Refrigeration cycle device

Abstract

To provide a refrigeration cycle apparatus capable of performing efficient operation even under a low-load condition. An air conditioner (100) includes a first refrigerant circuit (110), a second refrigerant circuit (120), a bypass flow path (130), and a bypass valve (132). The first refrigerant circuit includes a first compressor (10), a radiator (40), a first expansion valve (50), and a heat absorber (60). 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 to each other and includes an economizer (70), a first valve (80), and a second compressor (20). The economizer is disposed between the radiator and the heat absorber, and the second compressor sucks a refrigerant that has passed through the economizer. The bypass flow path connects a portion between the first valve and the second compressor and a portion between the heat absorber and the first compressor. The bypass valve is disposed in the bypass flow path. The second compressor is a compressor that is smaller in displacement than the first compressor.

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, and a refrigerant branched in the economizer from a main route for the refrigerant discharged from the first compressor to a first flow path and heading toward a heat absorber via a radiator is compressed by the second compressor and discharged to the first flow path.

[0003] In this refrigeration cycle apparatus, the second compressor is utilized, making it possible to improve its capability and efficiency.SUMMARY OF THE INVENTION <Technical Problem>

[0004] By the way, a refrigeration cycle apparatus is not always required to operate under a high load, but may be required to operate under a low load. An object of the present disclosure is to provide a refrigeration cycle apparatus capable of being efficiently operated under a low-load condition.<Solution to Problem>

[0005] A refrigeration cycle apparatus according to a first aspect comprises a first refrigerant circuit, a second refrigerant circuit, a bypass flow path, and a bypass valve. The first refrigerant circuit includes a first compressor, a radiator, a first expansion valve, and a heat absorber. The second refrigerant circuit includes an economizer, a first valve, and a second compressor. The second refrigerant circuit connects a portion between the first compressor and the radiator in the first refrigerant circuit and a portion between the radiator and the first expansion valve in the first refrigerant circuit. The economizer is disposed between the radiator and the heat absorber. The second compressor sucks a refrigerant that has passed through the economizer. The bypass flow path connects a portion between the first valve and the second compressor in the second refrigerant circuit and a portion between the heat absorber and the first compressor in the first refrigerant circuit. The bypass valve is disposed in the bypass flow path. The second compressor is a compressor that is smaller in displacement than the first compressor.

[0006] In the refrigeration cycle apparatus according to the first aspect, under a low-load condition, the bypass flow path is utilized, the first compressor is stopped, and the second compressor that is small in displacement and is suitable for operation under a low load is operated. Thus, it is possible to perform efficient operation even under the low-load condition.

[0007] A refrigeration cycle apparatus according to a second aspect is the refrigeration cycle apparatus according to the first aspect, in which the economizer includes a first economizer heat exchanger disposed between the radiator and the heat absorber. The first valve is an expansion valve. The first economizer heat exchanger is disposed between the first valve and the second compressor in the second refrigerant circuit. 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 that flows out of the radiator.

[0008] In the refrigeration cycle apparatus according to the second aspect, by compressing the refrigerant passing through the first economizer heat exchanger, it is possible to improve the capability and efficiency of the refrigeration cycle apparatus.

[0009] A refrigeration cycle apparatus according to a third aspect is the refrigeration cycle apparatus according to the second aspect, the branch portion is disposed between the radiator and the first economizer heat exchanger.

[0010] In the refrigeration cycle apparatus according to the third aspect, the refrigerant partially branches on an 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 third 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 whole of the refrigerant flowing out of the radiator flows through the first refrigerant circuit into the first economizer heat exchanger.

[0011] A refrigeration cycle apparatus according to a fourth aspect is the refrigeration cycle apparatus according to the second aspect or the third aspect, the bypass flow path connects a portion between the first valve and the first economizer heat exchanger in the second refrigerant circuit and a portion between the heat absorber and the first compressor in the first refrigerant circuit.

[0012] In the refrigeration cycle apparatus according to the fourth aspect, when the first compressor is stopped and the second compressor is operated, the refrigerant passing through the heat absorber and flowing into the bypass flow path exchanges heat with the refrigerant flowing through the first economizer heat exchanger on a side where the first refrigerant circuit is present before being sucked into the second compressor. Therefore, in the refrigeration cycle apparatus according to the fourth aspect, it is possible to improve performance and efficiency of the refrigeration cycle apparatus when the first compressor is stopped and the second compressor is operated.

[0013] A refrigeration cycle apparatus according to a fifth aspect is the refrigeration cycle apparatus according to any one of the second aspect to the fourth aspect and further includes a control unit. The control unit is configured to control operation of the first compressor, the second compressor, and the first valve. The control unit is configured to control an opening degree of the first valve to be equal to or smaller than a predetermined opening degree or to be closed in a case where the first compressor is stopped and the second compressor is operated.

[0014] In the refrigeration cycle apparatus according to the fifth aspect, it is possible to suppress, in amount, the refrigerant that does not pass through the heat absorber but is sucked into the second compressor, when the first compressor is stopped and the second compressor is operated, making it possible to suppress a decrease in performance and efficiency of the refrigeration cycle apparatus when the first compressor is stopped and the second compressor is operated.

[0015] A refrigeration cycle apparatus according to a sixth aspect is the refrigeration cycle apparatus according to any one of the second aspect to the fifth aspect, the bypass valve is a check valve that prevents the refrigerant from flowing from the portion between the first valve and the second compressor in the second refrigerant circuit to the portion between the heat absorber and the first compressor in the first refrigerant circuit.

[0016] In the refrigeration cycle apparatus according to the sixth aspect, it is possible to achieve, with a low-cost configuration, a refrigeration cycle in which the second compressor is operated in a state where the first compressor is stopped, and it is also possible to suppress a flow of the refrigerant from the bypass flow path to the first refrigerant circuit when both the first compressor and the second compressor are operated.

[0017] A refrigeration cycle apparatus according to a seventh aspect is the refrigeration cycle apparatus according to the fifth aspect, in which the bypass valve is an electromagnetic valve or an electrically-operated valve. The control unit is configured to further control the bypass valve. The control unit is configured to open the bypass valve when the first compressor is stopped and the second compressor is operated.

[0018] A refrigeration cycle apparatus according to an eighth aspect is the refrigeration cycle apparatus according to the first aspect, in which the economizer includes a second expansion valve and 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 gas refrigerant separated in the refrigerant vessel is sucked into the second compressor.

[0019] In the refrigeration cycle apparatus according to the eighth aspect, it is possible to use the second expansion valve and the refrigerant vessel to lower a temperature of the refrigerant flowing into the heat absorber, making it possible to improve the capability and efficiency of the refrigeration cycle apparatus.

[0020] A refrigeration cycle apparatus according to a ninth aspect is the refrigeration cycle apparatus according to the eighth aspect, in which the economizer 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 and the gas refrigerant flowing out of the refrigerant vessel.

[0021] In the refrigeration cycle apparatus according to the ninth 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.

[0022] A refrigeration cycle apparatus according to a tenth aspect is the refrigeration cycle apparatus according to the ninth aspect, in which the first valve is disposed between the refrigerant vessel and the second economizer heat exchanger. The bypass flow path is connected to a portion between the first valve and the second economizer heat exchanger.

[0023] In the refrigeration cycle apparatus according to the tenth aspect, when the first compressor is stopped and the second compressor is operated, the refrigerant passing through the heat absorber and flowing into the bypass flow path exchanges heat with the refrigerant flowing through a first economizer flow path in the second economizer heat exchanger before being sucked into the second compressor. Therefore, in the refrigeration cycle apparatus according to the tenth aspect, it is possible to improve the performance and efficiency of the refrigeration cycle apparatus when the first compressor is stopped and the second compressor is operated.

[0024] A refrigeration cycle apparatus according to an eleventh aspect is the refrigeration cycle apparatus according to any one of the eighth aspect to the tenth aspect and further includes a control unit. The control unit is configured to control operation of the first compressor, the second compressor, and the first valve. The control unit is configured to control an opening degree of the first valve to be equal to or smaller than a predetermined opening degree or to be closed when the first compressor is stopped and the second compressor is operated.

[0025] In the refrigeration cycle apparatus according to the eleventh aspect, it is possible to suppress, in amount, the refrigerant that does not pass through the heat absorber but is sucked into the second compressor, when the first compressor is stopped and the second compressor is operated, making it possible to suppress a decrease in performance and efficiency of the refrigeration cycle apparatus when the first compressor is stopped and the second compressor is operated.

[0026] A refrigeration cycle apparatus according to a twelfth aspect is the refrigeration cycle apparatus according to any one of the eighth aspect to the eleventh aspect, in which the bypass valve is a check valve that prevents the refrigerant from flowing from the portion between the first valve and the second compressor in the second refrigerant circuit to the portion between the heat absorber and the first compressor in the first refrigerant circuit.

[0027] In the refrigeration cycle apparatus according to the twelfth aspect, it is possible to achieve, with a low-cost configuration, a refrigeration cycle in which the first compressor is stopped and the second compressor is operated, and it is also possible to suppress a flow of the refrigerant from the bypass flow path to the first refrigerant circuit when both the first compressor and the second compressor are operated.

[0028] A refrigeration cycle apparatus according to a thirteenth aspect is the refrigeration cycle apparatus according to the eleventh aspect, in which the bypass valve is an electromagnetic valve or an electrically-operated valve. The control unit is further configured to further control the bypass valve. The control unit is configured to open the bypass valve when the first compressor is stopped and the second compressor is operated.

[0029] A refrigeration cycle apparatus according to a fourteenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the thirteenth aspect, in which the refrigerant contains CO 2 at least partially in its components.

[0030] In the refrigeration cycle apparatus according to the fourteenth aspect, a refrigerant containing CO 2 having a low global warming potential is used as the refrigerant, it is possible to achieve the refrigeration cycle apparatus having a low environmental load.

[0031] A refrigeration cycle apparatus according to a fifteenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the fourteenth aspect and has, as operating modes, a first mode in which both the first compressor and the second compressor are operated and a second mode in which the first compressor is stopped and the second compressor is operated. The operating mode is configured to be switched from the first mode to the second mode based on a value of suction pressure of the second compressor.

[0032] In the refrigeration cycle apparatus according to the fifteenth aspect, it is possible to detect that a low-load condition has been attained based on the value of the suction pressure of the second compressor, making it possible to perform efficient operation even under the low-load condition.

[0033] A refrigeration cycle apparatus according to a sixteenth aspect is the refrigeration cycle apparatus according to the fifteenth aspect, the operating mode is configured to be switched from the first mode to the second mode further based on a value of suction pressure of the first compressor.

[0034] In the refrigeration cycle apparatus according to the sixteenth aspect, it is possible to accurately detect that a low-load condition has been attained based on the value of the suction pressure of the first compressor and the value of the suction pressure of the second compressor, making it possible to perform efficient operation even under the low-load condition.

[0035] A refrigeration cycle apparatus according to a seventeenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the sixteenth aspect, has, as operating modes, a first mode in which both the first compressor and the second compressor are operated and a second mode in which the first compressor is stopped and the second compressor is operated. The operating mode is switched from the second mode to the first mode based on a number of rotations of the second compressor.

[0036] In the refrigeration cycle apparatus according to the seventeenth aspect, it is possible to detect an increase in load based on a value of the number of rotations of the second compressor and to allow the operating mode to shift to the first mode, making it possible to perform efficient operation.

[0037] A refrigeration cycle apparatus according to an eighteenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the seventeenth aspect, the refrigeration cycle apparatus has, as operating modes, only a first mode in which both the first compressor and the second compressor are operated and a second mode in which the first compressor is stopped and the second compressor is operated.BRIEF DESCRIPTION OF THE DRAWINGS

[0038] [Fig. 1] Fig. 1 is a schematic configuration diagram of an air conditioner according to a first 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. 4A] Fig. 4A is a flowchart according to an example for explaining change processing of a first mode to a second mode in the air conditioner illustrated in Fig. 1. [Fig. 4B] Fig. 4B is a flowchart according to another example for explaining the change processing of the first mode to the second mode in the air conditioner illustrated in Fig. 1. [Fig. 5] Fig. 5 is a flowchart according to an example for explaining change processing of the second mode to the first mode in the air conditioner illustrated in Fig. 1. [Fig. 6] Fig. 6 is a flowchart for explaining control when operation of the air conditioner illustrated in Fig. 1 is stopped. [Fig. 7] Fig. 7 is a schematic configuration diagram of an air conditioner according to Modification Example A. [Fig. 8A] Fig. 8A is a schematic configuration diagram of an air conditioner according to Modification Example B. [Fig. 8B] Fig. 8B is a schematic control block diagram of the air conditioner illustrated in Fig. 8A. [Fig. 9A] Fig. 9A is a schematic configuration diagram of an air conditioner according to an example of Modification Example C. [Fig. 9B] Fig. 9B is a schematic configuration diagram of an air conditioner according to another example of Modification Example C. [Fig. 10] Fig. 10 is a schematic configuration diagram of an air conditioner according to Modification Example D. [Fig. 11] Fig. 11 is a schematic configuration diagram of an air conditioner according to Modification Example E. [Fig. 12] Fig. 12 is a schematic configuration diagram of an air conditioner according to a second embodiment of the refrigeration cycle apparatus. DESCRIPTION OF EMBODIMENTS

[0039] Embodiments of a refrigeration cycle apparatus according to the present disclosure will now be described herein with reference to the accompanying drawings.<First Embodiment>(1) Overall Configuration

[0040] An overall configuration of an air conditioner 100 according to a first embodiment of a 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.

[0041] The air conditioner 100 is a device that uses a vapor compression refrigeration cycle to perform cooling or heating of air in a room in a building and the like, which is a target of a temperature adjustment, to perform cooling or heating of the room in the building and the like. Note that, although the target to which the temperature is to be adjusted by the air conditioner 100 is air in the present embodiment, the air conditioner 100 may be a device that cools or heats a medium such as water which is the target to which the temperature is to be adjusted. Furthermore, although the air conditioner 100 according to the present embodiment is a device capable of performing cooling and heating in a room in a building and the like, the air conditioner 100 may be a device dedicated for cooling.

[0042] 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. Especially, The refrigerant circuits 110, 120 in this air conditioner 100 are 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.

[0043] 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, 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, for example, on a rooftop and the like 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 connected by refrigerant connection pipes 6 to configure the first refrigerant circuit 110.

[0044] 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, 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 so that the first heat exchanger 40 functions as the radiator for the refrigerant and the second heat exchanger 60 functions as a heat absorber (evaporator) for the refrigerant).

[0045] The second refrigerant circuit 120 mainly includes a second compressor 20, an economizer 70, and a first valve 80.

[0046] The economizer 70 is disposed between the first heat exchanger 40 and the second heat exchanger 60 in the first refrigerant circuit 110, and further cools the refrigerant that flows out of the first heat exchanger 40 serving as the radiator and heads toward the second heat exchanger 60 serving as the heat absorber during the cooling operation. In the present embodiment, the economizer 70 includes an economizer heat exchanger 72 disposed between the first heat exchanger 40 and the second heat exchanger 60. The economizer heat exchanger 72 is an example of a first economizer heat exchanger. The economizer heat exchanger 72 is disposed to straddle the first refrigerant circuit 110 and the second refrigerant circuit 120.

[0047] In one of operating modes, for the cooling operation by the air conditioner 100, in which both the first compressor 10 and the second compressor 20 are operated (first mode for the cooling operation described later), the first valve 80 decompresses the refrigerant branched from the first refrigerant circuit 110 and will flow toward the economizer heat exchanger 72 in the second refrigerant circuit 120 and adjusts a flow rate of the refrigerant. In the first mode for the cooling operation described later, the second compressor 20 sucks and compresses the refrigerant that has passed through the first valve 80 and the economizer heat exchanger 72 and flows through the second refrigerant circuit 120.

[0048] The second refrigerant circuit 120 is used to improve a refrigeration cycle in performance during the cooling operation by the air conditioner 100 (in the first mode for the cooling operation described later). Specific description will be given below.

[0049] 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.

[0050] In contrast, in the air conditioner 100 according to the present disclosure, the second refrigerant circuit 120 is provided and 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 in the economizer heat exchanger 72 in the first mode for the cooling operation described later. 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).

[0051] Note that, different from the air conditioner 100 according to the present disclosure, performing intermediate injection of the refrigerant that has passed through the economizer heat exchanger 72 into the first compressor 10, without providing the second compressor 20, also makes it possible to acquire effects of improvements in capability and performance. However, since it is possible to desirably adjust intermediate pressure in the air conditioner 100 provided with the second compressor 20, it is also possible to improve the performance of the air conditioner 100 with respect to a configuration in which intermediate injection of the refrigerant that has passed through the economizer heat exchanger 72 into the first compressor 10 is performed.

[0052] The air conditioner 100 further includes, in addition to the first refrigerant circuit 110 and the second refrigerant circuit 120, a bypass flow path 130 connecting a portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 and a portion between the second heat exchanger 60 functioning as the heat absorber during the cooling operation and the first compressor 10 in the first refrigerant circuit 110 and a bypass valve 132 disposed in the bypass flow path 130.

[0053] The air conditioner 100 has, as the operating modes for the cooling operation, the first mode in which both the first compressor 10 and the second compressor 20 are operated and a second mode in which the first compressor 10 is stopped and the second compressor 20 is operated. The bypass flow path 130 and the bypass valve 132 are used to operate the air conditioner 100 in the second mode during the cooling operation.

[0054] Note that, in the present embodiment, in the cooling operation by the air conditioner 100 (as an operation state where the first heat exchanger 40 is used as the radiator and the second heat exchanger 60 is used as the heat absorber), no operating mode is provided in which operation of the second compressor 20 is stopped and only the first compressor 10 is operated (the air conditioner 100 has only the first mode and the second mode as the operating modes for the cooling operation). However, the present disclosure is not limited to this case, and the air conditioner 100 may have an operating mode for the cooling operation in which operation of the second compressor 20 is stopped and only the first compressor 10 is operated to perform cooling.

[0055] Details of the bypass flow path 130 and the bypass valve 132 and the first mode and the second mode for the cooling operation by the air conditioner 100 will be described later. Note that, in description below, to avoid redundant description, the first mode for the cooling operation may be simply referred to as the first mode and the second mode for the cooling operation may be simply referred to as the second mode.(2) Detailed Configuration

[0056] 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, the second refrigerant circuit 120, the bypass flow path 130, and the bypass valve 132. Various configurations of the air conditioner 100 will now be described herein in detail.

[0057] Note that, when the cooling operation is described below in Sections (2-1) First Refrigerant Circuit and (2-2) Second Refrigerant Circuit, operation and functions of various components in the first refrigerant circuit 110 and the second refrigerant circuit 120 when the air conditioner 100 performs the cooling operation in the first mode described above and flows of the refrigerant in the first refrigerant circuit 110 and the second refrigerant circuit 120 will be mainly described. The various components and the functions of the first refrigerant circuit 110 and the second refrigerant circuit 120 when the air conditioner 100 is operated in the second mode, and the flows of the refrigerant in the first refrigerant circuit 110 and the second refrigerant circuit 120 will be described in Section (2-3) Bypass Flow Path and Bypass Valve, together with the description regarding the bypass flow path 130 and the bypass valve 132.(2-1) First Refrigerant Circuit

[0058] 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 to each other by the pipes.

[0059] 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 preferably a scroll compressor that is high in efficiency at a large number of rotations. However, the type of the first compressor 10 may be another type of compressor.

[0060] 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.

[0061] 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 coupling states of the pipes as described below.

[0062] To set the state of the first refrigerant circuit 110 into the first state, the switching mechanism 30 connects a discharge port of the first compressor 10 and one end side of the first heat exchanger 40 to each other, and connects a suction port of the first compressor 10 and one end side of the second heat exchanger 60 to each other. Furthermore, to set the state of the first refrigerant circuit 110 into the second state, the switching mechanism 30 connects the discharge port of the first compressor 10 and the one end side of the second heat exchanger 60 to each other, and connects the suction port of the first compressor 10 and the one end side of the first heat exchanger 40 to each other.

[0063] Note that, when the air conditioner 100 is an apparatus dedicated for cooling, the air conditioner 100 may not include the switching mechanism 30.

[0064] 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.

[0065] 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 each other. The first heat exchanger 40 may be a heat exchanger that allows a medium such as water serving as a heat source and the refrigerant to exchange heat with each other.

[0066] The economizer heat exchanger 72 is disposed between the first heat exchanger 40 and the second heat exchanger 60, 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 72 is disposed between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120.

[0067] When the air conditioner 100 is operated in the first mode, the economizer heat exchanger 72 exchange heat between the refrigerant that flows out of the first heat exchanger 40 functioning as the radiator, 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 first heat exchanger 40 and flows through the economizer heat exchanger 72 toward the second heat exchanger 60 functioning as the heat absorber. As a result, when the air conditioner 100 is operated in the first mode, the refrigerant that has been cooled in the first heat exchanger 40 and that flows toward the second heat exchanger 60 (see a point c and a point d illustrated in Fig. 3B) is further cooled by the economizer heat exchanger 72 (see a point h illustrated in Fig. 3B). Note that, in the present embodiment, 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 72 (see Fig. 1).

[0068] 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 72 and the second heat exchanger 60. The first expansion valve 50 is, for example, an electronic expansion valve that is variable in opening degree.

[0069] 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 space that is 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 space that is the target of air conditioning, 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 space that is the target of air conditioning 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

[0070] The second refrigerant circuit 120 includes the second compressor 20, the economizer 70, and the first valve 80. The economizer 70 includes the economizer heat exchanger 72. The first valve 80 is, for example, an electronic expansion valve that is variable in opening degree.

[0071] 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. Therefore, following description of the flow of the refrigerant in the second refrigerant circuit 120 is given for describing the flow of the refrigerant during the cooling operation.

[0072] The second compressor 20 is a compressor that is smaller in displacement than the first compressor 10. In other words, a displacement volume of the second compressor 20 is smaller than a displacement volume of the first compressor 10. The reason of this configuration is that the second refrigerant circuit 120 (second compressor 20) is utilized in an auxiliary manner with respect to the first refrigerant circuit 110 (first compressor 10) in the first mode for the cooling operation.

[0073] The displacement of the second compressor 20 with respect to the displacement of the first compressor 10 is below 100%. Preferably, the displacement of the second compressor 20 with respect to the displacement of the first compressor 10 is below 80%. More preferably, the displacement of the second compressor 20 with respect to the displacement of the first compressor 10 ranges from a value equal to or greater than 30% to a value below 80%.

[0074] As described above, the air conditioner 100 according to the present embodiment has, as the operating modes for the cooling operation, the first mode in which both the first compressor 10 and the second compressor 20 are operated and the second mode in which the first compressor 10 is stopped and the second compressor 20 is operated. When a cooling load is low, the first compressor 10 that is large in displacement is stopped and the second compressor 20 that is small in displacement is operated as cooling operation of the second mode (instead of stopping the second compressor 20 that is small in displacement and operating the first compressor 10 that is large in displacement). Thus, there is an advantage that a controllable range of the capability of the air conditioner 100 expands.

[0075] Especially, when the displacement of the second compressor 20 with respect to the displacement of the first compressor 10 is below 80%, it is possible to allow operation of the air conditioner 100 to be continued (by allowing the second compressor 20 to be operated at a number of rotations equal to or greater than a minimum number of rotations) without causing the second compressor 20 to be operated and stopped in a frequently repeated manner even when the capability required for the air conditioner 100 is small (even during a low-load period).

[0076] Furthermore, setting the displacement of the second compressor 20 with respect to the displacement of the first compressor 10 to be equal to or greater than 30% makes it possible to suppress occurrence of such a situation that the capability of the air conditioner 100 becomes excessive or that the capability of the second compressor 20 becomes insufficient.

[0077] The second compressor 20 is a compressor that is variable in operating capacity and that includes an inverter-control-type motor. When the air conditioner 100 is operated in the first mode, the second compressor 20 is not always operated at a large capacity (number of rotations), and is often operated at a small capacity (in other words, at a small number of rotations). Therefore, in the present embodiment, the second compressor 20 is a rotary compressor (including a swing compressor) that is efficient even at a small number of rotations.

[0078] However, the type of the second compressor 20 is not limited to the rotary compressor, and may be another type of compressor that is smaller in displacement than the first compressor 10 (for example, a scroll compressor that is smaller in compression ratio than the first compressor 10).

[0079] The economizer heat exchanger 72 is, for example, a double-pipe-type heat exchanger or a plate-type heat exchanger. When the air conditioner 100 is operated in the first mode, the economizer heat exchanger 72 exchange heat between the refrigerant that flows out of the 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 first heat exchanger 40 and flows through the economizer heat exchanger 72 toward the second heat exchanger 60 in a state where mixing of the refrigerant does not occur. The refrigerant that has been decompressed by the first valve 80, has passed through the economizer heat exchanger 72, and has cooled the refrigerant flowing toward the second heat exchanger 60 when the air conditioner 100 is operated in the first mode 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) Bypass Flow Path and Bypass Valve

[0080] As described above, the bypass flow path 130 and the bypass valve 132 are used to operate the air conditioner 100 in the second mode for the cooling operation.

[0081] Firstly, the reason why the second mode is provided as one of the operating modes for the cooling operation by the air conditioner 100 will be described herein.

[0082] The first compressor 10 and the like is selected to allow the air conditioner 100 to operate even under a predetermined high-load condition. However, the air conditioner 100 is not always required to operate under a high load, but may be required to operate under a low load (for example, under a load equal to or lower than a load that is half of a maximum load). When the first compressor 10 is operated under such a low load, the first compressor 10 may be operated at a number of rotations outside a range of numbers of rotations, which is regarded as optimum from a viewpoint of efficiency. Furthermore, when the load is especially small, the capability may become excessive even when the number of rotations of the first compressor 10 or the second compressor 20 is reduced to the minimum number of rotations, and operation of the air conditioner 100 may have to be temporarily stopped, possibly resulting in a decrease in coefficient of performance (COP) of the air conditioner 100 due to that a situation arises that the air conditioner 100 is caused to be operated and stopped in a repeated manner.

[0083] Therefore, the air conditioner 100 is provided with the second mode under which a vapor compression refrigeration cycle is performed, in which the first compressor 10 is stopped and the second compressor 20 that is small in displacement is used, under a low-load condition, achieving efficient operation even under the low-load condition. Especially, in the present embodiment, the first compressor 10 that is a scroll compressor is stopped and the second compressor 20 that is a rotary compressor presenting good operation efficiency even at a small number of rotations is used, achieving efficient operation even under the low-load condition.

[0084] The air conditioner 100 is provided with the bypass flow path 130 connecting the portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 and the portion between the second heat exchanger 60 functioning as the heat absorber and the first compressor 10 in the first refrigerant circuit 110. Providing the bypass flow path 130 makes it possible to allow, when operation of the first compressor 10 is stopped and only the second compressor 20 is operated, the second compressor 20 to suck the refrigerant that has passed through the first heat exchanger 40 and the first expansion valve 50 and has cooled the air in the space that is the target of air conditioning in the second heat exchanger 60.

[0085] Especially, in the air conditioner 100, the bypass flow path 130 connects the portion between the first valve 80 and the economizer heat exchanger 72 in the second refrigerant circuit 120 and the portion between the second heat exchanger 60 and the suction side of the first compressor 10 in the first refrigerant circuit 110. Therefore, in this air conditioner 100, when the air conditioner 100 is operated in the second mode, the refrigerant passing through the second heat exchanger 60 and flowing into the bypass flow path 130 passes through the economizer heat exchanger 72 before being sucked into the second compressor 20 and exchanges heat in the economizer heat exchanger 72 with the refrigerant flowing from the first heat exchanger 40 to the second heat exchanger 60. Therefore, with this air conditioner 100, it is possible to improve the performance of the air conditioner 100 when the air conditioner 100 is operated in the second mode.

[0086] Note that, since, if the refrigerant is in a state of freely flowing through the bypass flow path 130, the pressure between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 becomes higher than the pressure between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110 (see Fig. 3B) when the air conditioner 100 is operated in the first mode, the refrigerant flows from the second refrigerant circuit 120 to the suction side of the first compressor 10. This possibly inhibits appropriate operation of the air conditioner 100. Therefore, the bypass valve 132 is provided in the bypass flow path 130. In the present embodiment, the bypass valve 132 is a check valve that prevents the refrigerant from flowing from the portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 to the portion between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110 (see Fig. 1).

[0087] Furthermore, if the first valve 80 remains at a large opening degree when the air conditioner 100 is operated in the second mode, the refrigerant that has passed through the first heat exchanger 40 may not flow into the second heat exchanger 60, but may flow into the second refrigerant circuit 120 from the branch portion 82. Therefore, preferably, when the air conditioner 100 is operated in the second mode, the opening degree of the first valve 80 is set to an opening degree equal to or lower than a predetermined opening degree (opening degree at which it is possible to suppress an inflow of the refrigerant at a large amount from the branch portion 82 into the second refrigerant circuit 120) or the first valve 80 is closed.(2-4) Pressure Equalization Mechanism

[0088] The pressure equalization mechanism 90 is a mechanism for achieving pressure equalization between the pressure on a discharge side of the second compressor 20 and the pressure on a suction side of the second compressor 20 when the second compressor 20 is stopped. Especially, the pressure equalization mechanism 90 as described herein is preferably provided when the second compressor 20 is a rotary compressor.

[0089] The pressure equalization mechanism 90 includes a flow path 92, a second valve 94, and a check valve 96.

[0090] The check valve 96 is provided between the discharge port of the second compressor 20 and a portion connecting the second refrigerant circuit 120 to the first refrigerant circuit 110 (a portion connecting the second refrigerant circuit 120 to a pipe connecting the discharge port of the first compressor 10 and the switching mechanism 30). The check valve 96 prevents the refrigerant from flowing from a side where the connecting portion between the second refrigerant circuit 120 and the first refrigerant circuit 110 is present to a side where the discharge port of the second compressor 20 is present. Note that, in a case where the air conditioner 100 does not perform the heating operation (does not include the switching mechanism 30) and a situation does not occur that the first compressor 10 is operated while the second compressor 20 is stopped, the check valve 96 may be omitted.

[0091] The 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 flow path 92 connects a portion between the discharge port of the second compressor 20 in the second refrigerant circuit 120 and the check valve 96 and the suction side of the second compressor 20 to each other.

[0092] Although illustrations are omitted, the flow path 92 may be a flow path that connects a portion between the discharge port of the first compressor 10 in the first refrigerant circuit 110 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 flow path 92 may be a flow path that connects a pipe coupling the discharge port of the first compressor 10 and the switching mechanism 30 and the suction side of the second compressor 20. Furthermore, the 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 between the second refrigerant circuit 120 and a pipe connecting the discharge port of the first compressor 10 and the switching mechanism 30).

[0093] The second valve 94 is a valve disposed in the 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.

[0094] When the second compressor 20 is stopped, the second valve 94 is controlled by the control device 8 to be described later and opened. As a result, pressure equalization between the discharge side of the second compressor 20 and the suction side of the second compressor 20 is achieved. For example, when the second compressor 20 is a rotary compressor, refrigerating machine oil in the second compressor 20 may flow out of the suction port of the second compressor 20, due to the characteristics of the compressor, when such a state continues that the pressure on the discharge side is higher than the pressure on the suction side. However, providing the pressure equalization mechanism 90 as described above suppresses occurrence of such a situation. Control for the second valve 94 by the control device 8 will be described later.(2-5) First Fan and Second Fan

[0095] The first fan 42 is housed inside a housing (illustrations are omitted) of the heat source unit 2, which houses the first compressor 10, the second compressor 20, the switching mechanism 30, the first heat exchanger 40, the economizer heat exchanger 72, the first expansion valve 50, the first valve 80, and the second valve 94, for example. The first fan 42 supplies the heat source air to the first heat exchanger 40 in the first refrigerant circuit 110, 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.

[0096] The second fan 62 is housed in the housing (illustrations are omitted) of the utilization unit 4, which houses the second heat exchanger 60, for example. The second fan 62 sucks the air from the space that is the target of air conditioning, and supplies the sucked air to the second heat exchanger 60 in the first refrigerant circuit 110, 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.(2-6) Control Device

[0097] The control device 8 is a device that controls operation of the air conditioner 100.

[0098] The control device 8 is electrically connected to the first compressor 10, the second compressor 20, 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 connected to each other to control operation of the air conditioner 100.

[0099] 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, for example), and the control device 8 is electrically connected to these sensors. For example, as illustrated in Fig. 1, the air conditioner 100 is provided with a first sensor 12 that measures suction pressure of the first compressor 10 and a second sensor 22 that measures suction pressure of the second compressor 20. The control device 8 is electrically connected to the first sensor 12 and the second sensor 22, and acquires results of measurement by these sensors.

[0100] 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 connected 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 and the like.

[0101] 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.(2-6-1) Heating Operation

[0102] To cause the air conditioner 100 to perform the heating operation, the control device 8 controls operation of the switching mechanism 30, sets 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 each at predetermined numbers of rotations.

[0103] Note that, during the heating operation, the control device 8 controls the first valve 80 and the second valve 94 to be each in a closed state, and does not operate the second compressor 20.

[0104] Note that, during the heating operation, high pressure in the refrigeration cycle is attained between the first compressor 10 and the second heat exchanger 60. Therefore, when the pressure between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 is lower than the high pressure in the refrigeration cycle, there is a possibility that the bypass valve 132 is opened and the refrigerant flows from an area between the first compressor 10 and the second heat exchanger 60, passes through the bypass flow path 130, and flows into an area between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120. However, since the first valve 80 is closed and operation of the second compressor 20 is stopped during the heating operation, the pressure in the area between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 (having no destination to which the refrigerant flows) immediately reaches the high pressure in the refrigeration cycle, and the refrigerant no longer flows through the bypass flow path 130.

[0105] Note that, when switching from the heating operation to the cooling operation, the control device 8 may perform a liquid-draining operation in which the first valve 80 is opened in a state where the state of the first refrigerant circuit 110 is the second state and the first compressor 10 is operated. As the first valve 80 is opened, the refrigerant at the high pressure in the refrigeration cycle in the bypass flow path 130 and the second refrigerant circuit 120 flows to a low-pressure side in the refrigeration cycle via the first valve 80. When performing the liquid-draining operation, the control device 8 opens the first valve 80, then causes the first compressor 10 to be stopped, and controls operation of the switching mechanism 30 to set the state of the first refrigerant circuit 110 to the first state.(2-6-2) Cooling Operation in First Mode

[0106] To cause the air conditioner 100 to perform the cooling operation in the first mode, the control device 8 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 in the air conditioner 100. Furthermore, the control device 8 operates the motors of the first fan 42 and the second fan 62 each at predetermined numbers of rotations.

[0107] Note that, during the cooling operation in the first mode, the control device 8 controls the second valve 94 to be in the closed state.(2-6-3) Cooling Operation in Second Mode

[0108] To cause the air conditioner 100 to perform the cooling operation in the second mode, the control device 8 stops the operation of the first compressor 10 and operates the second compressor 20.

[0109] Preferably, to cause the air conditioner 100 to perform the cooling operation in the second mode, the control device 8 controls the opening degree of the first valve 80 to be equal to or smaller than a predetermined opening degree or controls the first valve 80 to be closed.

[0110] In the air conditioner 100 during the cooling operation in the second mode, the refrigerant flows in such an aspect that is indicated by broken-line arrows illustrated in Fig. 1. Specific description will be given below.

[0111] The refrigerant that the second compressor 20 discharges passes through the switching mechanism 30 and flows to the first heat exchanger 40. The refrigerant that has flowed into the first heat exchanger 40 exchanges heat with the heat source air to dissipate heat, and the refrigerant that has flowed out of the first heat exchanger 40 passes through the economizer heat exchanger 72, is decompressed by the first expansion valve 50, and flows to the second heat exchanger 60. The refrigerant flowing through the economizer heat exchanger 72 internally toward the first expansion valve 50 exchanges heat with the refrigerant flowing through the economizer heat exchanger 72 internally from the bypass flow path 130 toward the second compressor 20, and dissipates heat. The refrigerant that has flowed into the second heat exchanger 60 exchanges heat with the air in the space that is the target of air conditioning to cool the air in the space that is the target of air conditioning. The refrigerant that has absorbed heat from the air in the space that is the target of air conditioning (that has been heated by the air in the space that is the target of air conditioning) in the second heat exchanger 60 flows into the bypass flow path 130, and flows through the bypass flow path 130 toward the second refrigerant circuit 120. The refrigerant that has flowed from the bypass flow path 130 into the second refrigerant circuit 120 flows into the economizer heat exchanger 72, exchanges heat with the refrigerant flowing through the economizer heat exchanger 72 internally toward the first expansion valve 50, and is thus heated. The refrigerant heated in the economizer heat exchanger 72 is sucked into the second compressor 20.

[0112] During the cooling operation in the second mode, the control device 8 controls the number of rotations of the motor in the second compressor 20 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 each at predetermined numbers of rotations.

[0113] Note that, during the cooling operation in the second mode, the control device 8 controls the second valve 94 to be in the closed state.(2-6-4) Changing of Operating Mode from First Mode to Second Mode

[0114] An example of change control in operating mode from the first mode to the second mode in the air conditioner 100 will now be described herein with reference to flowcharts illustrated in Fig. 4A and Fig. 4B.

[0115] An example of the change control in operating mode from the first mode to the second mode will now first be described herein with reference to the flowchart illustrated in Fig. 4A.

[0116] As a premise of the description, it is assumed that the air conditioner 100 is operated in the first mode (both the first compressor 10 and the second compressor 20 are operated) at a point in time when step S1 in the processing illustrated in Fig. 4A is to be performed. Furthermore, it is assumed that the control device 8 appropriately controls the number of rotations of each of the first compressor 10 and the second compressor 20 based on a load on the air conditioner 100 (to make it possible to acquire high efficiency as much as possible).

[0117] During operation of the air conditioner 100 in the first mode, the control device 8 acquires the suction pressure of the second compressor 20, which the second sensor 22 measures (step S1).

[0118] When it is determined that the suction pressure of the second compressor 20, which has been acquired at step S1, is equal to or lower than predetermined pressure (Yes at step S2), the control device 8 stops the operation of the first compressor 10 (step S3). On the other hand, when it is determined that the suction pressure of the second compressor 20 is higher than the predetermined pressure (No at step S2), the control device 8 continues operation of the air conditioner 100 in the first mode, and the processing returns to step S1.

[0119] A reason of why the change control is performed in such an aspect will now be described herein.

[0120] When the load on the air conditioner 100 decreases in the first mode, the control device 8 decreases the number of rotations of each of the first compressor 10 and the second compressor 20. When the load required for the air conditioner 100 decreases to some extent, the number of rotations of the second compressor 20 reaches an operable minimum number of rotations. When such a state is attained, as it is impossible to further decrease the number of rotations of the second compressor 20, the operation state of the air conditioner 100 deviates from an ideal operation state, the operation efficiency decreases, and the suction pressure of the second compressor 20 decreases.

[0121] Thus, the control device 8 stops operation of the first compressor 10 when the suction pressure of the second compressor 20 is, for example, equal to or lower than predetermined suction pressure that has been specified in advance (pressure at which efficient operation is difficult to attain in the operation in the first mode) (step S3).

[0122] Furthermore, preferably, to suppress an inflow of the refrigerant at a large amount from the branch portion 82 into the second refrigerant circuit 120, the control device 8 controls the opening degree of the first valve 80 to an opening degree equal to or smaller than a predetermined opening degree (opening degree at which it is possible to suppress an inflow of the refrigerant at a large amount from the branch portion 82 into the second refrigerant circuit 120), or controls the first valve 80 to cause the first valve 80 to be closed (see step S4).

[0123] Changing of the operating mode from the first mode to the second mode may be performed based on the flowchart illustrated in Fig. 4B.

[0124] A method for changing the operating mode according to the flowchart illustrated in Fig. 4B differs from the method for changing the operating mode according to the flowchart illustrated in Fig. 4A in that the suction pressure of the first compressor 10 is used in addition to the suction pressure of the second compressor 20 for determining whether or not to change the operating mode. Specific description will be given below.

[0125] During operation of the air conditioner 100 in the first mode, the control device 8 acquires the suction pressure of the second compressor 20, which the second sensor 22 measures (step S1). Furthermore, during operation of the air conditioner 100 in the first mode, the control device 8 acquires the suction pressure of the first compressor 10, which the first sensor 12 measures (step S1A).

[0126] Then, when it is determined that differential pressure between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10 is equal to or smaller than a predetermined value (Yes at step S2A), the control device 8 stops operation of the first compressor 10 (step S3). On the other hand, when it is determined that the differential pressure between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10 is greater than the predetermined value (No at step S2A), the control device 8 performs operation in the first mode, and the processing returns to step S1.

[0127] A reason why the change control is performed in such an aspect will now be described herein.

[0128] When the load on the air conditioner 100 decreases in the first mode, the control device 8 decreases the number of rotations of each of the first compressor 10 and the second compressor 20. When the load required for the air conditioner 100 decreases to some extent, the number of rotations of the second compressor 20 reaches an operable minimum number of rotations. When such a state is attained, as it is impossible to further decrease the number of rotations of the second compressor 20, the operation state of the air conditioner 100 deviates from the ideal operation state, the operation efficiency decreases, and the suction pressure of the second compressor 20 decreases and approaches the suction pressure of the first compressor 10.

[0129] Therefore, in the flowchart illustrated in Fig. 4B, the control device 8 determines that the operation state of the air conditioner 100 has deviated from the ideal operation state and the operation efficiency has decreased based on the differential pressure between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10.

[0130] Note that, although, here, an example in which the control device 8 determines whether or not the operation state of the air conditioner 100 has deviated from the ideal operation state from a difference between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10 is described, the present disclosure is not limited the example. For example, the control device 8 may determine whether or not the operation state of the air conditioner 100 has deviated from the ideal operation state based on a value of a ratio of the suction pressure of the second compressor 20 with respect to the suction pressure of the first compressor 10.

[0131] The control device 8 stops operation of the first compressor 10 when the differential pressure between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10 is, for example, equal to or lower than a predetermined value that has been specified in advance (value at which efficient operation is difficult to attain in the operation in the first mode) (step S3).

[0132] Furthermore, preferably, to suppress an inflow of the refrigerant at a large amount from the branch portion 82 into the second refrigerant circuit 120, similar to the flowchart illustrated in Fig. 4A, the control device 8 controls the opening degree of the first valve 80 to an opening degree equal to or smaller than the predetermined opening degree (opening degree at which it is possible to suppress an inflow of the refrigerant at a large amount from the branch portion 82 into the second refrigerant circuit 120), or controls the first valve 80 to cause the first valve 80 to be closed (see step S4).

[0133] Note that, an order of executing step S3 and step S4 in the flowcharts illustrated in Fig. 4A and Fig. 4B may be reversed, that is, step S3 may be executed after step S4 is executed. Alternatively, step S3 and step S4 may be performed in parallel (simultaneously).

[0134] Although, here, an example of determining whether or not to change the first mode to the second mode based on the suction pressure of the second compressor 20 or based on the suction pressure of the first compressor 10 and the suction pressure of the second compressor 20 is described, the determination of whether or not to change the first mode to the second mode may be performed with another method.

[0135] For example, in more detail, the ideal operation state in the first mode (discharge pressure (common to both the first compressor 10 and the second compressor 20), the suction pressure of the first compressor 10, the suction pressure of the second compressor 20, and the number of rotations of each of the first compressor 10 and the second compressor 20) may be calculated in advance, and the control device 8 may detect a deviation between the ideal operation state and an actual operation state and change the operating mode of the air conditioner 100 from the first mode to the second mode based on a magnitude of the deviation (when it is determined that the deviation is excessively large).(2-6-5) Changing of Operating Mode from Second Mode to First Mode

[0136] An example of change control from the second mode to the first mode in the air conditioner 100 will now be described herein with reference to a flowchart illustrated in Fig. 5.

[0137] As a premise of the description, it is assumed that the air conditioner 100 is operated in the second mode (operation of the first compressor 10 is stopped and only the second compressor 20 is operated) at a point in time when step S11 in the processing is to be performed. Furthermore, it is assumed that the control device 8 appropriately controls the number of rotation of the second compressor 20 based on a load on the air conditioner 100.

[0138] During operation of the air conditioner 100 in the second mode, the control device 8 acquires the number of rotations of the second compressor 20 (step S11). When it is determined that the acquired number of rotations of the second compressor 20 is equal to or greater than a predetermined number of rotations (Yes at step S12), the control device 8 starts operation of the first compressor 10 (step S13). Note that, when the number of rotations of the second compressor 20 is smaller than the predetermined number of rotations (No at step S12), the control device 8 continues operation of the air conditioner 100 in the second mode, and the processing returns to step S11.

[0139] A reason why the change control is performed in such an aspect will now be described herein.

[0140] When the load increases in the second mode, the control device 8 increases the number of rotations of the second compressor 20. However, when the load required for the air conditioner 100 increases to some extent, the number of rotations of the second compressor 20 reaches an operable maximum number of rotations, making it impossible to acquire further capability. Furthermore, when the load required for the air conditioner 100 increases to some extent, the efficiency starts to significantly decrease due to the characteristics of the second compressor 20 even when the number of rotations of the second compressor 20 has not reached the operable maximum number of rotations.

[0141] Therefore, the control device 8 starts operation of the first compressor 10 when the number of rotations of the second compressor 20 is, for example, equal to or greater than the predetermined number of rotations that has been specified in advance (number of rotations at which the efficiency of the second compressor 20 starts to decrease, for example) (step S13).

[0142] Note that, when the control device 8 has controlled the opening degree of the first valve 80 to be equal to or greater than the predetermined opening degree or has caused the first valve 80 to be closed in the second mode, the control device 8 starts control for the opening degree of the first valve 80 in the first mode to allow the refrigerant to flow at an appropriate amount from the branch portion 82 to the second refrigerant circuit 120 in accordance with the load (see step S14).(2-6-6) Pressure Equalization Control when operation of Air Conditioner is stopped

[0143] Pressure equalization control between the discharge side and the suction side of the second compressor 20 using the pressure equalization mechanism 90 when the air conditioner 100 is stopped will now be described herein with reference to a flowchart illustrated in Fig. 6.

[0144] At step S21, when the control device 8 has determined to stop operation of the air conditioner 100 (for example, when a stop instruction for the air conditioner 100 has been inputted to a non-illustrated remote controller of the air conditioner 100), the control device 8 opens the second valve 94 (step S22).

[0145] At step S23, the control device 8 determines 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 a pressure sensor (not illustrated) provided on the discharge side of the second compressor 20 and the pressure measured by the second sensor 22 provided on the suction side of the second compressor 20 with each other. 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 may determine 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.

[0146] When it is determined at step S23 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 S24).

[0147] As a result, a possibility that the refrigerating machine oil in the second compressor 20 flows out of the suction port of the second compressor 20 is reduced.(3) Features

[0148] Features of the air conditioner 100 in a state where the air conditioner 100 performs the cooling operation will now be described herein.

[0149] (3-1) The air conditioner 100 serving as an example of a refrigeration cycle apparatus includes the first refrigerant circuit 110, the second refrigerant circuit 120, the bypass flow path 130, and the bypass valve 132. The first refrigerant circuit 110 includes the first compressor 10, the first heat exchanger 40 serving as an example of a radiator, the first expansion valve 50, and the second heat exchanger 60 serving as an example of a heat absorber. The second refrigerant circuit 120 includes the economizer 70, the first valve 80, and the second compressor 20. The second refrigerant circuit 120 connects the portion between the first compressor 10 and the first heat exchanger 40 in the first refrigerant circuit 110 and the portion between the first heat exchanger 40 and the first expansion valve 50 in the first refrigerant circuit 110 to each other. The economizer 70 is disposed between the first heat exchanger 40 and the second heat exchanger 60. The second compressor 20 sucks the refrigerant that has passed through the economizer 70. The bypass flow path 130 connects the portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 and the portion between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110. The bypass valve 132 is disposed in the bypass flow path 130. The second compressor 20 is a compressor that is smaller in displacement than the first compressor 10.

[0150] In the air conditioner 100, under a low-load condition, the bypass flow path 130 is utilized, and only the second compressor 20 suitable for operation under a low load with small displacement is operated. Thus, it is possible to perform efficient operation even under a low-load condition.

[0151] (3-2) In the air conditioner 100, the economizer 70 includes the economizer heat exchanger 72 serving as an example of a first economizer heat exchanger disposed between the first heat exchanger 40 and the second heat exchanger 60. The first valve 80 is an expansion valve. The economizer heat exchanger 72 is disposed between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120. The economizer heat exchanger 72 exchanges heat between the refrigerant that flows out of the first heat exchanger 40, is branched from the first refrigerant circuit 110 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 first heat exchanger 40 to exchange heat with each other.

[0152] In this air conditioner 100, using the economizer heat exchanger 72 makes it possible to improve the capability and efficiency of the air conditioner 100.

[0153] (3-3) In the air conditioner 100, the branch portion 82 is disposed between the first heat exchanger 40 and the economizer heat exchanger 72.

[0154] In this air conditioner 100, the refrigerant partially branches on the upstream side of the economizer heat exchanger 72 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 72. 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 72, compared with a case where whole of the refrigerant flowing out of the first heat exchanger 40 flows through the first refrigerant circuit 110 into the economizer heat exchanger 72.

[0155] (3-4) In the air conditioner 100, the bypass flow path 130 connects the portion between the first valve 80 and the economizer heat exchanger 72 in the second refrigerant circuit 120 and the portion between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110.

[0156] In this air conditioner 100, when the first compressor 10 is stopped and the second compressor 20 is operated in the second mode for the cooling operation, the refrigerant passing through the second heat exchanger 60 and flowing into the bypass flow path 130 exchanges heat with the refrigerant flowing through the economizer heat exchanger 72 on the side where the first refrigerant circuit 110 is present before being sucked into the second compressor 20. Therefore, in this air conditioner 100, it is possible to improve the performance and efficiency of the air conditioner 100 when the first compressor 10 is stopped and the second compressor 20 is operated.

[0157] Note that, when it is considered only a point of making operation in the second mode possible, the bypass flow path 130 may alternatively connect a portion between the economizer heat exchanger 72 and the second compressor 20 in the second refrigerant circuit 120 and a portion between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110 to each other, as illustrated by two-dot chain lines in Fig. 1.

[0158] (3-5) The air conditioner 100 includes the control device 8. The control device 8 controls operation of the first compressor 10, the second compressor 20, and the first valve 80. The control device 8 controls the opening degree of the first valve 80 to be equal to or smaller than the predetermined opening degree or to be closed in a case where the first compressor 10 is stopped and the second compressor 20 is operated.

[0159] In this air conditioner 100, it is possible to suppress, in amount, the refrigerant that does not pass through the second heat exchanger 60 but is sucked into the second compressor 20, when the first compressor 10 is stopped and the second compressor 20 is operated, making it possible to suppress a decrease in performance and efficiency of the air conditioner 100 when the first compressor 10 is stopped and the second compressor 20 is operated.

[0160] (3-6) In the air conditioner 100, the bypass valve 132 is a check valve that prevents the refrigerant from flowing from the portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 to the portion between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110.

[0161] In this air conditioner 100, it is possible to achieve, with a low-cost configuration, operation in the second mode, and it is possible to suppress a flow of the refrigerant from the bypass flow path 130 to the first refrigerant circuit 110 when both the first compressor 10 and the second compressor 20 are operated.

[0162] (3-7) In the air conditioner 100, the refrigerant contains CO 2 at least partially in its components. Especially, in the embodiment described above, the refrigerant is a refrigerant of a single type that is CO 2 .

[0163] With this air conditioner 100, which uses, as the refrigerant, the refrigerant containing CO 2 having a small global warming potential, it is possible to achieve the air conditioner 100 having a small environmental load.

[0164] (3-8) The air conditioner 100 has, as the operating modes, the first mode in which both the first compressor 10 and the second compressor 20 are operated and the second mode in which the first compressor 10 is stopped and the second compressor 20 is operated. The control device 8 determines whether or not to switch the operating mode from the first mode to the second mode based on the value of the suction pressure of the second compressor 20.

[0165] With this air conditioner 100, it is possible to detect a fact that a low-load condition has been attained based on the value of the suction pressure of the second compressor 20, making it possible to perform efficient operation even under the low-load condition.

[0166] More preferably, the control device 8 determines whether or not to switch the operating mode from the first mode to the second mode based on the value of the suction pressure of the first compressor 10 in addition to the suction pressure of the second compressor 20.

[0167] In a case where the suction pressure of the first compressor 10 is further used, it is possible to accurately detect a fact that a low-load condition has been attained, making it possible to perform efficient operation even under the low-load condition.

[0168] (3-9) In the air conditioner 100, the control device 8 determines whether or not to switch the operating mode from the second mode to the first mode based on the number of rotations of the second compressor 20.

[0169] With this air conditioner 100, it is possible to detect an increase in load based on the value of the number of rotations of the second compressor 20 and to allow the operating mode to shift to the first mode, making it possible to perform efficient operation.(4) Modification Examples

[0170] 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

[0171] 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 72, the present disclosure is not limited to such an aspect.

[0172] As illustrated in Fig. 7, a branch portion 82a may be disposed between the economizer heat exchanger 72 and the second heat exchanger 60 used as the heat absorber during the cooling operation. However, in this case, whole of the refrigerant flowing out of the first heat exchanger 40 flows through the economizer heat exchanger 72 on the side where the first refrigerant circuit 110 is present, and then, the refrigerant partially branches and flows into the second refrigerant circuit 120, possibly causing the economizer heat exchanger 72 to be large in size, compared with that according to the embodiment described above.(4-2) Modification Example B

[0173] In the embodiment described above, the bypass valve 132 is a check valve.

[0174] However, the present disclosure is not limited to this case, and, as illustrated in Fig. 8A, a bypass valve 132a may be an electrically-operated valve. Alternatively, the bypass valve 132a may be an electromagnetic valve.

[0175] As illustrated in Fig. 8B, the control device 8 is electrically connected to the bypass valve 132a to control operation of the bypass valve 132a. Specifically, the control device 8 performs control to close the bypass valve 132a during the cooling operation in the first mode and the heating operation and open the bypass valve 132a during the cooling operation in the second mode (during the cooling operation in which the first compressor 10 is stopped and the second compressor 20 is operated).(4-3) Modification Example C

[0176] In the embodiment described above, although the economizer heat exchanger 72 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.

[0177] As illustrated in Fig. 9A, the economizer 70 may include a refrigerant vessel 74 (flash tank economizer) that is gas-liquid separable and that straddles the first refrigerant circuit 110 and the second refrigerant circuit 120, instead of the economizer heat exchanger 72. 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, for example, an electromagnetic valve or an electrically-operated valve that is variable in opening degree, and is closed during the heating operation and during the cooling operation in the second mode and is opened during the cooling operation in the first mode.

[0178] To describe a state where the air conditioner 100 performs the cooling operation in the first mode, the refrigerant vessel 74 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 74. The refrigerant flowed out of the first heat exchanger 40 and decompressed and brought into a two-phase state by the second expansion valve 84 flows into the refrigerant vessel 74. The gas refrigerant separated in the refrigerant vessel 74 is sucked into the second compressor 20.

[0179] In such a configuration, 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 during the cooling operation in the first mode, making it possible to improve the capability of the air conditioner 100.

[0180] Note that an aspect of the cooling operation in the second mode in the air conditioner 100 having the configuration illustrated in Fig. 9A is identical or similar to that of the embodiment described above, except that the refrigerant that has flowed from the bypass flow path 130 into the second refrigerant circuit 120 does not flow through the economizer heat exchanger 72 but flows to the second compressor 20.

[0181] Furthermore, as illustrated in Fig. 9B, the second refrigerant circuit 120 may include, in addition to the refrigerant vessel 74, a heat exchanger 72a (example of a second economizer heat exchanger) that is disposed so as to straddle the first refrigerant circuit 110 and the second refrigerant circuit 120. The heat exchanger 72a 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 72a is arranged to exchange heat, when the air conditioner 100 performs the cooling operation in the first mode, between the refrigerant flowing out of the first heat exchanger 40 toward the second expansion valve 84 and the gas refrigerant separated in the refrigerant vessel 74. In the heat exchanger 72a, the refrigerant that has exchanged heat with the refrigerant flowing through the first refrigerant circuit 110 is sucked into the second compressor 20. In this configuration, it is possible to further improve the capability of the air conditioner 100 during the cooling operation in the first mode by further using the heat exchanger 72a compared with that of the configuration illustrated in Fig. 9A.

[0182] Note that, in the configuration illustrated in Fig. 9B, the first valve 80a is an electromagnetic valve or an electrically-operated valve that is variable in opening degree and is disposed between the refrigerant vessel 74 and the heat exchanger 72a. Similar to the air conditioner 100 described with reference to Fig. 9A, the first valve 80a is closed during the heating operation and during the cooling operation in the second mode and is opened during the cooling operation in the first mode.

[0183] Preferably, the bypass flow path 130 is connected between the first valve 80a and the heat exchanger 72a, as illustrated in Fig. 9B. With such a configuration achieved as described above, when the first compressor 10 is stopped and the second compressor 20 is operated in the second mode for the cooling operation, the refrigerant passing through the second heat exchanger 60 and flowing into the bypass flow path 130 exchanges heat with the refrigerant flowing through the heat exchanger 72a on the side where the first refrigerant circuit 110 is present before being sucked into the second compressor 20. Therefore, with this air conditioner 100, it is possible to improve the performance and efficiency of the air conditioner 100 when the first compressor 10 is stopped and the second compressor 20 is operated.

[0184] However, when it is considered only a point of making operation in the second mode possible, the bypass flow path 130 may connect a portion between the heat exchanger 72a and the second compressor 20 in the second refrigerant circuit 120 and a portion between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110 (illustrations are omitted).

[0185] Note that, also in the air conditioner 100 according to Modification Example C, the second compressor 20 is not operated during the heating operation.(4-4) Modification Example D

[0186] In the embodiment described above, the second valve 94 for the pressure equalization mechanism 90 is opened when the second compressor 20 is stopped to achieve pressure equalization between the discharge side and the suction side of the second compressor 20.

[0187] However, as illustrated in Fig. 10, the flow path 92 and the second valve 94 for the pressure equalization mechanism 90 may not be provided. Also in the configuration as illustrated in Fig. 10, as the control device 8, when the second compressor 20 is stopped, opens the first valve 80 (for example, to an opening degree close to full opening) and maintains the first valve 80 in an opened state for a predetermined period in accordance with, for example, the flowcharts illustrated in Fig. 4 (second valve 94 is replaced with the first valve 80), it is possible to make the pressure on the suction side of the second compressor 20 to approach the pressure on the discharge side of the second compressor 20.(4-5) Modification Example E

[0188] In the embodiment described above, the bypass flow path 130 connects the portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 and the portion between the second heat exchanger 60 functioning as the heat absorber and the first compressor 10 in the first refrigerant circuit 110 (specifically, between the second heat exchanger 60 and the switching mechanism 30) to each other.

[0189] Alternatively, as illustrated in Fig. 11, the bypass flow path 130 may connect a portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 and a portion between the switching mechanism 30 and the suction port of the first compressor 10 to each other. With this configuration, the check valve represented by the bypass valve 132 does not open during the heating operation, and, during the heating operation, there is no occurrence of a flow of the refrigerant flowing into an area between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 through the bypass flow path 130.<Second Embodiment>

[0190] An air conditioner 100A according to the second embodiment will now be described herein with reference to Fig. 12. Note that, similar to the first embodiment, the air conditioner is an example of the refrigeration cycle apparatus, and the refrigeration cycle apparatus having a configuration of the second embodiment may be other than the air conditioner.

[0191] The air conditioner 100A is common to the air conditioner 100 according to the first embodiment in many points. For components of the air conditioner 100A, which are common to those of the air conditioner 100, reference signs identical or similar to those used in the first embodiment are used. Differences in the air conditioner 100A from the air conditioner 100 will be mainly described herein, and, for common points in the air conditioner 100A to those in the air conditioner 100, their descriptions will be omitted unless necessary.

[0192] One of the main differences in the air conditioner 100A from the air conditioner 100 is that, in the air conditioner 100A, both the first compressor 10 and the second compressor 20 are operated simultaneously not only during the cooling operation but also during the heating operation.

[0193] Furthermore, another one of the main differences in the air conditioner 100A from the air conditioner 100 is that the air conditioner 100A has a first mode in which both the compressor (first compressor 10) in the first refrigerant circuit 110 and the compressor (second compressor 20) in the second refrigerant circuit 120 are operated simultaneously and a mode in which operation of the compressor in the first refrigerant circuit 110 is stopped and the compressor in the second refrigerant circuit 120 is operated, during both the cooling operation and the heating operation. Note that, although detailed description is omitted, the air conditioner 100A may further have a mode in which only the compressor in the first refrigerant circuit 110 is operated (mode in which the first valve 80 is closed, the second compressor 20 is stopped, and the first compressor 10 is operated) in addition to the first mode and the second mode during both the cooling operation and the heating operation.

[0194] Furthermore, still another one of the main differences in the air conditioner 100A from the air conditioner 100 is that the air conditioner 100A includes a first oil return mechanism 200 and a second oil return mechanism 300. Note that the first oil return mechanism 200 and the second oil return mechanism 300 may be provided in the air conditioner 100 according to the first embodiment.

[0195] Note that, although the pressure equalization mechanism 90 is not illustrated in Fig. 11, different from the air conditioner 100 illustrated in Fig. 1, the pressure equalization mechanism 90 may also be provided in the air conditioner 100A.

[0196] The differences described above will now be described herein in detail.(1) First Mode during Heating Operation

[0197] In the air conditioner 100A, the first compressor 10 and the second compressor 20 are operated simultaneously also during the heating operation to improve its capability. In other words, the air conditioner 100A has an operating mode (first mode in the heating operation) in which the first valve 80 is opened and the second compressor 20 is operated together with the first compressor 10, also in a case where the switching mechanism 30 switching the state of the first refrigerant circuit 110 to the second state, the second heat exchanger 60 being used as the radiator (condenser), and the first heat exchanger 40 being used as the heat absorber (evaporator).

[0198] To allow the air conditioner 100A to be operated in the first mode during the heating operation, the first refrigerant circuit 110 in the air conditioner 100A is preferably provided, between the first heat exchanger 40 and the second heat exchanger 60, with a bridge circuit 140 in which four check valves allowing the refrigerant to flow only in directions of arrows illustrated in Fig. 11 are combined with each other. As the bridge circuit 140 is provided, the branch portion 82 is disposed between the radiator and the first expansion valve 50 in the flow direction of the refrigerant in the first refrigerant circuit 110, regardless of the states of the refrigerant circuits in the air conditioner 100A. Therefore, in the first refrigerant circuit 110, regardless of the states of the refrigerant circuits in the air conditioner 100, the refrigerant flowing out of the radiator flows into the bridge circuit 140 and is fed to the branch portion 82, and the refrigerant that has not branched to the second refrigerant circuit 120 at the branch portion 82 passes through the economizer heat exchanger 72 and the first expansion valve 50, then flows into the bridge circuit 140 again, and is fed to the heat absorber.

[0199] Control by the control device 8 when the heating operation is performed in the first mode will now be described herein.

[0200] To cause the air conditioner 100A to perform the heating operation in the first mode, the control device 8 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 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 each at predetermined numbers of rotations.(2) Second Mode during Heating Operation

[0201] The air conditioner 100A has an operating mode (second mode in the heating operation) in which the first compressor 10 is stopped and only the second compressor 20 is operated during the heating operation.

[0202] Similar to the air conditioner 100, the air conditioner 100A includes a bypass flow path 130A that connects a portion between the first valve 80 and the second compressor 20 and a portion between the heat absorber and the first compressor 10. However, similar to Modification Example E described above, one end of the bypass flow path 130A is connected to a suction flow path of the first compressor 10, which connects the switching mechanism 30 and the suction port of the first compressor 10 to each other (see a branch point P1 illustrated in Fig. 12). Another end of the bypass flow path 130A may be connected between the first valve 80 and an inlet of the economizer heat exchanger 72 as illustrated by a solid line in Fig. 12, or may be connected between an outlet of the economizer heat exchanger 72 and the second compressor 20 as illustrated by a two-dot chain line in Fig. 12.

[0203] Control by the control device 8 when the heating operation is performed in the second mode will now be described herein.

[0204] To cause the air conditioner 100A to perform the heating operation in the second mode, the control device 8 stops operation of the first compressor 10 and operates the second compressor 20.

[0205] Preferably, to cause the air conditioner 100A to perform the heating operation in the second mode, the control device 8 controls the opening degree of the first valve 80 to be equal to or smaller than the predetermined opening degree or controls the first valve 80 to be closed.

[0206] In the air conditioner 100A during the heating operation in the second mode, the refrigerant flows in such an aspect that is indicated by the broken-line arrows illustrated in Fig. 1. Specific description will be given below.

[0207] The refrigerant that the second compressor 20 discharges passes through the switching mechanism 30 and flows to the second heat exchanger 60. The refrigerant that has flowed into the second heat exchanger 60 exchanges heat with the air in the space that is the target of air conditioning to dissipate heat to heat the air in the space that is the target of air conditioning. The refrigerant that has flowed out of the second heat exchanger 60 passes through the bridge circuit 140, passes through the economizer heat exchanger 72, passes through the bridge circuit 140 again, is decompressed by the first expansion valve 50, and flows to the first heat exchanger 40. The refrigerant flowing through the economizer heat exchanger 72 internally toward the first expansion valve 50 exchanges heat with the refrigerant flowing through the economizer heat exchanger 72 internally from the bypass flow path 130A toward the second compressor 20, and dissipates heat. The refrigerant that has flowed into the first heat exchanger 40 exchanges heat with the heat source air, and is thus heated. The refrigerant that has absorbed heat from the heat source air in the first heat exchanger 40 (that has been heated by the heat source air) passes through the switching mechanism 30, flows into the suction flow path of the first compressor 10, flows from the branch point P1 into the bypass flow path 130A, and flows through the bypass flow path 130A toward the second refrigerant circuit 120. The refrigerant that has flowed into the second refrigerant circuit 120 flows into the economizer heat exchanger 72 (when the one end of the bypass flow path 130A is connected between the first valve 80 and the inlet of the economizer heat exchanger 72, as illustrated by the solid line in Fig. 12), exchanges heat with the refrigerant flowing through the economizer heat exchanger 72 internally toward the first expansion valve 50, and is thus heated. The refrigerant heated in the economizer heat exchanger 72 is sucked into the second compressor 20.

[0208] During the heating operation in the second mode, the control device 8 controls the number of rotations of the motor in the second compressor 20 and the opening degree of the first expansion valve 50 based on results of measurement by the various sensors 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 to operate each at predetermined numbers of rotations.(3) First Oil Return Mechanism and Second Oil Return Mechanism

[0209] The first oil return mechanism 200 is a mechanism that returns the refrigerating machine oil that the first compressor 10 discharges together with the refrigerant that has been compressed to the suction side of the second compressor 20. The second oil return mechanism 300 is a mechanism that returns the refrigerating machine oil that the second compressor 20 discharges together with the refrigerant that has been compressed to the suction side of the first compressor 10.

[0210] As the air conditioner 100A has a configuration to allow the oil that the first compressor 10 discharges to be returned to the second compressor 20 (instead of the first compressor 10) and to allow the oil that the second compressor 20 discharges to be returned to the first compressor 10 (instead of the second compressor 20), an automatic oil equalization effect is acquired. Thus, it is possible to suppress occurrence of a situation where the oil is accumulated in one of the compressors and oil is insufficient in another one of the compressors.

[0211] The first oil return mechanism 200 includes a first oil separator 210, a first oil return flow path 220, and a first decompression mechanism 230. The first oil separator 210 is disposed between the discharge port of the first compressor 10 and the switching mechanism 30, and separates the refrigerating machine oil from the refrigerant that flows in, which is discharged from the first compressor 10 and contains the refrigerating machine oil. The first oil return flow path 220 connects the first oil separator 210 and a suction flow path of the second compressor 20 (flow path between the first valve 80 and the suction port of the second compressor 20). The first decompression mechanism 230 is disposed in the first oil return flow path 220. The first decompression mechanism 230 is, for example, but not limited to, a capillary tube.

[0212] The refrigerating machine oil separated in the first oil separator 210 flows through the first oil return flow path 220 toward the suction flow path of the second compressor 20. Note that, since pressure of the refrigerating machine oil in the first oil separator 210 represents high pressure in the refrigeration cycle and pressure of the refrigerating machine oil in the suction flow path of the second compressor 20 represents intermediate pressure in the refrigeration cycle (see Fig. 3B), the refrigerating machine oil at the high pressure, which is separated in the first oil separator 210, is decompressed to the intermediate pressure by the first decompression mechanism 230 and flows into the suction flow path of the second compressor 20. Thus, the second compressor 20 is supplied with the refrigerating machine oil used for lubrication, for example, of a compression mechanism (illustrations are omitted) of the second compressor 20.

[0213] The second oil return mechanism 300 includes a second oil separator 310, a second oil return flow path 320, and a second decompression mechanism 330. The second oil separator 310 is disposed between the discharge port of the second compressor 20 and a connecting portion between the second refrigerant circuit 120 and a discharge flow path of the first compressor 10, and separates the refrigerating machine oil from the refrigerant that flows in, which is discharged from the second compressor 20 and contains the refrigerating machine oil. The second oil return flow path 320 connects the second oil separator 310 and the suction flow path of the first compressor 10 (flow path between the switching mechanism 30 and the suction port of the first compressor 10). The second decompression mechanism 330 is disposed in the second oil return flow path 320. The second decompression mechanism 330 is, for example, but not limited to, a capillary tube.

[0214] The refrigerating machine oil separated in the second oil separator 310 flows through the second oil return flow path 320 toward the suction flow path of the first compressor 10. Note that, since pressure of the refrigerating machine oil in the second oil separator 310 represents high pressure in the refrigeration cycle and pressure of the refrigerating machine oil in the suction flow path of the first compressor 10 represents low pressure in the refrigeration cycle (see Fig. 3B), the refrigerating machine oil at the high pressure, which is separated in the second oil separator 310, is decompressed to the low pressure by the second decompression mechanism 330 and flows into the suction flow path of the first compressor 10. Thus, the first compressor 10 is supplied with the refrigerating machine oil used for lubrication, for example, of a compression mechanism (illustrations are omitted) of the first compressor 10.

[0215] Note that, although illustrations are omitted, the first oil return flow path 220 may be provided with a valve that is opened only at a timing at which the refrigerating machine oil is necessary to be supplied to the second compressor 20 (which is opened when the second compressor 20 is operated and is closed when the second compressor 20 is stopped and only the first compressor 10 is operated, for example). Furthermore, although illustrations are omitted, the second oil return flow path 320 may be provided with a valve that is opened only at a timing at which the refrigerating machine oil is necessary to be supplied to the first compressor 10 (which is opened when the first compressor 10 is operated and is closed when the first compressor 10 is stopped and only the second compressor 20 is operated, for example).(4) Features

[0216] The air conditioner 100A has features identical or similar to those of the air conditioner 100 according to the first embodiment with respect to the cooling operation. Furthermore, the air conditioner 100A also has identical or similar features to those of the air conditioner 100 according to the first embodiment with respect to the heating operation when the radiator is replaced with the second heat exchanger 60 and the heat absorber is replaced with the first heat exchanger 40.(5) Modification Examples

[0217] It is also possible to apply the modification examples of the air conditioner 100 according to the embodiment described above to the air conditioner 100A within a range where no inconsistency arises. To avoid duplicity, their descriptions are omitted here.<Note>

[0218] While the embodiments of the present disclosure have 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

[0219] 8control device (control unit) 10first compressor 20second compressor 40first heat exchanger (radiator) 50first expansion valve 60second heat exchanger (heat absorber) 70economizer 72economizer heat exchanger (first economizer heat exchanger) 72aheat exchanger (second economizer heat exchanger) 80first valve 80afirst valve 82branch portion 82abranch portion 84second expansion valve 100air conditioner (refrigeration cycle apparatus) 100Aair conditioner (refrigeration cycle apparatus) 110first refrigerant circuit 120second refrigerant circuit 130bypass flow path 130Abypass flow path 132bypass valve 132abypass valve CITATION LIST PATENT LITERATURE

[0220] PTL 1: Japanese Unexamined Patent Application Publication No. 2005-49087

Examples

modification example

(4-1) Modification Example A

[0171]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 72, the present disclosure is not limited to such an aspect.

[0172]As illustrated in Fig. 7, a branch portion 82a may be disposed between the economizer heat exchanger 72 and the second heat exchanger 60 used as the heat absorber during the cooling operation. However, in this case, whole of the refrigerant flowing out of the first heat exchanger 40 flows through the economizer heat exchanger 72 on the side where the first refrigerant circuit 110 is present, and then, the refrigerant partially branches and flows into the second refrigerant circuit 120, possibly causing the economizer heat exchanger 72 to be large in size, compared with that accordin...

modification example b

(4-2) Modification Example B

[0173]In the embodiment described above, the bypass valve 132 is a check valve.

[0174]However, the present disclosure is not limited to this case, and, as illustrated in Fig. 8A, a bypass valve 132a may be an electrically-operated valve. Alternatively, the bypass valve 132a may be an electromagnetic valve.

[0175]As illustrated in Fig. 8B, the control device 8 is electrically connected to the bypass valve 132a to control operation of the bypass valve 132a. Specifically, the control device 8 performs control to close the bypass valve 132a during the cooling operation in the first mode and the heating operation and open the bypass valve 132a during the cooling operation in the second mode (during the cooling operation in which the first compressor 10 is stopped and the second compressor 20 is operated).

modification example c

(4-3) Modification Example C

[0176]In the embodiment described above, although the economizer heat exchanger 72 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.

[0177]As illustrated in Fig. 9A, the economizer 70 may include a refrigerant vessel 74 (flash tank economizer) that is gas-liquid separable and that straddles the first refrigerant circuit 110 and the second refrigerant circuit 120, instead of the economizer heat exchanger 72. 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, for example, an electromagnetic valve or an electrically-operated valve that is variable in opening degree, and is closed during the heating operation and during the cooling operation in the second mode and is opened during the c...

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, and a refrigerant branched in the economizer from a main route for the refrigerant discharged from the first compressor to a first flow path and heading toward a heat absorber via a radiator is compressed by the second compressor and discharged to the first flow path.

[0003] In this refrigeration cycle apparatus, the second compressor is utilized, making it possible to improve its capability and efficiency.SUMMARY OF THE INVENTION <Technical Problem>

[0004] By the way, a refrigeration cycle apparatus is not always required to operate under a high load, but may be required to operate under a low load. An object of the present disclosure is to provide a refrigeration cycle apparatus capable of being efficiently operated under a low-load condition.<Solution to Problem>

[0005] A refrigeration cycle apparatus according to a first aspect comprises a first refrigerant circuit, a second refrigerant circuit, a bypass flow path, and a bypass valve. The first refrigerant circuit includes a first compressor, a radiator, a first expansion valve, and a heat absorber. The second refrigerant circuit includes an economizer, a first valve, and a second compressor. The second refrigerant circuit connects a portion between the first compressor and the radiator in the first refrigerant circuit and a portion between the radiator and the first expansion valve in the first refrigerant circuit. The economizer is disposed between the radiator and the heat absorber. The second compressor sucks a refrigerant that has passed through the economizer. The bypass flow path connects a portion between the first valve and the second compressor in the second refrigerant circuit and a portion between the heat absorber and the first compressor in the first refrigerant circuit. The bypass valve is disposed in the bypass flow path. The second compressor is a compressor that is smaller in displacement than the first compressor.

[0006] In the refrigeration cycle apparatus according to the first aspect, under a low-load condition, the bypass flow path is utilized, the first compressor is stopped, and the second compressor that is small in displacement and is suitable for operation under a low load is operated. Thus, it is possible to perform efficient operation even under the low-load condition.

[0007] A refrigeration cycle apparatus according to a second aspect is the refrigeration cycle apparatus according to the first aspect, in which the economizer includes a first economizer heat exchanger disposed between the radiator and the heat absorber. The first valve is an expansion valve. The first economizer heat exchanger is disposed between the first valve and the second compressor in the second refrigerant circuit. 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 that flows out of the radiator.

[0008] In the refrigeration cycle apparatus according to the second aspect, by compressing the refrigerant passing through the first economizer heat exchanger, it is possible to improve the capability and efficiency of the refrigeration cycle apparatus.

[0009] A refrigeration cycle apparatus according to a third aspect is the refrigeration cycle apparatus according to the second aspect, the branch portion is disposed between the radiator and the first economizer heat exchanger.

[0010] In the refrigeration cycle apparatus according to the third aspect, the refrigerant partially branches on an 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 third 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 whole of the refrigerant flowing out of the radiator flows through the first refrigerant circuit into the first economizer heat exchanger.

[0011] A refrigeration cycle apparatus according to a fourth aspect is the refrigeration cycle apparatus according to the second aspect or the third aspect, the bypass flow path connects a portion between the first valve and the first economizer heat exchanger in the second refrigerant circuit and a portion between the heat absorber and the first compressor in the first refrigerant circuit.

[0012] In the refrigeration cycle apparatus according to the fourth aspect, when the first compressor is stopped and the second compressor is operated, the refrigerant passing through the heat absorber and flowing into the bypass flow path exchanges heat with the refrigerant flowing through the first economizer heat exchanger on a side where the first refrigerant circuit is present before being sucked into the second compressor. Therefore, in the refrigeration cycle apparatus according to the fourth aspect, it is possible to improve performance and efficiency of the refrigeration cycle apparatus when the first compressor is stopped and the second compressor is operated.

[0013] A refrigeration cycle apparatus according to a fifth aspect is the refrigeration cycle apparatus according to any one of the second aspect to the fourth aspect and further includes a control unit. The control unit is configured to control operation of the first compressor, the second compressor, and the first valve. The control unit is configured to control an opening degree of the first valve to be equal to or smaller than a predetermined opening degree or to be closed in a case where the first compressor is stopped and the second compressor is operated.

[0014] In the refrigeration cycle apparatus according to the fifth aspect, it is possible to suppress, in amount, the refrigerant that does not pass through the heat absorber but is sucked into the second compressor, when the first compressor is stopped and the second compressor is operated, making it possible to suppress a decrease in performance and efficiency of the refrigeration cycle apparatus when the first compressor is stopped and the second compressor is operated.

[0015] A refrigeration cycle apparatus according to a sixth aspect is the refrigeration cycle apparatus according to any one of the second aspect to the fifth aspect, the bypass valve is a check valve that prevents the refrigerant from flowing from the portion between the first valve and the second compressor in the second refrigerant circuit to the portion between the heat absorber and the first compressor in the first refrigerant circuit.

[0016] In the refrigeration cycle apparatus according to the sixth aspect, it is possible to achieve, with a low-cost configuration, a refrigeration cycle in which the second compressor is operated in a state where the first compressor is stopped, and it is also possible to suppress a flow of the refrigerant from the bypass flow path to the first refrigerant circuit when both the first compressor and the second compressor are operated.

[0017] A refrigeration cycle apparatus according to a seventh aspect is the refrigeration cycle apparatus according to the fifth aspect, in which the bypass valve is an electromagnetic valve or an electrically-operated valve. The control unit is configured to further control the bypass valve. The control unit is configured to open the bypass valve when the first compressor is stopped and the second compressor is operated.

[0018] A refrigeration cycle apparatus according to an eighth aspect is the refrigeration cycle apparatus according to the first aspect, in which the economizer includes a second expansion valve and 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 gas refrigerant separated in the refrigerant vessel is sucked into the second compressor.

[0019] In the refrigeration cycle apparatus according to the eighth aspect, it is possible to use the second expansion valve and the refrigerant vessel to lower a temperature of the refrigerant flowing into the heat absorber, making it possible to improve the capability and efficiency of the refrigeration cycle apparatus.

[0020] A refrigeration cycle apparatus according to a ninth aspect is the refrigeration cycle apparatus according to the eighth aspect, in which the economizer 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 and the gas refrigerant flowing out of the refrigerant vessel.

[0021] In the refrigeration cycle apparatus according to the ninth 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.

[0022] A refrigeration cycle apparatus according to a tenth aspect is the refrigeration cycle apparatus according to the ninth aspect, in which the first valve is disposed between the refrigerant vessel and the second economizer heat exchanger. The bypass flow path is connected to a portion between the first valve and the second economizer heat exchanger.

[0023] In the refrigeration cycle apparatus according to the tenth aspect, when the first compressor is stopped and the second compressor is operated, the refrigerant passing through the heat absorber and flowing into the bypass flow path exchanges heat with the refrigerant flowing through a first economizer flow path in the second economizer heat exchanger before being sucked into the second compressor. Therefore, in the refrigeration cycle apparatus according to the tenth aspect, it is possible to improve the performance and efficiency of the refrigeration cycle apparatus when the first compressor is stopped and the second compressor is operated.

[0024] A refrigeration cycle apparatus according to an eleventh aspect is the refrigeration cycle apparatus according to any one of the eighth aspect to the tenth aspect and further includes a control unit. The control unit is configured to control operation of the first compressor, the second compressor, and the first valve. The control unit is configured to control an opening degree of the first valve to be equal to or smaller than a predetermined opening degree or to be closed when the first compressor is stopped and the second compressor is operated.

[0025] In the refrigeration cycle apparatus according to the eleventh aspect, it is possible to suppress, in amount, the refrigerant that does not pass through the heat absorber but is sucked into the second compressor, when the first compressor is stopped and the second compressor is operated, making it possible to suppress a decrease in performance and efficiency of the refrigeration cycle apparatus when the first compressor is stopped and the second compressor is operated.

[0026] A refrigeration cycle apparatus according to a twelfth aspect is the refrigeration cycle apparatus according to any one of the eighth aspect to the eleventh aspect, in which the bypass valve is a check valve that prevents the refrigerant from flowing from the portion between the first valve and the second compressor in the second refrigerant circuit to the portion between the heat absorber and the first compressor in the first refrigerant circuit.

[0027] In the refrigeration cycle apparatus according to the twelfth aspect, it is possible to achieve, with a low-cost configuration, a refrigeration cycle in which the first compressor is stopped and the second compressor is operated, and it is also possible to suppress a flow of the refrigerant from the bypass flow path to the first refrigerant circuit when both the first compressor and the second compressor are operated.

[0028] A refrigeration cycle apparatus according to a thirteenth aspect is the refrigeration cycle apparatus according to the eleventh aspect, in which the bypass valve is an electromagnetic valve or an electrically-operated valve. The control unit is further configured to further control the bypass valve. The control unit is configured to open the bypass valve when the first compressor is stopped and the second compressor is operated.

[0029] A refrigeration cycle apparatus according to a fourteenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the thirteenth aspect, in which the refrigerant contains CO 2 at least partially in its components.

[0030] In the refrigeration cycle apparatus according to the fourteenth aspect, a refrigerant containing CO 2 having a low global warming potential is used as the refrigerant, it is possible to achieve the refrigeration cycle apparatus having a low environmental load.

[0031] A refrigeration cycle apparatus according to a fifteenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the fourteenth aspect and has, as operating modes, a first mode in which both the first compressor and the second compressor are operated and a second mode in which the first compressor is stopped and the second compressor is operated. The operating mode is configured to be switched from the first mode to the second mode based on a value of suction pressure of the second compressor.

[0032] In the refrigeration cycle apparatus according to the fifteenth aspect, it is possible to detect that a low-load condition has been attained based on the value of the suction pressure of the second compressor, making it possible to perform efficient operation even under the low-load condition.

[0033] A refrigeration cycle apparatus according to a sixteenth aspect is the refrigeration cycle apparatus according to the fifteenth aspect, the operating mode is configured to be switched from the first mode to the second mode further based on a value of suction pressure of the first compressor.

[0034] In the refrigeration cycle apparatus according to the sixteenth aspect, it is possible to accurately detect that a low-load condition has been attained based on the value of the suction pressure of the first compressor and the value of the suction pressure of the second compressor, making it possible to perform efficient operation even under the low-load condition.

[0035] A refrigeration cycle apparatus according to a seventeenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the sixteenth aspect, has, as operating modes, a first mode in which both the first compressor and the second compressor are operated and a second mode in which the first compressor is stopped and the second compressor is operated. The operating mode is switched from the second mode to the first mode based on a number of rotations of the second compressor.

[0036] In the refrigeration cycle apparatus according to the seventeenth aspect, it is possible to detect an increase in load based on a value of the number of rotations of the second compressor and to allow the operating mode to shift to the first mode, making it possible to perform efficient operation.

[0037] A refrigeration cycle apparatus according to an eighteenth aspect is the refrigeration cycle apparatus according to any one of the first aspect to the seventeenth aspect, the refrigeration cycle apparatus has, as operating modes, only a first mode in which both the first compressor and the second compressor are operated and a second mode in which the first compressor is stopped and the second compressor is operated.BRIEF DESCRIPTION OF THE DRAWINGS

[0038] [Fig. 1] Fig. 1 is a schematic configuration diagram of an air conditioner according to a first 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. 4A] Fig. 4A is a flowchart according to an example for explaining change processing of a first mode to a second mode in the air conditioner illustrated in Fig. 1. [Fig. 4B] Fig. 4B is a flowchart according to another example for explaining the change processing of the first mode to the second mode in the air conditioner illustrated in Fig. 1. [Fig. 5] Fig. 5 is a flowchart according to an example for explaining change processing of the second mode to the first mode in the air conditioner illustrated in Fig. 1. [Fig. 6] Fig. 6 is a flowchart for explaining control when operation of the air conditioner illustrated in Fig. 1 is stopped. [Fig. 7] Fig. 7 is a schematic configuration diagram of an air conditioner according to Modification Example A. [Fig. 8A] Fig. 8A is a schematic configuration diagram of an air conditioner according to Modification Example B. [Fig. 8B] Fig. 8B is a schematic control block diagram of the air conditioner illustrated in Fig. 8A. [Fig. 9A] Fig. 9A is a schematic configuration diagram of an air conditioner according to an example of Modification Example C. [Fig. 9B] Fig. 9B is a schematic configuration diagram of an air conditioner according to another example of Modification Example C. [Fig. 10] Fig. 10 is a schematic configuration diagram of an air conditioner according to Modification Example D. [Fig. 11] Fig. 11 is a schematic configuration diagram of an air conditioner according to Modification Example E. [Fig. 12] Fig. 12 is a schematic configuration diagram of an air conditioner according to a second embodiment of the refrigeration cycle apparatus. DESCRIPTION OF EMBODIMENTS

[0039] Embodiments of a refrigeration cycle apparatus according to the present disclosure will now be described herein with reference to the accompanying drawings.<First Embodiment>(1) Overall Configuration

[0040] An overall configuration of an air conditioner 100 according to a first embodiment of a 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.

[0041] The air conditioner 100 is a device that uses a vapor compression refrigeration cycle to perform cooling or heating of air in a room in a building and the like, which is a target of a temperature adjustment, to perform cooling or heating of the room in the building and the like. Note that, although the target to which the temperature is to be adjusted by the air conditioner 100 is air in the present embodiment, the air conditioner 100 may be a device that cools or heats a medium such as water which is the target to which the temperature is to be adjusted. Furthermore, although the air conditioner 100 according to the present embodiment is a device capable of performing cooling and heating in a room in a building and the like, the air conditioner 100 may be a device dedicated for cooling.

[0042] 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. Especially, The refrigerant circuits 110, 120 in this air conditioner 100 are 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.

[0043] 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, 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, for example, on a rooftop and the like 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 connected by refrigerant connection pipes 6 to configure the first refrigerant circuit 110.

[0044] 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, 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 so that the first heat exchanger 40 functions as the radiator for the refrigerant and the second heat exchanger 60 functions as a heat absorber (evaporator) for the refrigerant).

[0045] The second refrigerant circuit 120 mainly includes a second compressor 20, an economizer 70, and a first valve 80.

[0046] The economizer 70 is disposed between the first heat exchanger 40 and the second heat exchanger 60 in the first refrigerant circuit 110, and further cools the refrigerant that flows out of the first heat exchanger 40 serving as the radiator and heads toward the second heat exchanger 60 serving as the heat absorber during the cooling operation. In the present embodiment, the economizer 70 includes an economizer heat exchanger 72 disposed between the first heat exchanger 40 and the second heat exchanger 60. The economizer heat exchanger 72 is an example of a first economizer heat exchanger. The economizer heat exchanger 72 is disposed to straddle the first refrigerant circuit 110 and the second refrigerant circuit 120.

[0047] In one of operating modes, for the cooling operation by the air conditioner 100, in which both the first compressor 10 and the second compressor 20 are operated (first mode for the cooling operation described later), the first valve 80 decompresses the refrigerant branched from the first refrigerant circuit 110 and will flow toward the economizer heat exchanger 72 in the second refrigerant circuit 120 and adjusts a flow rate of the refrigerant. In the first mode for the cooling operation described later, the second compressor 20 sucks and compresses the refrigerant that has passed through the first valve 80 and the economizer heat exchanger 72 and flows through the second refrigerant circuit 120.

[0048] The second refrigerant circuit 120 is used to improve a refrigeration cycle in performance during the cooling operation by the air conditioner 100 (in the first mode for the cooling operation described later). Specific description will be given below.

[0049] 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.

[0050] In contrast, in the air conditioner 100 according to the present disclosure, the second refrigerant circuit 120 is provided and 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 in the economizer heat exchanger 72 in the first mode for the cooling operation described later. 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).

[0051] Note that, different from the air conditioner 100 according to the present disclosure, performing intermediate injection of the refrigerant that has passed through the economizer heat exchanger 72 into the first compressor 10, without providing the second compressor 20, also makes it possible to acquire effects of improvements in capability and performance. However, since it is possible to desirably adjust intermediate pressure in the air conditioner 100 provided with the second compressor 20, it is also possible to improve the performance of the air conditioner 100 with respect to a configuration in which intermediate injection of the refrigerant that has passed through the economizer heat exchanger 72 into the first compressor 10 is performed.

[0052] The air conditioner 100 further includes, in addition to the first refrigerant circuit 110 and the second refrigerant circuit 120, a bypass flow path 130 connecting a portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 and a portion between the second heat exchanger 60 functioning as the heat absorber during the cooling operation and the first compressor 10 in the first refrigerant circuit 110 and a bypass valve 132 disposed in the bypass flow path 130.

[0053] The air conditioner 100 has, as the operating modes for the cooling operation, the first mode in which both the first compressor 10 and the second compressor 20 are operated and a second mode in which the first compressor 10 is stopped and the second compressor 20 is operated. The bypass flow path 130 and the bypass valve 132 are used to operate the air conditioner 100 in the second mode during the cooling operation.

[0054] Note that, in the present embodiment, in the cooling operation by the air conditioner 100 (as an operation state where the first heat exchanger 40 is used as the radiator and the second heat exchanger 60 is used as the heat absorber), no operating mode is provided in which operation of the second compressor 20 is stopped and only the first compressor 10 is operated (the air conditioner 100 has only the first mode and the second mode as the operating modes for the cooling operation). However, the present disclosure is not limited to this case, and the air conditioner 100 may have an operating mode for the cooling operation in which operation of the second compressor 20 is stopped and only the first compressor 10 is operated to perform cooling.

[0055] Details of the bypass flow path 130 and the bypass valve 132 and the first mode and the second mode for the cooling operation by the air conditioner 100 will be described later. Note that, in description below, to avoid redundant description, the first mode for the cooling operation may be simply referred to as the first mode and the second mode for the cooling operation may be simply referred to as the second mode.(2) Detailed Configuration

[0056] 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, the second refrigerant circuit 120, the bypass flow path 130, and the bypass valve 132. Various configurations of the air conditioner 100 will now be described herein in detail.

[0057] Note that, when the cooling operation is described below in Sections (2-1) First Refrigerant Circuit and (2-2) Second Refrigerant Circuit, operation and functions of various components in the first refrigerant circuit 110 and the second refrigerant circuit 120 when the air conditioner 100 performs the cooling operation in the first mode described above and flows of the refrigerant in the first refrigerant circuit 110 and the second refrigerant circuit 120 will be mainly described. The various components and the functions of the first refrigerant circuit 110 and the second refrigerant circuit 120 when the air conditioner 100 is operated in the second mode, and the flows of the refrigerant in the first refrigerant circuit 110 and the second refrigerant circuit 120 will be described in Section (2-3) Bypass Flow Path and Bypass Valve, together with the description regarding the bypass flow path 130 and the bypass valve 132.(2-1) First Refrigerant Circuit

[0058] 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 to each other by the pipes.

[0059] 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 preferably a scroll compressor that is high in efficiency at a large number of rotations. However, the type of the first compressor 10 may be another type of compressor.

[0060] 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.

[0061] 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 coupling states of the pipes as described below.

[0062] To set the state of the first refrigerant circuit 110 into the first state, the switching mechanism 30 connects a discharge port of the first compressor 10 and one end side of the first heat exchanger 40 to each other, and connects a suction port of the first compressor 10 and one end side of the second heat exchanger 60 to each other. Furthermore, to set the state of the first refrigerant circuit 110 into the second state, the switching mechanism 30 connects the discharge port of the first compressor 10 and the one end side of the second heat exchanger 60 to each other, and connects the suction port of the first compressor 10 and the one end side of the first heat exchanger 40 to each other.

[0063] Note that, when the air conditioner 100 is an apparatus dedicated for cooling, the air conditioner 100 may not include the switching mechanism 30.

[0064] 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.

[0065] 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 each other. The first heat exchanger 40 may be a heat exchanger that allows a medium such as water serving as a heat source and the refrigerant to exchange heat with each other.

[0066] The economizer heat exchanger 72 is disposed between the first heat exchanger 40 and the second heat exchanger 60, 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 72 is disposed between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120.

[0067] When the air conditioner 100 is operated in the first mode, the economizer heat exchanger 72 exchange heat between the refrigerant that flows out of the first heat exchanger 40 functioning as the radiator, 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 first heat exchanger 40 and flows through the economizer heat exchanger 72 toward the second heat exchanger 60 functioning as the heat absorber. As a result, when the air conditioner 100 is operated in the first mode, the refrigerant that has been cooled in the first heat exchanger 40 and that flows toward the second heat exchanger 60 (see a point c and a point d illustrated in Fig. 3B) is further cooled by the economizer heat exchanger 72 (see a point h illustrated in Fig. 3B). Note that, in the present embodiment, 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 72 (see Fig. 1).

[0068] 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 72 and the second heat exchanger 60. The first expansion valve 50 is, for example, an electronic expansion valve that is variable in opening degree.

[0069] 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 space that is 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 space that is the target of air conditioning, 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 space that is the target of air conditioning 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

[0070] The second refrigerant circuit 120 includes the second compressor 20, the economizer 70, and the first valve 80. The economizer 70 includes the economizer heat exchanger 72. The first valve 80 is, for example, an electronic expansion valve that is variable in opening degree.

[0071] 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. Therefore, following description of the flow of the refrigerant in the second refrigerant circuit 120 is given for describing the flow of the refrigerant during the cooling operation.

[0072] The second compressor 20 is a compressor that is smaller in displacement than the first compressor 10. In other words, a displacement volume of the second compressor 20 is smaller than a displacement volume of the first compressor 10. The reason of this configuration is that the second refrigerant circuit 120 (second compressor 20) is utilized in an auxiliary manner with respect to the first refrigerant circuit 110 (first compressor 10) in the first mode for the cooling operation.

[0073] The displacement of the second compressor 20 with respect to the displacement of the first compressor 10 is below 100%. Preferably, the displacement of the second compressor 20 with respect to the displacement of the first compressor 10 is below 80%. More preferably, the displacement of the second compressor 20 with respect to the displacement of the first compressor 10 ranges from a value equal to or greater than 30% to a value below 80%.

[0074] As described above, the air conditioner 100 according to the present embodiment has, as the operating modes for the cooling operation, the first mode in which both the first compressor 10 and the second compressor 20 are operated and the second mode in which the first compressor 10 is stopped and the second compressor 20 is operated. When a cooling load is low, the first compressor 10 that is large in displacement is stopped and the second compressor 20 that is small in displacement is operated as cooling operation of the second mode (instead of stopping the second compressor 20 that is small in displacement and operating the first compressor 10 that is large in displacement). Thus, there is an advantage that a controllable range of the capability of the air conditioner 100 expands.

[0075] Especially, when the displacement of the second compressor 20 with respect to the displacement of the first compressor 10 is below 80%, it is possible to allow operation of the air conditioner 100 to be continued (by allowing the second compressor 20 to be operated at a number of rotations equal to or greater than a minimum number of rotations) without causing the second compressor 20 to be operated and stopped in a frequently repeated manner even when the capability required for the air conditioner 100 is small (even during a low-load period).

[0076] Furthermore, setting the displacement of the second compressor 20 with respect to the displacement of the first compressor 10 to be equal to or greater than 30% makes it possible to suppress occurrence of such a situation that the capability of the air conditioner 100 becomes excessive or that the capability of the second compressor 20 becomes insufficient.

[0077] The second compressor 20 is a compressor that is variable in operating capacity and that includes an inverter-control-type motor. When the air conditioner 100 is operated in the first mode, the second compressor 20 is not always operated at a large capacity (number of rotations), and is often operated at a small capacity (in other words, at a small number of rotations). Therefore, in the present embodiment, the second compressor 20 is a rotary compressor (including a swing compressor) that is efficient even at a small number of rotations.

[0078] However, the type of the second compressor 20 is not limited to the rotary compressor, and may be another type of compressor that is smaller in displacement than the first compressor 10 (for example, a scroll compressor that is smaller in compression ratio than the first compressor 10).

[0079] The economizer heat exchanger 72 is, for example, a double-pipe-type heat exchanger or a plate-type heat exchanger. When the air conditioner 100 is operated in the first mode, the economizer heat exchanger 72 exchange heat between the refrigerant that flows out of the 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 first heat exchanger 40 and flows through the economizer heat exchanger 72 toward the second heat exchanger 60 in a state where mixing of the refrigerant does not occur. The refrigerant that has been decompressed by the first valve 80, has passed through the economizer heat exchanger 72, and has cooled the refrigerant flowing toward the second heat exchanger 60 when the air conditioner 100 is operated in the first mode 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) Bypass Flow Path and Bypass Valve

[0080] As described above, the bypass flow path 130 and the bypass valve 132 are used to operate the air conditioner 100 in the second mode for the cooling operation.

[0081] Firstly, the reason why the second mode is provided as one of the operating modes for the cooling operation by the air conditioner 100 will be described herein.

[0082] The first compressor 10 and the like is selected to allow the air conditioner 100 to operate even under a predetermined high-load condition. However, the air conditioner 100 is not always required to operate under a high load, but may be required to operate under a low load (for example, under a load equal to or lower than a load that is half of a maximum load). When the first compressor 10 is operated under such a low load, the first compressor 10 may be operated at a number of rotations outside a range of numbers of rotations, which is regarded as optimum from a viewpoint of efficiency. Furthermore, when the load is especially small, the capability may become excessive even when the number of rotations of the first compressor 10 or the second compressor 20 is reduced to the minimum number of rotations, and operation of the air conditioner 100 may have to be temporarily stopped, possibly resulting in a decrease in coefficient of performance (COP) of the air conditioner 100 due to that a situation arises that the air conditioner 100 is caused to be operated and stopped in a repeated manner.

[0083] Therefore, the air conditioner 100 is provided with the second mode under which a vapor compression refrigeration cycle is performed, in which the first compressor 10 is stopped and the second compressor 20 that is small in displacement is used, under a low-load condition, achieving efficient operation even under the low-load condition. Especially, in the present embodiment, the first compressor 10 that is a scroll compressor is stopped and the second compressor 20 that is a rotary compressor presenting good operation efficiency even at a small number of rotations is used, achieving efficient operation even under the low-load condition.

[0084] The air conditioner 100 is provided with the bypass flow path 130 connecting the portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 and the portion between the second heat exchanger 60 functioning as the heat absorber and the first compressor 10 in the first refrigerant circuit 110. Providing the bypass flow path 130 makes it possible to allow, when operation of the first compressor 10 is stopped and only the second compressor 20 is operated, the second compressor 20 to suck the refrigerant that has passed through the first heat exchanger 40 and the first expansion valve 50 and has cooled the air in the space that is the target of air conditioning in the second heat exchanger 60.

[0085] Especially, in the air conditioner 100, the bypass flow path 130 connects the portion between the first valve 80 and the economizer heat exchanger 72 in the second refrigerant circuit 120 and the portion between the second heat exchanger 60 and the suction side of the first compressor 10 in the first refrigerant circuit 110. Therefore, in this air conditioner 100, when the air conditioner 100 is operated in the second mode, the refrigerant passing through the second heat exchanger 60 and flowing into the bypass flow path 130 passes through the economizer heat exchanger 72 before being sucked into the second compressor 20 and exchanges heat in the economizer heat exchanger 72 with the refrigerant flowing from the first heat exchanger 40 to the second heat exchanger 60. Therefore, with this air conditioner 100, it is possible to improve the performance of the air conditioner 100 when the air conditioner 100 is operated in the second mode.

[0086] Note that, since, if the refrigerant is in a state of freely flowing through the bypass flow path 130, the pressure between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 becomes higher than the pressure between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110 (see Fig. 3B) when the air conditioner 100 is operated in the first mode, the refrigerant flows from the second refrigerant circuit 120 to the suction side of the first compressor 10. This possibly inhibits appropriate operation of the air conditioner 100. Therefore, the bypass valve 132 is provided in the bypass flow path 130. In the present embodiment, the bypass valve 132 is a check valve that prevents the refrigerant from flowing from the portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 to the portion between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110 (see Fig. 1).

[0087] Furthermore, if the first valve 80 remains at a large opening degree when the air conditioner 100 is operated in the second mode, the refrigerant that has passed through the first heat exchanger 40 may not flow into the second heat exchanger 60, but may flow into the second refrigerant circuit 120 from the branch portion 82. Therefore, preferably, when the air conditioner 100 is operated in the second mode, the opening degree of the first valve 80 is set to an opening degree equal to or lower than a predetermined opening degree (opening degree at which it is possible to suppress an inflow of the refrigerant at a large amount from the branch portion 82 into the second refrigerant circuit 120) or the first valve 80 is closed.(2-4) Pressure Equalization Mechanism

[0088] The pressure equalization mechanism 90 is a mechanism for achieving pressure equalization between the pressure on a discharge side of the second compressor 20 and the pressure on a suction side of the second compressor 20 when the second compressor 20 is stopped. Especially, the pressure equalization mechanism 90 as described herein is preferably provided when the second compressor 20 is a rotary compressor.

[0089] The pressure equalization mechanism 90 includes a flow path 92, a second valve 94, and a check valve 96.

[0090] The check valve 96 is provided between the discharge port of the second compressor 20 and a portion connecting the second refrigerant circuit 120 to the first refrigerant circuit 110 (a portion connecting the second refrigerant circuit 120 to a pipe connecting the discharge port of the first compressor 10 and the switching mechanism 30). The check valve 96 prevents the refrigerant from flowing from a side where the connecting portion between the second refrigerant circuit 120 and the first refrigerant circuit 110 is present to a side where the discharge port of the second compressor 20 is present. Note that, in a case where the air conditioner 100 does not perform the heating operation (does not include the switching mechanism 30) and a situation does not occur that the first compressor 10 is operated while the second compressor 20 is stopped, the check valve 96 may be omitted.

[0091] The 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 flow path 92 connects a portion between the discharge port of the second compressor 20 in the second refrigerant circuit 120 and the check valve 96 and the suction side of the second compressor 20 to each other.

[0092] Although illustrations are omitted, the flow path 92 may be a flow path that connects a portion between the discharge port of the first compressor 10 in the first refrigerant circuit 110 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 flow path 92 may be a flow path that connects a pipe coupling the discharge port of the first compressor 10 and the switching mechanism 30 and the suction side of the second compressor 20. Furthermore, the 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 between the second refrigerant circuit 120 and a pipe connecting the discharge port of the first compressor 10 and the switching mechanism 30).

[0093] The second valve 94 is a valve disposed in the 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.

[0094] When the second compressor 20 is stopped, the second valve 94 is controlled by the control device 8 to be described later and opened. As a result, pressure equalization between the discharge side of the second compressor 20 and the suction side of the second compressor 20 is achieved. For example, when the second compressor 20 is a rotary compressor, refrigerating machine oil in the second compressor 20 may flow out of the suction port of the second compressor 20, due to the characteristics of the compressor, when such a state continues that the pressure on the discharge side is higher than the pressure on the suction side. However, providing the pressure equalization mechanism 90 as described above suppresses occurrence of such a situation. Control for the second valve 94 by the control device 8 will be described later.(2-5) First Fan and Second Fan

[0095] The first fan 42 is housed inside a housing (illustrations are omitted) of the heat source unit 2, which houses the first compressor 10, the second compressor 20, the switching mechanism 30, the first heat exchanger 40, the economizer heat exchanger 72, the first expansion valve 50, the first valve 80, and the second valve 94, for example. The first fan 42 supplies the heat source air to the first heat exchanger 40 in the first refrigerant circuit 110, 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.

[0096] The second fan 62 is housed in the housing (illustrations are omitted) of the utilization unit 4, which houses the second heat exchanger 60, for example. The second fan 62 sucks the air from the space that is the target of air conditioning, and supplies the sucked air to the second heat exchanger 60 in the first refrigerant circuit 110, 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.(2-6) Control Device

[0097] The control device 8 is a device that controls operation of the air conditioner 100.

[0098] The control device 8 is electrically connected to the first compressor 10, the second compressor 20, 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 connected to each other to control operation of the air conditioner 100.

[0099] 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, for example), and the control device 8 is electrically connected to these sensors. For example, as illustrated in Fig. 1, the air conditioner 100 is provided with a first sensor 12 that measures suction pressure of the first compressor 10 and a second sensor 22 that measures suction pressure of the second compressor 20. The control device 8 is electrically connected to the first sensor 12 and the second sensor 22, and acquires results of measurement by these sensors.

[0100] 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 connected 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 and the like.

[0101] 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.(2-6-1) Heating Operation

[0102] To cause the air conditioner 100 to perform the heating operation, the control device 8 controls operation of the switching mechanism 30, sets 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 each at predetermined numbers of rotations.

[0103] Note that, during the heating operation, the control device 8 controls the first valve 80 and the second valve 94 to be each in a closed state, and does not operate the second compressor 20.

[0104] Note that, during the heating operation, high pressure in the refrigeration cycle is attained between the first compressor 10 and the second heat exchanger 60. Therefore, when the pressure between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 is lower than the high pressure in the refrigeration cycle, there is a possibility that the bypass valve 132 is opened and the refrigerant flows from an area between the first compressor 10 and the second heat exchanger 60, passes through the bypass flow path 130, and flows into an area between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120. However, since the first valve 80 is closed and operation of the second compressor 20 is stopped during the heating operation, the pressure in the area between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 (having no destination to which the refrigerant flows) immediately reaches the high pressure in the refrigeration cycle, and the refrigerant no longer flows through the bypass flow path 130.

[0105] Note that, when switching from the heating operation to the cooling operation, the control device 8 may perform a liquid-draining operation in which the first valve 80 is opened in a state where the state of the first refrigerant circuit 110 is the second state and the first compressor 10 is operated. As the first valve 80 is opened, the refrigerant at the high pressure in the refrigeration cycle in the bypass flow path 130 and the second refrigerant circuit 120 flows to a low-pressure side in the refrigeration cycle via the first valve 80. When performing the liquid-draining operation, the control device 8 opens the first valve 80, then causes the first compressor 10 to be stopped, and controls operation of the switching mechanism 30 to set the state of the first refrigerant circuit 110 to the first state.(2-6-2) Cooling Operation in First Mode

[0106] To cause the air conditioner 100 to perform the cooling operation in the first mode, the control device 8 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 in the air conditioner 100. Furthermore, the control device 8 operates the motors of the first fan 42 and the second fan 62 each at predetermined numbers of rotations.

[0107] Note that, during the cooling operation in the first mode, the control device 8 controls the second valve 94 to be in the closed state.(2-6-3) Cooling Operation in Second Mode

[0108] To cause the air conditioner 100 to perform the cooling operation in the second mode, the control device 8 stops the operation of the first compressor 10 and operates the second compressor 20.

[0109] Preferably, to cause the air conditioner 100 to perform the cooling operation in the second mode, the control device 8 controls the opening degree of the first valve 80 to be equal to or smaller than a predetermined opening degree or controls the first valve 80 to be closed.

[0110] In the air conditioner 100 during the cooling operation in the second mode, the refrigerant flows in such an aspect that is indicated by broken-line arrows illustrated in Fig. 1. Specific description will be given below.

[0111] The refrigerant that the second compressor 20 discharges passes through the switching mechanism 30 and flows to the first heat exchanger 40. The refrigerant that has flowed into the first heat exchanger 40 exchanges heat with the heat source air to dissipate heat, and the refrigerant that has flowed out of the first heat exchanger 40 passes through the economizer heat exchanger 72, is decompressed by the first expansion valve 50, and flows to the second heat exchanger 60. The refrigerant flowing through the economizer heat exchanger 72 internally toward the first expansion valve 50 exchanges heat with the refrigerant flowing through the economizer heat exchanger 72 internally from the bypass flow path 130 toward the second compressor 20, and dissipates heat. The refrigerant that has flowed into the second heat exchanger 60 exchanges heat with the air in the space that is the target of air conditioning to cool the air in the space that is the target of air conditioning. The refrigerant that has absorbed heat from the air in the space that is the target of air conditioning (that has been heated by the air in the space that is the target of air conditioning) in the second heat exchanger 60 flows into the bypass flow path 130, and flows through the bypass flow path 130 toward the second refrigerant circuit 120. The refrigerant that has flowed from the bypass flow path 130 into the second refrigerant circuit 120 flows into the economizer heat exchanger 72, exchanges heat with the refrigerant flowing through the economizer heat exchanger 72 internally toward the first expansion valve 50, and is thus heated. The refrigerant heated in the economizer heat exchanger 72 is sucked into the second compressor 20.

[0112] During the cooling operation in the second mode, the control device 8 controls the number of rotations of the motor in the second compressor 20 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 each at predetermined numbers of rotations.

[0113] Note that, during the cooling operation in the second mode, the control device 8 controls the second valve 94 to be in the closed state.(2-6-4) Changing of Operating Mode from First Mode to Second Mode

[0114] An example of change control in operating mode from the first mode to the second mode in the air conditioner 100 will now be described herein with reference to flowcharts illustrated in Fig. 4A and Fig. 4B.

[0115] An example of the change control in operating mode from the first mode to the second mode will now first be described herein with reference to the flowchart illustrated in Fig. 4A.

[0116] As a premise of the description, it is assumed that the air conditioner 100 is operated in the first mode (both the first compressor 10 and the second compressor 20 are operated) at a point in time when step S1 in the processing illustrated in Fig. 4A is to be performed. Furthermore, it is assumed that the control device 8 appropriately controls the number of rotations of each of the first compressor 10 and the second compressor 20 based on a load on the air conditioner 100 (to make it possible to acquire high efficiency as much as possible).

[0117] During operation of the air conditioner 100 in the first mode, the control device 8 acquires the suction pressure of the second compressor 20, which the second sensor 22 measures (step S1).

[0118] When it is determined that the suction pressure of the second compressor 20, which has been acquired at step S1, is equal to or lower than predetermined pressure (Yes at step S2), the control device 8 stops the operation of the first compressor 10 (step S3). On the other hand, when it is determined that the suction pressure of the second compressor 20 is higher than the predetermined pressure (No at step S2), the control device 8 continues operation of the air conditioner 100 in the first mode, and the processing returns to step S1.

[0119] A reason of why the change control is performed in such an aspect will now be described herein.

[0120] When the load on the air conditioner 100 decreases in the first mode, the control device 8 decreases the number of rotations of each of the first compressor 10 and the second compressor 20. When the load required for the air conditioner 100 decreases to some extent, the number of rotations of the second compressor 20 reaches an operable minimum number of rotations. When such a state is attained, as it is impossible to further decrease the number of rotations of the second compressor 20, the operation state of the air conditioner 100 deviates from an ideal operation state, the operation efficiency decreases, and the suction pressure of the second compressor 20 decreases.

[0121] Thus, the control device 8 stops operation of the first compressor 10 when the suction pressure of the second compressor 20 is, for example, equal to or lower than predetermined suction pressure that has been specified in advance (pressure at which efficient operation is difficult to attain in the operation in the first mode) (step S3).

[0122] Furthermore, preferably, to suppress an inflow of the refrigerant at a large amount from the branch portion 82 into the second refrigerant circuit 120, the control device 8 controls the opening degree of the first valve 80 to an opening degree equal to or smaller than a predetermined opening degree (opening degree at which it is possible to suppress an inflow of the refrigerant at a large amount from the branch portion 82 into the second refrigerant circuit 120), or controls the first valve 80 to cause the first valve 80 to be closed (see step S4).

[0123] Changing of the operating mode from the first mode to the second mode may be performed based on the flowchart illustrated in Fig. 4B.

[0124] A method for changing the operating mode according to the flowchart illustrated in Fig. 4B differs from the method for changing the operating mode according to the flowchart illustrated in Fig. 4A in that the suction pressure of the first compressor 10 is used in addition to the suction pressure of the second compressor 20 for determining whether or not to change the operating mode. Specific description will be given below.

[0125] During operation of the air conditioner 100 in the first mode, the control device 8 acquires the suction pressure of the second compressor 20, which the second sensor 22 measures (step S1). Furthermore, during operation of the air conditioner 100 in the first mode, the control device 8 acquires the suction pressure of the first compressor 10, which the first sensor 12 measures (step S1A).

[0126] Then, when it is determined that differential pressure between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10 is equal to or smaller than a predetermined value (Yes at step S2A), the control device 8 stops operation of the first compressor 10 (step S3). On the other hand, when it is determined that the differential pressure between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10 is greater than the predetermined value (No at step S2A), the control device 8 performs operation in the first mode, and the processing returns to step S1.

[0127] A reason why the change control is performed in such an aspect will now be described herein.

[0128] When the load on the air conditioner 100 decreases in the first mode, the control device 8 decreases the number of rotations of each of the first compressor 10 and the second compressor 20. When the load required for the air conditioner 100 decreases to some extent, the number of rotations of the second compressor 20 reaches an operable minimum number of rotations. When such a state is attained, as it is impossible to further decrease the number of rotations of the second compressor 20, the operation state of the air conditioner 100 deviates from the ideal operation state, the operation efficiency decreases, and the suction pressure of the second compressor 20 decreases and approaches the suction pressure of the first compressor 10.

[0129] Therefore, in the flowchart illustrated in Fig. 4B, the control device 8 determines that the operation state of the air conditioner 100 has deviated from the ideal operation state and the operation efficiency has decreased based on the differential pressure between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10.

[0130] Note that, although, here, an example in which the control device 8 determines whether or not the operation state of the air conditioner 100 has deviated from the ideal operation state from a difference between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10 is described, the present disclosure is not limited the example. For example, the control device 8 may determine whether or not the operation state of the air conditioner 100 has deviated from the ideal operation state based on a value of a ratio of the suction pressure of the second compressor 20 with respect to the suction pressure of the first compressor 10.

[0131] The control device 8 stops operation of the first compressor 10 when the differential pressure between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10 is, for example, equal to or lower than a predetermined value that has been specified in advance (value at which efficient operation is difficult to attain in the operation in the first mode) (step S3).

[0132] Furthermore, preferably, to suppress an inflow of the refrigerant at a large amount from the branch portion 82 into the second refrigerant circuit 120, similar to the flowchart illustrated in Fig. 4A, the control device 8 controls the opening degree of the first valve 80 to an opening degree equal to or smaller than the predetermined opening degree (opening degree at which it is possible to suppress an inflow of the refrigerant at a large amount from the branch portion 82 into the second refrigerant circuit 120), or controls the first valve 80 to cause the first valve 80 to be closed (see step S4).

[0133] Note that, an order of executing step S3 and step S4 in the flowcharts illustrated in Fig. 4A and Fig. 4B may be reversed, that is, step S3 may be executed after step S4 is executed. Alternatively, step S3 and step S4 may be performed in parallel (simultaneously).

[0134] Although, here, an example of determining whether or not to change the first mode to the second mode based on the suction pressure of the second compressor 20 or based on the suction pressure of the first compressor 10 and the suction pressure of the second compressor 20 is described, the determination of whether or not to change the first mode to the second mode may be performed with another method.

[0135] For example, in more detail, the ideal operation state in the first mode (discharge pressure (common to both the first compressor 10 and the second compressor 20), the suction pressure of the first compressor 10, the suction pressure of the second compressor 20, and the number of rotations of each of the first compressor 10 and the second compressor 20) may be calculated in advance, and the control device 8 may detect a deviation between the ideal operation state and an actual operation state and change the operating mode of the air conditioner 100 from the first mode to the second mode based on a magnitude of the deviation (when it is determined that the deviation is excessively large).(2-6-5) Changing of Operating Mode from Second Mode to First Mode

[0136] An example of change control from the second mode to the first mode in the air conditioner 100 will now be described herein with reference to a flowchart illustrated in Fig. 5.

[0137] As a premise of the description, it is assumed that the air conditioner 100 is operated in the second mode (operation of the first compressor 10 is stopped and only the second compressor 20 is operated) at a point in time when step S11 in the processing is to be performed. Furthermore, it is assumed that the control device 8 appropriately controls the number of rotation of the second compressor 20 based on a load on the air conditioner 100.

[0138] During operation of the air conditioner 100 in the second mode, the control device 8 acquires the number of rotations of the second compressor 20 (step S11). When it is determined that the acquired number of rotations of the second compressor 20 is equal to or greater than a predetermined number of rotations (Yes at step S12), the control device 8 starts operation of the first compressor 10 (step S13). Note that, when the number of rotations of the second compressor 20 is smaller than the predetermined number of rotations (No at step S12), the control device 8 continues operation of the air conditioner 100 in the second mode, and the processing returns to step S11.

[0139] A reason why the change control is performed in such an aspect will now be described herein.

[0140] When the load increases in the second mode, the control device 8 increases the number of rotations of the second compressor 20. However, when the load required for the air conditioner 100 increases to some extent, the number of rotations of the second compressor 20 reaches an operable maximum number of rotations, making it impossible to acquire further capability. Furthermore, when the load required for the air conditioner 100 increases to some extent, the efficiency starts to significantly decrease due to the characteristics of the second compressor 20 even when the number of rotations of the second compressor 20 has not reached the operable maximum number of rotations.

[0141] Therefore, the control device 8 starts operation of the first compressor 10 when the number of rotations of the second compressor 20 is, for example, equal to or greater than the predetermined number of rotations that has been specified in advance (number of rotations at which the efficiency of the second compressor 20 starts to decrease, for example) (step S13).

[0142] Note that, when the control device 8 has controlled the opening degree of the first valve 80 to be equal to or greater than the predetermined opening degree or has caused the first valve 80 to be closed in the second mode, the control device 8 starts control for the opening degree of the first valve 80 in the first mode to allow the refrigerant to flow at an appropriate amount from the branch portion 82 to the second refrigerant circuit 120 in accordance with the load (see step S14).(2-6-6) Pressure Equalization Control when operation of Air Conditioner is stopped

[0143] Pressure equalization control between the discharge side and the suction side of the second compressor 20 using the pressure equalization mechanism 90 when the air conditioner 100 is stopped will now be described herein with reference to a flowchart illustrated in Fig. 6.

[0144] At step S21, when the control device 8 has determined to stop operation of the air conditioner 100 (for example, when a stop instruction for the air conditioner 100 has been inputted to a non-illustrated remote controller of the air conditioner 100), the control device 8 opens the second valve 94 (step S22).

[0145] At step S23, the control device 8 determines 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 a pressure sensor (not illustrated) provided on the discharge side of the second compressor 20 and the pressure measured by the second sensor 22 provided on the suction side of the second compressor 20 with each other. 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 may determine 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.

[0146] When it is determined at step S23 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 S24).

[0147] As a result, a possibility that the refrigerating machine oil in the second compressor 20 flows out of the suction port of the second compressor 20 is reduced.(3) Features

[0148] Features of the air conditioner 100 in a state where the air conditioner 100 performs the cooling operation will now be described herein.

[0149] (3-1) The air conditioner 100 serving as an example of a refrigeration cycle apparatus includes the first refrigerant circuit 110, the second refrigerant circuit 120, the bypass flow path 130, and the bypass valve 132. The first refrigerant circuit 110 includes the first compressor 10, the first heat exchanger 40 serving as an example of a radiator, the first expansion valve 50, and the second heat exchanger 60 serving as an example of a heat absorber. The second refrigerant circuit 120 includes the economizer 70, the first valve 80, and the second compressor 20. The second refrigerant circuit 120 connects the portion between the first compressor 10 and the first heat exchanger 40 in the first refrigerant circuit 110 and the portion between the first heat exchanger 40 and the first expansion valve 50 in the first refrigerant circuit 110 to each other. The economizer 70 is disposed between the first heat exchanger 40 and the second heat exchanger 60. The second compressor 20 sucks the refrigerant that has passed through the economizer 70. The bypass flow path 130 connects the portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 and the portion between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110. The bypass valve 132 is disposed in the bypass flow path 130. The second compressor 20 is a compressor that is smaller in displacement than the first compressor 10.

[0150] In the air conditioner 100, under a low-load condition, the bypass flow path 130 is utilized, and only the second compressor 20 suitable for operation under a low load with small displacement is operated. Thus, it is possible to perform efficient operation even under a low-load condition.

[0151] (3-2) In the air conditioner 100, the economizer 70 includes the economizer heat exchanger 72 serving as an example of a first economizer heat exchanger disposed between the first heat exchanger 40 and the second heat exchanger 60. The first valve 80 is an expansion valve. The economizer heat exchanger 72 is disposed between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120. The economizer heat exchanger 72 exchanges heat between the refrigerant that flows out of the first heat exchanger 40, is branched from the first refrigerant circuit 110 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 first heat exchanger 40 to exchange heat with each other.

[0152] In this air conditioner 100, using the economizer heat exchanger 72 makes it possible to improve the capability and efficiency of the air conditioner 100.

[0153] (3-3) In the air conditioner 100, the branch portion 82 is disposed between the first heat exchanger 40 and the economizer heat exchanger 72.

[0154] In this air conditioner 100, the refrigerant partially branches on the upstream side of the economizer heat exchanger 72 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 72. 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 72, compared with a case where whole of the refrigerant flowing out of the first heat exchanger 40 flows through the first refrigerant circuit 110 into the economizer heat exchanger 72.

[0155] (3-4) In the air conditioner 100, the bypass flow path 130 connects the portion between the first valve 80 and the economizer heat exchanger 72 in the second refrigerant circuit 120 and the portion between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110.

[0156] In this air conditioner 100, when the first compressor 10 is stopped and the second compressor 20 is operated in the second mode for the cooling operation, the refrigerant passing through the second heat exchanger 60 and flowing into the bypass flow path 130 exchanges heat with the refrigerant flowing through the economizer heat exchanger 72 on the side where the first refrigerant circuit 110 is present before being sucked into the second compressor 20. Therefore, in this air conditioner 100, it is possible to improve the performance and efficiency of the air conditioner 100 when the first compressor 10 is stopped and the second compressor 20 is operated.

[0157] Note that, when it is considered only a point of making operation in the second mode possible, the bypass flow path 130 may alternatively connect a portion between the economizer heat exchanger 72 and the second compressor 20 in the second refrigerant circuit 120 and a portion between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110 to each other, as illustrated by two-dot chain lines in Fig. 1.

[0158] (3-5) The air conditioner 100 includes the control device 8. The control device 8 controls operation of the first compressor 10, the second compressor 20, and the first valve 80. The control device 8 controls the opening degree of the first valve 80 to be equal to or smaller than the predetermined opening degree or to be closed in a case where the first compressor 10 is stopped and the second compressor 20 is operated.

[0159] In this air conditioner 100, it is possible to suppress, in amount, the refrigerant that does not pass through the second heat exchanger 60 but is sucked into the second compressor 20, when the first compressor 10 is stopped and the second compressor 20 is operated, making it possible to suppress a decrease in performance and efficiency of the air conditioner 100 when the first compressor 10 is stopped and the second compressor 20 is operated.

[0160] (3-6) In the air conditioner 100, the bypass valve 132 is a check valve that prevents the refrigerant from flowing from the portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 to the portion between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110.

[0161] In this air conditioner 100, it is possible to achieve, with a low-cost configuration, operation in the second mode, and it is possible to suppress a flow of the refrigerant from the bypass flow path 130 to the first refrigerant circuit 110 when both the first compressor 10 and the second compressor 20 are operated.

[0162] (3-7) In the air conditioner 100, the refrigerant contains CO 2 at least partially in its components. Especially, in the embodiment described above, the refrigerant is a refrigerant of a single type that is CO 2 .

[0163] With this air conditioner 100, which uses, as the refrigerant, the refrigerant containing CO 2 having a small global warming potential, it is possible to achieve the air conditioner 100 having a small environmental load.

[0164] (3-8) The air conditioner 100 has, as the operating modes, the first mode in which both the first compressor 10 and the second compressor 20 are operated and the second mode in which the first compressor 10 is stopped and the second compressor 20 is operated. The control device 8 determines whether or not to switch the operating mode from the first mode to the second mode based on the value of the suction pressure of the second compressor 20.

[0165] With this air conditioner 100, it is possible to detect a fact that a low-load condition has been attained based on the value of the suction pressure of the second compressor 20, making it possible to perform efficient operation even under the low-load condition.

[0166] More preferably, the control device 8 determines whether or not to switch the operating mode from the first mode to the second mode based on the value of the suction pressure of the first compressor 10 in addition to the suction pressure of the second compressor 20.

[0167] In a case where the suction pressure of the first compressor 10 is further used, it is possible to accurately detect a fact that a low-load condition has been attained, making it possible to perform efficient operation even under the low-load condition.

[0168] (3-9) In the air conditioner 100, the control device 8 determines whether or not to switch the operating mode from the second mode to the first mode based on the number of rotations of the second compressor 20.

[0169] With this air conditioner 100, it is possible to detect an increase in load based on the value of the number of rotations of the second compressor 20 and to allow the operating mode to shift to the first mode, making it possible to perform efficient operation.(4) Modification Examples

[0170] 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

[0171] 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 72, the present disclosure is not limited to such an aspect.

[0172] As illustrated in Fig. 7, a branch portion 82a may be disposed between the economizer heat exchanger 72 and the second heat exchanger 60 used as the heat absorber during the cooling operation. However, in this case, whole of the refrigerant flowing out of the first heat exchanger 40 flows through the economizer heat exchanger 72 on the side where the first refrigerant circuit 110 is present, and then, the refrigerant partially branches and flows into the second refrigerant circuit 120, possibly causing the economizer heat exchanger 72 to be large in size, compared with that according to the embodiment described above.(4-2) Modification Example B

[0173] In the embodiment described above, the bypass valve 132 is a check valve.

[0174] However, the present disclosure is not limited to this case, and, as illustrated in Fig. 8A, a bypass valve 132a may be an electrically-operated valve. Alternatively, the bypass valve 132a may be an electromagnetic valve.

[0175] As illustrated in Fig. 8B, the control device 8 is electrically connected to the bypass valve 132a to control operation of the bypass valve 132a. Specifically, the control device 8 performs control to close the bypass valve 132a during the cooling operation in the first mode and the heating operation and open the bypass valve 132a during the cooling operation in the second mode (during the cooling operation in which the first compressor 10 is stopped and the second compressor 20 is operated).(4-3) Modification Example C

[0176] In the embodiment described above, although the economizer heat exchanger 72 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.

[0177] As illustrated in Fig. 9A, the economizer 70 may include a refrigerant vessel 74 (flash tank economizer) that is gas-liquid separable and that straddles the first refrigerant circuit 110 and the second refrigerant circuit 120, instead of the economizer heat exchanger 72. 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, for example, an electromagnetic valve or an electrically-operated valve that is variable in opening degree, and is closed during the heating operation and during the cooling operation in the second mode and is opened during the cooling operation in the first mode.

[0178] To describe a state where the air conditioner 100 performs the cooling operation in the first mode, the refrigerant vessel 74 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 74. The refrigerant flowed out of the first heat exchanger 40 and decompressed and brought into a two-phase state by the second expansion valve 84 flows into the refrigerant vessel 74. The gas refrigerant separated in the refrigerant vessel 74 is sucked into the second compressor 20.

[0179] In such a configuration, 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 during the cooling operation in the first mode, making it possible to improve the capability of the air conditioner 100.

[0180] Note that an aspect of the cooling operation in the second mode in the air conditioner 100 having the configuration illustrated in Fig. 9A is identical or similar to that of the embodiment described above, except that the refrigerant that has flowed from the bypass flow path 130 into the second refrigerant circuit 120 does not flow through the economizer heat exchanger 72 but flows to the second compressor 20.

[0181] Furthermore, as illustrated in Fig. 9B, the second refrigerant circuit 120 may include, in addition to the refrigerant vessel 74, a heat exchanger 72a (example of a second economizer heat exchanger) that is disposed so as to straddle the first refrigerant circuit 110 and the second refrigerant circuit 120. The heat exchanger 72a 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 72a is arranged to exchange heat, when the air conditioner 100 performs the cooling operation in the first mode, between the refrigerant flowing out of the first heat exchanger 40 toward the second expansion valve 84 and the gas refrigerant separated in the refrigerant vessel 74. In the heat exchanger 72a, the refrigerant that has exchanged heat with the refrigerant flowing through the first refrigerant circuit 110 is sucked into the second compressor 20. In this configuration, it is possible to further improve the capability of the air conditioner 100 during the cooling operation in the first mode by further using the heat exchanger 72a compared with that of the configuration illustrated in Fig. 9A.

[0182] Note that, in the configuration illustrated in Fig. 9B, the first valve 80a is an electromagnetic valve or an electrically-operated valve that is variable in opening degree and is disposed between the refrigerant vessel 74 and the heat exchanger 72a. Similar to the air conditioner 100 described with reference to Fig. 9A, the first valve 80a is closed during the heating operation and during the cooling operation in the second mode and is opened during the cooling operation in the first mode.

[0183] Preferably, the bypass flow path 130 is connected between the first valve 80a and the heat exchanger 72a, as illustrated in Fig. 9B. With such a configuration achieved as described above, when the first compressor 10 is stopped and the second compressor 20 is operated in the second mode for the cooling operation, the refrigerant passing through the second heat exchanger 60 and flowing into the bypass flow path 130 exchanges heat with the refrigerant flowing through the heat exchanger 72a on the side where the first refrigerant circuit 110 is present before being sucked into the second compressor 20. Therefore, with this air conditioner 100, it is possible to improve the performance and efficiency of the air conditioner 100 when the first compressor 10 is stopped and the second compressor 20 is operated.

[0184] However, when it is considered only a point of making operation in the second mode possible, the bypass flow path 130 may connect a portion between the heat exchanger 72a and the second compressor 20 in the second refrigerant circuit 120 and a portion between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110 (illustrations are omitted).

[0185] Note that, also in the air conditioner 100 according to Modification Example C, the second compressor 20 is not operated during the heating operation.(4-4) Modification Example D

[0186] In the embodiment described above, the second valve 94 for the pressure equalization mechanism 90 is opened when the second compressor 20 is stopped to achieve pressure equalization between the discharge side and the suction side of the second compressor 20.

[0187] However, as illustrated in Fig. 10, the flow path 92 and the second valve 94 for the pressure equalization mechanism 90 may not be provided. Also in the configuration as illustrated in Fig. 10, as the control device 8, when the second compressor 20 is stopped, opens the first valve 80 (for example, to an opening degree close to full opening) and maintains the first valve 80 in an opened state for a predetermined period in accordance with, for example, the flowcharts illustrated in Fig. 4 (second valve 94 is replaced with the first valve 80), it is possible to make the pressure on the suction side of the second compressor 20 to approach the pressure on the discharge side of the second compressor 20.(4-5) Modification Example E

[0188] In the embodiment described above, the bypass flow path 130 connects the portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 and the portion between the second heat exchanger 60 functioning as the heat absorber and the first compressor 10 in the first refrigerant circuit 110 (specifically, between the second heat exchanger 60 and the switching mechanism 30) to each other.

[0189] Alternatively, as illustrated in Fig. 11, the bypass flow path 130 may connect a portion between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 and a portion between the switching mechanism 30 and the suction port of the first compressor 10 to each other. With this configuration, the check valve represented by the bypass valve 132 does not open during the heating operation, and, during the heating operation, there is no occurrence of a flow of the refrigerant flowing into an area between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 through the bypass flow path 130.<Second Embodiment>

[0190] An air conditioner 100A according to the second embodiment will now be described herein with reference to Fig. 12. Note that, similar to the first embodiment, the air conditioner is an example of the refrigeration cycle apparatus, and the refrigeration cycle apparatus having a configuration of the second embodiment may be other than the air conditioner.

[0191] The air conditioner 100A is common to the air conditioner 100 according to the first embodiment in many points. For components of the air conditioner 100A, which are common to those of the air conditioner 100, reference signs identical or similar to those used in the first embodiment are used. Differences in the air conditioner 100A from the air conditioner 100 will be mainly described herein, and, for common points in the air conditioner 100A to those in the air conditioner 100, their descriptions will be omitted unless necessary.

[0192] One of the main differences in the air conditioner 100A from the air conditioner 100 is that, in the air conditioner 100A, both the first compressor 10 and the second compressor 20 are operated simultaneously not only during the cooling operation but also during the heating operation.

[0193] Furthermore, another one of the main differences in the air conditioner 100A from the air conditioner 100 is that the air conditioner 100A has a first mode in which both the compressor (first compressor 10) in the first refrigerant circuit 110 and the compressor (second compressor 20) in the second refrigerant circuit 120 are operated simultaneously and a mode in which operation of the compressor in the first refrigerant circuit 110 is stopped and the compressor in the second refrigerant circuit 120 is operated, during both the cooling operation and the heating operation. Note that, although detailed description is omitted, the air conditioner 100A may further have a mode in which only the compressor in the first refrigerant circuit 110 is operated (mode in which the first valve 80 is closed, the second compressor 20 is stopped, and the first compressor 10 is operated) in addition to the first mode and the second mode during both the cooling operation and the heating operation.

[0194] Furthermore, still another one of the main differences in the air conditioner 100A from the air conditioner 100 is that the air conditioner 100A includes a first oil return mechanism 200 and a second oil return mechanism 300. Note that the first oil return mechanism 200 and the second oil return mechanism 300 may be provided in the air conditioner 100 according to the first embodiment.

[0195] Note that, although the pressure equalization mechanism 90 is not illustrated in Fig. 11, different from the air conditioner 100 illustrated in Fig. 1, the pressure equalization mechanism 90 may also be provided in the air conditioner 100A.

[0196] The differences described above will now be described herein in detail.(1) First Mode during Heating Operation

[0197] In the air conditioner 100A, the first compressor 10 and the second compressor 20 are operated simultaneously also during the heating operation to improve its capability. In other words, the air conditioner 100A has an operating mode (first mode in the heating operation) in which the first valve 80 is opened and the second compressor 20 is operated together with the first compressor 10, also in a case where the switching mechanism 30 switching the state of the first refrigerant circuit 110 to the second state, the second heat exchanger 60 being used as the radiator (condenser), and the first heat exchanger 40 being used as the heat absorber (evaporator).

[0198] To allow the air conditioner 100A to be operated in the first mode during the heating operation, the first refrigerant circuit 110 in the air conditioner 100A is preferably provided, between the first heat exchanger 40 and the second heat exchanger 60, with a bridge circuit 140 in which four check valves allowing the refrigerant to flow only in directions of arrows illustrated in Fig. 11 are combined with each other. As the bridge circuit 140 is provided, the branch portion 82 is disposed between the radiator and the first expansion valve 50 in the flow direction of the refrigerant in the first refrigerant circuit 110, regardless of the states of the refrigerant circuits in the air conditioner 100A. Therefore, in the first refrigerant circuit 110, regardless of the states of the refrigerant circuits in the air conditioner 100, the refrigerant flowing out of the radiator flows into the bridge circuit 140 and is fed to the branch portion 82, and the refrigerant that has not branched to the second refrigerant circuit 120 at the branch portion 82 passes through the economizer heat exchanger 72 and the first expansion valve 50, then flows into the bridge circuit 140 again, and is fed to the heat absorber.

[0199] Control by the control device 8 when the heating operation is performed in the first mode will now be described herein.

[0200] To cause the air conditioner 100A to perform the heating operation in the first mode, the control device 8 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 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 each at predetermined numbers of rotations.(2) Second Mode during Heating Operation

[0201] The air conditioner 100A has an operating mode (second mode in the heating operation) in which the first compressor 10 is stopped and only the second compressor 20 is operated during the heating operation.

[0202] Similar to the air conditioner 100, the air conditioner 100A includes a bypass flow path 130A that connects a portion between the first valve 80 and the second compressor 20 and a portion between the heat absorber and the first compressor 10. However, similar to Modification Example E described above, one end of the bypass flow path 130A is connected to a suction flow path of the first compressor 10, which connects the switching mechanism 30 and the suction port of the first compressor 10 to each other (see a branch point P1 illustrated in Fig. 12). Another end of the bypass flow path 130A may be connected between the first valve 80 and an inlet of the economizer heat exchanger 72 as illustrated by a solid line in Fig. 12, or may be connected between an outlet of the economizer heat exchanger 72 and the second compressor 20 as illustrated by a two-dot chain line in Fig. 12.

[0203] Control by the control device 8 when the heating operation is performed in the second mode will now be described herein.

[0204] To cause the air conditioner 100A to perform the heating operation in the second mode, the control device 8 stops operation of the first compressor 10 and operates the second compressor 20.

[0205] Preferably, to cause the air conditioner 100A to perform the heating operation in the second mode, the control device 8 controls the opening degree of the first valve 80 to be equal to or smaller than the predetermined opening degree or controls the first valve 80 to be closed.

[0206] In the air conditioner 100A during the heating operation in the second mode, the refrigerant flows in such an aspect that is indicated by the broken-line arrows illustrated in Fig. 1. Specific description will be given below.

[0207] The refrigerant that the second compressor 20 discharges passes through the switching mechanism 30 and flows to the second heat exchanger 60. The refrigerant that has flowed into the second heat exchanger 60 exchanges heat with the air in the space that is the target of air conditioning to dissipate heat to heat the air in the space that is the target of air conditioning. The refrigerant that has flowed out of the second heat exchanger 60 passes through the bridge circuit 140, passes through the economizer heat exchanger 72, passes through the bridge circuit 140 again, is decompressed by the first expansion valve 50, and flows to the first heat exchanger 40. The refrigerant flowing through the economizer heat exchanger 72 internally toward the first expansion valve 50 exchanges heat with the refrigerant flowing through the economizer heat exchanger 72 internally from the bypass flow path 130A toward the second compressor 20, and dissipates heat. The refrigerant that has flowed into the first heat exchanger 40 exchanges heat with the heat source air, and is thus heated. The refrigerant that has absorbed heat from the heat source air in the first heat exchanger 40 (that has been heated by the heat source air) passes through the switching mechanism 30, flows into the suction flow path of the first compressor 10, flows from the branch point P1 into the bypass flow path 130A, and flows through the bypass flow path 130A toward the second refrigerant circuit 120. The refrigerant that has flowed into the second refrigerant circuit 120 flows into the economizer heat exchanger 72 (when the one end of the bypass flow path 130A is connected between the first valve 80 and the inlet of the economizer heat exchanger 72, as illustrated by the solid line in Fig. 12), exchanges heat with the refrigerant flowing through the economizer heat exchanger 72 internally toward the first expansion valve 50, and is thus heated. The refrigerant heated in the economizer heat exchanger 72 is sucked into the second compressor 20.

[0208] During the heating operation in the second mode, the control device 8 controls the number of rotations of the motor in the second compressor 20 and the opening degree of the first expansion valve 50 based on results of measurement by the various sensors 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 to operate each at predetermined numbers of rotations.(3) First Oil Return Mechanism and Second Oil Return Mechanism

[0209] The first oil return mechanism 200 is a mechanism that returns the refrigerating machine oil that the first compressor 10 discharges together with the refrigerant that has been compressed to the suction side of the second compressor 20. The second oil return mechanism 300 is a mechanism that returns the refrigerating machine oil that the second compressor 20 discharges together with the refrigerant that has been compressed to the suction side of the first compressor 10.

[0210] As the air conditioner 100A has a configuration to allow the oil that the first compressor 10 discharges to be returned to the second compressor 20 (instead of the first compressor 10) and to allow the oil that the second compressor 20 discharges to be returned to the first compressor 10 (instead of the second compressor 20), an automatic oil equalization effect is acquired. Thus, it is possible to suppress occurrence of a situation where the oil is accumulated in one of the compressors and oil is insufficient in another one of the compressors.

[0211] The first oil return mechanism 200 includes a first oil separator 210, a first oil return flow path 220, and a first decompression mechanism 230. The first oil separator 210 is disposed between the discharge port of the first compressor 10 and the switching mechanism 30, and separates the refrigerating machine oil from the refrigerant that flows in, which is discharged from the first compressor 10 and contains the refrigerating machine oil. The first oil return flow path 220 connects the first oil separator 210 and a suction flow path of the second compressor 20 (flow path between the first valve 80 and the suction port of the second compressor 20). The first decompression mechanism 230 is disposed in the first oil return flow path 220. The first decompression mechanism 230 is, for example, but not limited to, a capillary tube.

[0212] The refrigerating machine oil separated in the first oil separator 210 flows through the first oil return flow path 220 toward the suction flow path of the second compressor 20. Note that, since pressure of the refrigerating machine oil in the first oil separator 210 represents high pressure in the refrigeration cycle and pressure of the refrigerating machine oil in the suction flow path of the second compressor 20 represents intermediate pressure in the refrigeration cycle (see Fig. 3B), the refrigerating machine oil at the high pressure, which is separated in the first oil separator 210, is decompressed to the intermediate pressure by the first decompression mechanism 230 and flows into the suction flow path of the second compressor 20. Thus, the second compressor 20 is supplied with the refrigerating machine oil used for lubrication, for example, of a compression mechanism (illustrations are omitted) of the second compressor 20.

[0213] The second oil return mechanism 300 includes a second oil separator 310, a second oil return flow path 320, and a second decompression mechanism 330. The second oil separator 310 is disposed between the discharge port of the second compressor 20 and a connecting portion between the second refrigerant circuit 120 and a discharge flow path of the first compressor 10, and separates the refrigerating machine oil from the refrigerant that flows in, which is discharged from the second compressor 20 and contains the refrigerating machine oil. The second oil return flow path 320 connects the second oil separator 310 and the suction flow path of the first compressor 10 (flow path between the switching mechanism 30 and the suction port of the first compressor 10). The second decompression mechanism 330 is disposed in the second oil return flow path 320. The second decompression mechanism 330 is, for example, but not limited to, a capillary tube.

[0214] The refrigerating machine oil separated in the second oil separator 310 flows through the second oil return flow path 320 toward the suction flow path of the first compressor 10. Note that, since pressure of the refrigerating machine oil in the second oil separator 310 represents high pressure in the refrigeration cycle and pressure of the refrigerating machine oil in the suction flow path of the first compressor 10 represents low pressure in the refrigeration cycle (see Fig. 3B), the refrigerating machine oil at the high pressure, which is separated in the second oil separator 310, is decompressed to the low pressure by the second decompression mechanism 330 and flows into the suction flow path of the first compressor 10. Thus, the first compressor 10 is supplied with the refrigerating machine oil used for lubrication, for example, of a compression mechanism (illustrations are omitted) of the first compressor 10.

[0215] Note that, although illustrations are omitted, the first oil return flow path 220 may be provided with a valve that is opened only at a timing at which the refrigerating machine oil is necessary to be supplied to the second compressor 20 (which is opened when the second compressor 20 is operated and is closed when the second compressor 20 is stopped and only the first compressor 10 is operated, for example). Furthermore, although illustrations are omitted, the second oil return flow path 320 may be provided with a valve that is opened only at a timing at which the refrigerating machine oil is necessary to be supplied to the first compressor 10 (which is opened when the first compressor 10 is operated and is closed when the first compressor 10 is stopped and only the second compressor 20 is operated, for example).(4) Features

[0216] The air conditioner 100A has features identical or similar to those of the air conditioner 100 according to the first embodiment with respect to the cooling operation. Furthermore, the air conditioner 100A also has identical or similar features to those of the air conditioner 100 according to the first embodiment with respect to the heating operation when the radiator is replaced with the second heat exchanger 60 and the heat absorber is replaced with the first heat exchanger 40.(5) Modification Examples

[0217] It is also possible to apply the modification examples of the air conditioner 100 according to the embodiment described above to the air conditioner 100A within a range where no inconsistency arises. To avoid duplicity, their descriptions are omitted here.<Note>

[0218] While the embodiments of the present disclosure have 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

[0219] 8control device (control unit) 10first compressor 20second compressor 40first heat exchanger (radiator) 50first expansion valve 60second heat exchanger (heat absorber) 70economizer 72economizer heat exchanger (first economizer heat exchanger) 72aheat exchanger (second economizer heat exchanger) 80first valve 80afirst valve 82branch portion 82abranch portion 84second expansion valve 100air conditioner (refrigeration cycle apparatus) 100Aair conditioner (refrigeration cycle apparatus) 110first refrigerant circuit 120second refrigerant circuit 130bypass flow path 130Abypass flow path 132bypass valve 132abypass valve CITATION LIST PATENT LITERATURE

[0220] PTL 1: Japanese Unexamined Patent Application Publication No. 2005-49087

Examples

modification example

(4-1) Modification Example A

[0171]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 72, the present disclosure is not limited to such an aspect.

[0172]As illustrated in Fig. 7, a branch portion 82a may be disposed between the economizer heat exchanger 72 and the second heat exchanger 60 used as the heat absorber during the cooling operation. However, in this case, whole of the refrigerant flowing out of the first heat exchanger 40 flows through the economizer heat exchanger 72 on the side where the first refrigerant circuit 110 is present, and then, the refrigerant partially branches and flows into the second refrigerant circuit 120, possibly causing the economizer heat exchanger 72 to be large in size, compared with that accordin...

modification example b

(4-2) Modification Example B

[0173]In the embodiment described above, the bypass valve 132 is a check valve.

[0174]However, the present disclosure is not limited to this case, and, as illustrated in Fig. 8A, a bypass valve 132a may be an electrically-operated valve. Alternatively, the bypass valve 132a may be an electromagnetic valve.

[0175]As illustrated in Fig. 8B, the control device 8 is electrically connected to the bypass valve 132a to control operation of the bypass valve 132a. Specifically, the control device 8 performs control to close the bypass valve 132a during the cooling operation in the first mode and the heating operation and open the bypass valve 132a during the cooling operation in the second mode (during the cooling operation in which the first compressor 10 is stopped and the second compressor 20 is operated).

modification example c

(4-3) Modification Example C

[0176]In the embodiment described above, although the economizer heat exchanger 72 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.

[0177]As illustrated in Fig. 9A, the economizer 70 may include a refrigerant vessel 74 (flash tank economizer) that is gas-liquid separable and that straddles the first refrigerant circuit 110 and the second refrigerant circuit 120, instead of the economizer heat exchanger 72. 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, for example, an electromagnetic valve or an electrically-operated valve that is variable in opening degree, and is closed during the heating operation and during the cooling operation in the second mode and is opened during the c...

Claims

1. A refrigeration cycle apparatus (100, 100A) 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 to each other, second refrigerant circuit including an economizer (70) disposed between the radiator and the heat absorber, a first valve (80, 80a), and a second compressor (20) configured to suck a refrigerant that has passed through the economizer; a bypass flow path (130, 130A) connecting a portion between the first valve and the second compressor and a portion between the heat absorber and the first compressor; and a bypass valve (132, 132a) disposed in the bypass flow path, the second compressor being a compressor that is smaller in displacement than the first compressor.

2. The refrigeration cycle apparatus according to claim 1, wherein the economizer includes a first economizer heat exchanger (72) disposed between the radiator and the heat absorber, the first valve is an expansion valve, the first economizer heat exchanger is disposed between the first valve and the second compressor in the second refrigerant circuit, and 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 that flows out of the radiator.

3. The refrigeration cycle apparatus according to claim 2, wherein the branch portion (82) is disposed between the radiator and the first economizer heat exchanger.

4. The refrigeration cycle apparatus according to claim 2 or 3, wherein the bypass flow path connects a portion between the first valve and the first economizer heat exchanger and a portion between the heat absorber and the first compressor to each other.

5. The refrigeration cycle apparatus according to any one of claims 2 to 4, further comprising a control unit (8) configured to control operation of the first compressor, the second compressor, and the first valve, the control unit is configured to control an opening degree of the first valve to be equal to or smaller than a predetermined opening degree or to be closed in a case where the first compressor is stopped and the second compressor is operated.

6. The refrigeration cycle apparatus according to any one of claims 2 to 5, wherein the bypass valve (132) is a check valve configured to prevent the refrigerant from flowing from the portion between the first valve and the second compressor to the portion between the heat absorber and the first compressor.

7. The refrigeration cycle apparatus according to claim 5, wherein the bypass valve (132a) is an electromagnetic valve or an electrically-operated valve, and the control unit is configured to further control the bypass valve to open the bypass valve in a case where the first compressor is stopped and the second compressor is operated.

8. The refrigeration cycle apparatus according to claim 1, wherein the economizer includes a second expansion valve (84) and a refrigerant vessel (74) that is configured to separate gas and liquid, into which the refrigerant decompressed and brought into a two-phase state flows by the second expansion valve, and the gas refrigerant separated in the refrigerant vessel is sucked into the second compressor.

9. The refrigeration cycle apparatus according to claim 8, wherein the economizer further includes a second economizer heat exchanger (72a), the second economizer heat exchanger being arranged to exchange heat between the refrigerant flowing out of the radiator and the gas refrigerant flowing out of the refrigerant vessel.

10. The refrigeration cycle apparatus according to claim 9, wherein the first valve (80a) is disposed between the refrigerant vessel and the second economizer heat exchanger, and the bypass flow path is connected to a portion between the first valve and the second economizer heat exchanger.

11. The refrigeration cycle apparatus according to any one of claims 8 to 10, further comprising a control unit (8) configured to control operation of the first compressor, the second compressor, and the first valve, wherein the control unit is configured to control an opening degree of the first valve to be equal to or smaller than a predetermined opening degree or to be closed in a case where the first compressor is stopped and the second compressor is operated.

12. The refrigeration cycle apparatus according to any one of claims 8 to 11, wherein the bypass valve (132) is a check valve configured to prevent the refrigerant from flowing from the portion between the first valve and the second compressor to the portion between the heat absorber and the first compressor.

13. The refrigeration cycle apparatus according to claim 11, wherein the bypass valve (132a) is an electromagnetic valve or an electrically-operated valve, and the control unit is configured to further control the bypass valve to open the bypass valve in a case where the first compressor is stopped and the second compressor is operated.

14. The refrigeration cycle apparatus according to any one of claims 1 to 13, wherein the refrigerant contains CO2 at least partially in its components.

15. The refrigeration cycle apparatus according to any one of claims 1 to 14, wherein the refrigeration cycle apparatus has, as operating modes, a first mode in which both the first compressor and the second compressor are operated and a second mode in which the first compressor is stopped and the second compressor is operated, and the operating mode is configured to be switched from the first mode to the second mode based on a value of suction pressure of the second compressor.

16. The refrigeration cycle apparatus according to claim 15, wherein the operating mode is configured to be switched from the first mode to the second mode further based on a value of suction pressure of the first compressor.

17. The refrigeration cycle apparatus according to any one of claims 1 to 16, wherein the refrigeration cycle apparatus has, as operating modes, a first mode in which both the first compressor and the second compressor are operated and a second mode in which the first compressor is stopped and the second compressor is operated, and the operating mode is switched from the second mode to the first mode based on a number of rotations of the second compressor.

18. The refrigeration cycle apparatus according to any one of claims 1 to 17, wherein the refrigeration cycle apparatus has, as operating modes, only a first mode in which both the first compressor and the second compressor are operated and a second mode in which the first compressor is stopped and the second compressor is operated.

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