Refrigeration Cycle Equipment

Abstract

To provide a refrigeration cycle device capable of operating efficiently even under low load conditions. An air conditioner (100) has 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 the first compressor and the radiator and the radiator and the first expansion valve, 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 draws refrigerant that has passed through the economizer. The bypass flow path connects the first valve and the second compressor and the heat absorber and the first compressor. The bypass valve is disposed in the bypass flow path. The second compressor has a smaller displacement than the first compressor.

Description

[Technical Field]

[0001] This relates to a refrigeration cycle device. [Background technology]

[0002] Patent Document 1 (JP 2005-49087 A) discloses a refrigeration cycle device in which a first compressor, a second compressor, and an economizer are provided in a refrigerant circuit, and the refrigerant that is discharged from the first compressor into a first flow path and diverted at the economizer from a main refrigerant path that passes through a radiator and heads toward a heat absorber is compressed by the second compressor and discharged into the first flow path.

[0003] In this refrigeration cycle device, the use of the second compressor can improve capacity and efficiency. DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0004] However, a refrigeration cycle device is not always required to operate under high load, but may be required to operate under low load. An object of the present disclosure is to provide a refrigeration cycle device that can operate efficiently under low load conditions. [Means for solving the problem]

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

[0006] In the refrigeration cycle device of the first aspect, under low load conditions, the bypass flow path is used, the first compressor is stopped, and the second compressor, which is suitable for operation under low load with a small displacement, is operated, thereby enabling efficient operation even under low load conditions.

[0007] A refrigeration cycle apparatus according to a second aspect is the refrigeration cycle apparatus of the first aspect, wherein 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 in the second refrigerant circuit, between the first valve and the second compressor. The first economizer heat exchanger flows out of the radiator and branches into the second refrigerant circuit at a branching portion, and exchanges heat between the refrigerant decompressed by the first valve and the refrigerant flowing out of the radiator.

[0008] In the refrigeration cycle device of the second aspect, the capacity and efficiency of the refrigeration cycle device can be improved by using the first economizer heat exchanger.

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

[0010] In the refrigeration cycle apparatus of the third aspect, a portion of the refrigerant branches off upstream of the first economizer heat exchanger in the refrigerant flow direction of the first refrigerant circuit and flows through the second refrigerant circuit to the first economizer heat exchanger. Therefore, in the refrigeration cycle apparatus of the third aspect, the capacity and efficiency of the refrigeration cycle apparatus can be improved while reducing the size of the first economizer heat exchanger, compared to a case in which all of the refrigerant flowing out of the radiator flows into the first economizer heat exchanger through the first refrigerant circuit.

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

[0012] In the refrigeration cycle apparatus of the fourth aspect, when the first compressor is stopped and the second compressor is operating, the refrigerant that passes through the heat absorber and flows into the bypass passage exchanges heat with the refrigerant flowing through the first economizer heat exchanger on the first refrigerant circuit side before being drawn into the second compressor. Therefore, in the refrigeration cycle apparatus of the fourth 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 operating.

[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, further comprising a control unit. The control unit controls the operation of the first compressor, the second compressor, and the first valve. When the first compressor is stopped and the second compressor is operated, the control unit controls the first valve so that the opening degree is equal to or less than a predetermined opening degree or so that the first valve is closed.

[0014] In the refrigeration cycle device of the fifth aspect, when the first compressor is stopped and the second compressor is operating, the amount of refrigerant drawn into the second compressor without passing through the heat absorber can be reduced, and a decrease in performance and efficiency of the refrigeration cycle device when the first compressor is stopped and the second compressor is operating can be reduced.

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

[0016] In the refrigeration cycle device of the sixth aspect, it is possible to realize a refrigeration cycle in which the second compressor is operated while the first compressor is stopped, with an inexpensive configuration, and further, when both the first compressor and the second compressor are operated, it is possible to suppress the flow of refrigerant from the bypass flow path to the first refrigerant circuit.

[0017] A refrigeration cycle apparatus according to a seventh aspect is the refrigeration cycle apparatus according to the fifth aspect, wherein the bypass valve is a solenoid valve or an electric valve. The control unit further controls the bypass valve. The control unit opens the bypass valve when stopping the first compressor and operating the second compressor.

[0018] A refrigeration cycle apparatus according to an eighth aspect is the refrigeration cycle apparatus of the first aspect, wherein the economizer includes a second expansion valve and a refrigerant container capable of gas-liquid separation. Refrigerant reduced in pressure by the second expansion valve and brought into a two-phase state flows into the refrigerant container. The gas refrigerant separated in the refrigerant container is drawn into the second compressor.

[0019] In the refrigeration cycle apparatus of the eighth aspect, the second expansion valve and the refrigerant container are used to lower the temperature of the refrigerant flowing into the heat absorber, thereby improving the capacity and efficiency of the refrigeration cycle apparatus.

[0020] A refrigeration cycle apparatus according to a ninth aspect is the refrigeration cycle apparatus of the eighth aspect, wherein the economizer further includes a second economizer heat exchanger. The second economizer heat exchanger is arranged so that heat exchange occurs between the refrigerant flowing out of the radiator and the gas refrigerant flowing out of the refrigerant container.

[0021] In the refrigeration cycle apparatus of the ninth aspect, by using a second economizer heat exchanger in addition to the refrigerant container, the capacity and efficiency of the refrigeration cycle apparatus can be further improved.

[0022] A refrigeration cycle apparatus according to a tenth aspect is the refrigeration cycle apparatus of the ninth aspect, wherein the first valve is disposed between the refrigerant container and the second economizer heat exchanger, and the bypass passage is connected between the first valve and the second economizer heat exchanger.

[0023] In the refrigeration cycle apparatus of the tenth aspect, when the first compressor is stopped and the second compressor is operating, the refrigerant that passes through the heat absorber and flows into the bypass passage exchanges heat with the refrigerant flowing through the first economizer passage in the second economizer heat exchanger before being drawn into the second compressor. Therefore, in the refrigeration cycle apparatus of 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 operating.

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

[0025] In the refrigeration cycle device of the eleventh aspect, when the first compressor is stopped and the second compressor is operating, the amount of refrigerant drawn into the second compressor without passing through the heat absorber can be reduced, and a decrease in performance and efficiency of the refrigeration cycle device when the first compressor is stopped and the second compressor is operating can be reduced.

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

[0027] In the refrigeration cycle device of the twelfth aspect, a refrigeration cycle can be realized with an inexpensive configuration in which the first compressor is stopped and the second compressor is operated, and further, when both the first compressor and the second compressor are operated, the flow of refrigerant from the bypass passage to the first refrigerant circuit can be suppressed.

[0028] A refrigeration cycle apparatus according to a thirteenth aspect is the refrigeration cycle apparatus according to the eleventh aspect, wherein the bypass valve is a solenoid valve or an electric valve. The control unit further controls the bypass valve. The control unit opens the bypass valve when stopping the first compressor and operating the second compressor.

[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, wherein the refrigerant contains CO2 as at least a part of its components.

[0030] In the refrigeration cycle device of the fourteenth aspect, a refrigerant containing CO2, which has a small global warming potential, is used as the refrigerant, and therefore a refrigeration cycle device with a small environmental load can be realized.

[0031] A refrigeration cycle apparatus according to a fifteenth aspect is the refrigeration cycle apparatus according to any one of the first to fourteenth aspects, having as operation 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 operation mode is switched from the first mode to the second mode based on the value of the 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 reached based on the value of the suction pressure of the second compressor, and to operate efficiently even under the low load condition.

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

[0034] In the refrigeration cycle device of the sixteenth aspect, it is possible to accurately detect when a low load condition has been reached based on the suction pressure value of the first compressor and the suction pressure value of the second compressor, and to operate efficiently even under low load conditions.

[0035] A refrigeration cycle apparatus according to a seventeenth aspect is the refrigeration cycle apparatus according to any one of the first to sixteenth aspects, having as operation 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 operation mode is switched from the second mode to the first mode based on the rotation speed of the second compressor.

[0036] In the refrigeration cycle apparatus according to the seventeenth aspect, an increase in load is detected based on the value of the rotation speed of the second compressor, and the operation mode is shifted to the first mode, thereby enabling efficient operation.

[0037] A refrigeration cycle device according to an 18th aspect is a refrigeration cycle device according to any one of the 1st aspect to the 17th aspect, wherein the refrigeration cycle device has only two 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. [Brief explanation of the drawings]

[0038] [Figure 1] 1 is a schematic configuration diagram of an air conditioner according to a first embodiment of a refrigeration cycle device. [Figure 2] FIG. 2 is a schematic control block diagram of the air conditioner of FIG. [Figure 3A] FIG. 1 is a schematic pH diagram of an air conditioner that does not have a second refrigerant circuit (an air conditioner that has only a first refrigerant circuit). [Figure 3B] FIG. 2 is a schematic pH diagram when the air conditioner of FIG. 1 is in cooling operation. [Figure 4A] 4 is a flowchart according to one example illustrating processing for changing the first mode to the second mode in the air conditioner of FIG. [Figure 4B] 10 is a flowchart according to another example for explaining the process of changing from the first mode to the second mode in the air conditioner of FIG. [Figure 5] 10 is a flowchart according to an example illustrating processing for changing the second mode to the first mode in the air conditioner of FIG. [Figure 6] 4 is a flowchart for explaining control when stopping operation of the air conditioner of FIG. [Figure 7] FIG. 10 is a schematic configuration diagram of an air conditioner according to a modified example A. [Figure 8A] FIG. 10 is a schematic configuration diagram of an air conditioner according to a modified example B. [Figure 8B] FIG. 8B is a schematic control block diagram of the air conditioner of FIG. 8A. [Figure 9A] FIG. 10 is a schematic configuration diagram of an air conditioner according to an example of Modification C. [Figure 9B] 10 is a schematic configuration diagram of an air conditioner according to another example of Modification C. FIG. [Figure 10] FIG. 10 is a schematic configuration diagram of an air conditioner according to a modified example D. [Figure 11] FIG. 10 is a schematic configuration diagram of an air conditioner according to Modification E. [Figure 12] FIG. 4 is a schematic configuration diagram of an air conditioner according to a second embodiment of the refrigeration cycle device. DETAILED DESCRIPTION OF THE INVENTION

[0039] Hereinafter, an embodiment of a refrigeration cycle device of the present disclosure will be described with reference to the drawings.

[0040] First Embodiment (1) Overall structure The overall configuration of an air conditioner 100 according to a first embodiment of the refrigeration cycle apparatus of the present disclosure will be described with reference to Fig. 1. Fig. 1 is a schematic diagram of the air conditioner 100.

[0041] The air conditioner 100 is a device that cools or heats the air in a building or other room, the temperature of which is to be adjusted, using a vapor compression refrigeration cycle. In this embodiment, the temperature of the air conditioner 100 is adjusted to air, but the air conditioner 100 may also be a device that cools or heats a medium, such as water, the temperature of which is to be adjusted. Furthermore, the air conditioner 100 of this embodiment is a device that is capable of cooling or heating the room of a building or other room, but the air conditioner 100 may also be a device that is dedicated to cooling.

[0042] As shown in Fig. 1, the air conditioner 100 mainly has a first refrigerant circuit 110 and a second refrigerant circuit 120. The refrigerant circuits 110, 120 of the air conditioner 100 are filled with a refrigerant that contains carbon dioxide (CO2) as at least a portion of its components, although this is not limited thereto. In particular, the refrigerant circuits 110, 120 of the air conditioner 100 are filled with a single refrigerant that is carbon dioxide. Carbon dioxide is a highly safe refrigerant that has a low global warming potential, a small environmental impact, and is non-toxic and non-flammable.

[0043] 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 this embodiment, the first compressor 10, the first heat exchanger 40, and the first expansion valve 50 are mounted in a heat source unit 2 that is located outdoors, for example, on the roof of a building, and the second heat exchanger 60 is mounted in a utilization unit 4 that is located in or near the space to be air-conditioned. In the air conditioner 100, the first refrigerant circuit 110 is configured by connecting the heat source unit 2 and the utilization unit 4 by refrigerant communication piping 6.

[0044] The second refrigerant circuit 120 connects between the first compressor 10 and the radiator (first heat exchanger 40) of the first refrigerant circuit 110, and between the radiator (first heat exchanger 40) of the first refrigerant circuit 110 and the first expansion valve 50, when the air conditioner 100 is in cooling operation (in other words, when the switching mechanism 30 connects the piping so that the first heat exchanger 40 functions as a refrigerant radiator and the second heat exchanger 60 functions as a refrigerant heat absorber (evaporator)).

[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 of the first refrigerant circuit 110, and during cooling operation, further cools the refrigerant that flows out from the first heat exchanger 40, which functions as a heat radiator, and flows toward the second heat exchanger 60, which functions as a heat absorber. In this embodiment, the economizer 70 has 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 across the first refrigerant circuit 110 and the second refrigerant circuit 120.

[0047] In a cooling operation mode of the air conditioner 100 in which both the first compressor 10 and the second compressor 20 are operating (a first cooling operation mode described below), the first valve 80 reduces the pressure of the refrigerant that branches off from the first refrigerant circuit 110 and flows through the second refrigerant circuit 120 to the economizer heat exchanger 72, and adjusts the flow rate of the refrigerant. In the first cooling operation mode described below, the second compressor 20 draws in and compresses the refrigerant that has passed through the first valve 80 and the economizer heat exchanger 72 and flowed through the second refrigerant circuit 120.

[0048] The second refrigerant circuit 120 is used to improve the performance of the refrigeration cycle during cooling operation of the air conditioner 100 (in a first mode of cooling operation, which will be described later).

[0049] Assuming that the second refrigerant circuit 120 does not exist (in other words, assuming that only the first refrigerant circuit 110 is present), the CO2 refrigerant (carbon dioxide refrigerant) used in the air conditioner 100 in particular has a relatively small refrigeration effect due to its characteristics (see the pH diagram in Figure 3A), so if one tries to obtain high capacity using only the first refrigerant circuit 110, there is a problem in that the size of the first compressor 10 will increase.

[0050] In contrast, the air conditioner 100 of the present disclosure is provided with a second refrigerant circuit 120, and in the first mode of cooling operation described below, in the economizer heat exchanger 72, heat is exchanged between the refrigerant flowing through the first refrigerant circuit 110 to the second heat exchanger 60 (heat absorber) and the refrigerant flowing through the second refrigerant circuit 120 to the second compressor 20, and the refrigerant flowing through the first refrigerant circuit 110 to the second heat exchanger 60 (heat absorber) is further cooled, thereby achieving improved capacity and performance of the air conditioner 100 compared to when only the first refrigerant circuit 110 is present (see the ph diagram in Figure 3B).

[0051] Unlike the air conditioner 100 of the present disclosure, the effect of improved capacity and performance can be achieved by not providing a second compressor 20 and by intermediately injecting the refrigerant that has passed through the economizer heat exchanger 72 into the first compressor 10. However, in an air conditioner 100 that is provided with a second compressor 20, the intermediate pressure can be adjusted as desired, so the air conditioner 100 can achieve improved performance even in a configuration in which the refrigerant that has passed through the economizer heat exchanger 72 is intermediately injected into the first compressor 10.

[0052] In addition to the first refrigerant circuit 110 and the second refrigerant circuit 120, the air conditioner 100 further has a bypass flow path 130 that connects between the first valve 80 of the second refrigerant circuit 120 and the second compressor 20, and between the second heat exchanger 60 that functions as a heat absorber during cooling operation of the first refrigerant circuit 110 and the first compressor 10, and a bypass valve 132 that is arranged in the bypass flow path 130.

[0053] The air conditioner 100 has two cooling operation modes: a 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 cooling operation.

[0054] In this embodiment, the air conditioning apparatus 100 operates in cooling mode (as an operating state in which the first heat exchanger 40 is used as a heat radiator and the second heat exchanger 60 is used as a heat sink) with the second compressor 20 stopped, and does not have an operating mode in which only the first compressor 10 is operated (the air conditioning apparatus 100 has only the first mode and the second mode as operating modes for cooling operation). However, this is not limited to this, and the air conditioner 100 may have an operating mode for cooling operation in which the second compressor 20 is stopped and only the first compressor 10 is operated to perform cooling.

[0055] Details will be provided below regarding the bypass flow path 130, the bypass valve 132, and the first and second cooling operation modes of the air conditioner 100. In the following explanation, to avoid redundancy, the first cooling operation mode may be simply referred to as the first mode, and the second cooling operation mode may be simply referred to as the second mode.

[0056] (2) Detailed configuration The air conditioner 100 has a first refrigerant circuit 110, a second refrigerant circuit 120, a bypass flow path 130, and a bypass valve 132, as well as a pressure equalizing mechanism 90, a first fan 42, a second fan 62, and a control device 8. The various components of the air conditioner 100 will be described in detail below.

[0057] When explaining cooling operation in the following sections (2-1) First Refrigerant Circuit and (2-2) Second Refrigerant Circuit, the operation and function of the various components of the first refrigerant circuit 110 and the second refrigerant circuit 120 and the flow of refrigerant in the first refrigerant circuit 110 and the second refrigerant circuit 120 when the air conditioner 100 is operating in cooling mode in the first mode will be mainly explained. The various components and function of the first refrigerant circuit 110 and the second refrigerant circuit 120 and the flow of refrigerant in the first refrigerant circuit 110 and the second refrigerant circuit 120 when the air conditioner 100 is operating in the second mode will be explained in section (2-3) Bypass Flow Path and Bypass Valve, together with an explanation of the bypass flow path 130 and the bypass valve 132.

[0058] (2-1) 1st refrigerant circuit The first refrigerant circuit 110 mainly includes a first compressor 10, a switching mechanism 30, a first heat exchanger 40, a first expansion valve 50, and a second heat exchanger 60, which are connected by piping.

[0059] The first compressor 10 is a variable operating capacity compressor having an inverter-controlled motor. In this embodiment, the first compressor 10 is preferably a scroll compressor that is efficient at high rotation speeds. However, the first compressor 10 may be of another type.

[0060] The switching mechanism 30 is a mechanism that switches the 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 the solid line of the switching mechanism 30 in FIG. 1), the first heat exchanger 40 functions as a refrigerant heat radiator, and the second heat exchanger 60 functions as a refrigerant heat absorber (evaporator). When the first refrigerant circuit 110 is in the second state (see the dashed line of the switching mechanism 30 in FIG. 1), the first heat exchanger 40 functions as a refrigerant evaporator, and the second heat exchanger 60 functions as a refrigerant heat radiator.

[0061] The switching mechanism 30 is a four-way switching valve. However, the switching mechanism 30 is not limited to a four-way switching valve, and may have multiple pipes and multiple valves and realize the following pipe connection states:

[0062] When the state of the first refrigerant circuit 110 is set to the first state, the switching mechanism 30 connects the discharge port of the first compressor 10 to one end of the first heat exchanger 40, and also connects the suction port of the first compressor 10 to one end of the second heat exchanger 60. When the state of the first refrigerant circuit 110 is set to the second state, the switching mechanism 30 connects the discharge port of the first compressor 10 to one end of the second heat exchanger 60, and also connects the suction port of the first compressor 10 to one end of the first heat exchanger 40.

[0063] It should be noted that if the air conditioner 100 is a device dedicated to cooling, the air conditioner 100 does not need to have the switching mechanism 30.

[0064] In the first heat exchanger 40, heat is exchanged between the refrigerant and air (heat source air) supplied by a first fan 42 described below. When the first refrigerant circuit 110 is in a first state, the first heat exchanger 40 functions as a radiator of the refrigerant, and the refrigerant is cooled by the heat source air in the first heat exchanger 40. When the first refrigerant circuit 110 is in a second state, the first heat exchanger 40 functions as a heat absorber (evaporator) of 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 having a large number of heat transfer tubes and fins.

[0065] The first heat exchanger 40 is not limited to a heat exchanger that exchanges heat between heat source air and a refrigerant, but may be a heat exchanger that exchanges heat between a medium such as water as a heat source and a refrigerant.

[0066] The economizer heat exchanger 72 is disposed in the first refrigerant circuit 110 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. The economizer heat exchanger 72 is disposed in the second refrigerant circuit 120 between the first valve 80 and the second compressor 20.

[0067] When the air conditioner 100 is operated in the first mode, the economizer heat exchanger 72 exchanges heat between the refrigerant that flows out of the first heat exchanger 40, which functions as a radiator, and branches into the second refrigerant circuit 120 at the branching section 82. The refrigerant is decompressed by the first valve 80 (described later) and flows through the economizer heat exchanger 72 toward the second heat exchanger 60, which functions as a heat absorber. As a result, when the air conditioner 100 is operated in the first mode, the refrigerant that flows toward the second heat exchanger 60, cooled in the first heat exchanger 40 (see points c and d in FIG. 3B), is further cooled by the economizer heat exchanger 72 (see point h in FIG. 3B). In this embodiment, the branching section 82 is disposed between the first heat exchanger 40, which functions as a radiator during cooling operation, and the economizer heat exchanger 72 (see FIG. 1).

[0068] The first expansion valve 50 reduces the pressure of 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 with a variable opening.

[0069] In the second heat exchanger 60, heat is exchanged between the refrigerant and the air in the space to be air-conditioned. The second heat exchanger 60 is housed in a housing (not shown), and the air in the space to be air-conditioned is supplied by a second fan 62 arranged in the housing. In the second heat exchanger 60, heat is exchanged between the refrigerant and the air in the space to be air-conditioned supplied by the second fan 62. When the first refrigerant circuit 110 is in a first state, the second heat exchanger 60 functions as a heat absorber of the refrigerant, and the air in the space to be air-conditioned is cooled by the refrigerant in the second heat exchanger 60. When the first refrigerant circuit 110 is in a second state, the second heat exchanger 60 functions as a radiator of the refrigerant, and the air in the space to be air-conditioned 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 having a large number of heat transfer tubes and fins.

[0070] (2-2)Second refrigerant circuit The second refrigerant circuit 120 includes a second compressor 20, an economizer 70, and a first valve 80. The economizer 70 includes an economizer heat exchanger 72. The first valve 80 is, for example, an electronic expansion valve with a variable opening.

[0071] The second refrigerant circuit 120 is mainly used during cooling operation (the second compressor 20 is operated during cooling operation), and is not used during heating operation. In other words, during heating operation, refrigerant basically does not flow through the second refrigerant circuit 120. Therefore, the following description of the flow of refrigerant in the second refrigerant circuit 120 will describe the flow of refrigerant during cooling operation.

[0072] The second compressor 20 is a compressor with a smaller displacement than the first compressor 10. In other words, the displacement volume of the second compressor 20 is smaller than the displacement volume of the first compressor 10. This is because the second refrigerant circuit 120 (second compressor 20) is used auxiliary to the first refrigerant circuit 110 (first compressor 10) in the first mode of cooling operation.

[0073] The ratio of the displacement of the second compressor 20 to the displacement of the first compressor 10 is less than 100%. Preferably, the ratio of the displacement of the second compressor 20 to the displacement of the first compressor 10 is less than 80%. More preferably, the ratio of the displacement of the second compressor 20 to the displacement of the first compressor 10 is in the range of 30% or more and less than 80%.

[0074] As described above, the air conditioner 100 of this embodiment has two cooling operation modes: a 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. When the cooling load is low, cooling operation in the second mode stops the first compressor 10 with a large displacement and operates with the second compressor 20 with a small displacement (rather than stopping the second compressor 20 with a small displacement and operating the first compressor 10 with a large displacement), which has the advantage of widening the controllable range of the capacity of the air conditioner 100.

[0075] In particular, when the displacement of the second compressor 20 is less than 80% of the displacement of the first compressor 10, even if the capacity required of the air conditioner 100 is small (even under low load), the air conditioner 100 can continue to operate without frequently causing the second compressor 20 to repeatedly start and stop (by operating the second compressor 20 at a minimum rotation speed or higher).

[0076] Furthermore, by setting the displacement of the second compressor 20 to be 30% or more of the displacement of the first compressor 10, the occurrence of excessive capacity of the air conditioner 100 and insufficient capacity of the second compressor 20 can be suppressed.

[0077] The second compressor 20 is a variable-capacity compressor having an inverter-controlled motor. When the air conditioner 100 is operated in the first mode, the second compressor 20 is not always operated at a high capacity (rotation speed), but is often operated at a low capacity (in other words, at a low rotation speed). Therefore, in this embodiment, the second compressor 20 is a rotary compressor (including a swing compressor) that is efficient even at a low rotation speed.

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

[0079] The economizer heat exchanger 72 is, for example, a double-pipe heat exchanger or a plate-type heat exchanger. When the air conditioner 100 operates in the first mode, the economizer heat exchanger 72 receives the refrigerant that flows out of the first heat exchanger 40, branches into the second refrigerant circuit 120 at the branching section 82, and is depressurized by the first valve 80. The refrigerant also flows out of the first heat exchanger 40, passes through the economizer heat exchanger 72, and flows toward the second heat exchanger 60. The two refrigerants exchange heat without mixing. When the air conditioner 100 operates in the first mode, the refrigerant that has been depressurized by the first valve 80 and flows toward the second heat exchanger 60 after passing through the economizer heat exchanger 72 cools the refrigerant, becomes gaseous, and is drawn into the second compressor 20 (see point f on the ph diagram in FIG. 3B).

[0080] (2-3) Bypass flow path and bypass valve As described above, the bypass flow path 130 and the bypass valve 132 are used to operate the air conditioner 100 in the second cooling mode.

[0081] First, the reason for providing the second mode as an operating mode for cooling operation of the air conditioner 100 will be explained.

[0082] The first compressor 10 and other components are selected so that the air conditioner 100 can operate under predetermined high-load conditions. However, the air conditioner 100 is not always required to operate under high loads; there are cases where it is required to operate under low loads (for example, at a load less than half the maximum load). When the first compressor 10 is operated under such low loads, the first compressor 10 may operate at a rotation speed below the optimum rotation speed range from the viewpoint of efficiency. Furthermore, when the load is particularly light, even if the rotation speed of the first compressor 10 or the second compressor 20 is reduced to the minimum rotation speed, the capacity may be excessive, forcing the air conditioner 100 to temporarily stop operation. This may result in a situation where the air conditioner 100 is repeatedly started and stopped, and may lower the COP of the air conditioner 100.

[0083] Therefore, the air conditioner 100 provides a second mode in which, under low load conditions, the first compressor 10 is stopped and a vapor compression refrigeration cycle is performed using the second compressor 20 with a small displacement, thereby achieving efficient operation even under low load conditions. In particular, in this embodiment, the first compressor 10, which is a scroll compressor, is stopped and the second compressor 20, which is a rotary compressor that operates efficiently even at low rotation speeds, is used, thereby achieving efficient operation even under low load conditions.

[0084] In the air conditioner 100, a bypass flow path 130 is provided that connects between the first valve 80 of the second refrigerant circuit 120 and the second compressor 20, and between the second heat exchanger 60 that functions as a heat absorber of the first refrigerant circuit 110 and the first compressor 10. By providing the bypass flow path 130, when operation of the first compressor 10 is stopped and only the second compressor 20 is operated, the second compressor 20 can draw in the refrigerant that has passed through the first heat exchanger 40 and the first expansion valve 50 and cooled the air in the space to be air-conditioned in the second heat exchanger 60.

[0085] In particular, in this air conditioner 100, the bypass flow path 130 connects between the first valve 80 and the economizer heat exchanger 72 of the second refrigerant circuit 120, and between the second heat exchanger 60 and the suction side of the first compressor 10 of the first refrigerant circuit 110. Therefore, in this air conditioner 100, when the air conditioner 100 is operated in the second mode, the refrigerant that passes through the second heat exchanger 60 and flows into the bypass flow path 130 passes through the economizer heat exchanger 72 before being drawn into the second compressor 20, and in the economizer heat exchanger 72, exchanges heat with the refrigerant flowing from the first heat exchanger 40 to the second heat exchanger 60. Therefore, in this air conditioner 100, the performance of the air conditioner 100 can be improved when the air conditioner 100 is operated in the second mode.

[0086] If the refrigerant flows freely through the bypass flow path 130, when the air conditioner 100 is operated in the first mode, the pressure between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 will be higher than the pressure between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110 (see FIG. 3B ). This could cause refrigerant to flow from the second refrigerant circuit 120 to the suction side of the first compressor 10, hindering proper operation of the air conditioner 100. For this reason, a bypass valve 132 is provided in the bypass flow path 130. In this embodiment, the bypass valve 132 is a check valve that prohibits refrigerant from flowing from between the first valve 80 and the second compressor 20 in the second refrigerant circuit 120 to between the second heat exchanger 60 and the first compressor 10 in the first refrigerant circuit 110 (see FIG. 1 ).

[0087] Furthermore, if the opening degree of the first valve 80 remains large when the air conditioner 100 is operated in the second mode, there is a risk that the refrigerant that has passed through the first heat exchanger 40 will flow from the branching portion 82 into the second refrigerant circuit 120 without flowing to the second heat exchanger 60. Therefore, preferably, when the air conditioner 100 is operated in the second mode, the opening degree of the first valve 80 is set to a predetermined opening degree or less (an opening degree that can prevent a large amount of refrigerant from flowing from the branching portion 82 into the second refrigerant circuit 120), or the first valve 80 is closed.

[0088] (2-4) Pressure equalization mechanism The pressure equalizing mechanism 90 is a mechanism that equalizes the pressure on the discharge side of the second compressor 20 and the pressure on the suction side of the second compressor 20 when the second compressor 20 is stopped. It is particularly preferable to provide such a pressure equalizing mechanism 90 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 connection portion of the second refrigerant circuit 120 with the first refrigerant circuit 110 (a connection portion of the second refrigerant circuit 120 with a pipe that connects the discharge port of the first compressor 10 with the switching mechanism 30). The check valve 96 prevents refrigerant from flowing from the connection portion of the second refrigerant circuit 120 with the first refrigerant circuit 110 to the discharge port of the second compressor 20. Note that the check valve 96 may be omitted if the air conditioner 100 does not perform heating operation (does not have the switching mechanism 30) and does not encounter a situation in which the first compressor 10 is operated with the second compressor 20 stopped.

[0091] The flow path 92 is a flow path that connects the discharge side of the second compressor 20 of the second refrigerant circuit 120 to the suction side of the second compressor 20 of the second refrigerant circuit 120. Specifically, the flow path 92 connects the discharge port of the second compressor 20 of the second refrigerant circuit 120 and the check valve 96 to the suction side of the second compressor 20.

[0092] Although not shown in the drawings, the flow path 92 may be a flow path that connects the discharge port of the first compressor 10 in the first refrigerant circuit 110 and a radiator (first heat exchanger 40) when the air conditioner 100 is performing cooling operation, with the suction side of the second compressor 20. Specifically, the flow path 92 may be a flow path that connects a pipe that connects the discharge port of the first compressor 10 and the switching mechanism 30, with the suction side of the second compressor 20. Furthermore, the flow path 92 may be a flow path that connects a connection portion of the second refrigerant circuit 120 with the first refrigerant circuit 110 (a connection portion between the second refrigerant circuit 120 and a pipe that connects the discharge port of the first compressor 10 and the switching mechanism 30) with the check valve 96, with the suction side of the second compressor 20.

[0093] The second valve 94 is a valve disposed in the flow path 92. The second valve 94 may be a solenoid valve that can be controlled only to open and close, or may be an electrically operated valve whose opening degree is variable.

[0094] The second valve 94 is opened under the control of the control device 8, which will be described later, when the second compressor 20 is stopped. As a result, the pressure on the discharge side of the second compressor 20 and the pressure on the suction side of the second compressor 20 are equalized. For example, if the second compressor 20 is a rotary compressor, due to the characteristics of the compressor, if the pressure on the discharge side remains higher than the pressure on the suction side, there is a possibility that the refrigeration oil in the second compressor 20 will flow out from the suction port of the second compressor 20. However, the provision of such a pressure equalizing mechanism 90 prevents such an occurrence. Control of the second valve 94 by the control device 8 will be described later.

[0095] (2-5) First fan and second fan The first fan 42 is housed in a housing (not shown) of the heat source unit 2 that 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, the second valve 94, etc. The first fan 42 supplies heat source air to the first heat exchanger 40 of the first refrigerant circuit 110 and promotes heat exchange between the refrigerant flowing through the first heat exchanger 40 and the heat source air. The type of the first fan 42 is not limited, but the first fan 42 is, for example, a propeller fan.

[0096] The second fan 62 is housed in a housing (not shown) of the utilization unit 4 that houses the second heat exchanger 60 and the like. The second fan 62 draws in air from the space to be air-conditioned and supplies it to the second heat exchanger 60 of the first refrigerant circuit 110, promoting heat exchange between the refrigerant flowing through the second heat exchanger 60 and the air to be temperature-adjusted. The type of the second fan 62 is not limited, but the second fan 62 is, for example, a cross-flow fan.

[0097] (2-6) Control device The control device 8 is a device that controls the 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 the operation of these electrically connected devices, thereby controlling the operation of the air conditioner 100.

[0099] The air conditioner 100 is also provided with various sensors (such as a temperature sensor that measures the temperature of the refrigerant, a pressure sensor that measures the pressure of the refrigerant, and a temperature sensor that measures the temperature of the space to be air-conditioned), and the control device 8 is electrically connected to these sensors. For example, as shown in FIG. 1, the air conditioner 100 is provided with a first sensor 12 that measures the suction pressure of the first compressor 10, and a second sensor 22 that measures the 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 the measurement results of these sensors.

[0100] In this embodiment, an electric circuit and a control board (not shown) mounted on the heat source unit 2 are communicatively connected to an electric circuit and a control board (not shown) mounted on the utilization unit 4, and these cooperate to function as a control device 8. For convenience, in Fig. 1, the control device 8 is shown in a position separate from the heat source unit 2, utilization unit 4, etc.

[0101] In this embodiment, the control device 8 includes a control and arithmetic device and a storage device. A processor such as a CPU can be used as the control and arithmetic device. The control and arithmetic device reads a program stored in the storage device and controls the operation of the air conditioner 100 in accordance with this program.

[0102] (2-6-1) Heating operation When causing the air conditioner 100 to perform heating operation, the control device 8 controls the operation of the switching mechanism 30 to set the state of the first refrigerant circuit 110 to the second state and operate the first compressor 10. The control device 8 controls the rotation speed of the motor of the first compressor 10 and the opening degree of the first expansion valve 50 based on the measurement results of various sensors (such as a temperature sensor that measures the temperature of the refrigerant, a pressure sensor that measures the pressure of the refrigerant, and a temperature sensor that measures the temperature of the space to be air-conditioned) arranged at various positions in the air conditioner 100. The control device 8 also operates the motors of the first fan 42 and the second fan 62 at predetermined rotation speeds.

[0103] During the heating operation, the control device 8 controls the first valve 80 and the second valve 94 to be closed, and the second compressor 20 is not operated.

[0104] During heating operation, the pressure between the first compressor 10 and the second heat exchanger 60 becomes high in the refrigeration cycle. Therefore, if the pressure between the first valve 80 and the second compressor 20 of the second refrigerant circuit 120 is lower than the high pressure in the refrigeration cycle, the bypass valve 132 opens, and there is a possibility that the refrigerant will flow from between the first compressor 10 and the second heat exchanger 60 through the bypass passage 130 into between the first valve 80 and the second compressor 20 of the second refrigerant circuit 120. However, during heating operation, the first valve 80 is closed and the operation of the second compressor 20 is stopped, so the pressure between the first valve 80 and the second compressor 20 of the second refrigerant circuit 120 (where there is no outlet for the refrigerant) quickly becomes high in the refrigeration cycle, and the refrigerant does not flow further through the bypass passage 130.

[0105] When switching from heating operation to cooling operation, the control device 8 may perform a liquid draining operation by opening the first valve 80 while the state of the first refrigerant circuit 110 is in the second state and the first compressor 10 is also operating. By opening the first valve 80, high-pressure refrigerant in the refrigeration cycle of the bypass passage 130 or the second refrigerant circuit 120 flows to the low-pressure side of the refrigeration cycle via the first valve 80. When performing the liquid draining operation, the control device 8 opens the first valve 80, then stops the first compressor 10 and controls the operation of the switching mechanism 30 to set the state of the first refrigerant circuit 110 to the first state.

[0106] (2-6-2) Cooling operation in the first mode When the air conditioner 100 is caused to perform 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 rotation speeds of the motors of the first compressor 10 and the second compressor 20 and the openings of the first expansion valve 50 and the first valve 80 based on the measurement results of various sensors (such as a temperature sensor that measures the temperature of the refrigerant, a pressure sensor that measures the pressure of the refrigerant, and a temperature sensor that measures the temperature of the space to be air-conditioned) arranged at various positions in the air conditioner 100. The control device 8 also operates the motors of the first fan 42 and the second fan 62 at predetermined rotation speeds.

[0107] During the cooling operation in the first mode, the control device 8 controls the second valve 94 to be closed.

[0108] (2-6-3) Cooling operation in the second mode When the control device 8 causes the air conditioner 100 to perform cooling operation in the second mode, it stops the operation of the first compressor 10 and operates the second compressor 20.

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

[0110] In cooling operation in the second mode, the refrigerant flows through the air conditioner 100 in a manner as indicated by the dashed arrows in Figure 1. This will be explained in more detail.

[0111] The refrigerant discharged from the second compressor 20 passes through the switching mechanism 30 and flows to the first heat exchanger 40. The refrigerant that flows into the first heat exchanger 40 exchanges heat with the heat source air and releases heat, and the refrigerant that flows 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 that flows inside the economizer heat exchanger 72 toward the first expansion valve 50 releases heat through heat exchange with refrigerant flowing inside the economizer heat exchanger 72 from the bypass passage 130 toward the second compressor 20. The refrigerant that flows into the second heat exchanger 60 exchanges heat with the air in the space to be air-conditioned, cooling the air in the space to be air-conditioned. The refrigerant that has absorbed heat from the air in the space to be air-conditioned in the second heat exchanger 60 (heated by the air in the space to be air-conditioned) 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 and is heated by heat exchange with the refrigerant flowing inside the economizer heat exchanger 72 toward the first expansion valve 50. The refrigerant heated in the economizer heat exchanger 72 is drawn into the second compressor 20.

[0112] During cooling operation in the second mode, the control device 8 controls the rotation speed of the motor of the second compressor 20 and the opening degree of the first expansion valve 50 based on the measurement results of various sensors (such as a temperature sensor that measures the temperature of the refrigerant, a pressure sensor that measures the pressure of the refrigerant, and a temperature sensor that measures the temperature of the space to be air-conditioned) arranged at various positions in the air conditioner 100. In addition, the control device 8 operates the motors of the first fan 42 and the second fan 62 at predetermined rotation speeds.

[0113] During the cooling operation in the second mode, the control device 8 controls the second valve 94 to be closed.

[0114] (2-6-4) Changing the operation mode from the first mode to the second mode An example of control for changing the operation mode from the first mode to the second mode in the air conditioner 100 will be described with reference to the flowcharts of FIGS. 4A and 4B.

[0115] First, an example of control for changing the operation mode from the first mode to the second mode will be described with reference to the flowchart in FIG. 4A.

[0116] 4A is performed. The controller 8 is also assumed to be appropriately controlling the rotation speeds of the first compressor 10 and the second compressor 20 based on the load of the air conditioner 100 (to achieve the highest possible efficiency).

[0117] While the air conditioner 100 is operating in the first mode, the control device 8 acquires the suction pressure of the second compressor 20 measured by the second sensor 22 (step S1).

[0118] If the control device 8 determines that the suction pressure of the second compressor 20 acquired in step S1 has dropped below a predetermined pressure (Yes in step S2), it stops the operation of the first compressor 10 (step S3). On the other hand, if the control device 8 determines that the suction pressure of the second compressor 20 is higher than the predetermined pressure (No in step S2), it continues the operation of the air conditioner 100 in the first mode, and the process returns to step S1.

[0119] The reason for performing the change control in this manner will be explained.

[0120] When the load on the air conditioner 100 decreases in the first mode, the control device 8 reduces the rotation speed of the first compressor 10 and the second compressor 20. When the load required of the air conditioner 100 decreases to a certain extent, the rotation speed of the second compressor 20 reaches the minimum rotation speed at which operation is possible. In this state, the rotation speed of the second compressor 20 cannot be reduced any further, so the operating state of the air conditioner 100 deviates from the ideal operating state, operating efficiency decreases, and the suction pressure of the second compressor 20 decreases.

[0121] Therefore, when the suction pressure of the second compressor 20 falls below a predetermined suction pressure (a pressure at which efficient operation in the first mode becomes difficult), the control device 8 stops operation of the first compressor 10 (step S3).

[0122] In addition, preferably, the control device 8 controls the opening degree of the first valve 80 to a predetermined opening degree or less (an opening degree that can prevent a large amount of refrigerant from flowing from the branching portion 82 into the second refrigerant circuit 120) in order to prevent a large amount of refrigerant from flowing from the branching portion 82 into the second refrigerant circuit 120, or controls the first valve 80 to close (see step S4).

[0123] The change of the operation mode from the first mode to the second mode may be performed based on the flowchart of FIG. 4B.

[0124] The method of changing the operation mode according to the flowchart of Fig. 4B differs from the method of changing the operation mode according to the flowchart of Fig. 4A in that the suction pressure of the first compressor 10 is used to determine whether to change the operation mode in addition to the suction pressure of the second compressor 20. This will be explained in detail.

[0125] The control device 8 acquires the suction pressure of the second compressor 20 measured by the second sensor 22 while the air conditioner 100 is operating in the first mode (step S1). Additionally, the control device 8 acquires the suction pressure of the first compressor 10 measured by the first sensor 12 while the air conditioner 100 is operating in the first mode (step S1A).

[0126] When the control device 8 determines that the differential pressure between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10 has dropped below a predetermined value (Yes in step S2A), it stops the operation of the first compressor 10 (step S3). On the other hand, when the control device 8 determines 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 in step S2A), it operates in the first mode, and the process returns to step S1.

[0127] The reason for performing the change control in this manner will be explained.

[0128] When the load on the air conditioner 100 decreases in the first mode, the control device 8 reduces the rotation speeds of the first compressor 10 and the second compressor 20. When the load required of the air conditioner 100 decreases to a certain extent, the rotation speed of the second compressor 20 reaches the minimum rotation speed at which operation is possible. In this state, the rotation speed of the second compressor 20 cannot be reduced any further, so the operating conditions of the air conditioner 100 deviate from the ideal operating conditions, operating 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 of Figure 4B, the control device 8 determines that the operating state of the air conditioner 100 has deviated from the ideal operating state and the operating efficiency has deteriorated 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, here, an example will be described in which the control device 8 determines whether the operating state of the air conditioner 100 deviates from the ideal operating state based on the difference between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10, but the present invention is not limited to this. For example, the control device 8 may determine whether the operating state of the air conditioner 100 deviates from the ideal operating state based on the value of the ratio of the suction pressure of the second compressor 20 to the suction pressure of the first compressor 10.

[0131] The control device 8 stops operation of the first compressor 10 (step S3) when the differential pressure between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10 becomes, for example, below a predetermined value (a value at which efficient operation in the first mode becomes difficult).

[0132] Furthermore, similar to the flowchart of Figure 4A, the control device 8 preferably controls the opening degree of the first valve 80 to a predetermined opening degree or less (an opening degree that can prevent a large amount of refrigerant from flowing from the branching portion 82 into the second refrigerant circuit 120) in order to prevent a large amount of refrigerant from flowing from the branching portion 82 into the second refrigerant circuit 120, or controls the first valve 80 to close (see step S4).

[0133] 4A and 4B, the order of execution of steps S3 and S4 may be reversed from that of the flowcharts of Figures 4A and 4B, and step S3 may be executed after step S4 is executed. Alternatively, steps S3 and S4 may be executed in parallel (simultaneously).

[0134] Here, an example is described in which it is determined whether to change from the first mode to the second mode based on the suction pressure of the second compressor 20, or the suction pressure of the first compressor 10 and the suction pressure of the second compressor 20, but the determination of whether to change from the first mode to the second mode may be made by other methods.

[0135] For example, in more detail, the ideal operating state in the first mode (discharge pressure (common to the first compressor 10 and the second compressor 20), suction pressure of the first compressor 10, suction pressure of the second compressor 20, and rotation speeds of the first compressor 10 and the second compressor 20) may be calculated in advance, and the control device 8 may detect the deviation between this ideal operating state and the actual operating state, and based on the magnitude of the deviation (if it determines that the deviation is excessively large), change the operating mode of the air conditioner 100 from the first mode to the second mode.

[0136] (2-6-5) Changing the operation mode from the second mode to the first mode An example of control for changing from the second mode to the first mode in the air conditioner 100 will be described with reference to the flowchart in FIG.

[0137] As a premise for the explanation, it is assumed that at the time the processing of step S11 is performed, the air conditioner 100 is operating in the second mode (the operation of the first compressor 10 is stopped, and only the second compressor 20 is operating). It is also assumed that the control device 8 is appropriately controlling the rotation speed of the second compressor 20 based on the load of the air conditioner 100.

[0138] The control device 8 acquires the rotation speed of the second compressor 20 while the air conditioner 100 is operating in the second mode (step S11). If the control device 8 determines that the acquired rotation speed of the second compressor 20 is equal to or greater than a predetermined rotation speed (Yes in step S12), it starts operation of the first compressor 10 (step S13). If the rotation speed of the second compressor 20 is lower than the predetermined rotation speed (No in step S12), the control device 8 continues operation of the air conditioner 100 in the second mode, and the process returns to step S11.

[0139] The reason for performing the change control in this manner will be explained.

[0140] When the load increases in the second mode, the control device 8 increases the rotation speed of the second compressor 20. However, when the load required of the air conditioner 100 increases to a certain extent, the rotation speed of the second compressor 20 reaches the maximum operable rotation speed, and no further capacity can be obtained. Furthermore, when the load required of the air conditioner 100 increases to a certain extent, the efficiency of the second compressor 20 begins to decrease significantly due to the characteristics of the second compressor 20, even if the rotation speed of the second compressor 20 has not reached the maximum operable rotation speed.

[0141] Therefore, when the rotation speed of the second compressor 20 reaches or exceeds a predetermined rotation speed (for example, the rotation speed at which the efficiency of the second compressor 20 begins to decrease), the control device 8 starts operating the first compressor 10 (step S13).

[0142] In addition, if the control device 8 controls the opening of the first valve 80 to a predetermined opening or less in the second mode or closes the first valve 80, the control device 8 starts controlling the opening of the first valve 80 in the first mode so that an appropriate amount of refrigerant flows from the branch section 82 to the second refrigerant circuit 120 depending on the load (see step S14).

[0143] (2-6-6) Pressure equalization control when the air conditioner is stopped Pressure equalization control on the discharge side and suction side of the second compressor 20 using the pressure equalization mechanism 90 when the air conditioner 100 is stopped will be described with reference to the flowchart of FIG.

[0144] In step S21, when the control device 8 decides to stop operation of the air conditioner 100 (for example, when an instruction to stop the air conditioner 100 is input to a remote control of the air conditioner 100 not shown), the control device 8 opens the second valve 94 (step S22).

[0145] In step S23, the control device 8 determines whether the pressure difference between the discharge side and the suction side of the second compressor 20 has been eliminated. Whether the pressure difference between the discharge side and the suction side of the second compressor 20 has been eliminated is determined, for example, by comparing the pressure measured by a pressure sensor (not shown) provided on the discharge side of the second compressor 20 with the pressure measured by the second sensor 22 provided on the suction side of the second compressor 20. Note that the method of determining whether the pressure difference between the discharge side and the suction side of the second compressor 20 has been eliminated does not necessarily use the results of pressure measurement by the pressure sensor. For example, the control device 8 may determine whether the pressure difference between the discharge side and the suction side of the second compressor 20 has been eliminated based on the time elapsed since the second valve 94 was opened. Specifically, the control device 8 may determine that the pressure difference between the discharge side and the suction side of the second compressor 20 has been eliminated when a predetermined time has elapsed since the second valve 94 was opened.

[0146] If it is determined in step S23 that the pressure difference 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, the possibility that the refrigeration oil in the second compressor 20 will flow out from the suction port of the second compressor 20 is reduced.

[0148] (3) Features Below, the characteristics of the air conditioner 100 when the air conditioner 100 is performing cooling operation will be described.

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

[0150] In the air conditioner 100, under low load conditions, the bypass flow path 130 is used and only the second compressor 20, which is suitable for operation under low load conditions with a small displacement, is operated, thereby enabling efficient operation even under low load conditions.

[0151] (3-2) In the air conditioner 100, the economizer 70 includes an economizer heat exchanger 72 as an example of a first economizer heat exchanger, which is 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 in the second refrigerant circuit 120, between the first valve 80 and the second compressor 20. The economizer heat exchanger 72 flows out of the first heat exchanger 40 and branches from the first refrigerant circuit 110 to the second refrigerant circuit 120 at a branching point 82, and performs heat exchange between the refrigerant decompressed by the first valve 80 and the refrigerant flowing out of the first heat exchanger 40.

[0152] In this air conditioner 100, by using the economizer heat exchanger 72, the capacity and efficiency of the air conditioner 100 can be improved.

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

[0154] In this air conditioner 100, a portion of the refrigerant branches off upstream of the economizer heat exchanger 72 in the refrigerant flow direction in the first refrigerant circuit 110, and flows through the second refrigerant circuit 120 to the economizer heat exchanger 72. Therefore, in this air conditioner 100, the capacity and efficiency of the air conditioner 100 can be improved while keeping the size of the economizer heat exchanger 72 down, compared to when all of the refrigerant flowing out of the first heat exchanger 40 passes through the first refrigerant circuit 110 and flows into the economizer heat exchanger 72.

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

[0156] In this air conditioner 100, in the second cooling operation mode, when the first compressor 10 is stopped and the second compressor 20 is operating, the refrigerant that passes through the second heat exchanger 60 and flows into the bypass flow path 130 exchanges heat with the refrigerant flowing through the economizer heat exchanger 72 on the first refrigerant circuit 110 side before being drawn into the second compressor 20. Therefore, in this air conditioner 100, the performance and efficiency of the air conditioner 100 can be improved when the first compressor 10 is stopped and the second compressor 20 is operating.

[0157] In addition, if only the point of enabling operation in the second mode is considered, the bypass passage 130 may connect between the economizer heat exchanger 72 and the second compressor 20 of the second refrigerant circuit 120 and between the second heat exchanger 60 and the first compressor 10 of the first refrigerant circuit 110, as shown by the two-dot chain line in Figure 1.

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

[0159] In this air conditioner 100, when the first compressor 10 is stopped and the second compressor 20 is operating, the amount of refrigerant that is sucked into the second compressor 20 without passing through the second heat exchanger 60 can be reduced, and a decrease in performance and efficiency of the air conditioner 100 can be reduced when the first compressor 10 is stopped and the second compressor 20 is operating.

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

[0161] This air conditioner 100 can operate in the second mode with an inexpensive configuration, and when both the first compressor 10 and the second compressor 20 are operating, the flow of refrigerant from the bypass passage 130 to the first refrigerant circuit 110 can be suppressed.

[0162] (3-7) In the air conditioner 100, the refrigerant contains CO2 as at least a portion of its components. In particular, in the above embodiment, the refrigerant is a single refrigerant of CO2.

[0163] In this air conditioner 100, a refrigerant containing CO2, which has a small global warming potential, is used as the refrigerant, and therefore an air conditioner 100 with a small environmental impact can be realized.

[0164] (3-8) The air conditioner 100 has two operating modes: a 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 control device 8 determines whether 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] This air conditioner 100 detects that a low load condition has been reached based on the value of the suction pressure of the second compressor 20, and is capable of operating efficiently even under low load conditions.

[0166] More preferably, the control device 8 determines whether to switch the operation 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] When the suction pressure of the first compressor 10 is further used, it is possible to accurately detect that a low load condition has been reached, and to operate efficiently even under a low load condition.

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

[0169] In this air conditioner 100, an increase in load is detected based on the value of the rotation speed of the second compressor 20, and the operation mode is shifted to the first mode, making it possible to perform efficient operation.

[0170] (4) Variations The following describes modified examples of the air conditioner 100 of the above embodiment. The following modified examples can be combined as appropriate.

[0171] (4-1) Variation A In the above embodiment, the branch section 82 branching from the first refrigerant circuit 110 to the second refrigerant circuit 120 is disposed between the first heat exchanger 40, which functions as a radiator during cooling operation, and the economizer heat exchanger 72, but is not limited to this configuration.

[0172] 7, the branching portion 82a may be disposed between the economizer heat exchanger 72 and the second heat exchanger 60 used as a heat absorber during cooling operation. In this case, however, the entire amount of refrigerant flowing out of the first heat exchanger 40 flows through the economizer heat exchanger 72 on the first refrigerant circuit 110 side, and then a portion of the refrigerant is diverted to flow into the second refrigerant circuit 120. Therefore, the size of the economizer heat exchanger 72 is likely to be larger than in the above embodiment.

[0173] (4-2) Variation B In the above embodiment, the bypass valve 132 is a check valve.

[0174] However, the present invention is not limited to this, and the bypass valve 132a may be an electrically operated valve as shown in Fig. 8A, or may be an electromagnetic valve.

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

[0176] (4-3) Variation C In the above embodiment, the economizer heat exchanger 72 is provided in the second refrigerant circuit 120 (straddling the first refrigerant circuit 110 and the second refrigerant circuit 120), but the present invention is not limited to this.

[0177] 9A, the economizer 70 may have a refrigerant container 74 (flash tank economizer) capable of gas-liquid separation, instead of the economizer heat exchanger 72, that straddles the first refrigerant circuit 110 and the second refrigerant circuit 120. A first valve 80a is provided in the second refrigerant circuit 120, and a second expansion valve 84 is provided in the first refrigerant circuit 110. The first valve 80a is, for example, a solenoid valve or an electrically operated valve with a variable opening, and is closed during heating operation and cooling operation in the second mode, and is opened during cooling operation in the first mode.

[0178] To explain the state in which the air conditioner 100 performs cooling operation in the first mode, the refrigerant container 74 is disposed between the first heat exchanger 40, which functions as a radiator of the refrigerant, and the second heat exchanger 60, which functions as a heat absorber of 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, which functions as a radiator, and the refrigerant container 74. The refrigerant that flows out of the first heat exchanger 40 and has been decompressed by the second expansion valve 84 to become a two-phase refrigerant flows into the refrigerant container 74. The gas refrigerant separated in the refrigerant container 74 is drawn into the second compressor 20.

[0179] Even with this configuration, during cooling operation in the first mode, the temperature of the refrigerant flowing into the second heat exchanger 60, which functions as a heat absorber for the refrigerant, can be lowered, thereby improving the capacity of the air conditioner 100.

[0180] The cooling operation mode of the second mode in the air conditioner 100 having the configuration of Figure 9A is the same as that of the above embodiment, except that the refrigerant that flows into the second refrigerant circuit 120 from the bypass flow path 130 flows to the second compressor 20 without passing through the economizer heat exchanger 72.

[0181] 9B , the second refrigerant circuit 120 may include, in addition to the refrigerant container 74, a heat exchanger 72a (an example of a second economizer heat exchanger) arranged across the first refrigerant circuit 110 and the second refrigerant circuit 120. The heat exchanger 72a is arranged in the first refrigerant circuit 110 between the first heat exchanger 40, which functions as a refrigerant radiator during cooling operation, and the second expansion valve 84. The heat exchanger 72a is arranged so that, when the air conditioner 100 performs cooling operation in the first mode, the refrigerant that leaves the first heat exchanger 40 and flows toward the second expansion valve 84 exchanges heat with the gas refrigerant separated in the refrigerant container 74. The refrigerant that has exchanged heat with the refrigerant flowing through the first refrigerant circuit 110 in the heat exchanger 72a is drawn into the second compressor 20. In this configuration, by further using the heat exchanger 72a, the capacity of the air conditioner 100 can be further improved during cooling operation in the first mode compared to the configuration of FIG. 9A.

[0182] 9B, the first valve 80a is a solenoid valve or a variable-opening motor-operated valve disposed between the refrigerant container 74 and the heat exchanger 72a. Similar to the air conditioner 100 described using FIG. 9A, the first valve 80a is closed during heating operation and cooling operation in the second mode, and is open during 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 shown in Fig. 9B. With this configuration, in the second mode of cooling operation, when the first compressor 10 is stopped and the second compressor 20 is operating, the refrigerant that passes through the second heat exchanger 60 and flows into the bypass flow path 130 exchanges heat with the refrigerant flowing through the heat exchanger 72a on the first refrigerant circuit 110 side before being drawn into the second compressor 20. Therefore, in this air conditioner 100, the performance and efficiency of the air conditioner 100 can be improved when the first compressor 10 is stopped and the second compressor 20 is operating.

[0184] However, if the sole consideration is to enable operation in the second mode, the bypass passage 130 may connect between the heat exchanger 72a of the second refrigerant circuit 120 and the second compressor 20, and between the second heat exchanger 60 of the first refrigerant circuit 110 and the first compressor 10 (not shown).

[0185] In the air conditioner 100 according to Modification C, the second compressor 20 is also not operated during heating operation.

[0186] (4-4) Variation D In the above embodiment, the second valve 94 of the pressure equalizing mechanism 90 is opened when the second compressor 20 is stopped, thereby equalizing the pressure between the discharge side and the suction side of the second compressor 20.

[0187] However, as shown in Fig. 10, the flow path 92 of the pressure equalizing mechanism 90 and the second valve 94 do not have to be provided. Even in the configuration as shown in Fig. 10, the control device 8 can make the pressure on the suction side of the second compressor 20 approach the pressure on the discharge side of the second compressor 20 by opening the first valve 80 (for example, to an opening degree close to full opening) when the second compressor 20 is stopped and maintaining the first valve 80 in an open state for a predetermined period of time according to, for example, the flowchart of Fig. 4 (replace the second valve 94 with the first valve 80).

[0188] (4-5) Variation E In the above embodiment, the bypass passage 130 connects between the first valve 80 and the second compressor 20 of the second refrigerant circuit 120 and between the second heat exchanger 60, which functions as a heat sink of the first refrigerant circuit 110, and the first compressor 10 (specifically, between the second heat exchanger 60 and the switching mechanism 30).

[0189] 11 , the bypass flow path 130 may connect between the first valve 80 and the second compressor 20 of the second refrigerant circuit 120 and between the switching mechanism 30 and the suction port of the first compressor 10. With this configuration, the check valve serving as the bypass valve 132 does not open during heating operation, and no refrigerant flows through the bypass flow path 130 into between the first valve 80 and the second compressor 20 of the second refrigerant circuit 120 during heating operation.

[0190] Second Embodiment An air conditioner 100A of the second embodiment will be described with reference to Fig. 12. As in the first embodiment, an air conditioner is an example of a refrigeration cycle device, and a refrigeration cycle device having the configuration of the second embodiment may be something other than an air conditioner.

[0191] The air conditioner 100A has many points in common with the air conditioner 100 of the first embodiment. The same reference numerals as in the first embodiment are used for the components of the air conditioner 100A that are common to the air conditioner 100. Below, differences between the air conditioner 100A and the air conditioner 100 will be mainly described, and explanations of the commonalities between the air conditioner 100A and the air conditioner 100 will be omitted unless necessary.

[0192] One of the main differences between air conditioner 100A and air conditioner 100 is that air conditioner 100A operates both first compressor 10 and second compressor 20 simultaneously during heating operation as well as cooling operation.

[0193] One of the main differences between the air conditioner 100A and the air conditioner 100 is that the air conditioner 100A has a first mode in which both the compressor of the first refrigerant circuit 110 (first compressor 10) and the compressor of the second refrigerant circuit 120 (second compressor 20) are operated simultaneously during both cooling and heating operations, and a mode in which operation of the compressor of the first refrigerant circuit 110 is stopped and the compressor of the second refrigerant circuit 120 is operated. Note that, although a detailed explanation is omitted, the air conditioner 100A may further have a mode in which only the compressor of the first refrigerant circuit 110 is operated (a 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 and second modes during both cooling and heating operations.

[0194] Furthermore, one of the main differences between the air conditioner 100A and the air conditioner 100 is that the air conditioner 100A has 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 also be provided in the air conditioner 100 of the first embodiment.

[0195] Unlike the air conditioner 100 in FIG. 1, the pressure equalizing mechanism 90 is not depicted in FIG. 11, but the air conditioner 100A may also be provided with a pressure equalizing mechanism 90.

[0196] The above differences will be described in detail below.

[0197] (1) First mode during heating operation The air conditioner 100A improves performance by simultaneously operating the first compressor 10 and the second compressor 20 even during heating operation. In other words, the air conditioner 100A has an operation mode (first mode during heating operation) in which the first valve 80 is opened and the second compressor 20 is operated together with the first compressor 10, even when the switching mechanism 30 switches the state of the first refrigerant circuit 110 to the second state, and the second heat exchanger 60 is used as a radiator (condenser) and the first heat exchanger 40 is used as a heat absorber (evaporator).

[0198] When operating the air conditioner 100A in the first mode during heating operation, a bridge circuit 140 combining four check valves that allows refrigerant to flow only in the direction of the arrows shown in Fig. 11 is preferably provided in the first refrigerant circuit 110 of the air conditioner 100A between the first heat exchanger 40 and the second heat exchanger 60. By providing the bridge circuit 140, a branch section 82 is located between the radiator and the first expansion valve 50 in the direction of refrigerant flow in the first refrigerant circuit 110, regardless of the state of the refrigerant circuit of the air conditioner 100A. Therefore, regardless of the state of the refrigerant circuit of the air conditioner 100, in the first refrigerant circuit 110, the refrigerant flowing out from the radiator flows into the bridge circuit 140 and is sent to the branch section 82, and the refrigerant that is not diverted to the second refrigerant circuit 120 at the branch section 82 passes through the economizer heat exchanger 72 and the first expansion valve 50, then flows into the bridge circuit 140 again and is sent to the heat absorber.

[0199] The control by the control device 8 when performing the heating operation in the first mode will be described.

[0200] When the air conditioner 100A is caused to perform 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 rotation speeds of the motors of the first compressor 10 and the second compressor 20 and the openings of the first expansion valve 50 and the first valve 80 based on the measurement results of various sensors arranged in various positions in the air conditioner 100. The control device 8 also operates the motors of the first fan 42 and the second fan 62 at predetermined rotation speeds.

[0201] (2) Second mode during heating operation The air conditioner 100A has an operation mode (second mode during heating operation) in which the first compressor 10 is stopped and the second compressor 20 is operated alone during heating operation.

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

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

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

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

[0206] In the heating operation in the second mode, the refrigerant flows through the air conditioner 100A in a manner as shown by the dashed arrows in Figure 1. This will be explained in more detail.

[0207] The refrigerant discharged from the second compressor 20 passes through the switching mechanism 30 and flows to the second heat exchanger 60. The refrigerant that flows into the second heat exchanger 60 exchanges heat with the air in the space to be air-conditioned, releasing heat and heating the air in the space to be air-conditioned. The refrigerant that flows out of the second heat exchanger 60 passes through the bridge circuit 140 and the economizer heat exchanger 72, passes through the bridge circuit 140 again, is depressurized by the first expansion valve 50, and flows to the first heat exchanger 40. The refrigerant flowing inside the economizer heat exchanger 72 toward the first expansion valve 50 releases heat through heat exchange with refrigerant flowing inside the economizer heat exchanger 72 from the bypass flow path 130A toward the second compressor 20. The refrigerant that flows into the first heat exchanger 40 exchanges heat with the heat-source air and is heated. The refrigerant that has absorbed heat from the heat source air in the first heat exchanger 40 (heated by the heat source air) passes through the switching mechanism 30 and flows into the suction passage of the first compressor 10, then flows into the bypass passage 130A from the branch point P1, and flows through the bypass passage 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 one end of the bypass passage 130A is connected between the first valve 80 and the inlet of the economizer heat exchanger 72 as shown by the solid line in FIG. 12 ) and is heated by heat exchange with the refrigerant flowing inside the economizer heat exchanger 72 toward the first expansion valve 50. The refrigerant heated in the economizer heat exchanger 72 is drawn into the second compressor 20.

[0208] During heating operation in the second mode, the control device 8 controls the rotation speed of the motor of the second compressor 20 and the opening degree of the first expansion valve 50 based on the measurement results of various sensors arranged at various positions in the air conditioner 100. The control device 8 also operates the motors of the first fan 42 and the second fan 62 at predetermined rotation speeds.

[0209] (3) First oil return mechanism and second oil return mechanism The first oil return mechanism 200 is a mechanism that returns the refrigeration oil discharged from the first compressor 10 together with the compressed refrigerant to the suction side of the second compressor 20. The second oil return mechanism 300 is a mechanism that returns the refrigeration oil discharged from the second compressor 20 together with the compressed refrigerant to the suction side of the first compressor 10.

[0210] In the air conditioner 100A, the oil discharged from the first compressor 10 is returned to the second compressor 20 (not to the first compressor 10), and the oil discharged from the second compressor 20 is returned to the first compressor 10 (not to the second compressor 20), thereby achieving an automatic oil equalization effect and preventing the occurrence of problems such as oil accumulating in one compressor and oil shortage in the other compressor.

[0211] The first oil return mechanism 200 includes a first oil separator 210, a first oil return path 220, and a first pressure reduction 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 refrigeration oil from the refrigerant discharged from the first compressor 10, which contains refrigeration oil. The first oil return path 220 connects the first oil separator 210 with the suction path of the second compressor 20 (the path between the first valve 80 and the suction port of the second compressor 20). The first pressure reduction mechanism 230 is disposed in the first oil return path 220. The first pressure reduction mechanism 230 is, for example, but not limited to, a capillary tube.

[0212] The refrigeration oil separated in the first oil separator 210 flows through the first oil return path 220 toward the suction path of the second compressor 20. Note that the pressure of the refrigeration oil in the first oil separator 210 is high in the refrigeration cycle, and the pressure in the suction path of the second compressor 20 is intermediate in the refrigeration cycle (see FIG. 3B ). Therefore, the high-pressure refrigeration oil separated in the first oil separator 210 is reduced to the intermediate pressure by the first pressure reducing mechanism 230 and flows into the suction path of the second compressor 20. As a result, refrigeration oil used for lubricating a compression mechanism (not shown) of the second compressor 20 is supplied to the second compressor 20.

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

[0214] The refrigeration oil separated in the second oil separator 310 flows through the second oil return path 320 toward the suction path of the first compressor 10. Note that the pressure of the refrigeration oil in the second oil separator 310 is high in the refrigeration cycle, and the pressure in the suction path of the first compressor 10 is low in the refrigeration cycle (see FIG. 3B), so the high-pressure refrigeration oil separated in the second oil separator 310 is reduced to low pressure by the second pressure reduction mechanism 330 and flows into the suction path of the first compressor 10. In this way, refrigeration oil used for lubricating a compression mechanism (not shown) of the first compressor 10 is supplied to the first compressor 10.

[0215] Although not shown, the first oil return path 220 may be provided with a valve that is opened only when it is necessary to supply refrigeration oil to the second compressor 20 (for example, a valve that is opened when the second compressor 20 is operating and that is closed when the second compressor 20 is stopped and only the first compressor 10 is operating). Furthermore, although not shown, the second oil return path 320 may be provided with a valve that is opened only when it is necessary to supply refrigeration oil to the first compressor 10 (for example, a valve that is opened when the first compressor 10 is operating and that is closed when the first compressor 10 is stopped and only the second compressor 20 is operating).

[0216] (4) Features The air conditioner 100A has the same characteristics in cooling operation as the air conditioner 100 of the first embodiment. Furthermore, the air conditioner 100A also has the same characteristics in heating operation as the air conditioner 100 of the first embodiment, if the radiator is replaced with the second heat exchanger 60 and the heat absorber is replaced with the first heat exchanger 40.

[0217] (5) Variations The modified examples of the air conditioner 100 of the above embodiment can also be applied to the air conditioner 100A to the extent that there is no contradiction. To avoid duplication, a description will be omitted here.

[0218] <Additional Notes> Although the embodiments of the present disclosure have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the present disclosure as defined in the claims. [Explanation of symbols]

[0219] 8 Control device (control unit) 10. First compressor 20 Second compressor 40 1st heat exchanger (radiator) 50 First expansion valve 60 Second heat exchanger (heat absorber) 70 Economizer 72 Economizer heat exchanger (first economizer heat exchanger) 72a Heat exchanger (second economizer heat exchanger) 80 First valve 80a First valve 82 Branch 82a Branch 84 Second expansion valve 100 Air conditioner (refrigeration cycle device) 100A Air Conditioner (Refrigeration Cycle Unit) 110 1st refrigerant circuit 120 Second refrigerant circuit 130 Bypass flow path 130A Bypass flow path 132 Bypass valve 132a Bypass valve [Prior art documents] [Patent documents]

[0220] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-49087

Claims

1. 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) including an economizer (70) disposed between the radiator and the heat absorber, connecting between the first compressor and the radiator and between the radiator and the first expansion valve, a first valve (80, 80a), and a second compressor (20) that draws in the refrigerant that has passed through the economizer; a bypass flow path (130, 130A) connecting between the first valve and the second compressor and between the heat absorber and the first compressor; a bypass valve (132, 132a) disposed in the bypass flow path; Equipped with The second compressor is a compressor having a smaller displacement than the first compressor. Refrigeration cycle device (100, 100A).

2. the economizer includes a first economizer heat exchanger (72) disposed between the heat radiator and the heat sink; The first valve is an expansion valve, the first economizer heat exchanger is disposed in the second refrigerant circuit between the first valve and the second compressor; the first economizer heat exchanger is configured to cause heat exchange between the refrigerant flowing out of the radiator and branching into the second refrigerant circuit at a branching portion (82, 82a) and the refrigerant decompressed by the first valve and the refrigerant flowing out of the radiator; The refrigeration cycle device according to claim 1.

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

4. the bypass flow path connects between the first valve and the first economizer heat exchanger and between the heat sink and the first compressor. The refrigeration cycle device according to claim 2.

5. a control unit (8) that controls operations of the first compressor, the second compressor, and the first valve, The control unit controls the opening degree of the first valve to be equal to or less than a predetermined opening degree or to be closed when the first compressor is stopped and the second compressor is operated. The refrigeration cycle device according to claim 2.

6. the bypass valve (132) is a check valve that prohibits the flow of refrigerant from between the first valve and the second compressor to between the heat sink and the first compressor. The refrigeration cycle device according to claim 2.

7. The bypass valve (132a) is a solenoid valve or an electric valve, the control unit further controls the bypass valve to open the bypass valve when stopping the first compressor and operating the second compressor. The refrigeration cycle device according to claim 5.

8. The economizer includes a second expansion valve (84) and a refrigerant container (74) capable of separating gas and liquid, into which a refrigerant reduced in pressure by the second expansion valve and brought into a two-phase state flows, The gas refrigerant separated in the refrigerant container is drawn into the second compressor. The refrigeration cycle device according to claim 1.

9. the economizer further comprises a second economizer heat exchanger (72a); the second economizer heat exchanger is disposed so as to exchange heat between the refrigerant flowing out of the radiator and the gas refrigerant flowing out of the refrigerant container. The refrigeration cycle device according to claim 8.

10. the first valve (80a) is disposed between the refrigerant container and the second economizer heat exchanger; the bypass flow path is connected between the first valve and the second economizer heat exchanger; The refrigeration cycle device according to claim 9.

11. a control unit (8) that controls operations of the first compressor, the second compressor, and the first valve, When the first compressor is stopped and the second compressor is operated, the control unit controls the opening degree of the first valve to be equal to or less than a predetermined opening degree, or controls the opening degree of the first valve to be closed. The refrigeration cycle device according to claim 8.

12. the bypass valve (132) is a check valve that prohibits the flow of refrigerant from between the first valve and the second compressor to between the heat sink and the first compressor. The refrigeration cycle device according to claim 8.

13. The bypass valve (132a) is a solenoid valve or an electric valve, the control unit further controls the bypass valve to open the bypass valve when stopping the first compressor and operating the second compressor. The refrigeration cycle device according to claim 11.

14. The refrigerant contains CO as at least a part of its components. ２ Including, The refrigeration cycle device according to any one of claims 1 to 13.

15. The refrigeration cycle device has, as operation 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 operation mode is switched from the first mode to the second mode based on a value of a suction pressure of the second compressor. The refrigeration cycle device according to any one of claims 1 to 13.

16. The operation mode is switched from the first mode to the second mode further based on a value of a suction pressure of the first compressor. The refrigeration cycle device according to claim 15.

17. The refrigeration cycle device has, as operation 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 operation mode is switched from the second mode to the first mode based on the rotation speed of the second compressor. The refrigeration cycle device according to any one of claims 1 to 13.

18. The refrigeration cycle device has, as operation 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. The refrigeration cycle device according to any one of claims 1 to 13.

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