EP4317845A1

EP4317845A1 - Refrigeration cycle device

Info

Publication number: EP4317845A1
Application number: EP22781287.2A
Authority: EP
Inventors: Atsushi Yoshimi; Takuro Yamada; Eiji Kumakura; Ikuhiro Iwata; Ryuhei Kaji; Takeru MIYAZAKI; Hiroki Ueda; Masaki Tanaka; Masaki Nakayama
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2021-03-31
Filing date: 2022-03-31
Publication date: 2024-02-07
Also published as: CN117597558A; WO2022211077A1; JP2022159196A; JP7208577B2; US20240019176A1

Abstract

Provided is a refrigeration cycle apparatus capable of efficiently performing a cooling operation and a heating operation using a low-pressure refrigerant and a high-pressure refrigerant. A refrigeration cycle apparatus (1) performs a heating operation by performing a two-stage refrigeration cycle, the two-stage refrigeration cycle including a use-side refrigeration cycle using a first refrigerant having 1 MPa or less at 30°C and a heat-source-side refrigeration cycle using a second refrigerant having 1.5 MPa or more at 30°C, and performs a cooling operation by performing a single-stage refrigeration cycle using the first refrigerant.

Description

TECHNICAL FIELD

The present disclosure relates to a refrigeration cycle apparatus.

BACKGROUND ART

To date, refrigeration cycle apparatuses have been proposed that use refrigerants with low global warming potential (GWP), taking into account the global environment.
For example, in a refrigeration cycle apparatus described in PTL 1 ( Japanese Unexamined Patent Application Publication No. 2015-197254 ), it is proposed to fill a refrigerant circuit with a working fluid having a GWP equal to or less than a predetermined value.

SUMMARY OF INVENTION

TECHNICAL PROBLEM

The refrigerants with low GWP described above include a low-pressure refrigerant used at a relatively low refrigerant pressure. Such a low-pressure refrigerant has low heat transfer capacity, and a sufficient amount of circulation of the refrigerant is difficult to secure during a heating operation, with the tendency that the heating operation is difficult to perform or the COP (Coefficient Of Performance) is low during the heating operation.
To address this, a two-stage refrigeration cycle in which a carbon dioxide refrigerant serving as a high-pressure refrigerant with low GWP is used as a heat-source-side refrigerant and a low-pressure refrigerant is used as a use-side refrigerant may be used to secure heating operation capacity. However, even in this case, the critical pressure of the carbon dioxide refrigerant on the heat-source side is exceeded during a cooling operation, and the COP is low during the cooling operation.
Accordingly, it is desirable to provide a refrigeration cycle apparatus capable of efficiently performing a cooling operation and a heating operation using a high-pressure refrigerant and a low-pressure refrigerant.

SOLUTION TO PROBLEM

A refrigeration cycle apparatus according to a first aspect performs a heating operation by performing a two-stage refrigeration cycle, the two-stage refrigeration cycle including a use-side refrigeration cycle using a first refrigerant and a heat-source-side refrigeration cycle using a second refrigerant. The first refrigerant has 1 MPa or less at 30°C. The second refrigerant has 1.5 MPa or more at 30°C. The refrigeration cycle apparatus performs a cooling operation by performing a single-stage refrigeration cycle using the first refrigerant.
In this refrigeration cycle apparatus, a two-stage refrigeration cycle is performed during the heating operation, the two-stage refrigeration cycle including a use-side refrigeration cycle using a first refrigerant that is a low-pressure refrigerant having 1 MPa or less at 30°C and a heat-source-side refrigeration cycle using a second refrigerant that is a high-pressure refrigerant having 1.5 MPa or more at 30°C. Thus, it is easy to secure heating capacity while achieving a high COP. In this refrigeration cycle apparatus, furthermore, a single-stage refrigeration cycle using the first refrigerant, which is a low-pressure refrigerant having 1 MPa or less at 30°C, is performed during the cooling operation. Thus, it is possible to perform the two-stage refrigeration cycle using the second refrigerant in the heat-source-side refrigeration cycle, without causing a reduction in COP due to the second refrigerant exceeding a critical pressure. Accordingly, the cooling operation and the heating operation can be efficiently performed using a high-pressure refrigerant and a low-pressure refrigerant.
A refrigeration cycle apparatus according to a second aspect is the refrigeration cycle apparatus according to the first aspect, including a cascade heat exchanger. The cascade heat exchanger includes a first cascade flow path and a second cascade flow path. The first cascade flow path is a flow path through which the first refrigerant flows during the heating operation. The second cascade flow path is a flow path that is independent of the first cascade flow path, and is a flow path through which the second refrigerant flows during the heating operation. The cascade heat exchanger is configured to exchange heat between the first refrigerant and the second refrigerant.
In this refrigeration cycle apparatus, the efficiency of heat exchange between the refrigerant flowing through the heat-source-side refrigeration cycle and the refrigerant flowing through the use-side refrigeration cycle can be increased.
A refrigeration cycle apparatus according to a third aspect is the refrigeration cycle apparatus according to the second aspect, further including a use heat exchanger. In the use heat exchanger, the first refrigerant radiates heat during the heating operation. During the heating operation, the first refrigerant evaporates when passing through the first cascade flow path, and the second refrigerant radiates heat when passing through the second cascade flow path.
In the use heat exchanger, the first refrigerant may condense during the heating operation.
The use heat exchanger is preferably a heat exchanger that processes a heat load. The refrigerant flowing through the use heat exchanger may exchange heat with air, or may exchange heat with a fluid such as brine or water.
In this refrigeration cycle apparatus, the heating operation can be efficiently performed.
A refrigeration cycle apparatus according to a fourth aspect is the refrigeration cycle apparatus according to any one of the first to third aspects, including a use heat exchanger and a first outdoor heat exchanger. In the use heat exchanger, the first refrigerant evaporates during the cooling operation. In the first outdoor heat exchanger, the first refrigerant radiates heat during the cooling operation.
In the first outdoor heat exchanger, the first refrigerant may condense during the cooling operation.
The first outdoor heat exchanger is not limited. For example, the refrigerant flowing through the first outdoor heat exchanger may exchange heat with air.
In this refrigeration cycle apparatus, the cooling operation can be efficiently performed by using an outdoor heat source.
A refrigeration cycle apparatus according to a fifth aspect is the refrigeration cycle apparatus according to any one of the first to fourth aspects, including a second outdoor heat exchanger. In the second outdoor heat exchanger, the second refrigerant evaporates during the heating operation.
The second outdoor heat exchanger is not limited. For example, the refrigerant flowing through the second outdoor heat exchanger may exchange heat with air.
In this refrigeration cycle apparatus, the heating operation can be efficiently performed by using an outdoor heat source.
A refrigeration cycle apparatus according to a sixth aspect performs a heating operation by performing a two-stage refrigeration cycle, the two-stage refrigeration cycle including a use-side refrigeration cycle using a first refrigerant and a heat-source-side refrigeration cycle using a second refrigerant. The first refrigerant has 1 MPa or less at 30°C. The second refrigerant has 1.5 MPa or more at 30°C. The refrigeration cycle apparatus performs a cooling operation by performing a two-stage refrigeration cycle, the two-stage refrigeration cycle including a use-side refrigeration cycle using the second refrigerant and a heat-source-side refrigeration cycle using the first refrigerant.
In this refrigeration cycle apparatus, a two-stage refrigeration cycle is performed during the heating operation, the two-stage refrigeration cycle including a use-side refrigeration cycle using a first refrigerant that is a low-pressure refrigerant having 1 MPa or less at 30°C and a heat-source-side refrigeration cycle using a second refrigerant that is a high-pressure refrigerant having 1.5 MPa or more at 30°C. Thus, it is easy to secure heating capacity while achieving a high COP. In this refrigeration cycle apparatus, furthermore, a two-stage refrigeration cycle is performed during the cooling operation, the two-stage refrigeration cycle including a use-side refrigeration cycle using the second refrigerant, which is a high-pressure refrigerant having 1.5 MPa or more at 30°C, and a heat-source-side refrigeration cycle using the first refrigerant, which is a low-pressure refrigerant having 1 MPa or less at 30°C. Thus, it is possible to perform the two-stage refrigeration cycle using the second refrigerant in the heat-source-side refrigeration cycle, without causing a reduction in COP due to the second refrigerant exceeding a critical pressure. Accordingly, the cooling operation and the heating operation can be efficiently performed using a high-pressure refrigerant and a low-pressure refrigerant.
A refrigeration cycle apparatus according to a seventh aspect is the refrigeration cycle apparatus according to the sixth aspect, including a cascade heat exchanger. The cascade heat exchanger includes a first cascade flow path and a second cascade flow path that is a flow path independent of the first cascade flow path. The first cascade flow path is a flow path through which the first refrigerant flows. The second cascade flow path is a flow path through which the second refrigerant flows. The cascade heat exchanger is configured to exchange heat between the first refrigerant and the second refrigerant.
In this refrigeration cycle apparatus, the efficiency of heat exchange between the refrigerant flowing through the heat-source-side refrigeration cycle and the refrigerant flowing through the use-side refrigeration cycle can be increased.
A refrigeration cycle apparatus according to an eighth aspect is the refrigeration cycle apparatus according to the seventh aspect, further including a use heat exchanger. The use heat exchanger includes a first use flow path and a second use flow path that is a flow path independent of the first use flow path. The first use flow path is a flow path through which the first refrigerant flows. The second use flow path is a flow path through which the second refrigerant flows.
The use heat exchanger is preferably a heat exchanger that processes a heat load. The refrigerant flowing through the use heat exchanger may exchange heat with air, or may exchange heat with a fluid such as brine or water.
In this refrigeration cycle apparatus, the use heat exchanger can perform heat load processing by using the first refrigerant and heat load processing by using the second refrigerant.
A refrigeration cycle apparatus according to a ninth aspect is the refrigeration cycle apparatus according to the eighth aspect, in which during the heating operation, the first refrigerant evaporates when passing through the first cascade flow path, the second refrigerant radiates heat when passing through the second cascade flow path, and the first refrigerant radiates heat when passing through the first use flow path.
The first refrigerant may condense when passing through the first use flow path during the heating operation.
In this refrigeration cycle apparatus, the heating operation can be efficiently performed.
A refrigeration cycle apparatus according to a tenth aspect is the refrigeration cycle apparatus according to the eighth or ninth aspect, in which during the cooling operation, the first refrigerant evaporates when passing through the first cascade flow path, the second refrigerant radiates heat when passing through the second cascade flow path, and the second refrigerant evaporates when passing through the second use flow path.
In this refrigeration cycle apparatus, the cooling operation can be efficiently performed.
A refrigeration cycle apparatus pertaining to an eleventh aspect is the refrigeration cycle apparatus pertaining to any of the eighth to tenth aspects, in which during the cooling operation, the first refrigerant evaporates when passing through the first use flow path, and the second refrigerant evaporates when passing through the second use flow path.
In this refrigeration cycle apparatus, the first refrigerant and the second refrigerant can be simultaneously evaporated in the use heat exchanger during the cooling operation.
A refrigeration cycle apparatus pertaining to a twelfth aspect is the refrigeration cycle apparatus pertaining to any of the eighth to eleventh aspects, in which during the heating operation, the first refrigerant radiates heat when passing through the first use flow path, and the second refrigerant radiates heat when passing through the second use flow path.
The first refrigerant may condense when passing through the first use flow path during the heating operation.
In this refrigeration cycle apparatus, the first refrigerant and the second refrigerant can simultaneously radiate heat in the use heat exchanger during the heating operation.
A refrigeration cycle apparatus according to a thirteenth aspect is the refrigeration cycle apparatus according to any one of the sixth to twelfth aspects, including a first outdoor heat exchanger. In the first outdoor heat exchanger, the first refrigerant radiates heat during the cooling operation.
In the first outdoor heat exchanger, the first refrigerant may condense during the cooling operation.
The first outdoor heat exchanger is not limited. For example, the refrigerant flowing through the first outdoor heat exchanger may exchange heat with air.
In this refrigeration cycle apparatus, the cooling operation can be efficiently performed by using an outdoor heat source.
A refrigeration cycle apparatus according to a fourteenth aspect is the refrigeration cycle apparatus according to any one of the sixth to thirteenth aspects, including a second outdoor heat exchanger. In the second outdoor heat exchanger, the second refrigerant evaporates during the heating operation.
The second outdoor heat exchanger is not limited. For example, the refrigerant flowing through the second outdoor heat exchanger may exchange heat with air.
In this refrigeration cycle apparatus, the heating operation can be efficiently performed by using an outdoor heat source.
A refrigeration cycle apparatus according to a fifteenth aspect is the refrigeration cycle apparatus according to any one of the first to fourteenth aspects, in which the first refrigerant includes at least one of R1234yf or R1234ze.
The first refrigerant may include only R1234yf or may include only R1234ze.
In this refrigeration cycle apparatus, an operation can be performed by using a refrigerant having a sufficiently low global warming potential (GWP).
A refrigeration cycle apparatus according to a sixteenth aspect is the refrigeration cycle apparatus according to any one of the first to fifteenth aspects, in which the second refrigerant includes carbon dioxide.
The second refrigerant may include only carbon dioxide.
In this refrigeration cycle apparatus, an operation can be performed by using a refrigerant having a sufficiently low ozone depletion potential (ODP) and a sufficiently low global warming potential (GWP).

Brief Description of Drawings

[Fig. 1] Fig. 1 is an overall configuration diagram of a refrigeration cycle apparatus according to a first embodiment.
[Fig. 2] Fig. 2 is a functional block configuration diagram of the refrigeration cycle apparatus according to the first embodiment.
[Fig. 3] Fig. 3 is a diagram illustrating how a refrigerant flows during a cooling operation according to the first embodiment.
[Fig. 4] Fig. 4 is a diagram illustrating how a refrigerant flows during a heating operation according to the first embodiment.
[Fig. 5] Fig. 5 is an overall configuration diagram of a refrigeration cycle apparatus according to a second embodiment.
[Fig. 6] Fig. 6 is a functional block configuration diagram of the refrigeration cycle apparatus according to the second embodiment.
[Fig. 7] Fig. 7 is a diagram illustrating how a refrigerant flows during a cooling operation according to the second embodiment.
[Fig. 8] Fig. 8 is a diagram illustrating how a refrigerant flows during a heating operation according to the second embodiment.
[Fig. 9] Fig. 9 is an overall configuration diagram of a refrigeration cycle apparatus according to a third embodiment.
[Fig. 10] Fig. 10 is a functional block configuration diagram of the refrigeration cycle apparatus according to the third embodiment.
[Fig. 11] Fig. 11 is a diagram illustrating how a refrigerant flows during a cooling operation according to the third embodiment.
[Fig. 12] Fig. 12 is a diagram illustrating how a refrigerant flows during a heating operation according to the third embodiment.
[Fig. 13] Fig. 13 is an overall configuration diagram of a refrigeration cycle apparatus according to a fourth embodiment.
[Fig. 14] Fig. 14 is a functional block configuration diagram of the refrigeration cycle apparatus according to the fourth embodiment.
[Fig. 15] Fig. 15 is a diagram illustrating how a refrigerant flows during a first cooling operation according to the fourth embodiment.
[Fig. 16] Fig. 16 is a diagram illustrating how a refrigerant flows during a second cooling operation according to the fourth embodiment.
[Fig. 17] Fig. 17 is a diagram illustrating how a refrigerant flows during a third cooling operation according to the fourth embodiment.
[Fig. 18] Fig. 18 is a diagram illustrating how a refrigerant flows during a first heating operation according to the fourth embodiment.
[Fig. 19] Fig. 19 is a diagram illustrating how a refrigerant flows during a second heating operation according to the fourth embodiment.
[Fig. 20] Fig. 20 is a diagram illustrating how a refrigerant flows during a third heating operation according to the fourth embodiment.

Description of Embodiments

(1) First Embodiment

Fig. 1 is a schematic configuration diagram of a refrigeration cycle apparatus 1 according to a first embodiment. Fig. 2 is a functional block configuration diagram of the refrigeration cycle apparatus 1 according to the first embodiment.
The refrigeration cycle apparatus 1 is an apparatus used to process a heat load through a vapor-compression refrigeration cycle operation. The refrigeration cycle apparatus 1 includes a heat-load circuit 90, a first refrigerant circuit 10, a second refrigerant circuit 20, an outdoor fan 9, and a controller 7.
The heat load to be processed by the refrigeration cycle apparatus 1 is not limited, and a fluid such as air, water, or brine may be subjected to heat exchange. In the refrigeration cycle apparatus 1 according to the present embodiment, water flowing through the heat-load circuit 90 is supplied to a heat-load heat exchanger 91, and the heat load in the heat-load heat exchanger 91 is processed. The heat-load circuit 90 is a circuit in which water serving as a heat medium circulates, and includes the heat-load heat exchanger 91, a pump 92, and a use heat exchanger 13 shared with the first refrigerant circuit 10. The pump 92 is driven and controlled by the controller 7, which will be described below, to circulate the water through the heat-load circuit 90. In the heat-load circuit 90, the water flows through a heat-load flow path 13c included in the use heat exchanger 13. As described below, the use heat exchanger 13 includes a first use flow path 13a through which a first refrigerant flowing through the first refrigerant circuit 10 passes. The water flowing through the heat-load flow path 13c of the use heat exchanger 13 exchanges heat with the first refrigerant flowing through the first use flow path 13a. As a result, the water is cooled during a cooling operation and is heated during a heating operation.
The first refrigerant circuit 10 includes a first compressor 11, a first switching mechanism 12, the use heat exchanger 13 shared with the heat-load circuit 90, a first use expansion valve 15, a second use expansion valve 16, a heat-source heat exchanger 17 shared with the second refrigerant circuit 20, and a first outdoor heat exchanger 18. The first refrigerant circuit 10 is filled with the first refrigerant, which is a low-pressure refrigerant, as a refrigerant. The first refrigerant is a refrigerant having 1 MPa or less at 30°C, and is a refrigerant including, for example, at least one of R1234yf or R1234ze. The first refrigerant may include only R1234yf or may include only R1234ze.
The first compressor 11 is a positive-displacement compressor to be driven by a compressor motor. The compressor motor is driven by electric power supplied via an inverter device. The first compressor 11 has an operating capacity that is changeable by varying a drive frequency that is the number of rotations of the compressor motor. A discharge side of the first compressor 11 is connected to the first switching mechanism 12. A suction side of the first compressor 11 is connected to a gas-refrigerant-side outlet of a first heat-source flow path 17a of the heat-source heat exchanger 17.
The first switching mechanism 12 includes a switching valve 12a and a switching valve 12b. The switching valve 12a and the switching valve 12b are connected in parallel to each other on the discharge side of the first compressor 11. The switching valve 12a is a three-way valve that switches between a state in which the discharge side of the first compressor 11 is connected to the first use flow path 13a of the use heat exchanger 13 and a state in which the suction side of the first compressor 11 is connected to the first use flow path 13a of the use heat exchanger 13. The switching valve 12b is a three-way valve that switches between a state in which the discharge side of the first compressor 11 is connected to the first outdoor heat exchanger 18 and a state in which the suction side of the first compressor 11 is connected to the first outdoor heat exchanger 18.
A gas refrigerant side of the first use flow path 13a of the use heat exchanger 13 through which the first refrigerant flowing through the first refrigerant circuit 10 passes is connected to the switching valve 12a. A liquid refrigerant side of the first use flow path 13a is connected to a first branch point A included in the first refrigerant circuit 10. The first refrigerant evaporates when flowing through the first use flow path 13a of the use heat exchanger 13 to cool the water flowing through the heat-load circuit 90. The first refrigerant condenses when flowing through the first use flow path 13a of the use heat exchanger 13 to heat the water flowing through the heat-load circuit 90.
At the first branch point A, a flow path extending from the liquid refrigerant side of the first use flow path 13a, a flow path extending to the side of the first use expansion valve 15 opposite to the heat-source heat exchanger 17 side, and a flow path extending to the side of the second use expansion valve 16 opposite to the first outdoor heat exchanger 18 side are connected.
The first use expansion valve 15 includes an electronic expansion valve that is adjustable in valve opening degree. In the first refrigerant circuit 10, the first use expansion valve 15 is disposed between the first branch point A and an inlet on a liquid refrigerant side of the first heat-source flow path 17a of the heat-source heat exchanger 17.
The second use expansion valve 16 includes an electronic expansion valve that is adjustable in valve opening degree. In the first refrigerant circuit 10, the second use expansion valve 16 is disposed between the first branch point A and an outlet on a liquid refrigerant side of the first outdoor heat exchanger 18.
The heat-source heat exchanger 17 is a cascade heat exchanger that includes the first heat-source flow path 17a through which the first refrigerant flowing through the first refrigerant circuit 10 passes, and a second heat-source flow path 17b through which a second refrigerant flowing through the second refrigerant circuit 20 passes, and that exchanges heat between the first refrigerant and the second refrigerant. In the heat-source heat exchanger 17, the first heat-source flow path 17a and the second heat-source flow path 17b are independent of each other, and the first refrigerant and the second refrigerant do not mix with each other. The gas-refrigerant-side outlet of the first heat-source flow path 17a of the heat-source heat exchanger 17 is connected to the suction side of the first compressor 11. The inlet on the liquid refrigerant side of the first heat-source flow path 17a of the heat-source heat exchanger 17 is connected to the first use expansion valve 15.
The first outdoor heat exchanger 18 includes a plurality of heat transfer tubes and a plurality of fins joined to the plurality of heat transfer tubes. In the present embodiment, the first outdoor heat exchanger 18 is arranged outdoors. The first refrigerant flowing through the first outdoor heat exchanger 18 exchanges heat with air sent to the first outdoor heat exchanger 18, thereby allowing the first outdoor heat exchanger 18 to function as a condenser of the first refrigerant.
The outdoor fan 9 generates an air flow of outdoor air passing through both the first outdoor heat exchanger 18 and a second outdoor heat exchanger 23.
The second refrigerant circuit 20 includes a second compressor 21, the heat-source heat exchanger 17 shared with the first refrigerant circuit 10, a first heat-source expansion valve 26, and the second outdoor heat exchanger 23. The second refrigerant circuit 20 is filled with the second refrigerant, which is a high-pressure refrigerant, as a refrigerant. The second refrigerant is a refrigerant having 1.5 MPa or more at 30°C. The second refrigerant may include carbon dioxide, or may include only carbon dioxide.
The second compressor 21 is a positive-displacement compressor to be driven by a compressor motor. The compressor motor is driven by electric power supplied via an inverter device. The second compressor 21 has an operating capacity that is changeable by varying a drive frequency that is the number of rotations of the compressor motor. A discharge side of the second compressor 21 is connected to an inlet on a gas refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17. A suction side of the second compressor 21 is connected to the second outdoor heat exchanger 23.
The inlet on the gas refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17 is connected to the discharge side of the second compressor 21. An outlet on a liquid refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17 is connected to the first heat-source expansion valve 26.
The first heat-source expansion valve 26 is disposed in a flow path between the liquid refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17 and a liquid refrigerant side of the second outdoor heat exchanger 23.
The second outdoor heat exchanger 23 includes a plurality of heat transfer tubes and a plurality of fins joined to the plurality of heat transfer tubes. In the present embodiment, the second outdoor heat exchanger 23 is arranged outdoors alongside the first outdoor heat exchanger 18. The second refrigerant flowing through the second outdoor heat exchanger 23 exchanges heat with air sent to the second outdoor heat exchanger 23, thereby allowing the second outdoor heat exchanger 23 to function as an evaporator of the second refrigerant.
The controller 7 controls the operation of the devices included in the heat-load circuit 90, the first refrigerant circuit 10, and the second refrigerant circuit 20. Specifically, the controller 7 includes a processor serving as a CPU provided for performing control, a memory, and the like.
In the refrigeration cycle apparatus 1 described above, the controller 7 controls the devices to execute a refrigeration cycle, thereby performing a cooling operation for processing a cooling load in the heat-load heat exchanger 91 and a heating operation for processing a heating load in the heat-load heat exchanger 91.

(1-1) Cooling Operation

During the cooling operation, as illustrated in Fig. 3, the first refrigerant circuit 10 performs a single-stage refrigeration cycle such that the use heat exchanger 13 functions as an evaporator of the first refrigerant and the first outdoor heat exchanger 18 functions as a condenser of the first refrigerant, and the second refrigerant circuit 20 does not perform a refrigeration cycle. Specifically, the switching valves 12a and 12b of the first switching mechanism 12 are switched to a connection state indicated by solid lines in Fig. 3, the pump 92, the first compressor 11, and the outdoor fan 9 are driven, the first use expansion valve 15 is fully closed, and the valve opening degree of the second use expansion valve 16 is controlled such that the degree of superheating of the first refrigerant to be sucked into the first compressor 11 satisfies a predetermined condition.
Accordingly, the first refrigerant discharged from the first compressor 11 is sent to the first outdoor heat exchanger 18 via the switching valve 12b of the first switching mechanism 12. The first refrigerant sent to the first outdoor heat exchanger 18 is condensed by heat exchange with the outdoor air supplied by the outdoor fan 9. The first refrigerant having passed through the first outdoor heat exchanger 18 is decompressed in the second use expansion valve 16, passes through the first branch point A, and is sent to the first use flow path 13a of the use heat exchanger 13. The first refrigerant flowing through the first use flow path 13a of the use heat exchanger 13 is evaporated by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The water cooled by this heat exchange is sent to the heat-load heat exchanger 91 in the heat-load circuit 90 to process the cooling load. The first refrigerant evaporated in the first use flow path 13a of the use heat exchanger 13 is sucked into the first compressor 11 via the switching valve 12a of the first switching mechanism 12.

(1-2) Heating Operation

During the heating operation, as illustrated in Fig. 4, the first refrigerant circuit 10 performs a refrigeration cycle such that the use heat exchanger 13 functions as a condenser of the first refrigerant and the heat-source heat exchanger 17 functions as an evaporator of the first refrigerant, and the second refrigerant circuit 20 performs a refrigeration cycle such that the heat-source heat exchanger 17 functions as a radiator of the second refrigerant and the second outdoor heat exchanger 23 functions as an evaporator of the second refrigerant. As a result, a two-stage refrigeration cycle is performed by the second refrigerant circuit 20 and the first refrigerant circuit 10 during the heating operation. Specifically, the switching valves 12a and 12b of the first switching mechanism 12 are switched to a connection state indicated by broken lines in Fig. 4, the pump 92, the first compressor 11, the second compressor 21, and the outdoor fan 9 are driven, the second use expansion valve 16 is fully closed, the valve opening degree of the first use expansion valve 15 is controlled such that the degree of superheating of the first refrigerant to be sucked into the first compressor 11 satisfies a predetermined condition, and the valve opening degree of the first heat-source expansion valve 26 is controlled such that the degree of superheating of the second refrigerant to be sucked into the second compressor 21 satisfies a predetermined condition.
Accordingly, the second refrigerant discharged from the second compressor 21 is sent to the heat-source heat exchanger 17. When flowing through the second heat-source flow path 17b, the second refrigerant radiates heat by heat exchange with the first refrigerant flowing through the first heat-source flow path 17a. The second refrigerant, which has radiated heat in the heat-source heat exchanger 17, is decompressed in the first heat-source expansion valve 26. Then, the second refrigerant is evaporated by heat exchange with the outdoor air supplied by the outdoor fan 9 in the second outdoor heat exchanger 23, and is sucked into the second compressor 21. The first refrigerant discharged from the first compressor 11 is sent to the first use flow path 13a of the use heat exchanger 13 via the switching valve 12a of the first switching mechanism 12. The first refrigerant flowing through the first use flow path 13a of the use heat exchanger 13 is condensed by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The water heated by this heat exchange is sent to the heat-load heat exchanger 91 in the heat-load circuit 90 to process the heating load. The first refrigerant condensed in the first use flow path 13a of the use heat exchanger 13 passes through the first branch point A and is then decompressed in the first use expansion valve 15. The first refrigerant decompressed by the first use expansion valve 15 is evaporated, when passing through the first heat-source flow path 17a of the heat-source heat exchanger 17, by heat exchange with the second refrigerant flowing through the second heat-source flow path 17b. The first refrigerant evaporated in the first heat-source flow path 17a of the heat-source heat exchanger 17 is sucked into the first compressor 11.

(1-3) Features of First Embodiment

In the refrigeration cycle apparatus 1 according to the first embodiment, the first refrigerant circuit 10 uses the first refrigerant having a sufficiently low global warming potential (GWP). Further, the second refrigerant circuit 20 uses the second refrigerant having a sufficiently low ozone depletion potential (ODP) and a sufficiently low global warming potential (GWP). Thus, global environmental deterioration can be reduced.
In addition, even when the first refrigerant circuit 10 uses the first refrigerant having a sufficiently low global warming potential (GWP), the two-stage refrigeration cycle in which the second refrigerant circuit 20 is used for the heat-source-side cycle and the first refrigerant circuit 10 is used for the use-side cycle is performed as the heating operation. This makes it easier to secure heating operation capacity than a single-stage refrigeration cycle in which the first refrigerant, which is a low-pressure refrigerant, is used.
During the cooling operation, the second refrigerant circuit 20 does not perform a refrigeration cycle, and the first refrigerant circuit 10 performs the single-stage refrigeration cycle although the second refrigerant circuit 20 uses carbon dioxide as the second refrigerant. This makes it possible to perform the cooling operation without causing a reduction in COP, as in the case of performing a single-stage refrigeration cycle using a carbon dioxide refrigerant, which is a high-pressure refrigerant, or as in the case of performing a two-stage refrigeration cycle in which carbon dioxide, which is a high-pressure refrigerant, is used in the heat-source-side cycle, the reduction in COP being due to the pressure of the carbon dioxide refrigerant exceeding the critical pressure. It is also possible to reduce the compression strength standards required for the components of the second refrigerant circuit 20 in which carbon dioxide, which is a high-pressure refrigerant, is used.

(2) Second Embodiment

Fig. 5 is a schematic configuration diagram of a refrigeration cycle apparatus 1a according to a second embodiment. Fig. 6 is a functional block configuration diagram of the refrigeration cycle apparatus 1a according to the second embodiment.
The refrigeration cycle apparatus 1a is an apparatus used to process a heat load through a vapor-compression refrigeration cycle operation. The refrigeration cycle apparatus 1a includes a heat-load circuit 90, a first refrigerant circuit 10, a second refrigerant circuit 20, an outdoor fan 9, and a controller 7.
The heat load to be processed by the refrigeration cycle apparatus 1a and the heat-load circuit 90 are similar to those according to the first embodiment.
A use heat exchanger 13 includes a heat-load flow path 13c through which the water flowing through the heat-load circuit 90 passes, a first use flow path 13a through which the first refrigerant flowing through the first refrigerant circuit 10 passes, and a second use flow path 13b through which the second refrigerant flowing through the second refrigerant circuit 20 passes. The water flowing through the heat-load flow path 13c of the use heat exchanger 13 exchanges heat with the first refrigerant flowing through the first use flow path 13a or the second refrigerant flowing through the second use flow path 13b. As a result, the water is cooled during a cooling operation and is heated during a heating operation.
The first refrigerant circuit 10 includes a first compressor 11, a first switching mechanism 12x, the use heat exchanger 13 shared with the heat-load circuit 90 and the second refrigerant circuit 20, a second use expansion valve 16, a third use expansion valve 14, a heat-source heat exchanger 17 shared with the second refrigerant circuit 20, and a first outdoor heat exchanger 18. The first refrigerant circuit 10 is filled with the first refrigerant, which is a low-pressure refrigerant, as a refrigerant. The first refrigerant is a refrigerant having 1 MPa or less at 30°C, and is a refrigerant including, for example, at least one of R1234yf or R1234ze. The first refrigerant may include only R1234yf or may include only R1234ze.
The specific configuration of the first compressor 11 is similar to that according to the first embodiment. A discharge side of the first compressor 11 is connected to the first switching mechanism 12x. A suction side of the first compressor 11 is connected to a gas-refrigerant-side outlet of a first heat-source flow path 17a of the heat-source heat exchanger 17.
The first switching mechanism 12x is a four-way switching valve that switches between a state in which the suction side of the first compressor 11 is connected to the first outdoor heat exchanger 18 while the discharge side of the first compressor 11 is connected to the first use flow path 13a of the use heat exchanger 13, and a state in which the suction side of the first compressor 11 is connected to the first use flow path 13a of the use heat exchanger 13 while the discharge side of the first compressor 11 is connected to the first outdoor heat exchanger 18.
A gas refrigerant side of the first use flow path 13a of the use heat exchanger 13 through which the first refrigerant flowing through the first refrigerant circuit 10 passes is connected to the first switching mechanism 12x. A liquid refrigerant side of the first use flow path 13a is connected to a flow path extending from the third use expansion valve 14. The first refrigerant condenses when flowing through the first use flow path 13a of the use heat exchanger 13 to heat the water flowing through the heat-load circuit 90.
The third use expansion valve 14 includes an electronic expansion valve that is adjustable in valve opening degree. The third use expansion valve 14 is disposed between the use heat exchanger 13 and a first branch point A in the first refrigerant circuit 10.
At the first branch point A, a flow path extending from the third use expansion valve 14, a flow path extending from a liquid refrigerant side of the first heat-source flow path 17a in the heat-source heat exchanger 17, and a flow path extending to the side of the second use expansion valve 16 opposite to the first outdoor heat exchanger 18 side are connected.
The second use expansion valve 16 is similar to that according to the first embodiment.
The heat-source heat exchanger 17 is similar to that according to the first embodiment. The gas-refrigerant-side outlet of the first heat-source flow path 17a of the heat-source heat exchanger 17 is connected to the suction side of the first compressor 11. An inlet on the liquid refrigerant side of the first heat-source flow path 17a of the heat-source heat exchanger 17 is connected to the first branch point A.
The first outdoor heat exchanger 18 is similar to that according to the first embodiment.
The outdoor fan 9 generates an air flow of outdoor air passing through both the first outdoor heat exchanger 18 and a second outdoor heat exchanger 23.
The second refrigerant circuit 20 includes a second compressor 21, the use heat exchanger 13 shared with the heat-load circuit 90 and the first refrigerant circuit 10, the heat-source heat exchanger 17 shared with the first refrigerant circuit 10, a first heat-source expansion valve 26, a second heat-source expansion valve 24, and the second outdoor heat exchanger 23. The second refrigerant circuit 20 is filled with the second refrigerant, which is a high-pressure refrigerant, as a refrigerant. The second refrigerant is a refrigerant having 1.5 MPa or more at 30°C. The second refrigerant may include carbon dioxide, or may include only carbon dioxide.
The specific configuration of the second compressor 21 is similar to that according to the first embodiment. A discharge side of the second compressor 21 is connected to an inlet on a gas refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17. A suction side of the second compressor 21 is connected to a flow path extending from a third branch point C in the second refrigerant circuit 20.
At the third branch point C, a flow path extending from the suction side of the second compressor 21, a flow path extending from an outlet on a gas refrigerant side of the second outdoor heat exchanger 23, and a flow path extending from the outlet on the gas refrigerant side of the second use flow path 13b of the use heat exchanger 13 are connected.
The inlet on the gas refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17 is connected to the discharge side of the second compressor 21. An outlet on a liquid refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17 is connected to a flow path extending from a second branch point B in the second refrigerant circuit 20. The second refrigerant radiates heat when flowing through the second heat-source flow path 17b of the heat-source heat exchanger 17 to evaporate the first refrigerant flowing through the first heat-source flow path 17a.
At the second branch point B, a flow path extending from the outlet on the liquid refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17, a flow path extending from the first heat-source expansion valve 26, and a flow path extending from the second heat-source expansion valve 24 are connected.
The first heat-source expansion valve 26 is disposed in a flow path between the second branch point B and an inlet on a liquid refrigerant side of the second outdoor heat exchanger 23.
The second outdoor heat exchanger 23 is similar to that according to the first embodiment.
The second heat-source expansion valve 24 is disposed in a flow path between the second branch point B and an inlet on a liquid refrigerant side of the second use flow path 13b of the use heat exchanger 13.
The second use flow path 13b of the use heat exchanger 13 through which the second refrigerant flowing through the second refrigerant circuit 20 passes is disposed in a flow path between the second heat-source expansion valve 24 and the third branch point C. The second refrigerant evaporates when flowing through the second use flow path 13b of the use heat exchanger 13 to cool the water flowing through the heat-load circuit 90.
The controller 7 controls the operation of the devices included in the heat-load circuit 90, the first refrigerant circuit 10, and the second refrigerant circuit 20. Specifically, the controller 7 includes a processor serving as a CPU provided for performing control, a memory, and the like.
In the refrigeration cycle apparatus 1a described above, the controller 7 controls the devices to execute a refrigeration cycle, thereby performing a cooling operation for processing a cooling load in the heat-load heat exchanger 91 and a heating operation for processing a heating load in the heat-load heat exchanger 91.

(2-1) Cooling Operation

During the cooling operation, as illustrated in Fig. 7, while the first refrigerant circuit 10 performs a refrigeration cycle such that the first outdoor heat exchanger 18 functions as a condenser of the first refrigerant and the heat-source heat exchanger 17 functions as an evaporator of the first refrigerant, the second refrigerant circuit 20 performs a refrigeration cycle such that the heat-source heat exchanger 17 functions as a radiator of the second refrigerant and the use heat exchanger 13 functions as an evaporator of the second refrigerant. As a result, a two-stage refrigeration cycle is performed. Specifically, the first switching mechanism 12x is switched to a connection state indicated by solid lines in Fig. 7, the pump 92, the first compressor 11, the second compressor 21, and the outdoor fan 9 are driven, the third use expansion valve 14 is fully closed, the first heat-source expansion valve 26 is fully closed, the valve opening degree of the second use expansion valve 16 is controlled such that the degree of superheating of the first refrigerant to be sucked into the first compressor 11 satisfies a predetermined condition, and the valve opening degree of the second heat-source expansion valve 24 is controlled such that the degree of superheating of the second refrigerant to be sucked into the second compressor 21 satisfies a predetermined condition.
Accordingly, the first refrigerant discharged from the first compressor 11 is sent to the first outdoor heat exchanger 18 via the first switching mechanism 12x. The first refrigerant sent to the first outdoor heat exchanger 18 is condensed by heat exchange with the outdoor air supplied by the outdoor fan 9. The first refrigerant having passed through the first outdoor heat exchanger 18 is decompressed in the second use expansion valve 16, passes through the first branch point A, and is sent to the first heat-source flow path 17a of the heat-source heat exchanger 17. The first refrigerant flowing through the first heat-source flow path 17a of the heat-source heat exchanger 17 is evaporated by heat exchange with the second refrigerant flowing through the second heat-source flow path 17b of the heat-source heat exchanger 17. The first refrigerant evaporated in the first heat-source flow path 17a of the heat-source heat exchanger 17 is sucked into the first compressor 11.
The second refrigerant discharged from the second compressor 21 is sent to the second heat-source flow path 17b of the heat-source heat exchanger 17. The second refrigerant flowing through the second heat-source flow path 17b of the heat-source heat exchanger 17 radiates heat by heat exchange with the first refrigerant flowing through the first heat-source flow path 17a of the heat-source heat exchanger 17. The second refrigerant having passed through the second heat-source flow path 17b of the heat-source heat exchanger 17 is decompressed in the second heat-source expansion valve 24 via the second branch point B, and flows into the use heat exchanger 13. The second refrigerant flowing through the second use flow path 13b of the use heat exchanger 13 is evaporated by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The water cooled by this heat exchange is sent to the heat-load heat exchanger 91 in the heat-load circuit 90 to process the cooling load. The second refrigerant having passed through the second use flow path 13b of the use heat exchanger 13 is sucked into the second compressor 21.

(2-2) Heating Operation

During the heating operation, as illustrated in Fig. 8, the first refrigerant circuit 10 performs a refrigeration cycle such that the use heat exchanger 13 functions as a condenser of the first refrigerant and the heat-source heat exchanger 17 functions as an evaporator of the first refrigerant, and the second refrigerant circuit 20 performs a refrigeration cycle such that the heat-source heat exchanger 17 functions as a radiator of the second refrigerant and the second outdoor heat exchanger 23 functions as an evaporator of the second refrigerant. As a result, a two-stage refrigeration cycle is performed by the second refrigerant circuit 20 and the first refrigerant circuit 10 during the heating operation. Specifically, the first switching mechanism 12x is switched to a connection state indicated by broken lines in Fig. 8, the pump 92, the first compressor 11, the second compressor 21, and the outdoor fan 9 are driven, the second use expansion valve 16 is fully closed, the second heat-source expansion valve 24 is fully closed, the valve opening degree of the third use expansion valve 14 is controlled such that the degree of superheating of the first refrigerant to be sucked into the first compressor 11 satisfies a predetermined condition, and the valve opening degree of the first heat-source expansion valve 26 is controlled such that the degree of superheating of the second refrigerant to be sucked into the second compressor 21 satisfies a predetermined condition.
Accordingly, the second refrigerant discharged from the second compressor 21 is sent to the heat-source heat exchanger 17. When flowing through the second heat-source flow path 17b, the second refrigerant radiates heat by heat exchange with the first refrigerant flowing through the first heat-source flow path 17a. The second refrigerant, which has radiated heat in the heat-source heat exchanger 17, passes through the second branch point B and is then decompressed in the first heat-source expansion valve 26. Then, the second refrigerant is evaporated by heat exchange with the outdoor air supplied by the outdoor fan 9 in the second outdoor heat exchanger 23, and is sucked into the second compressor 21. The first refrigerant discharged from the first compressor 11 is sent to the first use flow path 13a of the use heat exchanger 13 via the first switching mechanism 12x. The first refrigerant flowing through the first use flow path 13a of the use heat exchanger 13 is condensed by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The water heated by this heat exchange is sent to the heat-load heat exchanger 91 in the heat-load circuit 90 to process the heating load. The first refrigerant condensed in the first use flow path 13a of the use heat exchanger 13 is decompressed in the third use expansion valve 14. The first refrigerant decompressed in the third use expansion valve 14 passes through the first branch point A. After that, when passing through the first heat-source flow path 17a of the heat-source heat exchanger 17, the first refrigerant is evaporated by heat exchange with the second refrigerant flowing through the second heat-source flow path 17b. The first refrigerant evaporated in the first heat-source flow path 17a of the heat-source heat exchanger 17 is sucked into the first compressor 11.

(2-3) Features of Second Embodiment

In the refrigeration cycle apparatus 1a according to the present embodiment, as in the refrigeration cycle apparatus 1 according to the first embodiment, global environmental deterioration can be reduced. In addition, the two-stage refrigeration cycle is performed during the heating operation, thereby making it easy to secure the capacity. The two-stage refrigeration cycle is also performed during the cooling operation. However, the carbon dioxide refrigerant serving as the second refrigerant does not radiate heat in the second outdoor heat exchanger 23, nor is the carbon dioxide refrigerant serving as the second refrigerant evaporated in the heat-source heat exchanger 17 to condense the first refrigerant. Instead of this, in the heat-source heat exchanger 17, the carbon dioxide refrigerant serving as the second refrigerant radiates heat to evaporate the first refrigerant. As a result, the second refrigerant is evaporated in the use heat exchanger 13 to process the cooling load. This makes it possible to perform the cooling operation without causing a reduction in COP due to the pressure of the carbon dioxide refrigerant exceeding the critical pressure when the cooling operation is performed using the carbon dioxide refrigerant in the heat-source-side cycle of the two-stage refrigeration cycle. It is also possible to reduce the compression strength standards required for the components of the second refrigerant circuit 20 in which carbon dioxide, which is a high-pressure refrigerant, is used.

(3) Third Embodiment

Fig. 9 is a schematic configuration diagram of a refrigeration cycle apparatus 1b according to a third embodiment. Fig. 10 is a functional block configuration diagram of the refrigeration cycle apparatus 1b according to the third embodiment.
The refrigeration cycle apparatus 1b is an apparatus used to process a heat load through a vapor-compression refrigeration cycle operation. The refrigeration cycle apparatus 1b includes a heat-load circuit 90, a first refrigerant circuit 10, a second refrigerant circuit 20, an outdoor fan 9, and a controller 7.
The heat load to be processed by the refrigeration cycle apparatus 1b and the heat-load circuit 90 are similar to those according to the first embodiment.
A use heat exchanger 13 includes a heat-load flow path 13c through which the water flowing through the heat-load circuit 90 passes, a first use flow path 13a through which the first refrigerant flowing through the first refrigerant circuit 10 passes, and a second use flow path 13b through which the second refrigerant flowing through the second refrigerant circuit 20 passes. The water flowing through the heat-load flow path 13c of the use heat exchanger 13 exchanges heat with the first refrigerant flowing through the first use flow path 13a or the second refrigerant flowing through the second use flow path 13b. As a result, the water is cooled during a cooling operation and is heated during a heating operation.
The first refrigerant circuit 10 includes a first compressor 11, a first switching mechanism 12, the use heat exchanger 13 shared with the heat-load circuit 90 and the second refrigerant circuit 20, a first use expansion valve 15, a second use expansion valve 16, a third use expansion valve 14, a heat-source heat exchanger 17 shared with the second refrigerant circuit 20, and a first outdoor heat exchanger 18. The first refrigerant circuit 10 is filled with the first refrigerant, which is a low-pressure refrigerant, as a refrigerant. The first refrigerant is a refrigerant having 1 MPa or less at 30°C, and is a refrigerant including, for example, at least one of R1234yf or R1234ze. The first refrigerant may include only R1234yf or may include only R1234ze.
The specific configuration of the first compressor 11 is similar to that according to the first embodiment. A discharge side of the first compressor 11 is connected to the first switching mechanism 12. A suction side of the first compressor 11 is connected to a gas-refrigerant-side outlet of a first heat-source flow path 17a of the heat-source heat exchanger 17.
The first switching mechanism 12 includes a switching valve 12a and a switching valve 12b. The switching valve 12a and the switching valve 12b are connected in parallel to each other on the discharge side of the first compressor 11. The switching valve 12a is a three-way valve that switches between a state in which the discharge side of the first compressor 11 is connected to the first use flow path 13a of the use heat exchanger 13 and a state in which the suction side of the first compressor 11 is connected to the first use flow path 13a of the use heat exchanger 13. The switching valve 12b is a three-way valve that switches between a state in which the discharge side of the first compressor 11 is connected to the first outdoor heat exchanger 18 and a state in which the suction side of the first compressor 11 is connected to the first outdoor heat exchanger 18.
A gas refrigerant side of the first use flow path 13a of the use heat exchanger 13 through which the first refrigerant flowing through the first refrigerant circuit 10 passes is connected to the switching valve 12a of the first switching mechanism 12. A liquid refrigerant side of the first use flow path 13a is connected to a flow path extending from the third use expansion valve 14. The first refrigerant condenses when flowing through the first use flow path 13a of the use heat exchanger 13 to heat the water flowing through the heat-load circuit 90.
The third use expansion valve 14 includes an electronic expansion valve that is adjustable in valve opening degree. The third use expansion valve 14 is disposed between the use heat exchanger 13 and a first branch point A in the first refrigerant circuit 10.
At the first branch point A, a flow path extending from the third use expansion valve 14, a flow path extending from the first use expansion valve 15, and a flow path extending to the side of the second use expansion valve 16 opposite to the first outdoor heat exchanger 18 side are connected.
The first use expansion valve 15 is similar to that according to the first embodiment.
The second use expansion valve 16 is similar to that according to the first embodiment.
The heat-source heat exchanger 17 is similar to that according to the first embodiment. The gas-refrigerant-side outlet of the first heat-source flow path 17a of the heat-source heat exchanger 17 is connected to the suction side of the first compressor 11. An inlet on a liquid refrigerant side of the first heat-source flow path 17a of the heat-source heat exchanger 17 is connected to a flow path extending from the first use expansion valve 15.
The first outdoor heat exchanger 18 is similar to that according to the first embodiment.
The outdoor fan 9 generates an air flow of outdoor air passing through both the first outdoor heat exchanger 18 and a second outdoor heat exchanger 23.
The second refrigerant circuit 20 includes a second compressor 21, the use heat exchanger 13 shared with the heat-load circuit 90 and the first refrigerant circuit 10, the heat-source heat exchanger 17 shared with the first refrigerant circuit 10, a first heat-source expansion valve 26, a second heat-source expansion valve 24, and the second outdoor heat exchanger 23. The second refrigerant circuit 20 is filled with the second refrigerant, which is a high-pressure refrigerant, as a refrigerant. The second refrigerant is a refrigerant having 1.5 MPa or more at 30°C. The second refrigerant may include carbon dioxide, or may include only carbon dioxide.
The specific configuration of the second compressor 21 is similar to that according to the first embodiment. A discharge side of the second compressor 21 is connected to an inlet on a gas refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17. A suction side of the second compressor 21 is connected to a flow path extending from a third branch point C in the second refrigerant circuit 20.
At the third branch point C, a flow path extending from the suction side of the second compressor 21, a flow path extending from an outlet on a gas refrigerant side of the second outdoor heat exchanger 23, and a flow path extending from the outlet on the gas refrigerant side of the second use flow path 13b of the use heat exchanger 13 are connected.
The inlet on the gas refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17 is connected to the discharge side of the second compressor 21. An outlet on a liquid refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17 is connected to a flow path extending from a second branch point B in the second refrigerant circuit 20. The second refrigerant radiates heat when flowing through the second heat-source flow path 17b of the heat-source heat exchanger 17 to evaporate the first refrigerant flowing through the first heat-source flow path 17a.
At the second branch point B, a flow path extending from the outlet on the liquid refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17, a flow path extending from the first heat-source expansion valve 26, and a flow path extending from the second heat-source expansion valve 24 are connected.
The first heat-source expansion valve 26 is disposed in a flow path between the second branch point B and an inlet on a liquid refrigerant side of the second outdoor heat exchanger 23.
The second outdoor heat exchanger 23 is similar to that according to the first embodiment.
The second heat-source expansion valve 24 is disposed in a flow path between the second branch point B and an inlet on a liquid refrigerant side of the second use flow path 13b of the use heat exchanger 13.
The second use flow path 13b of the use heat exchanger 13 through which the second refrigerant flowing through the second refrigerant circuit 20 passes is disposed in a flow path between the second heat-source expansion valve 24 and the third branch point C. The second refrigerant evaporates when flowing through the second use flow path 13b of the use heat exchanger 13 to cool the water flowing through the heat-load circuit 90.
The controller 7 controls the operation of the devices included in the heat-load circuit 90, the first refrigerant circuit 10, and the second refrigerant circuit 20. Specifically, the controller 7 includes a processor serving as a CPU provided for performing control, a memory, and the like.
In the refrigeration cycle apparatus 1b described above, the controller 7 controls the devices to execute a refrigeration cycle, thereby performing a cooling operation for processing a cooling load in the heat-load heat exchanger 91 and a heating operation for processing a heating load in the heat-load heat exchanger 91.

(3-1) Cooling Operation

During the cooling operation, as illustrated in Fig. 11, while the first refrigerant circuit 10 performs a refrigeration cycle such that the first outdoor heat exchanger 18 functions as a condenser of the first refrigerant and the heat-source heat exchanger 17 functions as an evaporator of the first refrigerant, the second refrigerant circuit 20 performs a refrigeration cycle such that the heat-source heat exchanger 17 functions as a radiator of the second refrigerant and the use heat exchanger 13 functions as an evaporator of the second refrigerant. As a result, a two-stage refrigeration cycle is performed. Specifically, the switching valves 12a and 12b of the first switching mechanism 12 are switched to a connection state indicated by solid lines in Fig. 11, the pump 92, the first compressor 11, the second compressor 21, and the outdoor fan 9 are driven, the third use expansion valve 14 is fully closed, the first heat-source expansion valve 26 is fully closed, one of the first use expansion valve 15 and the second use expansion valve 16 is controlled to be fully opened while the valve opening degree of the other use expansion valve is controlled such that the degree of superheating of the first refrigerant to be sucked into the first compressor 11 satisfies a predetermined condition, and the valve opening degree of the second heat-source expansion valve 24 is controlled such that the degree of superheating of the second refrigerant to be sucked into the second compressor 21 satisfies a predetermined condition.
Accordingly, the first refrigerant discharged from the first compressor 11 is sent to the first outdoor heat exchanger 18 via the switching valve 12b of the first switching mechanism 12. The first refrigerant sent to the first outdoor heat exchanger 18 is condensed by heat exchange with the outdoor air supplied by the outdoor fan 9. The first refrigerant having passed through the first outdoor heat exchanger 18 is decompressed in the second use expansion valve 16 and passes through the first branch point A, or is decompressed in the first use expansion valve 15 after passing through the first branch point A. Then, the first refrigerant is sent to the first heat-source flow path 17a of the heat-source heat exchanger 17. The first refrigerant flowing through the first heat-source flow path 17a of the heat-source heat exchanger 17 is evaporated by heat exchange with the second refrigerant flowing through the second heat-source flow path 17b of the heat-source heat exchanger 17. The first refrigerant evaporated in the first heat-source flow path 17a of the heat-source heat exchanger 17 is sucked into the first compressor 11.
The second refrigerant discharged from the second compressor 21 is sent to the second heat-source flow path 17b of the heat-source heat exchanger 17. The second refrigerant flowing through the second heat-source flow path 17b of the heat-source heat exchanger 17 radiates heat by heat exchange with the first refrigerant flowing through the first heat-source flow path 17a of the heat-source heat exchanger 17. The second refrigerant having passed through the second heat-source flow path 17b of the heat-source heat exchanger 17 is decompressed in the second heat-source expansion valve 24 via the second branch point B, and flows into the use heat exchanger 13. The second refrigerant flowing through the second use flow path 13b of the use heat exchanger 13 is evaporated by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The water cooled by this heat exchange is sent to the heat-load heat exchanger 91 in the heat-load circuit 90 to process the cooling load. The second refrigerant having passed through the second use flow path 13b of the use heat exchanger 13 is sucked into the second compressor 21.

(3-2) Heating Operation

During the heating operation, as illustrated in Fig. 12, the first refrigerant circuit 10 performs a refrigeration cycle such that the use heat exchanger 13 functions as a condenser of the first refrigerant and the heat-source heat exchanger 17 functions as an evaporator of the first refrigerant, and the second refrigerant circuit 20 performs a refrigeration cycle such that the heat-source heat exchanger 17 functions as a radiator of the second refrigerant and the second outdoor heat exchanger 23 functions as an evaporator of the second refrigerant. As a result, a two-stage refrigeration cycle is performed by the second refrigerant circuit 20 and the first refrigerant circuit 10 during the heating operation. Specifically, the switching valves 12a and 12b of the first switching mechanism 12 are switched to a connection state indicated by broken lines in Fig. 12, the pump 92, the first compressor 11, the second compressor 21, and the outdoor fan 9 are driven, the second use expansion valve 16 is fully closed, the second heat-source expansion valve 24 is fully closed, the valve opening degree of the third use expansion valve 14 or the first use expansion valve 15 is controlled such that the degree of superheating of the first refrigerant to be sucked into the first compressor 11 satisfies a predetermined condition, and the valve opening degree of the first heat-source expansion valve 26 is controlled such that the degree of superheating of the second refrigerant to be sucked into the second compressor 21 satisfies a predetermined condition.
Accordingly, the second refrigerant discharged from the second compressor 21 is sent to the heat-source heat exchanger 17. When flowing through the second heat-source flow path 17b, the second refrigerant radiates heat by heat exchange with the first refrigerant flowing through the first heat-source flow path 17a. The second refrigerant, which has radiated heat in the heat-source heat exchanger 17, passes through the second branch point B and is then decompressed in the first heat-source expansion valve 26. Then, the second refrigerant is evaporated by heat exchange with the outdoor air supplied by the outdoor fan 9 in the second outdoor heat exchanger 23, and is sucked into the second compressor 21. The first refrigerant discharged from the first compressor 11 is sent to the first use flow path 13a of the use heat exchanger 13 via the switching valve 12a of the first switching mechanism 12. The first refrigerant flowing through the first use flow path 13a of the use heat exchanger 13 is condensed by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The water heated by this heat exchange is sent to the heat-load heat exchanger 91 in the heat-load circuit 90 to process the heating load. The first refrigerant condensed in the first use flow path 13a of the use heat exchanger 13 passes through the first branch point A after being decompressed in the third use expansion valve 14, or passes through the first branch point A and is then decompressed in the first use expansion valve 15. The first refrigerant having passed through the first branch point A is evaporated, when passing through the first heat-source flow path 17a of the heat-source heat exchanger 17, by heat exchange with the second refrigerant flowing through the second heat-source flow path 17b. The first refrigerant evaporated in the first heat-source flow path 17a of the heat-source heat exchanger 17 is sucked into the first compressor 11.

(3-3) Features of Third Embodiment

Like the refrigeration cycle apparatus 1 according to the first embodiment, the refrigeration cycle apparatus 1b according to the present embodiment can reduce global environmental deterioration and can easily secure heating operation capacity. The two-stage refrigeration cycle is also performed during the cooling operation. However, the carbon dioxide refrigerant serving as the second refrigerant does not radiate heat in the second outdoor heat exchanger 23, nor is the carbon dioxide refrigerant serving as the second refrigerant evaporated in the heat-source heat exchanger 17 to condense the first refrigerant. Instead of this, in the heat-source heat exchanger 17, the carbon dioxide refrigerant serving as the second refrigerant radiates heat to evaporate the first refrigerant. As a result, the second refrigerant is evaporated in the use heat exchanger 13 to process the cooling load. This makes it possible to perform the cooling operation without causing a reduction in COP due to the pressure of the carbon dioxide refrigerant exceeding the critical pressure when the cooling operation is performed using the carbon dioxide refrigerant in the heat-source-side cycle of the two-stage refrigeration cycle. It is also possible to reduce the compression strength standards required for the components of the second refrigerant circuit 20 in which carbon dioxide, which is a high-pressure refrigerant, is used.

(4) Fourth Embodiment

Fig. 13 is a schematic configuration diagram of a refrigeration cycle apparatus 1c according to a fourth embodiment. Fig. 14 is a functional block configuration diagram of the refrigeration cycle apparatus 1c according to the fourth embodiment.
The refrigeration cycle apparatus 1c is an apparatus used to process a heat load through a vapor-compression refrigeration cycle operation. The refrigeration cycle apparatus 1c includes a heat-load circuit 90, a first refrigerant circuit 10, a second refrigerant circuit 20, an outdoor fan 9, and a controller 7.
The heat load to be processed by the refrigeration cycle apparatus 1c and the heat-load circuit 90 are similar to those according to the first embodiment.
A use heat exchanger 13 includes a heat-load flow path 13c through which the water flowing through the heat-load circuit 90 passes, a first use flow path 13a through which the first refrigerant flowing through the first refrigerant circuit 10 passes, and a second use flow path 13b through which the second refrigerant flowing through the second refrigerant circuit 20 passes. The water flowing through the heat-load flow path 13c of the use heat exchanger 13 exchanges heat with the first refrigerant flowing through the first use flow path 13a and/or the second refrigerant flowing through the second use flow path 13b. As a result, the water is cooled during a cooling operation and is heated during a heating operation.
The first refrigerant circuit 10 includes a first compressor 11, a first switching mechanism 12, the use heat exchanger 13 shared with the heat-load circuit 90 and the second refrigerant circuit 20, a first use expansion valve 15, a second use expansion valve 16, a third use expansion valve 14, a heat-source heat exchanger 17 shared with the second refrigerant circuit 20, and a first outdoor heat exchanger 18. The first refrigerant circuit 10 is filled with the first refrigerant, which is a low-pressure refrigerant, as a refrigerant. The first refrigerant is a refrigerant having 1 MPa or less at 30°C, and is a refrigerant including, for example, at least one of R1234yf or R1234ze. The first refrigerant may include only R1234yf or may include only R1234ze.
The specific configuration of the first compressor 11 is similar to that according to the first embodiment. A discharge side and a suction side of the first compressor 11 are connected to different connection points of the first switching mechanism 12.
The first switching mechanism 12 includes a switching valve 12a, a switching valve 12b, and a switching valve 12c. The switching valve 12a, the switching valve 12b, and the switching valve 12c are connected in parallel to each other on the discharge side of the first compressor 11. The switching valve 12a is a three-way valve that switches between a state in which the discharge side of the first compressor 11 is connected to the first use flow path 13a of the use heat exchanger 13 and a state in which the suction side of the first compressor 11 is connected to the first use flow path 13a of the use heat exchanger 13. The switching valve 12b is a three-way valve that switches between a state in which the discharge side of the first compressor 11 is connected to the first outdoor heat exchanger 18 and a state in which the suction side of the first compressor 11 is connected to the first outdoor heat exchanger 18. The switching valve 12c is a three-way valve that switches between a state in which the discharge side of the first compressor 11 is connected to a first heat-source flow path 17a of the heat-source heat exchanger 17 and a state in which the suction side of the first compressor 11 is connected to the first heat-source flow path 17a of the heat-source heat exchanger 17.
A gas refrigerant side of the first use flow path 13a of the use heat exchanger 13 through which the first refrigerant flowing through the first refrigerant circuit 10 passes is connected to the switching valve 12a of the first switching mechanism 12. A liquid refrigerant side of the first use flow path 13a is connected to a flow path extending from the third use expansion valve 14. The first refrigerant evaporates when flowing through the first use flow path 13a of the use heat exchanger 13 to cool the water flowing through the heat-load circuit 90. The first refrigerant condenses when flowing through the first use flow path 13a of the use heat exchanger 13 to heat the water flowing through the heat-load circuit 90.
The third use expansion valve 14 includes an electronic expansion valve that is adjustable in valve opening degree. The third use expansion valve 14 is disposed between the use heat exchanger 13 and a first branch point A in the first refrigerant circuit 10.
At the first branch point A, a flow path extending from the third use expansion valve 14, a flow path extending from the first use expansion valve 15, and a flow path extending to the side of the second use expansion valve 16 opposite to the first outdoor heat exchanger 18 side are connected.
The first use expansion valve 15 is similar to that according to the first embodiment.
The second use expansion valve 16 is similar to that according to the first embodiment.
The heat-source heat exchanger 17 is similar to that according to the first embodiment. An outlet on a gas refrigerant side of the first heat-source flow path 17a of the heat-source heat exchanger 17 is connected to the switching valve 12c of the first switching mechanism 12. An inlet on a liquid refrigerant side of the first heat-source flow path 17a of the heat-source heat exchanger 17 is connected to a flow path extending from the first use expansion valve 15.
The first outdoor heat exchanger 18 is similar to that according to the first embodiment.
The outdoor fan 9 generates an air flow of outdoor air passing through both the first outdoor heat exchanger 18 and a second outdoor heat exchanger 23.
The second refrigerant circuit 20 includes a second compressor 21, a second switching mechanism 22, the use heat exchanger 13 shared with the heat-load circuit 90 and the first refrigerant circuit 10, the heat-source heat exchanger 17 shared with the first refrigerant circuit 10, a first heat-source expansion valve 26, a second heat-source expansion valve 24, a third heat-source expansion valve 25, and the second outdoor heat exchanger 23. The second refrigerant circuit 20 is filled with the second refrigerant, which is a high-pressure refrigerant, as a refrigerant. The second refrigerant is a refrigerant having 1.5 MPa or more at 30°C. The second refrigerant may include carbon dioxide, or may include only carbon dioxide.
The specific configuration of the second compressor 21 is similar to that according to the first embodiment. A discharge side and a suction side of the second compressor 21 are connected to different connection points of the second switching mechanism 22.
The second switching mechanism 22 includes a switching valve 22a, a switching valve 22b, and a switching valve 22c. The switching valve 22a, the switching valve 22b, and the switching valve 22c are connected in parallel to each other on the discharge side of the second compressor 21. The switching valve 22a is a three-way valve that switches between a state in which the discharge side of the second compressor 21 is connected to the second use flow path 13b of the use heat exchanger 13 and a state in which the suction side of the second compressor 21 is connected to the second use flow path 13b of the use heat exchanger 13. The switching valve 22b is a three-way valve that switches between a state in which the discharge side of the second compressor 21 is connected to the second outdoor heat exchanger 23 and a state in which the suction side of the second compressor 21 is connected to the second outdoor heat exchanger 23. The switching valve 22c is a three-way valve that switches between a state in which the discharge side of the second compressor 21 is connected to a second heat-source flow path 17b of the heat-source heat exchanger 17 and a state in which the suction side of the second compressor 21 is connected to the second heat-source flow path 17b of the heat-source heat exchanger 17.
An inlet on a gas refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17 is connected to the switching valve 22c of the second switching mechanism 22. An outlet on a liquid refrigerant side of the second heat-source flow path 17b of the heat-source heat exchanger 17 is connected to a flow path extending from the third heat-source expansion valve 25. The second refrigerant radiates heat when flowing through the second heat-source flow path 17b of the heat-source heat exchanger 17 to evaporate the first refrigerant flowing through the first heat-source flow path 17a.
At a second branch point B, a flow path extending from the third heat-source expansion valve 25, a flow path extending from the first heat-source expansion valve 26, and a flow path extending from the second heat-source expansion valve 24 are connected.
The first heat-source expansion valve 26 is disposed in a flow path between the second branch point B and an inlet on a liquid refrigerant side of the second outdoor heat exchanger 23.
The second outdoor heat exchanger 23 is similar to that according to the first embodiment.
The second heat-source expansion valve 24 is disposed in a flow path between the second branch point B and an inlet on a liquid refrigerant side of the second use flow path 13b of the use heat exchanger 13.
The second use flow path 13b of the use heat exchanger 13 through which the second refrigerant flowing through the second refrigerant circuit 20 passes is disposed in a flow path between the second heat-source expansion valves 24 and the switching valve 22a of the second switching mechanism 22. The second refrigerant evaporates when flowing through the second use flow path 13b of the use heat exchanger 13 to cool the water flowing through the heat-load circuit 90. The second refrigerant radiates heat when flowing through the second use flow path 13b of the use heat exchanger 13 to heat the water flowing through the heat-load circuit 90.
The controller 7 controls the operation of the devices included in the heat-load circuit 90, the first refrigerant circuit 10, and the second refrigerant circuit 20. Specifically, the controller 7 includes a processor serving as a CPU provided for performing control, a memory, and the like.
In the refrigeration cycle apparatus 1c described above, the controller 7 controls the devices to execute a refrigeration cycle, thereby performing a cooling operation for processing a cooling load in the heat-load heat exchanger 91 and a heating operation for processing a heating load in the heat-load heat exchanger 91.

(4-1) Cooling Operation

During the cooling operation, a first cooling operation, a second cooling operation, and a third cooling operation are selectively performed.
In the first cooling operation, as illustrated in Fig. 15, the first refrigerant circuit 10 performs a refrigeration cycle such that the first outdoor heat exchanger 18 functions as a condenser of the first refrigerant and the use heat exchanger 13 functions as an evaporator of the first refrigerant, and the second refrigerant circuit 20 causes the second compressor 21 to stop operation. As a result, a single-stage refrigeration cycle is performed. Specifically, the switching valves 12a, 12b, and 12c of the first switching mechanism 12 are switched to a connection state indicated by solid lines in Fig. 15, the pump 92, the first compressor 11, and the outdoor fan 9 are driven, the second use expansion valve 16 is fully opened, the first use expansion valve 15 is controlled to be fully closed, and the valve opening degree of the third use expansion valve 14 is controlled such that the degree of superheating of the first refrigerant to be sucked into the first compressor 11 satisfies a predetermined condition.
Accordingly, the first refrigerant discharged from the first compressor 11 is sent to the first outdoor heat exchanger 18 via the switching valve 12b of the first switching mechanism 12. The first refrigerant sent to the first outdoor heat exchanger 18 is condensed by heat exchange with the outdoor air supplied by the outdoor fan 9. The first refrigerant having passed through the first outdoor heat exchanger 18 passes through the second use expansion valve 16 and the first branch point A, is decompressed in the third use expansion valve 14, and then flows into the use heat exchanger 13. The first refrigerant flowing through the first use flow path 13a of the use heat exchanger 13 is evaporated by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The water cooled by this heat exchange is sent to the heat-load heat exchanger 91 in the heat-load circuit 90 to process the cooling load. The first refrigerant evaporated in the first use flow path 13a is sucked into the first compressor 11 via the switching valve 12a of the first switching mechanism 12.
The second cooling operation is performed when the single-stage refrigeration cycle performed by the first refrigerant circuit 10 causes insufficient capacity because the required temperature of the heat medium flowing through the heat-load circuit 90 drops to a predetermined value or less to increase the cooling load. The second cooling operation is performed, in particular, in a refrigeration cycle apparatus in which the heat medium flowing through the heat-load circuit 90 is antifreeze, when the temperature required in the heat-load circuit 90 is low. In the second cooling operation, as illustrated in Fig. 16, the first refrigerant circuit 10 performs a refrigeration cycle such that the first outdoor heat exchanger 18 functions as a condenser of the first refrigerant and the heat-source heat exchanger 17 functions as an evaporator of the first refrigerant, and the second refrigerant circuit 20 performs a refrigeration cycle such that the heat-source heat exchanger 17 functions as a radiator of the second refrigerant and the use heat exchanger 13 functions as an evaporator of the second refrigerant. As a result, a two-stage refrigeration cycle is performed. Specifically, the switching valves 12a, 12b, and 12c of the first switching mechanism 12 are switched to a connection state indicated by solid lines in Fig. 16, the switching valves 22a, 22b, and 22c of the second switching mechanism 22 are switched to a connection state indicated by solid lines in Fig. 16, and the pump 92, the first compressor 11, the second compressor 21, and the outdoor fan 9 are driven. Then, the second use expansion valve 16 is controlled to be fully opened, the third use expansion valve 14 is controlled to be fully closed, and the valve opening degree of the first use expansion valve 15 is controlled such that the degree of superheating of the first refrigerant to be sucked into the first compressor 11 satisfies a predetermined condition. Further, the first heat-source expansion valve 26 is controlled to be fully closed, the third heat-source expansion valve 25 is controlled to be fully opened, and the valve opening degree of the second heat-source expansion valve 24 is controlled such that the degree of superheating of the second refrigerant to be sucked into the second compressor 21 satisfies a predetermined condition.
Accordingly, the first refrigerant discharged from the first compressor 11 is sent to the first outdoor heat exchanger 18 via the switching valve 12b of the first switching mechanism 12. The first refrigerant sent to the first outdoor heat exchanger 18 is condensed by heat exchange with the outdoor air supplied by the outdoor fan 9. The first refrigerant having passed through the first outdoor heat exchanger 18 passes through the second use expansion valve 16, is decompressed in the first use expansion valve 15, and then flows into the heat-source heat exchanger 17. The first refrigerant flowing through the first heat-source flow path 17a of the heat-source heat exchanger 17 is evaporated by heat exchange with the second refrigerant flowing through the second heat-source flow path 17b. The first refrigerant evaporated in the heat-source heat exchanger 17 is sucked into the first compressor 11 via the switching valve 12c of the first switching mechanism 12. The second refrigerant discharged from the second compressor 21 is sent to the heat-source heat exchanger 17 via the switching valve 22c of the second switching mechanism 22. The second refrigerant flowing through the second heat-source flow path 17b of the heat-source heat exchanger 17 radiates heat by heat exchange with the first refrigerant flowing through the first heat-source flow path 17a. The second refrigerant having passed through the heat-source heat exchanger 17 passes through the third heat-source expansion valve 25, is decompressed in the second heat-source expansion valve 24, and then flows into the use heat exchanger 13. The second refrigerant flowing through the second use flow path 13b of the use heat exchanger 13 is evaporated by heat exchange with the antifreeze flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The antifreeze cooled by this heat exchange is sent to the heat-load heat exchanger 91 in the heat-load circuit 90 to process the cooling load. The second refrigerant evaporated in the use heat exchanger 13 is sucked into the second compressor 21 via the switching valve 22a of the second switching mechanism 22.
The third cooling operation is an operation performed when more emphasis is placed on the exercise of the capacity than the increase of the operation efficiency in a case where the temperature of the heat medium flowing through the heat-load circuit 90 is higher than a predetermined value and the cooling load is large. In the third cooling operation, parallel refrigeration cycles are performed by the first refrigerant circuit 10 and the second refrigerant circuit 20 to exercise the capacity more than when the single-stage refrigeration cycle using the first refrigerant or the two-stage refrigeration cycle in which the first refrigerant is used in the heat-source-side refrigeration cycle in the higher stage and the second refrigerant is used in the use-side refrigeration cycle in the lower stage is performed. In the third cooling operation, as illustrated in Fig. 17, the first refrigerant circuit 10 performs a refrigeration cycle such that the first outdoor heat exchanger 18 functions as a condenser of the first refrigerant and the use heat exchanger 13 functions as an evaporator of the first refrigerant, and the second refrigerant circuit 20 performs a refrigeration cycle such that the second outdoor heat exchanger 23 functions as a radiator of the second refrigerant and the use heat exchanger 13 functions as an evaporator of the second refrigerant. As a result, parallel refrigeration cycles are performed. Specifically, the switching valves 12a, 12b, and 12c of the first switching mechanism 12 are switched to a connection state indicated by solid lines in Fig. 17, the switching valves 22a, 22b, and 22c of the second switching mechanism 22 are switched to a connection state indicated by solid lines in Fig. 17, and the pump 92, the first compressor 11, the second compressor 21, and the outdoor fan 9 are driven. Then, the second use expansion valve 16 is controlled to be fully opened, the first use expansion valve 15 is controlled to be fully closed, and the valve opening degree of the third use expansion valve 14 is controlled such that the degree of superheating of the first refrigerant to be sucked into the first compressor 11 satisfies a predetermined condition. Further, the first heat-source expansion valve 26 is controlled to be fully opened, the third heat-source expansion valve 25 is controlled to be fully closed, and the valve opening degree of the second heat-source expansion valve 24 is controlled such that the degree of superheating of the second refrigerant to be sucked into the second compressor 21 satisfies a predetermined condition.
Accordingly, the first refrigerant discharged from the first compressor 11 is sent to the first outdoor heat exchanger 18 via the switching valve 12b of the first switching mechanism 12. The first refrigerant sent to the first outdoor heat exchanger 18 is condensed by heat exchange with the outdoor air supplied by the outdoor fan 9. The first refrigerant having passed through the first outdoor heat exchanger 18 passes through the second use expansion valve 16, is decompressed in the third use expansion valve 14, and then flows into the use heat exchanger 13. The first refrigerant flowing through the first use flow path 13a of the use heat exchanger 13 is evaporated by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The first refrigerant evaporated in the use heat exchanger 13 is sucked into the first compressor 11 via the switching valve 12a of the first switching mechanism 12. The second refrigerant discharged from the second compressor 21 is sent to the second outdoor heat exchanger 23 via the switching valve 22b of the second switching mechanism 22. The second refrigerant sent to the second outdoor heat exchanger 23 radiates heat by heat exchange with the outdoor air supplied by the outdoor fan 9. The second refrigerant having passed through the second outdoor heat exchanger 23 passes through the first heat-source expansion valve 26, is decompressed in the second heat-source expansion valve 24, and then flows into the use heat exchanger 13. The second refrigerant flowing through the second use flow path 13b of the use heat exchanger 13 is evaporated by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The water cooled by exchanging heat with the two refrigerants, namely, the first refrigerant and the second refrigerant, in the way described above is sent to the heat-load heat exchanger 91 in the heat-load circuit 90 to process the cooling load. The second refrigerant evaporated in the use heat exchanger 13 is sucked into the second compressor 21 via the switching valve 22a of the second switching mechanism 22.

(4-2) Heating Operation

During the heating operation, a first heating operation, a second heating operation, and a third heating operation are selectively performed.
The first heating operation is performed when the outside air temperature is equal to or higher than a predetermined value.
In the first heating operation, as illustrated in Fig. 18, the first refrigerant circuit 10 causes the use heat exchanger 13 to function as a condenser of the first refrigerant, and causes the first outdoor heat exchanger 18 to function as an evaporator of the first refrigerant, and the second refrigerant circuit 20 causes the second compressor 21 to stop operation. As a result, a single-stage refrigeration cycle is performed. Specifically, the switching valves 12a and 12b of the first switching mechanism 12 are switched to a connection state indicated by broken lines in Fig. 18 and the switching valve 12c are switched to a connection state indicated by solid line in Fig. 18, the pump 92, the first compressor 11, and the outdoor fan 9 are driven, the third use expansion valve 14 is fully opened, the first use expansion valve 15 is controlled to be fully closed, and the valve opening degree of the second use expansion valve 16 is controlled such that the degree of superheating of the first refrigerant to be sucked into the first compressor 11 satisfies a predetermined condition.
Accordingly, the first refrigerant discharged from the first compressor 11 is sent to the first use flow path 13a of the use heat exchanger 13 via the switching valve 12a of the first switching mechanism 12. The first refrigerant flowing through the first use flow path 13a of the use heat exchanger 13 is condensed by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The water heated by this heat exchange is sent to the heat-load heat exchanger 91 in the heat-load circuit 90 to process the heating load. The first refrigerant condensed in the first use flow path 13a of the use heat exchanger 13 passes through the third use expansion valve 14 and the first branch point A, is decompressed in the second use expansion valve 16, and then flows into the first outdoor heat exchanger 18. The first refrigerant sent to the first outdoor heat exchanger 18 is evaporated by heat exchange with the outdoor air supplied by the outdoor fan 9. The first refrigerant evaporated in the first outdoor heat exchanger 18 is sucked into the first compressor 11 via the switching valve 12b of the first switching mechanism 12.
The second heating operation is an operation performed when the outside air temperature drops to a predetermined value or lower and the capacity is difficult to secure with the single-stage refrigeration cycle using the first refrigerant in the first refrigerant circuit 10. In the second heating operation, as illustrated in Fig. 19, the first refrigerant circuit 10 performs a refrigeration cycle such that the use heat exchanger 13 functions as a condenser of the first refrigerant and the heat-source heat exchanger 17 functions as an evaporator of the first refrigerant, and the second refrigerant circuit 20 performs a refrigeration cycle such that the heat-source heat exchanger 17 functions as a radiator of the second refrigerant and the second outdoor heat exchanger 23 functions as an evaporator of the second refrigerant. As a result, a two-stage refrigeration cycle is performed. Specifically, the switching valves 12a, 12b, and 12c of the first switching mechanism 12 are switched to a connection state indicated by broken lines in Fig. 19, the switching valves 22a, 22b, and 22c of the second switching mechanism 22 are switched to a connection state indicated by solid lines in Fig. 19, and the pump 92, the first compressor 11, the second compressor 21, and the outdoor fan 9 are driven. Then, the second use expansion valve 16 is controlled to be fully closed, the third use expansion valve 14 is controlled to be fully opened, and the valve opening degree of the first use expansion valve 15 is controlled such that the degree of superheating of the first refrigerant to be sucked into the first compressor 11 satisfies a predetermined condition. Further, the second heat-source expansion valve 24 is controlled to be fully closed, the third heat-source expansion valve 25 is controlled to be fully opened, and the valve opening degree of the first heat-source expansion valve 26 is controlled such that the degree of superheating of the second refrigerant to be sucked into the second compressor 21 satisfies a predetermined condition.
Accordingly, the first refrigerant discharged from the first compressor 11 is sent to the use heat exchanger 13 via the switching valve 12a of the first switching mechanism 12. The first refrigerant flowing through the first use flow path 13a of the use heat exchanger 13 is condensed by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The water heated by this heat exchange is sent to the heat-load heat exchanger 91 in the heat-load circuit 90 to process the heating load. The first refrigerant having passed through the use heat exchanger 13 passes through the third use expansion valve 14, is decompressed in the first use expansion valve 15, and then flows into the heat-source heat exchanger 17. The first refrigerant flowing through the first heat-source flow path 17a of the heat-source heat exchanger 17 is evaporated by heat exchange with the second refrigerant flowing through the second heat-source flow path 17b. The first refrigerant evaporated in the heat-source heat exchanger 17 is sucked into the first compressor 11 via the switching valve 12c of the first switching mechanism 12. The second refrigerant discharged from the second compressor 21 is sent to the heat-source heat exchanger 17 via the switching valve 22c of the second switching mechanism 22. The second refrigerant flowing through the second heat-source flow path 17b of the heat-source heat exchanger 17 radiates heat by heat exchange with the first refrigerant flowing through the first heat-source flow path 17a. The second refrigerant having passed through the heat-source heat exchanger 17 passes through the third heat-source expansion valve 25, is decompressed in the first heat-source expansion valve 26, and then flows into the second outdoor heat exchanger 23. The second refrigerant sent to the second outdoor heat exchanger 23 is evaporated by heat exchange with the outdoor air supplied by the outdoor fan 9. The second refrigerant evaporated in the second outdoor heat exchanger 23 is sucked into the second compressor 21 via the switching valve 22b of the second switching mechanism 22.
The third heating operation is an operation performed when more emphasis is placed on the exercise of the capacity than the increase of the operation efficiency in a case where the temperature of the heat medium flowing through the heat-load circuit 90 is lower than a predetermined value and the heating load is large. In the third heating operation, parallel refrigeration cycles are performed by the first refrigerant circuit 10 and the second refrigerant circuit 20 to exercise the capacity more than the single-stage refrigeration cycle using the first refrigerant and more than the two-stage refrigeration cycle in which the first refrigerant is used in the heat-source-side refrigeration cycle in the higher stage and the second refrigerant is used in the use-side refrigeration cycle in the lower stage. In the third heating operation, as illustrated in Fig. 20, the first refrigerant circuit 10 performs a refrigeration cycle such that the use heat exchanger 13 functions as a condenser of the first refrigerant and the first outdoor heat exchanger 18 functions as an evaporator of the first refrigerant, and the second refrigerant circuit 20 performs a refrigeration cycle such that the use heat exchanger 13 functions as a radiator of the second refrigerant and the second outdoor heat exchanger 23 functions as an evaporator of the second refrigerant. As a result, parallel refrigeration cycles are performed. Specifically, the switching valves 12a, 12b, and 12c of the first switching mechanism 12 are switched to a connection state indicated by broken lines in Fig. 20, the switching valves 22a and 22c of the second switching mechanism 22 are switched to a connection state indicated by broken lines in Fig. 20, the switching valve 22b of the second switching mechanism 22 is switched to a connection state indicated by a solid line in Fig. 20, and the pump 92, the first compressor 11, the second compressor 21, and the outdoor fan 9 are driven. Then, the third use expansion valve 14 is controlled to be fully opened, the first use expansion valve 15 is controlled to be fully closed, and the valve opening degree of the second use expansion valve 16 is controlled such that the degree of superheating of the first refrigerant to be sucked into the first compressor 11 satisfies a predetermined condition. Further, the second heat-source expansion valve 24 is controlled to be fully opened, the third heat-source expansion valve 25 is controlled to be fully closed, and the valve opening degree of the first heat-source expansion valve 26 is controlled such that the degree of superheating of the second refrigerant to be sucked into the second compressor 21 satisfies a predetermined condition.
Accordingly, the first refrigerant discharged from the first compressor 11 is sent to the use heat exchanger 13 via the switching valve 12a of the first switching mechanism 12, and the first refrigerant flowing through the first use flow path 13a of the use heat exchanger 13 is condensed by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The first refrigerant having passed through the use heat exchanger 13 passes through the third use expansion valve 14, is decompressed in the second use expansion valve 16, and then flows into the first outdoor heat exchanger 18. The first refrigerant sent to the first outdoor heat exchanger 18 is evaporated by heat exchange with the outdoor air supplied by the outdoor fan 9. The first refrigerant evaporated in the first outdoor heat exchanger 18 is sucked into the first compressor 11 via the switching valve 12b of the first switching mechanism 12. The second refrigerant discharged from the second compressor 21 is sent to the use heat exchanger 13 via the switching valve 22a of the second switching mechanism 22. The second refrigerant flowing through the second use flow path 13b of the use heat exchanger 13 radiates heat by heat exchange with the water flowing through the heat-load flow path 13c of the use heat exchanger 13 included in the heat-load circuit 90. The water heated by exchanging heat with the two refrigerants, namely, the first refrigerant and the second refrigerant, in the way described above is sent to the heat-load heat exchanger 91 in the heat-load circuit 90 to process the heating load. The second refrigerant having passed through the use heat exchanger 13 passes through the second heat-source expansion valve 24, is decompressed in the first heat-source expansion valve 26, and then flows into the second outdoor heat exchanger 23. The second refrigerant sent to the second outdoor heat exchanger 23 is evaporated by heat exchange with the outdoor air supplied by the outdoor fan 9. The second refrigerant evaporated in the second outdoor heat exchanger 23 is sucked into the second compressor 21 via the switching valve 22b of the second switching mechanism 22.

(4-3) Features of Fourth Embodiment

Like the refrigeration cycle apparatus 1 according to the first embodiment, the refrigeration cycle apparatus 1c according to the present embodiment can reduce global environmental deterioration, and can easily secure heating operation capacity. Further, in addition to the single-stage refrigeration cycle and the two-stage refrigeration cycle, the parallel refrigeration cycles can be performed in both of the cooling operation and the heating operation. Thus, the capacity can be secured according to the situation.

While embodiments of the present disclosure have been described, it will be understood that various changes may be made in form and details without departing from the spirit and scope of the present disclosure as defined in the claims.

REFERENCE SIGNS LIST

1, 1a, 1b, 1c: refrigeration cycle apparatus
12: first switching mechanism
12x: first switching mechanism
13: use heat exchanger
13a: first use flow path
13b: second use flow path
13c: heat-load flow path
14: third use expansion valve
15: first use expansion valve
16: second use expansion valve
17: heat-source heat exchanger (cascade heat exchanger)
17a: first heat-source flow path (first cascade flow path)
17b: second heat-source flow path (second cascade flow path)
18: first outdoor heat exchanger
20: second refrigerant circuit
21: second compressor
23: second outdoor heat exchanger
24: second heat-source expansion valve
25: third heat-source expansion valve
26: first heat-source expansion valve
90: heat-load circuit
91: heat-load heat exchanger
92: pump

CITATION LIST

PATENT LITERATURE

PTL 1: Japanese Unexamined Patent Application Publication No. 2015-197254

Claims

A refrigeration cycle apparatus (1), wherein the refrigeration cycle apparatus
performs a heating operation by performing a two-stage refrigeration cycle, the two-stage refrigeration cycle including a use-side refrigeration cycle using a first refrigerant having 1 MPa or less at 30°C and a heat-source-side refrigeration cycle using a second refrigerant having 1.5 MPa or more at 30°C, and

performs a cooling operation by performing a single-stage refrigeration cycle using the first refrigerant.
The refrigeration cycle apparatus according to claim 1, comprising
a cascade heat exchanger (17) including a first cascade flow path (17a) through which the first refrigerant flows during the heating operation and a second cascade flow path (17b) that is independent of the first cascade flow path and through which the second refrigerant flows during the heating operation, the cascade heat exchanger (17) being configured to exchange heat between the first refrigerant and the second refrigerant.
The refrigeration cycle apparatus according to claim 2, further comprising
a use heat exchanger (13) in which the first refrigerant radiates heat during the heating operation, wherein

during the heating operation, the first refrigerant evaporates when passing through the first cascade flow path (17a), and the second refrigerant radiates heat when passing through the second cascade flow path (17b).
The refrigeration cycle apparatus according to any one of claims 1 to 3, comprising:
a use heat exchanger (13) in which the first refrigerant evaporates during the cooling operation; and

a first outdoor heat exchanger (18) in which the first refrigerant radiates heat during the cooling operation.
The refrigeration cycle apparatus according to any one of claims 1 to 4, comprising
a second outdoor heat exchanger (23) in which the second refrigerant evaporates during the heating operation.
A refrigeration cycle apparatus (1a, 1b, 1c), wherein the refrigeration cycle apparatus
performs a heating operation by performing a two-stage refrigeration cycle, the two-stage refrigeration cycle including a use-side refrigeration cycle using a first refrigerant having 1 MPa or less at 30°C and a heat-source-side refrigeration cycle using a second refrigerant having 1.5 MPa or more at 30°C, and

performs a cooling operation by performing a two-stage refrigeration cycle, the two-stage refrigeration cycle including a use-side refrigeration cycle using the second refrigerant and a heat-source-side refrigeration cycle using the first refrigerant.
The refrigeration cycle apparatus according to claim 6, comprising
a cascade heat exchanger (17) including a first cascade flow path (17a) through which the first refrigerant flows and a second cascade flow path (17b) that is independent of the first cascade flow path and through which the second refrigerant flows, the cascade heat exchanger (17) being configured to exchange heat between the first refrigerant and the second refrigerant.
The refrigeration cycle apparatus according to claim 7, further comprising
a use heat exchanger (13) including a first use flow path (13a) through which the first refrigerant flows and a second use flow path (13b) that is independent of the first use flow path and through which the second refrigerant flows.
The refrigeration cycle apparatus according to claim 8, wherein
during the heating operation, the first refrigerant evaporates when passing through the first cascade flow path (17a), the second refrigerant radiates heat when passing through the second cascade flow path (17b), and the first refrigerant radiates heat when passing through the first use flow path (13a).
The refrigeration cycle apparatus according to claim 8 or 9, wherein
during the cooling operation, the first refrigerant evaporates when passing through the first cascade flow path (17a), the second refrigerant radiates heat when passing through the second cascade flow path (17b), and the second refrigerant evaporates when passing through the second use flow path (13b).
The refrigeration cycle apparatus according to any one of claims 8 to 10, wherein
during the cooling operation, the first refrigerant evaporates when passing through the first use flow path (13a), and the second refrigerant evaporates when passing through the second use flow path (13b).
The refrigeration cycle apparatus according to any one of claims 8 to 11, wherein
during the heating operation, the first refrigerant radiates heat when passing through the first use flow path (13a), and the second refrigerant radiates heat when passing through the second use flow path (13b).
The refrigeration cycle apparatus according to any one of claims 6 to 12, comprising
a first outdoor heat exchanger (18) in which the first refrigerant radiates heat during the cooling operation.
The refrigeration cycle apparatus according to any one of claims 6 to 13, comprising
a second outdoor heat exchanger (23) in which the second refrigerant evaporates during the heating operation.
The refrigeration cycle apparatus according to any one of claims 1 to 14, wherein
the first refrigerant includes at least one of R1234yf or R1234ze.
The refrigeration cycle apparatus according to any one of claims 1 to 15, wherein
the second refrigerant includes carbon dioxide.