Refrigeration cycle equipment

Abstract

To provide a refrigeration cycle system that can operate efficiently even under low load conditions. [Solution] The air conditioner (100) has a first refrigerant circuit (110), a second refrigerant circuit (120), a bypass passage (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 located between the radiator and the heat absorber, and the second compressor draws in the refrigerant that has passed through the economizer. The bypass passage connects the first valve and the second compressor, and the heat absorber and the first compressor. The bypass valve is located in the bypass passage. The second compressor is a compressor with a smaller displacement than the first compressor.

Description

Technical Field

[0001] It relates to a refrigeration cycle device.

Background Art

[0002] In Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-49087), a refrigeration cycle device is disclosed in which a first compressor, a second compressor, and an economizer are provided in a refrigerant circuit, and the refrigerant that is branched off in the economizer from the main path of the refrigerant discharged from the first compressor to the first flow path and heading to the absorber via the radiator is compressed by the second compressor and discharged to the first flow path.

[0003] In this refrigeration cycle device, by using the second compressor, the capacity and efficiency can be improved.

Disclosure of the Invention

Problems to be Solved by the Invention

[0004] By the way, the refrigeration cycle device is not always required to operate at a high load, and there are cases where it is required to operate at a low load. The object of the present disclosure is to provide a refrigeration cycle device that can operate efficiently under low load conditions.

Means for Solving the Problems

[0005] The refrigeration cycle device according to the first aspect comprises a first refrigerant circuit, a second refrigerant circuit, a bypass passage, 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, and the radiator and the first expansion valve of the first refrigerant circuit. The economizer is located between the radiator and the heat absorber. The second compressor draws in the refrigerant that has passed through the economizer. The bypass passage connects the first valve and the second compressor of the second refrigerant circuit, and the heat absorber and the first compressor of the first refrigerant circuit. The bypass valve is located in the bypass passage. The second compressor is a compressor with a smaller displacement than the first compressor.

[0006] In the refrigeration cycle system described in the first perspective, under low-load conditions, the bypass flow path is utilized, the first compressor is stopped, and the second compressor, which is suitable for operation at low loads with a small displacement, is operated, thereby enabling efficient operation even under low-load conditions.

[0007] The refrigeration cycle apparatus according to the second aspect is the refrigeration cycle apparatus according to the first aspect, wherein the economizer includes a first economizer heat exchanger positioned between the radiator and the heat absorber. The first valve is an expansion valve. The first economizer heat exchanger is positioned in the second refrigerant circuit between the first valve and the second compressor. The first economizer heat exchanger flows out from the radiator, branches off to the second refrigerant circuit at the branching point, and exchanges heat between the refrigerant reduced in pressure by the first valve and the refrigerant flowing out from the radiator.

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

[0009] The refrigeration cycle device relating to the third aspect is the refrigeration cycle device relating to the second aspect, wherein the branching section is located between the radiator and the first economizer heat exchanger.

[0010] In the third-perspective refrigeration cycle system, 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 third-perspective refrigeration cycle system, compared to the case where all of the refrigerant flowing out from the radiator flows through the first refrigerant circuit to the first economizer heat exchanger, the size of the first economizer heat exchanger can be reduced while improving the capacity and efficiency of the refrigeration cycle system.

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

[0012] In the refrigeration cycle system of the fourth perspective, when the first compressor is stopped and the second compressor is operated, the refrigerant that flows through the heat absorption chamber into the bypass channel 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 system of the fourth perspective, the performance and efficiency of the refrigeration cycle system can be improved when the first compressor is stopped and the second compressor is operated.

[0013] The refrigeration cycle device relating to the fifth aspect is a refrigeration cycle device relating to either the second or 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 opening degree of the first valve to be less than or equal to a predetermined opening degree, or to close it.

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

[0015] The refrigeration cycle device relating to the sixth aspect is a refrigeration cycle device relating to either the second or fifth aspect, wherein the bypass valve is a check valve that prohibits the flow of refrigerant from between the first valve and the second compressor of the second refrigerant circuit to between the heat absorber and the first compressor of the first refrigerant circuit.

[0016] In the refrigeration cycle device of the sixth perspective, a refrigeration cycle can be realized with an inexpensive configuration in which the second compressor is operated while the first compressor is stopped, and furthermore, when both the first and second compressors are operating, the flow of refrigerant from the bypass passage to the first refrigerant circuit can be suppressed.

[0017] The refrigeration cycle device relating to the seventh aspect is the refrigeration cycle device relating to the fifth aspect, and 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] The refrigeration cycle device according to the eighth aspect is the refrigeration cycle device according to the first aspect, wherein the economizer includes a second expansion valve and a gas-liquid separable refrigerant container. Refrigerant, which has been depressurized by the second expansion valve and is in a two-phase state, flows into the refrigerant container. The gaseous refrigerant separated in the refrigerant container is drawn into a second compressor.

[0019] In the refrigeration cycle system described in the eighth perspective, the temperature of the refrigerant flowing into the heat absorber can be reduced by using the second expansion valve and the refrigerant container, thereby improving the capacity and efficiency of the refrigeration cycle system.

[0020] The refrigeration cycle device relating to the ninth aspect is the refrigeration cycle device relating to the eighth aspect, wherein the economizer further includes a second economizer heat exchanger. The second economizer heat exchanger is arranged so that the refrigerant flowing out from the radiator and the gaseous refrigerant flowing out from the refrigerant container exchange heat.

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

[0022] The refrigeration cycle device according to the tenth aspect is the refrigeration cycle device of the ninth aspect, and the first valve 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.

[0023] In the refrigeration cycle device of the tenth aspect, when the first compressor stops and the second compressor operates, before the refrigerant flowing through the heat absorber and flowing into the bypass flow path is sucked into the second compressor, heat exchange is performed with the refrigerant flowing through the first economizer flow path in the second economizer heat exchanger. Therefore, in the refrigeration cycle device of the tenth aspect, the performance and efficiency of the refrigeration cycle device when the first compressor stops and the second compressor operates can be improved.

[0024] The refrigeration cycle device according to the eleventh aspect is the refrigeration cycle device of any one of the eighth aspect to the tenth aspect, and further includes a control unit. The control unit controls the operations of the first compressor, the second compressor, and the first valve. When the control unit stops the first compressor and operates the second compressor, the control unit controls the opening degree of the first valve to be less than or equal to a predetermined opening degree, or controls the opening degree of the first valve to be closed.

[0025] In the refrigeration cycle device of the eleventh aspect, when the first compressor stops and the second compressor operates, the amount of refrigerant sucked into the second compressor without passing through the heat absorber can be suppressed, and the decrease in the performance and efficiency of the refrigeration cycle device when the first compressor stops and the second compressor operates can be suppressed.

[0026] The refrigeration cycle device according to the twelfth aspect is the refrigeration cycle device of any one of the eighth aspect to the eleventh aspect, and the bypass valve is a check valve that prohibits the flow of refrigerant 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 in which the first compressor stops and the second compressor operates can be realized with a low-cost configuration, and moreover, when both the first compressor and the second compressor are operated, the flow of refrigerant from the bypass flow path to the first refrigerant circuit can be suppressed.

[0028] The refrigeration cycle device according to the 13th aspect is the refrigeration cycle device of the 11th aspect, and the bypass valve is a solenoid valve or an electric valve. The control unit further controls the bypass valve. When the control unit stops the first compressor and operates the second compressor, the bypass valve is opened.

[0029] The refrigeration cycle device according to the 14th aspect is the refrigeration cycle device of any one of the 1st to 13th aspects, and the refrigerant contains CO2 in at least a part of its components.

[0030] In the refrigeration cycle device of the 14th aspect, since a refrigerant containing CO2 with a small global warming potential is used as the refrigerant, a refrigeration cycle device with a small environmental load can be realized.

[0031] The refrigeration cycle device according to the 15th aspect is the refrigeration cycle device of any one of the 1st to 14th aspects, and as the operation mode, it has 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 the value of the suction pressure of the second compressor.

[0032] In the refrigeration cycle device according to the 15th aspect, it is detected that the low load condition has occurred based on the value of the suction pressure of the second compressor, and efficient operation is possible even under the low load condition.

[0033] The refrigeration cycle device according to the 16th aspect is the refrigeration cycle device of the 15th aspect, and the operation mode is switched from the first mode to the second mode based further on the value of the suction pressure of the first compressor.

[0034] In the refrigeration cycle device according to the 16th aspect, based on the value of the suction pressure of the first compressor and the value of the suction pressure of the second compressor, it is accurately detected that the low load condition has occurred, and efficient operation is possible even under the low load condition.

[0035] The refrigeration cycle device relating to the 17th aspect is a refrigeration cycle device relating to either the 1st aspect or the 16th aspect, and has as operating modes a first mode in which both the first and second compressors are operated, and a second mode in which the first compressor is stopped and the second compressor is operated. The operating mode is switched from the second mode to the first mode based on the rotational speed of the second compressor.

[0036] In the refrigeration cycle system relating to the 17th aspect, it is possible to detect an increase in load based on the rotational speed of the second compressor and switch the operating mode to the first mode to perform efficient operation.

[0037] A refrigeration cycle device relating to the 18th aspect is a refrigeration cycle device relating to either the 1st aspect or the 17th aspect, wherein the refrigeration cycle device has only two operating modes: a first mode in which both the first and second compressors are operated, and a second mode in which the first compressor is stopped and the second compressor is operated. [Brief explanation of the drawing]

[0038] [Figure 1] This is a schematic diagram of the air conditioner according to the first embodiment of a refrigeration cycle device. [Figure 2] Figure 1 is a schematic control block diagram of the air conditioner. [Figure 3A] This is a schematic pH diagram of an air conditioner without a second refrigerant circuit (an air conditioner with only a first refrigerant circuit). [Figure 3B] This is a schematic pH diagram for the air conditioner shown in Figure 1 when it is in cooling operation. [Figure 4A] Figure 1 is a flowchart illustrating one example of the process for changing from the first mode to the second mode in an air conditioner. [Figure 4B] This flowchart illustrates another example of the process for changing from the first mode to the second mode in the air conditioner shown in Figure 1. [Figure 5] Figure 1 is a flowchart illustrating an example of the process for changing from the second mode to the first mode in an air conditioner. [Figure 6] Figure 1 is a flowchart illustrating the control process for stopping the operation of the air conditioner. [Figure 7] This is a schematic diagram of the air conditioner in modified example A. [Figure 8A] This is a schematic diagram of the air conditioner in modified example B. [Figure 8B] Figure 8A is a schematic control block diagram of the air conditioner. [Figure 9A] This is a schematic diagram of the air conditioner configuration according to an example of modified example C. [Figure 9B] This is a schematic diagram of the air conditioner configuration relating to another example of modified form C. [Figure 10] This is a schematic diagram of the air conditioner in modified example D. [Figure 11] This is a schematic diagram of the air conditioner in modified example E. [Figure 12] This is a schematic diagram of the air conditioner according to the second embodiment of the refrigeration cycle device. [Modes for carrying out the invention]

[0039] Embodiments of the refrigeration cycle apparatus of this disclosure will be described below with reference to the drawings.

[0040] <First Embodiment> (1) Overall structure The overall configuration of the air conditioner 100 of the first embodiment of the refrigeration cycle device of this disclosure will be described with reference to Figure 1. Figure 1 is a schematic diagram of the air conditioner 100.

[0041] The air conditioner 100 is a device that provides heating and cooling to the interior of a building or the like by using a vapor compression type refrigeration cycle to cool or heat the air inside the building or the like, which is the target of temperature control. In this embodiment, the target of temperature control by the air conditioner 100 is air, but the air conditioner 100 may also be a device that cools or heats a medium such as water, which is the target of temperature control. Furthermore, although the air conditioner 100 in this embodiment is a device that can provide heating and cooling to the interior of a building or the like, the air conditioner 100 may also be a device that provides cooling only.

[0042] As shown in Figure 1, the air conditioner 100 mainly has a first refrigerant circuit 110 and a second refrigerant circuit 120. The refrigerant circuits 110 and 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 an exhaustive list. In particular, the refrigerant circuits 110 and 120 of this air conditioner 100 are filled with a single refrigerant of carbon dioxide. Carbon dioxide is a highly safe refrigerant with a low global warming potential, low environmental impact, and no toxicity or flammability.

[0043] As shown in Figure 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 on a heat source unit 2 located outdoors, for example, on the roof of a building, while the second heat exchanger 60 is mounted on a utilization unit 4 located in or near the space to be air-conditioned. In the air conditioner 100, the first refrigerant circuit 110 is formed by connecting the heat source unit 2 and the utilization unit 4 with refrigerant connecting pipes 6.

[0044] The second refrigerant circuit 120 connects the first compressor 10 and the radiator (first heat exchanger 40) of the first refrigerant circuit 110, and the radiator (first heat exchanger 40) and the first expansion valve 50 of the first refrigerant circuit 110, when the air conditioner 100 is in cooling operation (in other words, when the switching mechanism 30 has connected 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 positioned between the first heat exchanger 40 and the second heat exchanger 60 of the first refrigerant circuit 110, and further cools the refrigerant flowing out of the first heat exchanger 40 (acting as a heat radiator) and heading towards the second heat exchanger 60 (acting as a heat absorber) during cooling operation. In this embodiment, the economizer 70 has an economizer heat exchanger 72 positioned between the first heat exchanger 40 and the second heat exchanger 60. The economizer heat exchanger 72 is an example of the first economizer heat exchanger. The economizer heat exchanger 72 is positioned across the first refrigerant circuit 110 and the second refrigerant circuit 120.

[0047] In the cooling operation mode of the air conditioner 100 in which both the first compressor 10 and the second compressor 20 are operated (the first cooling operation mode described later), 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 also adjusts the flow rate of the refrigerant. In the first cooling operation mode described later, 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 the cooling operation of the air conditioner 100 (in the first mode of cooling operation, which will be described later). This will be explained in detail.

[0049] Assuming that the second refrigerant circuit 120 does not exist (in other words, assuming that only the first refrigerant circuit 110 exists), the CO2 refrigerant (carbon dioxide refrigerant) used in the air conditioner 100, in particular, has a relatively small cooling effect due to its characteristics (see the pH diagram in Figure 3A). Therefore, if a large capacity is to be obtained using only the first refrigerant circuit 110, there is a problem in that the size of the first compressor 10 will have to be increased.

[0050] In contrast, the air conditioner 100 of this disclosure is provided with a second refrigerant circuit 120. In the first cooling mode, which will be described later, the refrigerant flowing from the first refrigerant circuit 110 to the second heat exchanger 60 (heat absorber) and the refrigerant flowing from the second refrigerant circuit 120 to the second compressor 20 exchange heat in the economizer heat exchanger 72. As a result, the refrigerant flowing from the first refrigerant circuit 110 to the second heat exchanger 60 (heat absorber) is further cooled. Therefore, compared to the case where only the first refrigerant circuit 110 is present, an improvement in the capacity and performance of the air conditioner 100 is achieved (see the ph diagram in Figure 3B).

[0051] Unlike the air conditioner 100 disclosed herein, the second compressor 20 is omitted, and the refrigerant that has passed through the economizer heat exchanger 72 is injected into the first compressor 10 as an intermediate injection, thereby improving capacity and performance. However, in the air conditioner 100 equipped with the second compressor 20, the intermediate pressure can be adjusted arbitrarily, so the air conditioner 100 can also improve performance compared to the configuration in which the refrigerant that has passed through the economizer heat exchanger 72 is injected into the first compressor 10 as an intermediate injection.

[0052] In addition to the first refrigerant circuit 110 and the second refrigerant circuit 120, the air conditioner 100 further includes a bypass passage 130 connecting the first valve 80 of the second refrigerant circuit 120 and the second compressor 20, and the second heat exchanger 60, which functions as a heat absorber during cooling operation of the first refrigerant circuit 110, and the first compressor 10, as well as a bypass valve 132 located in the bypass passage 130.

[0053] The air conditioner 100 has two operating modes for cooling operation: 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 passage 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 cooling operation of the air conditioner 100 (in the operating state where the first heat exchanger 40 is used as a heat radiator and the second heat exchanger 60 is used as a heat absorber) does not have an operating mode in which the second compressor 20 is stopped and only the first compressor 10 is operated (the air conditioner 100 has only a first mode and a second mode as operating modes for cooling operation). However, it 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 regarding the bypass flow path 130, the bypass valve 132, and the first and second modes of cooling operation of the air conditioner 100 will be described later. In the following explanation, to avoid redundancy, the first mode of cooling operation may be simply referred to as "first mode," and the second mode of cooling operation as "second mode."

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

[0057] In the sections (2-1) First Refrigerant Circuit and (2-2) Second Refrigerant Circuit below, when describing cooling operation, the operation and functions of the various components of the first refrigerant circuit 110 and the second refrigerant circuit 120, as well as the flow of refrigerant in the first refrigerant circuit 110 and the second refrigerant circuit 120, will be mainly described when the air conditioner 100 is operating in the first mode described above. The various components and functions of the first refrigerant circuit 110 and the second refrigerant circuit 120, as well as 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 described in section (2-3) Bypass Flow Channel and Bypass Valve, along with the explanation of the bypass flow channel 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-capacity compressor with an inverter-controlled motor. In this embodiment, the first compressor 10 is preferably a scroll compressor which has good efficiency at high rotational speeds. However, the first compressor 10 may be of other types.

[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 Figure 1), the first heat exchanger 40 functions as a refrigerant radiator, and the second heat exchanger 60 functions as a refrigerant evaporator. When the first refrigerant circuit 110 is in the second state (see the dashed line of the switching mechanism 30 in Figure 1), the first heat exchanger 40 functions as a refrigerant evaporator, and the second heat exchanger 60 functions as a refrigerant 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 to achieve the following pipe connection configuration.

[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 connects the inlet 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 connects the inlet port of the first compressor 10 to one end of the first heat exchanger 40.

[0063] Furthermore, if the air conditioner 100 is a cooling-only device, the air conditioner 100 does not need to have a switching mechanism 30.

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

[0065] Furthermore, the first heat exchanger 40 is not limited to a heat exchanger that exchanges heat between heat source air and a refrigerant. The first heat exchanger 40 may also 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 positioned 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 also positioned in the second refrigerant circuit 120 between the first valve 80 and the second compressor 20.

[0067] The economizer heat exchanger 72, when the air conditioner 100 is operated in the first mode, causes heat exchange between the refrigerant that flows out from the first heat exchanger 40, which functions as a heat radiator, and branches off to the second refrigerant circuit 120 at the branching section 82, where the refrigerant is depressurized by the first valve 80 (described later), and the refrigerant that flows out from the first heat exchanger 40 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 cooled in the first heat exchanger 40 (see points c and d in Figure 3B) that flows toward the second heat exchanger 60 is further cooled by the economizer heat exchanger 72 (see point h in Figure 3B). In this embodiment, the branching section 82 is located between the first heat exchanger 40, which functions as a heat radiator during cooling operation, and the economizer heat exchanger 72 (see Figure 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 located 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 electronically operated 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 casing (not shown), and air from the space to be air-conditioned is supplied by a second fan 62 located inside the casing. Heat exchange takes place in the second heat exchanger 60 between the air from the space to be air-conditioned supplied by the second fan 62 and the refrigerant. When the state of the first refrigerant circuit 110 is in the first state, the second heat exchanger 60 functions as a heat absorber for 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 state of the first refrigerant circuit 110 is in the second state, the second heat exchanger 60 functions as a heat radiator for 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 type 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 electronically expanded 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, the refrigerant basically does not flow through the second refrigerant circuit 120. Therefore, the following explanation of the refrigerant flow in the second refrigerant circuit 120 explains the refrigerant flow 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 that of the first compressor 10. This is because the second refrigerant circuit 120 (second compressor 20) is used auxiliaryly to the first refrigerant circuit 110 (first compressor 10) in the first mode of cooling operation.

[0073] The amount of displacement of the second compressor 20 relative to the displacement of the first compressor 10 is less than 100%. Preferably, the amount of displacement of the second compressor 20 relative to the displacement of the first compressor 10 is less than 80%. More preferably, the amount of displacement of the second compressor 20 relative 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 a first mode in which both the first compressor 10 and the second compressor 20 are operated as operating modes for cooling operation, 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, the second mode of cooling operation has the advantage of widening the controllable range of the air conditioner 100's capacity, because (instead of stopping the second compressor 20, which has a small displacement, and operating the first compressor 10, which has a large displacement) the first compressor 10, which has a large displacement, is stopped and the second compressor 20, which has a small displacement, is operated.

[0075] In particular, when the displacement of the second compressor 20 is less than 80% of the displacement of the first compressor 10, even when the required capacity of the air conditioner 100 is small (even at low load), the air conditioner 100 can be kept running without frequently starting and stopping the second compressor 20 (by operating the second compressor 20 at or above the minimum rotational speed).

[0076] Furthermore, by setting the displacement amount of the second compressor 20 to 30% or more of the displacement amount of the first compressor 10, it is possible to suppress the occurrence of excessive capacity in the air conditioner 100 and insufficient capacity in the second compressor 20.

[0077] The second compressor 20 is a variable-capacity compressor with 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 large capacity (rotational speed), but is often operated at a small capacity (in other words, at a low rotational speed). Therefore, in this embodiment, the second compressor 20 is a rotary compressor (including a swing compressor) that is efficient even at low rotational speeds.

[0078] However, the type of second compressor 20 is not limited to a rotary compressor, and may be other types of compressors 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-tube heat exchanger or a plate heat exchanger. When the air conditioner 100 is operated in the first mode, the economizer heat exchanger 72 receives refrigerant that flows out from the first heat exchanger 40, branches off to the second refrigerant circuit 120 at the branching section 82, and is depressurized by the first valve 80, and refrigerant that flows out from the first heat exchanger 40, passes through the economizer heat exchanger 72, and flows toward the second heat exchanger 60, and heat exchange takes place without the refrigerants mixing with each other. When the air conditioner 100 is operated in the first mode, the refrigerant that has been depressurized by the first valve 80 and cooled by passing through the economizer heat exchanger 72 and flow toward the second heat exchanger 60 becomes a gas and is drawn into the second compressor 20 (see point f in the ph diagram in Figure 3B).

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

[0081] First, I will explain the reason for providing a second operating mode for the cooling operation of the air conditioner 100.

[0082] The air conditioner 100 is equipped with a first compressor 10 and other components that allow it to operate even under specified high-load conditions. However, the air conditioner 100 is not always required to operate under high load conditions; sometimes it is required to operate under low load conditions (for example, at a load of less than half of the maximum load). When the first compressor 10 is operated under such low load conditions, there is a risk that the first compressor 10 will be operated at a rotational speed below the optimal rotational speed range from an efficiency standpoint. Furthermore, when the load is particularly small, even if the rotational speed of the first compressor 10 or the second compressor 20 is reduced to the minimum rotational speed, the capacity may become excessive, forcing the air conditioner 100 to be temporarily stopped. This can lead to repeated operation and stopping of the air conditioner 100, potentially lowering the COP of the air conditioner 100.

[0083] Therefore, the air conditioner 100 is provided with a second mode in which, under low load conditions, the first compressor 10 is stopped and a vapor compression type refrigeration cycle is performed using the second compressor 20, which has 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 has good operating efficiency even at low rotational speeds, is used, thereby achieving efficient operation even under low load conditions.

[0084] In the air conditioner 100, a bypass passage 130 is provided connecting the first valve 80 of the second refrigerant circuit 120 and the second compressor 20, and the second heat exchanger 60, which functions as a heat absorber in the first refrigerant circuit 110, and the first compressor 10. By providing the bypass passage 130, when the 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 air-conditioned space in the second heat exchanger 60.

[0085] In particular, in this air conditioner 100, the bypass passage 130 connects the first valve 80 of the second refrigerant circuit 120 and the economizer heat exchanger 72, and the second heat exchanger 60 of the first refrigerant circuit 110 and the suction side of the first compressor 10. Therefore, in this air conditioner 100, when the air conditioner 100 is operated in second mode, the refrigerant that passes through the second heat exchanger 60 and flows into the bypass passage 130 passes through the economizer heat exchanger 72 before being drawn into the second compressor 20, and in the economizer heat exchanger 72, it exchanges heat with the refrigerant that flows 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 it is operated in second mode.

[0086] Furthermore, if the refrigerant is allowed to flow freely through the bypass passage 130, when the air conditioner 100 is operated in the first mode, the pressure between the first valve 80 of the second refrigerant circuit 120 and the second compressor 20 will be higher than the pressure between the second heat exchanger 60 of the first refrigerant circuit 110 and the first compressor 10 (see Figure 3B). As a result, refrigerant may flow from the second refrigerant circuit 120 to the suction side of the first compressor 10, potentially hindering the proper operation of the air conditioner 100. Therefore, a bypass valve 132 is provided in the bypass passage 130. In this embodiment, the bypass valve 132 is a check valve that prevents the flow of refrigerant from between the first valve 80 of the second refrigerant circuit 120 and the second compressor 20 to between the second heat exchanger 60 of the first refrigerant circuit 110 and the first compressor 10 (see Figure 1).

[0087] Furthermore, when the air conditioner 100 is operated in the second mode, if the opening of the first valve 80 remains large, the refrigerant that has passed through the first heat exchanger 40 may not flow to the second heat exchanger 60 but instead flow from the branching section 82 into the second refrigerant circuit 120. Therefore, preferably, when the air conditioner 100 is operated in the second mode, the opening of the first valve 80 is set to a predetermined opening (an opening that can suppress the flow of a large amount of refrigerant from the branching section 82 into the second refrigerant circuit 120), or the first valve 80 is closed.

[0088] (2-4) Pressure equalization mechanism The pressure equalization 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. Such a pressure equalization mechanism 90 is particularly preferably provided when the second compressor 20 is a rotary compressor.

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

[0090] The check valve 96 is installed between the discharge port of the second compressor 20 and the connection point between the second refrigerant circuit 120 and the first refrigerant circuit 110 (the connection point between the second refrigerant circuit 120 and the piping connecting the discharge port of the first compressor 10 and the switching mechanism 30). The check valve 96 obstructs the flow of refrigerant from the side of the connection point between the second refrigerant circuit 120 and the first refrigerant circuit 110 to the side of the discharge port of the second compressor 20. However, if the air conditioner 100 is not operating in heating mode (without the switching mechanism 30) and the second compressor 20 is stopped, and a situation does not occur in which the first compressor 10 is operated, the check valve 96 may be omitted.

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

[0092] Although not shown in the diagram, the flow path 92 may be a flow path connecting the discharge port of the first compressor 10 in the first refrigerant circuit 110 and the radiator (first heat exchanger 40) when the air conditioner 100 is operating in cooling mode, and the suction side of the second compressor 20. Specifically, the flow path 92 may be a flow path connecting the piping that connects the discharge port of the first compressor 10 and the switching mechanism 30, and the suction side of the second compressor 20. Alternatively, the flow path 92 may be a flow path connecting the connection point between the second refrigerant circuit 120 and the first refrigerant circuit 110 (the connection point between the second refrigerant circuit 120 and the piping that connects the discharge port of the first compressor 10 and the switching mechanism 30), the check valve 96, and the suction side of the second compressor 20.

[0093] The second valve 94 is a valve located in the flow path 92. The second valve 94 may be a solenoid valve whose opening and closing can be controlled only, or it may be an electric valve with a variable opening.

[0094] The second valve 94 is opened by a control device 8, which will be described later, when the second compressor 20 is stopped. As a result, the pressure on the discharge side and 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, the refrigerant oil inside the second compressor 20 may leak out from the suction port of the second compressor 20. However, by providing such a pressure equalization mechanism 90, the occurrence of such a situation is suppressed. The 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 within the casing (not shown) of the heat source unit 2, which also 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, promoting 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 it is, for example, a propeller fan.

[0096] The second fan 62 is housed within the casing (not shown) of the utilization unit 4, which 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-controlled. The type of the second fan 62 is not limited, but for example, the second fan 62 is 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 Figure 2). The control device 8 controls the operation of the air conditioner 100 by controlling the operation of these electrically connected devices.

[0099] Furthermore, the air conditioner 100 is equipped with various sensors (such as a temperature sensor to measure the temperature of the refrigerant, a pressure sensor to measure the pressure of the refrigerant, and a temperature sensor to measure the temperature of the air-conditioned space), and the control device 8 is electrically connected to these sensors. For example, as shown in Figure 1, the air conditioner 100 is equipped 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, electrical circuits and control boards (not shown) mounted on the heat source unit 2 and electrical circuits and control boards (not shown) mounted on the utilization unit 4 are connected in a communication manner, and they cooperate to function as a control device 8. For convenience, in Figure 1, the control device 8 is shown in a location separate from the heat source unit 2 and utilization unit 4.

[0101] In this embodiment, the control device 8 includes a control calculation unit and a memory device. A processor such as a CPU can be used for the control calculation unit. The control calculation unit reads a program stored in the memory device and controls the operation of the air conditioner 100 according to this program.

[0102] (2-6-1) Heating operation When the control device 8 is to operate the air conditioner 100 in heating mode, it controls the operation of the switching mechanism 30 to set the state of the first refrigerant circuit 110 to the second state and operates the first compressor 10. Based on the measurement results of various sensors (temperature sensors for measuring the temperature of the refrigerant, pressure sensors for measuring the pressure of the refrigerant, temperature sensors for measuring the temperature of the air-conditioned space, etc.) placed at various locations on the air conditioner 100, the control device 8 controls the rotational speed of the motor of the first compressor 10 and the opening degree of the first expansion valve 50. The control device 8 also operates the motors of the first fan 42 and the second fan 62 at predetermined rotational speeds.

[0103] During 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 of the second refrigerant circuit 120 and the second compressor 20 is lower than the high pressure in the refrigeration cycle, the bypass valve 132 will open, and refrigerant may flow from between the first compressor 10 and the second heat exchanger 60 through the bypass passage 130 to the space 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 of the second refrigerant circuit 120 and the second compressor 20 (which has no outlet for the refrigerant) quickly becomes high in the refrigeration cycle, and no further refrigerant flows through the bypass passage 130.

[0105] Furthermore, when switching from heating operation to cooling operation, the control device 8 may perform a liquid drain operation by opening the first valve 80 while the first refrigerant circuit 110 is in the second state and the first compressor 10 is also operating. By opening the first valve 80, the high-pressure refrigerant in the refrigeration cycle in the bypass passage 130 and the second refrigerant circuit 120 flows to the low-pressure side of the refrigeration cycle through the first valve 80. When performing a liquid drain operation, after opening the first valve 80, the control device 8 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 first mode When the control device 8 causes the air conditioner 100 to perform cooling operation in the first mode, it operates the first compressor 10 and the second compressor 20. Based on the measurement results from various sensors (temperature sensors for measuring the temperature of the refrigerant, pressure sensors for measuring the pressure of the refrigerant, temperature sensors for measuring the temperature of the air-conditioned space, etc.) located at various positions on the air conditioner 100, the control device 8 controls the rotational speed of the motors of the first compressor 10 and the second compressor 20, as well as the opening degree of the first expansion valve 50 and the first valve 80. The control device 8 also operates the motors of the first fan 42 and the second fan 62 at a predetermined rotational speed.

[0107] Furthermore, during 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 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 degree of the first valve 80 to be less than or equal to a predetermined opening degree, or controls the first valve 80 to close.

[0110] In the second mode of cooling operation, the refrigerant flows through the air conditioner 100 in the manner shown by the dashed arrows in Figure 1. This will be explained in 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 flowing into the first heat exchanger 40 exchanges heat with the heat source air and dissipates heat. The refrigerant flowing out of the first heat exchanger 40 passes through the economizer heat exchanger 72, is depressurized by the first expansion valve 50, and flows to the second heat exchanger 60. The refrigerant flowing through the economizer heat exchanger 72 towards the first expansion valve 50 exchanges heat with the refrigerant flowing through the economizer heat exchanger 72 from the bypass flow path 130 towards the second compressor 20 and dissipates heat. The refrigerant flowing 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. In the second heat exchanger 60, the refrigerant that has absorbed heat from the air in the space to be air-conditioned (heated by the air in the space to be air-conditioned) flows into the bypass channel 130 and flows through the bypass channel 130 toward the second refrigerant circuit 120. The refrigerant that has flowed from the bypass channel 130 toward the second refrigerant circuit 120 flows into the economizer heat exchanger 72 and is heated by heat exchange with the refrigerant flowing toward the first expansion valve 50 inside the economizer heat exchanger 72. 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 rotational 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 (temperature sensors for measuring the temperature of the refrigerant, pressure sensors for measuring the pressure of the refrigerant, temperature sensors for measuring the temperature of the air-conditioned space, etc.) located at various positions on the air conditioner 100. The control device 8 also operates the motors of the first fan 42 and the second fan 62 at predetermined rotational speeds.

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

[0114] (2-6-4) Changing the operating mode from Mode 1 to Mode 2 An example of controlling the operation mode change from the first mode to the second mode in the air conditioner 100 will be explained with reference to the flowcharts in Figures 4A and 4B.

[0115] First, referring to the flowchart in Figure 4A, we will explain an example of control for changing the operating mode from the first mode to the second mode.

[0116] As a premise for this explanation, it is assumed that at the time of step S1 in Figure 4A, the air conditioner 100 is operating in the first mode (both the first compressor 10 and the second compressor 20 are operating). Furthermore, it is assumed that the control device 8 appropriately controls the rotational speeds of the first compressor 10 and the second compressor 20 (to obtain the highest possible efficiency) based on the load of the air conditioner 100.

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

[0118] If the control device 8 determines that the suction pressure of the second compressor 20, obtained in step S1, has fallen 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 a 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 change control in this manner will be explained.

[0120] In the first mode, when the load on the air conditioner 100 decreases, the control device 8 reduces the rotational speed of the first compressor 10 and the second compressor 20. When the load required for the air conditioner 100 decreases to a certain extent, the rotational speed of the second compressor 20 reaches the minimum operating speed. In this state, the rotational 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, the 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, for example, a predetermined suction pressure (a pressure at which efficient operation becomes difficult in the first mode), the control device 8 stops the operation of the first compressor 10 (step S3).

[0122] Preferably, the control device 8 controls the opening of the first valve 80 to a predetermined opening (an opening that can suppress the flow of a large amount of refrigerant from the branching section 82 to the second refrigerant circuit 120) or controls the first valve 80 to close in order to suppress the flow of a large amount of refrigerant from the branching section 82 to the second refrigerant circuit 120 (see step S4).

[0123] The change from the first mode to the second mode of operation may be performed according to the flowchart in Figure 4B.

[0124] The method for changing the operating mode using the flowchart in Figure 4B differs from the method using the flowchart in Figure 4A. In this method, in addition to the suction pressure of the second compressor 20, the suction pressure of the first compressor 10 is used to determine whether to change the operating mode. This will be explained in detail.

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

[0126] Then, if 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 fallen below a predetermined value (Yes in step S2A), it stops the operation of the first compressor 10 (step S3). On the other hand, if 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 a predetermined value (No in step S2A), it operates in the first mode, and the process returns to step S1.

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

[0128] In the first mode, when the load on the air conditioner 100 decreases, the control device 8 reduces the rotational speeds of the first compressor 10 and the second compressor 20. When the load required for the air conditioner 100 decreases to a certain extent, the rotational speed of the second compressor 20 reaches the minimum operating speed. In this state, the rotational 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, the 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 that 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] Here, we describe an example 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 this is not the only example. 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 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 the operation of the first compressor 10 when the differential pressure between the suction pressure of the second compressor 20 and the suction pressure of the first compressor 10 falls below, for example, a predetermined value (a value at which efficient operation becomes difficult in the first mode) (step S3).

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

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

[0134] This section describes an example of determining 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 both the first compressor 10 and the second compressor 20. However, the determination of whether to change from the first mode to the second mode may be made by other methods.

[0135] For example, the control device 8 may pre-calculate the ideal operating conditions 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 rotational speed of the first compressor 10 and the second compressor 20), detect the discrepancy between this ideal operating condition and the actual operating condition, and based on the magnitude of the discrepancy (if it determines that the discrepancy 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 operating mode from the second mode to the first mode An example of control for switching from the second mode to the first mode in the air conditioner 100 will be explained with reference to the flowchart in Figure 5.

[0137] As a premise for this explanation, it is assumed that at the time the process in step S11 is performed, the air conditioner 100 is operating in 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 appropriately controls the rotational speed of the second compressor 20 based on the load of the air conditioner 100.

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

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

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

[0141] Therefore, when the rotational speed of the second compressor 20 reaches, for example, a predetermined rotational speed (for example, the rotational 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] Furthermore, if the control device 8 controls the opening degree of the first valve 80 to a predetermined opening degree or closes the first valve 80 in the second mode, the control device 8 starts controlling the opening degree 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 according to the load (see step S14).

[0143] (2-6-6) Pressure equalization control when the air conditioner is stopped The equalization control of the discharge and suction sides of the second compressor 20 when the air conditioner 100 is stopped, using the pressure equalization mechanism 90, will be explained with reference to the flowchart in Figure 6.

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

[0145] In step S23, the control device 8 determines whether the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated. Whether the differential pressure 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 a second sensor 22 provided on the suction side of the second compressor 20. Note that the method for determining whether the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated does not have to use the pressure measurement results from the pressure sensor. For example, the control device 8 may determine whether the differential pressure 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 differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated after a predetermined time has elapsed since the second valve 94 was opened.

[0146] If the control device 8 determines in step S23 that the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated, it closes the second valve 94 (step S24).

[0147] As a result, the possibility of refrigerant oil in the second compressor 20 leaking out from the intake port of the second compressor 20 is reduced.

[0148] (3) Features The following describes the characteristics of the air conditioner 100 when it is operating in cooling mode.

[0149] (3-1) An air conditioner 100, an example of a refrigeration cycle system, includes a first refrigerant circuit 110, a second refrigerant circuit 120, a bypass passage 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, and the first heat exchanger 40 and the first expansion valve 50 of the first refrigerant circuit 110. The economizer 70 is positioned 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 passage 130 connects the first valve 80 of the second refrigerant circuit 120 to the second compressor 20, and the second heat exchanger 60 of the first refrigerant circuit 110 to the first compressor 10. The bypass valve 132 is located in the bypass passage 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, efficient operation can be achieved even under low-load conditions by utilizing the bypass passage 130 and operating only the second compressor 20, which is suitable for operation at low loads with a small displacement.

[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 located 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 located in the second refrigerant circuit 120 between the first valve 80 and the second compressor 20. The economizer heat exchanger 72 flows out from the first heat exchanger 40, branches off from the first refrigerant circuit 110 to the second refrigerant circuit 120 at the branching section 82, and exchanges heat between the refrigerant that has been depressurized by the first valve 80 and the refrigerant that has flowed out from the first heat exchanger 40.

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

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

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

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

[0156] In this air conditioner 100, in the second mode of cooling operation, when the first compressor 10 is stopped and the second compressor 20 is operated, 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 it is 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 operated.

[0157] Furthermore, if we consider only the aspect of enabling operation in the second mode, the bypass flow path 130 may be connected 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 dashed 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 started, the control device 8 controls the opening degree of the first valve 80 to be less than or equal to a predetermined opening degree, or to close it.

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

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

[0161] This air conditioner 100 enables operation in the second mode with an inexpensive configuration, and furthermore, when both the first compressor 10 and the second compressor 20 are in operation, 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] This air conditioner 100 uses a refrigerant containing CO2, which has a low global warming potential, thus enabling the realization of an air conditioner 100 with a low environmental impact.

[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 or not to switch the operating mode from the first mode to the second mode based on the suction pressure value of the second compressor 20.

[0165] This air conditioner 100 detects low-load conditions based on the suction pressure value of the second compressor 20, enabling efficient operation even under low-load conditions.

[0166] More preferably, the control device 8 determines whether or not to switch the operating mode from the first mode to the second mode based on the 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 utilized, low-load conditions can be detected with high accuracy, enabling efficient operation even under low-load conditions.

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

[0169] This air conditioner 100 can detect an increase in load based on the rotational speed of the second compressor 20 and switch the operating mode to the first mode to perform efficient operation.

[0170] (4) Variations A modified example of the air conditioner 100 of the above embodiment will now be described. Note that the following modifications can be combined as appropriate.

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

[0172] The branching section 82a may be positioned between the economizer heat exchanger 72 and the second heat exchanger 60, which is used as a heat absorber during cooling operation, as shown in Figure 7. However, in this case, the entire amount of refrigerant that flows out from 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 and flows to the second refrigerant circuit 120. Therefore, the size of the economizer heat exchanger 72 tends to be larger compared to the above embodiment.

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

[0174] However, this is not limited to this, and as shown in Figure 8A, the bypass valve 132a may be an electric valve. Alternatively, the bypass valve 132a may be a solenoid valve.

[0175] As shown in Figure 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 closes the bypass valve 132a during cooling and heating operation in the first mode, and controls it to open the bypass valve 132a 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) Modification C In the above embodiment, an economizer heat exchanger 72 is provided in the second refrigerant circuit 120 (spanning both the first refrigerant circuit 110 and the second refrigerant circuit 120), but the embodiment is not limited to this configuration.

[0177] As shown in Figure 9A, the economizer 70 may have a gas-liquid separation refrigerant container 74 (flash tank economizer) that spans between the first refrigerant circuit 110 and the second refrigerant circuit 120, instead of an economizer heat exchanger 72. The second refrigerant circuit 120 is provided with a first valve 80a, and the first refrigerant circuit 110 is provided with a second expansion valve 84. The first valve 80a is, for example, 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 opened during cooling operation in the first mode.

[0178] In the state where the air conditioner 100 is operating in cooling mode in the first mode, the refrigerant container 74 is located between the first heat exchanger 40, which functions as a refrigerant radiator, and the second heat exchanger 60, which functions as a refrigerant absorber (more specifically, between the first heat exchanger 40 and the first expansion valve 50). The second expansion valve 84 is located between the first heat exchanger 40, which functions as a radiator, and the refrigerant container 74. Refrigerant that has flowed out of the first heat exchanger 40 and been depressurized by the second expansion valve 84 to become a two-phase gas flows into the refrigerant container 74. The gaseous refrigerant separated in the refrigerant container 74 is drawn into the second compressor 20.

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

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

[0181] Furthermore, as shown in Figure 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) positioned between the first refrigerant circuit 110 and the second refrigerant circuit 120. The heat exchanger 72a is positioned 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 positioned so that when the air conditioner 100 performs cooling operation in the first mode, the refrigerant flowing out of the first heat exchanger 40 toward the second expansion valve 84 exchanges heat with the gaseous 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 shown in Figure 9A.

[0182] In the configuration shown in Figure 9B, the first valve 80a is a solenoid valve or a variable-opening electric valve located between the refrigerant container 74 and the heat exchanger 72a. Similar to the air conditioner 100 described using Figure 9A, the first valve 80a is closed during heating operation and cooling operation in the second mode, and opened during cooling operation in the first mode.

[0183] Preferably, the bypass passage 130 is connected between the first valve 80a and the heat exchanger 72a, as shown in Figure 9B. With this configuration, in the second mode of cooling operation, when the first compressor 10 is stopped and the second compressor 20 is operated, the refrigerant that flows through the second heat exchanger 60 into the bypass passage 130 exchanges heat with the refrigerant flowing through the heat exchanger 72a on the first refrigerant circuit 110 side before it is 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 operated.

[0184] However, if we consider only the point of enabling operation in the second mode, the bypass passage 130 may connect the heat exchanger 72a of the second refrigerant circuit 120 and the second compressor 20, and the second heat exchanger 60 of the first refrigerant circuit 110 and the first compressor 10 (not shown).

[0185] In addition, in the air conditioner 100 according to modified example C, the second compressor 20 is not operated during heating operation.

[0186] (4-4) Modification D In the above embodiment, the second valve 94 of the pressure equalization 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 Figure 10, the flow path 92 and second valve 94 of the pressure equalization mechanism 90 do not necessarily have to be provided. Even with a configuration like that in Figure 10, the control device 8 can open the first valve 80 (for example, to an opening close to fully open) when the second compressor 20 is stopped, and maintain the first valve 80 in an open state for a predetermined period of time, for example, according to the flowchart in Figure 4 (replacing the second valve 94 with the first valve 80), thereby bringing the pressure on the suction side of the second compressor 20 closer to the pressure on the discharge side of the second compressor 20.

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

[0189] Alternatively, as shown in Figure 11, the bypass passage 130 may connect the space between the first valve 80 of the second refrigerant circuit 120 and the second compressor 20, and the switching mechanism 30 and the intake port of the first compressor 10. With this configuration, the check valve acting as the bypass valve 132 does not open during heating operation, and no refrigerant flow occurs through the bypass passage 130 to the space between the first valve 80 of the second refrigerant circuit 120 and the second compressor 20 during heating operation.

[0190] <Second Embodiment> The air conditioner 100A of the second embodiment will be described with reference to Figure 12. Note that, as with the first embodiment, the air conditioner is an example of a refrigeration cycle device, and the refrigeration cycle device having the configuration of the second embodiment may be something other than an air conditioner.

[0191] Air conditioner 100A shares many similarities with air conditioner 100 of the first embodiment. The same reference numerals as in the first embodiment are used for components of air conditioner 100A that are common to air conditioner 100. Below, we will mainly describe the differences between air conditioner 100A and air conditioner 100, and will omit explanations of the similarities between air conditioner 100A and air conditioner 100 unless necessary.

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

[0193] Furthermore, one of the main differences between air conditioner 100A and air conditioner 100 is that 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 the operation of the compressor of the first refrigerant circuit 110 is stopped and the compressor of the second refrigerant circuit 120 is operated. Although a detailed explanation is omitted, air conditioner 100A may further have, in addition to the first and second modes, 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) during both cooling and heating operations.

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

[0195] Note that, unlike the air conditioner 100 in Figure 1, Figure 11 does not show the pressure equalization mechanism 90, but the air conditioner 100A may also be provided with the pressure equalization mechanism 90.

[0196] The differences mentioned above will be explained in detail.

[0197] (1) First mode during heating operation In the air conditioner 100A, the capacity is improved by operating the first compressor 10 and the second compressor 20 simultaneously even during heating operation. In other words, even when the switching mechanism 30 switches the state of the first refrigerant circuit 110 to the second state, using the second heat exchanger 60 as a heat radiator (condenser) and the first heat exchanger 40 as a heat absorber (evaporator), the air conditioner 100A has an operating 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.

[0198] When the air conditioner 100A is operated in the first mode during heating operation, preferably, the first refrigerant circuit 110 of the air conditioner 100A is provided with a bridge circuit 140 between the first heat exchanger 40 and the second heat exchanger 60, which is a combination of four check valves that allow refrigerant flow only in the direction of the arrows shown in Figure 11. With the bridge circuit 140 provided, regardless of the state of the refrigerant circuit of the air conditioner 100A, the branch section 82 is positioned between the radiator and the first expansion valve 50 in the direction of refrigerant flow in the first refrigerant circuit 110. Therefore, regardless of the state of the refrigerant circuit of the air conditioner 100, the refrigerant flowing out from the radiator into the first refrigerant circuit 110 flows into the bridge circuit 140 and is sent to the branching section 82. The refrigerant that is not diverted to the second refrigerant circuit 120 at the branching section 82 passes through the economizer heat exchanger 72 and the first expansion valve 50, then flows back into the bridge circuit 140 and is sent to the heat absorber.

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

[0200] When the control device 8 causes the air conditioner 100A to perform heating operation in the first mode, it operates the first compressor 10 and the second compressor 20. Based on the measurement results of various sensors placed at various locations on the air conditioner 100, the control device 8 controls the rotational speed of the motors of the first compressor 10 and the second compressor 20, as well as the opening degree of the first expansion valve 50 and the first valve 80. The control device 8 also operates the motors of the first fan 42 and the second fan 62 at a predetermined rotational speed.

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

[0202] The air conditioner 100A, like the air conditioner 100, has a bypass passage 130A connecting the first valve 80 and the second compressor 20, and the heat absorber and the first compressor 10. However, one end of the bypass passage 130A is connected to the intake passage of the first compressor 10, which connects the switching mechanism 30 and the intake port of the first compressor 10, as in the modified example E described above (see branch point P1 in Figure 12). The other end of the bypass passage 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 Figure 12, or between the outlet of the economizer heat exchanger 72 and the second compressor 20, as shown by the dashed line in Figure 12.

[0203] The control by the control device 8 when performing heating operation in the second mode will be explained below.

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

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

[0206] In heating operation using the second mode, the refrigerant flows through the air conditioner 100A in the manner shown by the dashed arrow in Figure 1. This will be explained in 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 flowing 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 flowing out of the second heat exchanger 60 passes through the bridge circuit 140 and the economizer heat exchanger 72, then 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 exchanges heat with the refrigerant flowing inside the economizer heat exchanger 72 toward the second compressor 20 from the bypass flow path 130A, releasing heat. The refrigerant flowing 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 intake passage of the first compressor 10, flows into the bypass passage 130A from branching 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 Figure 12), and is heated by heat exchange with the refrigerant flowing toward the first expansion valve 50 inside the economizer heat exchanger 72. 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 rotational 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 placed at various locations on the air conditioner 100. The control device 8 also operates the motors of the first fan 42 and the second fan 62 at predetermined rotational speeds.

[0209] (3) First oil return mechanism and second oil return mechanism The first oil return mechanism 200 is a mechanism that returns the refrigerant oil discharged by 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 refrigerant oil discharged by 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 by the first compressor 10 is returned to the second compressor 20 (not the first compressor 10), and the oil discharged by the second compressor 20 is returned to the first compressor 10 (not the second compressor 20). This configuration provides an automatic oil leveling effect, suppressing the occurrence of problems where oil accumulates in one compressor and the other compressor suffers from an oil shortage.

[0211] The first oil return mechanism 200 includes a first oil separator 210, a first oil return passage 220, and a first pressure reducing mechanism 230. The first oil separator 210 is located between the discharge port of the first compressor 10 and the switching mechanism 30 and separates the refrigerant oil from the discharged refrigerant of the first compressor 10, which contains the incoming refrigerant oil. The first oil return passage 220 connects the first oil separator 210 to the suction passage of the second compressor 20 (the passage between the first valve 80 and the suction port of the second compressor 20). The first pressure reducing mechanism 230 is located in the first oil return passage 220. The first pressure reducing mechanism 230 is, but is not limited to, a capillary tube, for example.

[0212] The refrigerant oil separated in the first oil separator 210 flows through the first oil return passage 220 toward the intake passage of the second compressor 20. Since the pressure of the refrigerant oil in the first oil separator 210 is the high pressure in the refrigeration cycle, and the pressure in the intake passage of the second compressor 20 is the intermediate pressure in the refrigeration cycle (see Figure 3B), the high-pressure refrigerant oil separated in the first oil separator 210 is reduced to the intermediate pressure by the first pressure reduction mechanism 230 and flows into the intake passage of the second compressor 20. In this way, the second compressor 20 is supplied with refrigerant oil to be used for lubrication of the compression mechanism (not shown) of the second compressor 20, etc.

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

[0214] The refrigerant oil separated in the second oil separator 310 flows through the second oil return passage 320 toward the intake passage of the first compressor 10. Since the pressure of the refrigerant oil in the second oil separator 310 is the high pressure in the refrigeration cycle, and the pressure in the intake passage of the first compressor 10 is the low pressure in the refrigeration cycle (see Figure 3B), the high-pressure refrigerant oil separated in the second oil separator 310 is reduced to a low pressure by the second pressure reduction mechanism 330 and flows into the intake passage of the first compressor 10. In this way, the first compressor 10 is supplied with refrigerant oil used for lubrication of the compression mechanism (not shown) of the first compressor 10, etc.

[0215] Although not shown in the diagram, the first oil return passage 220 may be provided with a valve that opens only when it is necessary to supply refrigerant oil to the second compressor 20 (for example, it opens when the second compressor 20 is running and closes when the second compressor 20 is stopped and only the first compressor 10 is running). Also, although not shown in the diagram, the second oil return passage 320 may be provided with a valve that opens only when it is necessary to supply refrigerant oil to the first compressor 10 (for example, it opens when the first compressor 10 is running and closes when the first compressor 10 is stopped and only the second compressor 20 is running).

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

[0217] (5) Variant Modifications of the air conditioner 100 in the above embodiment can also be applied to air conditioner 100A to the extent that they do not contradict each other. To avoid repetition in the explanation, the explanation is omitted here.

[0218] <Note> While embodiments of this disclosure have been described above, it should be understood that various modifications to the form and details are possible without departing from the intent and scope of this disclosure as described 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 Branching point 82a Branch 84. Second expansion valve 100 Air conditioners (refrigeration cycle devices) 100A Air Conditioner (Refrigeration Cycle System) 110 1st refrigerant circuit 120 Second refrigerant circuit 130 Bypass channel 130A Bypass Channel 132 Bypass valve 132a Bypass valve [Prior art documents] [Patent Documents]

[0220] [Patent Document 1] Japanese Patent Publication No. 2005-49087

Claims

1. A first refrigerant circuit (110) including a first compressor (10), a heat sink (40), a first expansion valve (50), and a heat absorber (60), A second refrigerant circuit (120) includes an economizer (70) positioned between the heat sink and the heat absorber, connecting the first compressor and the heat sink and the heat sink 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 passage (130, 130A) connects the first valve and the second compressor, and the heat absorber and the first compressor. Bypass valves (132, 132a) arranged in the bypass flow path, Equipped with, The second compressor is a compressor with a smaller displacement than the first compressor. Refrigeration cycle unit (100, 100A).

2. The economizer includes a first economizer heat exchanger (72) positioned between the heat sink and the heat absorber. The first valve is an expansion valve, The first economizer heat exchanger is positioned in the second refrigerant circuit between the first valve and the second compressor. The first economizer heat exchanger flows out from the heat sink and branches off to the second refrigerant circuit at the branching section (82, 82a), and exchanges heat between the refrigerant that has been depressurized by the first valve and the refrigerant that has flowed out from the heat sink. The refrigeration cycle apparatus according to claim 1.

3. The branch section (82) is positioned between the heat sink and the first economizer heat exchanger. The refrigeration cycle apparatus according to claim 2.

4. The bypass passage connects the first valve and the first economizer heat exchanger, and the heat absorber and the first compressor. The refrigeration cycle apparatus according to claim 2.

5. The system further comprises a control unit (8) that controls the operation of the first compressor, the second compressor, and the first valve, When the control unit stops the first compressor and starts the second compressor, it controls the opening of the first valve to be less than or equal to a predetermined opening, or to close it. The refrigeration cycle apparatus according to claim 2.

6. The bypass valve (132) is a check valve that prevents the flow of refrigerant from between the first valve and the second compressor to between the heat absorber and the first compressor. The refrigeration cycle apparatus 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 stop the first compressor and open the bypass valve when operating the second compressor. The refrigeration cycle apparatus according to claim 5.

8. The economizer includes a second expansion valve (84) and a gas-liquid separable refrigerant container (74) into which the refrigerant, which has been depressurized by the second expansion valve and is in a two-phase state, flows. The gaseous refrigerant separated in the refrigerant container is drawn into the second compressor. The refrigeration cycle apparatus according to claim 1.

9. The economizer further includes a second economizer heat exchanger (72a), The second economizer heat exchanger is arranged such that the refrigerant flowing out from the heat exchanger and the gaseous refrigerant flowing out from the refrigerant container exchange heat. The refrigeration cycle apparatus according to claim 8.

10. The first valve (80a) is positioned between the refrigerant container and the second economizer heat exchanger. The bypass channel is connected between the first valve and the second economizer heat exchanger. The refrigeration cycle apparatus according to claim 9.

11. The system further comprises a control unit (8) that controls the operation of the first compressor, the second compressor, and the first valve, When the control unit stops the first compressor and operates the second compressor, it controls the opening of the first valve to be less than or equal to a predetermined opening, or controls the opening of the first valve to be closed. The refrigeration cycle apparatus according to claim 8.

12. The bypass valve (132) is a check valve that prevents the flow of refrigerant from between the first valve and the second compressor to between the heat absorber and the first compressor. The refrigeration cycle apparatus 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 stop the first compressor and open the bypass valve when operating the second compressor. The refrigeration cycle apparatus according to claim 11.

14. The aforementioned refrigerant contains CO in at least part of its components. ２ including, A refrigeration cycle apparatus according to any one of claims 1 to 13.

15. The refrigeration cycle device has, as operating modes, a first mode in which both the first compressor and the second compressor are operated, and a second mode in which the first compressor is stopped and the second compressor is operated. The operating mode is switched from the first mode to the second mode based on the value of the suction pressure of the second compressor. A refrigeration cycle apparatus according to any one of claims 1 to 13.

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

17. The refrigeration cycle device has, as operating modes, a first mode in which both the first compressor and the second compressor are operated, and a second mode in which the first compressor is stopped and the second compressor is operated. The operating mode is switched from the second mode to the first mode based on the rotational speed of the second compressor. A refrigeration cycle apparatus according to any one of claims 1 to 13.

18. 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. A refrigeration cycle apparatus according to any one of claims 1 to 13.

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