Refrigeration cycle device

Abstract

Providing a refrigeration cycle apparatus capable of suppressing liquid compression. An air conditioner includes a first refrigerant circuit, a second refrigerant circuit, and a control device. The first refrigerant circuit includes a first compressor, a first heat exchanger functioning as a radiator during cooling operation, a first expansion valve, and a second heat exchanger functioning as a heat absorber during the cooling operation. The second refrigerant circuit c a portion between the first compressor and the first heat exchanger and a portion between the first heat exchanger and the first expansion valve. The second refrigerant circuit includes a second compressor and a first valve. The first valve is disposed on an upstream side of the second compressor. The control device controls the first compressor, the second compressor, the first expansion valve, and the first valve. The control device closes the first valve when the second compressor is to be stopped.

Description

TECHNICAL FIELD

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

[0002] PTL 1 (Japanese Unexamined Patent Application Publication No. 2005-49087) discloses a refrigeration cycle apparatus in which a refrigerant circuit is provided with a first compressor, a second compressor, and an economizer, a refrigerant is partially branched in the economizer from a main route in which the refrigerant discharged from the first compressor to a first flow path and heading toward a heat absorber via a radiator, and the refrigerant branched from the main route is compressed by the second compressor and discharged to the first flow path.

[0003] This refrigeration cycle apparatus can improve its capability and efficiency by using the economizer and the second compressor.SUMMARY OF INVENTION Technical Problem

[0004] In the refrigeration cycle apparatus according to PTL 1 (Japanese Unexamined Patent Application Publication No. 2005-49087), the refrigerant at high pressure, which has been cooled by the radiator, is supplied to the flow path between the economizer and a suction port of the second compressor when the second compressor is to be stopped. In such a refrigeration cycle apparatus as described above, when a temperature of outside air is low, a saturation temperature corresponding to the pressure becomes higher than the temperature of the outside air, possibly resulting in condensation of the refrigerant that has exchanged heat with the outside air in the flow path between the economizer and the suction port of the second compressor. If the refrigerant condenses at a large amount in the flow path between the economizer and the suction port of the second compressor, the second compressor may suck the liquid refrigerant that has condensed when the second compressor is started next time, and liquid compression may occur in the second compressor, possibly resulting in an abnormality in the second compressor.Solution to Problem

[0005] A refrigeration cycle apparatus according to a first aspect comprises a first refrigerant circuit, a second refrigerant circuit, and a control unit. The first refrigerant circuit includes a first compressor, a radiator, a first expansion valve, and a heat absorber. The second refrigerant circuit connects a portion between the first compressor and the radiator and a portion between the radiator and the first expansion valve. The second refrigerant circuit includes a second compressor and a first valve. The first valve is disposed on an upstream side of the second compressor. The control unit is configured to control the first compressor, the second compressor, the first expansion valve, and the first valve. The control unit is configured to close the first valve when the second compressor is to be stopped.

[0006] In the refrigeration cycle apparatus according to the first aspect, the first valve is disposed on the upstream side of the second compressor in the second refrigerant circuit, and the first valve is closed when the second compressor is to be stopped. Therefore, with this refrigeration cycle apparatus, even when the temperature of the outside air is relatively low, it is possible to suppress condensation of the refrigerant at a large amount on a suction side of the second compressor and to suppress liquid compression when the second compressor is started.

[0007] A refrigeration cycle apparatus according to a second aspect is the refrigeration cycle apparatus according to the first aspect in which the control unit is configured to close the first valve before the second compressor is stopped.

[0008] In the refrigeration cycle apparatus according to the second aspect, the second compressor is operated in a state where the first valve is closed and the refrigerant is prevented from flowing into an area downstream of the first valve. Therefore, in the refrigeration cycle apparatus according to the second aspect, even when the temperature of the outside air is relatively low, it is possible to suppress condensation of the refrigerant at a large amount on the suction side of the second compressor and to suppress liquid compression when the second compressor is started.

[0009] A refrigeration cycle apparatus according to a third aspect is the refrigeration cycle apparatus according to the first aspect or the second aspect and further includes a first sensor and a second sensor. The second compressor has a suction port. The first valve is an expansion valve. The first sensor is configured to measure a saturation temperature of the refrigerant that is present between the first valve and the suction port of the second compressor. The second sensor is configured to measure a temperature of the refrigerant to be sucked into the second compressor. The control unit is configured to control, when the second compressor is to be stopped, an opening degree of the first valve based on a result of the measurement by the first sensor and a result of the measurement by the second sensor.

[0010] Note herein that the recitation that the first sensor measures the saturation temperature includes a case where the first sensor measures a physical quantity correlated with the saturation temperature (physical quantity with which it is possible to know the saturation temperature of the refrigerant when a value of the physical quantity is known).

[0011] In the refrigeration cycle apparatus according to the third aspect, condensation of the refrigerant at a large amount on the suction side of the second compressor is easily suppressed, making it possible to make the refrigeration cycle apparatus highly reliable.

[0012] A refrigeration cycle apparatus according to a fourth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the third aspect, in which the control unit is configured to control, when the second compressor is to be stopped, the first valve so that the refrigerant to be sucked into the second compressor has a degree of superheating before the first valve is closed.

[0013] In the refrigeration cycle apparatus according to the fourth aspect, control of allowing the refrigerant to have a degree of superheating (to make the actual temperature of the refrigerant higher than the saturation temperature of the refrigerant) is performed before the second compressor is stopped. Therefore, condensation of the refrigerant at a large amount on the suction side of the second compressor is easily suppressed and it is possible to make the refrigeration cycle apparatus highly reliable.

[0014] A refrigeration cycle apparatus according to a fifth aspect is the refrigeration cycle apparatus according to the fourth aspect, in which the control unit is configured to control, when the second compressor is to be stopped, an opening degree of the first valve so that a degree of superheating of suction of the second compressor becomes equal to or higher than a predetermined degree of superheating.

[0015] In the refrigeration cycle apparatus according to the fifth aspect, it is possible to reduce the amount of the refrigerant that is present between the first valve and the suction port of the second compressor after the second compressor is stopped. Therefore, liquid compression is unlikely to occur in the second compressor and it is possible to make the refrigeration cycle apparatus highly reliable.

[0016] A refrigeration cycle apparatus according to a sixth aspect is the refrigeration cycle apparatus according to the third aspect in which the first sensor and the second sensor are disposed between the first valve and the second compressor. The first sensor is a pressure sensor.

[0017] In the refrigeration cycle apparatus according to the sixth aspect, it is possible to utilize the pressure sensor to accurately measure the saturation temperature of the refrigerant.

[0018] A refrigeration cycle apparatus according to a seventh aspect is the refrigeration cycle apparatus according to any one of the first aspect to the sixth aspect in which the second refrigerant circuit further includes a first economizer heat exchanger disposed between the radiator and the heat absorber. The first economizer heat exchanger is configured to exchange heat between the refrigerant that flows out of the radiator, is branched to the second refrigerant circuit at a branch portion, and is decompressed by the first valve, and the refrigerant flowing out of the radiator.

[0019] In the refrigeration cycle apparatus according to the seventh aspect, the first economizer heat exchanger improves the capability and efficiency of the refrigeration cycle apparatus.

[0020] A refrigeration cycle apparatus according to an eighth aspect is the refrigeration cycle apparatus according to the seventh aspect in which the branch portion is disposed between the radiator and the first economizer heat exchanger.

[0021] In the refrigeration cycle apparatus according to the eighth aspect, the refrigerant partially branches on the upstream side of the first economizer heat exchanger in a flow direction of the refrigerant in the first refrigerant circuit and flows through the second refrigerant circuit into the first economizer heat exchanger. Therefore, in the refrigeration cycle apparatus according to the eighth aspect, it is possible to improve the capability and efficiency of the refrigeration cycle apparatus while suppressing a size of the first economizer heat exchanger, compared with a case where the refrigerant flowing out of the radiator fully flows through the first refrigerant circuit into the first economizer heat exchanger.

[0022] A refrigeration cycle apparatus according to a ninth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the sixth aspect in which the first refrigerant circuit further includes a second expansion valve disposed between the radiator and the first expansion valve. The second refrigerant circuit further includes a refrigerant vessel that is configured to separate gas and liquid. The refrigerant decompressed and brought into a two-phase state by the second expansion valve flows into the refrigerant vessel. The first valve is disposed between the refrigerant vessel and the second compressor. The gas refrigerant separated in the refrigerant vessel is sucked into the second compressor.

[0023] In the refrigeration cycle apparatus according to the ninth aspect, the refrigerant vessel is used to lower the temperature of the refrigerant flowing into the heat absorber and improve the capability and efficiency of the refrigeration cycle apparatus with a relatively simple configuration.

[0024] A refrigeration cycle apparatus according to a tenth aspect is the refrigeration cycle apparatus according to the ninth aspect in which the second refrigerant circuit further includes a second economizer heat exchanger. The second economizer heat exchanger is arranged to exchange heat between the refrigerant flowing out of the radiator toward the second expansion valve and the gas refrigerant flowing out of the refrigerant vessel.

[0025] In the refrigeration cycle apparatus according to the tenth aspect, using the second economizer heat exchanger in addition to the refrigerant vessel makes it possible to further improve the capability and efficiency of the refrigeration cycle apparatus.

[0026] A refrigeration cycle apparatus according to an eleventh aspect is the refrigeration cycle apparatus according to any one of the first aspect to the tenth aspect in which the control unit is configured to open the first valve before the second compressor is started.

[0027] In the refrigeration cycle apparatus according to the eleventh aspect, by opening the first valve before the second compressor is started, it is possible to reduce differential pressure between the suction side and a discharge side of the second compressor and make it possible to bring the second compressor into a startable state.

[0028] A refrigeration cycle apparatus according to a twelfth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the eleventh aspect and further includes a bypass flow path and a second valve disposed in the bypass flow path. The bypass flow path connects the discharge side of the second compressor in the second refrigerant circuit and the suction side of the second compressor in the second refrigerant circuit. Alternatively, the bypass flow path connects a portion between the discharge port of the first compressor and the radiator in the first refrigerant circuit and the suction side of the second compressor in the second refrigerant circuit.

[0029] In the refrigeration cycle apparatus according to the twelfth aspect, opening the second valve can reduce the differential pressure between the suction side and the discharge side of the second compressor and bring the second compressor into the startable state.

[0030] A refrigeration cycle apparatus according to a thirteenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the twelfth aspect in which the refrigerant enclosed in the first refrigerant circuit and the second refrigerant circuit contains CO 2 at least partially in its components.

[0031] In the refrigeration cycle apparatus according to the thirteenth aspect, by using, as the refrigerant, a refrigerant containing at least CO 2 having a low global warming potential, it is possible to achieve the refrigeration cycle apparatus presenting a low environmental load.BRIEF DESCRIPTION OF DRAWINGS

[0032] <Fig. 1> Fig. 1 is a schematic configuration diagram of an air conditioner according to an embodiment of a refrigeration cycle apparatus. <Fig. 2> Fig. 2 is a schematic control block diagram of the air conditioner illustrated in Fig. 1. <Fig. 3A> Fig. 3A is a schematic p-h diagram of an air conditioner in which no second refrigerant circuit is present (air conditioner including only a first refrigerant circuit). <Fig. 3B> Fig. 3B is a schematic p-h diagram when cooling operation is performed in the air conditioner illustrated in Fig. 1. <Fig. 4> Fig. 4 is a flowchart for explaining control for the air conditioner with a control device when operation of a second compressor is to be stopped in the air conditioner illustrated in Fig. 1. <Fig. 5> Fig. 5 is a flowchart for explaining control for the air conditioner with the control device when operation of the second compressor is started in the air conditioner illustrated in Fig. 1. <Fig. 6> Fig. 6 is a schematic configuration diagram of an air conditioner according to Modification Example A. <Fig. 7> Fig. 7 is a schematic configuration diagram of an air conditioner according to Modification Example C. <Fig. 8A> Fig. 8A is a schematic configuration diagram of an air conditioner according to Modification Example D. <Fig. 8B> Fig. 8B is another example of the schematic configuration diagram of the air conditioner according to Modification Example D. DESCRIPTION OF EMBODIMENTS

[0033] An embodiment of a refrigeration cycle apparatus according to the present disclosure will now be described herein with reference to the accompanying drawings.(1) Overall Configuration

[0034] An overall configuration of an air conditioner 100 of an embodiment of the refrigeration cycle apparatus according to the present disclosure will now be described herein with reference to Fig. 1. Fig. 1 is a schematic configuration diagram of the air conditioner 100.

[0035] Note that the refrigeration cycle apparatus according to the present disclosure is not limited to the air conditioner, and may be an apparatus of another type, which uses a vapor compression refrigeration cycle to perform cooling or heating of a target for which a temperature is to be adjusted (medium such as air or water).

[0036] The air conditioner 100 is an apparatus that uses a vapor compression refrigeration cycle to cool or heat air in a room in a building, for example, representing a target to which the temperature is to be adjusted, to perform cooling or heating for the room in the building, for example. However, the air conditioner 100 may be an apparatus dedicated for cooling.

[0037] As illustrated in Fig. 1, the air conditioner 100 mainly includes a first refrigerant circuit 110 and a second refrigerant circuit 120. The refrigerant circuits 110, 120 in the air conditioner 100 are filled with, but not limited to, a refrigerant containing carbon dioxide (CO 2 ) at least partially in its components. The refrigerant circuits 110, 120 in the air conditioner 100 may be filled with a refrigerant of a single type that is carbon dioxide. Carbon dioxide serves as a refrigerant that has a low global warming potential, a low environmental load, and no toxicity or flammability, and is thus highly safe.

[0038] As illustrated in Fig. 1, the first refrigerant circuit 110 mainly includes a first compressor 10, a first heat exchanger 40, a first expansion valve 50, and a second heat exchanger 60. In the present embodiment, for example, the first compressor 10, the first heat exchanger 40, and the first expansion valve 50 are mounted in a heat source unit 2 disposed outdoors such as on a rooftop of the building, and the second heat exchanger 60 is mounted in a utilization unit 4 disposed in a space that is a target of air conditioning or near the space that is the target of air conditioning. In the air conditioner 100, the heat source unit 2 and the utilization unit 4 are coupled to each other by refrigerant connection pipes 6 to configure the first refrigerant circuit 110.

[0039] The second refrigerant circuit 120 connects a portion between the first compressor 10 and a radiator (first heat exchanger 40) in the first refrigerant circuit 110 and a portion between the radiator (first heat exchanger 40) and the first expansion valve 50 in the first refrigerant circuit 110 to each other, in the first refrigerant circuit 110 in which the air conditioner 100 is in a state of performing cooling operation (in other words, in a state where a switching mechanism 30 connects the pipes to allow the first heat exchanger 40 to function as the radiator for the refrigerant and the second heat exchanger 60 to function as a heat absorber (evaporator) for the refrigerant).

[0040] The second refrigerant circuit 120 includes a second compressor 20. Furthermore, the second refrigerant circuit 120 includes a first valve 80 and an economizer heat exchanger 70 disposed between the first heat exchanger 40 and the second heat exchanger 60 in the first refrigerant circuit 110. Note that the economizer heat exchanger 70 is disposed to straddle the first refrigerant circuit 110 and the second refrigerant circuit 120.

[0041] The second refrigerant circuit 120 is used to improve a refrigeration cycle in performance during the cooling operation by the air conditioner 100. Specific description will be given below.

[0042] When assuming that no second refrigerant circuit 120 is present (in other words, assuming that only the first refrigerant circuit 110 is provided), as the CO 2 refrigerant (carbon dioxide refrigerant) used in the air conditioner 100 has a relatively low refrigeration effect due to its characteristics (see a p-h diagram illustrated in Fig. 3A), an issue arises that the first compressor 10 is increased in size for acquiring high capability with only the first refrigerant circuit 110.

[0043] In contrast, in the air conditioner 100 according to the present disclosure, the second refrigerant circuit 120 is provided, and, in the economizer heat exchanger 70, the refrigerant flowing toward the second heat exchanger 60 (heat absorber) in the first refrigerant circuit 110 and the refrigerant flowing toward the second compressor 20 in the second refrigerant circuit 120 exchange heat with each other, and the refrigerant flowing toward the second heat exchanger 60 (heat absorber) in the first refrigerant circuit 110 is further cooled. Therefore, improvements in capability and performance of the air conditioner 100 are achieved, compared with a case where only the first refrigerant circuit 110 is present (see the p-h diagram illustrated in Fig. 3B).(2) Detailed Configuration

[0044] The air conditioner 100 includes a pressure equalization mechanism 90, a first fan 42, a second fan 62, and a control device 8, in addition to the first refrigerant circuit 110 and the second refrigerant circuit 120.

[0045] Various configurations of the air conditioner 100 will now be described herein in detail.(2-1) First Refrigerant Circuit

[0046] The first refrigerant circuit 110 mainly includes the first compressor 10, the switching mechanism 30, the first heat exchanger 40, the first expansion valve 50, and the second heat exchanger 60, which are connected each other by the pipes.

[0047] The first compressor 10 is a compressor that is variable in operating capacity and that includes an inverter-control-type motor. In the present embodiment, the first compressor 10 is a scroll compressor. However, the type of the first compressor 10 may be another type of compressor. The first compressor 10 sucks the refrigerant from a suction port 10a and discharges the refrigerant from a discharge port 10b.

[0048] The switching mechanism 30 is a mechanism that switches a state of the first refrigerant circuit 110 between a first state (cooling operation state) and a second state (heating operation state). When the first refrigerant circuit 110 is in the first state (see solid lines in the switching mechanism 30 illustrated in Fig. 1), the first heat exchanger 40 functions as the radiator for the refrigerant, and the second heat exchanger 60 functions as the heat absorber (evaporator) for the refrigerant. When the first refrigerant circuit 110 is in the second state (see broken lines in the switching mechanism 30 illustrated in Fig. 1), the first heat exchanger 40 functions as the evaporator for the refrigerant, and the second heat exchanger 60 functions as the radiator for the refrigerant.

[0049] The switching mechanism 30 is a four-way switching valve. However, the switching mechanism 30 is not limited to the four-way switching valve, and may include a plurality of pipes and a plurality of valves to achieve those connecting states of the pipes as described below.

[0050] To set the state of the first refrigerant circuit 110 into the first state, the switching mechanism 30 couples the discharge port 10b of the first compressor 10 and one end side of the first heat exchanger 40 to each other, and couples the suction port 10a of the first compressor 10 and one end side of the second heat exchanger 60 to each other (see the solid lines in the switching mechanism 30 illustrated in Fig. 1). Furthermore, to set the state of the first refrigerant circuit 110 into the second state, the switching mechanism 30 couples the discharge port 10b of the first compressor 10 and the one end side of the second heat exchanger 60 to each other, and couples the suction port 10a of the first compressor 10 and the one end side of the first heat exchanger 40 to each other (see the broken lines in the switching mechanism 30 illustrated in Fig. 1).

[0051] Note that, when the air conditioner 100 is an apparatus dedicated for cooling, the air conditioner 100 may not include the switching mechanism 30.

[0052] In the first heat exchanger 40, air (heat source air) that the first fan 42 described later supplies and the refrigerant exchange heat with each other. When the state of the first refrigerant circuit 110 is the first state, the first heat exchanger 40 functions as the radiator for the refrigerant, and the refrigerant is cooled by the heat source air in the first heat exchanger 40. When the state of the first refrigerant circuit 110 is the second state, the first heat exchanger 40 functions as the heat absorber (evaporator) for the refrigerant, and the refrigerant is heated by the heat source air in the first heat exchanger 40. The first heat exchanger 40 is, for example, a fin-and-tube heat exchanger including many heat transfer tubes and many fins.

[0053] Note that the first heat exchanger 40 is not limited to a heat exchanger in which the heat source air and the refrigerant exchange heat with each other. The first heat exchanger 40 may be a heat exchanger in which a medium such as water serving as a heat source and the refrigerant exchange heat with each other.

[0054] The economizer heat exchanger 70 that is an example of a first economizer heat exchanger is disposed between the first heat exchanger 40 and the second heat exchanger 60 in the first refrigerant circuit 110, more specifically, between the first heat exchanger 40 and the first expansion valve 50 in the first refrigerant circuit 110. Furthermore, the economizer heat exchanger 70 is disposed between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120. During the cooling operation, the economizer heat exchanger 70 exchanges heat between the refrigerant that flows out of the radiator (first heat exchanger 40), is branched to the second refrigerant circuit 120 at a branch portion 82, and is decompressed by the first valve 80 described later and the refrigerant that flows out of the radiator (first heat exchanger 40), passes through the economizer heat exchanger 70, and flows toward the heat absorber (second heat exchanger 60). As a result, during the cooling operation, the refrigerant that has been cooled in the radiator (first heat exchanger 40) and that flows toward the heat absorber (second heat exchanger 60) (see a point c and a point d illustrated in Fig. 3B) is further cooled by the economizer heat exchanger 70 (see a point h illustrated in Fig. 3B). Note that the branch portion 82 is disposed between the first heat exchanger 40 functioning as the radiator during the cooling operation and the economizer heat exchanger 70.

[0055] The first expansion valve 50 decompresses the refrigerant flowing between the first heat exchanger 40 and the second heat exchanger 60. The first expansion valve 50 is disposed between the first heat exchanger 40 and the second heat exchanger 60, more specifically, between the economizer heat exchanger 70 and the second heat exchanger 60. The first expansion valve 50 is, for example, an electronic expansion valve that is variable in opening degree.

[0056] In the second heat exchanger 60, the refrigerant and the air in the space that is the target of air conditioning exchange heat with each other. The second heat exchanger 60 is housed in a non-illustrated housing, to which the air in the air conditioning target space of the target of air conditioning is supplied by the second fan 62 disposed in the housing. In the second heat exchanger 60, the air in the air conditioning target space, which is supplied by the second fan 62, and the refrigerant exchange heat with each other. When the state of the first refrigerant circuit 110 is the first state, the second heat exchanger 60 functions as the heat absorber for the refrigerant, and the air in the air conditioning target space is cooled by the refrigerant in the second heat exchanger 60. When the state of the first refrigerant circuit 110 is the second state, the second heat exchanger 60 functions as the radiator for the refrigerant, and the air in the space that is the target of air conditioning is heated by the refrigerant in the second heat exchanger 60. The second heat exchanger 60 is, for example, a fin-and-tube heat exchanger including many heat transfer tubes and many fins.(2-2) Second Refrigerant Circuit

[0057] The second refrigerant circuit 120 includes the second compressor 20. Furthermore, the air conditioner 100 according to the present embodiment includes the economizer heat exchanger 70 that is an example of the first economizer heat exchanger and the first valve 80. The first valve 80 is disposed on the upstream side of the second compressor 20 in a flow direction of the refrigerant in the second refrigerant circuit 120. The first valve 80 is disposed between the branch portion 82 at which the second refrigerant circuit 120 branches from the first refrigerant circuit 110 and the economizer heat exchanger 70.

[0058] In the present embodiment, the first valve 80 is an electronic expansion valve that is variable in opening degree.

[0059] The second refrigerant circuit 120 is mainly used during the cooling operation (second compressor 20 is operated during the cooling operation), and is not used during heating operation. In other words, basically, the refrigerant does not flow through the second refrigerant circuit 120 during the heating operation.

[0060] The second compressor 20 is preferably a compressor that is variable in operating capacity and that includes an inverter-control-type motor. In the present embodiment, the second compressor 20 is a rotary compressor (including a swing compressor). However, the type of the second compressor 20 is not limited to the rotary compressor, and may be another type of compressor. The second compressor 20 discharges the refrigerant sucked from a suction port 20a from a discharge port 20b.

[0061] The economizer heat exchanger 70 is, for example, a double-pipe-type heat exchanger or a plate-type heat exchanger. The economizer heat exchanger 70 is disposed between the first heat exchanger 40 functioning as the radiator during the cooling operation and the second heat exchanger 60 functioning as the heat absorber during the cooling operation. As described above, during the cooling operation, the economizer heat exchanger 70 exchanges heat between the refrigerant that flows out of the radiator (first heat exchanger 40), is branched to the second refrigerant circuit 120 at the branch portion 82, and is decompressed by the first valve 80 and the refrigerant that flows out of the radiator (first heat exchanger 40), passes through the economizer heat exchanger 70, and will flow toward the heat absorber (second heat exchanger 60). The refrigerant that has been decompressed by the first valve 80, has passed through the economizer heat exchanger 70, and has cooled the refrigerant flowing toward the heat absorber (second heat exchanger 60) is brought into a gas state, and is sucked into the second compressor 20 (see a point f illustrated in the p-h diagram illustrated in Fig. 3B).(2-3) Pressure Equalization Mechanism

[0062] The pressure equalization mechanism 90 is a mechanism for achieving pressure equalization between pressure on a discharge side of the second compressor 20 and pressure on a suction side of the second compressor 20.

[0063] The pressure equalization mechanism 90 includes a bypass flow path 92 and a second valve 94. Furthermore, preferably, the pressure equalization mechanism 90 includes a check valve 96.

[0064] The check valve 96 is provided between the discharge port 20b of the second compressor 20 and a connecting portion of the second refrigerant circuit 120 and the first refrigerant circuit 110 (connecting portion between the second refrigerant circuit 120 and a pipe connecting the discharge port 10b of the first compressor 10 and the switching mechanism 30 to each other). The check valve 96 prevents the refrigerant from flowing from a side where the connecting portion of the second refrigerant circuit 120 and the first refrigerant circuit 110 to a side where the discharge port 20b of the second compressor 20.

[0065] The bypass flow path 92 is a flow path that connects the discharge side of the second compressor 20 in the second refrigerant circuit 120 and the suction side of the second compressor 20 in the second refrigerant circuit 120. Specifically, the bypass flow path 92 connects a portion between the discharge port 20b of the second compressor 20 and the check valve 96 and the suction side of the second compressor 20 in the second refrigerant circuit 120.

[0066] Note that, although illustrations are omitted, the bypass flow path 92 may be a flow path that connects a portion in the first refrigerant circuit 110 which is located between the discharge port 10b of the first compressor 10 and the radiator (first heat exchanger 40) when the air conditioner 100 performs the cooling operation and the suction side of the second compressor 20. Specifically, the bypass flow path 92 may be a flow path that connects a pipe connecting a portion between the discharge port 10b of the first compressor 10 and the switching mechanism 30 and the suction side of the second compressor 20. Furthermore, the bypass flow path 92 may be a flow path that connects the suction side of the second compressor 20 and a portion between the connecting portion of the second refrigerant circuit 120 to the first refrigerant circuit 110 (connecting portion of the second refrigerant circuit 120 to a pipe connecting a portion between the discharge port of the first compressor 10 and the switching mechanism 30) and the check valve 96.

[0067] The second valve 94 is a valve disposed in the bypass flow path 92. The second valve 94 may be an electromagnetic valve in which only opening and closing are controllable, or may be an electrically-operated valve that is variable in opening degree.

[0068] The second valve 94 is controlled to be opened by the control device 8 described later when it is intended to achieve pressure equalization between the discharge side of the second compressor 20 and the suction side of the second compressor 20. Specific control for the second valve 94 by the control device 8 will be described later.(2-4) First Fan and Second Fan

[0069] The first fan 42 is housed inside a housing (illustrations are omitted) of the heat source unit 2, which houses, for example, the first compressor 10, the second compressor 20, the switching mechanism 30, the first heat exchanger 40, the economizer heat exchanger 70, the first expansion valve 50, the first valve 80, and the second valve 94. The first fan 42 supplies the heat source air to the first heat exchanger 40 in the first refrigerant circuit 110 and urges exchanging of heat between the refrigerant flowing through the first heat exchanger 40 and the heat source air. Although the type of the first fan 42 is not limited, the first fan 42 is, for example, a propeller fan.

[0070] The second fan 62 is housed in the housing (illustrations are omitted) of the utilization unit 4, which houses the second heat exchanger 60 and the like. The second fan 62 sucks the air from the space that is the target of air conditioning, supplies the sucked air to the second heat exchanger 60 in the first refrigerant circuit 110, and urges exchanging of heat between the refrigerant flowing through the second heat exchanger 60 and the sucked air from the target of air conditioning. Although the type of the second fan 62 is not limited, the second fan 62 is, for example, a cross-flow fan.(2-5) Control Device

[0071] The control device 8 that is an example of a control unit is a device that controls operation of the air conditioner 100.

[0072] The control device 8 is electrically coupled to the first compressor 10, the second compressor 20, the switching mechanism 30, the first expansion valve 50, the first valve 80, the second valve 94, the first fan 42, and the second fan 62 (see Fig. 2). The control device 8 controls operation of these devices that are electrically coupled to each other to control operation of the air conditioner 100.

[0073] Furthermore, the air conditioner 100 is provided with various sensors (a temperature sensor for measuring a temperature of the refrigerant, a pressure sensor for measuring the pressure of the refrigerant, and a temperature sensor for measuring a temperature in the space that is the target of air conditioning and the like), and the control device 8 is electrically coupled to these sensors. For example, as illustrated in Fig. 1, the air conditioner 100 is provided with a second sensor (pressure sensor) 122 that measures suction pressure of the second compressor 20 and a second sensor (temperature sensor) 124 that measures a suction temperature of the second compressor 20. The first sensor 122 and the second sensor 124 are disposed between the economizer heat exchanger 70 and the suction port 20a of the second compressor 20, and, for example, near the suction port 20a of the second compressor 20. The control device 8 is electrically coupled to the first sensor 122 and the second sensor 124, and acquires results of measurement by the first sensor 122 and the second sensor 124. The control device 8 interprets the pressure measured by the first sensor 122 as a saturation temperature of the refrigerant.

[0074] In the present embodiment, a non-illustrated electric circuit and a non-illustrated control board mounted on the heat source unit 2 and a non-illustrated electric circuit and a non-illustrated control board mounted on the utilization unit 4 are communicably coupled to each other, and cooperate with each other to function as the control device 8. Note that, in Fig. 1, for purposes of convenience, the control device 8 is illustrated at a position separated from the heat source unit 2 and the utilization unit 4.

[0075] In the present embodiment, the control device 8 includes a control computation device and a memory device. As the control computation device, it is possible to use a processor such as a central processing unit (CPU). The control computation device reads a program stored in the memory device and controls operation of the air conditioner 100 according to the program.(2-5-1) Heating Operation

[0076] To cause the air conditioner 100 to perform the heating operation, the control device 8 controls operation of the switching mechanism 30 to set the state of the first refrigerant circuit 110 into the second state, and operates the first compressor 10. The control device 8 controls a number of rotations of the motor in the first compressor 10 and the opening degree of the first expansion valve 50 based on results of measurement by the various sensors (the temperature sensor for measuring the temperature of the refrigerant, the pressure sensor for measuring the pressure of the refrigerant, and the temperature sensor for measuring the temperature in the space that is the target of air conditioning, for example) disposed at various positions in the air conditioner 100. Furthermore, the control device 8 operates motors of the first fan 42 and the second fan 62 respectively at predetermined numbers of rotations.

[0077] Note that, during the heating operation, the control device 8 controls the first valve 80 and the second valve 94 in closed states, and does not operate the second compressor 20.(2-5-2) Cooling Operation

[0078] To cause the air conditioner 100 to perform the cooling operation, the control device 8 controls operation of the switching mechanism 30 to set the state of the first refrigerant circuit 110 into the first state, and, normally, operates the first compressor 10 and the second compressor 20. The control device 8 controls the numbers of rotations of the motors in the first compressor 10 and the second compressor 20 and the opening degrees of the first expansion valve 50 and the first valve 80 based on results of measurement by the various sensors (the temperature sensor for measuring the temperature of the refrigerant, the pressure sensor for measuring the pressure of the refrigerant, and the temperature sensor for measuring the temperature in the space that is the target of air conditioning, for example) disposed at the various positions on the air conditioner 100. Furthermore, the control device 8 operates the motors of the first fan 42 and the second fan 62 respectively at predetermined numbers of rotations.

[0079] Furthermore, when a load of the air conditioner 100 has decreased and it is assumed that operating only the first compressor 10 to perform the cooling operation is more efficient, the control device 8 stops operation of the second compressor 20 and operates only the first compressor 10 to perform the cooling operation. When the air conditioner 100 performs this operation, the control device 8 closes the first valve 80, as will be described later. Then, the control device 8 controls the number of rotations of the motor in the first compressor 10 and the opening degree of the first expansion valve 50 based on results of measurement by the various sensors (the temperature sensor for measuring the temperature of the refrigerant, the pressure sensor for measuring the pressure of the refrigerant, and the temperature sensor for measuring the temperature in the space that is the target of air conditioning, for example) disposed at the various positions in the air conditioner 100. Furthermore, the control device 8 operates the motors of the first fan 42 and the second fan 62 respectively at predetermined numbers of rotations.

[0080] Note that, during the cooling operation, the control device 8 controls the second valve 94 to be in the closed state.(2-5-3) Control when Operation of Second Compressor is to be stopped

[0081] In a case where operation of the second compressor 20 is stopped while the first valve 80 is opened, the refrigerant cooled by the first heat exchanger 40 functioning as the radiator flows into a portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 (hereinafter this portion will be referred to as a first portion 125), possibly increasing the pressure in the first portion 125. In a case where the refrigerant at high pressure, which has been cooled by the first heat exchanger 40, is present in the first portion 125, the temperature of outside air is relatively low so that the saturation temperature of the refrigerant, which corresponds to the pressure of the refrigerant that is present in the first portion 125, is higher than the temperature of the outside air, the refrigerant in the first portion 125 exchanges heat with the outside air, possibly resulting in condensation of the refrigerant in the first portion 125. When an amount of the condensation is large, the second compressor 20 may suck the liquid refrigerant that has condensed, when operation of the second compressor 20 is started, and liquid compression occurs, possibly resulting in an abnormality in the second compressor 20.

[0082] Therefore, in the air conditioner 100, when the second compressor 20 is to be stopped, the control device 8 closes the first valve 80 to suppress an inflow to the first portion 125. Preferably, the control device 8 closes the first valve 80 to suppress the inflow to the first portion 125 before the second compressor 20 is stopped.

[0083] An example of control for the air conditioner 100 by the control device 8 when the second compressor 20 is to be stopped will now be described herein with reference to a flowchart illustrated in Fig. 4.

[0084] A case where, in a state where the air conditioner 100 operates both the first compressor 10 and the second compressor 20 to perform the cooling operation, the load of the air conditioner 100 decreases, the second compressor 20 is stopped, and only the first compressor 10 is operated to continue the cooling operation will now be described herein as an example. However, the control when operation of the second compressor 20 is to be stopped, as will be described herein, may also be performed when the cooling operation of the air conditioner 100 is to be stopped (when operation of both the first compressor 10 and the second compressor 20 is to be stopped) in a state where both the first compressor 10 and the second compressor 20 are operated to perform the cooling operation.

[0085] The control device 8 determines whether or not to stop operation of the second compressor 20 in accordance with an operation state of the air conditioner 100 during the cooling operation in which both the first compressor 10 and the second compressor 20 are operated (step S1).

[0086] When it is determined to stop operation of the second compressor 20 at step S1, the control device 8 preferably controls the opening degree of the first valve 80 based on a result of measurement by the first sensor 122 and a result of measurement by the second sensor 124 while operation of the second compressor 20 is continued, instead of immediately causing the first valve 80 to be closed (step S2). For example, the control device 8 controls the opening degree of the first valve 80 based on a value acquired by subtracting a saturation temperature derived from the suction pressure of the second compressor 20, which is measured by the first sensor 122, from the temperature of the refrigerant to be sucked into the second compressor 20, which is measured by the second sensor 124. The control device 8 interprets the result of the measurement by the first sensor 122 as the saturation temperature, for example, based on a table indicating a relationship between the pressure and the saturation temperature of the refrigerant, which is stored in the memory unit of the control device 8, or based on a formula indicating the relationship between the pressure and the saturation temperature of the refrigerant, which is stored in the memory unit of the control device 8.

[0087] Specifically, the control device 8 controls the opening degree of the first valve 80 so that the value acquired by subtracting the saturation temperature derived from the suction pressure of the second compressor 20, which is measured by the first sensor 122, from the temperature of the refrigerant to be sucked into the second compressor 20, which is measured by the second sensor 124, to be at least larger than zero (in other words, to allow the refrigerant to be sucked into the second compressor 20 to have a degree of superheating).

[0088] More preferably, when the second compressor 20 is to be stopped, the control device 8 controls the opening degree of the first valve 80 to make a degree of superheating of suction of the second compressor 20 to be equal to or higher than a predetermined degree of superheating. For example, it is assumed that, during the cooling operation in which both the first compressor 10 and the second compressor 20 are operated, the control device 8 controls the opening degree of the first valve 80 to make the degree of superheating of suction of the second compressor 20 to be α (≥0). In this case, when the second compressor 20 is to be stopped, the control device 8 controls the opening degree of the first valve 80 to make the degree of superheating of suction of the second compressor 20 to be equal to or higher than a predetermined degree of superheating, which is higher than α. In other words, when the second compressor 20 is to be stopped, the control device 8 preferably controls the opening degree of the first valve 80 to be smaller than an opening degree when both the first compressor 10 and the second compressor 20 are used to perform the cooling operation (instead of immediately causing the first valve 80 to be closed fully).

[0089] Then, the control device 8 maintains the state where the refrigerant to be sucked by the second compressor 20 has the degree of superheating (preferably, a state where the refrigerant has the predetermined degree of superheating) for a predetermined time, and then closes the first valve 80 fully (step S3).

[0090] Then, the control device 8 preferably allows operation of the second compressor 20 to be continued for a predetermined time after the first valve 80 is closed (step S4), and then stops the second compressor 20 (step S5).

[0091] Note that, since such a state has been attained that there has been a pressure difference between the discharge side and the suction side of the second compressor 20, the second valve 94 disposed in the bypass flow path 92 may at this point in time be opened to achieve pressure equalization between the discharge side and the suction side of the second compressor 20 (step S5). Although, when such control is performed as described above, the refrigerant at high pressure flows into the suction side of the second compressor 20, the refrigerant that flows in is small in weight, since the refrigerant that flows in is the refrigerant that has not yet cooled by the first heat exchanger 40, i.e., that is relatively low in density.

[0092] When the second valve 94 is to be opened in this manner, the control device 8 determines at step S7 whether or not the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated. Whether or not the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated is determined by, for example, comparing the pressure measured by the pressure sensor (not illustrated) provided on the discharge side of the second compressor 20 with the pressure measured by the first sensor 122. Note that, as for the method for determining whether or not the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated, a method that uses a result of measurement of the pressure by the pressure sensor may not be used. For example, the control device 8 may determine whether or not the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated based on a time from when the second valve 94 is opened. Specifically, the control device 8 determines that the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated when a predetermined time has elapsed after the second valve 94 is opened.

[0093] When it is determined at step S7 that the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated, the control device 8 closes the second valve 94 (step S8).

[0094] Note that pressure equalization between the discharge side of the second compressor 20 and the suction side of the second compressor 20 is preferably performed when the second compressor 20 is a rotary compressor. One reason for this preference is that, due to the characteristics of the rotary compressor, refrigerating machine oil in the second compressor 20 may flow out of the suction port 20a of the second compressor 20, when such a state continues that the pressure on the discharge side is higher than the pressure on the suction side.(2-5-4) Control when Second Compressor is to be started

[0095] Control for operation of the air conditioner 100 by the control device 8 when operation of the second compressor 20 is to be started will now be described herein. As an example, for a case where operation of the second compressor 20 is to be started according to an increase in load when only the first compressor 10 is operated to perform the cooling operation, control when operation of the second compressor 20 is to be started will now be described herein with reference to a flowchart illustrated in Fig. 5.

[0096] The control device 8 determines whether or not to start operation of the second compressor 20 in accordance with an operation state of the air conditioner 100 during the cooling operation in which only the first compressor 10 is operated, and the processing proceeds to step S12 when it is determined to start operation of the second compressor 20 (step S1).

[0097] At step S12, the control device 8 opens the first valve 80.

[0098] Note that, while the cooling operation is performed by only operating the first compressor 10, there may be differential pressure between the discharge side of the second compressor 20 and the suction side of the second compressor 20. When no such pressure equalization by the pressure equalization mechanism 90 as described at step S6 to step S8 in the flowchart illustrated in Fig. 4 is performed, there is a possibility that there is large differential pressure between the discharge side and the suction side of the second compressor 20.

[0099] Therefore, the control device 8 preferably opens the first valve 80 at step S12, and then, waits for a predetermined time in this state. When the first valve 80 is opened, the pressure on the suction side of the second compressor 20 becomes high accordingly, and pressure equalization is achieved between the discharge side and the suction side of the second compressor 20, allowing the second compressor 20 to be in an operation-ready state.

[0100] Then, after the predetermined time has elapsed since when the first valve 80 has been opened (for example, after a predetermined time has elapsed, at which it is assumed that a decrease in pressure difference between the discharge side and the suction side of the second compressor 20 is suppressed), the control device 8 starts operation of the second compressor 20 (step S13). Alternatively, the control device 8 may use, as a trigger, that a difference between a measurement value of the non-illustrated pressure sensor provided on the discharge side of the second compressor 20 and a measurement value of the first sensor 122 becomes equal to or smaller than a predetermined value to start operation of the second compressor 20.

[0101] Then, to perform the cooling operation in which the first compressor 10 and the second compressor 20 are operated, the control device 8 starts controlling of the opening degree of the first valve 80 in addition to controlling of the numbers of rotations of the first compressor 10 and the second compressor 20 and the opening degree of the first expansion valve 50 (step S14).(3) Features

[0102] (3-1) The air conditioner 100 includes the first refrigerant circuit 110, the second refrigerant circuit 120, and the control device 8 serving as the example of the control unit. The first refrigerant circuit 110 includes the first compressor 10, the first heat exchanger 40 functioning as the radiator during the cooling operation, the first expansion valve 50, and the second heat exchanger 60 functioning as the heat absorber during the cooling operation. The second refrigerant circuit 120 connects a portion between the first compressor 10 and the first heat exchanger 40 and a portion between the first heat exchanger 40 and the first expansion valve 50. The second refrigerant circuit 120 includes the second compressor 20 and the first valve 80. The first valve 80 is disposed on the upstream side of the second compressor 20. The control device 8 controls the first compressor 10, the second compressor 20, the first expansion valve 50, and the first valve 80. The control device 8 closes the first valve 80 when the second compressor 20 is to be stopped.

[0103] In the air conditioner 100, the first valve 80 is disposed on the upstream side of the second compressor 20 in the second refrigerant circuit 120, and the first valve 80 is closed when the second compressor 20 is to be stopped. Therefore, with this air conditioner 100, even when the temperature of the outside air is relatively low, it is possible to suppress condensation of the refrigerant at a large amount on the suction side of the second compressor 20 and to suppress liquid compression when the second compressor 20 is started.

[0104] (3-2) In the air conditioner 100, the control device 8 closes the first valve 80 before the second compressor 20 is stopped.

[0105] In this air conditioner 100, the second compressor 20 is operated in a state where the first valve 80 is closed and the refrigerant is prevented from flowing into an area downstream of the first valve 80. Therefore, in this air conditioner 100, even when the temperature of the outside air is relatively low, it is possible to suppress condensation of the refrigerant at a large amount on the suction side of the second compressor 20 and to suppress liquid compression when the second compressor 20 is started.

[0106] (3-3) The air conditioner 100 includes the first sensor 122 and the second sensor 124. The second compressor 20 has the suction port 20a. The first valve 80 is an expansion valve. The first sensor 122 measures the saturation temperature of the refrigerant that is present between the first valve 80 and the suction port 20a of the second compressor 20. The second sensor 124 measures the temperature of the refrigerant to be sucked into the second compressor 20. The control device 8 controls, when the second compressor 20 is to be stopped, the opening degree of the first valve 80 based on a result of the measurement by the first sensor 122 and a result of the measurement by the second sensor 124.

[0107] Note herein that the description that the first sensor 122 measures the saturation temperature includes a case where the first sensor 122 measures a physical quantity correlated with the saturation temperature (physical quantity with which it is possible to know the saturation temperature of the refrigerant when a value of the physical quantity is known), in addition to an aspect of measuring the saturation temperature itself.

[0108] Specifically, in the present embodiment, the first sensor 122 and the second sensor 124 are disposed between the first valve 80 and the suction port 20a of the second compressor 20. Then, the first sensor 122 does not measure the saturation temperature of the refrigerant itself, but measures the pressure corresponding to the saturation temperature of the refrigerant. The control device 8 interprets the pressure measured by the first sensor 122 as the saturation temperature.

[0109] With the air conditioner 100, condensation of the refrigerant at a large amount on the suction side of the second compressor 20 is easily suppressed, making it possible to make the air conditioner 100 highly reliable.

[0110] (3-4) In the air conditioner 100, the control device 8 controls, when the second compressor 20 is to be stopped, the first valve 80 so that the refrigerant to be sucked into the second compressor 20 has a degree of superheating before the first valve 80 is closed.

[0111] Especially, the control device 8 controls, when the second compressor 20 is to be stopped, the opening degree of the first valve 80 so that a degree of superheating of suction of the second compressor 20 becomes equal to or higher than a predetermined degree of superheating.

[0112] With this air conditioner 100, it is possible to reduce the amount of the refrigerant that is present between the first valve 80 and the suction port 20a of the second compressor 20 after the second compressor 20 is stopped, and liquid compression is unlikely to occur in the second compressor 20, presenting high reliability.

[0113] (3-5) In the air conditioner 100, the second refrigerant circuit 120 includes the economizer heat exchanger 70 disposed between the first heat exchanger 40 and the second heat exchanger 60. During the cooling operation, the economizer heat exchanger 70 exchanges heat between the refrigerant that flows out of the first heat exchanger 40 functioning as the heat absorber, is branched to the second refrigerant circuit 120 at the branch portion 82, and is decompressed by the first valve 80, and the refrigerant flowing out of the first heat exchanger 40.

[0114] With the air conditioner 100, the economizer heat exchanger 70 improves the capability and efficiency of the air conditioner 100.

[0115] (3-6) In the air conditioner 100, the branch portion 82 is disposed between the first heat exchanger 40 functioning as the radiator during the cooling operation and the economizer heat exchanger 70.

[0116] In this air conditioner 100, the refrigerant partially branches on the upstream side of the economizer heat exchanger 70 in the flow direction of the refrigerant in the first refrigerant circuit 110 and flows through the second refrigerant circuit 120 into the economizer heat exchanger 70. Therefore, in this air conditioner 100, it is possible to improve the capability and efficiency of the air conditioner 100 while suppressing the size of the economizer heat exchanger 70, compared with a case where the refrigerant flowing out of the first heat exchanger 40 fully flows through the first refrigerant circuit 110 into the economizer heat exchanger 70.

[0117] (3-7) The air conditioner 100 includes the bypass flow path 92 and the second valve 94 disposed in the bypass flow path 92. The bypass flow path 92 connects the discharge side of the second compressor 20 in the second refrigerant circuit 120 and the suction side of the second compressor 20 in the second refrigerant circuit 120. Alternatively, the bypass flow path 92 connects a portion between the discharge port 10b of the first compressor 10 and the first heat exchanger 40 functioning as the radiator during refrigerant operation in the first refrigerant circuit 110 and the suction side of the second compressor 20 in the second refrigerant circuit 120.

[0118] In this air conditioner 100, opening the second valve 94 can reduce the differential pressure between the suction side and the discharge side of the second compressor 20 and bring the second compressor 20 into the startable state.

[0119] (3-8) In the air conditioner 100, the refrigerant enclosed in the first refrigerant circuit 110 and the second refrigerant circuit 120 contains CO 2 at least partially in its components.

[0120] In this air conditioner 100, by using, as the refrigerant, a refrigerant containing at least CO 2 having a small global warming potential, it is possible to achieve the air conditioner 100 presenting a low environmental load.(4) Modification Examples

[0121] Modification examples of the air conditioner 100 according to the embodiment described above will now be described herein. Note that it is possible to appropriately combine the modification examples described below.(4-1) Modification Example A

[0122] In the embodiment described above, the first sensor 122 is the pressure sensor that does not measure the saturation temperature itself but measures the pressure corresponding to the saturation temperature, and the control device 8 interprets a value of the pressure measured by the first sensor 122 as the saturation temperature. However, the present disclosure is not limited to this case, and the first sensor may be a temperature sensor that directly measures the saturation temperature.

[0123] In this case, a first sensor 122a representing a temperature sensor measures the temperature of the refrigerant at a position where the refrigerant flows in a gas-liquid two-phase state. For example, as illustrated in Fig. 6, the first sensor 122a is disposed between the first valve 80 and the economizer heat exchanger 70, through which the refrigerant in the gas-liquid two-phase state flows, and measures the temperature (saturation temperature) of the refrigerant flowing through this location.(4-2) Modification Example B

[0124] In the embodiment described above, when operation of the second compressor 20 is to be stopped, the control device 8 controls the opening degree of the first valve 80 based on the measurement values of the first sensor 122 and the second sensor 124, and makes the refrigerant to be sucked into the second compressor 20 to be in a state of having a degree of superheating (state where the degree of superheating is larger than 0).

[0125] However, the present disclosure is not limited to this case, and the air conditioner 100 may not be provided with the first sensor 122 and the second sensor 124 (or may not use results of measurement by the first sensor 122 and the second sensor 124), and the control device 8 may control and reduce the opening degree of the first valve 80 to a predetermined opening degree when operation of the second compressor 20 is to be stopped to make the refrigerant to be sucked into the second compressor 20 to have a degree of superheating (state where the degree of superheating is larger than 0).(4-3) Modification Example C

[0126] In the embodiment described above, although the branch portion 82 at which branching occurs from the first refrigerant circuit 110 to the second refrigerant circuit 120 is disposed between the first heat exchanger 40 functioning as the radiator during the cooling operation and the economizer heat exchanger 70, the present disclosure is not limited to such an aspect.

[0127] As illustrated in Fig. 7, a branch portion 82a may be disposed between the economizer heat exchanger 70 and the second heat exchanger 60 used as the heat absorber during the cooling operation. However, in this case, since all of the refrigerant flowing out of the first heat exchanger 40 flows through the economizer heat exchanger 70 on the side where the first refrigerant circuit 110 is present, and the refrigerant partially branches and flows into the second refrigerant circuit 120, possibly causing the economizer heat exchanger 70 to be large in size, compared with that according to the embodiment described above.(4-4) Modification Example D

[0128] In the embodiment described above, although the economizer heat exchanger 70 is provided in the second refrigerant circuit 120 (to straddle the first refrigerant circuit 110 and the second refrigerant circuit 120), the present disclosure is not limited to such an aspect.

[0129] As illustrated in Fig. 8A, the air conditioner 100 may include a refrigerant vessel 72 (flash tank economizer) that is gas-liquid separatable and that straddles the first refrigerant circuit 110 and the second refrigerant circuit 120, instead of the economizer heat exchanger 70. Then, the second refrigerant circuit 120 is provided with a first valve 80a, and the first refrigerant circuit 110 is provided with a second expansion valve 84. The first valve 80a is preferably an electrically-operated valve for which the opening degree is adjustable.

[0130] When operation of the second compressor 20 is to be stopped, the first valve 80a is controlled similarly to the first valve 80 according to the embodiment described above (see step S2 and step S3 in the flowchart illustrated in Fig. 4).

[0131] Furthermore, for example, to switch a state where the air conditioner 100 allows only the first compressor 10 to operate to perform the cooling operation to a state where the first compressor 10 and the second compressor 20 are operated to perform the cooling operation, the first valve 80a is opened before operation of the second compressor 20 is started, similar to control of the first valve 80 at step S12 in the flowchart illustrated in Fig. 5. However, when the pressure of the refrigerant in the refrigerant vessel 72 is intermediate pressure in the refrigeration cycle (due to decompression in the second expansion valve 84) and the pressure on the discharge side of the second compressor 20 is high pressure in the refrigeration cycle, pressure equalization may not be achieved between the pressure on the discharge side of the second compressor 20 and the pressure on the suction side of the second compressor 20, even though the first valve 80a is opened. Therefore, when it is assumed that there is a difference between the pressure on the discharge side of the second compressor 20 and the pressure on the suction side of the second compressor 20, the first valve 80a may be opened (step S12) and pressure equalization may be performed between the pressure on the discharge side of the second compressor 20 and the pressure on the suction side of the second compressor 20 using the pressure equalization mechanism 90 before operation of the second compressor 20 is started at step S13.

[0132] Note that, when the air conditioner 100 allows the first compressor 10 and the second compressor 20 to operate to perform the cooling operation, the first valve 80a is not controlled for its opening degree, but is adjusted to a predetermined opening degree (for example, fully opened), different from that at step S14 in the flowchart illustrated in Fig. 5.

[0133] A state where the air conditioner 100 illustrated in Fig. 8A performs the cooling operation will now be described herein. In the air conditioner 100, the refrigerant vessel 72 is disposed between the first heat exchanger 40 functioning as the radiator for the refrigerant and the second heat exchanger 60 functioning as the heat absorber for the refrigerant (more specifically, between the first heat exchanger 40 and the first expansion valve 50). The second expansion valve 84 is disposed between the first heat exchanger 40 functioning as the radiator and the refrigerant vessel 72. The control device 8 appropriately controls the opening degree of the second expansion valve 84 when operating both the first compressor 10 and the second compressor 20 to perform the cooling operation. Note that, when the second compressor 20 is to be stopped to perform the cooling operation, the opening degree of the second expansion valve 84 is not controlled. When both the first compressor 10 and the second compressor 20 are operated to perform the cooling operation, the refrigerant that flows out of the first heat exchanger 40, is decompressed by the second expansion valve 84, and brought into the two-phase state flows into the refrigerant vessel 72. The gas refrigerant separated in the refrigerant vessel 72 is sucked into the second compressor 20.

[0134] Also, in the air conditioner 100 having the configuration illustrated in Fig. 8A, it is possible to lower the temperature of the refrigerant flowing into the second heat exchanger 60 functioning as the heat absorber for the refrigerant, when both the first compressor 10 and the second compressor 20 are operated to perform the cooling operation, making it possible to improve the capability of the air conditioner 100.

[0135] Furthermore, as illustrated in Fig. 8B, the second refrigerant circuit 120 may include, in addition to the refrigerant vessel 72, a heat exchanger 70a (example of a second economizer heat exchanger) disposed to straddle the first refrigerant circuit 110 and the second refrigerant circuit 120. The heat exchanger 70a is disposed, in the first refrigerant circuit 110, between the first heat exchanger 40 functioning as the radiator for the refrigerant during the cooling operation and the second expansion valve 84. The heat exchanger 70a is arranged to exchange heat, when the air conditioner 100 allows both the first compressor 10 and the second compressor 20 to operate to perform the cooling operation, between the refrigerant that flows out of the first heat exchanger 40 toward the second expansion valve 84 and the gas refrigerant separated in the refrigerant vessel 72. The refrigerant that has exchanged heat in the heat exchanger 70a with the refrigerant flowing through the first refrigerant circuit 110 is sucked into the second compressor 20. With this configuration, further using the heat exchanger 70a makes it possible to further improve the capability of the air conditioner 100 during the cooling operation in a first mode, compared with that of the configuration illustrated in Fig. 8A.

[0136] In the configuration illustrated in Fig. 8B, the control for the first valve 80a and other components when operation of the second compressor 20 is to be stopped / operation of the second compressor 20 is to be started is as described with reference to the configuration illustrated in Fig. 8A.

[0137] Note that, also in the configurations illustrated in Fig. 8A and Fig. 8B, the second refrigerant circuit 120 is not used during the heating operation. During the heating operation, the second compressor 20 is not operated, the first valve 80a is closed, and the opening degree of the second expansion valve 84 is controlled to a predetermined opening degree and is not changed during the heating operation.(4-5) Modification Example E

[0138] Different from Modification Example D, the first valve 80a may be an electromagnetic valve that is changeable to be only fully opened and fully closed, in the configurations illustrated in Fig. 8A and Fig. 8B. Then, the control at step S2 illustrated in Fig. 4 and the control at step S14 illustrated in Fig. 5 may not be performed.

[0139] Even in such a configuration, since the second compressor 20 is operated for a predetermined time in a state where the first valve 80a is closed, it is possible to suppress condensation of the refrigerant at a large amount on the suction side of the second compressor 20 and to suppress liquid compression when the second compressor 20 is started.(4-6) Modification Example F

[0140] In the embodiment described above, the pressure equalization mechanism 90 is provided for pressure equalization between the discharge side and the suction side of the second compressor 20, and the second valve 94 is opened to achieve pressure equalization between the discharge side and the suction side of the second compressor 20.

[0141] However, in a case where opening the first valve 80 can achieve pressure equalization between the discharge side and the suction side before the second compressor 20 is started, the pressure equalization mechanism 90 may not be provided.<Note>

[0142] While the embodiment of the present disclosure has been described above, it will be understood that various changes in form and detail may be made therein without departing from the spirit and scope of the present disclosure as set forth in the appended claims.REFERENCE SIGNS LIST

[0143] 8control device (control unit) 10first compressor 20second compressor 20asuction port 40first heat exchanger (radiator) 50first expansion valve 60second heat exchanger (heat absorber) 70economizer heat exchanger (first economizer heat exchanger) 70aheat exchanger (second economizer heat exchanger) 72refrigerant vessel 80, 80afirst valve 82, 82abranch portion 84second expansion valve 92bypass flow path 94second valve 100air conditioner (refrigeration cycle apparatus) 110first refrigerant circuit 120second refrigerant circuit 122first sensor (pressure sensor) 122afirst sensor (temperature sensor) 124second sensor CITATION LIST PATENT LITERATURE

[0144] PTL 1: Japanese Unexamined Patent Application Publication No. 2005-49087

Examples

modification examples

(4) Modification Examples

[0121]Modification examples of the air conditioner 100 according to the embodiment described above will now be described herein. Note that it is possible to appropriately combine the modification examples described below.

modification example

(4-1) Modification Example A

[0122]In the embodiment described above, the first sensor 122 is the pressure sensor that does not measure the saturation temperature itself but measures the pressure corresponding to the saturation temperature, and the control device 8 interprets a value of the pressure measured by the first sensor 122 as the saturation temperature. However, the present disclosure is not limited to this case, and the first sensor may be a temperature sensor that directly measures the saturation temperature.

[0123]In this case, a first sensor 122a representing a temperature sensor measures the temperature of the refrigerant at a position where the refrigerant flows in a gas-liquid two-phase state. For example, as illustrated in Fig. 6, the first sensor 122a is disposed between the first valve 80 and the economizer heat exchanger 70, through which the refrigerant in the gas-liquid two-phase state flows, and measures the temperature (saturation temperature) of the refrigeran...

modification example b

(4-2) Modification Example B

[0124]In the embodiment described above, when operation of the second compressor 20 is to be stopped, the control device 8 controls the opening degree of the first valve 80 based on the measurement values of the first sensor 122 and the second sensor 124, and makes the refrigerant to be sucked into the second compressor 20 to be in a state of having a degree of superheating (state where the degree of superheating is larger than 0).

[0125]However, the present disclosure is not limited to this case, and the air conditioner 100 may not be provided with the first sensor 122 and the second sensor 124 (or may not use results of measurement by the first sensor 122 and the second sensor 124), and the control device 8 may control and reduce the opening degree of the first valve 80 to a predetermined opening degree when operation of the second compressor 20 is to be stopped to make the refrigerant to be sucked into the second compressor 20 to have a degree of superh...

TECHNICAL FIELD

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

[0002] PTL 1 (Japanese Unexamined Patent Application Publication No. 2005-49087) discloses a refrigeration cycle apparatus in which a refrigerant circuit is provided with a first compressor, a second compressor, and an economizer, a refrigerant is partially branched in the economizer from a main route in which the refrigerant discharged from the first compressor to a first flow path and heading toward a heat absorber via a radiator, and the refrigerant branched from the main route is compressed by the second compressor and discharged to the first flow path.

[0003] This refrigeration cycle apparatus can improve its capability and efficiency by using the economizer and the second compressor.SUMMARY OF INVENTION Technical Problem

[0004] In the refrigeration cycle apparatus according to PTL 1 (Japanese Unexamined Patent Application Publication No. 2005-49087), the refrigerant at high pressure, which has been cooled by the radiator, is supplied to the flow path between the economizer and a suction port of the second compressor when the second compressor is to be stopped. In such a refrigeration cycle apparatus as described above, when a temperature of outside air is low, a saturation temperature corresponding to the pressure becomes higher than the temperature of the outside air, possibly resulting in condensation of the refrigerant that has exchanged heat with the outside air in the flow path between the economizer and the suction port of the second compressor. If the refrigerant condenses at a large amount in the flow path between the economizer and the suction port of the second compressor, the second compressor may suck the liquid refrigerant that has condensed when the second compressor is started next time, and liquid compression may occur in the second compressor, possibly resulting in an abnormality in the second compressor.Solution to Problem

[0005] A refrigeration cycle apparatus according to a first aspect comprises a first refrigerant circuit, a second refrigerant circuit, and a control unit. The first refrigerant circuit includes a first compressor, a radiator, a first expansion valve, and a heat absorber. The second refrigerant circuit connects a portion between the first compressor and the radiator and a portion between the radiator and the first expansion valve. The second refrigerant circuit includes a second compressor and a first valve. The first valve is disposed on an upstream side of the second compressor. The control unit is configured to control the first compressor, the second compressor, the first expansion valve, and the first valve. The control unit is configured to close the first valve when the second compressor is to be stopped.

[0006] In the refrigeration cycle apparatus according to the first aspect, the first valve is disposed on the upstream side of the second compressor in the second refrigerant circuit, and the first valve is closed when the second compressor is to be stopped. Therefore, with this refrigeration cycle apparatus, even when the temperature of the outside air is relatively low, it is possible to suppress condensation of the refrigerant at a large amount on a suction side of the second compressor and to suppress liquid compression when the second compressor is started.

[0007] A refrigeration cycle apparatus according to a second aspect is the refrigeration cycle apparatus according to the first aspect in which the control unit is configured to close the first valve before the second compressor is stopped.

[0008] In the refrigeration cycle apparatus according to the second aspect, the second compressor is operated in a state where the first valve is closed and the refrigerant is prevented from flowing into an area downstream of the first valve. Therefore, in the refrigeration cycle apparatus according to the second aspect, even when the temperature of the outside air is relatively low, it is possible to suppress condensation of the refrigerant at a large amount on the suction side of the second compressor and to suppress liquid compression when the second compressor is started.

[0009] A refrigeration cycle apparatus according to a third aspect is the refrigeration cycle apparatus according to the first aspect or the second aspect and further includes a first sensor and a second sensor. The second compressor has a suction port. The first valve is an expansion valve. The first sensor is configured to measure a saturation temperature of the refrigerant that is present between the first valve and the suction port of the second compressor. The second sensor is configured to measure a temperature of the refrigerant to be sucked into the second compressor. The control unit is configured to control, when the second compressor is to be stopped, an opening degree of the first valve based on a result of the measurement by the first sensor and a result of the measurement by the second sensor.

[0010] Note herein that the recitation that the first sensor measures the saturation temperature includes a case where the first sensor measures a physical quantity correlated with the saturation temperature (physical quantity with which it is possible to know the saturation temperature of the refrigerant when a value of the physical quantity is known).

[0011] In the refrigeration cycle apparatus according to the third aspect, condensation of the refrigerant at a large amount on the suction side of the second compressor is easily suppressed, making it possible to make the refrigeration cycle apparatus highly reliable.

[0012] A refrigeration cycle apparatus according to a fourth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the third aspect, in which the control unit is configured to control, when the second compressor is to be stopped, the first valve so that the refrigerant to be sucked into the second compressor has a degree of superheating before the first valve is closed.

[0013] In the refrigeration cycle apparatus according to the fourth aspect, control of allowing the refrigerant to have a degree of superheating (to make the actual temperature of the refrigerant higher than the saturation temperature of the refrigerant) is performed before the second compressor is stopped. Therefore, condensation of the refrigerant at a large amount on the suction side of the second compressor is easily suppressed and it is possible to make the refrigeration cycle apparatus highly reliable.

[0014] A refrigeration cycle apparatus according to a fifth aspect is the refrigeration cycle apparatus according to the fourth aspect, in which the control unit is configured to control, when the second compressor is to be stopped, an opening degree of the first valve so that a degree of superheating of suction of the second compressor becomes equal to or higher than a predetermined degree of superheating.

[0015] In the refrigeration cycle apparatus according to the fifth aspect, it is possible to reduce the amount of the refrigerant that is present between the first valve and the suction port of the second compressor after the second compressor is stopped. Therefore, liquid compression is unlikely to occur in the second compressor and it is possible to make the refrigeration cycle apparatus highly reliable.

[0016] A refrigeration cycle apparatus according to a sixth aspect is the refrigeration cycle apparatus according to the third aspect in which the first sensor and the second sensor are disposed between the first valve and the second compressor. The first sensor is a pressure sensor.

[0017] In the refrigeration cycle apparatus according to the sixth aspect, it is possible to utilize the pressure sensor to accurately measure the saturation temperature of the refrigerant.

[0018] A refrigeration cycle apparatus according to a seventh aspect is the refrigeration cycle apparatus according to any one of the first aspect to the sixth aspect in which the second refrigerant circuit further includes a first economizer heat exchanger disposed between the radiator and the heat absorber. The first economizer heat exchanger is configured to exchange heat between the refrigerant that flows out of the radiator, is branched to the second refrigerant circuit at a branch portion, and is decompressed by the first valve, and the refrigerant flowing out of the radiator.

[0019] In the refrigeration cycle apparatus according to the seventh aspect, the first economizer heat exchanger improves the capability and efficiency of the refrigeration cycle apparatus.

[0020] A refrigeration cycle apparatus according to an eighth aspect is the refrigeration cycle apparatus according to the seventh aspect in which the branch portion is disposed between the radiator and the first economizer heat exchanger.

[0021] In the refrigeration cycle apparatus according to the eighth aspect, the refrigerant partially branches on the upstream side of the first economizer heat exchanger in a flow direction of the refrigerant in the first refrigerant circuit and flows through the second refrigerant circuit into the first economizer heat exchanger. Therefore, in the refrigeration cycle apparatus according to the eighth aspect, it is possible to improve the capability and efficiency of the refrigeration cycle apparatus while suppressing a size of the first economizer heat exchanger, compared with a case where the refrigerant flowing out of the radiator fully flows through the first refrigerant circuit into the first economizer heat exchanger.

[0022] A refrigeration cycle apparatus according to a ninth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the sixth aspect in which the first refrigerant circuit further includes a second expansion valve disposed between the radiator and the first expansion valve. The second refrigerant circuit further includes a refrigerant vessel that is configured to separate gas and liquid. The refrigerant decompressed and brought into a two-phase state by the second expansion valve flows into the refrigerant vessel. The first valve is disposed between the refrigerant vessel and the second compressor. The gas refrigerant separated in the refrigerant vessel is sucked into the second compressor.

[0023] In the refrigeration cycle apparatus according to the ninth aspect, the refrigerant vessel is used to lower the temperature of the refrigerant flowing into the heat absorber and improve the capability and efficiency of the refrigeration cycle apparatus with a relatively simple configuration.

[0024] A refrigeration cycle apparatus according to a tenth aspect is the refrigeration cycle apparatus according to the ninth aspect in which the second refrigerant circuit further includes a second economizer heat exchanger. The second economizer heat exchanger is arranged to exchange heat between the refrigerant flowing out of the radiator toward the second expansion valve and the gas refrigerant flowing out of the refrigerant vessel.

[0025] In the refrigeration cycle apparatus according to the tenth aspect, using the second economizer heat exchanger in addition to the refrigerant vessel makes it possible to further improve the capability and efficiency of the refrigeration cycle apparatus.

[0026] A refrigeration cycle apparatus according to an eleventh aspect is the refrigeration cycle apparatus according to any one of the first aspect to the tenth aspect in which the control unit is configured to open the first valve before the second compressor is started.

[0027] In the refrigeration cycle apparatus according to the eleventh aspect, by opening the first valve before the second compressor is started, it is possible to reduce differential pressure between the suction side and a discharge side of the second compressor and make it possible to bring the second compressor into a startable state.

[0028] A refrigeration cycle apparatus according to a twelfth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the eleventh aspect and further includes a bypass flow path and a second valve disposed in the bypass flow path. The bypass flow path connects the discharge side of the second compressor in the second refrigerant circuit and the suction side of the second compressor in the second refrigerant circuit. Alternatively, the bypass flow path connects a portion between the discharge port of the first compressor and the radiator in the first refrigerant circuit and the suction side of the second compressor in the second refrigerant circuit.

[0029] In the refrigeration cycle apparatus according to the twelfth aspect, opening the second valve can reduce the differential pressure between the suction side and the discharge side of the second compressor and bring the second compressor into the startable state.

[0030] A refrigeration cycle apparatus according to a thirteenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the twelfth aspect in which the refrigerant enclosed in the first refrigerant circuit and the second refrigerant circuit contains CO 2 at least partially in its components.

[0031] In the refrigeration cycle apparatus according to the thirteenth aspect, by using, as the refrigerant, a refrigerant containing at least CO 2 having a low global warming potential, it is possible to achieve the refrigeration cycle apparatus presenting a low environmental load.BRIEF DESCRIPTION OF DRAWINGS

[0032] <Fig. 1> Fig. 1 is a schematic configuration diagram of an air conditioner according to an embodiment of a refrigeration cycle apparatus. <Fig. 2> Fig. 2 is a schematic control block diagram of the air conditioner illustrated in Fig. 1. <Fig. 3A> Fig. 3A is a schematic p-h diagram of an air conditioner in which no second refrigerant circuit is present (air conditioner including only a first refrigerant circuit). <Fig. 3B> Fig. 3B is a schematic p-h diagram when cooling operation is performed in the air conditioner illustrated in Fig. 1. <Fig. 4> Fig. 4 is a flowchart for explaining control for the air conditioner with a control device when operation of a second compressor is to be stopped in the air conditioner illustrated in Fig. 1. <Fig. 5> Fig. 5 is a flowchart for explaining control for the air conditioner with the control device when operation of the second compressor is started in the air conditioner illustrated in Fig. 1. <Fig. 6> Fig. 6 is a schematic configuration diagram of an air conditioner according to Modification Example A. <Fig. 7> Fig. 7 is a schematic configuration diagram of an air conditioner according to Modification Example C. <Fig. 8A> Fig. 8A is a schematic configuration diagram of an air conditioner according to Modification Example D. <Fig. 8B> Fig. 8B is another example of the schematic configuration diagram of the air conditioner according to Modification Example D. DESCRIPTION OF EMBODIMENTS

[0033] An embodiment of a refrigeration cycle apparatus according to the present disclosure will now be described herein with reference to the accompanying drawings.(1) Overall Configuration

[0034] An overall configuration of an air conditioner 100 of an embodiment of the refrigeration cycle apparatus according to the present disclosure will now be described herein with reference to Fig. 1. Fig. 1 is a schematic configuration diagram of the air conditioner 100.

[0035] Note that the refrigeration cycle apparatus according to the present disclosure is not limited to the air conditioner, and may be an apparatus of another type, which uses a vapor compression refrigeration cycle to perform cooling or heating of a target for which a temperature is to be adjusted (medium such as air or water).

[0036] The air conditioner 100 is an apparatus that uses a vapor compression refrigeration cycle to cool or heat air in a room in a building, for example, representing a target to which the temperature is to be adjusted, to perform cooling or heating for the room in the building, for example. However, the air conditioner 100 may be an apparatus dedicated for cooling.

[0037] As illustrated in Fig. 1, the air conditioner 100 mainly includes a first refrigerant circuit 110 and a second refrigerant circuit 120. The refrigerant circuits 110, 120 in the air conditioner 100 are filled with, but not limited to, a refrigerant containing carbon dioxide (CO 2 ) at least partially in its components. The refrigerant circuits 110, 120 in the air conditioner 100 may be filled with a refrigerant of a single type that is carbon dioxide. Carbon dioxide serves as a refrigerant that has a low global warming potential, a low environmental load, and no toxicity or flammability, and is thus highly safe.

[0038] As illustrated in Fig. 1, the first refrigerant circuit 110 mainly includes a first compressor 10, a first heat exchanger 40, a first expansion valve 50, and a second heat exchanger 60. In the present embodiment, for example, the first compressor 10, the first heat exchanger 40, and the first expansion valve 50 are mounted in a heat source unit 2 disposed outdoors such as on a rooftop of the building, and the second heat exchanger 60 is mounted in a utilization unit 4 disposed in a space that is a target of air conditioning or near the space that is the target of air conditioning. In the air conditioner 100, the heat source unit 2 and the utilization unit 4 are coupled to each other by refrigerant connection pipes 6 to configure the first refrigerant circuit 110.

[0039] The second refrigerant circuit 120 connects a portion between the first compressor 10 and a radiator (first heat exchanger 40) in the first refrigerant circuit 110 and a portion between the radiator (first heat exchanger 40) and the first expansion valve 50 in the first refrigerant circuit 110 to each other, in the first refrigerant circuit 110 in which the air conditioner 100 is in a state of performing cooling operation (in other words, in a state where a switching mechanism 30 connects the pipes to allow the first heat exchanger 40 to function as the radiator for the refrigerant and the second heat exchanger 60 to function as a heat absorber (evaporator) for the refrigerant).

[0040] The second refrigerant circuit 120 includes a second compressor 20. Furthermore, the second refrigerant circuit 120 includes a first valve 80 and an economizer heat exchanger 70 disposed between the first heat exchanger 40 and the second heat exchanger 60 in the first refrigerant circuit 110. Note that the economizer heat exchanger 70 is disposed to straddle the first refrigerant circuit 110 and the second refrigerant circuit 120.

[0041] The second refrigerant circuit 120 is used to improve a refrigeration cycle in performance during the cooling operation by the air conditioner 100. Specific description will be given below.

[0042] When assuming that no second refrigerant circuit 120 is present (in other words, assuming that only the first refrigerant circuit 110 is provided), as the CO 2 refrigerant (carbon dioxide refrigerant) used in the air conditioner 100 has a relatively low refrigeration effect due to its characteristics (see a p-h diagram illustrated in Fig. 3A), an issue arises that the first compressor 10 is increased in size for acquiring high capability with only the first refrigerant circuit 110.

[0043] In contrast, in the air conditioner 100 according to the present disclosure, the second refrigerant circuit 120 is provided, and, in the economizer heat exchanger 70, the refrigerant flowing toward the second heat exchanger 60 (heat absorber) in the first refrigerant circuit 110 and the refrigerant flowing toward the second compressor 20 in the second refrigerant circuit 120 exchange heat with each other, and the refrigerant flowing toward the second heat exchanger 60 (heat absorber) in the first refrigerant circuit 110 is further cooled. Therefore, improvements in capability and performance of the air conditioner 100 are achieved, compared with a case where only the first refrigerant circuit 110 is present (see the p-h diagram illustrated in Fig. 3B).(2) Detailed Configuration

[0044] The air conditioner 100 includes a pressure equalization mechanism 90, a first fan 42, a second fan 62, and a control device 8, in addition to the first refrigerant circuit 110 and the second refrigerant circuit 120.

[0045] Various configurations of the air conditioner 100 will now be described herein in detail.(2-1) First Refrigerant Circuit

[0046] The first refrigerant circuit 110 mainly includes the first compressor 10, the switching mechanism 30, the first heat exchanger 40, the first expansion valve 50, and the second heat exchanger 60, which are connected each other by the pipes.

[0047] The first compressor 10 is a compressor that is variable in operating capacity and that includes an inverter-control-type motor. In the present embodiment, the first compressor 10 is a scroll compressor. However, the type of the first compressor 10 may be another type of compressor. The first compressor 10 sucks the refrigerant from a suction port 10a and discharges the refrigerant from a discharge port 10b.

[0048] The switching mechanism 30 is a mechanism that switches a state of the first refrigerant circuit 110 between a first state (cooling operation state) and a second state (heating operation state). When the first refrigerant circuit 110 is in the first state (see solid lines in the switching mechanism 30 illustrated in Fig. 1), the first heat exchanger 40 functions as the radiator for the refrigerant, and the second heat exchanger 60 functions as the heat absorber (evaporator) for the refrigerant. When the first refrigerant circuit 110 is in the second state (see broken lines in the switching mechanism 30 illustrated in Fig. 1), the first heat exchanger 40 functions as the evaporator for the refrigerant, and the second heat exchanger 60 functions as the radiator for the refrigerant.

[0049] The switching mechanism 30 is a four-way switching valve. However, the switching mechanism 30 is not limited to the four-way switching valve, and may include a plurality of pipes and a plurality of valves to achieve those connecting states of the pipes as described below.

[0050] To set the state of the first refrigerant circuit 110 into the first state, the switching mechanism 30 couples the discharge port 10b of the first compressor 10 and one end side of the first heat exchanger 40 to each other, and couples the suction port 10a of the first compressor 10 and one end side of the second heat exchanger 60 to each other (see the solid lines in the switching mechanism 30 illustrated in Fig. 1). Furthermore, to set the state of the first refrigerant circuit 110 into the second state, the switching mechanism 30 couples the discharge port 10b of the first compressor 10 and the one end side of the second heat exchanger 60 to each other, and couples the suction port 10a of the first compressor 10 and the one end side of the first heat exchanger 40 to each other (see the broken lines in the switching mechanism 30 illustrated in Fig. 1).

[0051] Note that, when the air conditioner 100 is an apparatus dedicated for cooling, the air conditioner 100 may not include the switching mechanism 30.

[0052] In the first heat exchanger 40, air (heat source air) that the first fan 42 described later supplies and the refrigerant exchange heat with each other. When the state of the first refrigerant circuit 110 is the first state, the first heat exchanger 40 functions as the radiator for the refrigerant, and the refrigerant is cooled by the heat source air in the first heat exchanger 40. When the state of the first refrigerant circuit 110 is the second state, the first heat exchanger 40 functions as the heat absorber (evaporator) for the refrigerant, and the refrigerant is heated by the heat source air in the first heat exchanger 40. The first heat exchanger 40 is, for example, a fin-and-tube heat exchanger including many heat transfer tubes and many fins.

[0053] Note that the first heat exchanger 40 is not limited to a heat exchanger in which the heat source air and the refrigerant exchange heat with each other. The first heat exchanger 40 may be a heat exchanger in which a medium such as water serving as a heat source and the refrigerant exchange heat with each other.

[0054] The economizer heat exchanger 70 that is an example of a first economizer heat exchanger is disposed between the first heat exchanger 40 and the second heat exchanger 60 in the first refrigerant circuit 110, more specifically, between the first heat exchanger 40 and the first expansion valve 50 in the first refrigerant circuit 110. Furthermore, the economizer heat exchanger 70 is disposed between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120. During the cooling operation, the economizer heat exchanger 70 exchanges heat between the refrigerant that flows out of the radiator (first heat exchanger 40), is branched to the second refrigerant circuit 120 at a branch portion 82, and is decompressed by the first valve 80 described later and the refrigerant that flows out of the radiator (first heat exchanger 40), passes through the economizer heat exchanger 70, and flows toward the heat absorber (second heat exchanger 60). As a result, during the cooling operation, the refrigerant that has been cooled in the radiator (first heat exchanger 40) and that flows toward the heat absorber (second heat exchanger 60) (see a point c and a point d illustrated in Fig. 3B) is further cooled by the economizer heat exchanger 70 (see a point h illustrated in Fig. 3B). Note that the branch portion 82 is disposed between the first heat exchanger 40 functioning as the radiator during the cooling operation and the economizer heat exchanger 70.

[0055] The first expansion valve 50 decompresses the refrigerant flowing between the first heat exchanger 40 and the second heat exchanger 60. The first expansion valve 50 is disposed between the first heat exchanger 40 and the second heat exchanger 60, more specifically, between the economizer heat exchanger 70 and the second heat exchanger 60. The first expansion valve 50 is, for example, an electronic expansion valve that is variable in opening degree.

[0056] In the second heat exchanger 60, the refrigerant and the air in the space that is the target of air conditioning exchange heat with each other. The second heat exchanger 60 is housed in a non-illustrated housing, to which the air in the air conditioning target space of the target of air conditioning is supplied by the second fan 62 disposed in the housing. In the second heat exchanger 60, the air in the air conditioning target space, which is supplied by the second fan 62, and the refrigerant exchange heat with each other. When the state of the first refrigerant circuit 110 is the first state, the second heat exchanger 60 functions as the heat absorber for the refrigerant, and the air in the air conditioning target space is cooled by the refrigerant in the second heat exchanger 60. When the state of the first refrigerant circuit 110 is the second state, the second heat exchanger 60 functions as the radiator for the refrigerant, and the air in the space that is the target of air conditioning is heated by the refrigerant in the second heat exchanger 60. The second heat exchanger 60 is, for example, a fin-and-tube heat exchanger including many heat transfer tubes and many fins.(2-2) Second Refrigerant Circuit

[0057] The second refrigerant circuit 120 includes the second compressor 20. Furthermore, the air conditioner 100 according to the present embodiment includes the economizer heat exchanger 70 that is an example of the first economizer heat exchanger and the first valve 80. The first valve 80 is disposed on the upstream side of the second compressor 20 in a flow direction of the refrigerant in the second refrigerant circuit 120. The first valve 80 is disposed between the branch portion 82 at which the second refrigerant circuit 120 branches from the first refrigerant circuit 110 and the economizer heat exchanger 70.

[0058] In the present embodiment, the first valve 80 is an electronic expansion valve that is variable in opening degree.

[0059] The second refrigerant circuit 120 is mainly used during the cooling operation (second compressor 20 is operated during the cooling operation), and is not used during heating operation. In other words, basically, the refrigerant does not flow through the second refrigerant circuit 120 during the heating operation.

[0060] The second compressor 20 is preferably a compressor that is variable in operating capacity and that includes an inverter-control-type motor. In the present embodiment, the second compressor 20 is a rotary compressor (including a swing compressor). However, the type of the second compressor 20 is not limited to the rotary compressor, and may be another type of compressor. The second compressor 20 discharges the refrigerant sucked from a suction port 20a from a discharge port 20b.

[0061] The economizer heat exchanger 70 is, for example, a double-pipe-type heat exchanger or a plate-type heat exchanger. The economizer heat exchanger 70 is disposed between the first heat exchanger 40 functioning as the radiator during the cooling operation and the second heat exchanger 60 functioning as the heat absorber during the cooling operation. As described above, during the cooling operation, the economizer heat exchanger 70 exchanges heat between the refrigerant that flows out of the radiator (first heat exchanger 40), is branched to the second refrigerant circuit 120 at the branch portion 82, and is decompressed by the first valve 80 and the refrigerant that flows out of the radiator (first heat exchanger 40), passes through the economizer heat exchanger 70, and will flow toward the heat absorber (second heat exchanger 60). The refrigerant that has been decompressed by the first valve 80, has passed through the economizer heat exchanger 70, and has cooled the refrigerant flowing toward the heat absorber (second heat exchanger 60) is brought into a gas state, and is sucked into the second compressor 20 (see a point f illustrated in the p-h diagram illustrated in Fig. 3B).(2-3) Pressure Equalization Mechanism

[0062] The pressure equalization mechanism 90 is a mechanism for achieving pressure equalization between pressure on a discharge side of the second compressor 20 and pressure on a suction side of the second compressor 20.

[0063] The pressure equalization mechanism 90 includes a bypass flow path 92 and a second valve 94. Furthermore, preferably, the pressure equalization mechanism 90 includes a check valve 96.

[0064] The check valve 96 is provided between the discharge port 20b of the second compressor 20 and a connecting portion of the second refrigerant circuit 120 and the first refrigerant circuit 110 (connecting portion between the second refrigerant circuit 120 and a pipe connecting the discharge port 10b of the first compressor 10 and the switching mechanism 30 to each other). The check valve 96 prevents the refrigerant from flowing from a side where the connecting portion of the second refrigerant circuit 120 and the first refrigerant circuit 110 to a side where the discharge port 20b of the second compressor 20.

[0065] The bypass flow path 92 is a flow path that connects the discharge side of the second compressor 20 in the second refrigerant circuit 120 and the suction side of the second compressor 20 in the second refrigerant circuit 120. Specifically, the bypass flow path 92 connects a portion between the discharge port 20b of the second compressor 20 and the check valve 96 and the suction side of the second compressor 20 in the second refrigerant circuit 120.

[0066] Note that, although illustrations are omitted, the bypass flow path 92 may be a flow path that connects a portion in the first refrigerant circuit 110 which is located between the discharge port 10b of the first compressor 10 and the radiator (first heat exchanger 40) when the air conditioner 100 performs the cooling operation and the suction side of the second compressor 20. Specifically, the bypass flow path 92 may be a flow path that connects a pipe connecting a portion between the discharge port 10b of the first compressor 10 and the switching mechanism 30 and the suction side of the second compressor 20. Furthermore, the bypass flow path 92 may be a flow path that connects the suction side of the second compressor 20 and a portion between the connecting portion of the second refrigerant circuit 120 to the first refrigerant circuit 110 (connecting portion of the second refrigerant circuit 120 to a pipe connecting a portion between the discharge port of the first compressor 10 and the switching mechanism 30) and the check valve 96.

[0067] The second valve 94 is a valve disposed in the bypass flow path 92. The second valve 94 may be an electromagnetic valve in which only opening and closing are controllable, or may be an electrically-operated valve that is variable in opening degree.

[0068] The second valve 94 is controlled to be opened by the control device 8 described later when it is intended to achieve pressure equalization between the discharge side of the second compressor 20 and the suction side of the second compressor 20. Specific control for the second valve 94 by the control device 8 will be described later.(2-4) First Fan and Second Fan

[0069] The first fan 42 is housed inside a housing (illustrations are omitted) of the heat source unit 2, which houses, for example, the first compressor 10, the second compressor 20, the switching mechanism 30, the first heat exchanger 40, the economizer heat exchanger 70, the first expansion valve 50, the first valve 80, and the second valve 94. The first fan 42 supplies the heat source air to the first heat exchanger 40 in the first refrigerant circuit 110 and urges exchanging of heat between the refrigerant flowing through the first heat exchanger 40 and the heat source air. Although the type of the first fan 42 is not limited, the first fan 42 is, for example, a propeller fan.

[0070] The second fan 62 is housed in the housing (illustrations are omitted) of the utilization unit 4, which houses the second heat exchanger 60 and the like. The second fan 62 sucks the air from the space that is the target of air conditioning, supplies the sucked air to the second heat exchanger 60 in the first refrigerant circuit 110, and urges exchanging of heat between the refrigerant flowing through the second heat exchanger 60 and the sucked air from the target of air conditioning. Although the type of the second fan 62 is not limited, the second fan 62 is, for example, a cross-flow fan.(2-5) Control Device

[0071] The control device 8 that is an example of a control unit is a device that controls operation of the air conditioner 100.

[0072] The control device 8 is electrically coupled to the first compressor 10, the second compressor 20, the switching mechanism 30, the first expansion valve 50, the first valve 80, the second valve 94, the first fan 42, and the second fan 62 (see Fig. 2). The control device 8 controls operation of these devices that are electrically coupled to each other to control operation of the air conditioner 100.

[0073] Furthermore, the air conditioner 100 is provided with various sensors (a temperature sensor for measuring a temperature of the refrigerant, a pressure sensor for measuring the pressure of the refrigerant, and a temperature sensor for measuring a temperature in the space that is the target of air conditioning and the like), and the control device 8 is electrically coupled to these sensors. For example, as illustrated in Fig. 1, the air conditioner 100 is provided with a second sensor (pressure sensor) 122 that measures suction pressure of the second compressor 20 and a second sensor (temperature sensor) 124 that measures a suction temperature of the second compressor 20. The first sensor 122 and the second sensor 124 are disposed between the economizer heat exchanger 70 and the suction port 20a of the second compressor 20, and, for example, near the suction port 20a of the second compressor 20. The control device 8 is electrically coupled to the first sensor 122 and the second sensor 124, and acquires results of measurement by the first sensor 122 and the second sensor 124. The control device 8 interprets the pressure measured by the first sensor 122 as a saturation temperature of the refrigerant.

[0074] In the present embodiment, a non-illustrated electric circuit and a non-illustrated control board mounted on the heat source unit 2 and a non-illustrated electric circuit and a non-illustrated control board mounted on the utilization unit 4 are communicably coupled to each other, and cooperate with each other to function as the control device 8. Note that, in Fig. 1, for purposes of convenience, the control device 8 is illustrated at a position separated from the heat source unit 2 and the utilization unit 4.

[0075] In the present embodiment, the control device 8 includes a control computation device and a memory device. As the control computation device, it is possible to use a processor such as a central processing unit (CPU). The control computation device reads a program stored in the memory device and controls operation of the air conditioner 100 according to the program.(2-5-1) Heating Operation

[0076] To cause the air conditioner 100 to perform the heating operation, the control device 8 controls operation of the switching mechanism 30 to set the state of the first refrigerant circuit 110 into the second state, and operates the first compressor 10. The control device 8 controls a number of rotations of the motor in the first compressor 10 and the opening degree of the first expansion valve 50 based on results of measurement by the various sensors (the temperature sensor for measuring the temperature of the refrigerant, the pressure sensor for measuring the pressure of the refrigerant, and the temperature sensor for measuring the temperature in the space that is the target of air conditioning, for example) disposed at various positions in the air conditioner 100. Furthermore, the control device 8 operates motors of the first fan 42 and the second fan 62 respectively at predetermined numbers of rotations.

[0077] Note that, during the heating operation, the control device 8 controls the first valve 80 and the second valve 94 in closed states, and does not operate the second compressor 20.(2-5-2) Cooling Operation

[0078] To cause the air conditioner 100 to perform the cooling operation, the control device 8 controls operation of the switching mechanism 30 to set the state of the first refrigerant circuit 110 into the first state, and, normally, operates the first compressor 10 and the second compressor 20. The control device 8 controls the numbers of rotations of the motors in the first compressor 10 and the second compressor 20 and the opening degrees of the first expansion valve 50 and the first valve 80 based on results of measurement by the various sensors (the temperature sensor for measuring the temperature of the refrigerant, the pressure sensor for measuring the pressure of the refrigerant, and the temperature sensor for measuring the temperature in the space that is the target of air conditioning, for example) disposed at the various positions on the air conditioner 100. Furthermore, the control device 8 operates the motors of the first fan 42 and the second fan 62 respectively at predetermined numbers of rotations.

[0079] Furthermore, when a load of the air conditioner 100 has decreased and it is assumed that operating only the first compressor 10 to perform the cooling operation is more efficient, the control device 8 stops operation of the second compressor 20 and operates only the first compressor 10 to perform the cooling operation. When the air conditioner 100 performs this operation, the control device 8 closes the first valve 80, as will be described later. Then, the control device 8 controls the number of rotations of the motor in the first compressor 10 and the opening degree of the first expansion valve 50 based on results of measurement by the various sensors (the temperature sensor for measuring the temperature of the refrigerant, the pressure sensor for measuring the pressure of the refrigerant, and the temperature sensor for measuring the temperature in the space that is the target of air conditioning, for example) disposed at the various positions in the air conditioner 100. Furthermore, the control device 8 operates the motors of the first fan 42 and the second fan 62 respectively at predetermined numbers of rotations.

[0080] Note that, during the cooling operation, the control device 8 controls the second valve 94 to be in the closed state.(2-5-3) Control when Operation of Second Compressor is to be stopped

[0081] In a case where operation of the second compressor 20 is stopped while the first valve 80 is opened, the refrigerant cooled by the first heat exchanger 40 functioning as the radiator flows into a portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 (hereinafter this portion will be referred to as a first portion 125), possibly increasing the pressure in the first portion 125. In a case where the refrigerant at high pressure, which has been cooled by the first heat exchanger 40, is present in the first portion 125, the temperature of outside air is relatively low so that the saturation temperature of the refrigerant, which corresponds to the pressure of the refrigerant that is present in the first portion 125, is higher than the temperature of the outside air, the refrigerant in the first portion 125 exchanges heat with the outside air, possibly resulting in condensation of the refrigerant in the first portion 125. When an amount of the condensation is large, the second compressor 20 may suck the liquid refrigerant that has condensed, when operation of the second compressor 20 is started, and liquid compression occurs, possibly resulting in an abnormality in the second compressor 20.

[0082] Therefore, in the air conditioner 100, when the second compressor 20 is to be stopped, the control device 8 closes the first valve 80 to suppress an inflow to the first portion 125. Preferably, the control device 8 closes the first valve 80 to suppress the inflow to the first portion 125 before the second compressor 20 is stopped.

[0083] An example of control for the air conditioner 100 by the control device 8 when the second compressor 20 is to be stopped will now be described herein with reference to a flowchart illustrated in Fig. 4.

[0084] A case where, in a state where the air conditioner 100 operates both the first compressor 10 and the second compressor 20 to perform the cooling operation, the load of the air conditioner 100 decreases, the second compressor 20 is stopped, and only the first compressor 10 is operated to continue the cooling operation will now be described herein as an example. However, the control when operation of the second compressor 20 is to be stopped, as will be described herein, may also be performed when the cooling operation of the air conditioner 100 is to be stopped (when operation of both the first compressor 10 and the second compressor 20 is to be stopped) in a state where both the first compressor 10 and the second compressor 20 are operated to perform the cooling operation.

[0085] The control device 8 determines whether or not to stop operation of the second compressor 20 in accordance with an operation state of the air conditioner 100 during the cooling operation in which both the first compressor 10 and the second compressor 20 are operated (step S1).

[0086] When it is determined to stop operation of the second compressor 20 at step S1, the control device 8 preferably controls the opening degree of the first valve 80 based on a result of measurement by the first sensor 122 and a result of measurement by the second sensor 124 while operation of the second compressor 20 is continued, instead of immediately causing the first valve 80 to be closed (step S2). For example, the control device 8 controls the opening degree of the first valve 80 based on a value acquired by subtracting a saturation temperature derived from the suction pressure of the second compressor 20, which is measured by the first sensor 122, from the temperature of the refrigerant to be sucked into the second compressor 20, which is measured by the second sensor 124. The control device 8 interprets the result of the measurement by the first sensor 122 as the saturation temperature, for example, based on a table indicating a relationship between the pressure and the saturation temperature of the refrigerant, which is stored in the memory unit of the control device 8, or based on a formula indicating the relationship between the pressure and the saturation temperature of the refrigerant, which is stored in the memory unit of the control device 8.

[0087] Specifically, the control device 8 controls the opening degree of the first valve 80 so that the value acquired by subtracting the saturation temperature derived from the suction pressure of the second compressor 20, which is measured by the first sensor 122, from the temperature of the refrigerant to be sucked into the second compressor 20, which is measured by the second sensor 124, to be at least larger than zero (in other words, to allow the refrigerant to be sucked into the second compressor 20 to have a degree of superheating).

[0088] More preferably, when the second compressor 20 is to be stopped, the control device 8 controls the opening degree of the first valve 80 to make a degree of superheating of suction of the second compressor 20 to be equal to or higher than a predetermined degree of superheating. For example, it is assumed that, during the cooling operation in which both the first compressor 10 and the second compressor 20 are operated, the control device 8 controls the opening degree of the first valve 80 to make the degree of superheating of suction of the second compressor 20 to be α (≥0). In this case, when the second compressor 20 is to be stopped, the control device 8 controls the opening degree of the first valve 80 to make the degree of superheating of suction of the second compressor 20 to be equal to or higher than a predetermined degree of superheating, which is higher than α. In other words, when the second compressor 20 is to be stopped, the control device 8 preferably controls the opening degree of the first valve 80 to be smaller than an opening degree when both the first compressor 10 and the second compressor 20 are used to perform the cooling operation (instead of immediately causing the first valve 80 to be closed fully).

[0089] Then, the control device 8 maintains the state where the refrigerant to be sucked by the second compressor 20 has the degree of superheating (preferably, a state where the refrigerant has the predetermined degree of superheating) for a predetermined time, and then closes the first valve 80 fully (step S3).

[0090] Then, the control device 8 preferably allows operation of the second compressor 20 to be continued for a predetermined time after the first valve 80 is closed (step S4), and then stops the second compressor 20 (step S5).

[0091] Note that, since such a state has been attained that there has been a pressure difference between the discharge side and the suction side of the second compressor 20, the second valve 94 disposed in the bypass flow path 92 may at this point in time be opened to achieve pressure equalization between the discharge side and the suction side of the second compressor 20 (step S5). Although, when such control is performed as described above, the refrigerant at high pressure flows into the suction side of the second compressor 20, the refrigerant that flows in is small in weight, since the refrigerant that flows in is the refrigerant that has not yet cooled by the first heat exchanger 40, i.e., that is relatively low in density.

[0092] When the second valve 94 is to be opened in this manner, the control device 8 determines at step S7 whether or not the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated. Whether or not the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated is determined by, for example, comparing the pressure measured by the pressure sensor (not illustrated) provided on the discharge side of the second compressor 20 with the pressure measured by the first sensor 122. Note that, as for the method for determining whether or not the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated, a method that uses a result of measurement of the pressure by the pressure sensor may not be used. For example, the control device 8 may determine whether or not the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated based on a time from when the second valve 94 is opened. Specifically, the control device 8 determines that the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated when a predetermined time has elapsed after the second valve 94 is opened.

[0093] When it is determined at step S7 that the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated, the control device 8 closes the second valve 94 (step S8).

[0094] Note that pressure equalization between the discharge side of the second compressor 20 and the suction side of the second compressor 20 is preferably performed when the second compressor 20 is a rotary compressor. One reason for this preference is that, due to the characteristics of the rotary compressor, refrigerating machine oil in the second compressor 20 may flow out of the suction port 20a of the second compressor 20, when such a state continues that the pressure on the discharge side is higher than the pressure on the suction side.(2-5-4) Control when Second Compressor is to be started

[0095] Control for operation of the air conditioner 100 by the control device 8 when operation of the second compressor 20 is to be started will now be described herein. As an example, for a case where operation of the second compressor 20 is to be started according to an increase in load when only the first compressor 10 is operated to perform the cooling operation, control when operation of the second compressor 20 is to be started will now be described herein with reference to a flowchart illustrated in Fig. 5.

[0096] The control device 8 determines whether or not to start operation of the second compressor 20 in accordance with an operation state of the air conditioner 100 during the cooling operation in which only the first compressor 10 is operated, and the processing proceeds to step S12 when it is determined to start operation of the second compressor 20 (step S1).

[0097] At step S12, the control device 8 opens the first valve 80.

[0098] Note that, while the cooling operation is performed by only operating the first compressor 10, there may be differential pressure between the discharge side of the second compressor 20 and the suction side of the second compressor 20. When no such pressure equalization by the pressure equalization mechanism 90 as described at step S6 to step S8 in the flowchart illustrated in Fig. 4 is performed, there is a possibility that there is large differential pressure between the discharge side and the suction side of the second compressor 20.

[0099] Therefore, the control device 8 preferably opens the first valve 80 at step S12, and then, waits for a predetermined time in this state. When the first valve 80 is opened, the pressure on the suction side of the second compressor 20 becomes high accordingly, and pressure equalization is achieved between the discharge side and the suction side of the second compressor 20, allowing the second compressor 20 to be in an operation-ready state.

[0100] Then, after the predetermined time has elapsed since when the first valve 80 has been opened (for example, after a predetermined time has elapsed, at which it is assumed that a decrease in pressure difference between the discharge side and the suction side of the second compressor 20 is suppressed), the control device 8 starts operation of the second compressor 20 (step S13). Alternatively, the control device 8 may use, as a trigger, that a difference between a measurement value of the non-illustrated pressure sensor provided on the discharge side of the second compressor 20 and a measurement value of the first sensor 122 becomes equal to or smaller than a predetermined value to start operation of the second compressor 20.

[0101] Then, to perform the cooling operation in which the first compressor 10 and the second compressor 20 are operated, the control device 8 starts controlling of the opening degree of the first valve 80 in addition to controlling of the numbers of rotations of the first compressor 10 and the second compressor 20 and the opening degree of the first expansion valve 50 (step S14).(3) Features

[0102] (3-1) The air conditioner 100 includes the first refrigerant circuit 110, the second refrigerant circuit 120, and the control device 8 serving as the example of the control unit. The first refrigerant circuit 110 includes the first compressor 10, the first heat exchanger 40 functioning as the radiator during the cooling operation, the first expansion valve 50, and the second heat exchanger 60 functioning as the heat absorber during the cooling operation. The second refrigerant circuit 120 connects a portion between the first compressor 10 and the first heat exchanger 40 and a portion between the first heat exchanger 40 and the first expansion valve 50. The second refrigerant circuit 120 includes the second compressor 20 and the first valve 80. The first valve 80 is disposed on the upstream side of the second compressor 20. The control device 8 controls the first compressor 10, the second compressor 20, the first expansion valve 50, and the first valve 80. The control device 8 closes the first valve 80 when the second compressor 20 is to be stopped.

[0103] In the air conditioner 100, the first valve 80 is disposed on the upstream side of the second compressor 20 in the second refrigerant circuit 120, and the first valve 80 is closed when the second compressor 20 is to be stopped. Therefore, with this air conditioner 100, even when the temperature of the outside air is relatively low, it is possible to suppress condensation of the refrigerant at a large amount on the suction side of the second compressor 20 and to suppress liquid compression when the second compressor 20 is started.

[0104] (3-2) In the air conditioner 100, the control device 8 closes the first valve 80 before the second compressor 20 is stopped.

[0105] In this air conditioner 100, the second compressor 20 is operated in a state where the first valve 80 is closed and the refrigerant is prevented from flowing into an area downstream of the first valve 80. Therefore, in this air conditioner 100, even when the temperature of the outside air is relatively low, it is possible to suppress condensation of the refrigerant at a large amount on the suction side of the second compressor 20 and to suppress liquid compression when the second compressor 20 is started.

[0106] (3-3) The air conditioner 100 includes the first sensor 122 and the second sensor 124. The second compressor 20 has the suction port 20a. The first valve 80 is an expansion valve. The first sensor 122 measures the saturation temperature of the refrigerant that is present between the first valve 80 and the suction port 20a of the second compressor 20. The second sensor 124 measures the temperature of the refrigerant to be sucked into the second compressor 20. The control device 8 controls, when the second compressor 20 is to be stopped, the opening degree of the first valve 80 based on a result of the measurement by the first sensor 122 and a result of the measurement by the second sensor 124.

[0107] Note herein that the description that the first sensor 122 measures the saturation temperature includes a case where the first sensor 122 measures a physical quantity correlated with the saturation temperature (physical quantity with which it is possible to know the saturation temperature of the refrigerant when a value of the physical quantity is known), in addition to an aspect of measuring the saturation temperature itself.

[0108] Specifically, in the present embodiment, the first sensor 122 and the second sensor 124 are disposed between the first valve 80 and the suction port 20a of the second compressor 20. Then, the first sensor 122 does not measure the saturation temperature of the refrigerant itself, but measures the pressure corresponding to the saturation temperature of the refrigerant. The control device 8 interprets the pressure measured by the first sensor 122 as the saturation temperature.

[0109] With the air conditioner 100, condensation of the refrigerant at a large amount on the suction side of the second compressor 20 is easily suppressed, making it possible to make the air conditioner 100 highly reliable.

[0110] (3-4) In the air conditioner 100, the control device 8 controls, when the second compressor 20 is to be stopped, the first valve 80 so that the refrigerant to be sucked into the second compressor 20 has a degree of superheating before the first valve 80 is closed.

[0111] Especially, the control device 8 controls, when the second compressor 20 is to be stopped, the opening degree of the first valve 80 so that a degree of superheating of suction of the second compressor 20 becomes equal to or higher than a predetermined degree of superheating.

[0112] With this air conditioner 100, it is possible to reduce the amount of the refrigerant that is present between the first valve 80 and the suction port 20a of the second compressor 20 after the second compressor 20 is stopped, and liquid compression is unlikely to occur in the second compressor 20, presenting high reliability.

[0113] (3-5) In the air conditioner 100, the second refrigerant circuit 120 includes the economizer heat exchanger 70 disposed between the first heat exchanger 40 and the second heat exchanger 60. During the cooling operation, the economizer heat exchanger 70 exchanges heat between the refrigerant that flows out of the first heat exchanger 40 functioning as the heat absorber, is branched to the second refrigerant circuit 120 at the branch portion 82, and is decompressed by the first valve 80, and the refrigerant flowing out of the first heat exchanger 40.

[0114] With the air conditioner 100, the economizer heat exchanger 70 improves the capability and efficiency of the air conditioner 100.

[0115] (3-6) In the air conditioner 100, the branch portion 82 is disposed between the first heat exchanger 40 functioning as the radiator during the cooling operation and the economizer heat exchanger 70.

[0116] In this air conditioner 100, the refrigerant partially branches on the upstream side of the economizer heat exchanger 70 in the flow direction of the refrigerant in the first refrigerant circuit 110 and flows through the second refrigerant circuit 120 into the economizer heat exchanger 70. Therefore, in this air conditioner 100, it is possible to improve the capability and efficiency of the air conditioner 100 while suppressing the size of the economizer heat exchanger 70, compared with a case where the refrigerant flowing out of the first heat exchanger 40 fully flows through the first refrigerant circuit 110 into the economizer heat exchanger 70.

[0117] (3-7) The air conditioner 100 includes the bypass flow path 92 and the second valve 94 disposed in the bypass flow path 92. The bypass flow path 92 connects the discharge side of the second compressor 20 in the second refrigerant circuit 120 and the suction side of the second compressor 20 in the second refrigerant circuit 120. Alternatively, the bypass flow path 92 connects a portion between the discharge port 10b of the first compressor 10 and the first heat exchanger 40 functioning as the radiator during refrigerant operation in the first refrigerant circuit 110 and the suction side of the second compressor 20 in the second refrigerant circuit 120.

[0118] In this air conditioner 100, opening the second valve 94 can reduce the differential pressure between the suction side and the discharge side of the second compressor 20 and bring the second compressor 20 into the startable state.

[0119] (3-8) In the air conditioner 100, the refrigerant enclosed in the first refrigerant circuit 110 and the second refrigerant circuit 120 contains CO 2 at least partially in its components.

[0120] In this air conditioner 100, by using, as the refrigerant, a refrigerant containing at least CO 2 having a small global warming potential, it is possible to achieve the air conditioner 100 presenting a low environmental load.(4) Modification Examples

[0121] Modification examples of the air conditioner 100 according to the embodiment described above will now be described herein. Note that it is possible to appropriately combine the modification examples described below.(4-1) Modification Example A

[0122] In the embodiment described above, the first sensor 122 is the pressure sensor that does not measure the saturation temperature itself but measures the pressure corresponding to the saturation temperature, and the control device 8 interprets a value of the pressure measured by the first sensor 122 as the saturation temperature. However, the present disclosure is not limited to this case, and the first sensor may be a temperature sensor that directly measures the saturation temperature.

[0123] In this case, a first sensor 122a representing a temperature sensor measures the temperature of the refrigerant at a position where the refrigerant flows in a gas-liquid two-phase state. For example, as illustrated in Fig. 6, the first sensor 122a is disposed between the first valve 80 and the economizer heat exchanger 70, through which the refrigerant in the gas-liquid two-phase state flows, and measures the temperature (saturation temperature) of the refrigerant flowing through this location.(4-2) Modification Example B

[0124] In the embodiment described above, when operation of the second compressor 20 is to be stopped, the control device 8 controls the opening degree of the first valve 80 based on the measurement values of the first sensor 122 and the second sensor 124, and makes the refrigerant to be sucked into the second compressor 20 to be in a state of having a degree of superheating (state where the degree of superheating is larger than 0).

[0125] However, the present disclosure is not limited to this case, and the air conditioner 100 may not be provided with the first sensor 122 and the second sensor 124 (or may not use results of measurement by the first sensor 122 and the second sensor 124), and the control device 8 may control and reduce the opening degree of the first valve 80 to a predetermined opening degree when operation of the second compressor 20 is to be stopped to make the refrigerant to be sucked into the second compressor 20 to have a degree of superheating (state where the degree of superheating is larger than 0).(4-3) Modification Example C

[0126] In the embodiment described above, although the branch portion 82 at which branching occurs from the first refrigerant circuit 110 to the second refrigerant circuit 120 is disposed between the first heat exchanger 40 functioning as the radiator during the cooling operation and the economizer heat exchanger 70, the present disclosure is not limited to such an aspect.

[0127] As illustrated in Fig. 7, a branch portion 82a may be disposed between the economizer heat exchanger 70 and the second heat exchanger 60 used as the heat absorber during the cooling operation. However, in this case, since all of the refrigerant flowing out of the first heat exchanger 40 flows through the economizer heat exchanger 70 on the side where the first refrigerant circuit 110 is present, and the refrigerant partially branches and flows into the second refrigerant circuit 120, possibly causing the economizer heat exchanger 70 to be large in size, compared with that according to the embodiment described above.(4-4) Modification Example D

[0128] In the embodiment described above, although the economizer heat exchanger 70 is provided in the second refrigerant circuit 120 (to straddle the first refrigerant circuit 110 and the second refrigerant circuit 120), the present disclosure is not limited to such an aspect.

[0129] As illustrated in Fig. 8A, the air conditioner 100 may include a refrigerant vessel 72 (flash tank economizer) that is gas-liquid separatable and that straddles the first refrigerant circuit 110 and the second refrigerant circuit 120, instead of the economizer heat exchanger 70. Then, the second refrigerant circuit 120 is provided with a first valve 80a, and the first refrigerant circuit 110 is provided with a second expansion valve 84. The first valve 80a is preferably an electrically-operated valve for which the opening degree is adjustable.

[0130] When operation of the second compressor 20 is to be stopped, the first valve 80a is controlled similarly to the first valve 80 according to the embodiment described above (see step S2 and step S3 in the flowchart illustrated in Fig. 4).

[0131] Furthermore, for example, to switch a state where the air conditioner 100 allows only the first compressor 10 to operate to perform the cooling operation to a state where the first compressor 10 and the second compressor 20 are operated to perform the cooling operation, the first valve 80a is opened before operation of the second compressor 20 is started, similar to control of the first valve 80 at step S12 in the flowchart illustrated in Fig. 5. However, when the pressure of the refrigerant in the refrigerant vessel 72 is intermediate pressure in the refrigeration cycle (due to decompression in the second expansion valve 84) and the pressure on the discharge side of the second compressor 20 is high pressure in the refrigeration cycle, pressure equalization may not be achieved between the pressure on the discharge side of the second compressor 20 and the pressure on the suction side of the second compressor 20, even though the first valve 80a is opened. Therefore, when it is assumed that there is a difference between the pressure on the discharge side of the second compressor 20 and the pressure on the suction side of the second compressor 20, the first valve 80a may be opened (step S12) and pressure equalization may be performed between the pressure on the discharge side of the second compressor 20 and the pressure on the suction side of the second compressor 20 using the pressure equalization mechanism 90 before operation of the second compressor 20 is started at step S13.

[0132] Note that, when the air conditioner 100 allows the first compressor 10 and the second compressor 20 to operate to perform the cooling operation, the first valve 80a is not controlled for its opening degree, but is adjusted to a predetermined opening degree (for example, fully opened), different from that at step S14 in the flowchart illustrated in Fig. 5.

[0133] A state where the air conditioner 100 illustrated in Fig. 8A performs the cooling operation will now be described herein. In the air conditioner 100, the refrigerant vessel 72 is disposed between the first heat exchanger 40 functioning as the radiator for the refrigerant and the second heat exchanger 60 functioning as the heat absorber for the refrigerant (more specifically, between the first heat exchanger 40 and the first expansion valve 50). The second expansion valve 84 is disposed between the first heat exchanger 40 functioning as the radiator and the refrigerant vessel 72. The control device 8 appropriately controls the opening degree of the second expansion valve 84 when operating both the first compressor 10 and the second compressor 20 to perform the cooling operation. Note that, when the second compressor 20 is to be stopped to perform the cooling operation, the opening degree of the second expansion valve 84 is not controlled. When both the first compressor 10 and the second compressor 20 are operated to perform the cooling operation, the refrigerant that flows out of the first heat exchanger 40, is decompressed by the second expansion valve 84, and brought into the two-phase state flows into the refrigerant vessel 72. The gas refrigerant separated in the refrigerant vessel 72 is sucked into the second compressor 20.

[0134] Also, in the air conditioner 100 having the configuration illustrated in Fig. 8A, it is possible to lower the temperature of the refrigerant flowing into the second heat exchanger 60 functioning as the heat absorber for the refrigerant, when both the first compressor 10 and the second compressor 20 are operated to perform the cooling operation, making it possible to improve the capability of the air conditioner 100.

[0135] Furthermore, as illustrated in Fig. 8B, the second refrigerant circuit 120 may include, in addition to the refrigerant vessel 72, a heat exchanger 70a (example of a second economizer heat exchanger) disposed to straddle the first refrigerant circuit 110 and the second refrigerant circuit 120. The heat exchanger 70a is disposed, in the first refrigerant circuit 110, between the first heat exchanger 40 functioning as the radiator for the refrigerant during the cooling operation and the second expansion valve 84. The heat exchanger 70a is arranged to exchange heat, when the air conditioner 100 allows both the first compressor 10 and the second compressor 20 to operate to perform the cooling operation, between the refrigerant that flows out of the first heat exchanger 40 toward the second expansion valve 84 and the gas refrigerant separated in the refrigerant vessel 72. The refrigerant that has exchanged heat in the heat exchanger 70a with the refrigerant flowing through the first refrigerant circuit 110 is sucked into the second compressor 20. With this configuration, further using the heat exchanger 70a makes it possible to further improve the capability of the air conditioner 100 during the cooling operation in a first mode, compared with that of the configuration illustrated in Fig. 8A.

[0136] In the configuration illustrated in Fig. 8B, the control for the first valve 80a and other components when operation of the second compressor 20 is to be stopped / operation of the second compressor 20 is to be started is as described with reference to the configuration illustrated in Fig. 8A.

[0137] Note that, also in the configurations illustrated in Fig. 8A and Fig. 8B, the second refrigerant circuit 120 is not used during the heating operation. During the heating operation, the second compressor 20 is not operated, the first valve 80a is closed, and the opening degree of the second expansion valve 84 is controlled to a predetermined opening degree and is not changed during the heating operation.(4-5) Modification Example E

[0138] Different from Modification Example D, the first valve 80a may be an electromagnetic valve that is changeable to be only fully opened and fully closed, in the configurations illustrated in Fig. 8A and Fig. 8B. Then, the control at step S2 illustrated in Fig. 4 and the control at step S14 illustrated in Fig. 5 may not be performed.

[0139] Even in such a configuration, since the second compressor 20 is operated for a predetermined time in a state where the first valve 80a is closed, it is possible to suppress condensation of the refrigerant at a large amount on the suction side of the second compressor 20 and to suppress liquid compression when the second compressor 20 is started.(4-6) Modification Example F

[0140] In the embodiment described above, the pressure equalization mechanism 90 is provided for pressure equalization between the discharge side and the suction side of the second compressor 20, and the second valve 94 is opened to achieve pressure equalization between the discharge side and the suction side of the second compressor 20.

[0141] However, in a case where opening the first valve 80 can achieve pressure equalization between the discharge side and the suction side before the second compressor 20 is started, the pressure equalization mechanism 90 may not be provided.<Note>

[0142] While the embodiment of the present disclosure has been described above, it will be understood that various changes in form and detail may be made therein without departing from the spirit and scope of the present disclosure as set forth in the appended claims.REFERENCE SIGNS LIST

[0143] 8control device (control unit) 10first compressor 20second compressor 20asuction port 40first heat exchanger (radiator) 50first expansion valve 60second heat exchanger (heat absorber) 70economizer heat exchanger (first economizer heat exchanger) 70aheat exchanger (second economizer heat exchanger) 72refrigerant vessel 80, 80afirst valve 82, 82abranch portion 84second expansion valve 92bypass flow path 94second valve 100air conditioner (refrigeration cycle apparatus) 110first refrigerant circuit 120second refrigerant circuit 122first sensor (pressure sensor) 122afirst sensor (temperature sensor) 124second sensor CITATION LIST PATENT LITERATURE

[0144] PTL 1: Japanese Unexamined Patent Application Publication No. 2005-49087

Examples

modification examples

(4) Modification Examples

[0121]Modification examples of the air conditioner 100 according to the embodiment described above will now be described herein. Note that it is possible to appropriately combine the modification examples described below.

modification example

(4-1) Modification Example A

[0122]In the embodiment described above, the first sensor 122 is the pressure sensor that does not measure the saturation temperature itself but measures the pressure corresponding to the saturation temperature, and the control device 8 interprets a value of the pressure measured by the first sensor 122 as the saturation temperature. However, the present disclosure is not limited to this case, and the first sensor may be a temperature sensor that directly measures the saturation temperature.

[0123]In this case, a first sensor 122a representing a temperature sensor measures the temperature of the refrigerant at a position where the refrigerant flows in a gas-liquid two-phase state. For example, as illustrated in Fig. 6, the first sensor 122a is disposed between the first valve 80 and the economizer heat exchanger 70, through which the refrigerant in the gas-liquid two-phase state flows, and measures the temperature (saturation temperature) of the refrigeran...

modification example b

(4-2) Modification Example B

[0124]In the embodiment described above, when operation of the second compressor 20 is to be stopped, the control device 8 controls the opening degree of the first valve 80 based on the measurement values of the first sensor 122 and the second sensor 124, and makes the refrigerant to be sucked into the second compressor 20 to be in a state of having a degree of superheating (state where the degree of superheating is larger than 0).

[0125]However, the present disclosure is not limited to this case, and the air conditioner 100 may not be provided with the first sensor 122 and the second sensor 124 (or may not use results of measurement by the first sensor 122 and the second sensor 124), and the control device 8 may control and reduce the opening degree of the first valve 80 to a predetermined opening degree when operation of the second compressor 20 is to be stopped to make the refrigerant to be sucked into the second compressor 20 to have a degree of superh...

Claims

1. A refrigeration cycle apparatus (100) comprising: a first refrigerant circuit (110) including a first compressor (10), a radiator (40), a first expansion valve (50), and a heat absorber (60); a second refrigerant circuit (120) connecting a portion between the first compressor and the radiator and a portion between the radiator and the first expansion valve, the second refrigerant circuit including a second compressor (20) and a first valve (80, 80a) disposed on an upstream side of the second compressor; and a control unit (8) configured to control the first compressor, the second compressor, the first expansion valve, and the first valve, the control unit being configured to close the first valve when the second compressor is to be stopped.

2. The refrigeration cycle apparatus according to claim 1, wherein the control unit is configured to close the first valve before the second compressor is stopped.

3. The refrigeration cycle apparatus according to claim 1 or 2, further comprising a first sensor (122, 122a) and a second sensor (124), wherein the second compressor has a suction port (20a), the first valve is an expansion valve, the first sensor is configured to measure a saturation temperature of a refrigerant that is present between the first valve and the suction port of the second compressor, the second sensor is configured to measure a temperature of the refrigerant to be sucked into the second compressor, and the control unit is configured to control, when the second compressor is to be stopped, an opening degree of the first valve based on a result of the measurement by the first sensor and a result of the measurement by the second sensor.

4. The refrigeration cycle apparatus according to any one of claims 1 to 3, wherein, the control unit is configured to control, when the second compressor is to be stopped, the first valve so that the refrigerant to be sucked into the second compressor has a degree of superheating before the first valve is closed.

5. The refrigeration cycle apparatus according to claim 4, wherein the control unit is configured to control, when the second compressor is to be stopped, an opening degree of the first valve so that a degree of superheating of suction of the second compressor becomes equal to or higher than a predetermined degree of superheating.

6. The refrigeration cycle apparatus according to claim 3, wherein the first sensor and the second sensor are disposed between the first valve and the suction port of the second compressor, and the first sensor (122) is a pressure sensor.

7. The refrigeration cycle apparatus according to any one of claims 1 to 6, wherein the second refrigerant circuit further includes a first economizer heat exchanger (70) disposed between the radiator and the heat absorber, the first economizer heat exchanger is configured to exchange heat between the refrigerant that flows out of the radiator, is branched to the second refrigerant circuit at a branch portion (82, 82a), and is decompressed by the first valve, and the refrigerant flowing out of the radiator.

8. The refrigeration cycle apparatus according to claim 7, wherein the branch portion (82) is disposed between the radiator and the first economizer heat exchanger.

9. The refrigeration cycle apparatus according to any one of claims 1 to 6, wherein the first refrigerant circuit further includes a second expansion valve (84) disposed between the radiator and the first expansion valve, the second refrigerant circuit further includes a refrigerant vessel (72) that is configured to separate gas and liquid, into which the refrigerant decompressed and brought into a two-phase state by the second expansion valve flows, the first valve is disposed between the refrigerant vessel and the second compressor, and the gas refrigerant separated in the refrigerant vessel is sucked into the second compressor.

10. The refrigeration cycle apparatus according to claim 9, wherein the second refrigerant circuit further includes a second economizer heat exchanger (70a), and the second economizer heat exchanger is arranged to exchange heat between the refrigerant flowing out of the radiator toward the second expansion valve and the gas refrigerant flowing out of the refrigerant vessel.

11. The refrigeration cycle apparatus according to any one of claims 1 to 10, wherein the control unit is configured to open the first valve before the second compressor is started.

12. The refrigeration cycle apparatus according to any one of claims 1 to 11, further comprising: a bypass flow path (92) that connects a discharge side of the second compressor in the second refrigerant circuit or a portion between a discharge port of the first compressor and the radiator in the first refrigerant circuit and a suction side of the second compressor in the second refrigerant circuit; and a second valve (94) disposed in the bypass flow path.

13. The refrigeration cycle apparatus according to any one of claims 1 to 12, wherein the refrigerant enclosed in the first refrigerant circuit and the second refrigerant circuit contains CO2 at least partially in its components.

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