Refrigeration cycle device

Abstract

A first switching mechanism (15) is switchable between a first state in which a discharge side of a first compressor (11) is connected to a first water heat exchanger (14) or a refrigerant heat exchanger (30) and a second state in which the discharge side of the first compressor (11) is connected to a heat source heat exchanger (12). In a defrosting operation for defrosting the heat source heat exchanger (12), a control unit (100) drives the first refrigerant circuit (10) with the first switching mechanism (15) set in the second state.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a refrigeration cycle apparatus.BACKGROUND ART

[0002] Patent Document 1 discloses a refrigeration cycle apparatus including a high-stage refrigerant circuit and a low-stage refrigerant circuit. The high-stage refrigerant circuit includes a high-stage compressor, a six-way valve, a high-stage refrigerant heat exchanger, a high-stage expansion valve, a cascade heat exchanger, and a first heating medium heat exchanger, and circulates a high-stage refrigerant. The low-stage refrigerant circuit includes a low-stage compressor, a four-way valve, a cascade heat exchanger, a low-stage expansion valve, and a second heating medium heat exchanger, and circulates a low-stage refrigerant.CITATION LISTPATENT DOCUMENT

[0003] Patent Document 1: WO2021 / 106084SUMMARY OF THE INVENTIONTECHNICAL PROBLEM

[0004] To eliminate deterioration of performance of a heat source heat exchanger due to frost formed thereon and other purposes, it is desirable that a refrigeration cycle apparatus such as one mentioned above performs a defrosting operation for defrosting the heat source heat exchanger.SOLUTION TO THE PROBLEM

[0005] A first aspect of the present disclosure relates to a refrigeration cycle apparatus. This refrigeration cycle apparatus includes: a first refrigerant circuit (10) through which a first refrigerant circulates; a second refrigerant circuit (20) through which a second refrigerant circulates; a refrigerant heat exchanger (30) configured to exchange heat between the first refrigerant in the first refrigerant circuit (10) and the second refrigerant in the second refrigerant circuit (20); a water circuit (40) through which water circulates; and a control unit (100) configured to control the first refrigerant circuit (10) and the second refrigerant circuit (20), the first refrigerant circuit (10) including a first compressor (11), a heat source heat exchanger (12), a first expansion valve (13), a first water heat exchanger (14), and a first switching mechanism (15), the second refrigerant circuit (20) including a second compressor (21), a second water heat exchanger (22), and a second expansion valve (23), the first water heat exchanger (14) being configured to exchange heat between the first refrigerant in the first refrigerant circuit (10) and the water in the water circuit (40), the second water heat exchanger (22) being configured to exchange heat between the second refrigerant in the second refrigerant circuit (20) and the water in the water circuit (40), the first switching mechanism (15) being switchable between a first state in which a discharge side of the first compressor (11) is connected to the first water heat exchanger (14) or the refrigerant heat exchanger (30) and a second state in which the discharge side of the first compressor (11) is connected to the heat source heat exchanger (12), in a defrosting operation for defrosting the heat source heat exchanger (12), the control unit (100) driving the first refrigerant circuit (10) with the first switching mechanism (15) set in the second state.

[0006] According to the first aspect, in the defrosting operation, the high-temperature and high-pressure first refrigerant discharged from the first compressor (11) can be supplied to the heat source heat exchanger (12) by driving the first refrigerant circuit (10) with the first switching mechanism (15) set in the second state. Thus, the heat source heat exchanger (12) can be defrosted.

[0007] A second aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the first aspect. In the second aspect, the first refrigerant circuit (10) includes: a gas flow path (61) connected to a gas side of the first water heat exchanger (14); a liquid flow path (62) connected to a liquid side of the first water heat exchanger (14); a connection flow path (63) connecting the gas flow path (61) and the liquid flow path (62); and a second switching mechanism (60), and the second switching mechanism (60) is switchable between a third state in which the first refrigerant flows through the first water heat exchanger (14) without flowing through the connection flow path (63) and a fourth state in which the first refrigerant flows through the connection flow path (63) without flowing through the first water heat exchanger (14).

[0008] According to the second aspect, it is possible to switch between the operation in which the first refrigerant passes through the first water heat exchanger (14) and the operation in which the first refrigerant is kept from passing through the first water heat exchanger (14). This can improve the degree of freedom in the operation of the refrigeration cycle apparatus (1).

[0009] A third aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the second aspect. In the third aspect, in the defrosting operation, the control unit (100) drives the first refrigerant circuit (10) such that the heat source heat exchanger (12) functions as a radiator and that the refrigerant heat exchanger (30) in the first refrigerant circuit (10) functions as a heat absorber.

[0010] According to the third aspect, in the defrosting operation, heat obtained in the refrigerant heat exchanger (30) can be used to defrost the heat source heat exchanger (12). This can facilitate defrosting of the heat source heat exchanger (12).

[0011] A fourth aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the third aspect. In the fourth aspect, the defrosting operation includes a first operation, and in the first operation, the control unit (100) drives the first refrigerant circuit (10) with the second switching mechanism (60) set in the fourth state.

[0012] According to the fourth aspect, in the first operation, the first refrigerant can be prevented from flowing through the first water heat exchanger (14). This configuration can reduce a decrease in the temperature of water in the water circuit (40) as compared with a case in which the first refrigerant flows through the first water heat exchanger (14) and the first water heat exchanger (14) functions as a heat absorber.

[0013] A fifth aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the fourth aspect. In the fifth aspect, the defrosting operation includes the first operation and a second operation that is performed after the first operation ends, and in the second operation, the control unit (100) drives the first refrigerant circuit (10) with the second switching mechanism (60) switched from the fourth state to the third state.

[0014] According to the fifth aspect, in the second operation, the first water heat exchanger (14) can function as a heat absorber. Thus, in the second operation, heat obtained in the first water heat exchanger (14) can be used to defrost the heat source heat exchanger (12). This can facilitate defrosting of the heat source heat exchanger (12) as compared with a case in which only the first operation is performed in the defrosting operation.

[0015] A sixth aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the fifth aspect. In the sixth aspect, the water circuit (40) has a pump (41), and the control unit (100) drives the pump (41) in the second operation.

[0016] According to the sixth aspect, driving the pump (41) in the second operation can prevent water in the water circuit (40) from stagnating in the first water heat exchanger (14). This can reduce a decrease in the water temperature in the water circuit (40) in the first water heat exchanger (14).

[0017] A seventh aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the sixth aspect. In the seventh aspect, the control unit (100) drives the pump (41) in the first operation.

[0018] According to the seventh aspect, in the first operation that is performed before the second operation, driving the pump (41) can prevent water in the water circuit (40) from stagnating in the first water heat exchanger (14) before the start of the second operation. This can make it easier to reduce a decrease in the water temperature in the water circuit (40) in the first water heat exchanger (14) in the second operation.

[0019] An eighth aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the fourth aspect. In the eighth aspect, the defrosting operation includes the first operation and a second operation that is performed after the first operation ends, and in the second operation, the control unit (100) drives the first refrigerant circuit (10) with the second switching mechanism (60) set in the fourth state, and drives the second refrigerant circuit (20) such that the second refrigerant flows through the second compressor (21), the second water heat exchanger (22), the second expansion valve (23), and the refrigerant heat exchanger (30) in sequence, and an opening degree of the second expansion valve (23) in the second operation is greater than an opening degree of the second expansion valve (23) in a heating operation in which the second water heat exchanger (22) functions as a radiator and the refrigerant heat exchanger (30) in the second refrigerant circuit (20) functions as a heat absorber.

[0020] According to the eighth aspect, the second refrigerant circuit (20) is driven in a state in which the opening degree of the second expansion valve (23) in the second operation is greater than the opening degree of the second expansion valve (23) in the heating operation, thereby enabling, in the second operation, heat dissipation of the high-temperature and high-pressure second refrigerant discharged from the second compressor (21) to the first refrigerant in the first refrigerant circuit (10) in the refrigerant heat exchanger (30). Thus, in the second operation, heat obtained in the refrigerant heat exchanger (30) (heat of the second refrigerant discharged from the second compressor (21)) can be used to defrost the heat source heat exchanger (12). This can facilitate defrosting of the heat source heat exchanger (12).

[0021] A ninth aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the eighth aspect. In the ninth aspect, the control unit (100) drives the second refrigerant circuit (20) such that the second compressor (21) is intermittently driven in the second operation.

[0022] According to the ninth aspect, the second compressor (21) is intermittently driven in the second operation, thereby making it possible to keep the temperature of the second refrigerant discharged from the second compressor (21) from rising too much. Accordingly, high-temperature anomalies in the second refrigerant circuit (20) (anomalies in which the temperature of the second refrigerant exceeds allowable temperatures) can be reduced.

[0023] A tenth aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the eighth or ninth aspect. In the tenth aspect, the water circuit (40) has a pump (41), and the control unit (100) stops the pump (41) in the second operation.

[0024] According to the tenth aspect, the pump (41) is stopped in the second operation, thereby preventing water in the water circuit (40) from flowing through the first water heat exchanger (14) and the second water heat exchanger (22). Accordingly, it is possible to reduce heat dissipation in the second water heat exchanger (22) from the second refrigerant in the second refrigerant circuit (20) to water in the water circuit (40) in the second operation; therefore, heat of the second refrigerant discharged from the second compressor (21) can be effectively used to defrost the heat source heat exchanger (12).

[0025] An eleventh aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the fourth aspect. In the eleventh aspect, the second refrigerant circuit (20) includes a third switching mechanism (24), the third switching mechanism (24) is switchable between a fifth state in which a discharge side of the second compressor (21) is connected to the second water heat exchanger (22) and a sixth state in which the discharge side of the second compressor (21) is connected to the refrigerant heat exchanger (30), and in the first operation, the control unit (100) drives the second refrigerant circuit (20) with the third switching mechanism (24) set in the sixth state.

[0026] According to the eleventh aspect, it is possible, in the first operation, to cause the high-temperature and high-pressure second refrigerant discharged from the second compressor (21) to dissipate heat to the first refrigerant in the first refrigerant circuit (10) in the refrigerant heat exchanger (30). Thus, in the second operation, heat obtained in the refrigerant heat exchanger (30) (heat of the second refrigerant discharged from the second compressor (21)) can be used to defrost the heat source heat exchanger (12). This can facilitate defrosting of the heat source heat exchanger (12).

[0027] A twelfth aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the second aspect. In the twelfth aspect, the second switching mechanism (60) includes: a first valve (64) provided in the connection flow path (63); and a second valve (65) provided between a connection point between the connection flow path (63) and the liquid flow path (62) and the liquid side of the first water heat exchanger (14) in the liquid flow path (62), and the second valve (65) is an electric valve.

[0028] According to the twelfth aspect, by using an electric valve as the second valve (65) of the second switching mechanism (60), the amount of the first refrigerant flowing through the first water heat exchanger (14) can be controlled. This can improve the degree of freedom in control over the first water heat exchanger (14).

[0029] A thirteenth aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the twelfth aspect. In the thirteenth aspect, in the defrosting operation, the control unit (100) drives the first refrigerant circuit (10) such that the first expansion valve (13) is set in an open state, that the first valve (64) is set in a closed state, and that the first refrigerant flows through the first compressor (11), the heat source heat exchanger (12), the first expansion valve (13), the refrigerant heat exchanger (30), the second valve (65), and the first water heat exchanger (14) in sequence, and an opening degree of the first expansion valve (13) in the defrosting operation is greater than an opening degree of the second valve (65) in the defrosting operation.

[0030] According to the thirteenth aspect, in the defrosting operation, the heat source heat exchanger (12) and the refrigerant heat exchanger (30) in the first refrigerant circuit (10) can function as radiators, and the first water heat exchanger (14) can function as a heat absorber. It is therefore possible to increase the degree of subcooling of the first refrigerant in the refrigerant heat exchanger (30), thereby improving the coefficient of performance (COP) in the defrosting operation.

[0031] A fourteenth aspect of the present disclosure is an embodiment of the refrigeration cycle apparatus of the thirteenth aspect. In the fourteenth aspect, the water circuit (40) has a pump (41), and in the defrosting operation, the control unit (100) drives the second refrigerant circuit (20) such that the second refrigerant flows through the second compressor (21), the second water heat exchanger (22), the second expansion valve (23), and the refrigerant heat exchanger (30) in sequence, and drives the pump (41).

[0032] According to the fourteenth aspect, in the defrosting operation, the second refrigerant circuit (20) can be driven such that the second water heat exchanger (22) functions as a radiator and that the refrigerant heat exchanger (30) in the second refrigerant circuit (20) functions as a heat absorber. Accordingly, the water in the water circuit (40) can be heated in the second water heat exchanger (22), which facilitates subcooling of the first refrigerant in the refrigerant heat exchanger (30). Further, driving the pump (41) in the defrosting operation can prevent water in the water circuit (40) from stagnating in the first water heat exchanger (14) and the second water heat exchanger (22) and allows the water heated in the second water heat exchanger (22) to circulate through the water circuit (40). This can reduce a decrease in the water temperature in the water circuit (40).BRIEF DESCRIPTION OF THE DRAWINGS

[0033] [FIG. 1] FIG. 1 is a piping system diagram illustrating an example configuration of a refrigeration cycle apparatus according to a first embodiment. [FIG. 2] FIG. 2 is a block diagram illustrating an example connection between components of the refrigeration cycle apparatus according to the first embodiment. [FIG. 3] FIG. 3 is a piping system diagram illustrating an example flow of refrigerant in a heating operation. [FIG. 4] FIG. 4 is a piping system diagram illustrating an example flow of refrigerant in a first operation included in a defrosting operation of the first embodiment. [FIG. 5] FIG. 5 is a piping system diagram illustrating an example flow of refrigerant in a second operation included in the defrosting operation of the first embodiment. [FIG. 6] FIG. 6 is a flowchart showing an example operation switching in the defrosting operation. [FIG. 7] FIG. 7 is a piping system diagram illustrating an example flow of refrigerant in a second operation included in a defrosting operation of a second embodiment. [FIG. 8] FIG. 8 is a piping system diagram illustrating an example configuration of a refrigeration cycle apparatus according to a third embodiment and an example flow of refrigerant in a defrosting operation. [FIG. 9] FIG. 9 is a piping system diagram illustrating an example configuration of a refrigeration cycle apparatus according to a fourth embodiment and an example flow of refrigerant in a defrosting operation. DESCRIPTION OF EMBODIMENTS

[0034] Embodiments will be described in detail below with reference to the drawings. The same reference characters denote the same or equivalent components in the drawings, and the description thereof will not be repeated. The present disclosure is not limited to the embodiments shown below, and various changes can be made within the scope without departing from the technical concept of the present disclosure. Since each of the drawings is intended to illustrate the present disclosure conceptually, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for the sake of ease of understanding.(First Embodiment)

[0035] FIG. 1 illustrates an example configuration of a refrigeration cycle apparatus (1) according to a first embodiment. In this example, the refrigeration cycle apparatus (1) constitutes a hot water supply apparatus that generates hot water. The hot water generated by the hot water supply apparatus is stored in a hot water storage tank (not shown) and supplied to a predetermined target. The refrigeration cycle apparatus (1) includes an outdoor unit (OU) installed outdoors and an indoor unit (IU) installed indoors.

[0036] As illustrated in FIG. 1, the refrigeration cycle apparatus (1) includes a first refrigerant circuit (10), a second refrigerant circuit (20), a refrigerant heat exchanger (30), and a water circuit (40). The first refrigerant circuit (10) is filled with a first refrigerant, and the first refrigerant circulates through the first refrigerant circuit (10). The second refrigerant circuit (20) is filled with a second refrigerant different from the first refrigerant, and the second refrigerant circulates through the second refrigerant circuit (20). In this example, the first refrigerant is carbon dioxide, and the second refrigerant is propane (R290).

[0037] The refrigeration cycle apparatus (1) performs a binary (two-stage) refrigeration cycle. Specifically, the low-stage first refrigerant circuit (10) and the high-stage second refrigerant circuit (20) are connected through the refrigerant heat exchanger (30). In this example, the refrigerant heat exchanger (30) includes a first flow path (30a) through which the first refrigerant in the first refrigerant circuit (10) flows and a second flow path (30b) through which the second refrigerant in the second refrigerant circuit (20) flows. In other words, the first refrigerant circuit (10) includes the first flow path (30a) of the refrigerant heat exchanger (30), and the second refrigerant circuit (20) includes the second flow path (30b) of the refrigerant heat exchanger (30). The refrigerant heat exchanger (30) will be described in detail later.[First Refrigerant Circuit]

[0038] The first refrigerant circuit (10) performs a refrigeration cycle using the first refrigerant. In this example, the first refrigerant circuit (10) includes a first compressor (11), a heat source heat exchanger (12), a first expansion valve (13), a first water heat exchanger (14), a first four-way switching valve (15), and a receiver (16). The first refrigerant circuit (10) includes a bridge circuit (50), a gas flow path (61), a liquid flow path (62), a connection flow path (63), and a bypass mechanism (60). Near the heat source heat exchanger (12), an outdoor fan (17) is provided which transfers outdoor air (an example of heat source air) to the heat source heat exchanger (12) such that the outdoor air passes through the heat source heat exchanger (12). The outdoor fan (17) is an example of a heat source fan that transfers the heat source air to the heat source heat exchanger (12).

[0039] The first compressor (11), the heat source heat exchanger (12), the first expansion valve (13), the first four-way switching valve (15), the receiver (16), and the bridge circuit (50) are provided in the outdoor unit (OU). The first water heat exchanger (14) and the bypass mechanism (60) are provided in the indoor unit (IU).

[0040] The first compressor (11) compresses a refrigerant sucked therein and discharges the compressed refrigerant. For example, the first compressor (11) is a high-pressure dome compressor.

[0041] The heat source heat exchanger (12) functions as a radiator or an evaporator (a heat absorber). In this example, the heat source heat exchanger (12) is configured as an air heat exchanger that exchanges heat between "outdoor air transferred to the heat source heat exchanger (12) by the outdoor fan (17)" and the "first refrigerant flowing through the heat source heat exchanger (12)."

[0042] The first expansion valve (13) is an example of a decompression mechanism configured to decompress the first refrigerant. In this example, the first expansion valve (13) is configured as an electric valve having an adjustable opening degree.

[0043] The first water heat exchanger (14) exchanges heat between the first refrigerant in the first refrigerant circuit (10) and water in the water circuit (40). In this example, the first water heat exchanger (14) is configured as a plate heat exchanger. Specifically, the first water heat exchanger (14) has a first flow path (14a) through which the first refrigerant in the first refrigerant circuit (10) flows and a second flow path (14b) through which water in the water circuit (40) flows, and exchanges heat between the first refrigerant in the first flow path (14a) and the water in the second flow path (14b). The first water heat exchanger (14) functions as a radiator or an evaporator.

[0044] The first four-way switching valve (15) has a first port (P1), a second port (P2), a third port (P3), and a fourth port (P4). The first four-way switching valve (15) is switchable between a first state, in which the first port (P1) and the second port (P2) communicate with each other and the third port (P3) and the fourth port (P4) communicate with each other, and a second state, in which the first port (P1) and the third port (P3) communicate with each other and the second port (P2) and the fourth port (P4) communicate with each other.

[0045] In this example, in the first four-way switching valve (15), the first port (P1) is connected to the discharge side of the first compressor (11), and the second port (P2) is connected to the gas side of the first water heat exchanger (14) via the gas flow path (61). The third port (P3) is connected to the gas side of the heat source heat exchanger (12), and the fourth port (P4) is connected to the suction side of the first compressor (11). The first flow path (30a) of the refrigerant heat exchanger (30) is connected to the liquid side of the first water heat exchanger (14) via the liquid flow path (62).

[0046] The first four-way switching valve (15) is an example of a first switching mechanism. The first switching mechanism is switchable between the first state, in which the discharge side of the first compressor (11) is connected to the first water heat exchanger (14) or the refrigerant heat exchanger (30), and the second state, in which the discharge side of the first compressor (11) is connected to the heat source heat exchanger (12).

[0047] The receiver (16) stores the first refrigerant and separates the first refrigerant into a gas refrigerant and a liquid refrigerant. For example, the receiver (16) is constituted by a pressure vessel.

[0048] The bridge circuit (50) includes a first pipe (51), a second pipe (52), a third pipe (53), a fourth pipe (54), and four check valves (CV). The four check valves (CV) are arranged in one-to-one correspondence with the four pipes (the first to fourth pipes (51 to 54)). Each of the check valves (CV) allows the refrigerant to flow in the direction indicated by the arrow shown in FIG. 1, and prevents the refrigerant from flowing in the opposite direction.

[0049] The outflow end of the first pipe (51) and the outflow end of the second pipe (52) are connected to the inlet side of the receiver (16). The inflow end of the third pipe (53) and the inflow end of the fourth pipe (54) are connected to the outlet side of the receiver (16). The inflow end of the first pipe (51) and the outflow end of the third pipe (53) are connected to the liquid side of the heat source heat exchanger (12). The inflow end of the second pipe (52) and the outflow end of the fourth pipe (54) are connected to the first flow path (30a) of the refrigerant heat exchanger (30).

[0050] In this example, the first expansion valve (13) is disposed on the outlet side of the receiver (16). The first refrigerant that flows out of the receiver (16) flows through the first expansion valve (13), and then flows into the heat source heat exchanger (12) or the refrigerant heat exchanger (30) through the bridge circuit (50). In other words, the first expansion valve (13) is disposed between the receiver (16) and each of the heat source heat exchanger (12) and the refrigerant heat exchanger (30). Specifically, in the heating operation to be described later, the first expansion valve (13) is disposed between the receiver (16) and the heat source heat exchanger (12); in a defrosting operation to be described later, the first expansion valve (13) is disposed between the receiver (16) and the refrigerant heat exchanger (30).

[0051] The gas flow path (61) is connected to the gas side of the first water heat exchanger (14). In this example, one end of the gas flow path (61) is connected to the gas side of the first water heat exchanger (14). The other end of the gas flow path (61) is connected to the second port (P2) of the first four-way switching valve (15).

[0052] The liquid flow path (62) is connected to the liquid side of the first water heat exchanger (14). In this example, one end of the liquid flow path (62) is connected to the liquid side of the first water heat exchanger (14). The other end of the liquid flow path (62) is connected to the first flow path (30a) of the refrigerant heat exchanger (30).

[0053] The connection flow path (63) connects the gas flow path (61) and the liquid flow path (62). In this example, one end of the connection flow path (63) is connected to the gas flow path (61) that connects the gas side of the first water heat exchanger (14) and the second port (P2) of the first four-way switching valve (15). The other end of the connection flow path (63) is connected to the liquid flow path (62) that connects the liquid side of the first water heat exchanger (14) and the first flow path (30a) of the refrigerant heat exchanger (30).

[0054] The bypass mechanism (60) is switchable between a third state, in which the first refrigerant flows through the first water heat exchanger (14) without flowing through the connection flow path (63), and a fourth state, in which the first refrigerant flows through the connection flow path (63) without flowing through the first water heat exchanger (14). The bypass mechanism (60) is an example of a second switching mechanism.

[0055] In this example, the bypass mechanism (60) includes a first valve (64) and a second valve (65). The first valve (64) is provided in the connection flow path (63). The second valve (65) is provided between the "connection point between the liquid flow path (62) and the connection flow path (63)" and the "liquid side of the first water heat exchanger (14)" in the liquid flow path (62). In this example, the first valve (64) and the second valve (65) are each configured as an on-off valve (e.g., an electromagnetic valve) that is switchable between an open state and a closed state.[Second Refrigerant Circuit]

[0056] The second refrigerant circuit (20) performs a refrigeration cycle using the second refrigerant. In this example, the second refrigerant circuit (20) includes a second compressor (21), a second water heat exchanger (22), and a second expansion valve (23). The second refrigerant circuit (20) is provided in the indoor unit (IU).

[0057] In this example, propane, which is a highly flammable refrigerant, is used as the refrigerant which fills the second refrigerant circuit (20). A highly flammable refrigerant may ignite. For example, according to the standard IEC 60335-2-40 Ed.7, when the second refrigerant circuit (20) is filled with propane as a refrigerant and installed indoors, a restriction is imposed on the floor area of a device installation room (a room where the second refrigerant circuit (20) is installed) and a safety measure against leakage needs to be taken if the refrigerant amount exceeds 152 g. In this embodiment, the second refrigerant circuit (20) is installed in the indoor unit (IU). Thus, the amount of the refrigerant which fills the second refrigerant circuit (20) is restricted. For this reason, the amount of the refrigerant which fills the second refrigerant circuit (20) is smaller than the amount of the refrigerant which fills the first refrigerant circuit (10). For example, the amount of the refrigerant which fills the first refrigerant circuit (10) is 15 times or more and 25 times or less the amount of the refrigerant which fills the second refrigerant circuit (20). For example, if the amount of the refrigerant which fills the second refrigerant circuit (20) is 152 g or less, the amount of refrigerant which fills the first refrigerant circuit (10) is 2500 g or more and 3500 g or less.

[0058] The second compressor (21) compresses the refrigerant sucked therein and discharges the compressed refrigerant. For example, the second compressor (21) is a high-pressure dome compressor.

[0059] The second water heat exchanger (22) exchanges heat between the second refrigerant in the second refrigerant circuit (20) and water in the water circuit (40). In this example, the second water heat exchanger (22) is configured as a plate heat exchanger. Specifically, the second water heat exchanger (22) has a first flow path (22a) through which the second refrigerant in the second refrigerant circuit (20) flows and a second flow path (22b) through which water in the water circuit (40) flows, and exchanges heat between the second refrigerant in the first flow path (22a) and the water in the second flow path (22b). The second water heat exchanger (22) functions as a radiator or an evaporator.

[0060] The second expansion valve (23) is an example of a decompression mechanism configured to decompress the second refrigerant. In this example, the second expansion valve (23) is configured as an electric valve having an adjustable opening degree.

[0061] In this example, the discharge side of the second compressor (21) is connected to the first flow path (22a) of the second water heat exchanger (22), and the suction side of the second compressor (21) is connected to the second flow path (30b) of the refrigerant heat exchanger (30). The first flow path (22a) of the second water heat exchanger (22) is connected to the second flow path (30b) of the refrigerant heat exchanger (30) via the second expansion valve (23).[Refrigerant Heat Exchanger]

[0062] The refrigerant heat exchanger (30) exchanges heat between the first refrigerant in the first refrigerant circuit (10) and the second refrigerant in the second refrigerant circuit (20). In this example, the refrigerant heat exchanger (30) is configured as a plate heat exchanger. Specifically, the refrigerant heat exchanger (30) has the first flow path (30a) through which the first refrigerant in the first refrigerant circuit (10) flows and the second flow path (30b) through which the second refrigerant in the second refrigerant circuit (20) flows, and exchanges heat between the first refrigerant in the first flow path (30a) and the second refrigerant in the second flow path (30b).

[0063] The refrigerant heat exchanger (30) functions as a radiator or an evaporator. Specifically, when heat is dissipated from the first refrigerant to the second refrigerant in the refrigerant heat exchanger (30), the refrigerant heat exchanger (30) in the first refrigerant circuit (10) functions as a "radiator" and the refrigerant heat exchanger (30) in the second refrigerant circuit (20) functions as an "evaporator." On the other hand, when heat is dissipated from the second refrigerant to the first refrigerant in the refrigerant heat exchanger (30), the refrigerant heat exchanger (30) in the first refrigerant circuit (10) functions as an "evaporator" and the refrigerant heat exchanger (30) in the second refrigerant circuit (20) functions as a "radiator."[Water Circuit]

[0064] Water to be supplied to the predetermined target circulates in the water circuit (40). In this example, the water circuit (40) includes a pump (41) configured to circulate water. The water circuit (40) is provided with a hot water storage tank (not shown) configured to store the heated water. In the water circuit (40), the pump (41), the second flow path (22b) of the second water heat exchanger (22), the second flow path (14b) of the first water heat exchanger (14), and the hot water storage tank are connected in sequence.[Various Sensors]

[0065] The refrigeration cycle apparatus (1) is provided with various sensors (80), such as a pressure sensor and a temperature sensor. Examples of the physical quantities detected by the various sensors (80) include the physical quantities related to the first refrigerant circuit (10), the physical quantities related to the second refrigerant circuit (20), and the physical quantities related to the water circuit (40). Various types of information detected by the various sensors (80) are transmitted to a control unit (100) to be described later.

[0066] Examples of the physical quantities related to the first refrigerant circuit (10) include the pressure and temperature of the high-pressure refrigerant in the first refrigerant circuit (10), the pressure and temperature of the low-pressure refrigerant in the first refrigerant circuit (10), the degree of superheat of the first refrigerant at the outlet of the heat exchanger functioning as an evaporator in the first refrigerant circuit (10), and the temperature of outdoor air transferred to the heat source heat exchanger (12). For example, the high-pressure refrigerant in the first refrigerant circuit (10) is the first refrigerant discharged from the first compressor (11), and the low-pressure refrigerant in the first refrigerant circuit (10) is the first refrigerant to be sucked into the first compressor (11).

[0067] Examples of the physical quantities related to the second refrigerant circuit (20) include the pressure and temperature of the high-pressure refrigerant in the second refrigerant circuit (20), the pressure and temperature of the low-pressure refrigerant in the second refrigerant circuit (20), and the degree of superheat of the second refrigerant at the outlet of the heat exchanger functioning as an evaporator in the second refrigerant circuit (20). For example, the high-pressure refrigerant in the second refrigerant circuit (20) is the second refrigerant discharged from the second compressor (21), and the low-pressure refrigerant in the second refrigerant circuit (20) is the second refrigerant to be sucked into the second compressor (21).

[0068] Examples of the physical quantities related to the water circuit (40) include the temperature of water flowing into the second flow path (14b) of the first water heat exchanger (14), and the temperature of water flowing into the second flow path (22b) of the second water heat exchanger (22).

[0069] The various sensors (80) may be sensors that directly detect the above physical quantities or may be sensors that indirectly detect or estimate the above physical quantities.[Control Unit]

[0070] The refrigeration cycle apparatus (1) includes the control unit (100). The control unit (100) includes a micro controller unit (MCU), an electric circuit, and an electronic circuit. The MCU includes a central processing unit (CPU), a memory, and a communication interface. The memory stores various programs to be executed by the CPU (processor). The memory stores information and data used to control the refrigeration cycle apparatus (1) (for example, set values such as thresholds); information and data obtained by the various sensors (80) (for example, measured values); information and data input from the outside of the refrigeration cycle apparatus (1) (for example, command values); and the like. The control unit (100) may be configured as one physically isolated element or may be configured as two or more physically separated elements.

[0071] The control unit (100) controls the first refrigerant circuit (10) and the second refrigerant circuit (20). Specifically, the control unit (100) controls the components of the first refrigerant circuit (10) and the second refrigerant circuit (20) based on various types of information detected by the various sensors (80) and instructions entered by an operator for the refrigeration cycle apparatus (1), for example. For example, the operator enters an intended instruction into the control unit (100) by entering an operation corresponding to the intended instruction into an operating section (not shown), such as a remote controller. The operating section transmits a signal corresponding to the operation to the control unit (100).

[0072] In this example, the control unit (100) controls the startup and stop of the first compressor (11), the rotational speed of the first compressor (11), the opening degree of the first expansion valve (13), the switching of the first four-way switching valve (15), the startup and stop of the outdoor fan (17), the rotational speed of the outdoor fan (17), opening and closing of the first valve (64), opening and closing of the second valve (65), the startup and stop of the second compressor (21), the rotational speed of the second compressor (21), the opening degree of the second expansion valve (23), and the startup and stop of the pump (41), for example.[Heating Operation]

[0073] The heating operation performed in the refrigeration cycle apparatus (1) will be described with reference to FIG. 3. The heating operation is an operation for heating water in the water circuit (40). In the heating operation shown in FIG. 3, the first water heat exchanger (14) and the refrigerant heat exchanger (30) function as radiators, and the heat source heat exchanger (12) functions as an evaporator, in the first refrigerant circuit (10); and the second water heat exchanger (22) functions as a radiator, and the refrigerant heat exchanger (30) functions as an evaporator, in the second refrigerant circuit (20). In this heating operation, water in the water circuit (40) is heated in the first water heat exchanger (14) and the second water heat exchanger (22).

[0074] Specifically, in the heating operation, the control unit (100) sets the first four-way switching valve (15) in the first state. Thus, the discharge side of the first compressor (11) is connected to the gas flow path (61). The control unit (100) sets the first valve (64) in the closed state and the second valve (65) in the open state. Thus, the bypass mechanism (60) turns to the "third state in which the first refrigerant flows through the first water heat exchanger (14) without flowing through the connection flow path (63)." The control unit (100) sets the first compressor (11), the outdoor fan (17), the second compressor (21), and the pump (41) in a driven state, and appropriately adjusts the opening degree of the first expansion valve (13) and the opening degree of the second expansion valve (23).

[0075] In the first refrigerant circuit (10), the first refrigerant flows through the first compressor (11), the first water heat exchanger (14), the refrigerant heat exchanger (30), the receiver (16), the first expansion valve (13), and the heat source heat exchanger (12) in sequence.

[0076] Specifically, in the first refrigerant circuit (10), the first refrigerant discharged from the first compressor (11) dissipates heat to water in the water circuit (40) in the first water heat exchanger (14). The water in the water circuit (40) is therefore heated. The first refrigerant that flows out of the first water heat exchanger (14) dissipates heat to the second refrigerant in the second refrigerant circuit (20) in the refrigerant heat exchanger (30). The degree of subcooling of the first refrigerant therefore increases. The first refrigerant that flows out of the refrigerant heat exchanger (30) is decompressed in the first expansion valve (13) after passing through the receiver (16), and absorbs heat from outdoor air and evaporates in the heat source heat exchanger (12). The first refrigerant that flows out of the heat source heat exchanger (12) is sucked into the first compressor (11).

[0077] In the second refrigerant circuit (20), the second refrigerant flows through the second compressor (21), the second water heat exchanger (22), the second expansion valve (23), and the refrigerant heat exchanger (30) in sequence.

[0078] Specifically, in the second refrigerant circuit (20), the second refrigerant discharged from the second compressor (21) dissipates heat to water in the water circuit (40) in the second water heat exchanger (22). The water in the water circuit (40) is therefore heated. The second refrigerant that flows out of the second water heat exchanger (22) is decompressed in the second expansion valve (23), and absorbs heat from the first refrigerant in the first refrigerant circuit (10) and evaporates in the refrigerant heat exchanger (30). The refrigerant that flows out of the refrigerant heat exchanger (30) is sucked into the second compressor (21).

[0079] In the water circuit (40), water transferred by the pump (41) flows through the second water heat exchanger (22) and the first water heat exchanger (14) in sequence. Specifically, the water discharged from the pump (41) is heated in the second water heat exchanger (22) and the first water heat exchanger (14) and flows into the hot water storage tank. As can be seen, the water heated in the water circuit (40) is used to generate hot water in the hot water storage tank.[First Variation of Heating Operation]

[0080] In the heating operation described above, the first refrigerant may be prevented from flowing through the first water heat exchanger (14). In this case, the refrigerant heat exchanger (30) function as a radiator, and the heat source heat exchanger (12) functions as an evaporator, in the first refrigerant circuit (10); and the second water heat exchanger (22) functions as a radiator, and the refrigerant heat exchanger (30) functions as an evaporator, in the second refrigerant circuit (20). In the first variation of the heating operation, water in the water circuit (40) is heated in the second water heat exchanger (22), whereas water in the water circuit (40) is not heated in the first water heat exchanger (14).

[0081] Specifically, in the first variation of the heating operation, the control unit (100) sets the first valve (64) in the open state and the second valve (65) in the closed state. Thus, the bypass mechanism (60) turns to the "fourth state in which the first refrigerant flows through the connection flow path (63) without flowing through the first water heat exchanger (14)." The other control in the first variation of the heating operation is similar to the control in the heating operation illustrated in FIG. 3.[Second Variation of Heating Operation]

[0082] In the heating operation described above, the second refrigerant may be prevented from flowing through the second water heat exchanger (22). In this case, the first water heat exchanger (14) and the refrigerant heat exchanger (30) function as radiators, and the heat source heat exchanger (12) functions as an evaporator, in the first refrigerant circuit (10). The second refrigerant circuit (20) is stopped. In the second variation of the heating operation, water in the water circuit (40) is heated in the first water heat exchanger (14), whereas water in the water circuit (40) is not heated in the second water heat exchanger (22).

[0083] Specifically, in the second variation of the heating operation, the control unit (100) stops the second compressor (21) and does not adjust the opening degree of the second expansion valve (23). The other control in the second variation of the heating operation is similar to the control in the heating operation illustrated in FIG. 3.

[0084] In the refrigeration cycle apparatus (1), the control unit (100) may switch among the heating operation, the first variation of the heating operation, and the second variation of the heating operation, based on a target temperature of water in the water circuit (40) to be supplied to a predetermined target or a temperature of water flowing in the first water heat exchanger (14) or the second water heat exchanger (22).[Defrosting Operation]

[0085] Next, the defrosting operation performed in the refrigeration cycle apparatus (1) of the first embodiment will be described with reference to FIGS. 4 and 5. The defrosting operation is an operation for defrosting the heat source heat exchanger (12). Continuation of the heating operation may cause frost to form on the heat source heat exchanger (12) functioning as an evaporator in the first refrigerant circuit (10). The frost that forms on the heat source heat exchanger (12) reduces the performance of the heat source heat exchanger (12). Thus, it is desirable to perform the defrosting operation for defrosting the heat source heat exchanger (12).

[0086] In the defrosting operation, the control unit (100) drives the first refrigerant circuit (10) with the first four-way switching valve (15) set in the second state (the state in which the discharge side of the first compressor (11) is connected to the heat source heat exchanger (12)).

[0087] In the first embodiment, in the defrosting operation, the control unit (100) drives the first refrigerant circuit (10) such that the heat source heat exchanger (12) functions as a radiator and that the refrigerant heat exchanger (30) in the first refrigerant circuit (10) functions as an evaporator.

[0088] In the first embodiment, the defrosting operation includes a first operation and a second operation that is performed after the first operation ends. The control unit (100) determines whether or not a condition for ending the first operation and starting the second operation (a switching condition) is satisfied. When determining that the switching condition is satisfied after the start of the first operation, the control unit (100) ends the first operation and starts the second operation.

[0089] Examples of the switching condition include: the condition that the difference between the "temperature of the first refrigerant at the inlet of the first flow path (30a) of the refrigerant heat exchanger (30)" and the "temperature of the first refrigerant at the outlet of the first flow path (30a) of the refrigerant heat exchanger (30)" is a predetermined value or less; the condition that a predetermined time has elapsed since the first operation was started; and the condition that the degree of superheat of the first refrigerant at the outlet of the first flow path (30a) of the refrigerant heat exchanger (30) is a predetermined value or less. These conditions are examples of conditions regarded as indicating that the residual heat of the refrigerant heat exchanger (30) cannot be used for the defrosting operation (that no residual heat of the refrigerant heat exchanger (30) that can be used for the defrosting operation remains).

[0090] In the first operation, the control unit (100) drives the first refrigerant circuit (10) with the bypass mechanism (60) set in the fourth state (the state in which the first refrigerant flows through the connection flow path (63) without flowing through the first water heat exchanger (14)). In the first operation, the control unit (100) drives the pump (41).

[0091] In the second operation, the control unit (100) drives the first refrigerant circuit (10) with the bypass mechanism (60) switched from the fourth state to the third state (the state in which the first refrigerant flows through the first water heat exchanger (14) without flowing through the connection flow path (63)). In the second operation, the control unit (100) drives the pump (41).[First Operation of Defrosting Operation]

[0092] Next, the first operation included in the defrosting operation will be described with reference to FIG. 4. In the first operation, in the first refrigerant circuit (10), the heat source heat exchanger (12) functions as a radiator, and the refrigerant heat exchanger (30) functions as an evaporator. The second refrigerant circuit (20) is stopped.

[0093] Specifically, in the first operation, the control unit (100) sets the first four-way switching valve (15) in the second state. Thus, the discharge side of the first compressor (11) is connected to the heat source heat exchanger (12). The control unit (100) sets the first valve (64) in the open state and the second valve (65) in the closed state. Thus, the bypass mechanism (60) turns to the "fourth state in which the first refrigerant flows through the connection flow path (63) without flowing through the first water heat exchanger (14)." The control unit (100) sets the first compressor (11), the outdoor fan (17), and the pump (41) in the driven state, and the second compressor (21) in the stopped state, and appropriately adjusts the opening degree of the first expansion valve (13).

[0094] In the first refrigerant circuit (10), the first refrigerant flows through the first compressor (11), the heat source heat exchanger (12), the receiver (16), the first expansion valve (13), and the refrigerant heat exchanger (30) in sequence, and bypasses the first water heat exchanger (14).

[0095] Specifically, in the first refrigerant circuit (10), the first refrigerant discharged from the first compressor (11) dissipates heat to outdoor air in the heat source heat exchanger (12). Thus, the heat source heat exchanger (12) is heated. As a result, the heat source heat exchanger (12) is defrosted. The first refrigerant that flows out of the heat source heat exchanger (12) is decompressed in the first expansion valve (13) after passing through the receiver (16), and absorbs heat from the second refrigerant in the second refrigerant circuit (20) and evaporates in the refrigerant heat exchanger (30). In the refrigerant heat exchanger (30), the first refrigerant absorbs residual heat of the refrigerant heat exchanger (30). The first refrigerant that flows out of the refrigerant heat exchanger (30) is sucked into the first compressor (11) after bypassing the first water heat exchanger (14).

[0096] In the water circuit (40), water transferred by the pump (41) flows through the second water heat exchanger (22) and the first water heat exchanger (14) in sequence.[Second Operation of Defrosting Operation]

[0097] Next, the second operation included in the defrosting operation will be described with reference to FIG. 5. In the second operation, in the first refrigerant circuit (10), the heat source heat exchanger (12) functions as a radiator, and the refrigerant heat exchanger (30) and the first water heat exchanger (14) function as evaporators. The second refrigerant circuit (20) remains stopped.

[0098] Specifically, in the second operation, the control unit (100) sets the first valve (64) in the closed state and the second valve (65) in the open state. Thus, the bypass mechanism (60) turns to the "third state in which the first refrigerant flows through the first water heat exchanger (14) without flowing through the connection flow path (63)." The other control in the second operation is similar to the control in the first operation.

[0099] In the first refrigerant circuit (10), the first refrigerant flows through the first compressor (11), the heat source heat exchanger (12), the receiver (16), the first expansion valve (13), the refrigerant heat exchanger (30), and the first water heat exchanger (14) in sequence.

[0100] Specifically, in the first refrigerant circuit (10), the first refrigerant discharged from the first compressor (11) dissipates heat to outdoor air in the heat source heat exchanger (12). Thus, the heat source heat exchanger (12) is heated. As a result, the heat source heat exchanger (12) is defrosted. The refrigerant that flows out of the heat source heat exchanger (12) is decompressed in the first expansion valve (13) after passing through the receiver (16), and absorbs heat from the second refrigerant in the second refrigerant circuit (20) and evaporates in the refrigerant heat exchanger (30). The first refrigerant that flows out of the refrigerant heat exchanger (30) absorbs heat from water in the water circuit (40) and evaporates in the first water heat exchanger (14). The first refrigerant that flows out of the first water heat exchanger (14) is sucked into the first compressor (11).

[0101] In the water circuit (40), water transferred by the pump (41) flows through the second water heat exchanger (22) and the first water heat exchanger (14) in sequence.[Operation Switching in Defrosting Operation]

[0102] Next, operation switching in the defrosting operation will be described with reference to FIG. 6. In this example, the first operation is started when the heating operation is switched to the defrosting operation; thereafter, the first operation is switched to the second operation. Specifically, the following processes are performed when a defrosting operation start condition (a condition for starting the defrosting operation) is satisfied during the heating operation.<Step (ST11)>

[0103] The control unit (100) stops the first compressor (11) and the second compressor (21).<Step (ST12)>

[0104] Next, the control unit (100) sets the first valve (64) in the open state.<Step (ST13)>

[0105] Next, the control unit (100) sets the second valve (65) in the closed state.<Step (ST14)>

[0106] Next, the control unit (100) switches the first four-way switching valve (15) from the first state to the second state.<Step (ST15)>

[0107] Next, the control unit (100) starts the first compressor (11). Thus, the first operation is started. Subsequently, the process of Step (ST16) is performed.<Step (ST16)>

[0108] The control unit (100) determines whether or not the difference between the temperature of the first refrigerant at the inlet of the first flow path (30a) of the refrigerant heat exchanger (30) and the temperature of the first refrigerant at the outlet of the first flow path (30a) of the refrigerant heat exchanger (30) is a predetermined value or less. The process of Step (ST16) is repeatedly performed until the temperature difference between the inlet and outlet of the first flow path (30a) of the refrigerant heat exchanger (30) becomes the predetermined value or less, and when the temperature difference between the inlet and outlet of the first flow path (30a) of the refrigerant heat exchanger (30) becomes the predetermined value or less, the process of Step (ST17) is performed.<Step (ST17)>

[0109] The control unit (100) sets the second valve (65) in the open state.<Step (ST18)>

[0110] Next, the control unit (100) sets the first valve (64) in the closed state. Thus, the second operation is started. Subsequently, the process of Step (ST19) is performed.<Step (ST19)>

[0111] The control unit (100) determines whether or not a defrosting operation ending condition (a condition for ending the defrosting operation) is satisfied. The process of Step (ST19) is repeatedly performed until the defrosting operation ending condition is satisfied, and when the defrosting operation ending condition is satisfied, the defrosting operation ends, and the heating operation is restarted.[Advantages of First Embodiment]

[0112] As described above, in the refrigeration cycle apparatus (1) of the first embodiment, the first four-way switching valve (15) (first switching mechanism) is switchable between the first state, in which the discharge side of the first compressor (11) is connected to the first water heat exchanger (14) or the refrigerant heat exchanger (30), and the second state, in which the discharge side of the first compressor (11) is connected to the heat source heat exchanger (12). In the defrosting operation for defrosting the heat source heat exchanger (12), the control unit (100) drives the first refrigerant circuit (10) with the first four-way switching valve (15) set in the second state.

[0113] According to the above configuration, in the defrosting operation, the high-temperature and high-pressure first refrigerant discharged from the first compressor (11) can be supplied to the heat source heat exchanger (12) by driving the first refrigerant circuit (10) with the first switching mechanism (15) set in the second state. Thus, the heat source heat exchanger (12) can be defrosted.

[0114] In the refrigeration cycle apparatus (1) of the first embodiment, the bypass mechanism (60) (second switching mechanism) is switchable between the third state, in which the first refrigerant flows through the first water heat exchanger (14) without flowing through the connection flow path (63), and the fourth state, in which the first refrigerant flows through the connection flow path (63) without flowing through the first water heat exchanger (14).

[0115] According to the above configuration, it is possible to switch between the operation in which the first refrigerant passes through the first water heat exchanger (14) and the operation in which the first refrigerant is kept from passing through the first water heat exchanger (14). This can improve the degree of freedom in the operation of the refrigeration cycle apparatus (1). For example, an operation that prevents the first refrigerant from flowing through the first water heat exchanger (14) (first operation) can be performed before an operation that allows the first refrigerant to flow through the first water heat exchanger (14) (second operation). This can delay a decrease in the water temperature in the water circuit (40) and improve comfort.

[0116] In the refrigeration cycle apparatus (1) of the first embodiment, in the defrosting operation, the control unit (100) drives the first refrigerant circuit (10) such that the heat source heat exchanger (12) functions as a radiator and that the refrigerant heat exchanger (30) in the first refrigerant circuit (10) functions as an evaporator (heat absorber).

[0117] According to the above configuration, in the defrosting operation, heat obtained in the refrigerant heat exchanger (30) can be used to defrost the heat source heat exchanger (12). This can facilitate defrosting of the heat source heat exchanger (12).

[0118] In the refrigeration cycle apparatus (1) of the first embodiment, the defrosting operation includes the first operation. In the first operation, the control unit (100) drives the first refrigerant circuit (10) with the bypass mechanism (60) (second switching mechanism) set in the fourth state.

[0119] According to the above configuration, in the first operation, the first refrigerant can be prevented from flowing through the first water heat exchanger (14). This configuration can reduce a decrease in the temperature of water in the water circuit (40) as compared with a case in which the first refrigerant flows through the first water heat exchanger (14) and the first water heat exchanger (14) functions as an evaporator (heat absorber).

[0120] In the refrigeration cycle apparatus (1) of the first embodiment, the defrosting operation includes the first operation described above and the second operation that is performed after the first operation ends. In the second operation, the control unit (100) drives the first refrigerant circuit (10) with the bypass mechanism (60) (second switching mechanism) switched from the fourth state to the third state.

[0121] According to the above configuration, in the second operation, the first water heat exchanger (14) can function as an evaporator (heat absorber). Thus, in the second operation, heat obtained in the first water heat exchanger (14) can be used to defrost the heat source heat exchanger (12). This can facilitate defrosting of the heat source heat exchanger (12) as compared with a case in which only the first operation is performed in the defrosting operation.

[0122] In the refrigeration cycle apparatus (1) of the first embodiment, the control unit (100) drives the pump (41) in the second operation.

[0123] According to the above configuration, driving the pump (41) in the second operation can prevent water in the water circuit (40) from stagnating in the first water heat exchanger (14). This can reduce a decrease in the water temperature in the water circuit (40) in the first water heat exchanger (14).

[0124] In the refrigeration cycle apparatus (1) of the first embodiment, the control unit (100) drives the pump (41) in the first operation.

[0125] According to the above configuration, in the first operation that is performed before the second operation, driving the pump (41) can prevent water in the water circuit (40) from stagnating in the first water heat exchanger (14) before the start of the second operation. This can make it easier to reduce a decrease in the water temperature in the water circuit (40) in the first water heat exchanger (14) in the second operation.(Second Embodiment)

[0126] A refrigeration cycle apparatus (1) of a second embodiment differs from the refrigeration cycle apparatus (1) of the first embodiment in the control in the second operation included in the defrosting operation. The other configuration and processes of the refrigeration cycle apparatus (1) of the second embodiment are similar to the configuration and processes of the refrigeration cycle apparatus (1) of the first embodiment.[Second Operation of Defrosting Operation]

[0127] In the second operation included in the defrosting operation of the second embodiment, the control unit (100) drives the first refrigerant circuit (10) with the bypass mechanism (60) set in the fourth state. Further, the control unit (100) drives the second refrigerant circuit (20) such that the second refrigerant flows through the second compressor (21), the second water heat exchanger (22), the second expansion valve (23), and the refrigerant heat exchanger (30) in sequence. The opening degree of the second expansion valve (23) in the second operation is greater than the opening degree (e.g., the assumed maximum opening degree) of the second expansion valve (23) during the heating operation in which the second water heat exchanger (22) functions as a radiator and the refrigerant heat exchanger (30) in the second refrigerant circuit (20) functions as an evaporator. For example, the second expansion valve (23) in the second operation is fully open.

[0128] In the second embodiment, the control unit (100) drives the second refrigerant circuit (20) such that the second compressor (21) is intermittently driven in the second operation. In the second operation, the control unit (100) stops the pump (41).

[0129] Next, the second operation included in the defrosting operation of the second embodiment will be described with reference to FIG. 7. In the second operation of the second embodiment, in the first refrigerant circuit (10), the heat source heat exchanger (12) functions as a radiator and the refrigerant heat exchanger (30) functions as an evaporator. In the second refrigerant circuit (20), the second refrigerant dissipates heat in the refrigerant heat exchanger (30).

[0130] Specifically, in the second operation, the control unit (100) maintains the first valve (64) in the open state and maintains the second valve (65) in the closed state. Thus, the bypass mechanism (60) is maintained in the "fourth state in which the first refrigerant flows through the connection flow path (63) without flowing through the first water heat exchanger (14)." The control unit (100) maintains the first compressor (11) and the outdoor fan (17) in the driven state and continues to adjust the opening degree of the first expansion valve (13).

[0131] In the second operation, the control unit (100) sets the opening degree of the second expansion valve (23) to a predetermined opening degree, and intermittently sets the second compressor (21) in the driven state. The predetermined opening degree is set to be an opening degree (e.g., a fully-open state) that allows the second refrigerant has been discharged from the second compressor (21) and passed through the second water heat exchanger (22) and the second expansion valve (23) in sequence to dissipate heat in the refrigerant heat exchanger (30).

[0132] In the first refrigerant circuit (10), the first refrigerant flows through the first compressor (11), the heat source heat exchanger (12), the receiver (16), the first expansion valve (13), and the refrigerant heat exchanger (30) in sequence, and bypasses the first water heat exchanger (14).

[0133] Specifically, in the first refrigerant circuit (10), the first refrigerant discharged from the first compressor (11) dissipates heat to outdoor air in the heat source heat exchanger (12). Thus, the heat source heat exchanger (12) is heated. As a result, the heat source heat exchanger (12) is defrosted. The refrigerant that flows out of the heat source heat exchanger (12) is decompressed in the first expansion valve (13) after passing through the receiver (16), and absorbs heat from the second refrigerant in the second refrigerant circuit (20) and evaporates in the refrigerant heat exchanger (30). The first refrigerant that flows out of the refrigerant heat exchanger (30) is sucked into the first compressor (11) after bypassing the first water heat exchanger (14).

[0134] In the second refrigerant circuit (20), the second refrigerant flows through the second compressor (21), the second water heat exchanger (22), the second expansion valve (23) maintained at the predetermined opening degree, and the refrigerant heat exchanger (30) in sequence.

[0135] Specifically, the second refrigerant discharged from the second compressor (21) flows through the second water heat exchanger (22) and the second expansion valve (23) maintained at the predetermined opening degree (e.g., the fully-open state) in sequence, and dissipates heat to the first refrigerant in the first refrigerant circuit (10) in the refrigerant heat exchanger (30).

[0136] Since the pump (41) is stopped in the water circuit (40), water in the water circuit (40) does not flow through the first water heat exchanger (14) and the second water heat exchanger (22).[Advantages of Second Embodiment]

[0137] The refrigeration cycle apparatus (1) of the second embodiment can provide advantages that are similar to those of the refrigeration cycle apparatus (1) of the first embodiment. For example, the high-temperature and high-pressure first refrigerant discharged from the first compressor (11) can be supplied to the heat source heat exchanger (12); therefore, the heat source heat exchanger (12) can be defrosted.

[0138] In the refrigeration cycle apparatus (1) of the second embodiment, in the second operation included in the defrosting operation, the control unit (100) drives the first refrigerant circuit (10) with the bypass mechanism (60) (second switching mechanism) set in the fourth state, and drives the second refrigerant circuit (20) such that the second refrigerant flows through the second compressor (21), the second water heat exchanger (22), the second expansion valve (23), and the refrigerant heat exchanger (30) in sequence. The opening degree of the second expansion valve (23) in the second operation is greater than the opening degree of the second expansion valve (23) in the heating operation in which the second water heat exchanger (22) functions as a radiator and the refrigerant heat exchanger (30) in the second refrigerant circuit (20) functions as an evaporator (heat absorber).

[0139] According to the above configuration, the second refrigerant circuit (20) is driven in a state in which the opening degree of the second expansion valve (23) in the second operation is greater than the opening degree of the second expansion valve (23) in the heating operation, thereby enabling, in the second operation, heat dissipation of the high-temperature and high-pressure second refrigerant discharged from the second compressor (21) to the first refrigerant in the first refrigerant circuit (10) in the refrigerant heat exchanger (30). Thus, in the second operation, heat obtained in the refrigerant heat exchanger (30) (heat of the second refrigerant discharged from the second compressor (21)) can be used to defrost the heat source heat exchanger (12). This can facilitate defrosting of the heat source heat exchanger (12).

[0140] In the refrigeration cycle apparatus (1) of the second embodiment, the control unit (100) drives the second refrigerant circuit (20) such that the second compressor (21) is intermittently driven in the second operation.

[0141] According to the above configuration, the second compressor (21) is intermittently driven in the second operation, thereby making it possible to keep the temperature of the second refrigerant discharged from the second compressor (21) from rising too much. Accordingly, high-temperature anomalies in the second refrigerant circuit (20) (anomalies in which the temperature of the second refrigerant exceeds allowable temperatures) can be reduced.

[0142] In the refrigeration cycle apparatus (1) of the second embodiment, the control unit (100) stops the pump (41) in the second operation.

[0143] According to the above configuration, the pump (41) is stopped in the second operation, thereby preventing water in the water circuit (40) from flowing through the first water heat exchanger (14) and the second water heat exchanger (22). Accordingly, it is possible to reduce heat dissipation in the second water heat exchanger (22) from the second refrigerant in the second refrigerant circuit (20) to water in the water circuit (40) in the second operation; therefore, heat of the second refrigerant discharged from the second compressor (21) can be effectively used to defrost the heat source heat exchanger (12).(Third Embodiment)

[0144] FIG. 8 illustrates an example configuration of a refrigeration cycle apparatus (1) according to a third embodiment. The refrigeration cycle apparatus (1) of the third embodiment differs from the refrigeration cycle apparatus (1) of the first embodiment in the "configuration of the second refrigerant circuit (20)," the "control in the heating operation," and "control in a refrigerant collection operation." The other configuration and processes of the refrigeration cycle apparatus (1) of the third embodiment are similar to the configuration and processes of the refrigeration cycle apparatus (1) of the first embodiment.

[0145] The second refrigerant circuit (20) of the third embodiment includes a second four-way switching valve (24) in addition to the components of the second refrigerant circuit (20) of the first embodiment shown in FIG. 1.

[0146] The second four-way switching valve (24) has a first port (P1), a second port (P2), a third port (P3), and a fourth port (P4). The second four-way switching valve (24) is switchable between a fifth state, in which the first port (P1) and the second port (P2) communicate with each other and the third port (P3) and the fourth port (P4) communicate with each other, and a sixth state (state shown in FIG. 8), in which the first port (P1) and the third port (P3) communicate with each other and the second port (P2) and the fourth port (P4) communicate with each other.

[0147] In this example, in the second four-way switching valve (24), the first port (P1) is connected to the discharge side of the second compressor (21), and the second port (P2) is connected to the first flow path (22a) of the second water heat exchanger (22). The third port (P3) is connected to the second flow path (30b) of the refrigerant heat exchanger (30), and the fourth port (P4) is connected to the suction side of the second compressor (21). The first flow path (22a) of the second water heat exchanger (22) is connected to the second flow path (30b) of the refrigerant heat exchanger (30) via the second expansion valve (23).

[0148] The second four-way switching valve (24) is an example of a third switching mechanism. The third switching mechanism is switchable between the fifth state, in which the discharge side of the second compressor (21) is connected to the second water heat exchanger (22), and the sixth state, in which the discharge side of the second compressor (21) is connected to the refrigerant heat exchanger (30).[Heating Operation]

[0149] In the heating operation of the third embodiment, the control unit (100) drives the second refrigerant circuit (20) with the second four-way switching valve (24) set in the fifth state (the state in which the discharge side of the second compressor (21) is connected to the second water heat exchanger (22)).

[0150] Control over the second refrigerant circuit (20) in the heating operation of the third embodiment (control of the second compressor (21) and the second expansion valve (23)) is similar to the control over the second refrigerant circuit (20) in the heating operation of the first embodiment. The flow and change in state (heat dissipation and heat absorption) of the second refrigerant in the second refrigerant circuit (20) in the heating operation of the third embodiment are similar to the flow and change in state of the second refrigerant in the second refrigerant circuit (20) in the heating operation of the first embodiment.[Defrosting Operation]

[0151] The defrosting operation of the third embodiment includes a first operation but does not include a second operation. In the first operation included in the defrosting operation of the third embodiment, the control unit (100) drives the second refrigerant circuit (20) with the second four-way switching valve (24) set in the sixth state (the state in which the discharge side of the second compressor (21) is connected to the refrigerant heat exchanger (30)). Control of the first refrigerant circuit (10) and the water circuit (40) in the first operation included in the defrosting operation of the third embodiment is similar to the control of the first refrigerant circuit (10) and the water circuit (40) in the first operation included in the defrosting operation of the first embodiment.

[0152] Next, the first operation included in the defrosting operation of the third embodiment will be described with reference to FIG. 8. In the first operation of the third embodiment, in the first refrigerant circuit (10), the heat source heat exchanger (12) functions as a radiator and the refrigerant heat exchanger (30) functions as an evaporator. In the second refrigerant circuit (20), the refrigerant heat exchanger (30) functions as a radiator and the second water heat exchanger (22) functions as an evaporator.

[0153] Specifically, in the first operation of the third embodiment, the control unit (100) sets the second four-way switching valve (24) in the sixth state. Thus, the discharge side of the second compressor (21) is connected to the refrigerant heat exchanger (30). The control unit (100) sets the second compressor (21) in the driven state and appropriately adjusts the opening degree of the second expansion valve (23). The other control in the first operation of the third embodiment (control over the first refrigerant circuit (10) and the water circuit (40)) is similar to the control in the first operation of the first embodiment.

[0154] In the second refrigerant circuit (20), the second refrigerant flows through the second compressor (21), the refrigerant heat exchanger (30), the second expansion valve (23), and the second water heat exchanger (22) in sequence. Specifically, in the second refrigerant circuit (20), the second refrigerant discharged from the second compressor (21) dissipates heat to the first refrigerant in the first refrigerant circuit (10) in the refrigerant heat exchanger (30). The second refrigerant that flows out of the refrigerant heat exchanger (30) is decompressed in the second expansion valve (23), and absorbs heat from water in the water circuit (40) in the second water heat exchanger (22). The second refrigerant that flows out of the second water heat exchanger (22) is sucked into the second compressor (21).[Advantages of Third Embodiment]

[0155] The refrigeration cycle apparatus (1) of the third embodiment can provide advantages that are similar to those of the refrigeration cycle apparatus (1) of the first embodiment. For example, the high-temperature and high-pressure first refrigerant discharged from the first compressor (11) can be supplied to the heat source heat exchanger (12); therefore, the heat source heat exchanger (12) can be defrosted.

[0156] In the refrigeration cycle apparatus (1) of the third embodiment, the second four-way switching valve (24) (third switching mechanism) is switchable between the fifth state, in which the discharge side of the second compressor (21) is connected to the second water heat exchanger (22), and the sixth state, in which the discharge side of the second compressor (21) is connected to the refrigerant heat exchanger (30). In the first operation included in the defrosting operation, the control unit (100) drives the second refrigerant circuit (20) with the second four-way switching valve (24) (third switching mechanism) set in the sixth state.

[0157] According to the above configuration, it is possible, in the first operation, to cause the high-temperature and high-pressure second refrigerant discharged from the second compressor (21) to dissipate heat to the first refrigerant in the first refrigerant circuit (10) in the refrigerant heat exchanger (30). Thus, in the first operation, heat obtained in the refrigerant heat exchanger (30) (heat of the second refrigerant discharged from the second compressor (21)) can be used to defrost the heat source heat exchanger (12). This can facilitate defrosting of the heat source heat exchanger (12).(Fourth Embodiment)

[0158] FIG. 9 illustrates a configuration of a refrigeration cycle apparatus (1) according to a fourth embodiment. The refrigeration cycle apparatus (1) of the fourth embodiment differs from the refrigeration cycle apparatus (1) of the first embodiment in the second valve (65) of the bypass mechanism (60) and control in the defrosting operation. The other configuration and processes of the refrigeration cycle apparatus (1) of the fourth embodiment are similar to the configuration and processes of the refrigeration cycle apparatus (1) of the first embodiment.

[0159] The second valve (65) of the bypass mechanism (60) of the fourth embodiment is an electric valve having an adjustable opening degree.

[0160] In the defrosting operation of the fourth embodiment, the control unit (100) drives the first refrigerant circuit (10) such that the first expansion valve (13) and the second valve (65) are set in the open state, that the first valve (64) is set in the closed state, and that the first refrigerant flows through the first compressor (11), the heat source heat exchanger (12), the first expansion valve (13), the refrigerant heat exchanger (30), the second valve (65), and the first water heat exchanger (14) in sequence. The opening degree of the first expansion valve (13) in the defrosting operation is greater than the opening degree (e.g., the assumed maximum opening degree) of the second valve (65) in the defrosting operation. For example, the first expansion valve (13) in the defrosting operation is fully open.

[0161] In the defrosting operation of the fourth embodiment, the control unit (100) drives the second refrigerant circuit (20) such that the second refrigerant flows through the second compressor (21), the second water heat exchanger (22), the second expansion valve (23), and the refrigerant heat exchanger (30) in sequence. In the defrosting operation of the fourth embodiment, the control unit (100) drives the pump (41).

[0162] Next, the defrosting operation of the fourth embodiment will be described with reference to FIG. 9. In the defrosting operation, in the first refrigerant circuit (10), the heat source heat exchanger (12) and the refrigerant heat exchanger (30) function as radiators, and the first water heat exchanger (14) functions as an evaporator; in the second refrigerant circuit (20), the second water heat exchanger (22) functions as a radiator, and the refrigerant heat exchanger (30) functions as an evaporator.

[0163] Specifically, in the defrosting operation, the control unit (100) sets the first four-way switching valve (15) in the second state. Thus, the discharge side of the first compressor (11) is connected to the heat source heat exchanger (12). The control unit (100) sets the first valve (64) in the closed state and the second valve (65) in the open state. Thus, the bypass mechanism (60) turns to the "third state in which the first refrigerant flows through the first water heat exchanger (14) without flowing through the connection flow path (63)." The control unit (100) sets the first compressor (11), the outdoor fan (17), the second compressor (21), and the pump (41) in the driven state, and appropriately adjusts the opening degree of the second valve (65).

[0164] In the first refrigerant circuit (10), the first refrigerant flows through the first compressor (11), the heat source heat exchanger (12), the receiver (16), the first expansion valve (13), the refrigerant heat exchanger (30), the second valve (65), and the first water heat exchanger (14) in sequence.

[0165] Specifically, in the first refrigerant circuit (10), the first refrigerant discharged from the first compressor (11) dissipates heat to outdoor air in the heat source heat exchanger (12). Thus, the heat source heat exchanger (12) is heated. As a result, the heat source heat exchanger (12) is defrosted. The first refrigerant that flows out of the heat source heat exchanger (12) passes through the receiver (16) and then passes through the first expansion valve (13) maintained at a predetermined opening degree (e.g., in the fully-open state), and dissipates heat to the second refrigerant in the second refrigerant circuit (20) in the refrigerant heat exchanger (30). The degree of subcooling of the first refrigerant therefore increases. The first refrigerant that flows out of the refrigerant heat exchanger (30) is decompressed in the second valve (65) and dissipates heat and evaporates in the first water heat exchanger (14). The first refrigerant that flows out of the first water heat exchanger (14) is sucked into the first compressor (11).

[0166] In the second refrigerant circuit (20), the second refrigerant flows through the second compressor (21), the second water heat exchanger (22), the second expansion valve (23), and the refrigerant heat exchanger (30) in sequence.

[0167] Specifically, in the second refrigerant circuit (20), the second refrigerant discharged from the second compressor (21) dissipates heat to water in the water circuit (40) in the second water heat exchanger (22). The second refrigerant that flows out of the second water heat exchanger (22) is decompressed in the second expansion valve (23), and absorbs heat from the first refrigerant in the first refrigerant circuit (10) and evaporates in the refrigerant heat exchanger (30). The second refrigerant that flows out of the refrigerant heat exchanger (30) is sucked into the second compressor (21).

[0168] In the water circuit (40), water transferred by the pump (41) flows through the second water heat exchanger (22) and the first water heat exchanger (14) in sequence. Specifically, water discharged from the pump (41) receives heat from the second refrigerant in the second refrigerant circuit (20) in the second water heat exchanger (22), and the heat of the water is absorbed by the first refrigerant in the first refrigerant circuit (10) in the first water heat exchanger (14). The water then flows into the hot water storage tank.[Advantages of Fourth Embodiment]

[0169] The refrigeration cycle apparatus (1) of the fourth embodiment can provide advantages that are similar to those of the refrigeration cycle apparatus (1) of the first embodiment. For example, the high-temperature and high-pressure first refrigerant discharged from the first compressor (11) can be supplied to the heat source heat exchanger (12); therefore, the heat source heat exchanger (12) can be defrosted.

[0170] In the refrigeration cycle apparatus (1) of the fourth embodiment, the bypass mechanism (60) (second switching mechanism) includes the first valve (64) provided in the connection flow path (63) and the second valve (65) provided between the connection point between the connection flow path (63) and the liquid flow path (62) and the liquid side of the first water heat exchanger (14) in the liquid flow path (62). The second valve (65) is an electric valve.

[0171] According to the above configuration, by using an electric valve as the second valve (65) of the second switching mechanism (60), the amount of the first refrigerant flowing through the first water heat exchanger (14) can be controlled. This can improve the degree of freedom in control over the first water heat exchanger (14).

[0172] In the refrigeration cycle apparatus (1) of the fourth embodiment, the control unit (100) drives the first refrigerant circuit (10) such that, in the defrosting operation, the first expansion valve (13) is set in the open state, that the first valve (64) is set in the closed state, and that the first refrigerant flows through the first compressor (11), the heat source heat exchanger (12), the first expansion valve (13), the refrigerant heat exchanger (30), the second valve (65), and the first water heat exchanger (14) in sequence. The opening degree of the first expansion valve (13) in the defrosting operation is greater than the opening degree of the second valve (65) in the defrosting operation.

[0173] According to the above configuration, in the defrosting operation, the heat source heat exchanger (12) and the refrigerant heat exchanger (30) in the first refrigerant circuit (10) can function as radiators, and the first water heat exchanger (14) can function as an evaporator (heat absorber). It is therefore possible to increase the degree of subcooling of the first refrigerant in the refrigerant heat exchanger (30), thereby improving the coefficient of performance (COP) in the defrosting operation.

[0174] In the refrigeration cycle apparatus (1) of the fourth embodiment, in the defrosting operation, the control unit (100) drives the second refrigerant circuit (20) such that the second refrigerant flows through the second compressor (21), the second water heat exchanger (22), the second expansion valve (23), and the refrigerant heat exchanger (30) in sequence, and drives the pump (41).

[0175] According to the above configuration, in the defrosting operation, the second refrigerant circuit (20) can be driven such that the second water heat exchanger (22) functions as a radiator and that the refrigerant heat exchanger (30) in the second refrigerant circuit (20) functions as an evaporator (heat absorber). Accordingly, the water in the water circuit (40) can be heated in the second water heat exchanger (22), which facilitates subcooling of the first refrigerant in the refrigerant heat exchanger (30).

[0176] According to the above configuration, driving the pump (41) in the defrosting operation can prevent water in the water circuit (40) from stagnating in the first water heat exchanger (14) and the second water heat exchanger (22) and allows the water heated in the second water heat exchanger (22) to circulate through the water circuit (40). This can reduce a decrease in the water temperature in the water circuit (40).(Other Embodiments)

[0177] The above embodiments may be modified as follows.

[0178] The refrigeration cycle apparatus (1) does not have to include the receiver (16) and the bridge circuit (50). In this case, the first expansion valve (13) may be disposed between the heat source heat exchanger (12) and the refrigerant heat exchanger (30).

[0179] The "first four-way switching valve (15)" has been described as an example of the first switching mechanism, but the first switching mechanism is not limited thereto. For example, the first switching mechanism may include two three-way valves, or may be configured as a combination of other types of valves.

[0180] The case in which the bypass mechanism (60), which is an example of the second switching mechanism, includes the "first valve (64)" and the "second valve (65)" has been described as an example, but this case is merely an example. For example, the bypass mechanism (60) may include a three-way valve.

[0181] The "second four-way switching valve (24)" has been described as an example of the third switching mechanism, but the third switching mechanism is not limited thereto. For example, the third switching mechanism may include two three-way valves, or may be configured as a combination of other types of valves.

[0182] While the embodiments and variations thereof have been described above, it will be understood that various changes in form and details may be made without departing from the spirit and scope of the claims. The elements according to embodiments, the variations thereof, and the other embodiments may be combined and replaced with each other appropriately. In addition, the expressions of "first", "second", "third", . . . , in the specification and claims are used to distinguish the terms to which these expressions are given, and do not limit the number and order of the terms.INDUSTRIAL APPLICABILITY

[0183] As described above, the present disclosure is useful for a refrigeration cycle apparatus.DESCRIPTION OF REFERENCE CHARACTERS

[0184] 1Refrigeration Cycle Apparatus 10First Refrigerant Circuit 11First Compressor 12Heat Source Heat Exchanger 13First Expansion Valve 14First Water Heat Exchanger 15First Four-Way Switching Valve (First Switching Mechanism) 16Receiver 17Outdoor Fan 20Second Refrigerant Circuit 21Second Compressor 22Second Water Heat Exchanger 23Second Expansion Valve 24Second Four-Way Switching Valve (Third Switching Mechanism) 30Refrigerant Heat Exchanger 40Water Circuit 41Pump 50Bridge Circuit 60Bypass Mechanism (Second Switching Mechanism) 61Gas Flow Path 62Liquid Flow Path 63Connection Flow Path 64First Valve 65Second Valve 100Control Unit

Claims

1. A refrigeration cycle apparatus comprising: a first refrigerant circuit (10) through which a first refrigerant circulates; a second refrigerant circuit (20) through which a second refrigerant circulates; a refrigerant heat exchanger (30) configured to exchange heat between the first refrigerant in the first refrigerant circuit (10) and the second refrigerant in the second refrigerant circuit (20); a water circuit (40) through which water circulates; and a control unit (100) configured to control the first refrigerant circuit (10) and the second refrigerant circuit (20), the first refrigerant circuit (10) including a first compressor (11), a heat source heat exchanger (12), a first expansion valve (13), a first water heat exchanger (14), and a first switching mechanism (15), the second refrigerant circuit (20) including a second compressor (21), a second water heat exchanger (22), and a second expansion valve (23), the first water heat exchanger (14) being configured to exchange heat between the first refrigerant in the first refrigerant circuit (10) and the water in the water circuit (40), the second water heat exchanger (22) being configured to exchange heat between the second refrigerant in the second refrigerant circuit (20) and the water in the water circuit (40), the first switching mechanism (15) being switchable between a first state in which a discharge side of the first compressor (11) is connected to the first water heat exchanger (14) or the refrigerant heat exchanger (30) and a second state in which the discharge side of the first compressor (11) is connected to the heat source heat exchanger (12), in a defrosting operation for defrosting the heat source heat exchanger (12), the control unit (100) driving the first refrigerant circuit (10) with the first switching mechanism (15) set in the second state.

2. The refrigeration cycle apparatus of claim 1, wherein the first refrigerant circuit (10) includes: a gas flow path (61) connected to a gas side of the first water heat exchanger (14); a liquid flow path (62) connected to a liquid side of the first water heat exchanger (14); a connection flow path (63) connecting the gas flow path (61) and the liquid flow path (62); and a second switching mechanism (60), and the second switching mechanism (60) is switchable between a third state in which the first refrigerant flows through the first water heat exchanger (14) without flowing through the connection flow path (63) and a fourth state in which the first refrigerant flows through the connection flow path (63) without flowing through the first water heat exchanger (14).

3. The refrigeration cycle apparatus of claim 2, wherein in the defrosting operation, the control unit (100) drives the first refrigerant circuit (10) such that the heat source heat exchanger (12) functions as a radiator and that the refrigerant heat exchanger (30) in the first refrigerant circuit (10) functions as a heat absorber.

4. The refrigeration cycle apparatus of claim 3, wherein the defrosting operation includes a first operation, and in the first operation, the control unit (100) drives the first refrigerant circuit (10) with the second switching mechanism (60) set in the fourth state.

5. The refrigeration cycle apparatus of claim 4, wherein the defrosting operation includes the first operation and a second operation that is performed after the first operation ends, and in the second operation, the control unit (100) drives the first refrigerant circuit (10) with the second switching mechanism (60) switched from the fourth state to the third state.

6. The refrigeration cycle apparatus of claim 5, wherein the water circuit (40) has a pump (41), and the control unit (100) drives the pump (41) in the second operation.

7. The refrigeration cycle apparatus of claim 6, wherein the control unit (100) drives the pump (41) in the first operation.

8. The refrigeration cycle apparatus of claim 4, wherein the defrosting operation includes the first operation and a second operation that is performed after the first operation ends, and in the second operation, the control unit (100) drives the first refrigerant circuit (10) with the second switching mechanism (60) set in the fourth state, and drives the second refrigerant circuit (20) such that the second refrigerant flows through the second compressor (21), the second water heat exchanger (22), the second expansion valve (23), and the refrigerant heat exchanger (30) in sequence, and an opening degree of the second expansion valve (23) in the second operation is greater than an opening degree of the second expansion valve (23) in a heating operation in which the second water heat exchanger (22) functions as a radiator and the refrigerant heat exchanger (30) in the second refrigerant circuit (20) functions as a heat absorber.

9. The refrigeration cycle apparatus of claim 8, wherein the control unit (100) drives the second refrigerant circuit (20) such that the second compressor (21) is intermittently driven in the second operation.

10. The refrigeration cycle apparatus of claim 8 or 9, wherein the water circuit (40) has a pump (41), and the control unit (100) stops the pump (41) in the second operation.

11. The refrigeration cycle apparatus of claim 4, wherein the second refrigerant circuit (20) includes a third switching mechanism (24), the third switching mechanism (24) is switchable between a fifth state in which a discharge side of the second compressor (21) is connected to the second water heat exchanger (22) and a sixth state in which the discharge side of the second compressor (21) is connected to the refrigerant heat exchanger (30), and in the first operation, the control unit (100) drives the second refrigerant circuit (20) with the third switching mechanism (24) set in the sixth state.

12. The refrigeration cycle apparatus of claim 2, wherein the second switching mechanism (60) includes: a first valve (64) provided in the connection flow path (63); and a second valve (65) provided between a connection point between the connection flow path (63) and the liquid flow path (62) and the liquid side of the first water heat exchanger (14) in the liquid flow path (62), and the second valve (65) is an electric valve.

13. The refrigeration cycle apparatus of claim 12, wherein in the defrosting operation, the control unit (100) drives the first refrigerant circuit (10) such that the first expansion valve (13) is set in an open state, that the first valve (64) is set in a closed state, and that the first refrigerant flows through the first compressor (11), the heat source heat exchanger (12), the first expansion valve (13), the refrigerant heat exchanger (30), the second valve (65), and the first water heat exchanger (14) in sequence, and an opening degree of the first expansion valve (13) in the defrosting operation is greater than an opening degree of the second valve (65) in the defrosting operation.

14. The refrigeration cycle apparatus of claim 13, wherein the water circuit (40) has a pump (41), and in the defrosting operation, the control unit (100) drives the second refrigerant circuit (20) such that the second refrigerant flows through the second compressor (21), the second water heat exchanger (22), the second expansion valve (23), and the refrigerant heat exchanger (30) in sequence, and drives the pump (41).

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