 is stopped, the first refrigerant in the cascade heat exchanger 30 is cooled, thereby preventing liquefaction. Since the first circuit 10 is operated in this state, the liquefied first refrigerant is prevented from flowing into the first compressor 11. Therefore, compression of the liquefied first refrigerant by the first compressor 11 (liquid compression) is prevented, thereby reducing the occurrence of a breakdown of the first compressor 11.

[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 before the first circuit 10 during cooling operation.

[0110] Here, by operating the second circuit 20 before the first circuit 10, when the high-pressure second refrigerant passes through the second heat exchanger 23 of the second circuit 20 and then passes through the cascade heat exchanger 30, heat can be imparted to the first refrigerant collected in the cascade heat exchanger 30. This heat can heat the first refrigerant, allowing the liquefied first refrigerant to be vaporized. This further reduces the possibility of the liquefied first refrigerant flowing into the first compressor 11.

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

[0112] During heating operation, if 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. Therefore, if the first refrigerant accumulates 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 first circuit 10 is started to operate 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, if the second circuit 20 is operated before the first circuit 10 during the first cooling operation after the heating operation, the high-pressure second refrigerant that has passed through the second heat exchanger 23 can vaporize the liquefied first refrigerant in the first flow path 31 of the cascade heat exchanger 30 as it passes through the second flow path 32 of the cascade heat exchanger 30.

[0113] (4-3) The refrigeration cycle device 1 according to this embodiment is the refrigeration cycle device 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 outlet temperature of the cascade heat exchanger 30 in the second circuit 20 becomes equal to or less than a certain level, it is determined that heat from the second refrigerant has been transferred to the first refrigerant in the cascade heat exchanger 30, causing the first refrigerant to evaporate. Since the first circuit 10 is operated in this state, it is possible to further prevent the liquefied first refrigerant from flowing into the first compressor 11.

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

[0116] Here, when the first compressor 11 is started, the opening degree of the first expansion mechanism 13 is slightly open or fully closed, which prevents the first refrigerant in the first circuit 10 from flowing directly into the first compressor 11. This further prevents the liquefied first refrigerant from flowing into the first compressor 11.

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

[0118] In this way, 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 device 1 according to this embodiment is any one of the refrigeration cycle devices 1 described above in (4-1) to (4-5), and 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 the refrigeration cycle apparatus 1 according to any one of the above (4-1) to (4-6), in which the first heat exchanger 12 is a flat multi-hole pipe.

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

[0123] (4-8) The refrigeration cycle device 1 according to this embodiment is any one of the refrigeration cycle devices 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 shared, so even if the first circuit 10 is stopped, outdoor air flows through the first heat exchanger 12 as long as the second circuit 20 is operating. Therefore, heat exchange occurs between the first refrigerant collected in the first heat exchanger 12 and the outdoor air, making it easier to collect liquefied first refrigerant in the first heat exchanger 12. This further prevents the liquefied first refrigerant from flowing into the first compressor 11.

[0125] (4-9) The refrigeration cycle device 1 according to this embodiment is the refrigeration cycle device 1 according to any one of (4-1) to (4-8) above, wherein 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] 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, so the stop control of this embodiment has the effect of suppressing liquid compression.

[0128] (4-10) The refrigeration cycle device 1 according to this embodiment is any one of the refrigeration cycle devices 1 described above in (4-1) to (4-9), and 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.

[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 amount of first refrigerant that flows into the cascade heat exchanger 30 and liquefies can be reduced. This further reduces the amount of liquefied first refrigerant that flows into the first compressor 11.

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

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

[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), wherein the first refrigerant is flammable, toxic, or has a GWP exceeding 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 according to (4-12) above, 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 sufficient cooling 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, thereby increasing capacity.

[0136] (5) Modifications (5-1) Modification 1 (5-1-1) Start Control In the above embodiment, the start control during cooling operation is described as an example in which the control unit 6 starts 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. However, this is not limited to this. In this modification, the control unit 6 starts 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 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 device according to this modification is the refrigeration cycle device described above in (4-2), in which 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.

[0139] Here, when a predetermined time has elapsed since the second circuit 20 began operating, it is determined that heat from the second refrigerant has been transferred to the first refrigerant in the cascade heat exchanger 30, causing the first refrigerant to evaporate. Since the first circuit 10 is operated in this state, it is possible to further prevent the liquefied first refrigerant from flowing into the first compressor 11.

[0140] (5-2) Modification 2 In the above embodiment, the first expansion mechanism 13 is fully closed when the second circuit 20 is in heating operation and the first circuit 10 is stopped. However, 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 operating 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 apparatus of this modified example, the first expansion mechanism 13 is fully closed, thereby reducing the amount of first refrigerant flowing into the cascade heat exchanger 30. This makes it possible to further prevent the liquefied first refrigerant from flowing into the first compressor 11.

[0143] (5-3) Modification 3 In the above embodiment, the start control and stop control are performed when the air conditioning operation is started and stopped, but the start control and stop control may also be applied when the operation of the first circuit 10 is stopped or started during the air conditioning operation.

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

[0145] (5-4) Modification 4 In the above embodiment, the control unit 6 is provided in the second machine chamber S22 of the second circuit 20, and the control unit 6 starts operation of the first circuit 10 based on the start of operation of the second circuit 20. However, this is not limiting.

[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 the operation of the first circuit 10 based on instructions from the second control unit.

[0147] (5-5) Modification 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 an accumulator and a sub-accumulator, which further reduces the amount of first refrigerant charged into the first circuit 10. Therefore, the refrigeration cycle apparatus 1 is very useful when using a highly flammable (A3) refrigerant such as R290.

[0149] (5-6) Modification 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 modification 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) Modification 7 In the above embodiment, the refrigeration cycle apparatus 1 is described as an example in which one indoor unit 3 is connected to one outdoor unit 2. However, the present modification is not limited to this. In the refrigeration cycle apparatus of this modification, multiple indoor units are connected to one outdoor unit.

[0151] (5-8) Modification 8 In the above embodiment, the refrigeration cycle apparatus 1 that performs cooling operation and heating operation has been described as an example, but this is not limiting. The refrigeration cycle apparatus of the present disclosure may also perform a dehumidifying operation. During the dehumidifying 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 apparatus of the present disclosure may be an air conditioning apparatus 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 as defined in the claims.

[0153] REFRIGERATION CYCLE DEVICE 1 : REFRIGERATION CYCLE DEVICE 6 : CONTROL UNIT 10 : FIRST CIRCUIT 11 : FIRST COMPRESSOR 12 : FIRST HEAT EXCHANGER 13 : FIRST EXPANSION MECHANISM 14 : FIRST ACCUMULATOR (ACCUMULATOR) 20 : SECOND CIRCUIT 21 : SECOND COMPRESSOR 23 : SECOND HEAT EXCHANGER 24 : SECOND EXPANSION MECHANISM 25 : THIRD HEAT EXCHANGER 30 : CASCADE HEAT EXCHANGER 43 : FAN

[0154] Patent No. 5430604

Claims

1. A refrigeration cycle device (1), comprising: 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), and through 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), and through which a second refrigerant circulates; and a control unit (6) that performs stop control to collect the first refrigerant in the first heat exchanger before stopping operation of the first circuit.

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

3. The refrigeration cycle apparatus according to claim 2, wherein the control unit starts 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.

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

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

6. The refrigeration cycle device according to claim 5, 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.

7. The refrigeration cycle device according to any one of claims 1 to 6, wherein the control unit controls an operation of the first circuit and an operation of the second circuit.

8. A refrigeration cycle device according to any one of claims 1 to 7, wherein the first heat exchanger is a flat multi-hole tube.

9. The refrigeration cycle apparatus according to any one of claims 1 to 8, further comprising a fan (43) for sending outdoor air to the first heat exchanger and the second heat exchanger.

10. The refrigeration cycle device according to any one of claims 1 to 9, wherein the first circuit further includes an accumulator (14).

11. A refrigeration cycle device according to any one of claims 1 to 10, wherein the control unit fully closes the first expansion mechanism while the second circuit is in operation and the first circuit is stopped.

12. The refrigeration cycle apparatus according to any one of claims 1 to 11, wherein the control unit performs heating operation and cooling operation.

13. The refrigeration cycle device according to any one of claims 1 to 12, wherein the first refrigerant is flammable, toxic, or has a GWP of more than 500.

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