Refrigeration cycle equipment

Abstract

There is a need for refrigeration cycle systems that enable highly efficient operation. [Solution] The air conditioner (100) has a first refrigerant circuit (110) and a second refrigerant circuit (120). The first refrigerant circuit includes a first compressor (10), a first heat exchanger (40) that functions as a refrigerant radiator, a first expansion valve (50), and a second heat exchanger (60) that functions as a refrigerant absorber. 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 (20). The suction pressure of the first compressor is lower than the suction pressure of the second compressor. The first compressor is a scroll compressor, and the second compressor is a rotary compressor. Alternatively, the first compressor is a scroll compressor with a first design compression ratio, and the second compressor is a scroll compressor with a second design compression ratio smaller than the first design compression ratio.

Description

Technical Field

[0001] It relates to a refrigeration cycle device.

Background Art

[0002] Conventionally, depending on the use of the refrigeration cycle device and the type of refrigerant used, etc., like the refrigeration cycle device of Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-49087), a plurality of compressors are provided in the refrigerant circuit of the refrigeration cycle device, and refrigerants with different pressures are inhaled into each of the compressors, and the compressed refrigerants of the plurality of compressors are discharged into a single refrigerant flow path in some cases.

Disclosure of the Invention

Problems to be Solved by the Invention

[0003] In such a refrigeration cycle device, depending on the selection of the compressor, efficient operation may be difficult, but Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-49087) does not disclose a configuration of a refrigeration cycle device that enables highly efficient operation.

Means for Solving the Problems

[0004] The refrigeration cycle device according to the first aspect includes a first refrigerant circuit and a second refrigerant circuit. The first refrigerant circuit includes a first compressor, a radiator, a first expansion valve, and an absorber. The second refrigerant circuit connects between the first compressor and the radiator and between the radiator and the first expansion valve. The second refrigerant circuit includes a second compressor. The suction pressure of the first compressor is lower than the suction pressure of the second compressor.

[0005] The first compressor is a scroll compressor, and the second compressor is a rotary compressor. Or, the first compressor is a scroll compressor with a first design compression ratio, and the second compressor is a scroll compressor with a second design compression ratio smaller than the first design compression ratio. <on

[0006] In the refrigeration cycle system according to the first perspective, the second refrigerant circuit is connected to the first refrigerant circuit between the first compressor and the radiator, so the discharge pressures of the first and second compressors are the same. Also, in the refrigeration cycle system according to the first perspective, the suction pressure of the first compressor is lower than the suction pressure of the second compressor. Therefore, in the refrigeration cycle system according to the first perspective, the compression ratio of the first compressor is greater than that of the second compressor.

[0007] By using a scroll compressor, which is efficient at high compression ratios, as the first compressor, and a rotary compressor, which is efficient at low compression ratios, as the second compressor, an efficient refrigeration cycle system can be realized.

[0008] Furthermore, even when the first compressor is a scroll compressor with a high design compression ratio and the second compressor is a scroll compressor with a low design compression ratio, both compressors can be operated in an efficient range, resulting in an efficient refrigeration cycle system.

[0009] A refrigeration cycle device relating to the second aspect is a refrigeration cycle device relating to the first aspect, wherein the second refrigerant circuit further includes a second expansion valve and an economizer heat exchanger disposed between a radiator and a heat absorber. The 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, which has been depressurized by the second expansion valve, and the refrigerant that has flowed out from the radiator. The refrigerant, which has been depressurized by the second expansion valve and passed through the economizer heat exchanger, is drawn into the second compressor.

[0010] In the refrigeration cycle system from the second perspective, the capacity and performance can be improved by compressing the refrigerant that has passed through the economizer heat exchanger with a second compressor.

[0011] 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 economizer heat exchanger.

[0012] In the third-perspective refrigeration cycle system, a portion of the refrigerant flowing out of the radiator is diverted to the second refrigerant circuit, which flows through the second expansion valve to the economizer heat exchanger, while the remainder flows through the economizer heat exchanger to the first expansion valve. Therefore, in the third-perspective refrigeration cycle system, the capacity of the refrigeration cycle system can be improved while suppressing the size of the economizer heat exchanger, compared to the case where the entire amount of refrigerant flowing out of the radiator flows into the economizer heat exchanger without being diverted.

[0013] A refrigeration cycle device relating to the fourth aspect is a refrigeration cycle device relating to the first aspect, wherein the first refrigerant circuit further includes a second expansion valve. The second refrigerant circuit further includes a gas-liquid separable refrigerant container. The refrigerant container is positioned between a heat exchanger and a heat absorber, and receives refrigerant that flows out of the heat exchanger and is depressurized by the second expansion valve to become a two-phase state. The gaseous refrigerant separated in the refrigerant container is drawn into a second compressor.

[0014] In the refrigeration cycle system described in the fourth perspective, the temperature of the refrigerant flowing into the heat absorber can be lowered to improve the capacity of the refrigeration cycle system.

[0015] The refrigeration cycle device relating to the fifth aspect is the refrigeration cycle device relating to the fourth aspect, wherein the second refrigerant circuit further includes a heat exchanger. The heat exchanger is arranged so that the refrigerant flowing out of the radiator toward the second expansion valve and the gaseous refrigerant separated in the refrigerant container exchange heat.

[0016] In the fifth aspect of refrigeration cycle systems, the capacity of the refrigeration cycle system can be improved by further using heat exchangers.

[0017] The refrigeration cycle device relating to the sixth aspect is a refrigeration cycle device relating to either the second aspect or the fifth aspect, and the second refrigerant circuit and the second compressor are rotary compressors. At least when the load is 47% or less, the rotational speed of the first compressor is greater than the rotational speed of the second compressor.

[0018] In the sixth aspect of the refrigeration cycle system, under frequently used, relatively low-load conditions (a 47% load condition, which is one of the conditions for calculating SEER), a scroll compressor, which is efficient in the high-speed range, is operated at a higher rotational speed than a rotary compressor, which is efficient in the low-speed range, thus enabling efficient operation.

[0019] The refrigeration cycle device relating to the seventh aspect is the refrigeration cycle device relating to the sixth aspect, wherein the rotational speed of the first compressor is greater than the rotational speed of the second compressor when the load is at least 74% or less.

[0020] In the refrigeration cycle system of the seventh perspective, even under a wide range of load conditions (including the 74% load condition which is one of the conditions for calculating SEER), the scroll compressor, which is efficient in the high-speed range, operates at a higher rotational speed than the rotary compressor, which is efficient in the low-speed range, thus enabling even more efficient operation.

[0021] The refrigeration cycle device relating to the eighth aspect is a refrigeration cycle device relating to any of the first or seventh aspects, wherein the refrigerant filling the first refrigerant circuit and the second refrigerant circuit contains CO2 as at least a part of its components.

[0022] In the refrigeration cycle system described in the eighth 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.

[0023] The refrigeration cycle device relating to the ninth aspect is a refrigeration cycle device relating to either the second aspect or the seventh aspect, and the second compressor is a rotary compressor. The refrigerant filling the first and second refrigerant circuits is CO2.

[0024] In the refrigeration cycle system described in the ninth perspective, CO2, which has a low global warming potential, is used as the refrigerant, thus enabling the realization of a refrigeration cycle system with a low environmental impact.

[0025] The refrigeration cycle device according to the 10th aspect is the refrigeration cycle device of the 9th aspect, and the ratio of the discharge amount of the second compressor to the discharge amount of the first compressor is determined such that the rotation speed of the second compressor is greater than the minimum rotation speed at which continuous operation is possible when the load is 47%.

[0026] In the refrigeration cycle device of the 10th aspect, by suppressing the rotation speed of the second compressor (rotary compressor) at high loads as low as possible, high-efficiency operation can be achieved even at high loads. In other words, the efficiency of the refrigeration cycle at high loads can be maintained higher by making the ratio of the discharge amount of the second compressor to the discharge amount of the first compressor as large as possible.

[0027] However, if only the rotation speed of the second compressor is suppressed as low as possible, at relatively small load conditions with frequent operation (the condition of 47% load which is one of the conditions for calculating SEER), the rotation speed of the second compressor becomes too low to continue continuous operation, and as a result, SEER may decrease.

[0028] In contrast, in the refrigeration cycle device of the 10th aspect, since the ratio of the discharge amount of the second compressor to the discharge amount of the first compressor is determined such that the rotation speed of the second compressor is greater than the minimum rotation speed at which continuous operation is possible when the load is 47%, a decrease in SEER can be suppressed.

[0029] The refrigeration cycle device according to the 11th aspect is the refrigeration cycle device of the 9th or 10th aspect, and the ratio of the discharge amount of the second compressor to the discharge amount of the first compressor is determined such that the rotation speed of the second compressor is less than the maximum rotation speed at which continuous operation is possible when the load is 100%.

[0030] If a refrigeration cycle is designed such that the rotational speed of the second compressor exceeds the maximum rotational speed at which continuous operation is possible when the load is 100%, then when the load actually reaches 100%, in order to continue operating the second compressor, its rotational speed will be reduced to the maximum rotational speed, and the insufficient capacity will be compensated for by operating the first compressor at a rotational speed higher than the ideal rotational speed. In this operating condition, the efficiency of the refrigeration cycle is reduced when the load is 100%.

[0031] In contrast, in the refrigeration cycle device of the 11th perspective, the ratio of the displacement amount of the second compressor to the displacement amount of the first compressor is determined such that the rotational speed of the second compressor is smaller than the maximum rotational speed at which continuous operation is possible when the load is 100%, thereby suppressing the decrease in SEER.

[0032] A refrigeration cycle device according to the 12th aspect is a refrigeration cycle device according to either the 1st aspect or the 11th aspect, further comprising a bypass passage, a valve, and a control unit. The bypass passage connects the discharge side of the second compressor of the second refrigerant circuit to the suction side of the second compressor of the second refrigerant circuit. Alternatively, the bypass passage connects the discharge port and radiator of the first compressor in the first refrigerant circuit to the suction side of the second compressor of the second refrigerant circuit. The valve is located in the bypass passage. The control unit controls the operation of the valve. The control unit opens the valve when the second compressor is stopped.

[0033] In this refrigeration cycle system, when the second compressor is stopped, the differential pressure between the discharge side and the suction side of the second compressor is reduced. This differential pressure prevents the refrigerant oil inside the second compressor from leaking out of the suction port of the second compressor. [Brief explanation of the drawing]

[0034] [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 4] Figure 1 is a flowchart illustrating the control of the second compressor when it is shut down in the air conditioner. [Figure 5] This is a pH diagram that conceptually depicts the ideal balance of the refrigeration cycle for different loads. [Figure 6] This diagram illustrates an example of how to determine the maximum value of the ratio of the displacement amount of the second compressor to the displacement amount of the first compressor. [Figure 7] This diagram illustrates an example of how to determine the minimum value of the ratio of the displacement amount of the second compressor to the displacement amount of the first compressor. [Figure 8A] This is a schematic diagram of the air conditioner in modified example A. [Figure 8B] This is a schematic diagram of the air conditioner in modified example B. [Figure 8C] This is another example of a schematic diagram of the air conditioner in modified form B. [Figure 9] This is a schematic diagram of the air conditioner in modified example D. [Figure 10] This is a schematic diagram of the refrigeration and freezing system according to a second embodiment of the refrigeration cycle system. [Modes for carrying out the invention]

[0035] Embodiments of the refrigeration cycle apparatus of this disclosure will be described below with reference to the drawings.

[0036] <First Embodiment> An air conditioner 100 according to a first embodiment of the refrigeration cycle device of this disclosure will be described with reference to the drawings. However, the refrigeration cycle device of this disclosure is not limited to an air conditioner, and may be other types of devices (e.g., chillers) that use a vapor compression type refrigeration cycle to cool or heat a temperature control target (such as a medium like air or water).

[0037] (1) Overall structure The overall configuration of the air conditioner 100 will be explained with reference to Figure 1. Figure 1 is a schematic diagram of the air conditioner 100.

[0038] The air conditioner 100 is a device that cools or heats the indoor air of a building or the like, which is the target of temperature control, by using a vapor compression type refrigeration cycle. Furthermore, although the air conditioner 100 in this embodiment is a device that can cool or heat the indoor air of a building or the like, the air conditioner 100 may also be a device that only provides cooling.

[0039] 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.

[0040] 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.

[0041] 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)).

[0042] The second refrigerant circuit 120 mainly includes a second compressor 20. The second refrigerant circuit 120 also includes a second expansion 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.

[0043] 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.

[0044] 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.

[0045] 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).

[0046] Unlike the air conditioner 100 disclosed herein, the second compressor 20 is omitted, and the refrigerant that has passed through the economizer heat exchanger 70 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 70 is injected into the first compressor 10 as an intermediate injection.

[0047] (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.

[0048] This section provides a detailed explanation of the various components of the air conditioner 100.

[0049] (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.

[0050] The first compressor 10 is a scroll compressor. The first compressor 10 is a variable-capacity compressor with an inverter-controlled motor.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Furthermore, if the air conditioner 100 is a cooling-only device, the air conditioner 100 does not need to have a switching mechanism 30.

[0055] 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.

[0056] 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.

[0057] The economizer heat exchanger 70 is positioned 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 positioned between the second expansion valve 80 and the second compressor 20 in the second refrigerant circuit 120. During cooling operation, the economizer heat exchanger 70 exchanges heat between the refrigerant that flows out of the radiator (first heat exchanger 40), branches off to the second refrigerant circuit 120 at the branching section 82, and is depressurized by the second expansion valve 80 (described later), and the refrigerant that flows out of the radiator (first heat exchanger 40), passes through the economizer heat exchanger 70, and flows toward the heat absorber (second heat exchanger 60). As a result, during 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.

[0058] 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.

[0059] 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.

[0060] (2-2)Second refrigerant circuit The second refrigerant circuit 120 includes a second compressor 20. The air conditioner 100 of this embodiment also has an economizer heat exchanger 70 and a second expansion valve 80. The second expansion valve 80 is, for example, an electronically controlled expansion valve with a variable opening.

[0061] 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.

[0062] The second compressor 20 is a rotary compressor (including a swing compressor). The second compressor 20 is a variable-capacity compressor with an inverter-controlled motor.

[0063] The economizer heat exchanger 70 is, for example, a double-tube heat exchanger or a plate heat exchanger. In the economizer heat exchanger 70, as described above, during cooling operation, 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 second expansion valve 80, 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) exchange heat. The refrigerant that has been depressurized by the second expansion valve 80 and cooled by passing through the economizer heat exchanger 70 and flowing 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).

[0064] Here, we will explain why a scroll compressor is used for the first compressor 10 and a rotary compressor is used for the second compressor 20.

[0065] In the air conditioner 100, as shown in Figure 3B, the suction pressure of the first compressor 10 (see point a in Figure 3B) is lower than the suction pressure of the second compressor 20 (see point f in Figure 3B). In contrast, the second compressor 20 discharges refrigerant between the first compressor 10 and the first heat exchanger 40 (radiator) of the first refrigerant circuit 110, so the discharge pressure of the first compressor 10 (see point b in Figure 3B) and the discharge pressure of the second compressor 20 (see point g in Figure 3B) are the same. Therefore, the compression ratio of the first compressor 10 is greater than that of the second compressor 20 (see Figure 3B).

[0066] Here, we will explain the differences in characteristics between scroll compressors and rotary compressors.

[0067] Scroll compressors have a structure in which multiple compression chambers are formed in the compression mechanism, resulting in a small pressure difference between compression chambers and suppression of refrigerant leakage between compression chambers. Therefore, scroll compressors generally achieve higher efficiency under high differential pressure conditions compared to rotary compressors. On the other hand, in scroll compressors, the compression ratio is determined by the design of the spiral of the scroll compression mechanism, and under conditions where the compression ratio is significantly lower than the design compression ratio, there is a problem of reduced efficiency due to overcompression losses. In short, scroll compressors can achieve efficient operation under conditions where the pressure ratio is relatively high (close to the design compression ratio).

[0068] On the other hand, rotary compressors have a general characteristic that while they can operate efficiently under relatively low operating conditions (hereinafter simply referred to as compressor rotation speed), as the rotation speed increases, friction losses increase and efficiency tends to decrease. In other words, when increasing the rotation speed of a rotary compressor to obtain a high pressure ratio, efficiency tends to decrease.

[0069] Therefore, in this air conditioner 100, a scroll compressor is used for the first compressor 10, which has a high compression ratio, and a rotary compressor is used for the second compressor 20, which has a low compression ratio. By adopting this configuration, this air conditioner 100 achieves more efficient operation compared to cases where scroll compressors of the same specifications are used for both the first compressor 10 and the second compressor 20, or where rotary compressors are used for both the first compressor 10 and the second compressor 20.

[0070] (2-3) 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.

[0071] The pressure equalization mechanism 90 includes a bypass channel 92, a bypass valve 94, and a check valve 96.

[0072] 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 does not perform heating operation (does not have the switching mechanism 30) and the second compressor 20 is stopped, and a situation does not occur in which only the first compressor 10 is operated, the check valve 96 may be omitted.

[0073] 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 discharge port of the second compressor 20 of the second refrigerant circuit 120 to the check valve 96 to the suction side of the second compressor 20.

[0074] Although not shown in the diagram, the bypass passage 92 may also be a passage 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 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 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), the check valve 96, and the suction side of the second compressor 20.

[0075] The bypass valve 94 is a valve located in the bypass passage 92. The bypass 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.

[0076] The bypass 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. This pressure equalization is performed because, if the second compressor 20 is a rotary compressor, due to the characteristics of the compressor, if the pressure on the discharge side remains higher than the pressure on the suction side, there is a possibility that the refrigerant oil inside the second compressor 20 may leak out from the suction port of the second compressor 20. The specific control of the bypass valve 94 by the control device 8 will be described later.

[0077] (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 second expansion valve 80, the bypass valve 94, and the like. 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.

[0078] 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.

[0079] (2-5) Control device The control device 8 is a device that controls the operation of the air conditioner 100.

[0080] 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 second expansion valve 80, the bypass 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.

[0081] 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.

[0082] 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.

[0083] (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.

[0084] During heating operation, the control device 8 controls the second expansion valve 80 and the bypass valve 94 to be closed, and the second compressor 20 is not operated.

[0085] (2-5-2) Cooling operation When the control device 8 initiates cooling operation of the air conditioner 100, it controls the operation of the switching mechanism 30 to set the state of the first refrigerant circuit 110 to the first state and 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.) 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 second expansion valve 80. The control device 8 also operates the motors of the first fan 42 and the second fan 62 at predetermined rotational speeds.

[0086] Furthermore, the control device 8 controls the bypass valve 94 to a closed state during cooling operation.

[0087] (2-5-3) Pressure equalization control when cooling operation is stopped The equalization control of the discharge and suction sides of the second compressor 20 when the second compressor 20 is stopped using the equalization mechanism 90 will be explained with reference to the flowchart in Figure 4. Note that when the second compressor 20 is stopped, this includes cases where the operation of the entire air conditioner 100 is stopped, as well as cases where only the second compressor 20 is stopped for some reason while the operation of the first compressor 10 continues.

[0088] The control device 8 decides whether to stop the operation of the second compressor 20 during cooling operation (when both the first compressor 10 and the second compressor 20 are in operation) (step S1). Stopping the operation of the second compressor 20 may include stopping the operation of the entire air conditioner 100 as described above, or stopping only the second compressor 20 while continuing to operate the first compressor 10.

[0089] In step S1, when the control device 8 decides to stop the operation of the second compressor 20, the control device 8 opens the bypass valve 94 (step S2).

[0090] In step S3, 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 pressure sensor (not shown) 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 sensors. 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 bypass 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 bypass valve 94 was opened.

[0091] If the control device 8 determines in step S3 that the differential pressure between the discharge side and the suction side of the second compressor 20 has been eliminated, it closes the bypass valve 94 (step S4).

[0092] 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.

[0093] (3) Method for determining the ratio of the displacement of the second compressor to the displacement of the first compressor In the air conditioner 100, a scroll compressor is used for the first compressor 10 and a rotary compressor is used for the second compressor 20, thereby achieving an efficient air conditioner 100.

[0094] To further improve the efficiency of the air conditioner 100, it is preferable to appropriately determine the ratio of the displacement volume (excluded volume) of the second compressor 20 to the displacement volume (excluded volume) of the first compressor 10 (hereinafter simply referred to as the displacement ratio). The method for determining the displacement ratio is described below.

[0095] The Seasonal Energy Efficiency Ratio (SEER) is used as the criterion for evaluating the cooling performance of the air conditioner 100. SEER is calculated by calculating the efficiency under multiple load conditions. Specifically, SEER is calculated from the efficiency under conditions such as 100% load and an outside temperature of 35°C (referred to as condition A for convenience of explanation), 74% load and an outside temperature of 30°C (referred to as condition B for convenience of explanation), and 47% load and an outside temperature of 25°C (referred to as condition C for convenience of explanation). Therefore, in order to achieve an air conditioner 100 with a high SEER, efficient operation under these multiple conditions is desired. In particular, the efficiency under condition C has a significant impact on the SEER value, and is therefore important for evaluating the performance of the air conditioner 100 under relatively low load conditions.

[0096] Now, the ratio of the refrigerant circulation rate in the second compressor 20 to the refrigerant circulation rate in the first compressor 10 (referred to as the refrigerant circulation rate ratio) under the above conditions A to C can be determined from the refrigeration cycle that achieves an ideal balance (the pH diagram shown in Figure 5) by determining the type of refrigerant (in other words, defining the pressure-temperature characteristics specific to the refrigerant) and making several assumptions. For example, the value of β / α in Figure 5 is the preferred refrigerant circulation rate ratio under condition C. The refrigerant circulation rate ratio tends to decrease as the load changes from high load conditions to low load conditions, as shown in Figure 5.

[0097] The assumptions used in calculating the above refrigerant circulation ratio include, for example, that the suction pressure (intermediate pressure) of the second compressor 20 is the synergistic mean of the discharge pressure and suction pressure of the first compressor 10, the economizer heat exchanger 70 is a counterflow cascade heat exchanger with a temperature difference of 5K on each outlet side, the suction superheat of the first compressor 10 is 5K, and the high pressure is determined to maximize the COP. However, the assumptions used should be appropriately determined based on the actual operating conditions of the air conditioner 100.

[0098] Once the refrigerant circulation ratio is determined, the required rotational speeds for each compressor 10 and 20 can be determined from the intake density of each compressor 10 and 20 and the ratio of the displacement amount (excluded volume) of the second compressor 20 to the displacement amount (excluded volume) of the first compressor 10 (displacement ratio). Since the intake density of each compressor 10 and 20 is determined from the refrigeration cycle that achieves an ideal balance, the required rotational speeds for each compressor 10 and 20 can be determined by determining the ratio of the displacement amounts.

[0099] This section explains how to determine the appropriate ratio of displacement amounts based on the required rotational speeds of each compressor 10 and 20 under conditions A to C (particularly based on the required rotational speeds of each compressor 10 and 20 under conditions A and C).

[0100] As mentioned above, the second compressor 20 is a rotary compressor. In order to obtain high efficiency for the air conditioner 100, considering the characteristics of the rotary compressor as described above, it is preferable that the rotational speed of the second compressor 20 be as small as possible in all of conditions A to C. Specifically, considering only the matter of suppressing the rotational speed of the rotary compressor, as shown in Figure 6(a), it is preferable that the rotational speed of the second compressor 20 be determined to be smaller than the rotational speed of the first compressor 10 in all of conditions A to C.

[0101] However, if the rotational speed of the second compressor 20 is set in this manner, under low load condition C, the rotational speed of the second compressor 20 may fall below the minimum possible continuous operation speed of the second compressor 20, which is determined from the specifications of the second compressor 20. When this happens, the efficiency of the air conditioner 100 under condition C decreases, and the SEER of the air conditioner 100 drops significantly.

[0102] Therefore, it is preferable that the displacement ratio is determined such that the rotational speed of the second compressor 20 is greater than the minimum number of rotational speeds at which the second compressor 20 can operate continuously, even under low load conditions C (including when the load is 47%) (so that the state shown in Figure 6(b) is achieved).

[0103] The method for determining the maximum displacement ratio can be expressed by the following equation 1. <Expression 1> Displacement amount of the second compressor 20 / Displacement amount of the first compressor 10 (displacement ratio) ≤ Rotational speed of the first compressor 10 in operating conditions that can achieve maximum capacity (rated capacity) × 47% × 11% ÷ Minimum rotational speed of the second compressor 20 that can normally operate continuously

[0104] Here, the value "47%" represents the load value under condition C, and the value "11%" represents the optimal volumetric flow rate ratio of the first compressor 10 to the second compressor 20 under the temperature conditions specified for condition C (specifically, an ambient temperature of 25°C and an evaporation temperature of 5°C). This value is determined from the physical properties of the refrigerant used in the aforementioned air conditioner 100 and the ideal balanced refrigeration cycle determined based on assumptions.

[0105] However, if we focus solely on the fact that the second compressor 20 can be operated continuously under condition C, then under the high-load condition A, the rotational speed of the second compressor 20 may exceed the maximum number of times the second compressor 20 can be operated continuously, which is determined by the specifications of the second compressor 20 (see Figure 7(a)).

[0106] In this case, in practice, operation can be continued by operating the second compressor 20 at its maximum rotational speed and compensating for the capacity deficiency by operating the first compressor 10 at a rotational speed greater than ideal (see Figure 7(b)). However, such operation would reduce the efficiency under condition A.

[0107] Therefore, it is preferable that the displacement ratio is determined such that, even under the high load condition A (when the load is 100%), the rotational speed of the second compressor 20 is smaller than the maximum number of times the second compressor 20 can operate continuously (as shown in Figure 7(c)).

[0108] The method for determining the minimum displacement ratio can be expressed by the following equation 2. <Expression 2> Displacement amount of the second compressor 20 / Displacement amount of the first compressor 10 (displacement ratio) ≥ Rotational speed of the first compressor 10 in an operating condition that can achieve maximum capacity (rated capacity) × 28% ÷ Maximum rotational speed of the second compressor 20 that can normally operate continuously

[0109] The value "28%" here represents the optimal volumetric flow rate ratio of the first compressor 10 to the second compressor 20 under the temperature conditions specified in Condition A (specifically, an ambient temperature of 35°C and an evaporation temperature of 0°C). This value is determined from the physical properties of the refrigerant used in the aforementioned air conditioner 100 and the ideal balanced refrigeration cycle determined based on assumptions.

[0110] As mentioned above, in all of conditions A to C, it is preferable that the rotational speed of the second compressor 20 is smaller than that of the first compressor 10. However, if the air conditioner 100 is designed to satisfy equations 1 and 2 above, and to minimize the size of the second compressor 20 considering cost, then, as shown in Figure 7(c), in the high-load region (at least under condition A in the example of Figure 7(c)), the rotational speed of the second compressor 20 may be larger than that of the first compressor 10. However, since condition A has a relatively small contribution to the SEER value (in other words, the period during which the air conditioner 100 is operated under high-load conditions such as condition A is not very long throughout the year), the SEER of the air conditioner 100 is likely to be maintained at a high level even with such a design.

[0111] However, from the viewpoint of the efficiency of the air conditioner 100, it is preferable to suppress the rotational speed of the second compressor 20 (rotary compressor) as much as possible (because the period during which the air conditioner 100 is operated under low-load conditions such as condition C is relatively long). Therefore, at least when the load is 47% or less (at least under condition C), it is preferable that the rotational speed of the first compressor 10 is greater than the rotational speed of the second compressor 20. Furthermore, at least when the load is 74% or less (at least under condition B), it is even more preferable that the rotational speed of the first compressor 10 is greater than the rotational speed of the second compressor 20.

[0112] (4) Features The following describes the characteristics of the air conditioner 100 when it is operating in cooling mode.

[0113] (4-1) An air conditioner 100, an example of a refrigeration cycle system, has a first refrigerant circuit 110 and a second refrigerant circuit 120. The first refrigerant circuit 110 includes a first compressor 10, a first heat exchanger 40 that functions as a refrigerant radiator, a first expansion valve 50, and a second heat exchanger 60 that functions as a refrigerant absorber. 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. The suction pressure of the first compressor 10 is lower than the suction pressure of the second compressor 20. The first compressor 10 is a scroll compressor, and the second compressor is a rotary compressor.

[0114] In the air conditioner 100, the second refrigerant circuit 120 is connected to the first refrigerant circuit 110 between the first compressor 10 and the first heat exchanger 40, so the discharge pressures of the first compressor 10 and the second compressor 20 are the same. Also, in the air conditioner 100, the suction pressure of the first compressor 10 is lower than the suction pressure of the second compressor. Therefore, in the air conditioner 100, the compression ratio of the first compressor 10 is higher than that of the second compressor 20.

[0115] By using a scroll compressor, which is efficient at high compression ratios, for the first compressor 10, and a rotary compressor, which is efficient at low compression ratios, for the second compressor 20, an efficient air conditioner 100 can be realized.

[0116] (4-2) In the air conditioner 100, the second refrigerant circuit 120 includes a second expansion valve 80 and an economizer heat exchanger 70 positioned between the first heat exchanger 40 and the second heat exchanger 60. The economizer heat exchanger 70 receives refrigerant flowing out from the first heat exchanger 40, branches off to the second refrigerant circuit 120 at the branching section 82, and exchanges heat between the refrigerant reduced in pressure by the second expansion valve 80 and the refrigerant flowing out from the first heat exchanger 40. The refrigerant that has been reduced in pressure by the second expansion valve 80 and passed through the economizer heat exchanger 70 is drawn into the second compressor 20.

[0117] In this air conditioner 100, the capacity and performance can be improved by compressing the refrigerant that has passed through the economizer heat exchanger 70 by the second compressor 20.

[0118] (4-3) In the air conditioner 100, the branching section 82 is located between the first heat exchanger 40 and the economizer heat exchanger 70.

[0119] In this air conditioner 100, a portion of the refrigerant flowing out from the first heat exchanger 40 is diverted to the second refrigerant circuit 120, which then passes through the second expansion valve 80 to the economizer heat exchanger 70, while the remainder flows through the economizer heat exchanger 70 to the first expansion valve 50. Therefore, compared to a case where the entire amount of refrigerant flowing out from the first heat exchanger 40 flows into the economizer heat exchanger 70 without being diverted, the air conditioner 100 can improve its capacity while keeping the size of the economizer heat exchanger 70 down.

[0120] (4-4) In the air conditioner 100, it is preferable that the rotational speed of the first compressor 10 is greater than the rotational speed of the second compressor 20 when the load is at least 47% or less.

[0121] In this air conditioner 100, under frequently used, relatively low-load conditions (under a load of 47%, which is one of the conditions for calculating SEER), the scroll compressor (first compressor 10), which is efficient in the high-speed range, operates at a higher rotational speed than the rotary compressor (second compressor 20), which is efficient in the low-speed range, thus enabling efficient operation.

[0122] In the air conditioner 100, it is even more preferable that the rotational speed of the first compressor 10 is greater than the rotational speed of the second compressor 20 when the load is at least 74% or less.

[0123] In this air conditioner 100, even under a wide range of load conditions (including the 74% load condition which is one of the conditions for calculating SEER), the scroll compressor (first compressor 10), which is efficient in the high-speed range, operates at a higher rotational speed than the rotary compressor (second compressor 20), which is efficient in the low-speed range, thus enabling even more efficient operation.

[0124] (4-5) In the air conditioner 100, the refrigerant supplied to the first refrigerant circuit 110 and the second refrigerant circuit 120 contains CO2 as at least a portion of its components.

[0125] In particular, in the air conditioner 100 of the above embodiment, the refrigerant filled into the first refrigerant circuit 110 and the second refrigerant circuit 120 is CO2.

[0126] Because air conditioner 100 uses CO2, which has a low global warming potential, as a refrigerant, it is possible to realize air conditioner 100 with a low environmental impact.

[0127] (4-6) In the air conditioner 100, the ratio of the displacement of the second compressor to the displacement of the first compressor 10 is determined such that, when the load is 47%, the rotational speed of the second compressor is greater than the minimum rotational speed at which continuous operation is possible.

[0128] In this air conditioner 100, by keeping the rotational speed of the second compressor 20 (rotary compressor) as low as possible during high load, highly efficient operation can be achieved even under high load conditions. In other words, the greater the ratio of the displacement amount of the second compressor 20 to the displacement amount of the first compressor 10, the more efficient the refrigeration cycle can be maintained under high load conditions.

[0129] However, simply suppressing the rotational speed of the second compressor 20 to the lowest possible level may result in the rotational speed of the second compressor 20 becoming too low under relatively low load conditions with frequent operation (such as the 47% load condition, which is one of the conditions for calculating SEER), making it impossible to continue continuous operation, and consequently, the SEER may decrease.

[0130] In contrast, in this air conditioner 100, the ratio of the displacement amount of the second compressor 20 to the displacement amount of the first compressor 10 is determined such that when the load is 47%, the rotational speed of the second compressor 20 is greater than the minimum rotational speed at which continuous operation is possible, thereby suppressing a decrease in SEER.

[0131] (4-7) In the air conditioner 100, the ratio of the displacement of the second compressor 20 to the displacement of the first compressor 10 is determined such that, when the load is 100%, the rotational speed of the second compressor 20 is less than the maximum rotational speed at which continuous operation is possible.

[0132] If the air conditioner 100 is designed such that, when the load is 100%, the rotational speed of the second compressor 20 exceeds the maximum rotational speed at which continuous operation is possible, then when the load actually reaches 100%, in order to continue operating the second compressor 20, the rotational speed of the second compressor 20 will be reduced to the maximum rotational speed, and the insufficient capacity will be compensated for by operating the first compressor 10 at a rotational speed higher than the ideal rotational speed. In this operating condition, the efficiency of the air conditioner 100 when the load is 100% will decrease.

[0133] In contrast, in this air conditioner 100, the ratio of the displacement amount of the second compressor 20 to the displacement amount of the first compressor 10 is determined such that when the load is 100%, the rotational speed of the second compressor 20 is less than the maximum rotational speed at which continuous operation is possible, thereby suppressing a decrease in SEER.

[0134] (4-8) The air conditioner 100 includes a bypass passage 92, a bypass valve 94 as an example of a valve, and a control device 8 as an example of a control unit. 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 92 connects the discharge port of the first compressor 10 in the first refrigerant circuit 110 to the first heat exchanger 40 to the suction side of the second compressor 20 of the second refrigerant circuit 120. The bypass valve 94 is located in the bypass passage 92. The control device 8 controls the operation of the bypass valve 94. The control device 8 opens the bypass valve 94 when the second compressor 20 is stopped.

[0135] In this air conditioner 100, when the second compressor 20 is stopped, the differential pressure between the discharge side and the suction side of the second compressor 20 is reduced. This differential pressure prevents the refrigerant oil inside the second compressor 20, which is a rotary compressor, from flowing out of the suction port of the second compressor 20.

[0136] (5) Variant 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.

[0137] (5-1) 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 70. However, the embodiment is not limited to this configuration.

[0138] 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 8A. 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, so the size of the economizer heat exchanger 70 tends to be larger compared to the above embodiment.

[0139] (5-2) Variation B 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.

[0140] As shown in Figure 8B, the second refrigerant circuit 120 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. Furthermore, instead of providing a second expansion valve 80 in the second refrigerant circuit 120, a second expansion valve 84 may be provided in the first refrigerant circuit 110. Although not shown in the figures, if the air conditioner 100 is performing heating operation, it is preferable to provide a valve (for example, a solenoid valve controlled by the control device 8 during heating operation) between the refrigerant container 72 of the second refrigerant circuit 120 and the second compressor 20 to prevent refrigerant from flowing through the second refrigerant circuit 120 during heating operation.

[0141] In the air conditioner 100 operating in cooling mode, the refrigerant container 72 is positioned 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 positioned between the first heat exchanger 40, which functions as a radiator, and the refrigerant container 72. Refrigerant that flows out of the first heat exchanger 40 and is depressurized by the second expansion valve 84 to become a two-phase gas flows into the refrigerant container 72. The gaseous refrigerant separated in the refrigerant container 72 is drawn into the second compressor 20. Note that in this air conditioner 100 as well, the second compressor 20 is not operated during heating mode.

[0142] 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.

[0143] Furthermore, as shown in Figure 8C, the second refrigerant circuit 120 may include, in addition to the refrigerant container 72, a heat exchanger 70b (economizer heat exchanger) positioned between the first refrigerant circuit 110 and the second refrigerant circuit 120. The heat exchanger 70b 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 70b is configured to exchange heat between the refrigerant flowing out of the first heat exchanger 40 toward the second expansion valve 84 and 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 70b is drawn into the second compressor 20. In this air conditioner 100 as well, the second compressor 20 is not operated during heating operation.

[0144] Although not shown in the diagram, if the air conditioner 100 is performing heating operation, it is preferable that a valve (for example, a solenoid valve controlled by the control device 8 during heating operation) is provided between the refrigerant container 72 of the second refrigerant circuit 120 and the heat exchanger 70b to obstruct the flow of refrigerant so that refrigerant does not flow through the second refrigerant circuit 120 during heating operation.

[0145] In this configuration, by further using the heat exchanger 70b, the capacity of the air conditioner 100 can be further improved during cooling operation compared to the configuration shown in Figure 8B.

[0146] (5-3) Modification C In the above embodiment, a scroll compressor is used for the first compressor 10 and a rotary compressor is used for the second compressor 20, thereby realizing an efficient air conditioner 100.

[0147] However, the configuration is not limited to the above embodiment. The first compressor 10 may be a scroll compressor with a first design compression ratio, and the second compressor 20 may be a scroll compressor with a second design compression ratio smaller than the first design compression ratio.

[0148] As described above, in the air conditioner 100, the compression ratio of the second compressor 20 is smaller than that of the first compressor 10. Therefore, even when the first compressor 10 is a scroll compressor with a large design compression ratio and the second compressor 20 is a scroll compressor with a small design compression ratio, both compressors 10 and 20 can be operated in an efficient range, resulting in an efficient refrigeration cycle system.

[0149] (5-4) Modification D In the above embodiment, the bypass 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.

[0150] However, as shown in Figure 9, the bypass passage 92 and bypass valve 94 of the pressure equalization mechanism 90 do not necessarily need to be provided. Even with the configuration shown in Figure 9, the control device 8 can open the second expansion valve 80 (for example, to an opening close to fully open) when the second compressor 20 is stopped, and maintain the second expansion valve 80 in an open state for a predetermined period of time, for example, according to the flowchart in Figure 4 (replacing the bypass valve 94 with the second expansion 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.

[0151] (5-5) Variation E In the above embodiment, the case in which the second compressor 20 is operated during cooling operation is described as an example, but the second compressor 20 may also be operated during heating operation. In other words, the second compressor 20 may be operated when the first heat exchanger 40 functions as a heat absorber and the second heat exchanger 60 functions as a heat radiator. With this configuration, it is possible to improve the capacity and performance of the air conditioner 100 even during heating operation.

[0152] <Second Embodiment> Configurations such as using a scroll compressor as the first compressor 10 and a rotary compressor as the second compressor 20, or using a scroll compressor with a first design compression ratio as the first compressor 10 and a scroll compressor with a second design compression ratio smaller than the first design compression ratio as the second compressor 20, are also useful when applied to a refrigeration cycle device (refrigeration / freezing device 200) with a configuration like that shown in Figure 10.

[0153] As shown in Figure 10, the refrigeration / freezing device 200 includes a first compressor 210, a second compressor 220, a first heat exchanger 240, a freezing expansion valve 250a, a refrigeration expansion valve 250b, a freezing heat exchanger 260a, and a refrigeration heat exchanger 260b.

[0154] The refrigeration / freezing device 200 has a first refrigerant circuit 200a which includes a first compressor 210, a first heat exchanger 240 as a heat sink, a refrigeration expansion valve 250a as a first expansion valve, and a refrigeration heat exchanger 260a as a heat absorber. The refrigeration / freezing device 200 also has a second refrigerant circuit 200b which connects the first compressor 210 and the first heat exchanger 240, and the first heat exchanger 240 and the refrigeration expansion valve 250a. The second refrigerant circuit 200b includes a second compressor 220. The second refrigerant circuit 200b further includes a refrigeration expansion valve 250b and a refrigeration heat exchanger 260b.

[0155] The first heat exchanger 240 functions as a refrigerant heat exchanger, where the refrigerant exchanges heat with a medium such as water or heat source air, which serves as a heat source.

[0156] The refrigeration heat exchanger 260a is used for cooling the inside of a freezer, and the refrigeration heat exchanger 260b is used for cooling the inside of a refrigerator. The refrigeration expansion valve 250a is used to adjust the pressure and flow rate of the refrigerant sent to the refrigeration heat exchanger 260a. The refrigeration expansion valve 250b is used to adjust the pressure and flow rate of the refrigerant sent to the refrigeration heat exchanger 260b.

[0157] Because the refrigeration heat exchanger 260a and the refrigerator heat exchanger 260b have different applications (required refrigerant temperatures), the evaporation pressure in the refrigeration heat exchanger 260a is lower than the evaporation pressure in the refrigerator heat exchanger 260b. Therefore, the suction pressure of the first compressor 210 is lower than the suction pressure of the second compressor 220. In other words, it is smaller than the compression ratio and the differential pressure between discharge pressure and suction pressure in the second compressor 220, and also smaller than the compression ratio and the differential pressure between discharge pressure and suction pressure in the first compressor 210. This is similar to the relationship between the compression ratio and the differential pressure between discharge pressure and suction pressure in the second compressor 20 and the compression ratio and the differential pressure between discharge pressure and suction pressure in the first compressor 10 in the first embodiment.

[0158] Therefore, in the refrigeration and freezing apparatus 200 of the second embodiment, configurations such as using a scroll compressor for the first compressor 210 and a rotary compressor for the second compressor 220, or using a scroll compressor with a first design compression ratio for the first compressor 210 and a scroll compressor with a second design compression ratio smaller than the first design compression ratio for the second compressor 220, are also useful.

[0159] Although not shown in the diagrams or explanations, if the second compressor 220 is a rotary compressor, the refrigeration / freezing device 200 may also be provided with the pressure equalization mechanism 90 described in the above embodiment for the second compressor 220, and when the second compressor 220 is stopped, the bypass valve may be opened for a predetermined period of time, or (instead of providing the pressure equalization mechanism 90) the refrigeration expansion valve 250b may be fully opened for a predetermined period of time.

[0160] <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]

[0161] 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 Heat Exchanger 70b heat exchanger 72 Refrigerant containers 80. Second expansion valve 82 Branching point 84. Second expansion valve 92 Bypass channel 94 Bypass valve (valve) 100 Air conditioners (refrigeration cycle devices) 110 1st refrigerant circuit 120 Second refrigerant circuit 200 Refrigeration and Freezing Equipment (Refrigeration Cycle Equipment) 210 First Compressor 220 Second Compressor 240 1st heat exchanger (radiator) 250a Refrigeration expansion valve (first expansion valve) 260a Refrigeration heat exchanger (heat absorber) [Prior art documents] [Patent Documents]

[0162] [Patent Document 1] Japanese Patent Publication No. 2005-49087

Claims

1. A first refrigerant circuit (110,200a) including a first compressor (10,210), a heat sink (40,240), a first expansion valve (50,250a), and a heat absorber (60,260a), The system includes a second refrigerant circuit (120, 200b) which includes a second compressor (20, 220) connecting the first compressor and the heat sink, and the heat sink and the first expansion valve, The suction pressure of the first compressor is lower than the suction pressure of the second compressor. The first compressor is a scroll compressor, and the second compressor is a rotary compressor. Or, The first compressor is a scroll compressor with a first design compression ratio, and the second compressor is a scroll compressor with a second design compression ratio smaller than the first design compression ratio. Refrigeration cycle device (100, 200).

2. The second refrigerant circuit (120) further includes a second expansion valve (80) and an economizer heat exchanger (70) positioned between the radiator (40) and the heat absorber (60), The economizer heat exchanger flows out from the heat sink and branches off to the second refrigerant circuit at the branching section (82), and exchanges heat between the refrigerant that has been depressurized by the second expansion valve and the refrigerant that has flowed out from the heat sink. The refrigerant, which has been depressurized by the second expansion valve and passed through the economizer heat exchanger, is drawn into the second compressor (20). The refrigeration cycle apparatus (100) according to claim 1.

3. The branch section is located between the heat sink and the economizer heat exchanger. The refrigeration cycle apparatus according to claim 2.

4. The first refrigerant circuit (110) further includes a second expansion valve (84), The second refrigerant circuit (120) is positioned between the heat sink (40) and the heat absorber (60), and further includes a gas-liquid separable refrigerant container (72) into which the refrigerant flowing out from the heat sink and reduced in pressure by the second expansion valve to become a two-phase state flows. The gaseous refrigerant separated in the refrigerant container is drawn into the second compressor (20). The refrigeration cycle apparatus (100) according to claim 1.

5. The second refrigerant circuit further includes a heat exchanger (70b), The heat exchanger is arranged such that the refrigerant flowing out of the heat radiator toward the second expansion valve and the gaseous refrigerant separated in the refrigerant container exchange heat. The refrigeration cycle apparatus according to claim 4.

6. The second compressor is a rotary compressor, At least when the load is 47% or less, the rotational speed of the first compressor (10) is greater than the rotational speed of the second compressor. The refrigeration cycle apparatus according to claim 2 or 4.

7. At least when the load is 74% or less, the rotational speed of the first compressor is greater than the rotational speed of the second compressor. The refrigeration cycle apparatus according to claim 6.

8. The refrigerant filled into the first refrigerant circuit (110, 200a) and the second refrigerant circuit (120, 200b) contains CO as at least a portion of its components. ２ including, A refrigeration cycle apparatus (100, 200) according to claim 1 or 2.

9. The second compressor is a rotary compressor, The refrigerant to be filled into the first refrigerant circuit (110) and the second refrigerant circuit is CO ２ That is, The refrigeration cycle apparatus according to claim 2.

10. The ratio of the displacement amount of the second compressor to the displacement amount of the first compressor (10) is determined such that, when the load is 47%, the rotational speed of the second compressor is greater than the minimum rotational speed at which continuous operation is possible. The refrigeration cycle apparatus according to claim 9.

11. The ratio of the displacement amount of the second compressor to the displacement amount of the first compressor (10) is determined such that, when the load is 100%, the rotational speed of the second compressor is less than the maximum rotational speed at which continuous operation is possible. The refrigeration cycle apparatus according to claim 9 or 10.

12. A bypass passage (92) connects the discharge side of the second compressor (20) of the second refrigerant circuit (120), or the space between the discharge port of the first compressor (10) in the first refrigerant circuit (110) and the heat sink (40), and the suction side of the second compressor of the second refrigerant circuit, A valve (94) is arranged in the bypass flow path, A control unit (8) that controls the operation of the valve, Furthermore, The control unit opens the valve when the second compressor stops. A refrigeration cycle device (100) according to claim 1 or 2.

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