Refrigeration cycle device

Abstract

A refrigeration cycle device (1) is provided with: a first circuit (5a) through which a first refrigerant circulates; a second circuit (10) through which the carbon dioxide refrigerant and the refrigerator oil circulate; a cascade heat exchanger (35) for heating the carbon dioxide refrigerant by means of the first refrigerant; and a control unit (80). The second circuit has: a second compressor; a container provided on the suction side of the second compressor and storing a carbon dioxide refrigerant and refrigerator oil; a suction pipe (23a) that connects the suction side of the second compressor and the container; an oil return passage (23b) for returning the refrigerator oil from the lower part of the container to the suction pipe; and a valve provided in the oil return passage. The control unit implements activation control for opening the oil return valve after starting circulation of the first refrigerant in the first circuit.

Description

Technical Field

[0001] The present disclosure relates to a refrigeration cycle device. Background Art

[0002] Patent document 1 (Japanese Patent No. 5425221) discloses a refrigeration cycle device including a refrigerant circuit, wherein the refrigerant circuit connects an outdoor unit and an indoor unit via a gas pipe and a liquid pipe and circulates a refrigerant. Carbon dioxide (CO2) as a refrigerant and polyalkylene glycol (PAG) oil incompatible with carbon dioxide as a refrigeration oil are sealed inside the refrigerant circuit. Summary of the invention Technical problem to be solved by the invention

[0003] As disclosed in the above-mentioned Patent Document 1, in a refrigeration cycle device using carbon dioxide refrigerant, if a refrigeration oil that is incompatible with the carbon dioxide refrigerant is used, the density of the refrigeration oil becomes lower than the density of the refrigerant in the low temperature region of the carbon dioxide refrigerant. In this case, the liquid refrigerant is retained in the lower part of the storage tank, and therefore, the liquid refrigerant flows into the compressor. Technical solutions adopted to solve technical problems

[0004] The refrigeration cycle device of the first viewpoint includes a first circuit, a second circuit, a cascade heat exchanger and a control unit. The first circuit is for circulating a first refrigerant. The second circuit is for circulating a carbon dioxide refrigerant and refrigeration oil. The cascade heat exchanger heats the carbon dioxide refrigerant by the first refrigerant. The second circuit has a second compressor, a container, a suction piping, an oil return passage and a valve. The container is arranged on the suction side of the second compressor to store the carbon dioxide refrigerant and the refrigeration oil. The suction piping connects the suction side of the second compressor to the container. The oil return passage returns the refrigeration oil from the lower part of the container to the suction piping. The valve is arranged on the oil return passage. The control unit implements a startup control of opening the valve after starting to circulate the first refrigerant in the first circuit.

[0005] At the start of the operation of heating the carbon dioxide refrigerant by the first refrigerant, the outside air temperature is low, and therefore, the temperature of the carbon dioxide refrigerant in the container is sometimes low. In this case, in the refrigeration cycle device of the first viewpoint, by starting to circulate the first refrigerant in the first circuit, the temperature of the carbon dioxide refrigerant in the container of the second circuit can be increased via the cascade heat exchanger. Therefore, even if the outside air temperature is low, a normal state in which the density of the carbon dioxide refrigerant is lower than the density of the refrigeration oil can be formed in the container. After reaching the normal state, the valve of the oil return passage extending from the lower part of the container is opened, so that the liquid phase carbon dioxide refrigerant (hereinafter also referred to as "liquid refrigerant") can be suppressed from flowing to the oil return passage. Therefore, the liquid refrigerant can be suppressed from flowing into the second compressor.

[0006] The refrigeration cycle device of the second viewpoint is based on the refrigeration cycle device of the first viewpoint, and the control unit opens the valve when the temperature or pressure of the carbon dioxide refrigerant and the refrigeration oil in the container is above a specified temperature or a specified pressure corresponding to a boundary temperature, wherein the boundary temperature is a temperature at which the density of the carbon dioxide refrigerant in the container becomes equal to the density of the refrigeration oil.

[0007] In the refrigeration cycle device of the second viewpoint, when the temperature or pressure of the carbon dioxide refrigerant and the refrigeration oil in the container is above a predetermined temperature or predetermined pressure corresponding to a boundary temperature at which the density of the carbon dioxide refrigerant in the container becomes equal to the density of the refrigeration oil, it can be determined that the density of the refrigerant in the container and the density of the refrigeration oil have become normal. Therefore, the liquid refrigerant can be further suppressed from flowing into the second compressor.

[0008] A refrigeration cycle apparatus according to a third aspect is the refrigeration cycle apparatus according to the first aspect or the second aspect, wherein the control unit starts circulating the carbon dioxide refrigerant in the second circuit after starting circulating the first refrigerant in the first circuit.

[0009] In the refrigeration cycle device of the third aspect, by starting to circulate the first refrigerant in the first circuit, the temperature of the refrigerant in the container of the second circuit is increased via the cascade heat exchanger, and then the carbon dioxide refrigerant is started to circulate in the second circuit. Therefore, the efficiency of the operation of the second circuit can be improved.

[0010] A refrigeration cycle apparatus according to a fourth aspect is the refrigeration cycle apparatus according to the third aspect, wherein the control unit opens the valve after starting to circulate the carbon dioxide refrigerant in the second circuit.

[0011] In the refrigeration cycle device of the fourth aspect, the first refrigerant circulates in the first circuit, and the carbon dioxide refrigerant circulates in the second circuit, so that the temperature of the carbon dioxide refrigerant in the container can be efficiently increased. As a result, the density of the refrigerant in the container and the density of the refrigeration oil can be easily normalized. After the normal state is reached, the valve of the oil return passage is opened, so that the liquid refrigerant can be easily suppressed from flowing into the second compressor.

[0012] A refrigeration cycle apparatus according to a fifth aspect is the refrigeration cycle apparatus according to the first aspect or the second aspect, wherein the control unit starts the operation of the first circuit and the operation of the second circuit at the same time.

[0013] As in the refrigeration cycle apparatus according to the fifth aspect, the circulation of the first refrigerant in the first circuit and the circulation of the carbon dioxide refrigerant in the second circuit may be performed simultaneously.

[0014] The refrigeration cycle device of the sixth aspect is the refrigeration cycle device of any one of the first to fifth aspects, wherein the control unit performs startup control when the outside air temperature is below the first temperature, and does not perform startup control when the outside air temperature exceeds the first temperature.

[0015] In the refrigeration cycle device of the sixth aspect, when the density of the refrigerant in the container and the density of the refrigerating machine oil are not in a normal state due to the outside air temperature being below the first temperature, the liquid refrigerant can be suppressed from flowing into the second compressor by implementing the startup control. On the other hand, when the density of the refrigerant in the container and the density of the refrigerating machine oil are in a normal state due to the outside air temperature exceeding the first temperature, the liquid refrigerant can be suppressed from flowing into the second compressor even if the valve of the oil return passage is not closed.

[0016] A refrigeration cycle device according to a seventh aspect is the refrigeration cycle device according to the sixth aspect, wherein the control unit simultaneously starts the operation of the first circuit, the operation of the second circuit, and the opening of the valve when the outside air temperature exceeds the first temperature.

[0017] In the refrigeration cycle device of the seventh aspect, when the density of the refrigerant in the container and the density of the refrigerating machine oil are not in a normal state due to the outside air temperature being below the first temperature, the liquid refrigerant can be suppressed from flowing into the second compressor by opening the valve after starting the operation of the first circuit. On the other hand, when the density of the refrigerant in the container and the density of the refrigerating machine oil are in a normal state due to the outside air temperature exceeding the first temperature, the operation of the first circuit, the operation of the second circuit, and the opening of the valve of the oil return passage can be performed simultaneously.

[0018] A refrigeration cycle device according to an eighth aspect is the refrigeration cycle device according to any one of the first to seventh aspects, wherein the first refrigerant includes R32, R454C, propane, R1234yf, R1234ze, or ammonia.

[0019] In the refrigeration cycle apparatus of the eighth aspect, by circulating the first refrigerant containing R32, R454C, propane, R1234yf, R1234ze or ammonia in the first circuit, heat exchange with the carbon dioxide refrigerant can be efficiently performed in the cascade heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the refrigeration cycle device. Figure 2 This is a schematic functional block diagram of a refrigeration cycle device. Figure 3 It is a diagram showing the operation (flow of refrigerant) of the refrigeration cycle device in full cooling operation. Figure 4 It is a diagram showing the operation (flow of refrigerant) of the refrigeration cycle device in the full heating operation. Figure 5 It is a diagram showing the operation (flow of refrigerant) of the refrigeration cycle apparatus in the cooling main operation. Figure 6 It is a diagram showing the operation (flow of refrigerant) of the refrigeration cycle device in the heating main operation. Figure 7 This is a diagram showing a control flow at the time of startup of the heating only operation and the heating main operation of the refrigeration cycle device. Figure 8 It is a diagram showing a control flow at the time of startup of the heating only operation and the heating main operation of the refrigeration cycle device according to the modification. Fig. 9 It is a diagram showing a control flow at the time of startup of the heating only operation and the heating main operation of the refrigeration cycle device according to the modification. Fig.10 It is a diagram showing a control flow at the time of startup of the heating only operation and the heating main operation of the refrigeration cycle device according to the modification. DETAILED DESCRIPTION

[0021] (1) Structure of refrigeration system Figure 1 and Figure 2 The refrigeration cycle device 1 shown is a device used for cooling and heating indoors in a building or the like by performing a vapor compression refrigeration cycle operation.

[0022] The refrigeration cycle device 1 has a first circuit (primary circuit) 5a, a second circuit (secondary circuit) 10, and a cascade heat exchanger 35. The refrigeration cycle device 1 of this embodiment has a binary refrigerant circuit composed of a vapor compression type first circuit 5a and a vapor compression type second circuit 10, and performs a binary refrigeration cycle.

[0023] The first circuit 5a circulates a first refrigerant and a first refrigerating machine oil. The first refrigerant includes, for example, at least one of an HFC-based refrigerant and an HFO-based refrigerant. The first refrigerant in this embodiment is R32. The first refrigerating machine oil is, for example, polyvinyl ether oil.

[0024] The second circuit 10 circulates carbon dioxide refrigerant and second refrigerating machine oil. The second refrigerating machine oil is, for example, incompatible with carbon dioxide. The second refrigerating machine oil in the present embodiment is polyalkylene glycol oil.

[0025] The first circuit 5 a and the second circuit 10 are thermally connected via a cascade heat exchanger 35 .

[0026] The refrigeration cycle device 1 is configured such that the first unit 5, the cascade unit 2, and the second units 4a, 4b, 4c are connected to each other via pipes. The first unit 5 and the cascade unit 2 are connected by a first connecting pipe 112 and a second connecting pipe 111. The cascade unit 2 and the plurality of branch units 6a, 6b, 6c are connected by three connecting pipes: a third connecting pipe 7, a fourth connecting pipe 8, and a fifth connecting pipe 9. The plurality of branch units 6a, 6b, 6c and the plurality of utilization units 3a, 3b, 3c are connected by first connecting pipes 15a, 15b, 15c and second connecting pipes 16a, 16b, 16c.

[0027] In the present embodiment, the first unit 5 is one. In the present embodiment, the cascade unit 2 is one. In the present embodiment, the second units 4a, 4b, 4c are three. In detail, the second units 4a, 4b, 4c include branching units 6a, 6b, 6c and utilization units 3a, 3b, 3c. The plurality of utilization units 3a, 3b, 3c of the second units 4a, 4b, 4c are the first utilization unit 3a, the second utilization unit 3b, and the third utilization unit 3c. The plurality of branching units 6a, 6b, 6c of the second units 4a, 4b, 4c are the first branching unit 6a, the second branching unit 6b, and the third branching unit 6c.

[0028] Furthermore, in the refrigeration cycle device 1, each utilization unit 3a, 3b, 3c is configured to be able to perform cooling operation or heating operation independently, and to be able to perform heat recovery between the utilization units by transferring refrigerant from the utilization unit performing heating operation to the utilization unit performing cooling operation. Specifically, in the present embodiment, heat recovery is performed by executing cooling main operation and heating main operation in which cooling operation and heating operation are performed simultaneously. Furthermore, in the refrigeration cycle device 1, it is configured to balance the heat load of the cascade unit 2 based on the overall heat load of the plurality of utilization units 3a, 3b, 3c in which the above-mentioned heat recovery (cooling main operation, heating main operation) is also considered.

[0029] (2) First circuit The first circuit 5a includes a first compressor 71, a first switching mechanism 72, a first heat exchanger 74, a first expansion valve 76, a first subcooling heat exchanger 103, a first subcooling circuit 104, a first subcooling expansion valve 104a, a second stop valve 108, a second expansion valve 102, a cascade heat exchanger 35 common to the second circuit 10, a first stop valve 109, and a first storage tank 105. In addition, the first circuit 5a includes a first flow path 35b of the cascade heat exchanger 35.

[0030] The first compressor 71 is a device for compressing the first refrigerant, and is constituted by, for example, a positive displacement compressor of a scroll type or the like whose operating capacity can be varied by performing inverter control on the compressor motor 71 a.

[0031] The first accumulator 105 is provided in the middle of the suction flow path connecting the first switching mechanism 72 and the suction side of the first compressor 71 .

[0032] When the cascade heat exchanger 35 functions as an evaporator of the first refrigerant, the first switching mechanism 72 is in a fourth connection state (see Figure 1 In addition, when the cascade heat exchanger 35 functions as a radiator of the first refrigerant, the first switching mechanism 72 is changed to a fifth connection state (see FIG. 1 ) that connects the discharge side of the first compressor 71 and the gas side of the first flow path 35b of the cascade heat exchanger 35. Figure 1 Thus, the first switching mechanism 72 is a device capable of switching the flow path of the refrigerant in the first circuit 5a, and is composed of, for example, a four-way reversing valve. Furthermore, by changing the switching state of the first switching mechanism 72, the cascade heat exchanger 35 can function as an evaporator or radiator of the first refrigerant.

[0033] The cascade heat exchanger 35 is a device for performing heat exchange between a refrigerant such as R32 as a first refrigerant and a carbon dioxide refrigerant without mixing with each other. The cascade heat exchanger 35 is composed of, for example, a plate heat exchanger. The cascade heat exchanger 35 has a second flow path 35a belonging to the second circuit 10 and a first flow path 35b belonging to the first circuit 5a. The gas side of the second flow path 35a is connected to the second switching mechanism 22 via the third heat source pipe 25, and the liquid side of the second flow path 35a is connected to the heat source side expansion valve 36 via the fourth heat source pipe 26. The gas side of the first flow path 35b is connected to the first compressor 71 via the first refrigerant pipe 113, the first connecting pipe 112, the first stop valve 109, and the first switching mechanism 72, and the liquid side of the first flow path 35b is connected to the second refrigerant pipe 114 provided with the second expansion valve 102.

[0034] The first heat exchanger 74 is a device for performing heat exchange between the first refrigerant and the outdoor air. In the first heat exchanger 74, the first refrigerant obtains cooling energy or heating energy from the outdoor air as a heat source. The gas side of the first heat exchanger 74 is connected to the pipe extending from the first switching mechanism 72. The first heat exchanger 74 is composed of, for example, a fin-tube heat exchanger composed of a plurality of heat transfer tubes and fins.

[0035] The first expansion valve 76 is provided in a pipe extending from the liquid side of the first heat exchanger 74 to the first subcooling heat exchanger 103. The first expansion valve 76 is an electric expansion valve whose opening degree can be adjusted, and adjusts the flow rate of the first refrigerant flowing in the liquid side portion of the first circuit 5a.

[0036] The first subcooling circuit 104 branches off from between the first expansion valve 76 and the first subcooling heat exchanger 103, and is connected to a portion of the suction flow path between the first switching mechanism 72 and the first storage tank 105. The first subcooling expansion valve 104a is an electric expansion valve capable of adjusting the opening degree, and is disposed in the first subcooling circuit 104 at an upstream side of the first subcooling heat exchanger 103 to adjust the flow rate of the first refrigerant, etc.

[0037] The first subcooling heat exchanger 103 is a heat exchanger that exchanges heat between the refrigerant flowing from the first expansion valve 76 toward the second stop valve 108 and the refrigerant in the first subcooling circuit 104 that has been decompressed in the first subcooling expansion valve 104 a .

[0038] The first communication pipe 112 is a pipe connecting the first unit 5 and the cascade unit 2. The second communication pipe 111 is a pipe connecting the first unit 5 and the cascade unit 2.

[0039] The second expansion valve 102 is provided in the second refrigerant pipe 114. The second expansion valve 102 is an electric expansion valve whose opening degree can be adjusted, and adjusts the flow rate of the first refrigerant flowing in the first flow path 35b of the cascade heat exchanger 35 and the like.

[0040] The first stop valve 109 is provided between the first communication pipe 112 and the first switching mechanism 72. The second stop valve 108 is provided between the second communication pipe 111 and the first subcooling heat exchanger 103.

[0041] (3) Second circuit (3-1) Overview of the Second Circuit The second circuit 10 is constituted in a manner that a plurality of utilization units 3a, 3b, 3c, a plurality of branch units 6a, 6b, 6c and a cascade unit 2 are connected to each other. Each utilization unit 3a, 3b, 3c is connected to the corresponding branch unit 6a, 6b, 6c one-to-one. Specifically, the utilization unit 3a and the branch unit 6a are connected via the first connecting pipe 15a and the second connecting pipe 16a, the utilization unit 3b and the branch unit 6b are connected via the first connecting pipe 15b and the second connecting pipe 16b, and the utilization unit 3c and the branch unit 6c are connected via the first connecting pipe 15c and the second connecting pipe 16c. In addition, each branch unit 6a, 6b, 6c is connected to the cascade unit 2 via three connecting pipes, namely, the third connecting pipe 7, the fourth connecting pipe 8 and the fifth connecting pipe 9. Specifically, the third connecting pipe 7, the fourth connecting pipe 8 and the fifth connecting pipe 9 extending from the cascade unit 2 are respectively branched into a plurality of pipes and connected to each branch unit 6a, 6b, 6c.

[0042] Depending on the operating state, either the gas-liquid two-phase refrigerant or the liquid refrigerant flows in the third communication pipe 7. Depending on the operating state, either the gas refrigerant or the supercritical refrigerant flows in the fourth communication pipe 8. Depending on the operating state, either the gas-liquid two-phase refrigerant or the gas refrigerant flows in the fifth communication pipe 9.

[0043] The second circuit 10 is configured such that a heat source circuit 12, branch circuits 14a, 14b, 14c, and utilization circuits 13a, 13b, 13c are connected to each other.

[0044] (3-2) Heat source circuit The heat source circuit 12 mainly includes a second compressor 21, a second switching mechanism 22, a first heat source pipe 28, a second heat source pipe 29, an intake flow path 23, a discharge flow path 24, a third heat source pipe 25, a fourth heat source pipe 26, a fifth heat source pipe 27, a cascade heat exchanger 35, a heat source side expansion valve 36, a third stop valve 32, a fourth stop valve 33, a fifth stop valve 31, a second storage tank 30, an oil separator 34, an oil return circuit 40, a second receiver 45, a bypass circuit 46, a bypass expansion valve 46a, a second subcooling heat exchanger 47, a second subcooling circuit 48, a second subcooling expansion valve 48a, an oil return passage 23b, and an oil return valve 23c. In addition, the heat source circuit 12 of the second circuit 10 includes a second flow path 35a of the cascade heat exchanger 35.

[0045] The second compressor 21 is a device for compressing the carbon dioxide refrigerant of the heat source circuit 12 of the second circuit, and is composed of, for example, a positive displacement compressor such as a scroll type that can make the operating capacity variable by inverter control of the compressor motor 21a. In addition, the second compressor 21 is controlled so that the greater the load, the greater the operating capacity according to the load during operation.

[0046] The second switching mechanism 22 is a mechanism capable of switching the connection state of the second circuit 10, especially the flow path of the refrigerant in the heat source circuit 12. In the present embodiment, the second switching mechanism 22 includes a discharge side communication portion 22x, a suction side communication portion 22y, a first switching valve 22a, and a second switching valve 22b. The discharge side communication portion 22x is connected to the end of the discharge flow path 24 on the side opposite to the second compressor 21. The suction side communication portion 22y is connected to the end of the suction flow path 23 on the side opposite to the second compressor 21. The first switching valve 22a and the second switching valve 22b are arranged in parallel with each other between the discharge flow path 24 and the suction flow path 23 of the second compressor 21. The first switching valve 22a is connected to one end of the discharge side communication portion 22x and one end of the suction side communication portion 22y. The second switching valve 22b is connected to the other end of the discharge side communication portion 22x and the other end of the suction side communication portion 22y. In the present embodiment, the first switching valve 22a and the second switching valve 22b are both composed of four-way reversing valves. The first switching valve 22a and the second switching valve 22b respectively have four connection ports, namely, a first connection port, a second connection port, a third connection port, and a fourth connection port. In the first switching valve 22a and the second switching valve 22b of the present embodiment, each fourth port is a connection port that is closed and not connected to the flow path of the second circuit 10. In the first switching valve 22a, the first connection port is connected to one end of the discharge side communication part 22x, the second connection port is connected to the third heat source pipe 25 extending from the second flow path 35a of the cascade heat exchanger 35, and the third connection port is connected to one end of the suction side communication part 22y. The first switching valve 22a switches between a switching state in which the first connection port is connected to the second connection port and the third connection port is connected to the fourth connection port and a switching state in which the third connection port is connected to the second connection port and the first connection port is connected to the fourth connection port. In the second switching valve 22b, the first connection port is connected to the other end of the discharge side communication part 22x, the second connection port is connected to the first heat source pipe 28, and the third connection port is connected to the other end of the suction side communication part 22y. The second switching valve 22b switches between a switching state in which the first connection port is connected to the second connection port and the third connection port is connected to the fourth connection port and a switching state in which the third connection port is connected to the second connection port and the first connection port is connected to the fourth connection port.

[0047] In the case where the cascade heat exchanger 35 functions as a radiator of the carbon dioxide refrigerant and the carbon dioxide refrigerant discharged from the second compressor 21 is prevented from being transported to the fourth connecting pipe 8, the second switching mechanism 22 is switched to a first connection state in which the discharge flow path 24 and the third heat source pipe 25 are connected through the first switching valve 22a and the first heat source pipe 28 and the suction flow path 23 are connected through the second switching valve 22b. The first connection state of the second switching mechanism 22 is a connection state adopted in the full cooling operation described later. In addition, in the case where the cascade heat exchanger 35 functions as an evaporator of the carbon dioxide refrigerant, the second switching mechanism 22 is switched to a second connection state in which the discharge flow path 24 and the first heat source pipe 28 are connected through the second switching valve 22b and the third heat source pipe 25 and the suction flow path 23 are connected through the first switching valve 22a. The second connection state of the second switching mechanism 22 is a connection state adopted in the full heating operation described later and the heating main operation. In addition, when the cascade heat exchanger 35 functions as a heat sink for the carbon dioxide refrigerant and the carbon dioxide refrigerant discharged from the second compressor 21 is delivered to the fourth connecting pipe 8, the second switching mechanism 22 is switched to a third connection state in which the discharge flow path 24 and the third heat source pipe 25 are connected via the first switching valve 22a and the discharge flow path 24 and the first heat source pipe 28 are connected via the second switching valve 22b. The third connection state of the second switching mechanism 22 is a connection state adopted during the refrigeration main operation described later.

[0048] As described above, the cascade heat exchanger 35 is a device for performing heat exchange between a refrigerant such as R32 as the first refrigerant flowing in the first circuit 5a and a carbon dioxide refrigerant flowing in the second circuit 10 without mixing with each other. In addition, the cascade heat exchanger 35 has a second flow path 35a through which the carbon dioxide refrigerant of the second circuit 10 flows and a first flow path 35b through which the first refrigerant of the first circuit 5a flows, and thus it is shared by the first unit 5 and the cascade unit 2. In addition, in the present embodiment, the cascade heat exchanger 35 is arranged inside the cascade shell of the cascade unit 2. The gas side of the first flow path 35b of the cascade heat exchanger 35 passes through the first refrigerant piping 113 and extends to the first communication piping 112 outside the cascade shell. The liquid side of the first flow path 35b of the cascade heat exchanger 35 passes through the second refrigerant piping 114 provided with the second expansion valve 102 and extends to the second communication piping 111 outside the cascade shell.

[0049] The heat source side expansion valve 36 is an electric expansion valve whose opening degree can be adjusted and connected to the liquid side of the cascade heat exchanger 35 in order to adjust the flow rate of the carbon dioxide refrigerant flowing through the cascade heat exchanger 35 . The heat source side expansion valve 36 is provided in the fourth heat source pipe 26 .

[0050] The third stop valve 32, the fourth stop valve 33, and the fifth stop valve 31 are valves provided at the connection ports with external equipment and piping (specifically, the connecting piping 7, 8, and 9). Specifically, the third stop valve 32 is connected to the fourth connecting piping 8 drawn out from the cascade unit 2. The fourth stop valve 33 is connected to the fifth connecting piping 9 drawn out from the cascade unit 2. The fifth stop valve 31 is connected to the third connecting piping 7 drawn out from the cascade unit 2.

[0051] The first heat source pipe 28 is a refrigerant pipe that connects the third stop valve 32 and the second switching mechanism 22. Specifically, the first heat source pipe 28 connects the third stop valve 32 and the second switching valve 22b in the second switching mechanism 22 to each other.

[0052] The suction flow path 23 is a flow path connecting the second switching mechanism 22 and the suction side of the second compressor 21. Specifically, the suction flow path 23 connects the suction side communication portion 22y in the second switching mechanism 22 and the suction side of the second compressor 21. A second accumulator 30 is provided in the middle of the suction flow path 23.

[0053] The suction flow path 23 includes a suction pipe 23a. The suction pipe 23a connects the suction side of the second compressor 21 to the second accumulator 30. Here, one end of the suction pipe 23a is connected to the suction side of the second compressor 21, and the other end of the suction pipe 23a is connected to the upper part of the second accumulator 30.

[0054] The second heat source pipe 29 is a refrigerant pipe that connects the fourth stop valve 33 and the middle of the suction flow path 23. In addition, in the present embodiment, the second heat source pipe 29 is connected to the suction flow path 23 at a connection portion in the suction flow path 23, which is a portion between the suction side connecting portion 22y in the second switching mechanism 22 and the second storage tank 30.

[0055] The discharge flow path 24 is a refrigerant pipe connecting the discharge side of the second compressor 21 and the second switching mechanism 22. Specifically, the discharge flow path 24 connects the discharge side of the second compressor 21 and the discharge-side communication portion 22x in the second switching mechanism 22.

[0056] The third heat source pipe 25 is a refrigerant pipe that connects the second switching mechanism 22 and the gas side of the cascade heat exchanger 35. Specifically, the third heat source pipe 25 connects the second connection port of the first switching valve 22a in the second switching mechanism 22 and the gas side end of the second flow path 35a in the cascade heat exchanger 35.

[0057] The fourth heat source pipe 26 is a refrigerant pipe that connects the liquid side (the side opposite to the gas side, the side opposite to the side where the second switching mechanism 22 is provided) of the cascade heat exchanger 35 and the second receiver 45. Specifically, the fourth heat source pipe 26 connects the liquid side end (the end opposite to the gas side) of the second flow path 35a in the cascade heat exchanger 35 and the second receiver 45.

[0058] The second receiver 45 stores carbon dioxide refrigerant. The second receiver 45 is provided between the liquid side of the cascade heat exchanger 35 and the second heat exchangers 52a, 52b, 52c. The fourth heat source pipe 26, the fifth heat source pipe 27 and the bypass circuit 46 extend from the second receiver 45.

[0059] The bypass circuit 46 connects the second heat exchangers 52a, 52b, 52c and the cascade heat exchanger 35 and the suction pipe 23a described later. Here, the bypass circuit 46 is a refrigerant pipe that connects the upper region inside the second receiver 45, that is, the gas phase region, and the suction flow path 23. Specifically, the bypass circuit 46 is connected between the second switching mechanism 22 and the second storage tank 30 in the suction flow path 23.

[0060] A bypass expansion valve 46a is provided in the bypass circuit 46. The bypass expansion valve 46a is an electric expansion valve that can adjust the amount of refrigerant introduced from the second receiver 45 to the suction side of the second compressor 21 by adjusting the opening degree.

[0061] The fifth heat source pipe 27 is a refrigerant pipe that connects the second receiver 45 and the fifth stop valve 31 .

[0062] The second subcooling circuit 48 is a refrigerant pipe that connects a portion of the fifth heat source pipe 27 and the suction flow path 23. Specifically, the second subcooling circuit 48 is connected between the second switching mechanism 22 and the second storage tank 30 in the suction flow path 23. In addition, in the present embodiment, the second subcooling circuit 48 extends in a branched manner from between the second receiver 45 and the second subcooling heat exchanger 47.

[0063] The second subcooling heat exchanger 47 is a heat exchanger that performs heat exchange using the refrigerant flowing in the flow path belonging to the fifth heat source piping 27 and the refrigerant flowing in the flow path belonging to the second subcooling circuit 48. In the present embodiment, it is arranged between the portion of the fifth heat source piping 27 where the second subcooling circuit 48 branches and the fifth stop valve 31. The second subcooling expansion valve 48a is arranged between the portion of the second subcooling circuit 48 where the fifth heat source piping 27 branches and the second subcooling heat exchanger 47. The second subcooling expansion valve 48a supplies the second subcooling heat exchanger 47 with a decompressed refrigerant and is an electric expansion valve capable of adjusting the opening.

[0064] The second storage tank 30 is provided on the suction side of the second compressor 21. The second storage tank 30 is a container for storing carbon dioxide refrigerant and second refrigeration oil. The second storage tank 30 is a gas-liquid separator that separates the inflowing fluid into a liquid phase and a gas phase. The suction pipe 23a, the oil return passage 23b described later, and the portion of the suction flow path 23 connected to the second switching mechanism 22 extend from the second storage tank 30.

[0065] The second storage tank 30 includes a main body portion 30a, an inlet 30b, a refrigerant outlet 30c, and an oil outlet 30d.

[0066] The main body 30a has a sealable shape. The main body 30a is not particularly limited, and may be, for example, a cylindrical shape or a U-shape.

[0067] The inlet 30b allows a mixture of carbon dioxide refrigerant and the second refrigeration oil to flow into the main body 30a. The inlet 30b allows carbon dioxide refrigerant to flow into the main body 30a from a portion of the suction flow path 23 connected to the second switching mechanism 22. The inlet 30b is provided at the upper portion of the main body 30a.

[0068] The refrigerant outflow port 30c discharges the carbon dioxide refrigerant stored in the main body portion 30a. The refrigerant outflow port 30c is provided at the upper portion of the main body portion 30a. The refrigerant outflow port 30c returns the carbon dioxide refrigerant to the suction pipe 23a.

[0069] The oil outflow port 30d discharges the refrigerating machine oil stored in the main body portion 30a. The oil outflow port 30d is provided at the lower portion of the main body portion 30a. The oil outflow port 30d sends the second refrigerating machine oil to the oil return passage 23b.

[0070] The oil return passage 23b is provided so as to connect the lower portion of the second accumulator 30 and the suction pipe 23a. The oil return passage 23b returns the second refrigerating machine oil from the lower portion of the second accumulator 30 to the suction pipe 23a.

[0071] In the present embodiment, the "lower portion of the second tank 30" is the bottom surface of the main body 30a serving as a container. In other words, one end of the oil return passage 23b is connected to the bottom surface of the main body 30a of the second tank 30. In addition, the bottom surface of the main body 30a includes a downwardly curved structure, an upwardly curved structure, a flat structure, and the like.

[0072] The oil return valve 23c is controlled to be open, so that the second refrigeration oil separated in the second accumulator 30 passes through the oil return passage 23b and further through the suction pipe 23a, and returns to the suction side of the second compressor 21.

[0073] The oil return valve 23c may be an electromagnetic valve controlled to open and close or an electric valve whose opening degree can be adjusted as long as it has a mechanism to narrow the oil return passage 23b. In the present embodiment, the oil return valve 23c is an electromagnetic valve that opens or closes the oil return passage 23b.

[0074] The oil separator 34 is provided in the middle of the discharge flow path 24. The oil separator 34 is a device for separating the second refrigeration oil discharged from the second compressor 21 along with the carbon dioxide refrigerant from the carbon dioxide refrigerant and returning the second refrigeration oil to the second compressor 21.

[0075] The oil return circuit 40 is provided to connect the oil separator 34 and the suction flow path 23. The flow path extending from the oil separator 34 of the oil return circuit 40 has an oil return flow path 41, and the oil return flow path 41 extends in a manner of merging with the portion between the second accumulator 30 and the suction side of the second compressor 21 in the suction flow path 23. An oil return on-off valve 44 is provided in the middle of the oil return flow path 41. By controlling the oil return on-off valve 44 to an open state, the second refrigerating machine oil separated in the oil separator 34 passes through the oil return flow path 41 and returns to the suction side of the second compressor 21. Here, in the present embodiment, when the second compressor 21 is in the operating state in the second circuit 10, the oil return on-off valve 44 controls the amount of the second refrigerating machine oil returning through the oil return circuit 40 by repeatedly maintaining the open state for a predetermined time and maintaining the closed state for a predetermined time. In addition, the oil return on-off valve 44 is an electromagnetic valve that is controlled to be opened and closed in the present embodiment, but it may also be an electric expansion valve that can adjust the opening degree.

[0076] In addition, the heat source circuit 12 constituting the second circuit 10 also has a sensor that measures at least one of the temperature and pressure of the carbon dioxide refrigerant and the second refrigeration oil on the suction side of the second compressor 21. Here, a second suction temperature sensor 88 and a second suction pressure sensor 37 are provided, and the second suction temperature sensor 88 is used as a sensor to measure the temperature of the carbon dioxide refrigerant and the second refrigeration oil on the suction side of the second compressor 21, and the second suction pressure sensor 37 is used as a sensor to measure the pressure of the carbon dioxide refrigerant and the second refrigeration oil on the suction side of the second compressor 21.

[0077] (3-3) Using the loop The following describes the utilization loops 13a, 13b, and 13c. Since the utilization loops 13b and 13c have the same structure as the utilization loop 13a, the symbols "b" or "c" are marked on the utilization loops 13b and 13c instead of "a" representing the various parts of the utilization loop 13a, and the description of each part is omitted.

[0078] The utilization circuit 13 a mainly includes a second heat exchanger 52 a , a first utilization pipe 57 a , a second utilization pipe 56 a , and a utilization-side expansion valve 51 a .

[0079] The second heat exchanger 52a is a device for performing heat exchange between the refrigerant and the indoor air, and is composed of, for example, a fin-tube heat exchanger, which is composed of a plurality of heat transfer tubes and fins. In addition, the plurality of second heat exchangers 52a, 52b, 52c are connected in parallel with respect to the second switching mechanism 22, the suction flow path 23, and the cascade heat exchanger 35.

[0080] One end of the second utilization pipe 56a is connected to the liquid side (the side opposite to the gas side) of the second heat exchanger 52a of the first utilization unit 3a. The other end of the second utilization pipe 56a is connected to the second connecting pipe 16a. The utilization side expansion valve 51a is provided in the middle of the second utilization pipe 56a.

[0081] The usage-side expansion valve 51a is an electric expansion valve capable of adjusting the opening degree, and performs adjustment of the flow rate of the refrigerant flowing through the second heat exchanger 52a, etc. The usage-side expansion valve 51a is provided in the second usage pipe 56a.

[0082] One end of the first utilization pipe 57a is connected to the gas side of the second heat exchanger 52a of the first utilization unit 3a. In the present embodiment, the first utilization pipe 57a is connected to the side of the second heat exchanger 52a opposite to the utilization side expansion valve 51a side. The other end of the first utilization pipe 57a is connected to the first connecting pipe 15a.

[0083] (3-4) Bifurcation loop The following describes the branching circuits 14a, 14b, and 14c. Since the branching circuits 14b and 14c have the same structure as the branching circuit 14a, the branching circuits 14b and 14c are marked with "b" or "c" instead of the symbol "a" representing the various parts of the branching circuit 14a, and the description of each part is omitted.

[0084] The branch circuit 14a mainly includes a joining pipe 62a, a first branch pipe 63a, a second branch pipe 64a, a first regulating valve 66a, a second regulating valve 67a, a bypass pipe 69a, a check valve 68a, and a third branch pipe 61a.

[0085] One end of the merging pipe 62a is connected to the first connecting pipe 15a. The first branch pipe 63a and the second branch pipe 64a are branched and connected to the other end of the merging pipe 62a.

[0086] The side of the first branch pipe 63a opposite to the merging pipe 62a side is connected to the fourth communication pipe 8. The first branch pipe 63a is provided with an openable and closable first regulating valve 66a.

[0087] The side of the second branch pipe 64a opposite to the joining pipe 62a side is connected to the fifth communication pipe 9. The second branch pipe 64a is provided with an openable and closable second regulating valve 67a.

[0088] The bypass pipe 69a is a refrigerant pipe that connects a portion of the first branch pipe 63a that is closer to the fourth communication pipe 8 than the first regulating valve 66a and a portion of the second branch pipe 64a that is closer to the fifth communication pipe 9 than the second regulating valve 67a. A check valve 68a is provided in the middle of the bypass pipe 69a. The check valve 68a allows only the refrigerant to flow from the second branch pipe 64a side to the first branch pipe 63a side, and does not allow the refrigerant to flow from the first branch pipe 63a side to the second branch pipe 64a side.

[0089] One end of the third branch pipe 61 a is connected to the second connection pipe 16 a , and the other end of the third branch pipe 61 a is connected to the third communication pipe 7 .

[0090] Furthermore, when the first branch unit 6a performs the full cooling operation described later, by setting the first regulating valve 66a to the closed state and the second regulating valve 67a to the open state, it can play the following role. The first branch unit 6a transports the refrigerant that passes through the third connecting pipe 7 and flows into the third branch pipe 61a to the second connecting pipe 16a. In addition, the refrigerant that passes through the second connecting pipe 16a and flows in the second utilization pipe 56a of the first utilization unit 3a passes through the utilization side expansion valve 51a and is transported to the second heat exchanger 52a of the first utilization unit 3a. Furthermore, the refrigerant transported to the second heat exchanger 52a evaporates due to heat exchange with the indoor air and flows in the first connecting pipe 15a via the first utilization pipe 57a. The refrigerant flowing in the first connecting pipe 15a is transported to the confluence pipe 62a of the first branch unit 6a. The refrigerant flowing in the confluence pipe 62a does not flow to the first branch pipe 63a, but flows to the second branch pipe 64a. The refrigerant flowing in the second branch pipe 64a passes through the second regulating valve 67a. A portion of the refrigerant after passing through the second regulating valve 67a is delivered to the fifth connecting pipe 9. In addition, the remaining portion of the refrigerant after passing through the second regulating valve 67a flows in a manner branched to the bypass pipe 69a provided with a check valve 68a, and is delivered to the fourth connecting pipe 8 after flowing through a portion of the first branch pipe 63a. As a result, the total flow path cross-sectional area when the carbon dioxide refrigerant in a gas state evaporated in the second heat exchanger 52a is delivered to the second compressor 21 can be increased, and thus the pressure loss can be reduced.

[0091] In addition, when the first branch unit 6a performs the cooling main operation described later and the heating main operation, when the room is cooled in the first utilization unit 3a, by setting the first regulating valve 66a to the closed state and the second regulating valve 67a to the open state, the following function can be achieved. The first branch unit 6a transports the refrigerant that passes through the third connecting pipe 7 and flows into the third branch pipe 61a to the second connecting pipe 16a. In addition, the refrigerant that passes through the second connecting pipe 16a and flows in the second utilization pipe 56a of the first utilization unit 3a passes through the utilization side expansion valve 51a and is transported to the second heat exchanger 52a of the first utilization unit 3a. And, the refrigerant transported to the second heat exchanger 52a evaporates due to heat exchange with the indoor air, and then flows in the first connection pipe 15a via the first utilization pipe 57a. The refrigerant flowing in the first connection pipe 15a is transported to the confluence pipe 62a of the first branch unit 6a. The refrigerant flowing through the merging pipe 62 a flows into the second branching pipe 64 a , passes through the second regulating valve 67 a , and is then sent to the fifth communication pipe 9 .

[0092] In addition, when the first branch unit 6a performs the full heating operation described later, by setting the second regulating valve 67a to the closed state and the first regulating valve 66a to the open state, the following effect can be achieved. In the first branch unit 6a, the refrigerant that passes through the fourth connecting pipe 8 and flows into the first branch pipe 63a passes through the first regulating valve 66a and is transported to the confluence pipe 62a. The refrigerant that flows through the confluence pipe 62a flows in the first utilization pipe 57a of the utilization unit 3a via the first connecting pipe 15a and is transported to the second heat exchanger 52a. Then, the refrigerant transported to the second heat exchanger 52a, after heat is dissipated due to heat exchange with the indoor air, passes through the utilization side expansion valve 51a provided in the second utilization pipe 56a. The refrigerant that passes through the second utilization pipe 56a flows in the third branch pipe 61a of the first branch unit 6a via the second connecting pipe 16a and is transported to the third communication pipe 7.

[0093] In addition, when the first branch unit 6a performs the cooling main operation described later and the heating main operation, when the room is heated in the first utilization unit 3a, by setting the second regulating valve 67a to a closed state and the first regulating valve 66a to an open state, the following effect can be achieved. In the first branch unit 6a, the refrigerant that passes through the fourth connecting pipe 8 and flows into the first branch pipe 63a passes through the first regulating valve 66a and is transported to the confluence pipe 62a. The refrigerant that flows through the confluence pipe 62a flows in the first utilization pipe 57a of the utilization unit 3a via the first connecting pipe 15a and is transported to the second heat exchanger 52a. Then, the refrigerant transported to the second heat exchanger 52a passes through the utilization side expansion valve 51a provided in the second utilization pipe 56a after heat is dissipated due to heat exchange with the indoor air. The refrigerant that has passed through the second utilization pipe 56 a flows through the second connection pipe 16 a and into the third branch pipe 61 a of the first branch unit 6 a , and is then sent to the third communication pipe 7 .

[0094] Not only the first branching unit 6a has the above function, but the second branching unit 6b and the third branching unit 6c also have the above function. Therefore, the first branching unit 6a, the second branching unit 6b, and the third branching unit 6c can switch each second heat exchanger 52a, 52b, and 52c to function as an evaporator of the refrigerant or as a radiator of the refrigerant.

[0095] (4) Unit 1 The first unit 5 is arranged in a space different from the space where the second units 4a, 4b, 4c (specifically, the utilization units 3a, 3b, 3c and the branching units 6a, 6b, 6c) are arranged. Here, the first unit 5 is arranged on the roof of the building.

[0096] The first unit 5 is configured to include a part of the first circuit 5 a , a first fan 75 , various sensors, and a first control unit 70 in a first casing (not shown).

[0097] The first unit 5 has a first compressor 71, a first switching mechanism 72, a first heat exchanger 74, a first expansion valve 76, a first subcooling heat exchanger 103, a first subcooling circuit 104, a first subcooling expansion valve 104a, a second stop valve 108, a first stop valve 109 and a first storage tank 105 as part of the first circuit 5a.

[0098] The first fan 75 is provided in the first unit 5, and generates an air flow that guides outdoor air to the first heat exchanger 74, exchanges heat with the first refrigerant flowing in the first heat exchanger 74, and then discharges the air to the outside. The first fan 75 is driven by a first fan motor 75a.

[0099] In addition, various sensors are provided in the first unit 5. Specifically, an external air temperature sensor 77, a first discharge pressure sensor 78, a first suction pressure sensor 79, a first suction temperature sensor 81, and a first heat exchange temperature sensor 82 are provided in the first unit 5. The external air temperature sensor 77 detects the temperature of the outdoor air before passing through the first heat exchanger 74. The first discharge pressure sensor 78 detects the pressure of the first refrigerant discharged from the first compressor 71. The first suction pressure sensor 79 detects the pressure of the first refrigerant sucked into the first compressor 71. The first suction temperature sensor 81 detects the temperature of the first refrigerant sucked into the first compressor 71. The first heat exchange temperature sensor 82 detects the temperature of the refrigerant flowing in the first heat exchanger 74.

[0100] The first control unit 70 controls the operation of each component 71 (71a), 72, 75 (75a), 76, 104a provided in the first unit 5. The first control unit 70 has a processor such as a CPU or a microcomputer and a memory provided for controlling the first unit 5, and can exchange control signals and the like with a remote controller (not shown), and can exchange control signals and the like with the heat source side control unit 20 of the cascade unit 2, the branch unit control units 60a, 60b, 60c, and the utilization side control units 50a, 50b, 50c.

[0101] (5) Cascade unit The cascade unit 2 is arranged in a space different from the space where the second units 4a, 4b, 4c (specifically, the utilization units 3a, 3b, 3c and the branching units 6a, 6b, 6c) are arranged. Here, the cascade unit 2 is arranged on the roof of the building.

[0102] The cascade unit 2 is connected to the branch units 6a, 6b, 6c via the communication pipes 7, 8, 9, and constitutes a part of the second circuit 10. The cascade unit 2 is connected to the first unit 5 via the communication pipes 111, 112, and constitutes a part of the first circuit 5a.

[0103] The cascade unit 2 is configured to include the above-mentioned heat source circuit 12, various sensors, a heat source side control unit 20, a second expansion valve 102 constituting a part of the first circuit 5a, a first refrigerant piping 113 and a second refrigerant piping 114 in a cascade housing (not shown).

[0104] Various sensors are provided in the cascade unit 2. Specifically, the cascade unit 2 is provided with the second suction pressure sensor 37, the second discharge pressure sensor 38, the second discharge temperature sensor 39, the second suction temperature sensor 88, the cascade temperature sensor 83, the receiver outlet temperature sensor 84, the bypass circuit temperature sensor 85, the subcooling outlet temperature sensor 86, and the subcooling circuit temperature sensor 87. The second suction pressure sensor 37 detects the pressure of the carbon dioxide refrigerant on the suction side of the second compressor 21. The second discharge pressure sensor 38 detects the pressure of the carbon dioxide refrigerant on the discharge side of the second compressor 21. The second discharge temperature sensor 39 detects the temperature of the carbon dioxide refrigerant on the discharge side of the second compressor 21. The second suction temperature sensor 88 detects the temperature of the carbon dioxide refrigerant on the suction side of the second compressor 21. The cascade temperature sensor 83 detects the temperature of the carbon dioxide refrigerant flowing between the second flow path 35a of the cascade heat exchanger 35 and the heat source side expansion valve 36. The receiver outlet temperature sensor 84 detects the temperature of the carbon dioxide refrigerant flowing between the second receiver 45 and the second subcooling heat exchanger 47. The bypass circuit temperature sensor 85 detects the temperature of the carbon dioxide refrigerant flowing on the downstream side of the bypass expansion valve 46a in the bypass circuit 46. The subcooling outlet temperature sensor 86 detects the temperature of the carbon dioxide refrigerant flowing between the second subcooling heat exchanger 47 and the fifth stop valve 31. The subcooling circuit temperature sensor 87 detects the temperature of the carbon dioxide refrigerant flowing through the outlet of the second subcooling heat exchanger 47 in the second subcooling circuit 48.

[0105] The heat source side control unit 20 controls the operation of each component 21 (21a), 22, 23c, 36, 44, 46a, 48a, 102 provided inside the cascade housing (not shown) of the cascade unit 2. The heat source side control unit 20 has a processor such as a CPU or a microcomputer and a memory provided for controlling the cascade unit 2, and is configured to be able to exchange control signals and the like with the first control unit 70 of the first unit 5, the utilization side control units 50a, 50b, 50c of the utilization units 3a, 3b, 3c, and the branch unit control units 60a, 60b, 60c.

[0106] In addition, in this way, the heat source side control unit 20 can control not only the components of the heat source circuit 12 constituting the second circuit 10, but also the second expansion valve 102 constituting a part of the first circuit 5a. Therefore, the heat source side control unit 20 can make the condition of the heat source circuit 12 close to the desired condition by controlling the valve opening of the second expansion valve 102 based on the condition of the heat source circuit 12 controlled by itself. Specifically, the carbon dioxide refrigerant flowing in the second flow path 35a of the cascade heat exchanger 35 in the heat source circuit 12 can control the heat received from the first refrigerant flowing in the first flow path 35b of the cascade heat exchanger 35 or the heat provided to the first refrigerant.

[0107] (6) Unit 2 The second units 4a, 4b, 4c include utilization units 3a, 3b, 3c, branching units 6a, 6b, 6c, first connection pipes 15a, 15b, 15c, and second connection pipes 16a, 16b, 16c.

[0108] (6-1) Utilization Unit The utilization units 3a, 3b, and 3c are installed by being embedded in, suspended from, or hung on a ceiling in a room of a building or the like, or by being hung on a wall in a room or the like.

[0109] The utilization units 3 a , 3 b , and 3 c are connected to the cascade unit 2 via communication pipes 7 , 8 , and 9 .

[0110] The utilization units 3 a , 3 b , 3 c include utilization circuits 13 a , 13 b , 13 c that constitute a part of the second circuit 10 .

[0111] The following describes the structures of the side units 3a, 3b, and 3c. In addition, since the second utilization unit 3b and the third utilization unit 3c have the same structure as the first utilization unit 3a, only the structure of the first utilization unit 3a is described here, and the letters "b" or "c" are respectively marked on the structures of the second utilization unit 3b and the third utilization unit 3c instead of the letter "a" representing the symbols of the various parts of the first utilization unit 3a, and the description of each part is omitted.

[0112] The first usage unit 3a mainly includes the above-mentioned usage circuit 13a, the second fan 53a, the usage-side control unit 50a, and various sensors. In addition, the second fan 53a includes a second fan motor 54a.

[0113] The second fan 53a draws indoor air into the utilization unit 3a, exchanges heat with the refrigerant flowing in the second heat exchanger 52a, and then generates an air flow supplied to the room as supply air. The second fan 53a is driven by a second fan motor 54a.

[0114] The utilization unit 3a is provided with a liquid side temperature sensor 58a, which detects the temperature of the refrigerant on the liquid side of the second heat exchanger 52a. In addition, the utilization unit 3a is provided with an indoor temperature sensor 55a, which detects the indoor temperature, which is the temperature of the air introduced from the room before passing through the second heat exchanger 52a.

[0115] The utilization side control unit 50a controls the actions of the components 51a, 53a (54a) constituting the utilization unit 3a. The utilization side control unit 50a has a processor such as a CPU or a microcomputer and a memory provided for controlling the utilization unit 3a, and can exchange control signals and the like with a remote controller (not shown), and can exchange control signals and the like with the heat source side control unit 20 of the cascade unit 2, the branch unit control units 60a, 60b, 60c, and the first control unit 70 of the first unit 5.

[0116] The second usage unit 3b includes a usage circuit 13b, a second fan 53b, a usage-side control unit 50b, and a second fan motor 54b. The third usage unit 3c includes a usage circuit 13c, a second fan 53c, a usage-side control unit 50c, and a second fan motor 54c.

[0117] (6-2) Bifurcation unit The branching units 6a, 6b, and 6c are installed in a space behind a ceiling in a building or the like.

[0118] The branching units 6a, 6b, and 6c are connected to the utilization units 3a, 3b, and 3c in a one-to-one correspondence. The branching units 6a, 6b, and 6c are connected to the cascade unit 2 via the communication pipes 7, 8, and 9.

[0119] Next, the structures of the branching units 6a, 6b, and 6c are described. In addition, since the second branching unit 6b and the third branching unit 6c have the same structure as the first branching unit 6a, only the structure of the first branching unit 6a is described here, and the structures of the second branching unit 6b and the third branching unit 6c are respectively marked with the letter "b" or "c" instead of the letter "a" representing the symbols of the various parts of the first branching unit 6a, and the description of each part is omitted.

[0120] The first branching unit 6a mainly includes the above-mentioned branching circuit 14a and a branching unit control unit 60a.

[0121] The branch unit control unit 60a controls the actions of the components 66a and 67a constituting the branch unit 6a. The branch unit control unit 60a has a processor such as a CPU or a microcomputer and a memory provided for controlling the branch unit 6a, and can exchange control signals and the like with a remote controller (not shown), and with the heat source side control unit 20 of the cascade unit 2, the utilization units 3a, 3b, 3c, and the first control unit 70 of the first unit 5.

[0122] In addition, the second branch unit 6b includes a branch circuit 14b and a branch unit control unit 60b. The third branch unit 6c includes a branch circuit 14c and a branch unit control unit 60c.

[0123] (7) Control unit (7-1) Overview In the refrigeration cycle device 1, the heat source side control unit 20, the utilization side control units 50a, 50b, 50c, the branch unit control units 60a, 60b, 60c, and the first control unit 70 are connected to each other via wires or wirelessly so as to be able to communicate with each other, thereby constituting a control unit 80. Therefore, the control unit 80 controls the actions of each component 21 (21a), 22, 23c, 36, 44, 46a, 48a, 51a, 51b, 51c, 53a, 53b, 53c (54a, 54b, 54c), 66a, 66b, 66c, 67a, 67b, 67c, 71 (71a), 72, 75 (75a), 76, 104a, etc. based on the detection information of various sensors 37, 38, 39, 83, 84, 85, 86, 87, 88, 77, 78, 79, 81, 82, 58a, 58b, 58c, 56a, 56b, 56c, etc. and the instruction information received from a remote control not shown in the figure.

[0124] Here, the control unit 80 switches between the operation of heating the carbon dioxide refrigerant by the first refrigerant in the cascade heat exchanger 35 (in this embodiment, full heating operation or heating-dominated operation) and the operation of cooling the carbon dioxide refrigerant by the first refrigerant (in this embodiment, full cooling operation or cooling-dominated operation). In this way, in order to switch the heating and cooling of the carbon dioxide refrigerant in the cascade heat exchanger 35, the heat source side control unit 20 of the control unit 80 controls the second switching mechanism 22. Specifically, the control unit 80 controls the second switching mechanism 22 to switch between a first state in which the cascade heat exchanger 35 functions as a radiator of the carbon dioxide refrigerant and a second state in which the cascade heat exchanger 35 functions as an evaporator of the carbon dioxide refrigerant.

[0125] (7-2) Control during startup The following describes the startup control performed by the control unit 80 when starting the refrigeration cycle operation of the refrigeration cycle device 1. In addition, the normal refrigeration cycle operation of the refrigeration cycle device 1 includes full refrigeration operation, full heating operation, refrigeration-based operation, and heating-based operation. In this embodiment, the control unit 80 performs startup control when the carbon dioxide refrigerant is heated by the first refrigerant in the cascade heat exchanger 35. Here, the control unit 80 performs startup control during full heating operation and heating-based operation.

[0126] After the first refrigerant starts to circulate in the first circuit 5a, the control unit 80 performs a start-up control to open the oil return valve 23c. Specifically, when the control unit 80 receives a command for heating operation or heating main operation from a remote controller or the like, the control unit 80 performs a control to increase the opening degree of the oil return valve 23c after the first compressor 71 is started to circulate the first refrigerant in the first circuit 5a.

[0127] When the temperature of the carbon dioxide refrigerant in the second accumulator 30 disposed outdoors is low due to the low outside air temperature at the start of the full heating operation or the heating main operation, the density of the second refrigerating machine oil may be lower than the density of the carbon dioxide refrigerant. In this case, the second refrigerating machine oil is in an abnormal state above the carbon dioxide refrigerant in the second accumulator 30. In this abnormal state, the control unit 80 controls to close the oil return valve 23c, thereby preventing the carbon dioxide refrigerant from flowing out to the oil return passage 23b provided with the oil return valve 23c. In addition, by performing the startup control, the first refrigerant starts to circulate in the first circuit 5a, so that the temperature of the carbon dioxide refrigerant in the second accumulator 30 of the second circuit 10 can be increased through the cascade heat exchanger 35. Thus, a normal state in which the density of the carbon dioxide refrigerant is lower than the density of the second refrigerating machine oil can be formed. In other words, the control unit 80 controls to place the second refrigerating machine oil below the carbon dioxide refrigerant in the second accumulator 30. In other words, the control unit 80 prevents the second refrigerating machine oil from reversing from below the carbon dioxide refrigerant to above in the second accumulator 30. Furthermore, after reaching the normal state, the control unit 80 controls to open the oil return valve 23c, thereby causing the second refrigerating machine oil to flow from the oil return valve 23c to the oil return passage 23b, and preventing the carbon dioxide refrigerant from flowing out.

[0128] In the present embodiment, when starting the heating only operation or the heating main operation, the controller 80 first circulates the first refrigerant in the first circuit 5a, then circulates the carbon dioxide refrigerant in the second circuit 10, and then opens the oil return valve 23c.

[0129] Specifically, after the control unit 80 starts to circulate the first refrigerant in the first circuit 5a, it starts to circulate the carbon dioxide refrigerant in the second circuit 10. Here, when the condensation temperature of the first refrigerant in the cascade heat exchanger 35 rises to a predetermined value or more by circulating the first refrigerant in the first circuit 5a, the control unit 80 starts the second compressor 21 and starts to circulate the carbon dioxide refrigerant in the second circuit 10.

[0130] In addition, the control unit 80 opens the oil return valve 23c after starting to circulate the carbon dioxide refrigerant in the second circuit 10. Here, when the temperature or pressure of the carbon dioxide refrigerant and the second refrigeration oil in the second storage tank 30 reaches or exceeds a predetermined temperature or a predetermined pressure corresponding to a boundary temperature, the control unit 80 opens the oil return valve 23c, wherein the boundary temperature is a temperature at which the density of the carbon dioxide refrigerant in the second storage tank 30 becomes equal to the density of the second refrigeration oil.

[0131] In addition, "predetermined temperature or predetermined pressure" is a temperature or pressure equal to or higher than the boundary temperature, and preferably a temperature or pressure exceeding the boundary temperature. When the second refrigerating machine oil is polyalkylene glycol, the boundary temperature is -15°C.

[0132] In this embodiment, the control unit 80 obtains the temperature or pressure of the carbon dioxide refrigerant and the second refrigerating machine oil flowing in the suction pipe 23a from a sensor that measures at least one of the temperature and pressure of the carbon dioxide refrigerant and the second refrigerating machine oil on the suction side of the second compressor 21 in order to determine whether the temperature or pressure of the carbon dioxide refrigerant and the second refrigerating machine oil in the second storage tank 30 is above a predetermined temperature or a predetermined pressure. Here, the control unit 80 obtains the temperature or pressure of the carbon dioxide refrigerant and the second refrigerating machine oil flowing in the suction pipe 23a from at least one of the second suction temperature sensor 88 and the second suction pressure sensor 37. In addition, the control unit 80 determines whether the obtained temperature or pressure is above a predetermined temperature or a predetermined pressure corresponding to a boundary temperature, wherein the boundary temperature is a temperature at which the density of the carbon dioxide refrigerant in the second storage tank 30 becomes equal to the density of the second refrigerating machine oil.

[0133] Furthermore, in the present embodiment, the control unit 80 implements startup control when the external air temperature is below the first temperature, and does not implement startup control when the external air temperature exceeds the first temperature. The control unit 80 has a first temperature associated with startup control. The first temperature is a temperature at which the density of the carbon dioxide refrigerant is higher than the density of the refrigeration oil due to the low temperature of the carbon dioxide refrigerant in the second storage tank 30. The first temperature is, for example, -20°C. Furthermore, the control unit 80 obtains the external air temperature from the external air temperature sensor 77, and determines whether the obtained external air temperature is below the first temperature. Furthermore, the control unit 80 implements startup control when it is determined that the external air temperature is below the first temperature, and does not implement startup control when it is determined that the external air temperature exceeds the first temperature.

[0134] Here, when the outside air temperature exceeds the first temperature, the control unit 80 starts the operation of the first circuit 5a, the operation of the second circuit 10, and the opening action of the oil return valve 23c at the same time. In addition, "simultaneously" means, for example, that the control unit 80 issues an instruction to start the first compressor 71, an instruction to start the second compressor 21, and an instruction to open the oil return valve 23c at the same time. Therefore, it includes the case where the circulation of the first refrigerant in the first circuit 5a, the circulation of the carbon dioxide refrigerant in the second circuit 10, and the opening action of the oil return valve 23c start at exactly the same time and the case where any one of them starts slightly earlier.

[0135] (8) Operation of refrigeration cycle device Next, use Figure 3 to Figure 6 The operation of the refrigeration cycle apparatus 1 will be described.

[0136] The refrigeration cycle operation of the refrigeration cycle device 1 can be mainly divided into cooling-only operation, heating-only operation, cooling-dominant operation, and heating-dominant operation.

[0137] Here, full cooling operation is a refrigeration cycle operation in which only the utilization unit operates the second heat exchanger 52a, 52b, 52c as an evaporator of the carbon dioxide refrigerant, and the cascade heat exchanger 35 acts as a radiator of the carbon dioxide refrigerant for the evaporation load of the entire utilization unit.

[0138] The full heating operation is a refrigeration cycle operation in which only the utilization unit in which the second heat exchangers 52a, 52b, 52c function as radiators of the carbon dioxide refrigerant exists, and the cascade heat exchanger 35 functions as an evaporator of the carbon dioxide refrigerant for the heat dissipation load of the entire utilization unit.

[0139] The cooling-main operation is an operation in which the utilization unit in which the second heat exchangers 52a, 52b, 52c function as evaporators of the carbon dioxide refrigerant and the utilization unit in which the second heat exchangers 52a, 52b, 52c function as radiators of the refrigerant are mixed. The cooling-main operation is a refrigeration cycle operation in which, when the evaporation load is the main part of the heat load of the entire utilization unit, the cascade heat exchanger 35 functions as a radiator of the carbon dioxide refrigerant in order to handle the evaporation load of the entire utilization unit.

[0140] The heating-main operation is an operation in which the utilization unit in which the second heat exchangers 52a, 52b, 52c function as evaporators of the refrigerant and the utilization unit in which the second heat exchangers 52a, 52b, 52c function as radiators of the refrigerant are mixed. The heating-main operation is a refrigeration cycle operation in which, when the heat dissipation load is the main part of the heat load of the entire utilization unit, the cascade heat exchanger 35 is made to function as an evaporator of the carbon dioxide refrigerant in order to deal with the heat dissipation load of the entire utilization unit.

[0141] In addition, the operation of the refrigeration cycle device 1 including the refrigeration cycle operation is performed by the control unit 80 .

[0142] (8-1) Full refrigeration operation In the full cooling operation, for example, the second heat exchangers 52a, 52b, 52c of the utilization units 3a, 3b, 3c are all operated as evaporators of the refrigerant. In addition, in the full cooling operation, the cascade heat exchanger 35 is operated as a heat sink for the carbon dioxide refrigerant. In this full cooling operation, the first circuit 5a and the second circuit 10 of the refrigeration cycle device 1 are operated as follows. Figure 3 In addition, Figure 3 The arrows indicated in the first circuit 5a and the arrows indicated in the second circuit 10 indicate the flow of the refrigerant during the cooling only operation.

[0143] Specifically, in the first unit 5, the first switching mechanism 72 is switched to the fourth connection state, so that the cascade heat exchanger 35 functions as an evaporator of the first refrigerant. Figure 3The connection state shown by the solid line in the first switching mechanism 72 of . Thus, in the first unit 5, the first refrigerant discharged from the first compressor 71 passes through the first switching mechanism 72, and performs heat exchange with the external air supplied from the first fan 75 in the first heat exchanger 74 to dissipate heat. The first refrigerant after dissipating heat in the first heat exchanger 74 passes through the first expansion valve 76 controlled to be fully open, a part of the refrigerant passes through the first subcooling heat exchanger 103 and flows to the second stop valve 108, and the other part of the refrigerant branches and flows to the first subcooling circuit 104. The refrigerant flowing in the first subcooling circuit 104 is decompressed when passing through the first subcooling expansion valve 104a. The refrigerant flowing from the first expansion valve 76 to the second stop valve 108 performs heat exchange in the first subcooling heat exchanger 103 with the refrigerant decompressed by the first subcooling expansion valve 104a and flowing in the first subcooling circuit 104, and is cooled to a subcooled state. The first refrigerant that has become a supercooled state passes through the second connecting pipe 111, and is decompressed when passing through the second expansion valve 102. Here, the valve opening of the second expansion valve 102 is controlled so that the superheat of the first refrigerant sucked into the first compressor 71 meets the specified conditions. When the first refrigerant after being decompressed by the second expansion valve 102 flows in the first flow path 35b of the cascade heat exchanger 35, it evaporates by heat exchange with the carbon dioxide refrigerant flowing in the second flow path 35a, and flows to the first connecting pipe 112. The first refrigerant reaches the first switching mechanism 72 after passing through the first connecting pipe 112 and the first stop valve 109. The refrigerant passing through the first switching mechanism 72 merges with the refrigerant flowing in the first supercooling circuit 104, and is then sucked into the first compressor 71 via the first storage tank 105.

[0144] In addition, in the cascade unit 2, by switching the second switching mechanism 22 to the first connection state, the cascade heat exchanger 35 functions as a radiator of the carbon dioxide refrigerant. In addition, in the first connection state of the second switching mechanism 22, the discharge flow path 24 is connected to the third heat source pipe 25 through the first switching valve 22a, and the first heat source pipe 28 is connected to the suction flow path 23 through the second switching valve 22b. Here, the opening of the heat source side expansion valve 36 is adjusted. In the first to third utilization units 3a, 3b, 3c, the second regulating valves 67a, 67b, 67c are controlled to be in the open state. As a result, the second heat exchangers 52a, 52b, 52c of the utilization units 3a, 3b, 3c all function as evaporators of the refrigerant. In addition, all the second heat exchangers 52a, 52b, 52c of the utilization units 3a, 3b, 3c are connected to the suction side of the second compressor 21 of the cascade unit 2 via the first utilization pipes 57a, 57b, 57c, the first connecting pipes 15a, 15b, 15c, the converging pipes 62a, 62b, 62c, the second branch pipes 64a, 64b, 64c, the bypass pipes 69a, 69b, 69c, a part of the first branch pipes 63a, 63b, 63c, the fourth communication pipe 8, and the fifth communication pipe 9. In addition, the opening of the second subcooling expansion valve 48a is controlled so that the subcooling degree of the carbon dioxide refrigerant flowing from the outlet of the second subcooling heat exchanger 47 toward the third communication pipe 7 satisfies a predetermined condition. The bypass expansion valve 46a is controlled to be in a closed state. In the utilization units 3a, 3b, and 3c, the opening degrees of the utilization-side expansion valves 51a, 51b, and 51c are adjusted.

[0145] In the second circuit 10, the high-pressure carbon dioxide refrigerant compressed and discharged by the second compressor 21 passes through the first switching valve 22a of the second switching mechanism 22 and is sent to the second flow path 35a of the cascade heat exchanger 35. In the cascade heat exchanger 35, the high-pressure carbon dioxide refrigerant flowing in the second flow path 35a dissipates heat, and the first refrigerant flowing in the first flow path 35b of the cascade heat exchanger 35 evaporates. The carbon dioxide refrigerant that has dissipated heat in the cascade heat exchanger 35 flows into the second receiver 45 after passing through the heat source side expansion valve 36 whose opening is adjusted. A part of the carbon dioxide refrigerant flowing out of the second receiver 45 flows into the second subcooling circuit 48 in a branched manner, and after being decompressed in the second subcooling expansion valve 48a, it merges with the suction flow path 23. In the second subcooling heat exchanger 47, another part of the refrigerant flowing out of the second receiver 45 is cooled by the refrigerant flowing in the second subcooling circuit 48, and is sent to the third communication pipe 7 through the fifth stop valve 31.

[0146] Furthermore, the refrigerant delivered to the third communication pipe 7 is branched into three and passes through the third branch pipes 61a, 61b, 61c of the first to third branch units 6a, 6b, 6c. Then, the refrigerant flowing through the second connection pipes 16a, 16b, 16c is delivered to the second utilization pipes 56a, 56b, 56c of the first to third utilization units 3a, 3b, 3c. The refrigerant delivered to the second utilization pipes 56a, 56b, 56c is delivered to the utilization side expansion valves 51a, 51b, 51c of the utilization units 3a, 3b, 3c.

[0147] Next, the carbon dioxide refrigerant that has passed through the utilization side expansion valves 51a, 51b, 51c whose openings have been adjusted exchanges heat with the indoor air supplied by the second fans 53a, 53b, 53c in the second heat exchangers 52a, 52b, 52c. As a result, the carbon dioxide refrigerant flowing through the second heat exchangers 52a, 52b evaporates and becomes a low-pressure gas refrigerant. The indoor air is cooled and supplied to the room. As a result, the indoor space is cooled. The low-pressure gas refrigerant evaporated in the second heat exchangers 52a, 52b, 52c flows through the first utilization pipes 57a, 57b, 57c, flows through the first connecting pipes 15a, 15b, 15c, and is then transported to the converging pipes 62a, 62b, 62c of the first to third branch units 6a, 6b, 6c.

[0148] The low-pressure gas refrigerant delivered to the converging pipes 62a, 62b, 62c flows to the second branch pipes 64a, 64b, 64c. A portion of the carbon dioxide refrigerant that has passed through the second regulating valves 67a, 67b, 67c in the second branch pipes 64a, 64b, 64c is delivered to the fifth connecting pipe 9. The remaining refrigerant that has passed through the second regulating valves 67a, 67b, 67c passes through the bypass pipes 69a, 69b, 69c, flows through a portion of the first branch pipes 63a, 63b, 63c, and is then delivered to the fourth connecting pipe 8.

[0149] Next, the low-pressure gas refrigerant delivered to the fourth connecting pipe 8 and the fifth connecting pipe 9 passes through the third stop valve 32, the fourth stop valve 33, the first heat source pipe 28, the second heat source pipe 29, the second switching valve 22b of the second switching mechanism 22, the suction flow path 23, the second storage tank 30 and the suction pipe 23a, and returns to the suction side of the second compressor 21.

[0150] Furthermore, the second refrigerating machine oil circulating in the second circuit 10 returns from the lower portion of the second accumulator 30 to the suction side of the second compressor 21 through the oil return passage 23 b , the oil return valve 23 c , and the suction pipe 23 a .

[0151] In this way, the operation in full cooling operation is performed.

[0152] Furthermore, in the heating only operation, the opening degree of the oil return valve 23 c is controlled by the control unit 80 based on the superheat degree (discharge superheat degree) of the carbon dioxide refrigerant discharged from the second compressor 21 in order to prevent the liquid refrigerant from flowing into the second compressor 21 .

[0153] (8-2) Full heating operation In the full heating operation, for example, the second heat exchangers 52a, 52b, 52c of the utilization units 3a, 3b, 3c are all operated as radiators of the refrigerant. In addition, in the full heating operation, the cascade heat exchanger 35 is operated as an evaporator of the carbon dioxide refrigerant. In this full heating operation, the first circuit 5a and the second circuit 10 of the refrigeration cycle device 1 are operated as follows. Figure 4 As shown. Figure 4 The arrows indicated in the first circuit 5a and the arrows indicated in the second circuit 10 indicate the flow of the refrigerant during the heating only operation.

[0154] Specifically, in the first unit 5, by switching the first switching mechanism 72 to the fifth connection state, the cascade heat exchanger 35 functions as a heat sink for the first refrigerant. The fifth connection state of the first switching mechanism 72 is Figure 4 The first switching mechanism 72 of the first unit 5 is connected in a state shown by a dotted line. As a result, in the first unit 5, the first refrigerant discharged from the first compressor 71 and passing through the first switching mechanism 72 further passes through the first communication pipe 112 and is transported to the first flow path 35b of the cascade heat exchanger 35. The refrigerant flowing in the first flow path 35b of the cascade heat exchanger 35 is condensed by heat exchange with the carbon dioxide refrigerant flowing in the second flow path 35a. When the first refrigerant condensed in the cascade heat exchanger 35 flows in the second refrigerant pipe 114, it passes through the second expansion valve 102 controlled to be fully open. The refrigerant after passing through the second expansion valve 102 flows in the order of the second communication pipe 111, the second stop valve 108, and the first subcooling heat exchanger 103, and is decompressed in the first expansion valve 76. In addition, during the full heating operation, since the first subcooling expansion valve 104a is controlled to be closed, the refrigerant does not flow in the first subcooling circuit 104, and therefore, heat exchange in the first subcooling heat exchanger 103 is not performed. In addition, the first expansion valve 76 is controlled, for example, in a valve opening degree so that the superheat of the first refrigerant sucked into the first compressor 71 satisfies a predetermined condition. The refrigerant decompressed in the first expansion valve 76 exchanges heat with the outside air supplied from the first fan 75 in the first heat exchanger 74 to evaporate, passes through the first switching mechanism 72 and the first storage tank 105, and is sucked into the first compressor 71.

[0155] In addition, in the cascade unit 2, the second switching mechanism 22 is switched to the second connection state. Thus, the cascade heat exchanger 35 functions as an evaporator of the carbon dioxide refrigerant. In the second connection state of the second switching mechanism 22, the discharge flow path 24 is connected to the first heat source pipe 28 through the second switching valve 22b, and the third heat source pipe 25 is connected to the suction flow path 23 through the first switching valve 22a. In addition, the opening of the heat source side expansion valve 36 is adjusted. In the first to third branching units 6a, 6b, 6c, the first regulating valves 66a, 66b, 66c are controlled to be in the open state, and the second regulating valves 67a, 67b, 67c are controlled to be in the closed state. Thus, the second heat exchangers 52a, 52b, 52c of the utilization units 3a, 3b, 3c all function as radiators of the refrigerant. Furthermore, the second heat exchangers 52a, 52b, 52c of the utilization units 3a, 3b, 3c and the discharge side of the second compressor 21 of the cascade unit 2 are connected via the discharge flow path 24, the first heat source pipe 28, the fourth communication pipe 8, the first branch pipes 63a, 63b, 63c, the confluence pipes 62a, 62b, 62c, the first connecting pipes 15a, 15b, 15c and the first utilization pipes 57a, 57b, 57c. In addition, the second subcooling expansion valve 48a and the bypass expansion valve 46a are controlled to be closed. In the utilization units 3a, 3b, 3c, the opening of the utilization side expansion valves 51a, 51b, 51c is adjusted.

[0156] In the second circuit 10, the high-pressure carbon dioxide refrigerant compressed and discharged by the second compressor 21 passes through the second switching valve 22b of the second switching mechanism 22 and is delivered to the first heat source pipe 28. The refrigerant delivered to the first heat source pipe 28 passes through the third stop valve 32 and is delivered to the fourth communication pipe 8.

[0157] Then, the high-pressure refrigerant delivered to the fourth communication pipe 8 is branched into three and delivered to the first branch pipes 63a, 63b, 63c of each utilization unit 3a, 3b, 3c in operation. The high-pressure carbon dioxide refrigerant delivered to the first branch pipes 63a, 63b, 63c passes through the first regulating valves 66a, 66b, 66c and flows in the converging pipes 62a, 62b, 62c. Then, the refrigerant flowing through the first connecting pipes 15a, 15b, 15c and the first utilization pipes 57a, 57b, 57c is delivered to the second heat exchangers 52a, 52b, 52c.

[0158] Next, the high-pressure carbon dioxide refrigerant delivered to the second heat exchanger 52a, 52b, 52c exchanges heat with the indoor air supplied by the second fan 53a, 53b, 53c in the second heat exchanger 52a, 52b, 52c. As a result, the carbon dioxide refrigerant flowing in the second heat exchanger 52a, 52b, 52c dissipates heat. The indoor air is heated and supplied to the room. As a result, the indoor space is heated. The carbon dioxide refrigerant after dissipating heat in the second heat exchanger 52a, 52b, 52c flows in the second utilization pipe 56a, 56b, 56c and passes through the utilization side expansion valve 51a, 51b, 51c whose opening is adjusted. Then, the refrigerant flowing through the second connecting pipe 16a, 16b, 16c flows in the third branch pipe 61a, 61b, 61c of each branch unit 6a, 6b, 6c.

[0159] Next, the carbon dioxide refrigerant sent to the third branch pipes 61 a , 61 b ​​, and 61 c is sent to the third communication pipe 7 and merges therewith.

[0160] Next, the carbon dioxide refrigerant delivered to the third communication pipe 7 passes through the fifth stop valve 31 and is delivered to the heat source side expansion valve 36. The refrigerant delivered to the heat source side expansion valve 36 is flow-regulated in the heat source side expansion valve 36 and then delivered to the cascade heat exchanger 35. In the cascade heat exchanger 35, the carbon dioxide refrigerant flowing in the second flow path 35a evaporates and becomes a low-pressure gas refrigerant and is delivered to the second switching mechanism 22, and the first refrigerant flowing in the first flow path 35b of the cascade heat exchanger 35 is condensed. Next, the low-pressure gas refrigerant delivered to the first switching valve 22a of the second switching mechanism 22 passes through the suction flow path 23, the second accumulator 30, and the suction pipe 23a, and returns to the suction side of the second compressor 21.

[0161] Furthermore, the second refrigerating machine oil circulating in the second circuit 10 returns from the lower portion of the second accumulator 30 to the suction side of the second compressor 21 through the oil return passage 23 b , the oil return valve 23 c , and the suction pipe 23 a .

[0162] In this way, the operation in the full heating operation is performed.

[0163] (8-3) Refrigeration main operation In the cooling-main operation, for example, the second heat exchangers 52a and 52b of the units 3a and 3b function as evaporators of the refrigerant, and the second heat exchanger 52c of the unit 3c functions as a radiator of the refrigerant. In addition, in the cooling-main operation, the cascade heat exchanger 35 functions as a radiator of the carbon dioxide refrigerant. In this cooling-main operation, the first circuit 5a and the second circuit 10 of the refrigeration cycle device 1 function as follows. Figure 5 As shown. Figure 5The arrows indicated in the first circuit 5a and the arrows indicated in the second circuit 10 indicate the flow of the refrigerant during the cooling main operation.

[0164] Specifically, in the first unit 5, by switching the first switching mechanism 72 to the fourth connection state ( Figure 5 The first refrigerant discharged from the first compressor 71 passes through the first switching mechanism 72 and is condensed by heat exchange with the external air supplied from the first fan 75 in the first heat exchanger 74. The first refrigerant condensed in the first heat exchanger 74 passes through the first expansion valve 76 controlled to be fully open, and a part of the refrigerant passes through the first subcooling heat exchanger 103 and flows to the second stop valve 108, and the other part of the refrigerant branches and flows to the first subcooling circuit 104. The refrigerant flowing in the first subcooling circuit 104 is decompressed when passing through the first subcooling expansion valve 104a. The refrigerant flowing from the first expansion valve 76 to the second stop valve 108 is heat exchanged between the first subcooling heat exchanger 103 and the refrigerant decompressed by the first subcooling expansion valve 104a and flowing in the first subcooling circuit 104, and is cooled to a subcooled state. The refrigerant that has become a supercooled state flows in the second connecting pipe 111 and is decompressed in the second expansion valve 102. In addition, at this time, the second expansion valve 102, for example, its valve opening is controlled so that the superheat of the refrigerant sucked into the first compressor 71 meets the specified conditions. When the first refrigerant after being decompressed by the second expansion valve 102 flows in the first flow path 35b of the cascade heat exchanger 35, it evaporates by heat exchange with the carbon dioxide refrigerant flowing in the second flow path 35a, and flows to the first connecting pipe 112. The first refrigerant reaches the first switching mechanism 72 after passing through the first connecting pipe 112 and the first stop valve 109. The refrigerant passing through the first switching mechanism 72 merges with the refrigerant flowing in the first supercooling circuit 104, and is then sucked into the first compressor 71 via the first storage tank 105.

[0165] In addition, in the cascade unit 2, the second switching mechanism 22 is switched to the third connection state in which the discharge flow path 24 is connected to the third heat source pipe 25 through the first switching valve 22a and the discharge flow path 24 is connected to the first heat source pipe 28 through the second switching valve 22b, so that the cascade heat exchanger 35 functions as a heat sink for the carbon dioxide refrigerant. In addition, the opening degree of the heat source side expansion valve 36 is adjusted. In the first to third branch units 6a, 6b, 6c, the first regulating valve 66c and the second regulating valves 67a, 67b are controlled to be in an open state, and the first regulating valves 66a, 66b and the second regulating valve 67c are controlled to be in a closed state. Thus, the second heat exchangers 52a, 52b of the utilization units 3a, 3b function as evaporators of the refrigerant, and the second heat exchanger 52c of the utilization unit 3c functions as a heat sink for the refrigerant. In addition, the second heat exchangers 52a, 52b of the utilization units 3a, 3b and the suction side of the second compressor 21 of the cascade unit 2 are connected via the fifth connecting pipe 9, and the second heat exchanger 52c of the utilization unit 3c and the discharge side of the second compressor 21 of the cascade unit 2 are connected via the fourth connecting pipe 8. In addition, the opening of the second subcooling expansion valve 48a is controlled so that the subcooling degree of the carbon dioxide refrigerant flowing toward the third connecting pipe 7 at the outlet of the second subcooling heat exchanger 47 satisfies the prescribed condition. The bypass expansion valve 46a is controlled to be closed. In the utilization units 3a, 3b, 3c, the opening of the utilization side expansion valves 51a, 51b, 51c is adjusted.

[0166] In the above-mentioned second circuit 10, a portion of the high-pressure carbon dioxide refrigerant compressed and discharged by the second compressor 21 passes through the second switching valve 22b of the second switching mechanism 22, the first heat source piping 28 and the third stop valve 32 and is transported to the fourth connecting piping 8, and the remaining portion passes through the first switching valve 22a of the second switching structure 22 and the third heat source piping 25 and is transported to the second flow path 35a of the cascade heat exchanger 35.

[0167] Next, the high-pressure refrigerant sent to the fourth communication pipe 8 is sent to the first branch pipe 63c. The high-pressure refrigerant sent to the first branch pipe 63c passes through the first regulating valve 66c and the converging pipe 62c and is sent to the second heat exchanger 52c of the utilization unit 3c.

[0168] Next, the high-pressure refrigerant delivered to the second heat exchanger 52c exchanges heat with the indoor air supplied by the second fan 53c in the second heat exchanger 52c. As a result, the carbon dioxide refrigerant flowing in the second heat exchanger 52c dissipates heat. The indoor air is heated and supplied to the room, and the heating operation of the utilization unit 3c is performed. The carbon dioxide refrigerant that has dissipated heat in the second heat exchanger 52c flows through the second utilization pipe 56c, and the flow rate is adjusted in the utilization side expansion valve 51c. Then, the carbon dioxide refrigerant flowing through the second connecting pipe 16c is delivered to the third branch pipe 61c of the branch unit 6c.

[0169] Next, the carbon dioxide refrigerant sent to the third branch pipe 61 c is sent to the third communication pipe 7 .

[0170] In addition, the high-pressure refrigerant delivered to the second flow path 35a of the cascade heat exchanger 35 exchanges heat with the first refrigerant flowing in the first flow path 35b in the cascade heat exchanger 35, thereby dissipating heat. The carbon dioxide refrigerant after dissipating heat in the cascade heat exchanger 35 is flow-regulated in the heat source side expansion valve 36 and then flows into the second receiver 45. A portion of the carbon dioxide refrigerant flowing out of the second receiver 45 flows in a branched manner to the second subcooling circuit 48, and merges with the suction flow path 23 after being decompressed in the second subcooling expansion valve 48a. In the second subcooling heat exchanger 47, another portion of the refrigerant flowing out of the second receiver 45 is cooled by the refrigerant flowing in the second subcooling circuit 48, and is then delivered to the third connecting pipe 7 through the fifth stop valve 31, and merges with the refrigerant after dissipating heat in the second heat exchanger 52c.

[0171] Next, the refrigerant that has merged in the third communication pipe 7 is branched into two and delivered to the third branch pipes 61a and 61b of the branch units 6a and 6b. Then, the refrigerant flowing in the second connecting pipes 16a and 16b is delivered to the second utilization pipes 56a and 56b of the first and second utilization units 3a and 3b. The refrigerant flowing in the second utilization pipes 56a and 56b passes through the utilization side expansion valves 51a and 51b of the utilization units 3a and 3b.

[0172] Next, the refrigerant that has passed through the utilization side expansion valves 51a and 51b whose openings have been adjusted exchanges heat with the indoor air supplied by the second fans 53a and 53b in the second heat exchangers 52a and 52b. As a result, the refrigerant flowing in the second heat exchangers 52a and 52b evaporates and becomes a low-pressure gas refrigerant. The indoor air is cooled and supplied to the room. As a result, the indoor space is cooled. The low-pressure gas refrigerant evaporated in the second heat exchangers 52a and 52b is transported to the converging pipes 62a and 62b of the first and second branching units 6a and 6b.

[0173] Then, the low-pressure gas refrigerant sent to the joining pipes 62a and 62b passes through the second regulating valves 67a and 67b and the second branch pipes 64a and 64b, and is sent to the fifth communication pipe 9 and joins there.

[0174] Next, the low-pressure gas refrigerant sent to the fifth communication pipe 9 passes through the fourth stop valve 33 , the second heat source pipe 29 , the suction flow path 23 , the second accumulator 30 , and the suction pipe 23 a , and returns to the suction side of the second compressor 21 .

[0175] Furthermore, the second refrigerating machine oil circulating in the second circuit 10 returns from the lower portion of the second accumulator 30 to the suction side of the second compressor 21 through the oil return passage 23 b , the oil return valve 23 c , and the suction pipe 23 a .

[0176] In this way, the operation in the cooling main operation is performed.

[0177] (8-4) Heating main operation In the heating-main operation, for example, the following operation is performed: the second heat exchangers 52a and 52b of the utilization units 3a and 3b function as radiators of the refrigerant, and the second heat exchanger 52c functions as an evaporator of the refrigerant. In addition, in the heating-main operation, the cascade heat exchanger 35 functions as an evaporator of the carbon dioxide refrigerant. In this heating-main operation, the first circuit 5a and the second circuit 10 of the refrigeration cycle device 1 are as follows: Figure 6 As shown. Figure 6 The arrows indicated in the first circuit 5a and the arrows indicated in the second circuit 10 indicate the flow of the refrigerant during the heating main operation.

[0178] Specifically, in the first unit 5, by switching the first switching mechanism 72 to the fifth connection state, the cascade heat exchanger 35 functions as a heat sink for the first refrigerant. The fifth connection state of the first switching mechanism 72 is Figure 6The first switching mechanism 72 of the first unit 5 is connected in a state shown by a dotted line. Thus, in the first unit 5, the first refrigerant discharged from the first compressor 71, passing through the first switching mechanism 72 and passing through the first stop valve 109 passes through the first communication pipe 112 and is transported to the first flow path 35b of the cascade heat exchanger 35. The refrigerant flowing in the first flow path 35b of the cascade heat exchanger 35 is condensed by heat exchange with the carbon dioxide refrigerant flowing in the second flow path 35a. The first refrigerant condensed in the cascade heat exchanger 35 passes through the second expansion valve 102 controlled to be fully open, and then flows in the order of the second communication pipe 111, the second stop valve 108, and the first subcooling heat exchanger 103, and is decompressed in the first expansion valve 76. In addition, during the heating main operation, since the first subcooling expansion valve 104a is controlled to be closed, the refrigerant does not flow in the first subcooling circuit 104, and therefore, the heat exchange in the first subcooling heat exchanger 103 is not performed. In addition, the valve opening of the first expansion valve 76 is controlled, for example, so that the superheat of the refrigerant sucked into the first compressor 71 satisfies a predetermined condition. The refrigerant decompressed in the first expansion valve 76 exchanges heat with the outside air supplied from the first fan 75 in the first heat exchanger 74 to evaporate, passes through the first switching mechanism 72 and the first storage tank 105, and is sucked into the first compressor 71.

[0179] In the cascade unit 2, the second switching mechanism 22 is switched to the second connection state. In the second connection state of the second switching mechanism 22, the discharge flow path 24 is connected to the first heat source pipe 28 through the second switching valve 22b, and the third heat source pipe 25 is connected to the suction flow path 23 through the first switching valve 22a. Thus, the cascade heat exchanger 35 functions as an evaporator of the carbon dioxide refrigerant. In addition, the opening degree of the heat source side expansion valve 36 is adjusted. In the first to third branching units 6a, 6b, and 6c, the first regulating valves 66a, 66b and the second regulating valve 67c are controlled to be in an open state, and the first regulating valve 66c and the second regulating valves 67a, 67b are controlled to be in a closed state. Thus, the second heat exchangers 52a and 52b of the utilization units 3a and 3b function as radiators of the refrigerant, and the second heat exchanger 52c of the utilization unit 3c functions as an evaporator of the refrigerant. Furthermore, the second heat exchanger 52c of the utilization unit 3c and the suction side of the second compressor 21 of the cascade unit 2 are connected via the first utilization pipe 57c, the first connecting pipe 15c, the converging pipe 62c, the second branching pipe 64c, and the fifth connecting pipe 9. In addition, the second heat exchangers 52a, 52b of the utilization units 3a, 3b and the discharge side of the second compressor 21 of the cascade unit 2 are connected via the discharge flow path 24, the first heat source pipe 28, the fourth connecting pipe 8, the first branching pipe 63a, 63b, the converging pipe 62a, 62b, the first connecting pipe 15a, 15b, and the first utilization pipes 57a, 57b. In addition, the second supercooling expansion valve 48a and the bypass expansion valve 46a are controlled to be closed. In the utilization units 3a, 3b, and 3c, the opening of the utilization side expansion valves 51a, 51b, and 51c is adjusted.

[0180] In the second circuit 10 , the high-pressure carbon dioxide refrigerant compressed and discharged by the second compressor 21 passes through the second switching valve 22 b of the second switching mechanism 22 , the first heat source pipe 28 , and the third stop valve 32 , and is sent to the fourth communication pipe 8 .

[0181] Next, the high-pressure refrigerant delivered to the fourth communication pipe 8 is branched into two and delivered to the first branch pipes 63a and 63b of the first branch unit 6a and the second branch unit 6b respectively connected to the first utilization unit 3a and the second utilization unit 3b in operation. The high-pressure refrigerant delivered to the first branch pipes 63a and 63b passes through the first regulating valves 66a and 66b, the converging pipes 62a and 62b, and the first connecting pipes 15a and 15b, and is delivered to the second heat exchangers 52a and 52b of the first utilization unit 3a and the second utilization unit 3b.

[0182] Next, the high-pressure carbon dioxide refrigerant delivered to the second heat exchangers 52a and 52b exchanges heat with the indoor air supplied by the second fans 53a and 53b in the second heat exchangers 52a and 52b. As a result, the refrigerant flowing in the second heat exchangers 52a and 52b dissipates heat. The indoor air is heated and supplied to the room. As a result, the indoor space is heated. The refrigerant that dissipates heat in the second heat exchangers 52a and 52b flows in the second utilization pipes 56a and 56b and passes through the utilization side expansion valves 51a and 51b whose openings are adjusted. Then, the refrigerant flowing in the second connecting pipes 16a and 16b passes through the third branch pipes 61a and 61b of the branch units 6a and 6b and is delivered to the third connecting pipe 7.

[0183] Next, part of the refrigerant sent to the third communication pipe 7 is sent to the third branch pipe 61 c of the branch unit 6 c , and the rest is sent to the heat source side expansion valve 36 through the fifth stop valve 31 .

[0184] Next, the refrigerant sent to the third branch pipe 61c flows through the second connection pipe 16c, flows through the second usage pipe 56c of the usage unit 3c, and is sent to the usage-side expansion valve 51c.

[0185] Next, the refrigerant that has passed through the utilization side expansion valve 51c whose opening is adjusted exchanges heat with the indoor air supplied by the second fan 53c in the second heat exchanger 52c. As a result, the refrigerant flowing in the second heat exchanger 52c evaporates and becomes a low-pressure gas refrigerant. The indoor air is cooled and supplied to the room. As a result, the indoor space is cooled. The low-pressure gas refrigerant evaporated in the second heat exchanger 52c passes through the first utilization pipe 57c and the first connecting pipe 15c and is transported to the confluence pipe 62c.

[0186] Next, the low-pressure gas refrigerant sent to the joining pipe 62 c passes through the second regulating valve 67 c and the second branch pipe 64 c and is sent to the fifth communication pipe 9 .

[0187] Next, the low-pressure gas refrigerant sent to the fifth communication pipe 9 passes through the fourth stop valve 33 , the second heat source pipe 29 , the suction flow path 23 , the second accumulator 30 , and the suction pipe 23 a , and returns to the suction side of the second compressor 21 .

[0188] In addition, the carbon dioxide refrigerant delivered to the heat source side expansion valve 36 exchanges heat with the first refrigerant flowing in the first flow path 35b in the second flow path 35a of the cascade heat exchanger 35 after passing through the heat source side expansion valve 36 whose opening is adjusted. As a result, the refrigerant flowing in the second flow path 35a of the cascade heat exchanger 35 evaporates and becomes a low-pressure gas refrigerant, and is delivered to the first switching valve 22a of the second switching mechanism 22. The low-pressure gas refrigerant delivered to the first switching valve 22a of the second switching mechanism 22 merges with the low-pressure gas refrigerant evaporated in the second heat exchanger 52c in the suction flow path 23. The merged refrigerant returns to the suction side of the second compressor 21 via the second storage tank 30 and the suction pipe 23a.

[0189] In this way, the operation in the heating main operation is performed.

[0190] Furthermore, in the heating main operation, the opening degree of the oil return valve 23 c is controlled by the control unit 80 based on the superheat (discharge superheat) of the carbon dioxide refrigerant discharged from the second compressor 21 in order to prevent the liquid refrigerant from flowing into the second compressor 21 .

[0191] (9) Control method during startup Below, refer to Figure 7 The control method at the start of the above-mentioned heating only operation and heating-main operation will be described. In the present embodiment, the control unit 80 sets the oil return valve 23c to the closed state before starting the heating only operation and the heating-main operation.

[0192] First, when the control unit 80 receives a command for heating operation or heating main operation from a remote controller, the control unit 80 determines whether the outside air temperature is below the first temperature (step S1). In step S1, when the control unit 80 determines that the outside air temperature exceeds the first temperature, the density of the carbon dioxide refrigerant and the density of the refrigeration oil are in a normal state, so the control unit 80 does not implement the startup control and transfers to step S7.

[0193] In step S7, the control unit 80 starts circulating the first refrigerant in the first circuit 5a, starts circulating the carbon dioxide refrigerant in the second circuit 10, and opens the oil return valve 23c. Here, the control unit 80 starts the first compressor 71 and the second compressor 21 at the same time and opens the oil return valve 23c.

[0194] On the other hand, when it is determined that the outside air temperature is the first temperature or lower, the control unit 80 performs the start-up control. Specifically, the control unit 80 starts the first refrigerant to circulate in the first circuit 5a (step S2). In step S2, the control unit 80 starts the first compressor 71.

[0195] Next, the control unit 80 starts to circulate the carbon dioxide refrigerant in the second circuit 10 (step S3). Step S3 of the present embodiment is implemented when the first refrigerant is circulated in the first circuit 5a so that the condensation temperature of the first refrigerant in the cascade heat exchanger 35 rises to a prescribed value or above. Specifically, the control unit 80 determines whether the condensation temperature of the first refrigerant rises to a prescribed value or above. When it is determined that the condensation temperature of the first refrigerant is less than the prescribed value, the control unit 80 does not circulate carbon dioxide in the second circuit 10. On the other hand, when it is determined that the condensation temperature of the first refrigerant is above the prescribed value, the control unit 80 starts the second compressor 21 to start circulating the carbon dioxide refrigerant in the second circuit 10.

[0196] Next, the control unit 80 determines whether the temperature or pressure of the carbon dioxide refrigerant and the refrigeration oil in the second storage tank 30 is above a predetermined temperature or a predetermined pressure corresponding to a boundary temperature (step S4), wherein the boundary temperature is a temperature at which the density of the carbon dioxide refrigerant and the density of the refrigeration oil in the second storage tank 30 become equal. Here, the control unit 80 performs the above determination by obtaining the temperature or pressure of the carbon dioxide refrigerant and the second refrigeration oil flowing in the suction pipe 23a from at least one of the second suction temperature sensor 88 and the second suction pressure sensor 37.

[0197] In step S4, when it is determined that the temperature or pressure of the carbon dioxide refrigerant and the second refrigeration oil in the second storage tank 30 is above the specified temperature or the specified pressure, the density of the carbon dioxide refrigerant and the density of the refrigeration oil are in a normal state, and therefore, the control unit 80 opens the return oil valve 23c (step S5).

[0198] On the other hand, in step S4, when it is determined that the temperature or pressure of the carbon dioxide refrigerant and the second refrigerating machine oil in the second storage tank 30 is lower than the predetermined temperature or predetermined pressure, the density of the carbon dioxide refrigerant and the density of the refrigerating machine oil in the second storage tank 30 are reversed, and therefore, the control unit 80 maintains the closed state of the oil return valve 23c (step S6). Then, the process returns to the step of determining that the temperature or pressure of the carbon dioxide refrigerant and the second refrigerating machine oil in the second storage tank 30 is higher than the predetermined temperature or predetermined pressure (step S4).

[0199] (10) Features (10-1) The refrigeration cycle device 1 of the present embodiment includes a first circuit 5a, a second circuit 10, a cascade heat exchanger 35, and a control unit 80. The first circuit 5a is used for the circulation of the first refrigerant. The second circuit 10 is used for the circulation of the carbon dioxide refrigerant and the refrigeration oil (the second refrigeration oil in the present embodiment). The cascade heat exchanger 35 heats the carbon dioxide refrigerant by the first refrigerant. The second circuit 10 has a second compressor 21, a container (the second storage tank 30 in the present embodiment), a suction pipe 23a, an oil return passage 23b, and a valve (the oil return valve 23c in the present embodiment). The second storage tank 30 is provided on the suction side of the second compressor 21 to store the carbon dioxide refrigerant and the refrigeration oil. The suction pipe 23a connects the suction side of the second compressor 21 to the second storage tank 30. The oil return passage 23b returns the second refrigeration oil from the lower part of the second storage tank 30 to the suction pipe 23a. The oil return valve 23c is provided on the oil return passage 23b. The control unit 80 performs a startup control to open the oil return valve 23c after the first refrigerant starts to circulate in the first circuit 5a.

[0200] At the start of the operation (in this embodiment, the full heating operation and the heating main operation) of heating the carbon dioxide refrigerant by the first refrigerant, the outside air temperature is low, so the temperature of the carbon dioxide refrigerant in the second storage tank 30 may be low. In this case, in the refrigeration cycle device 1 of this embodiment, by starting to circulate the first refrigerant in the first circuit 5a, the temperature of the carbon dioxide refrigerant in the container of the second circuit 10 can be increased through the cascade heat exchanger 35. Therefore, even if the outside air temperature is low, a normal state in which the density of the carbon dioxide refrigerant is lower than the density of the refrigeration oil can be formed in the second storage tank 30. After the normal state is reached, the oil return valve 23c of the oil return passage 23b extending from the lower part of the second storage tank 30 is opened, so that the carbon dioxide refrigerant in the liquid phase can be suppressed from flowing into the oil return passage 23b. Therefore, it is possible to suppress the liquid refrigerant from flowing into the second compressor 21.

[0201] In this way, even if the outside air temperature is low, the start-up control can be performed to achieve a normal state in which the density of the carbon dioxide refrigerant is lower than the density of the refrigeration oil in the second storage tank 30. Therefore, in the refrigeration cycle device 1 of this embodiment, even if the component for heating the second storage tank 30 is omitted, the liquid refrigerant can be suppressed from flowing into the second compressor 21.

[0202] (10-2) The refrigeration cycle device 1 of this embodiment is based on the refrigeration cycle device 1 of the above-mentioned (10-1). When the temperature or pressure of the carbon dioxide refrigerant and the refrigeration oil in the second storage tank 30 is above the specified temperature or the specified pressure corresponding to the boundary temperature, the control unit 80 opens the return oil valve 23c during the startup control, wherein the boundary temperature is the temperature at which the density of the carbon dioxide refrigerant in the second storage tank 30 becomes equal to the density of the refrigeration oil.

[0203] Here, when the temperature or pressure of the carbon dioxide refrigerant and the refrigeration oil in the second storage tank 30 is equal to or higher than a predetermined temperature or a predetermined pressure corresponding to a boundary temperature at which the density of the carbon dioxide refrigerant and the density of the refrigeration oil in the second storage tank 30 become equal, it can be determined that the density of the refrigerant and the density of the refrigeration oil in the second storage tank 30 have become normal. Therefore, the inflow of the liquid refrigerant into the second compressor 21 can be further suppressed.

[0204] (10-3) The refrigeration cycle device 1 of this embodiment is based on the refrigeration cycle device 1 described above (10-1) or (10-2), and the control unit 80 starts circulating the carbon dioxide refrigerant in the second circuit 10 after starting to circulate the first refrigerant in the first circuit 5a during startup control.

[0205] Here, the temperature of the carbon dioxide refrigerant in the second storage tank 30 of the second circuit 10 is increased through the cascade heat exchanger 35 by starting to circulate the first refrigerant in the first circuit 5a, and then the carbon dioxide refrigerant starts to circulate in the second circuit 10. Therefore, the efficiency of the operation of the second circuit 10 can be improved.

[0206] (10-4) The refrigeration cycle device 1 of the present embodiment is the refrigeration cycle device 1 of (10-3) above, and the control unit 80 opens the oil return valve 23c after the carbon dioxide refrigerant starts to circulate in the second circuit 10 during the startup control.

[0207] Here, the first refrigerant circulates in the first circuit 5a, and the carbon dioxide refrigerant circulates in the second circuit 10, so that the temperature of the carbon dioxide refrigerant in the second storage tank 30 can be efficiently increased. As a result, the density of the refrigerant in the second storage tank 30 and the density of the refrigeration oil can be easily normalized. After the normal state is reached, the oil return valve 23c of the oil return passage 23b is opened, so that the liquid refrigerant can be easily suppressed from flowing into the second compressor 21.

[0208] (10-5) The refrigeration cycle device 1 of this embodiment is based on any one of the refrigeration cycle devices 1 described above (10-1) to (10-4), and the control unit 80 performs startup control when the external air temperature is below the first temperature, and does not perform startup control when the external air temperature exceeds the first temperature.

[0209] Here, when the density of the refrigerant in the second storage tank 30 and the density of the refrigerating machine oil are not in a normal state due to the outside air temperature being lower than the first temperature, the start-up control can be implemented to suppress the liquid refrigerant from flowing into the second compressor 21. On the other hand, when the density of the refrigerant in the second storage tank 30 and the density of the refrigerating machine oil are in a normal state due to the outside air temperature exceeding the first temperature, the liquid refrigerant can be suppressed from flowing into the second compressor 21 even if the oil return valve 23c of the oil return passage 23b is not closed.

[0210] (10-6) The refrigeration cycle device 1 of this embodiment is based on the refrigeration cycle device 1 mentioned above (10-5), and the control unit 80 starts the operation of the first circuit 5a, the operation of the second circuit 10 and the opening action of the return oil valve 23c at the same time when the external air temperature exceeds the first temperature.

[0211] Here, when the density of the refrigerant in the second storage tank 30 and the density of the refrigerating machine oil are not in a normal state due to the outside air temperature being lower than the first temperature, the liquid refrigerant can be suppressed from flowing into the second compressor 21 by the start control of opening the oil return valve 23c after starting the operation of the first circuit 5a. On the other hand, when the density of the refrigerant in the second storage tank 30 and the density of the refrigerating machine oil are in a normal state due to the outside air temperature exceeding the first temperature, the operation start of the first circuit 5a, the operation start of the second circuit 10, and the opening of the oil return valve 23c of the oil return passage 23b can be implemented simultaneously.

[0212] (10-7) The refrigeration cycle device 1 of the present embodiment is any one of the refrigeration cycle devices 1 described above (10-1) to (10-6), wherein the first refrigerant is R32.

[0213] Here, by circulating R32 in the first circuit 5 a , heat exchange with the carbon dioxide refrigerant can be efficiently performed in the cascade heat exchanger 35 .

[0214] (11) Modification (11-1) Modification 1 In the above-mentioned embodiment, the control unit 80 performs the startup control of circulating the first refrigerant in the first circuit 5a, then circulating the carbon dioxide refrigerant in the second circuit 10, and then opening the oil return valve 23c at the start of the full heating operation or the heating-main operation, but the present invention is not limited thereto. In the present modified example, the control unit 80 performs the following startup control at the start of the full heating operation or the heating-main operation: circulating the first refrigerant in the first circuit 5a, then opening the oil return valve 23c, and then circulating the carbon dioxide refrigerant in the second circuit 10.

[0215] Specifically, if Figure 8 As shown, first, the control unit 80 determines whether the outside air temperature is below the first temperature (step S1). In step S1, when it is determined that the outside air temperature exceeds the first temperature, the density of the carbon dioxide refrigerant and the density of the refrigeration oil are in a normal state, so the control unit 80 simultaneously starts the operation of the first circuit 5a, the operation of the second circuit 10, and the opening action of the oil return valve 23c (step S7).

[0216] On the other hand, when it is determined in step S1 that the outside air temperature is the first temperature or lower, the control unit 80 performs the startup control. Specifically, the control unit 80 starts circulating the first refrigerant in the first circuit 5a (step S2).

[0217] Next, the control unit 80 determines whether the temperature or pressure of the carbon dioxide refrigerant and the refrigeration oil in the second storage tank 30 is above the specified temperature or specified pressure corresponding to the boundary temperature (step S4), wherein the boundary temperature is the temperature at which the density of the carbon dioxide refrigerant in the second storage tank 30 becomes equal to the density of the refrigeration oil.

[0218] In step S4, when it is determined that the temperature or pressure of the carbon dioxide refrigerant and the second refrigerating machine oil in the second storage tank 30 is lower than the specified temperature or the specified pressure, the density of the carbon dioxide refrigerant and the density of the refrigerating machine oil in the second storage tank 30 are reversed, so the control unit 80 maintains the closed state of the oil return valve 23c (step S6). Then, the process returns to the step of determining that the temperature or pressure of the carbon dioxide refrigerant and the second refrigerating machine oil in the second storage tank 30 is higher than the specified temperature or the specified pressure (step S4).

[0219] On the other hand, in step S4, when it is determined that the temperature or pressure of the carbon dioxide refrigerant and the second refrigeration oil in the second storage tank 30 is above the specified temperature or the specified pressure, the density of the carbon dioxide refrigerant and the density of the refrigeration oil are in a normal state, and therefore, the control unit 80 opens the return oil valve 23c (step S5).

[0220] Next, the control unit 80 starts circulating the carbon dioxide refrigerant in the second circuit 10 (step S3 ).

[0221] (11-2) Modification 2 In the above embodiment, the control unit 80 performs a startup control to circulate the first refrigerant in the first circuit 5a, then circulate the carbon dioxide refrigerant in the second circuit 10, and then open the oil return valve 23c when starting the full heating operation or the heating main operation, but the present invention is not limited to this. In this modified example, the control unit 80 performs a startup control to simultaneously operate the first circuit 5a and the second circuit 10 when starting the full heating operation or the heating main operation.

[0222] Specifically, if Fig. 9 As shown, first, the control unit 80 determines whether the outside air temperature is below the first temperature (step S1). In step S1, when it is determined that the outside air temperature exceeds the first temperature, the density of the carbon dioxide refrigerant and the density of the refrigeration oil are in a normal state, so the control unit 80 simultaneously starts the operation of the first circuit 5a, the operation of the second circuit 10, and the opening action of the oil return valve 23c (step S7).

[0223] On the other hand, when it is determined in step S1 that the outside air temperature is the first temperature or lower, the control unit 80 proceeds to step S11 to perform the startup control.

[0224] In step S11, the first refrigerant starts to circulate in the first circuit 5a, and the carbon dioxide starts to circulate in the second circuit 10. Here, the first compressor 71 and the second compressor 21 are started at the same time.

[0225] Next, the control unit 80 determines whether the temperature or pressure of the carbon dioxide refrigerant and the refrigeration oil in the second storage tank 30 is above the specified temperature or specified pressure corresponding to the boundary temperature (step S4), wherein the boundary temperature is the temperature at which the density of the carbon dioxide refrigerant in the second storage tank 30 becomes equal to the density of the refrigeration oil.

[0226] In step S4, when it is determined that the temperature or pressure of the carbon dioxide refrigerant and the second refrigerating machine oil in the second storage tank 30 is lower than the specified temperature or the specified pressure, the density of the carbon dioxide refrigerant and the density of the refrigerating machine oil in the second storage tank 30 are reversed, so the control unit 80 maintains the closed state of the oil return valve 23c (step S6). Then, the process returns to the step of determining that the temperature or pressure of the carbon dioxide refrigerant and the second refrigerating machine oil in the second storage tank 30 is higher than the specified temperature or the specified pressure (step S4).

[0227] On the other hand, in step S4, when it is determined that the temperature or pressure of the carbon dioxide refrigerant and the second refrigeration oil in the second storage tank 30 is above the specified temperature or the specified pressure, the density of the carbon dioxide refrigerant and the density of the refrigeration oil are in a normal state, and therefore, the control unit 80 opens the return oil valve 23c (step S5).

[0228] As described above, the refrigeration cycle apparatus 1 of this modification is the refrigeration cycle apparatus 1 of (10-1) or (10-2) described above, and the control unit 80 starts the operation of the first circuit 5a and the operation of the second circuit 10 simultaneously during the startup control.

[0229] In this manner, the circulation of the first refrigerant in the first circuit 5 a and the circulation of the carbon dioxide refrigerant in the second circuit 10 can also be performed simultaneously.

[0230] In addition, “simultaneously” means, for example, that the control unit 80 instructs the start of the first compressor 71 and the second compressor 21 at the same time. Therefore, it includes the case where the circulation of the first refrigerant in the first circuit 5a and the circulation of the carbon dioxide refrigerant in the second circuit 10 start at exactly the same time and the case where either one starts slightly earlier.

[0231] (11-3) Modification 3 In the above-mentioned present embodiment, the control unit 80 sets the oil return valve 23c to the closed state before starting the full heating operation and the heating main operation, but the present invention is not limited thereto. The oil return valve 23c may also be set to the open state before starting the full heating operation and the heating main operation. In this modified example, when the evaporation temperature of the carbon dioxide refrigerant in the cascade heat exchanger 35 is above a predetermined value, the oil return valve 23c is set to the open state before the circulation of the carbon dioxide refrigerant in the second circuit 10.

[0232] (11-4) Modification 4 In the above embodiment, the control unit 80 starts the operation of the first circuit 5a, the operation of the second circuit 10, and the opening action of the oil return valve 23c at the same time when the outside air temperature exceeds the first temperature, but the present invention is not limited thereto. In the refrigeration cycle device of the present disclosure, the control unit 80 can arbitrarily instruct the order of starting the operation of the first circuit 5a, starting the operation of the second circuit 10, and opening the oil return valve 23c when the outside air temperature exceeds the first temperature. In this modified example, when the outside air temperature exceeds the first temperature, the first circuit 5a and the second circuit 10 are started at the same time, and the opening action of the oil return valve 23c is performed before or after the start of the first circuit 5a and the second circuit 10.

[0233] (11-5) Modification 5 In the above-mentioned embodiment and variants 1 to 4, the control unit 80 performs the startup control when the outside air temperature is below the first temperature, but the present invention is not limited thereto. In this variant, the control unit 80 performs the startup control regardless of the outside air temperature when starting the full heating operation or the heating main operation. In other words, Fig.10 As shown, omitted Figure 7 to Figure 10 A step of determining whether the outside air temperature is below a first temperature (step S1).

[0234] (11-6) Modification Example 6 In the above-mentioned embodiment and the first to fifth modified examples, when the temperature or pressure of the carbon dioxide refrigerant and the refrigeration oil in the second storage tank 30 is above the prescribed temperature or prescribed pressure corresponding to the boundary temperature at which the density of the carbon dioxide refrigerant in the second storage tank 30 becomes equal to the density of the refrigeration oil, the control unit 80 opens the oil return valve 23c, but the present invention is not limited thereto. In the present modified example, the control unit 80 starts to circulate the first refrigerant in the first circuit 5a, and then opens the oil return valve 23c after a prescribed time. In addition, the prescribed time is the time to raise the temperature of the carbon dioxide refrigerant by circulating the first refrigerant so that the inside of the second storage tank 30 becomes normal.

[0235] (11-7) Modification Example 7 In the above-mentioned embodiment, the control unit 80 implements the startup control at the start of the full heating operation and the start of the heating main operation, but it is not limited to this. In the refrigeration cycle device of the present disclosure, the control unit 80 may also implement the startup control at the start of the full heating operation or the start of the heating main operation. In addition, in the refrigeration cycle device of the present disclosure, the control unit 80 may also implement the startup control at the start of either the full cooling operation or the cooling main operation.

[0236] (11-8) Modification 8 In the above embodiment, polyalkylene glycol is used as an example of the second refrigeration oil used in the second circuit 10, but it is not limited thereto. The second refrigeration oil disclosed in the present invention may be non-miscible with the carbon dioxide refrigerant, or may be miscible with the carbon dioxide refrigerant but with a small amount of miscibility.

[0237] (11-9) Modification Example 9 In the above embodiment, R32 is used as an example of the first refrigerant used in the first circuit 5a, but the present invention is not limited thereto. As the first refrigerant used in the first circuit 5a, for example, R32, R454C, propane, R1234yf, R1234ze, ammonia, or a refrigerant containing any of these can be used.

[0238] (11-10) Modification Example 10 In the above embodiment, the second circuit 10 has three connecting pipes 7, 8, and 9, but is not limited thereto. The refrigeration cycle device of this modification has two connecting pipes. This modification is applied, for example, to a structure in which a plurality of utilization units 3a, 3b, and 3c cannot perform cooling operation or heating operation independently, a structure in which the second unit is one, and the like.

[0239] (11-11) Modification Example 11 In the above embodiment, the refrigeration cycle device 1 is described as an example in which one cascade unit 2 is connected to one first unit 5, but the present invention is not limited thereto. In the refrigeration cycle device 1 of this modification, a plurality of cascade units 2 are connected in parallel to one first unit 5.

[0240] (11-12) Modification Example 12 In the above embodiment, the refrigeration cycle apparatus 1 is described as an example in which a plurality of second units 4a, 4b, 4c are connected to one cascade unit 2, but the present invention is not limited thereto. In the refrigeration cycle apparatus of this modification, one second unit is connected to one cascade unit 2.

[0241] (11-13) Modification 13 In the above embodiment, as the first unit 5, an outdoor unit having a first fan 75 for supplying outdoor air for heat exchange with the first refrigerant to the first heat exchanger 74 is described as an example, but the present invention is not limited thereto. In this modified example, the first unit does not have the first fan 75, and in the first heat exchanger 74, the first refrigerant is heat exchanged with water as a heat source.

[0242] As mentioned above, although embodiment of this disclosure is described, it should be understood that various changes in form and details can be made without departing from the spirit and scope of this disclosure described in the claims. Explanation of symbols

[0243] 1. Refrigeration cycle device; 5a first circuit; 10 Second circuit; 21 second compressor; 23a suction pipe; 23b oil return passage; 23c oil return valve (valve); 30 second storage tank (container); 35 cascade heat exchanger; 52a, 52b, 52c second heat exchanger; 71 first compressor; 74 first heat exchanger; 80 Control Unit. Prior art literature Patent Literature

[0244] Patent Document 1: Japanese Patent No. 5425221

Claims

1. A refrigeration cycle device (1), characterized in that: include: A first circuit (5a) for circulating a first refrigerant; A second circuit (10) for circulating carbon dioxide refrigerant and refrigeration oil; a cascade heat exchanger (35), wherein the cascade heat exchanger heats the carbon dioxide refrigerant via the first refrigerant; and A control unit (80), The second circuit has: A second compressor (21); a container (30), which is arranged on the suction side of the second compressor and stores the carbon dioxide refrigerant and the refrigeration oil; a suction pipe (23a) connecting the suction side of the second compressor to the container; an oil return passage (23b) for returning the refrigeration oil from the lower portion of the container to the suction pipe; as well as A valve (23c) is provided in the oil return passage. The control unit performs startup control to open the valve after the first refrigerant starts to circulate in the first circuit.

2. The refrigeration cycle device according to claim 1, characterized in that: When the temperature or pressure of the carbon dioxide refrigerant and the refrigeration oil in the container is above a specified temperature or a specified pressure corresponding to a boundary temperature, the control unit opens the valve, and the boundary temperature is a temperature at which the density of the carbon dioxide refrigerant in the container becomes equal to the density of the refrigeration oil.

3. The refrigeration cycle device according to claim 1 or 2, characterized in that: The control unit starts circulating the carbon dioxide refrigerant in the second circuit after starting circulating the first refrigerant in the first circuit.

4. The refrigeration cycle device according to claim 3, characterized in that: The control unit opens the valve after starting to circulate the carbon dioxide refrigerant in the second circuit.

5. The refrigeration cycle device according to claim 1 or 2, characterized in that: The control unit starts the operation of the first circuit and the operation of the second circuit at the same time.

6. The refrigeration cycle device according to any one of claims 1 to 5, characterized in that: The control unit performs the activation control when the outside air temperature is equal to or lower than a first temperature, and does not perform the activation control when the outside air temperature exceeds the first temperature.

7. The refrigeration cycle device according to claim 6, characterized in that: The control unit starts the operation of the first circuit, the operation of the second circuit, and the opening operation of the valve at the same time when the outside air temperature exceeds the first temperature.

8. The refrigeration cycle device according to any one of claims 1 to 7, characterized in that: The first refrigerant includes R32, R454C, propane, R1234yf, R1234ze or ammonia.

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