Refrigeration cycle equipment

Abstract

To provide a refrigeration cycle device capable of suppressing liquid compression. [Solution] The air conditioner has a first refrigerant circuit, a second refrigerant circuit, and a control device. The first refrigerant circuit includes a first compressor, a first heat exchanger that functions as a radiator during cooling operation, a first expansion valve, and a second heat exchanger that functions as a heat absorber during cooling operation. The second refrigerant circuit connects the first compressor and the first heat exchanger, and the first heat exchanger and the first expansion valve. The second refrigerant circuit includes a second compressor and a first valve. The first valve is located upstream of the second compressor. The control device controls the first compressor, the second compressor, the first expansion valve, and the first valve. When the control device stops the second compressor, it closes the first valve.

Description

Technical Field

[0001] It relates to a refrigeration cycle device.

Background Art

[0002] In Patent Document 1 (Japanese Patent Laid-Open No. 2005-49087), a first compressor, a second compressor, and an economizer are provided in a refrigerant circuit, and a part of the refrigerant is diverted in the economizer from the main path of the refrigerant discharged from the first compressor to the first flow path and flowing through the radiator and then to the absorber, and the refrigerant diverted from the main path is compressed by the second compressor and discharged to the first flow path. A refrigeration cycle device is disclosed.

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

Disclosure of the Invention

Problems to be Solved by the Invention

[0004] In the refrigeration cycle device of Patent Document 1 (Japanese Patent Laid-Open No. 2005-49087), when the second compressor stops, high-pressure refrigerant cooled by the radiator is supplied to the flow path between the economizer and the inlet of the second compressor. In such a refrigeration cycle device, when the outside air temperature is low, the pressure-equivalent saturation temperature becomes higher than the outside air temperature, and the refrigerant that has exchanged heat with the outside air may condense in the flow path between the economizer and the inlet of the second compressor. If a large amount of refrigerant condenses in the flow path between the economizer and the inlet of the second compressor, when the second compressor is started next, the second compressor may suck the condensed liquid refrigerant, liquid compression may occur in the second compressor, and the second compressor may fail.

Means for Solving the Problems

[0005] The refrigeration cycle device according to the first aspect comprises a first refrigerant circuit, a second refrigerant circuit, and a control unit. The first refrigerant circuit includes a first compressor, a radiator, a first expansion valve, and a heat absorber. The second refrigerant circuit connects the first compressor and the radiator, and the radiator and the first expansion valve. The second refrigerant circuit includes a second compressor and a first valve. The first valve is located upstream of the second compressor. The control unit controls the first compressor, the second compressor, the first expansion valve, and the first valve. When the control unit stops the second compressor, it closes the first valve.

[0006] In the refrigeration cycle system of the first perspective, the first valve is located upstream of the second compressor in the second refrigerant circuit, and the first valve is closed when the second compressor stops. Therefore, in this refrigeration cycle system, even when the ambient temperature is relatively low, the condensation of a large amount of refrigerant on the suction side of the second compressor can be suppressed, thereby suppressing liquid compression when the second compressor starts up.

[0007] The refrigeration cycle device relating to the second aspect is the refrigeration cycle device relating to the first aspect, wherein the control unit closes the first valve before stopping the second compressor.

[0008] In the refrigeration cycle system of the second perspective, the second compressor is operated with the first valve closed, preventing refrigerant from flowing downstream of the first valve. Therefore, in the refrigeration cycle system of the second perspective, even when the ambient temperature is relatively low, the condensation of a large amount of refrigerant on the suction side of the second compressor can be suppressed, thereby suppressing liquid compression during startup of the second compressor.

[0009] A refrigeration cycle device relating to the third aspect is a refrigeration cycle device relating to the first or second aspect, further comprising a first sensor and a second sensor. The second compressor has an intake port. The first valve is an expansion valve. The first sensor measures the saturation temperature of the refrigerant between the first valve and the intake port of the second compressor. The second sensor measures the temperature of the refrigerant drawn into the second compressor. When stopping the second compressor, the control unit controls the opening degree of the first valve based on the measurement results of the first sensor and the measurement results of the second sensor.

[0010] Furthermore, the statement here that the first sensor measures the saturation temperature includes cases where the first sensor measures a physical quantity correlated with the saturation temperature (a physical quantity whose value, if known, allows for the determination of the refrigerant's saturation temperature).

[0011] In the third-party refrigeration cycle system, the condensation of a large amount of refrigerant on the suction side of the second compressor is easily suppressed, enabling the realization of a highly reliable refrigeration cycle system.

[0012] The refrigeration cycle device relating to the fourth aspect is a refrigeration cycle device relating to either the first or third aspect, wherein the control unit controls the first valve so that the refrigerant drawn in by the second compressor becomes superheated before closing the first valve when stopping the second compressor.

[0013] In the refrigeration cycle system of the fourth perspective, by applying superheating (making the actual temperature of the refrigerant greater than the saturation temperature of the refrigerant) before stopping the second compressor, the condensation of a large amount of refrigerant on the suction side of the second compressor is particularly suppressed, and a highly reliable refrigeration cycle system can be realized.

[0014] The refrigeration cycle device relating to the fifth aspect is the refrigeration cycle device relating to the fourth aspect, wherein the control unit controls the opening degree of the first valve so that the suction superheat of the second compressor is equal to or greater than a predetermined superheat when stopping the second compressor.

[0015] In the fifth aspect of the refrigeration cycle system, the amount of refrigerant present between the first valve and the inlet of the second compressor after the second compressor has stopped can be particularly reduced, and a highly reliable refrigeration cycle system in which liquid compression is less likely to occur in the second compressor can be realized.

[0016] The refrigeration cycle device relating to the sixth aspect is the refrigeration cycle device relating to the third aspect, wherein the first sensor and the second sensor are arranged between the first valve and the second compressor. The first sensor is a pressure sensor.

[0017] In the refrigeration cycle system described in the sixth perspective, a pressure sensor can be used to accurately measure the saturation temperature of the refrigerant.

[0018] The refrigeration cycle device relating to the seventh aspect is a refrigeration cycle device relating to any of the first to sixth aspects, wherein the second refrigerant circuit further includes a first economizer heat exchanger positioned between a radiator and a heat absorber. The first economizer heat exchanger flows out from the radiator, branches off to the second refrigerant circuit at a branching point, and exchanges heat between the refrigerant, which has been depressurized by a first valve, and the refrigerant that has flowed out from the radiator.

[0019] In the refrigeration cycle system described in the seventh perspective, the capacity and efficiency of the refrigeration cycle system can be improved by using the first economizer heat exchanger.

[0020] The refrigeration cycle device relating to the eighth aspect is the refrigeration cycle device relating to the seventh aspect, wherein the branching section is located between the radiator and the first economizer heat exchanger.

[0021] In the refrigeration cycle system of the eighth perspective, a portion of the refrigerant branches off upstream of the first economizer heat exchanger in the refrigerant flow direction of the first refrigerant circuit and flows through the second refrigerant circuit to the first economizer heat exchanger. Therefore, in the refrigeration cycle system of the eighth perspective, the capacity and efficiency of the refrigeration cycle system can be improved while suppressing the size of the first economizer heat exchanger, compared to the case where the entire amount of refrigerant flowing out from the radiator flows through the first refrigerant circuit to the first economizer heat exchanger.

[0022] A refrigeration cycle device according to the ninth aspect is a refrigeration cycle device according to any of the first to sixth aspects, wherein the first refrigerant circuit further includes a second expansion valve disposed between a radiator and a first expansion valve. The second refrigerant circuit further includes 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. A first valve is disposed between the refrigerant container and a second compressor. The gaseous refrigerant separated in the refrigerant container is drawn into the second compressor.

[0023] In the refrigeration cycle system described in the ninth perspective, the temperature of the refrigerant flowing into the heat absorber is lowered using a refrigerant container, thereby improving the capacity and efficiency of the refrigeration cycle system with a relatively simple configuration.

[0024] The refrigeration cycle device according to the tenth aspect is the refrigeration cycle device of the ninth aspect, and the second refrigerant circuit further includes a second economizer heat exchanger. The second economizer heat exchanger is arranged so that the refrigerant flowing from the radiator toward the second expansion valve and the gaseous refrigerant flowing out of the refrigerant container exchange heat.

[0025] In the refrigeration cycle device of the tenth aspect, by using the second economizer heat exchanger in addition to the refrigerant container, the capacity and efficiency of the refrigeration cycle device can be further improved.

[0026] The refrigeration cycle device according to the eleventh aspect is any one of the refrigeration cycle devices from the first aspect to the tenth aspect, and the control unit opens the first valve before starting the second compressor.

[0027] In the refrigeration cycle device of the eleventh aspect, by opening the first valve before starting the second compressor, the differential pressure between the suction side and the discharge side of the second compressor can be reduced, and the second compressor can be led to a state where it can be started.

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

[0029] In the refrigeration cycle device of the twelfth aspect, by opening the second valve, the differential pressure between the suction side and the discharge side of the second compressor can be reduced, and the second compressor can be led to a state where it can be started.

[0030] The refrigeration cycle device according to the thirteenth aspect is any one of the refrigeration cycle devices from the first aspect to the twelfth aspect, and the refrigerant enclosed in the first refrigerant circuit and the second refrigerant circuit contains CO2 in at least a part of its components.

[0031] In the refrigeration cycle system described in the 13th perspective, a refrigerant containing at least CO2, which has a low global warming potential, is used, thus enabling the realization of a refrigeration cycle system with a low environmental impact. [Brief explanation of the drawing]

[0032] [Figure 1] This is a schematic diagram of an air conditioner according to one embodiment of a refrigeration cycle system. [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 4] This is a flowchart illustrating the control of the air conditioner by the control device when the second compressor in the air conditioner shown in Figure 1 is shut down. [Figure 5] This is a flowchart illustrating the control of the air conditioner by the control device when the second compressor starts up in the air conditioner shown in Figure 1. [Figure 6] This is a schematic diagram of the air conditioner in modified example A. [Figure 7] This is a schematic diagram of the air conditioner in modified example C. [Figure 8A] This is a schematic diagram of the air conditioner in modified example D. [Figure 8B] This is another example of a schematic diagram of the air conditioner in modified form D. [Modes for carrying out the invention]

[0033] Embodiments of the refrigeration cycle apparatus of this disclosure will be described below with reference to the drawings.

[0034] (1) Overall structure The overall configuration of the air conditioner 100 according to one 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.

[0035] Furthermore, the refrigeration cycle device described herein is not limited to an air conditioner, but may be any other type of device that uses a vapor compression type refrigeration cycle to cool or heat (at least cool) a temperature-controlled object (such as a medium like air or water).

[0036] The air conditioner 100 is a device that uses a vapor compression type refrigeration cycle to cool or heat the indoor air of a building or the like, thereby providing heating and cooling to the interior of the building or the like. However, the air conditioner 100 may be a device that provides cooling only.

[0037] 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.

[0038] 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.

[0039] 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)).

[0040] The second refrigerant circuit 120 includes a second compressor 20. The second refrigerant circuit 120 also includes a first valve 80 and an economizer heat exchanger 70 positioned between the first heat exchanger 40 and the second heat exchanger 60 of the first refrigerant circuit 110. The economizer heat exchanger 70 is positioned across both the first refrigerant circuit 110 and the second refrigerant circuit 120.

[0041] The second refrigerant circuit 120 is used to improve the performance of the refrigeration cycle during the cooling operation of the air conditioner 100. This will be explained in detail.

[0042] 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.

[0043] In contrast, the air conditioner 100 of this disclosure is provided with a second refrigerant circuit 120, and in the economizer heat exchanger 70, 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, and the refrigerant flowing from the first refrigerant circuit 110 to the second heat exchanger 60 (heat absorber) is further cooled, thereby improving the capacity and performance of the air conditioner 100 compared to when only the first refrigerant circuit 110 is present (see the ph diagram in Figure 3B).

[0044] (2) Detailed configuration The air conditioner 100 includes a first refrigerant circuit 110 and a second refrigerant circuit 120, as well as a pressure equalization mechanism 90, a first fan 42, a second fan 62, and a control device 8.

[0045] This section provides a detailed explanation of the various components of the air conditioner 100.

[0046] (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.

[0047] The first compressor 10 is a variable-capacity compressor with an inverter-controlled motor. In this embodiment, the first compressor 10 is a scroll compressor. However, the type of first compressor 10 may be other types of compressors. The first compressor 10 draws in refrigerant from the inlet 10a and discharges it from the discharge port 10b.

[0048] 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.

[0049] 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.

[0050] When the state of the first refrigerant circuit 110 is set to the first state, the switching mechanism 30 connects the discharge port 10b of the first compressor 10 to one end of the first heat exchanger 40, and connects the suction port 10a of the first compressor 10 to one end of the second heat exchanger 60 (see the solid line of the switching mechanism 30 in Figure 1). When the state of the first refrigerant circuit 110 is set to the second state, the switching mechanism 30 connects the discharge port 10b of the first compressor 10 to one end of the second heat exchanger 60, and connects the suction port 10a of the first compressor 10 to one end of the first heat exchanger 40 (see the dashed line of the switching mechanism 30 in Figure 1).

[0051] Furthermore, if the air conditioner 100 is a cooling-only device, the air conditioner 100 does not need to have a switching mechanism 30.

[0052] 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.

[0053] 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.

[0054] An example of a first economizer heat exchanger is the economizer heat exchanger 70, which is located between the first heat exchanger 40 and the second heat exchanger 60 of the first refrigerant circuit 110, more specifically, between the first heat exchanger 40 and the first expansion valve 50 of the first refrigerant circuit 110. The economizer heat exchanger 70 is also located in the second refrigerant circuit 120, between the first valve 80 and the second compressor 20. During cooling operation, the economizer heat exchanger 70 exchanges heat between the refrigerant that flows out from the radiator (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 (described later), and the refrigerant that flows out from the radiator (first heat exchanger 40), passes through the economizer heat exchanger 70, and flows toward the heat absorber (second heat exchanger 60). As a result, during cooling operation, the refrigerant cooled in the heat exchanger (first heat exchanger 40) (see points c and d in Figure 3B) that flows toward the heat absorber (second heat exchanger 60) is further cooled by the economizer heat exchanger 70 (see point h in Figure 3B). The branching section 82 is positioned between the first heat exchanger 40, which functions as a heat exchanger during cooling operation, and the economizer heat exchanger 70.

[0055] 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 70 and the second heat exchanger 60. The first expansion valve 50 is, for example, an electronically expanded valve with a variable opening.

[0056] 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.

[0057] (2-2)Second refrigerant circuit The second refrigerant circuit 120 includes a second compressor 20. The air conditioner 100 of this embodiment also includes an economizer heat exchanger 70, which is an example of a first economizer heat exchanger, and a first valve 80. The first valve 80 is positioned upstream of the second compressor 20 in the refrigerant flow direction in the second refrigerant circuit 120. The first valve 80 is positioned between the branching point 82 where the second refrigerant circuit 120 branches off from the first refrigerant circuit 110 and the economizer heat exchanger 70.

[0058] In this embodiment, the first valve 80 is an electronically controlled expansion valve with a variable opening degree.

[0059] 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.

[0060] The second compressor 20 is preferably a variable-capacity compressor having an inverter-controlled motor. In this embodiment, the second compressor 20 is a rotary compressor (including a swing compressor). However, the type of second compressor 20 is not limited to a rotary compressor, and other types of compressors may be used. The second compressor 20 draws in refrigerant from the inlet 20a and discharges it from the discharge port 20b.

[0061] The economizer heat exchanger 70 is, for example, a double-tube heat exchanger or a plate-type heat exchanger. The economizer heat exchanger 70 is positioned between the first heat exchanger 40, which functions as a heat radiator during cooling operation, and the second heat exchanger 60, which functions as a heat absorber during cooling operation. In the economizer heat exchanger 70, as described above, during cooling operation, the refrigerant that flows out from the heat radiator (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 the refrigerant that flows out from the heat radiator (first heat exchanger 40), passes through the economizer heat exchanger 70 and flows toward the heat absorber (second heat exchanger 60) exchange heat. The refrigerant, which has been depressurized by the first valve 80 and cooled as it passes through the economizer heat exchanger 70 and flows toward the heat absorber (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).

[0062] (2-3) Pressure equalization mechanism The pressure equalization mechanism 90 is a mechanism for equalizing the pressure on the discharge side of the second compressor 20 and the pressure on the suction side of the second compressor 20.

[0063] The pressure equalization mechanism 90 includes a bypass passage 92 and a second valve 94. Preferably, the pressure equalization mechanism 90 also includes a check valve 96.

[0064] The check valve 96 is installed between the discharge port 20b 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 10b 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 20b of the second compressor 20.

[0065] The bypass passage 92 is a passage 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 bypass passage 92 connects the space between the discharge port 20b of the second compressor 20 of the second refrigerant circuit 120 and the check valve 96 to the suction side of the second compressor 20.

[0066] Although not shown in the diagram, the bypass passage 92 may also be a passage connecting the discharge port 10b of the first compressor 10 in the first refrigerant circuit 110 and the radiator (first heat exchanger 40) when the air conditioner 100 is in cooling operation, and the suction side of the second compressor 20. Specifically, the bypass passage 92 may be a passage connecting the piping that connects the discharge port 10b of the first compressor 10 and the switching mechanism 30, and the suction side of the second compressor 20. Alternatively, the bypass passage 92 may be a passage 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) and the check valve 96, and the suction side of the second compressor 20.

[0067] The second valve 94 is a valve located in the bypass passage 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.

[0068] The second valve 94 is opened under control by the control device 8, which will be described later, when equalizing the pressure between the discharge side and the suction side of the second compressor 20. The specific control of the second valve 94 by the control device 8 will be described later.

[0069] (2-4) 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 70, 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.

[0070] 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.

[0071] (2-5) Control device A control device 8, which is an example of a control unit, is a device that controls the operation of the air conditioner 100.

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

[0073] 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 second sensor (pressure sensor) 122 for measuring the suction pressure of the second compressor 20 and a second sensor (temperature sensor) 124 for measuring the suction temperature of the second compressor 20. The first sensor 122 and the second sensor 124 are positioned between the economizer heat exchanger 70 and the suction port 20a of the second compressor 20, for example, near the suction port 20a of the second compressor 20. The control device 8 is electrically connected to the first sensor 122 and the second sensor 124 and acquires the measurement results of the first sensor 122 and the second sensor 124. The control device 8 converts the pressure measured by the first sensor 122 into the saturation temperature of the refrigerant.

[0074] 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.

[0075] 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.

[0076] (2-5-1) 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.

[0077] 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.

[0078] (2-5-2) Cooling operation When the control device 8 causes the air conditioner 100 to perform cooling operation, it controls the operation of the switching mechanism 30 to set the state of the first refrigerant circuit 110 to the first state, and normally operates the first compressor 10 and the second compressor 20. 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 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.

[0079] Furthermore, if the load on the air conditioner 100 decreases and it is more efficient to operate only the first compressor 10 for cooling, the control device 8 stops the operation of the second compressor 20 and operates only the first compressor 10 for cooling. When the air conditioner 100 operates in this manner, the control device 8 closes the first valve 80, as will be described later. The control device 8 then controls the rotation speed of the motor of the first compressor 10 and the opening degree of the first expansion valve 50 based on the measurement results of various sensors (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 rotation speeds.

[0080] Furthermore, the control device 8 controls the second valve 94 to a closed state during cooling operation.

[0081] (2-5-3) Control when the second compressor is stopped When the operation of the second compressor 20 is stopped, if the first valve 80 is open, refrigerant cooled by the first heat exchanger 40, which functions as a radiator, may flow into the space between the first valve 80 of the second refrigerant circuit 120 and the second compressor 20 (hereinafter referred to as the first section 125), potentially causing the pressure in the first section 125 to rise. If high-pressure refrigerant cooled by the first heat exchanger 40 is present in the first section 125, and the ambient temperature is relatively low, and the saturation temperature of the refrigerant corresponding to the pressure of the refrigerant present in the first section 125 is higher than the ambient temperature, the refrigerant in the first section 125 may exchange heat with the ambient air, potentially causing the refrigerant to condense within the first section 125. If the amount of condensation is large, when the operation of the second compressor 20 is started, the condensed liquid refrigerant may be drawn into the second compressor 20, causing liquid compression and potentially leading to a malfunction of the second compressor 20.

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

[0083] An example of controlling the air conditioner 100 by the control device 8 when stopping the second compressor 20 will be explained with reference to the flowchart in Figure 4.

[0084] Here, we will explain using the example of a case where, while the air conditioner 100 is operating in cooling mode with both the first compressor 10 and the second compressor 20 running, the load on the air conditioner 100 decreases, the second compressor 20 is stopped, and cooling operation continues with only the first compressor 10 running. However, the control for stopping the operation of the second compressor 20 as described here may also be performed when stopping the cooling operation of the air conditioner 100 (when stopping the operation of both the first compressor 10 and the second compressor 20) while both the first compressor 10 and the second compressor 20 are running in cooling mode.

[0085] When operating in cooling mode, with both the first compressor 10 and the second compressor 20 running, the control device 8 determines whether or not to stop the operation of the second compressor 20, depending on the operating status of the air conditioner 100 (step S1).

[0086] When the control device 8 decides to stop the operation of the second compressor 20 in step S1, it preferably does not immediately close the first valve 80, but continues to operate the second compressor 20 while controlling the opening degree of the first valve 80 based on the measurement results of the first sensor 122 and the measurement results of the second sensor 124 (step S2). For example, the control device 8 controls the opening degree of the first valve 80 based on a value obtained by subtracting the saturation temperature derived from the suction pressure of the second compressor 20 measured by the first sensor 122 from the temperature of the refrigerant drawn into the second compressor 20 as measured by the second sensor 124. The control device 8 converts the measurement result of the first sensor 122 into a saturation temperature, for example, based on a table showing the relationship between refrigerant pressure and saturation temperature stored in the memory of the control device 8, or based on a mathematical formula showing the relationship between refrigerant pressure and saturation temperature stored in the memory of the control device 8.

[0087] Specifically, the control device 8 controls the opening degree of the first valve 80 so that the value obtained by subtracting the saturation temperature, which is derived from the intake pressure of the second compressor 20 measured by the first sensor 122, from the temperature of the refrigerant drawn into the second compressor 20 as measured by the second sensor 124, is at least greater than zero (in other words, so that the refrigerant drawn into the second compressor 20 becomes superheated).

[0088] More preferably, when the control device 8 stops the second compressor 20, it controls the opening of the first valve 80 so that the suction superheat of the second compressor 20 is equal to or greater than a predetermined superheat. For example, suppose that during cooling operation in which both the first compressor 10 and the second compressor 20 are in operation, the control device 8 controls the opening of the first valve 80 so that the suction superheat of the second compressor 20 is equal to α (≧0). In this case, when the control device 8 stops the second compressor 20, it controls the opening of the first valve 80 so that the suction superheat of the second compressor 20 is equal to or greater than a predetermined superheat greater than α. In other words, when the control device 8 stops the second compressor 20, it is preferable to control the opening of the first valve 80 to be smaller than the opening when cooling operation is being performed using both the first compressor 10 and the second compressor 20 (rather than suddenly closing the first valve 80 completely).

[0089] Then, the control device 8 maintains the state in which the refrigerant drawn in by the second compressor 20 is superheated (preferably to a predetermined superheated state) for a predetermined time, and then completely closes the first valve 80 (step S3).

[0090] Preferably, the control device 8 continues to operate the second compressor 20 for a predetermined time after closing the first valve 80 (step S4), and then stops the second compressor 20 (step S5).

[0091] In this state, there is a pressure difference between the discharge side and the suction side of the second compressor 20. At this point, the second valve 94 located in the bypass passage 92 may be opened to equalize the pressure between the discharge side and the suction side of the second compressor 20 (step S5). With this control, high-pressure refrigerant flows into the suction side of the second compressor 20. However, since the incoming refrigerant is a relatively low-density refrigerant before cooling by the first heat exchanger 40, the amount of incoming refrigerant is small in weight.

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

[0093] If the control device 8 determines in step S7 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 S8).

[0094] Furthermore, it is especially preferable to equalize the pressure between the discharge side and the suction side of the second compressor 20 when the second compressor 20 is a rotary compressor. This is because, due to the characteristics of a rotary compressor, if the pressure on the discharge side remains higher than the pressure on the suction side, there is a possibility that the refrigerant oil inside the second compressor 20 may leak out from the suction port 20a of the second compressor 20.

[0095] (2-5-4) Control of the second compressor during startup This section describes the control of the air conditioner 100 by the control device 8 when starting the operation of the second compressor 20. Referring to the flowchart in Figure 5, this section explains the control of the second compressor 20 when it is started due to an increase in load or other reasons, while the first compressor 10 is operating in cooling mode.

[0096] When operating in cooling mode with only the first compressor 10 running, the control device 8 decides whether or not to start operating the second compressor 20 according to the operating status of the air conditioner 100. If it decides to start operating the second compressor 20, it proceeds to step S12 (step S1).

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

[0098] Furthermore, when operating only the first compressor 10 for cooling, there may be a pressure difference between the discharge side and the suction side of the second compressor 20. In particular, when pressure equalization by the pressure equalization mechanism 90, as explained in steps S6 to S8 of the flowchart in Figure 4, is not performed, there may be a large pressure difference between the discharge side and the suction side of the second compressor 20.

[0099] Therefore, the control device 8 preferably opens the first valve 80 in step S12 and then waits in that state for a predetermined time. By opening the first valve 80, the suction side of the second compressor 20 also becomes high pressure, the discharge side and suction side of the second compressor 20 are pressure-equalized, and the second compressor 20 becomes ready for operation.

[0100] Then, the control device 8 starts operating the second compressor 20 after a predetermined time has elapsed since opening the first valve 80 (for example, after a predetermined time after which it is assumed that the decrease in the pressure difference between the discharge side and the suction side of the second compressor 20 will be suppressed) (step S13). Alternatively, the control device 8 may start operating the second compressor 20 when the difference between the measured value of a pressure sensor (not shown) provided on the discharge side of the second compressor 20 and the measured value of the first sensor 122 becomes smaller than or equal to a predetermined value.

[0101] Then, in order to perform cooling operation by operating the first compressor 10 and the second compressor 20, the control device 8 starts controlling the rotational speed of the first compressor 10 and the second compressor 20, as well as the opening degree of the first expansion valve 50, and also starts controlling the opening degree of the first valve 80 (step S14).

[0102] (3) Features (3-1) The air conditioner 100 includes a first refrigerant circuit 110, a second refrigerant circuit 120, and a control device 8 as an example of a control unit. The first refrigerant circuit 110 includes a first compressor 10, a first heat exchanger 40 that functions as a radiator during cooling operation, a first expansion valve 50, and a second heat exchanger 60 that functions as a heat absorber during cooling operation. The second refrigerant circuit 120 connects the first compressor 10 and the first heat exchanger 40, and the first heat exchanger 40 and the first expansion valve 50. The second refrigerant circuit 120 includes a second compressor 20 and a first valve 80. The first valve 80 is located upstream of the second compressor 20. The control device 8 controls the first compressor 10, the second compressor 20, the first expansion valve 50, and the first valve 80. When the control device 8 stops the second compressor 20, it closes the first valve 80.

[0103] In the air conditioner 100, a first valve 80 is located upstream of the second compressor 20 in the second refrigerant circuit 120, and the first valve 80 is closed when the second compressor 20 stops. Therefore, in this air conditioner 100, even when the outside air temperature is relatively low, the condensation of a large amount of refrigerant on the suction side of the second compressor 20 can be suppressed, thereby suppressing liquid compression when the second compressor 20 starts up.

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

[0105] In this air conditioner 100, the first valve 80 is closed, and the second compressor 20 is operated with no refrigerant flowing downstream of the first valve 80. Therefore, even when the outside air temperature is relatively low, this air conditioner 100 can suppress the condensation of a large amount of refrigerant on the suction side of the second compressor 20, thereby suppressing liquid compression when the second compressor 20 is started.

[0106] (3-3) The air conditioner 100 has a first sensor 122 and a second sensor 124. The second compressor 20 has an intake port 20a. The first valve 80 is an expansion valve. The first sensor 122 measures the saturation temperature of the refrigerant between the first valve 80 and the intake port 20a of the second compressor 20. The second sensor 124 measures the temperature of the refrigerant drawn into the second compressor 20. When stopping the second compressor 20, the control device 8 controls the opening degree of the first valve 80 based on the measurement results of the first sensor 122 and the measurement results of the second sensor 124.

[0107] The statement here that the first sensor 122 measures the saturation temperature includes not only the case where the first sensor 122 measures the saturation temperature itself, but also the case where it measures a physical quantity correlated with the saturation temperature (a physical quantity whose value, if known, allows for the determination of the saturation temperature of the refrigerant).

[0108] Specifically, in this embodiment, the first sensor 122 and the second sensor 124 are positioned between the first valve 80 and the inlet 20a of the second compressor 20. The first sensor 122 measures the pressure equivalent to the refrigerant's saturation temperature, rather than the refrigerant's saturation temperature itself. The control device 8 converts the pressure measured by the first sensor 122 into the saturation temperature.

[0109] In the air conditioner 100, the condensation of a large amount of refrigerant on the intake side of the second compressor 20 is easily suppressed, resulting in a highly reliable air conditioner 100.

[0110] (3-4) In the air conditioner 100, when the control device 8 stops the second compressor 20, it controls the first valve 80 so that the refrigerant drawn in by the second compressor 20 becomes superheated before closing the first valve 80.

[0111] In particular, when the control device 8 stops the second compressor 20, it controls the opening degree of the first valve 80 so that the suction superheat level of the second compressor 20 is equal to or greater than a predetermined superheat level.

[0112] In this air conditioner 100, the amount of refrigerant present between the first valve 80 and the suction port 20a of the second compressor 20 after the second compressor 20 has stopped can be particularly reduced, making liquid compression less likely to occur in the second compressor 20 and thus highly reliable.

[0113] (3-5) In the air conditioner 100, the second refrigerant circuit 120 includes an economizer heat exchanger 70 positioned between the first heat exchanger 40 and the second heat exchanger 60. During cooling operation, the economizer heat exchanger 70 receives refrigerant flowing out from the first heat exchanger 40, which functions as a heat absorber, and branches off to the second refrigerant circuit 120 at the branching section 82, where it exchanges heat between the refrigerant reduced in pressure by the first valve 80 and the refrigerant flowing out from the first heat exchanger 40.

[0114] In this air conditioner 100, the capacity and efficiency of the air conditioner 100 can be improved by using the economizer heat exchanger 70.

[0115] (3-6) In the air conditioner 100, the branching section 82 is positioned between the first heat exchanger 40, which functions as a radiator during cooling operation, and the economizer heat exchanger 70.

[0116] In this air conditioner 100, upstream of the economizer heat exchanger 70 in the flow direction of the refrigerant in 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 70. Therefore, in this air conditioner 100, compared to the case where the entire amount of refrigerant flowing out from the first heat exchanger 40 flows through the first refrigerant circuit 110 to the economizer heat exchanger 70, the size of the economizer heat exchanger 70 can be reduced while improving the capacity and efficiency of the air conditioner 100.

[0117] (3-7) The air conditioner 100 has a bypass passage 92 and a second valve 94 located in the bypass passage 92. The bypass passage 92 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. Alternatively, the bypass passage connects the discharge port 10b of the first compressor 10 in the first refrigerant circuit 110 to the first heat exchanger 40 which functions as a radiator during refrigerant operation to the suction side of the second compressor 20 of the second refrigerant circuit 120.

[0118] In this air conditioner 100, opening the second valve 94 reduces the differential pressure between the suction side and the discharge side of the second compressor 20, thereby enabling the second compressor 20 to start up.

[0119] (3-8) In the air conditioner 100, the refrigerant sealed in the first refrigerant circuit 110 and the second refrigerant circuit 120 contains CO2 as at least a portion of its components.

[0120] In this air conditioner 100, a refrigerant containing at least CO2, which has a low global warming potential, is used, thus enabling the realization of an air conditioner 100 with a low environmental impact.

[0121] (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.

[0122] (4-1) Variation A In the above embodiment, the first sensor 122 is a pressure sensor that measures the pressure equivalent to the saturation temperature, rather than the saturation temperature itself, and the control device 8 interprets the pressure value measured by the first sensor 122 as the saturation temperature. However, it is not limited to this, and the first sensor may be a temperature sensor that directly measures the saturation temperature.

[0123] In this case, the first sensor 122a, which is a temperature sensor, measures the temperature of the refrigerant as it flows in a gas-liquid two-phase state. For example, as shown in Figure 6, the first sensor 122a is placed between the first valve 80 through which the gas-liquid two-phase refrigerant flows and the economizer heat exchanger 70, and measures the temperature (saturation temperature) of the refrigerant flowing at this location.

[0124] (4-2) Modification B In the above embodiment, when the operation of the second compressor 20 is stopped, the control device 8 controls the opening degree of the first valve 80 based on the measured values ​​of the first sensor 122 and the second sensor 124, and keeps the refrigerant drawn in by the second compressor 20 in a superheated state (a state in which the superheat is greater than 0).

[0125] However, the invention is not limited to this, and the air conditioner 100 may not be equipped with the first sensor 122 and the second sensor 124 (or may not use the measurement results of the first sensor 122 and the second sensor 124), and the control device 8 may, when the operation of the second compressor 20 is stopped, control the opening degree of the first valve 80 to a predetermined opening degree so that the refrigerant drawn in by the second compressor 20 becomes superheated (a state in which the superheat degree is greater than 0).

[0126] (4-3) Modification C 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 70. However, the embodiment is not limited to this configuration.

[0127] The branching section 82a may be positioned between the economizer heat exchanger 70 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 70 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 70 tends to be larger compared to the above embodiment.

[0128] (4-4) Modification D In the above embodiment, an economizer heat exchanger 70 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.

[0129] As shown in Figure 8A, the air conditioner 100 may have a gas-liquid separation refrigerant container 72 (flash tank economizer) that spans between the first refrigerant circuit 110 and the second refrigerant circuit 120, instead of an economizer heat exchanger 70. The second refrigerant circuit 120 is provided with a first valve 80a, and the first refrigerant circuit 110 is provided with a second expansion valve 84. The first valve 80a is preferably an electrically operated valve with adjustable opening.

[0130] When stopping the operation of the second compressor 20, the first valve 80a is controlled in the same manner as the first valve 80 in the above embodiment (see steps S2 and S3 of the flowchart in Figure 4).

[0131] Furthermore, for example, when switching from a state in which the air conditioner 100 is operating only the first compressor 10 for cooling to a state in which both the first compressor 10 and the second compressor 20 are operating for cooling, the first valve 80a is opened before the start of operation of the second compressor 20, similar to the control of the first valve 80 in step S12 of the flowchart in Figure 5. However, the refrigerant pressure in the refrigerant container 72 is the intermediate pressure in the refrigeration cycle (because it is reduced by the second expansion valve 84), and if the pressure on the discharge side of the second compressor 20 is the high pressure in the refrigeration cycle, even if the first valve 80a is opened, the pressure on the discharge side of the second compressor 20 and the pressure on the suction side of the second compressor 20 may not equalize. Therefore, if it is assumed that there is a difference between the pressure on the discharge side of the second compressor 20 and the pressure on the suction side of the second compressor 20, the first valve 80a may be opened (step S12) before starting operation of the second compressor 20 in step S13, and the pressure equalization mechanism 90 may be used to equalize the pressure on the discharge side of the second compressor 20 and the pressure on the suction side of the second compressor 20.

[0132] When the air conditioner 100 operates the first compressor 10 and the second compressor 20 to perform cooling operation, the opening degree of the first valve 80a is not controlled, as in step S14 of the flowchart in Figure 5, but is adjusted to a predetermined opening degree (for example, fully open).

[0133] The following describes the state in which the air conditioner 100 shown in Figure 8A is performing cooling operation. In the air conditioner 100, the refrigerant container 72 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 72. When the control device 8 operates both the first compressor 10 and the second compressor 20 to perform cooling operation, it appropriately controls the opening degree of the second expansion valve 84. Note that when the second compressor 20 is stopped to perform cooling operation, the opening degree of the second expansion valve 84 is not controlled. When both the first compressor 10 and the second compressor 20 are operated to perform cooling operation, the refrigerant that flows out from the first heat exchanger 40 and is depressurized by the second expansion valve 84 to become a two-phase state flows into the refrigerant container 72. The gaseous refrigerant separated in the refrigerant container 72 is drawn into the second compressor 20.

[0134] Even with the air conditioner 100 configured as shown in Figure 8A, when both the first compressor 10 and the second compressor 20 are operated for cooling, the temperature of the refrigerant flowing into the second heat exchanger 60, which functions as a refrigerant heat absorber, can be lowered, thereby improving the capacity of the air conditioner 100.

[0135] Furthermore, as shown in Figure 8B, the second refrigerant circuit 120 may include, in addition to the refrigerant container 72, a heat exchanger 70a (an example of a second economizer heat exchanger) positioned between the first refrigerant circuit 110 and the second refrigerant circuit 120. The heat exchanger 70a 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 70a is positioned so that when the air conditioner 100 operates both the first compressor 10 and the second compressor 20 for cooling operation, 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 72. The refrigerant that has exchanged heat with the refrigerant flowing through the first refrigerant circuit 110 in the heat exchanger 70a is drawn into the second compressor 20. In this configuration, by further using the heat exchanger 70a, 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 8A.

[0136] In the configuration shown in Figure 8B, the control of the first valve 80a, etc., when stopping the operation of the second compressor 20 and when starting the operation of the second compressor 20 is as described in the configuration shown in Figure 8A.

[0137] In addition, even in the configurations shown in Figures 8A and 8B, the second refrigerant circuit 120 is not used during heating operation. During heating operation, the second compressor 20 is not operated, the first valve 80a is closed, and the second expansion valve 84 is controlled to a predetermined opening degree, and the opening degree is not changed during heating operation.

[0138] (4-5) Modification E Unlike modified example D, in the configurations of Figures 8A and 8B, the first valve 80a may be a solenoid valve that can only be switched between fully open and fully closed. Furthermore, the control in step S2 in Figure 4 and the control in step S14 in Figure 5 may not be performed.

[0139] Even with this configuration, since the second compressor 20 is operated for a predetermined time with the first valve 80a closed, the condensation of a large amount of refrigerant on the suction side of the second compressor 20 is suppressed, thereby suppressing liquid compression when the second compressor 20 is started.

[0140] (4-6) Modification F In the above embodiment, a pressure equalization mechanism 90 is provided to equalize the pressure between the discharge side and the suction side of the second compressor 20, and the pressure between the discharge side and the suction side of the second compressor 20 is equalized by opening the second valve 94.

[0141] However, if it is possible to equalize the pressure between the discharge side and the suction side before starting the second compressor 20 by opening the first valve 80, then the pressure equalization mechanism 90 does not need to be provided.

[0142] <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]

[0143] 8. Control device (control unit) 10. First Compressor 20. Second Compressor 20a Inlet 40 1st heat exchanger (radiator) 50 First expansion valve 60 Second heat exchanger (heat absorber) 70 Economizer Heat Exchanger (First Economizer Heat Exchanger) 70a heat exchanger (second economizer heat exchanger) 72 Refrigerant containers 80,80a First valve 82,82a Branch 84. Second expansion valve 92 Bypass channel 94 Second valve 100 Air conditioners (refrigeration cycle devices) 110 1st refrigerant circuit 120 Second refrigerant circuit 122 First sensor (pressure sensor) 122a First sensor (temperature sensor) 124 Second Sensor [Prior art documents] [Patent Documents]

[0144] [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) is provided, which connects the first compressor and the heat sink and the heat sink and the first expansion valve, and includes a second compressor (20) and a first valve (80, 80a) located upstream of the second compressor. The system comprises the first compressor, the second compressor, the first expansion valve, and a control unit (8) that controls the first valve, When the control unit stops the second compressor, it closes the first valve. Refrigeration cycle device (100).

2. The control unit closes the first valve before stopping the second compressor. The refrigeration cycle apparatus according to claim 1.

3. The system further comprises a first sensor (122, 122a) and a second sensor (124), The second compressor has an inlet (20a), The first valve is an expansion valve, The first sensor measures the saturation temperature of the refrigerant between the first valve and the inlet of the second compressor. The second sensor measures the temperature of the refrigerant being drawn into the second compressor. When stopping the second compressor, the control unit controls the opening degree of the first valve based on the measurement results of the first sensor and the measurement results of the second sensor. A refrigeration cycle apparatus according to claim 1 or 2.

4. When the control unit stops the second compressor, it controls the first valve before closing the first valve so that the refrigerant drawn in by the second compressor becomes superheated. The refrigeration cycle apparatus according to claim 1.

5. When the control unit stops the second compressor, it controls the opening of the first valve so that the suction superheat of the second compressor is equal to or greater than a predetermined superheat. The refrigeration cycle apparatus according to claim 4.

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

7. The second refrigerant circuit further includes a first economizer heat exchanger (70) positioned between the heat sink and the heat absorber, 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. A refrigeration cycle apparatus according to claim 1 or 2.

8. The branch section (82) is positioned between the heat sink and the first economizer heat exchanger. The refrigeration cycle apparatus according to claim 7.

9. The first refrigerant circuit further includes a second expansion valve (84) positioned between the heat sink and the first expansion valve, The second refrigerant circuit further includes a gas-liquid separable refrigerant container (72) into which the refrigerant, which has been depressurized by the second expansion valve and is in a two-phase state, flows. The first valve is positioned between the refrigerant container and the second compressor. The gaseous refrigerant separated in the refrigerant container is drawn into the second compressor. A refrigeration cycle apparatus according to claim 1 or 2.

10. The second refrigerant circuit further includes a second economizer heat exchanger (70a), The second economizer heat exchanger is arranged such that the refrigerant flowing out of the heat sink toward the second expansion valve and the gaseous refrigerant flowing out of the refrigerant container exchange heat. The refrigeration cycle apparatus according to claim 9.

11. The control unit opens the first valve before starting the second compressor. A refrigeration cycle apparatus according to claim 1 or 2.

12. A bypass passage (92) connecting the discharge side of the second compressor in the second refrigerant circuit, or the space between the discharge port of the first compressor in the first refrigerant circuit and the heat sink, and the suction side of the second compressor in the second refrigerant circuit, A second valve (94) is arranged in the bypass passage, Furthermore, A refrigeration cycle apparatus according to claim 1 or 2.

13. The refrigerant sealed in the first refrigerant circuit and the second refrigerant circuit contains CO in at least part of its components. ２ including, A refrigeration cycle apparatus according to claim 1 or 2.

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