Refrigeration cycle equipment

Abstract

To provide a refrigeration cycle system that can improve capacity and efficiency while suppressing an increase in the size of the device. [Solution] The air conditioner 100 has a first refrigerant circuit 10 including a first compressor 20, a radiator, a first expansion valve 28, and a heat absorber, a second refrigerant circuit 50, and a first injection passage 60. The second refrigerant circuit includes a second compressor 52 located between a first connection P1 and a second connection P2, and a second expansion valve 54 located between the second connection and the second compressor. The first connection is located between the first compressor and the radiator. The second connection is located between the radiator and the heat absorber. The first injection passage connects a third connection P3 to the injection port 20i of the first compressor. The third connection is located between the second connection and the intake port 52s of the second compressor.

Description

Technical Field

[0001] It relates to a refrigeration cycle device.

Background Art

[0002] In Patent Document 1 (European Patent No. 2203693), a part of the refrigerant flowing from the compressor through the radiator to the absorber in the main refrigerant circuit is made to flow into a sub-refrigerant circuit, and the refrigerant at an intermediate pressure is compressed by a compressor provided in the sub-refrigerant circuit and discharged to the radiator of the main refrigerant circuit. A refrigeration cycle device is described.

[0003] In this refrigeration cycle device, by using the sub-refrigerant circuit, it is possible to suppress the enlargement of the compressor in the main refrigerant circuit and improve the capacity and efficiency of the refrigeration cycle device.

Disclosure of the Invention

Problems to be Solved by the Invention

[0004] However, there is room for further improvement in capacity and efficiency in the refrigeration cycle device of Patent Document 1 (European Patent No. 2203693).

Means for Solving the Problems

[0005] [[ID=3,3]]The refrigeration cycle device of the first aspect includes a first refrigerant circuit, a second refrigerant circuit, and a first injection flow path. The first refrigerant circuit includes a first compressor, a radiator, a first expansion valve, and an absorber. The second refrigerant circuit includes a second compressor and a second expansion valve. The second compressor is disposed between a first connection portion and a second connection portion. The first connection portion is disposed between the first compressor and the radiator. The second connection portion is disposed between the radiator and the absorber. The second expansion valve is disposed between the second connection portion and the second compressor. The first injection flow path connects a third connection portion and an injection port of the first compressor. The third connection portion is disposed between the second connection portion and the suction port of the second compressor.

[0006] In the refrigeration cycle system described in the first perspective, by injecting a portion of the refrigerant flowing through the second refrigerant circuit into the first compressor, it is possible to improve the capacity and efficiency of the refrigeration cycle system while suppressing the need to increase the size of the first compressor.

[0007] The refrigeration cycle device according to the second aspect is the refrigeration cycle device according to the first aspect, wherein the third connection part is located between the second expansion valve and the intake port of the second compressor.

[0008] In the refrigeration cycle system from the second perspective, the refrigerant flowing through the intake passage of the second compressor is used for injection. By controlling the rotational speed of the second compressor, the pressure of the injected refrigerant can be precisely controlled to an appropriate value, making it easier to improve the efficiency of the refrigeration cycle system.

[0009] The refrigeration cycle device of the third aspect is a refrigeration cycle device of the first or second aspect, wherein the injection port of the first compressor is located above the third connection part.

[0010] In the third-party refrigeration cycle system, the occurrence of a malfunction in which liquid refrigerant accumulated in the first injection passage flows from the injection port to the first compressor can be suppressed.

[0011] The refrigeration cycle device of the fourth aspect is the refrigeration cycle device of the third aspect, wherein the first compressor is a scroll compressor and the second compressor is a rotary compressor having an accumulator. The third connection is located upstream of the accumulator of the second compressor.

[0012] The refrigeration cycle device of the fifth aspect is a refrigeration cycle device of any of the first to fourth aspects, further comprising a first valve installed in a first injection flow path.

[0013] In the fifth aspect of the refrigeration cycle system, closing the first valve when the refrigeration cycle system is stopped can suppress the accumulation of oil and refrigerant in the first injection passage.

[0014] The refrigeration cycle device according to the sixth aspect is the refrigeration cycle device according to the fifth aspect, further comprising a first sensor for detecting the temperature of the refrigerant discharged from the first compressor. The opening degree of the first valve is controlled based on the detection result of the first sensor.

[0015] In the refrigeration cycle system of the sixth aspect, an appropriate amount of refrigerant can be injected into the first compressor.

[0016] The refrigeration cycle device of the seventh aspect is the refrigeration cycle device of the sixth aspect, in which, when the temperature detected by the first sensor is lower than a first value, the opening degree of the first valve is controlled to be small.

[0017] In the refrigeration cycle system described in the seventh perspective, the occurrence of wet operation in the first compressor can be suppressed.

[0018] The refrigeration cycle device of the eighth aspect is a refrigeration cycle device of any of the first to seventh aspects, further comprising a first heat exchanger. The first heat exchanger is positioned between the second expansion valve and the inlet of the second compressor. In the first heat exchanger, heat exchange occurs between the refrigerant flowing from the second expansion valve to the inlet of the second compressor and the refrigerant flowing from the radiator to the heat absorber.

[0019] In the refrigeration cycle system of the eighth perspective, the refrigerant flowing to the heat absorber is cooled by the refrigerant flowing through the second refrigerant circuit, thereby increasing the refrigeration effect. This makes it possible to improve the capacity and efficiency of the refrigeration cycle system while suppressing the need to increase the size of the first compressor.

[0020] The refrigeration cycle apparatus of the ninth aspect is the refrigeration cycle apparatus of the eighth aspect, wherein the flow path length between the refrigerant outlet of the first heat exchanger toward the second compressor and the third connection is shorter than the flow path length between the third connection and the inlet of the second compressor.

[0021] In the refrigeration cycle system described in the ninth perspective, the performance of the refrigeration cycle system can be improved by reducing the pressure loss in the second refrigerant circuit.

[0022] The refrigeration cycle device of the tenth aspect is any one of the refrigeration cycle devices from the first aspect to the ninth aspect, and further includes a flash tank disposed at the second connection portion.

[0023] In the refrigeration cycle device of the tenth aspect, the refrigerant can be stored in the flash tank according to the load, so that it is easy to adjust the amount of refrigerant flowing through the first injection flow path, and the adjustment of surplus refrigerant is also possible.

[0024] The refrigeration cycle device of the eleventh aspect is the refrigeration cycle device of the tenth aspect, and further includes a third expansion valve disposed between the radiator and the flash tank.

[0025] In the refrigeration cycle device of the eleventh aspect, the liquid refrigerant and the gas refrigerant can be separated at an appropriate ratio in the flash tank by the third expansion valve.

[0026] The refrigeration cycle device of the twelfth aspect is the refrigeration cycle device of the tenth aspect or the eleventh aspect, and further includes a first valve disposed in the first injection flow path. The third connection portion is disposed between the flash tank and the second expansion valve.

[0027] In the refrigeration cycle device of the twelfth aspect, the suction pressure of the second compressor and the pressure of the refrigerant injected into the first compressor can be set to different values, and by adjusting each to an appropriate value, the performance can be optimized.

[0028] The refrigeration cycle device of the thirteenth aspect is any one of the refrigeration cycle devices from the tenth aspect to the twelfth aspect, and the flow path length between the flash tank and the third connection portion is shorter than the flow path length between the third connection portion and the suction port of the second compressor.

[0029] In the refrigeration cycle device of the thirteenth aspect, the pressure loss in the second refrigerant circuit can be reduced to improve the performance of the refrigeration cycle device.

[0030] The refrigeration cycle device of the 14th aspect is a refrigeration cycle device of any of the 10th to 13th aspects, further comprising a second sensor. The second sensor is located between the flash tank and the first expansion valve. The second sensor detects a physical quantity correlated with pressure.

[0031] The refrigeration cycle device of the 15th perspective is the refrigeration cycle device of the 14th perspective, in which the opening of the second expansion valve is controlled to be large when the pressure corresponding to the physical quantity detected by the second sensor is greater than the second value. The opening of the second expansion valve is controlled to be small when the pressure corresponding to the physical quantity detected by the second sensor is smaller than the third value which is less than or equal to the second value.

[0032] In the refrigeration cycle system described in the 15th perspective, it is possible to optimize the pressure inside the flash tank.

[0033] The refrigeration cycle device of the 16th aspect is a refrigeration cycle device of any of the 15th aspects of the 1st aspect, wherein the second expansion valve is closed before the second compressor is stopped.

[0034] In the refrigeration cycle system of the 16th aspect, the accumulation of refrigerant and oil between the second expansion valve and the second compressor, and in the first injection passage can be suppressed. Furthermore, in the refrigeration cycle system of the 16th aspect, the accumulation of liquid refrigerant between the second expansion valve and the intake port of the second compressor, and in the first injection passage can be suppressed, thereby preventing liquid refrigerant from being drawn into the second compressor when the second compressor is restarted, and preventing excessive refrigerant from being injected into the first compressor.

[0035] The refrigeration cycle device of the 17th aspect is a refrigeration cycle device of any of the 16th aspects of the first aspect, further comprising a third sensor. The third sensor detects a physical quantity correlated with the suction pressure of the second compressor. When the pressure corresponding to the physical quantity detected by the third sensor is greater than the fourth value, the opening degree of the second expansion valve is controlled to be smaller.

[0036] In the refrigeration cycle system described in the 17th perspective, it is possible to suppress wet operation of the second compressor and the injection of excess refrigerant into the first compressor.

[0037] The refrigeration cycle apparatus of the 18th aspect is a refrigeration cycle apparatus of any of the 17th aspects of the first aspect, further comprising a bypass passage and a second valve. The bypass passage connects the second expansion valve and the inlet of the second compressor to a fourth connection. The fourth connection is located between the heat absorber and the inlet of the first compressor. The second valve is located in the bypass passage. When the second compressor is operated while the first compressor is stopped, the second valve allows the flow of refrigerant.

[0038] In the refrigeration cycle system described in the 18th perspective, when the required capacity of the refrigeration cycle system decreases, it is possible to perform a refrigeration cycle using only the second compressor, thereby achieving efficient operation in accordance with the required capacity of the refrigeration cycle system.

[0039] The refrigeration cycle apparatus of the 19th aspect is a refrigeration cycle apparatus of any of the 18th aspects of the first aspect, further comprising a second injection passage, a fourth expansion valve, and a second heat exchanger. The second injection passage connects a fifth connector to the injection port of a second compressor. The fifth connector is located between the radiator and the second connector. The fourth expansion valve is located in the second injection passage. The second heat exchanger is located between the fourth expansion valve and the injection port of the second compressor. In the second heat exchanger, heat exchange occurs between the refrigerant flowing from the fourth expansion valve to the injection port of the second compressor and the refrigerant flowing from the fifth connector to the heat absorber.

[0040] The refrigeration cycle system described in the 19th perspective can achieve efficient operation. [Brief explanation of the drawing]

[0041] [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 3] Figure 1 shows a schematic pH diagram for the air conditioner during cooling operation. [Figure 4] Figure 1 is a schematic side view of the area around the first and second compressors of the air conditioner. [Figure 5A] This diagram shows the flow of refrigerant when the air conditioner shown in Figure 1 is operating in cooling mode in simultaneous operation mode. [Figure 5B] This diagram shows the refrigerant flow when the air conditioner shown in Figure 1 is operating in cooling mode with the first compressor running alone. [Figure 5C] This diagram shows the refrigerant flow when the air conditioner shown in Figure 1 is operating in cooling mode with the second compressor operating alone. [Figure 6A] This is a flowchart for controlling the switching between the simultaneous operation mode and the first compressor standalone operation mode. [Figure 6B] This is a flowchart for controlling the switching between the operating modes of the first compressor alone and the second compressor alone. [Figure 7] This is a flowchart for controlling the opening degree of the first valve in simultaneous operation mode. [Figure 8] This is a flowchart for controlling the opening degree of the second expansion valve in simultaneous operation mode. [Figure 9] This is a schematic diagram of the air conditioner according to modified example 1A. [Figure 10] This is a schematic diagram of the air conditioner according to modified example 1B. [Figure 11] This is a schematic diagram of the air conditioner according to the second embodiment of the refrigeration cycle device. [Figure 12] Figure 11 is a schematic pH diagram for an air conditioner during cooling operation. [Figure 13] This is a schematic diagram of the air conditioner according to modified example 2A. [Figure 14] Figure 13 is a schematic pH diagram for an air conditioner during cooling operation. [Figure 15] This is a schematic diagram of the air conditioner according to modified example 2B. [Modes for carrying out the invention]

[0042] Embodiments of the refrigeration cycle apparatus described herein will be explained with reference to the drawings.

[0043] <First Embodiment> An air conditioner 100 according to the first embodiment of the refrigeration cycle device will be described with reference to the drawings. Note that the refrigeration cycle device of this disclosure is not limited to an air conditioner, and may be other types of devices that use a vapor compression type refrigeration cycle to cool or heat a temperature-controlled object (such as air or a medium like water).

[0044] (1) Overview The overview of the air conditioner 100 will be explained with reference to Figure 1.

[0045] The air conditioner 100 is a device that performs a vapor compression type refrigeration cycle to cool or heat the air in the space to be air-conditioned, thereby providing heating and cooling to the space. The air conditioner 100 may also be a device for cooling only.

[0046] The refrigerant circuit of the air conditioner 100 includes a first refrigerant circuit 10, a second refrigerant circuit 50, a first injection channel 60, and a bypass channel 70 (see Figure 1). The refrigerant circuit of the air conditioner 100 is filled with a refrigerant that contains CO2 (carbon dioxide) as at least a portion of its components. In particular, in this embodiment, the refrigerant circuit of the air conditioner 100 is filled with a single refrigerant of CO2. CO2 is a highly safe refrigerant with a low global warming potential and is non-toxic and non-flammable. However, the type of refrigerant is not limited to a single refrigerant of CO2 or a refrigerant containing CO2, but may also be other types of refrigerants such as HFC refrigerants, HFO refrigerants, or natural refrigerants other than CO2.

[0047] The first refrigerant circuit 10 is the main refrigerant circuit and mainly includes a first compressor 20, a flow path switching mechanism 22, a heat source heat exchanger 24, a bridge circuit 26, an economizer heat exchanger 56, a first expansion valve 28, and a utilization heat exchanger 30. Here, the heat source heat exchanger 24 is a heat exchanger in which a medium as a heat source and the refrigerant exchange heat, and the utilization heat exchanger 30 is a heat exchanger in which the object to be temperature controlled and the refrigerant exchange heat.

[0048] The second refrigerant circuit 50 is a sub-refrigerant circuit. The second refrigerant circuit 50 connects the first connection part P1 and the second connection part P2. The first connection part P1 and the second connection part P2 are the connection points between the first refrigerant circuit 10 and the second refrigerant circuit 50. The first connection part P1 is located in the first refrigerant circuit 10 between the discharge port 20d of the first compressor 20 and the radiator (heat source heat exchanger 24 during cooling operation, heat utilization heat exchanger 30 during heating operation, and the same applies hereafter). Specifically, as shown in Figure 1, the first connection part P1 is located in the discharge pipe 11b of the first refrigerant circuit 10, which will be described later. The second connection part P2 is located in the first refrigerant circuit 10 between the radiator and the heat absorber (heat utilization heat exchanger 30 during cooling operation, heat source heat exchanger 24 during heating operation, and the same applies hereafter), as shown in Figure 1.

[0049] As shown in Figure 1, the second refrigerant circuit 50 mainly includes a second compressor 52, a second expansion valve 54, and an economizer heat exchanger 56. As shown in Figure 1, the economizer heat exchanger 56 is positioned to straddle the first refrigerant circuit 10 and the second refrigerant circuit 50. In the economizer heat exchanger 56, the refrigerant flowing from the radiator to the heat absorber in the first refrigerant circuit 10 and the refrigerant that branches off from the first refrigerant circuit 10 and flows through the second refrigerant circuit 50 to the second compressor 52 exchange heat.

[0050] The first injection passage 60 connects the third connection P3 to the injection port 20i of the first compressor 20. The third connection P3 is the connection point between the second refrigerant circuit 50 and the first injection passage 60. As shown in Figure 1, the third connection P3 is located in the second refrigerant circuit 50 between the second connection P2 and the suction port 52s of the second compressor 52. The first injection passage 60 is used to inject a portion of the refrigerant flowing through the second refrigerant circuit 50 into the refrigerant that is being compressed by the compression mechanism (not shown) of the first compressor 20.

[0051] The bypass passage 70 connects the fourth connection point P4 and the connection point Pa. The fourth connection point P4 is the connection point between the bypass passage 70 and the first refrigerant circuit 10. The connection point Pa is the connection point between the bypass passage 70 and the second refrigerant circuit 50 or the first injection passage 60. In the first refrigerant circuit 10, the fourth connection point P4 is located between the heat absorber and the suction port 20s of the first compressor 20. Specifically, as shown in Figure 1, the fourth connection point P4 is located in the suction pipe 11a of the first refrigerant circuit 10, which will be described later. The connection point Pa is located in the suction pipe 51a of the second refrigerant circuit 50, which will be described later. More specifically, as shown in Figure 1, the connection point Pa is located in the second refrigerant circuit 50, between the second expansion valve 54 and the suction port 52s of the second compressor 52. Although not shown in the illustration, the connection point Pa may also be located in the first injection passage 60, as shown in Figure 1. In other words, the connection point Pa is located on the suction side of the second compressor 52.

[0052] The second refrigerant circuit 50 and the first injection flow path 60 are used to improve the performance of the refrigeration cycle, as described below.

[0053] Assuming that the second refrigerant circuit 50 does not exist (and only the first refrigerant circuit 10 exists), if one attempts to increase the capacity of the air conditioner 100, one might consider enlarging the first compressor 20. However, enlarging the first compressor 20 leads to an increase in the weight of the air conditioner 100 and an increase in the amount of refrigerant charged in the refrigerant circuit of the air conditioner 100, thus increasing the cost of the air conditioner 100. In particular, when using CO2 as a refrigerant, due to the characteristics of CO2, the cooling effect is relatively small, so if one tries to obtain a larger capacity by enlarging the first compressor 20, the first compressor 20 tends to become larger.

[0054] In contrast, in the air conditioner 100 of this disclosure, a portion of the refrigerant flowing from the radiator to the heat absorber in the first refrigerant circuit 10 is diverted to the second refrigerant circuit 50, and the refrigerant flowing in the second refrigerant circuit 50 and the refrigerant flowing from the first refrigerant circuit 10 to the heat absorber are heat exchanged in the economizer heat exchanger 56. With this configuration, the refrigerant flowing from the first refrigerant circuit 10 to the heat absorber can be further cooled in the economizer heat exchanger 56, and the capacity and performance of the air conditioner 100 can be improved while suppressing the need to enlarge the first compressor 20 compared to the case where only the first refrigerant circuit 10 exists.

[0055] By providing the second refrigerant circuit 50 in this way, it is possible to enhance the refrigeration effect and improve the capacity and performance of the air conditioner 100 while suppressing the need to enlarge the first compressor 20. However, even in this case, if the required capacity of the air conditioner 100 is large, the size of the first compressor 20 will be relatively large, and the amount of refrigerant that needs to be charged into the refrigerant circuit of the air conditioner 100 will be relatively large.

[0056] Therefore, the air conditioner 100 is further provided with a first injection passage 60, which injects the intermediate-pressure refrigerant in the refrigeration cycle (the refrigerant flowing through the second refrigerant circuit 50) into the injection port 20i of the first compressor 20. With this configuration, the amount of high-pressure refrigerant discharged from the first compressor 20 can be increased compared to when the first injection passage 60 is not provided, thereby improving the capacity of the air conditioner 100. As a result, the air conditioner 100 of this disclosure can suppress the enlargement of the first compressor 20 compared to when the first injection passage 60 is not provided, and can achieve effects such as suppressing the increase in refrigerant charge amount, suppressing the increase in power consumption, and suppressing the increase in weight of the air conditioner 100. In addition, the air conditioner 100 of this disclosure, by suppressing the enlargement of the first compressor 20 with the first injection passage 60, allows for finer capacity control (compared to when a large first compressor 20 is used), and the temperature controllability of the air conditioner 100 can be improved. Furthermore, since the inverter control of the second compressor 52 allows the pressure of the refrigerant injected into the first compressor 20 to be adjusted to an appropriate pressure, the performance of the air conditioner 100 is more easily improved compared to the case where refrigerant at an intermediate pressure is injected into the first compressor 20 from a location other than the second refrigerant circuit 50.

[0057] Furthermore, since the heat exchanger used here serves as both an evaporator for supplying gaseous refrigerant to the second refrigerant circuit 50 and a heat exchanger for injection into the first compressor 20, the number of parts can be reduced.

[0058] The purpose of providing the bypass channel 70 will be explained later.

[0059] (2) Details The air conditioner 100 mainly comprises a first refrigerant circuit 10, a second refrigerant circuit 50, a first injection channel 60, a bypass channel 70, as well as a first fan 32, a second fan 34, and a control unit 8 (see Figures 1 and 2). The various components of the air conditioner 100 will be described in detail below.

[0060] (2-1) 1st refrigerant circuit The first refrigerant circuit 10 mainly includes a first compressor 20, a flow path switching mechanism 22, a heat source heat exchanger 24, a bridge circuit 26, an economizer heat exchanger 56, a first expansion valve 28, and a utilization heat exchanger 30, and these components are connected by piping. The bridge circuit 26 may be omitted.

[0061] The first compressor 20 is a variable-capacity compressor with an inverter-controlled motor. While not limiting the type of compressor, the first compressor 20 is preferably a scroll compressor (the reasons for the preference of a scroll compressor will be explained later).

[0062] The first compressor 20 has an inlet 20s, a discharge port 20d, and an injection port 20i. When the second compressor 52 is operating together with the first compressor 20, refrigerant at an intermediate pressure in the refrigeration cycle is supplied to the injection port 20i via the first injection passage 60.

[0063] The first compressor 20 compresses the refrigerant drawn in from the inlet 20s. When refrigerant at an intermediate pressure in the refrigeration cycle is supplied to the injection port 20i, the refrigerant at an intermediate pressure in the refrigeration cycle that flows in from the injection port 20i is supplied to the compression mechanism of the first compressor 20 during the compression process. At this time, the compression mechanism of the first compressor 20 compresses the refrigerant drawn in from the inlet 20s as well as the refrigerant supplied to the injection port 20i, and finally discharges it from the discharge port 20d as high-pressure refrigerant in the refrigeration cycle.

[0064] The flow path switching mechanism 22 switches the state of the refrigerant circuit of the air conditioner 100 between a first state (cooling operation state) and a second state (heating operation state). When the refrigerant circuit of the air conditioner 100 is in the first state (see the solid line of the flow path switching mechanism 22 in Figure 1), the heat source heat exchanger 24 functions as a refrigerant heat radiator, and the utilization heat exchanger 30 functions as a refrigerant heat absorber. When the first refrigerant circuit 10 is in the second state (see the dashed line of the flow path switching mechanism 22 in Figure 1), the heat source heat exchanger 24 functions as a refrigerant heat absorber, and the utilization heat exchanger 30 functions as a refrigerant heat radiator.

[0065] Furthermore, if the air conditioner 100 is a cooling-only device, the air conditioner 100 does not need to have a flow path switching mechanism 22. In this case, the bridge circuit 26 is also unnecessary.

[0066] In this embodiment, the flow path switching mechanism 22 is a four-way switching valve. The four ports of the four-way switching valve, which is the flow path switching mechanism 22, are connected to an intake pipe 11a, one end of which is connected to the intake port 20a of the first compressor 20; a discharge pipe 11b, one end of which is connected to the discharge port 20d of the first compressor 20; a first pipe 11c, one end of which is connected to the heat source heat exchanger 24; and a third pipe 11e, one end of which is connected to the utilization heat exchanger 30. When the state of the refrigerant circuit of the air conditioner 100 is set to a first state, the flow path switching mechanism 22 connects the discharge pipe 11b to the first pipe 11c and the intake pipe 11a to the third pipe 11e. When the state of the refrigerant circuit is set to a second state, the flow path switching mechanism 22 connects the discharge pipe 11b to the third pipe 11e and the intake pipe 11a to the first pipe 11c.

[0067] Here, regardless of the physical structure employed, the portion connecting the discharge port 20d of the first compressor 20 to the flow path switching mechanism 22 will be referred to as the discharge pipe 11b, and the portion connecting the suction port 20s of the first compressor 20 to the flow path switching mechanism 22 will be referred to as the suction pipe 11a. For example, physically, a structure can be envisioned in which a pipe extending from the discharge port 20d of the first compressor 20 is connected to a pipe 1 that connects the discharge port 52d of the second compressor 52 (described later) to the flow path switching mechanism 22. In this case, the portion of the piping that connects the discharge port 20d of the first compressor 20 to the flow path switching mechanism 22 is defined as the discharge pipe 11b (piping that constitutes the first refrigerant circuit 10), and the portion from the discharge port 52d of the second compressor 52 to the junction of the piping connecting the discharge port 52d of the second compressor 52 to the flow path switching mechanism 22 and the piping extending from the discharge port 20d of the first compressor 20 is referred to as the discharge pipe 51b, which will be described later.

[0068] Furthermore, the flow path switching mechanism 22 is not limited to a four-way switching valve, but may have multiple pipes and multiple valves to achieve the above-described pipe connection state.

[0069] In the heat source heat exchanger 24, heat exchange occurs between the heat source medium (in this case, outside air supplied by the first fan 32 as a heat source) and the refrigerant. When the refrigerant circuit of the air conditioner 100 is in the first state, the heat source heat exchanger 24 functions as a refrigerant radiator (or condenser if a refrigerant with condensation properties is used in the heat source heat exchanger 24), and the refrigerant is cooled by the heat source air in the heat source heat exchanger 24. When the refrigerant circuit of the air conditioner 100 is in the second state, the heat source heat exchanger 24 functions as a refrigerant absorber (evaporator), and the refrigerant is heated by the heat source air in the heat source heat exchanger 24. The heat source heat exchanger 24 is, for example, a fin-and-tube type heat exchanger having a large number of heat transfer tubes and fins.

[0070] The heat source medium used in the heat source heat exchanger 24 may be a liquid such as water. If the heat source medium is a liquid, a heat exchanger of an appropriate type should be selected for the heat source heat exchanger 24 accordingly.

[0071] The economizer heat exchanger 56 is an example of a first heat exchanger. The economizer heat exchanger 56 is, for example, a double-tube heat exchanger or a plate heat exchanger. As shown in Figure 1, the economizer heat exchanger 56 is located in the first refrigerant circuit 10 between the heat source heat exchanger 24 and the utilization heat exchanger 30 (the second pipe 11d connecting the heat source heat exchanger 24 and the utilization heat exchanger 30). The economizer heat exchanger 56 is provided so as to straddle the first refrigerant circuit 10 and the second refrigerant circuit 50, and is located in the second refrigerant circuit 50 between the second expansion valve 54 and the suction port 20s of the second compressor 52 (see Figure 1). The economizer heat exchanger 56 exchanges heat between the refrigerant that flows out from the radiator, branches off from the first refrigerant circuit 10 to the second refrigerant circuit 50 at the second connection point P2, and the refrigerant that flows out from the radiator, passes through the economizer heat exchanger 56, and flows toward the heat absorber.

[0072] With the economizer heat exchanger 56 in place, for example, if the refrigerant circuit of the air conditioner 100 is in the first state, the refrigerant cooled in the heat radiator (here, the heat source heat exchanger 24) that flows toward the heat absorber (here, the utilization heat exchanger 30) (see point d in Figure 3; point d in Figure 3 indicates the state of the refrigerant at point d in Figure 1; the same applies to other symbols in Figure 3) is further cooled by the economizer heat exchanger 56 (see point h in Figure 3). The ph diagram and explanation based on it when the refrigerant circuit of the air conditioner 100 is in the second state are omitted.

[0073] Furthermore, a bridge circuit 26 is provided, which combines four check valves that allow refrigerant flow only in the direction of the arrows shown in Figure 1. As a result, the second connection point P2 is positioned between the radiator and the first expansion valve 28 in the direction of refrigerant flow in the first refrigerant circuit 10, regardless of the state of the refrigerant circuit of the air conditioner 100 (whether in the first or second state). Regardless of the state of the refrigerant circuit of the air conditioner 100, the refrigerant flowing out from the radiator flows into the bridge circuit 26 and is sent to the second connection point P2. Then, after passing through the economizer heat exchanger 56 and the first expansion valve 28, it flows back into the bridge circuit 26 and is sent to the heat absorber.

[0074] The first expansion valve 28 is, for example, an electronically operated expansion valve with a variable opening, but other types of expansion mechanisms commonly used in refrigeration cycle systems may be used. The first expansion valve 28 is positioned between the heat source heat exchanger 24 and the utilization heat exchanger 30 and reduces the pressure of the refrigerant flowing between the heat source heat exchanger 24 and the utilization heat exchanger 30. With the provision of the bridge circuit 26, the first expansion valve 28 is positioned between the economizer heat exchanger 56 and the heat absorber in the direction of refrigerant flow in the first refrigerant circuit 10, regardless of the state of the refrigerant circuit of the air conditioner 100.

[0075] In the utilization heat exchanger 30, heat is exchanged between the refrigerant and the air in the space to be air-conditioned. The utilization heat exchanger 30 is housed in a casing (not shown) located in or near the space to be air-conditioned, and air from the space to be air-conditioned is supplied by a second fan 34 located inside the casing. Heat exchange takes place in the utilization heat exchanger 30 between the air from the space to be air-conditioned supplied by the second fan 34 and the refrigerant. When the refrigerant circuit of the air conditioner 100 is in the first state, the utilization heat exchanger 30 functions as a refrigerant heat absorber (evaporator), and the air in the space to be air-conditioned is cooled by the refrigerant. When the refrigerant circuit of the air conditioner 100 is in the second state, the utilization heat exchanger 30 functions as a refrigerant heat radiator (condenser), and the air in the space to be air-conditioned is heated by the refrigerant. The utilization heat exchanger 30 is, for example, a fin-and-tube type heat exchanger having a large number of heat transfer tubes and fins.

[0076] Furthermore, if the temperature of the refrigeration cycle system is controlled for a liquid such as water, an appropriate type of heat exchanger should be selected accordingly.

[0077] (2-2)Second refrigerant circuit The second refrigerant circuit 50 includes a second compressor 52 and a second expansion valve 54. The second refrigerant circuit 50 also includes an economizer heat exchanger 56.

[0078] The second compressor 52 is located in the piping connecting the first connection P1 and the second connection P2. In other words, the second compressor 52 is located between the first connection P1 and the second connection P2. Of the piping connecting the first connection P1 and the second connection P2, the piping connecting the second connection P2 and the suction port 52s of the second compressor 52 is called the suction pipe 51a, and the piping connecting the first connection P1 and the discharge port 52d of the second compressor 52 is called the discharge pipe 51b.

[0079] The second compressor 52 is a variable-capacity compressor with an inverter-controlled motor. While not limited to a specific type of compressor, the second compressor 52 is preferably a rotary compressor (the reasons for the preference of a rotary compressor will be explained later). The second compressor 52 has an inlet 52s and a discharge port 52d. The second compressor 52 compresses the refrigerant drawn in from the inlet 52s and ultimately discharges it from the discharge port 52d as high-pressure refrigerant in the refrigeration cycle.

[0080] The second expansion valve 54 is, for example, an electronically operated expansion valve with a variable opening, but other types of expansion mechanisms commonly used in refrigeration cycle systems may also be used. The second expansion valve 54 is positioned between the second connection P2 of the suction pipe 51a and the economizer heat exchanger 56 in the direction of refrigerant flow (see Figure 1). The second expansion valve 54 has the function of reducing the pressure of the refrigerant flowing toward the economizer heat exchanger 56 or adjusting the flow rate of the refrigerant flowing toward the economizer heat exchanger 56.

[0081] In the economizer heat exchanger 56, as described above, the refrigerant that flows out from the radiator, branches off to the second refrigerant circuit 50 at the second connection point P2, and is depressurized by the second expansion valve 54, exchanges heat with the refrigerant that flows out from the radiator, passes through the economizer heat exchanger 56, and flows toward the heat absorber. The refrigerant that has been depressurized by the second expansion valve 54 (for example, when the state of the refrigerant circuit of the air conditioner 100 is in the first state, see point e in the ph diagram in Figure 3), and has been cooled as it passes through the economizer heat exchanger 56 and flows toward the heat absorber, becomes a gas (for example, when the state of the refrigerant circuit of the air conditioner 100 is in the first state, see point f in the ph diagram in Figure 3), and is drawn into the second compressor 52.

[0082] Here, we will explain, using cooling operation as an example, why it is preferable to use a scroll compressor for the first compressor 20 and a rotary compressor for the second compressor 52.

[0083] In the air conditioner 100, as shown in Figure 3, the suction pressure of the first compressor 20 (see point a) is lower than the suction pressure of the second compressor 52 (see point f). On the other hand, since the second compressor 52 discharges refrigerant to the discharge pipe 11b of the first refrigerant circuit 10, as shown in Figure 3, the discharge pressure of the first compressor 20 (see point b) and the discharge pressure of the second compressor 52 (see point g) are the same. Therefore, the compression ratio of the first compressor 20 is greater than the compression ratio of the second compressor 52 (see Figure 3).

[0084] 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).

[0085] 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.

[0086] Therefore, in this air conditioner 100, a scroll compressor is used for the first compressor 20, which has a high compression ratio, and a rotary compressor is used for the second compressor 52, which has a low compression ratio. By adopting this configuration, this air conditioner 100 can achieve more efficient operation compared to cases where scroll compressors of the same specifications are used for both the first compressor 20 and the second compressor 52, or where rotary compressors are used for both the first compressor 20 and the second compressor 52.

[0087] (2-3) First injection channel The first injection channel 60 connects the third connection part P3 to the injection port 20i of the first compressor 20, and injects a portion of the refrigerant flowing through the second refrigerant circuit 50 into the first compressor 20.

[0088] The third connection part P3 is located in the second refrigerant circuit 50 between the second connection part P2 and the suction port 52s of the second compressor 52 (in other words, in the suction pipe 51a). In particular, in this embodiment, the third connection part P3 is located between the second expansion valve 54 and the suction port 52s of the second compressor 52.

[0089] Here, regardless of the physical structure adopted, the portion connecting the third connection part P3 and the suction port 52s of the second compressor 52 is referred to as the suction pipe 51a. For example, physically, a structure can be envisioned in which a pipe extending from the suction pipe 51a of the second compressor 52 is connected to a pipe connecting the third connection part P3 and the injection port 20i of the first compressor 20. Here, even in such a case, the portion of the piping connecting the third connection part P3 and the suction port 52s of the second compressor 52 is defined as the suction pipe 51a (piping constituting the second refrigerant circuit 50), and the portion from the injection port 20i of the first compressor 20 to the junction of the pipe connecting the third connection part P3 and the injection port 20i of the first compressor 20 and the pipe extending from the suction port 52s of the second compressor 52 is referred to as the first injection flow path 60.

[0090] Furthermore, it is preferable that the injection port 20i of the first compressor 20 be positioned above the third connection part P3, as shown in Figure 4. This configuration suppresses the occurrence of problems where condensed liquid refrigerant accumulates in the first injection passage 60 and flows into the first compressor 20 from the injection port 20i.

[0091] In this embodiment, the second compressor 52 is a rotary compressor, as described above. Because rotary compressors are generally structurally prone to liquid compression, the second compressor 52 has an accumulator 52a located in the suction pipe 51a, as shown in Figure 4. The third connection part P3 may be located upstream of the accumulator 52a of the second compressor 52 (closer to the second expansion valve 54 than the accumulator 52a).

[0092] Thus, when an accumulator 52a is provided in the suction pipe 51a and the third connection part P3 is located upstream of the accumulator 52a (above the accumulator 52a, as shown in Figure 4), the third connection part P3 may be located at a relatively high position. Therefore, if the first compressor 20 and the second compressor 52 are simply installed on the floor of the housing (not shown) that houses them, the third connection part P3 may be located above the injection port 20i of the first compressor 20. In such cases, in order to position the injection port 20i of the first compressor 20 higher than the third connection part P3, a base 21 may be provided on the floor of the housing, and the first compressor 20 may be installed on the base 21.

[0093] Furthermore, the first injection passage 60 may be provided with a sloping section 60a, as shown in Figure 3. The sloping section 60a becomes higher as it approaches the injection port 20i and lower as it approaches the third connection section P3. By providing such a sloping section 60a in the first injection passage 60, it is possible to suppress the problem of refrigerant rapidly flowing from the second refrigerant circuit 50 to the injection port 20i of the first compressor 20 when the first compressor 20 is started.

[0094] The third connection part P3 may be arranged such that the flow path length L1 between the refrigerant outlet 56o of the economizer heat exchanger 56 leading to the second compressor 52 and the third connection part P3 is shorter than the flow path length L2 between the third connection part P3 and the suction port 52s of the second compressor 52 (in FIG. 1, for convenience of drawing, the length of the part indicated by "L2" is shorter than the length of the part indicated by "L1", but actually, it is preferable that L1 < L2). Thus, in the suction pipe 51a, the flow path length L1 between the refrigerant outlet 56o of the economizer heat exchanger 56 through which a relatively large amount of refrigerant flows and the third connection part P3 is made shorter than the flow path length L2 between the third connection part P3 through which a relatively small amount of refrigerant flows (the refrigerant flowing between the refrigerant outlet 56o of the economizer heat exchanger 56 and the third connection part P3, from which the refrigerant branching to the first injection flow path 60 from the third connection part P3 decreases) and the suction port 52s of the second compressor 52, thereby suppressing the pressure loss in the suction pipe 51a and improving the performance of the air conditioner 100.

[0095] A first valve 62 for controlling the flow of the refrigerant injected into the first compressor 20 may be provided in the first injection flow path 60.

[0096] The first valve 62 is, for example, an electric valve whose opening degree can be adjusted. For example, when stopping the second compressor 52, by closing the first valve 62 before stopping the second compressor 52, it is possible to suppress the accumulation of oil and refrigerant in the first injection flow path 60. Also, by providing the first valve 62 in the first injection flow path 60 and controlling the opening degree of the first valve 62 as described later, it is possible to suppress the occurrence of wet operation in the first compressor 20. The control of the first valve 62 for suppressing the occurrence of wet operation in the first compressor 20 will be described later.

[0097] When the opening degree of the first valve 62 is not controlled, the first valve 62 may be a check valve that allows the flow of refrigerant from the third connection part P3 to the injection port 20i and prevents the flow of refrigerant from the injection port 20i to the third connection part P3.

[0098] (2 - 4) Bypass flow path The air conditioner 100 has three operating modes that can be used depending on the air conditioning load for both cooling and heating operations.

[0099] The three operating modes include simultaneous operation mode, first compressor standalone operation mode, and second compressor standalone operation mode. Simultaneous operation mode is an operating mode in which both the first compressor 20 and the second compressor 52 are operated, and is the operating mode used when the air conditioning load is highest among the three operating modes. Second compressor standalone operation mode is an operating mode in which only the second compressor 52 is operated while the first compressor 20 is stopped, and is the operating mode used when the air conditioning load is lowest among the three operating modes. First compressor standalone operation mode is an operating mode in which only the first compressor 20 is operated while the second compressor 52 is stopped, and is the operating mode used when the air conditioning load is moderate among the three operating modes.

[0100] The bypass channel 70 is used when the air conditioner 100 is operating in the second compressor-only operation mode, as described above. This will be explained in detail.

[0101] In the refrigerant circuit of the air conditioner 100 shown in Figure 1, let's assume that there is no bypass flow path 70. In this state, for example, let's set the refrigerant circuit of the air conditioner 100 to the first state (refrigerant operation state), and operate only the second compressor 52 while stopping the first compressor 20. In this case, in order to return the refrigerant discharged by the second compressor 52 to the intake port 52s of the second compressor 52, the refrigerant discharged from the second compressor 52 and passing through the heat source heat exchanger 24 must be allowed to flow into the second refrigerant circuit 50 from the second connection part P2. However, in this refrigerant flow state, no refrigerant flows to the utilization heat exchanger 30. In other words, if there is no bypass flow path 70, the air conditioner 100 cannot perform cooling operation by operating only the second compressor 52.

[0102] Therefore, the air conditioner 100 has a bypass flow path 70 as shown in Figure 1, and is configured to close the second expansion valve 54 when the second compressor is operating alone. As a result, in the air conditioner 100, for example, when the refrigerant circuit of the air conditioner 100 is set to the first state (refrigerant operation state), the first compressor 20 is stopped, and only the second compressor 52 is operated, the refrigerant discharged by the second compressor 52 is flowed in the order of the heat source heat exchanger 24, the first expansion valve 28, and the utilization heat exchanger 30 (establishing a refrigeration cycle) to perform cooling operation (see Figure 5C).

[0103] Furthermore, a check valve 72 is provided in the bypass passage 70 to prevent the refrigerant flowing through the second refrigerant circuit 50 from passing through the bypass passage 70 and flowing into the suction pipe 11a during simultaneous operation. The check valve 72 obstructs the flow of refrigerant from connection point Pa to the fourth connection point P4 in the bypass passage 70, while allowing the flow of refrigerant from the fourth connection point P4 to connection point Pa. Due to the presence of the check valve 72, refrigerant does not flow through the bypass passage 70 in simultaneous operation mode, but refrigerant flows through the bypass passage 70 in the second compressor standalone operation mode.

[0104] In addition, a solenoid valve or an electric valve may be provided in place of the check valve 72 in the bypass flow path 70. In this case, the control unit 8, which will be described later, should control the opening and closing of these valves so that in the simultaneous operation mode, the refrigerant flowing through the second refrigerant circuit 50 does not flow into the suction pipe 11a, and in the second compressor standalone operation mode, the refrigerant flows from the suction pipe 11a into the suction pipe 51a of the second refrigerant circuit 50.

[0105] (2-5) First fan and second fan The first fan 32 is housed within a casing (not shown) that houses the heat source heat exchanger 24. The first fan 32 supplies heat source air to the heat source heat exchanger 24 of the first refrigerant circuit 10, promoting heat exchange between the refrigerant flowing through the heat source heat exchanger 24 and the heat source air. The type of the first fan 32 is not limited, but it is, for example, a propeller fan.

[0106] The second fan 34 is housed within a casing (not shown) that houses the heat exchanger 30. The second fan 34 draws in air from the space to be air-conditioned and supplies it to the heat exchanger 30 of the first refrigerant circuit 10, promoting heat exchange between the refrigerant flowing through the heat exchanger 30 and the air to be temperature-controlled. The type of the second fan 34 is not limited, but it is, for example, a cross-flow fan.

[0107] (2-6) Control Unit The control unit 8 controls the operation of the air conditioner 100.

[0108] The control unit 8 is electrically connected to the first compressor 20, the second compressor 52, the flow path switching mechanism 22, the first expansion valve 28, the second expansion valve 54, the first valve 62, the first fan 32, and the second fan 34 (see Figure 2).

[0109] Furthermore, the control unit 8 is electrically connected to various sensors (temperature sensors, pressure sensors, etc.) provided at various locations in the air conditioner 100. For example, the control unit 8 is provided in the discharge pipe 11b, etc., and is electrically connected to a temperature sensor 12 that detects the temperature of the refrigerant discharged from the first compressor 20 (see Figures 1 and 2). The temperature sensor 12 is an example of the first sensor in the claims. The control unit 8 is also provided in the suction pipe 51a, etc., and is electrically connected to a pressure sensor 53 that detects the suction pressure of the second compressor 52 (see Figures 1 and 2). The air conditioner 100 may be provided with a temperature sensor 53' that detects a physical quantity corresponding to the suction pressure of the second compressor 52 (for example, a temperature sensor that measures the temperature of the refrigerant that flows into the economizer heat exchanger 56 after passing through the second expansion valve 54) instead of the pressure sensor 53 (see the temperature sensor 53' drawn with a dashed line in Figure 1), and the control unit 8 may be electrically connected to the temperature sensor 53' (see Figures 1 and 2). The pressure sensor 53 and temperature sensor 53' are examples of the third sensor in the claims. Other sensors are not shown or described.

[0110] In this embodiment, the control unit 8 includes a control calculation device and a memory device. A processor such as a CPU can be used for the control calculation device. The control calculation device reads a program stored in the memory device and controls the operation of the air conditioner 100 according to this program. The control unit 8 controls the operation of various electrically connected devices based on user instructions to the air conditioner 100 and sensor detection values, thereby causing the air conditioner 100 to perform cooling or heating operations. The control of various devices by the control unit 8 during cooling and heating operations will be described below.

[0111] (2-6-1) Control of various equipment during cooling and heating operations (A) Cooling operation (A-1) Simultaneous operation mode When the control unit 8 causes the air conditioner 100 to perform cooling operation in simultaneous operation mode, it controls the operation of the flow path switching mechanism 22 to set the refrigerant circuit to the first state and operates the first compressor 20 and the second compressor 52. When the control unit 8 causes the air conditioner 100 to perform cooling operation in simultaneous operation mode, it opens the first valve 62 and injects a portion of the refrigerant flowing through the second refrigerant circuit 50 into the first compressor 20. The control of the opening degree of the first valve 62 will be described later. The control unit 8 also controls the rotational speed of the first compressor 20 and the second compressor 52, and the opening degrees of the first expansion valve 28 and the second expansion valve 54, based on the measurement results of various sensors (sensors that measure the temperature and pressure of the refrigerant, temperature sensors that measure the temperature of the air-conditioned space, etc.) placed at various positions on the air conditioner 100. The control unit 8 also operates the motors of the first fan 32 and the second fan 34 at predetermined rotational speeds.

[0112] When performing cooling operation in simultaneous operation mode, the refrigerant flows through the refrigerant circuit of the air conditioner 100 as indicated by the arrows in Figure 5A (in Figure 5A, arrows indicating the direction of refrigerant flow in check valves where refrigerant does not flow are omitted). Note that in Figure 5A, for the sake of simplicity, the economizer heat exchanger 56 is depicted in such a way that the refrigerant flowing through the second refrigerant circuit 50 and the refrigerant flowing through the first refrigerant circuit 10 flow in the same direction. However, from the viewpoint of heat exchange efficiency, the refrigerant flowing through the second refrigerant circuit 50 and the refrigerant flowing through the first refrigerant circuit 10 may flow in opposite directions in the economizer heat exchanger 56 (the refrigerant flow in the economizer heat exchanger 56 may be counterflow).

[0113] (A-2) First compressor standalone operation mode When the control unit 8 causes the air conditioner 100 to perform cooling operation in the first compressor-only operation mode, it controls the operation of the flow path switching mechanism 22 to set the refrigerant circuit to the first state, closes the second expansion valve 54 and the first valve 62, stops the second compressor 52, and operates the first compressor 20. The control unit 8 also controls the rotation speed of the first compressor 20 and the opening degree of the first expansion valve 28 based on the measurement results of various sensors placed at various locations on the air conditioner 100. In addition, the control unit 8 operates the motors of the first fan 32 and the second fan 34 at predetermined rotation speeds.

[0114] Although it is explained here that the second expansion valve 54 and the first valve 62 are closed in the first compressor standalone operation mode, the control unit 8 may open the second expansion valve 54 and the first valve 62, control the opening degree of at least one of the second expansion valve 54 and the first valve 62, and inject the refrigerant that flows into the second refrigerant circuit 50 and is reduced to an intermediate pressure by at least one of the second expansion valve 54 and the first valve 62 into the injection port 20i of the first compressor 20 via the first injection passage 60.

[0115] When performing cooling operation in the first compressor standalone operation mode, the refrigerant flows through the refrigerant circuit of the air conditioner 100 as indicated by the arrows in Figure 5B (in Figure 5B, arrows indicating the direction of refrigerant flow in check valves where refrigerant does not flow are omitted).

[0116] (A-3) Second compressor standalone operation mode When the control unit 8 causes the air conditioner 100 to perform cooling operation in second compressor-only operation mode, it controls the operation of the flow path switching mechanism 22 to set the refrigerant circuit to the first state, closes the second expansion valve 54 and the first valve 62, stops the first compressor 20, and operates the second compressor 52. The control unit 8 also controls the rotation speed of the second compressor 52 and the opening degree of the first expansion valve 28 based on the measurement results of various sensors placed at various locations on the air conditioner 100. The control unit 8 also operates the motors of the first fan 32 and the second fan 34 at predetermined rotation speeds.

[0117] When performing cooling operation in the second compressor standalone operation mode, the refrigerant flows through the refrigerant circuit of the air conditioner 100 as indicated by the arrows in Figure 5C (in Figure 5C, arrows indicating the direction of refrigerant flow in check valves where refrigerant does not flow are omitted).

[0118] (B) Heating operation The control of the air conditioner 100 by the control unit 8 during heating operation is the same in simultaneous operation mode, first compressor standalone operation mode, and second compressor standalone operation mode, except that the operation of the flow path switching mechanism 22 is controlled to set the refrigerant circuit to the second state. Detailed explanations are omitted to avoid repetition.

[0119] (2-6-2) Switching operating modes Referring to Figures 6A and 6B, the switching of operating modes between the simultaneous operation mode and the first compressor standalone operation mode, and between the first compressor standalone operation mode and the second compressor standalone operation mode will be explained.

[0120] (A) Switching between simultaneous operation mode and first compressor standalone operation mode. As a premise for this explanation, it is assumed that the air conditioner 100 is operating in simultaneous operation mode (step S1).

[0121] In this state, the control unit 8 determines whether the capacity of the air conditioner 100 is excessive (step S2). For example, if the control unit 8 controls the rotational speed of the first compressor 20 in accordance with the air conditioning load and the rotational speed falls below a predetermined value, it determines that the capacity of the air conditioner 100 is excessive for the air conditioning load. Step S2 is repeated until the control unit 8 determines that the capacity of the air conditioner 100 is excessive. Once the control unit 8 determines that the capacity of the air conditioner 100 is excessive, the process proceeds to step S3.

[0122] In step S3, the control unit 8 closes the second expansion valve 54. Also, in step S4, the control unit 8 closes the first valve 62. Note that the order of steps S3 and S4 may be reversed, and steps S3 and S4 may be performed simultaneously.

[0123] Subsequently, in step S5, the control unit 8 stops the operation of the second compressor 52. As a result of stopping the operation of the second compressor 52, the operating mode of the air conditioner 100 changes from simultaneous operation mode to first compressor-only operation mode.

[0124] In this case, by executing steps S3 and S4 before step S5, it is possible to suppress the retention of excess refrigerant and oil in the suction pipe 51a and bypass passage 70, thereby preventing wet operation in the second compressor 52 or the supply of excess refrigerant to the first compressor 20 when the simultaneous operation mode is restarted. Furthermore, it is preferable that the second expansion valve 54 and the first valve 62 be closed before the second compressor 52 is stopped, not only when transitioning from the simultaneous operation mode to the first compressor-only operation mode, but also when stopping the air conditioner 100 (when both the first compressor 20 and the second compressor 52 are stopped).

[0125] The control unit 8 determines whether the capacity of the air conditioner 100 is insufficient when the first compressor is operating in standalone mode (step S6). For example, if the control unit 8 controls the rotational speed of the first compressor 20 in accordance with the air conditioning load and the rotational speed exceeds a predetermined value, it determines that the capacity of the air conditioner 100 is insufficient for the air conditioning load. Step S6 is repeated until the control unit 8 determines that the capacity of the air conditioner 100 is insufficient. If the control unit 8 determines that the capacity of the air conditioner 100 is insufficient, the process proceeds to step S7.

[0126] In step S7, the control unit 8 starts operating the second compressor 52.

[0127] Subsequently, the control unit 8 opens the second expansion valve 54 in step S8, and then opens the first valve 62 at an appropriate timing in step S9.

[0128] When the second compressor 52 is started and the second expansion valve 54 and the first valve 62 are opened, the operating mode of the air conditioner 100 changes from the first compressor-only operation mode to the simultaneous operation mode and returns to step S1.

[0129] (B) Switching between the operation mode of the first compressor alone and the operation mode of the second compressor alone. As a premise for this explanation, it is assumed that the air conditioner 100 is operating in the first compressor-only operation mode (step S11).

[0130] In this state, the control unit 8 determines whether the capacity of the air conditioner 100 is excessive (step S12). For example, if the control unit 8 controls the rotational speed of the first compressor 20 in accordance with the air conditioning load and the rotational speed falls below a predetermined value, it determines that the capacity of the air conditioner 100 is excessive for the air conditioning load. Step S12 is repeated until the control unit 8 determines that the capacity of the air conditioner 100 is excessive. If the control unit 8 determines that the capacity of the air conditioner 100 is excessive, the process proceeds to step S13.

[0131] In step S13, the control unit 8 stops the first compressor 20.

[0132] Next, in step S14, the control unit 8 starts the second compressor 52.

[0133] As a result of the processing in steps S13 and S14, the operating mode of the air conditioner 100 changes from the first compressor-only operation mode to the second compressor-only operation mode.

[0134] The control unit 8 determines whether the capacity of the air conditioner 100 is insufficient when the second compressor is operating in standalone mode (step S15). For example, if the control unit 8 controls the rotational speed of the second compressor 52 in accordance with the air conditioning load and the rotational speed exceeds a predetermined value, it determines that the capacity of the air conditioner 100 is insufficient for the air conditioning load. Step S15 is repeated until the control unit 8 determines that the capacity of the air conditioner 100 is insufficient. If the control unit 8 determines that the capacity of the air conditioner 100 is insufficient, the process proceeds to step S16.

[0135] In step S16, the control unit 8 stops the second compressor 52.

[0136] Next, in step S17, the control unit 8 starts the first compressor 20.

[0137] As a result of the processing in steps S16 and S17, the operating mode of the air conditioner 100 changes from the second compressor-only operation mode to the first compressor-only operation mode. Then, the process returns to step S11.

[0138] (2-6-3) Control of the opening degree of the first valve Referring to Figure 7, the control of the opening degree of the first valve 62 in the simultaneous operation mode will be explained.

[0139] When operating the air conditioner 100 in simultaneous operation mode, the control unit 8 controls the first valve 62 to a predetermined opening degree at the start of operation (step S21).

[0140] The control unit 8 monitors the measured value of the temperature sensor 12 (discharge temperature of the first compressor 20), and when operating the air conditioner 100 in simultaneous operation mode, the control unit 8 controls the opening degree of the first valve 62 based on the discharge temperature of the first compressor 20 detected by the temperature sensor 12.

[0141] Specifically, if the discharge temperature of the first compressor 20 falls below a first threshold (the first value in the claims) (if the determination in step S22 is Yes), the control unit 8 proceeds to step S23. Also, if the discharge temperature of the first compressor 20 rises above a second threshold (if the determination in step S22 is No and the determination in step S24 is Yes), the control unit 8 proceeds to step S25.

[0142] In step S23, the control unit 8 reduces the opening of the first valve 62. For example, by using the upper limit of the discharge temperature at which wet operation may occur in the first compressor 20 (the temperature at which wet operation may occur in the first compressor 20 if the discharge temperature falls below that value) as the first threshold, wet operation of the first compressor 20 caused by injection from the first injection passage 60 is suppressed. After step S23 is executed, the process returns to step S22.

[0143] In step S25, the control unit 8 increases the opening degree of the first valve 62. The second threshold value is greater than the first threshold value. The control in step S24 prevents the discharge temperature of the first compressor 20 from becoming excessively high, and allows an appropriate amount of refrigerant at an intermediate pressure to be injected into the first compressor 20. After step S25 is performed, the process returns to step S22.

[0144] Furthermore, if the discharge temperature of the first compressor 20 is above the first threshold, and the discharge temperature of the first compressor 20 is above the second threshold (if the determination in step S22 is No, and the determination in step S24 is No), the process returns to step S22.

[0145] (2-6-4) Control of the opening degree of the second expansion valve The opening degree control of the second expansion valve 54 will be explained with reference to Figure 8.

[0146] If the rotational speed of the second compressor 52 is greater than a predetermined value (for example, if the rotational speed of the second compressor 52 is at its maximum rotational speed, and the answer is Yes in step S31), the control unit 8 determines whether the suction pressure of the second compressor 52 measured by the pressure sensor 53, or the suction pressure obtained from the temperature measured by the temperature sensor 53' (a physical quantity correlated with the suction pressure of the second compressor 52), is greater than a predetermined value (target suction pressure) (step S32). If the control unit 8 determines Yes in step S32, the control unit 8 reduces the opening of the second expansion valve 54 by a predetermined amount (step S33).

[0147] If No is determined in step S32, or after the processing in step S33 is completed, the process returns to step S31.

[0148] If the suction pressure of the second compressor 52 is higher than the target suction pressure, it means that the amount of refrigerant supplied to the second compressor 52 is excessive. In this case, if Yes is determined in step S32, the opening of the second expansion valve 54 is controlled to be small, thereby reducing the amount of refrigerant flowing into the second refrigerant circuit 50, and suppressing the occurrence of wet operation of the second compressor 52 when the second compressor 52 is operating under high load conditions. Furthermore, by suppressing the amount of refrigerant flowing into the second refrigerant circuit 50, it is also possible to suppress the occurrence of a situation in which excessive refrigerant is supplied to the first compressor 20 via the first injection passage 60.

[0149] (3) Features (3-1) An air conditioner 100 according to one embodiment of a refrigeration cycle device includes a first refrigerant circuit 10, a second refrigerant circuit 50, and a first injection flow path 60. The first refrigerant circuit 10 includes a first compressor 20, a radiator (a heat source heat exchanger 24 during cooling operation, and a utilization heat exchanger 30 during heating operation), a first expansion valve 28, and a heat absorber (a utilization heat exchanger 30 during cooling operation, and a heat source heat exchanger 24 during heating operation). The second refrigerant circuit 50 includes a second compressor 52 and a second expansion valve 54. The second compressor 52 is located between a first connection part P1 and a second connection part P2. The first connection part P1 and the second connection part P2 are connection parts between the first refrigerant circuit 10 and the second refrigerant circuit 50. The first connection part P1 is located in the first refrigerant circuit 10 between the first compressor 20 and the radiator. The second connection part P2 is located in the first refrigerant circuit 10 between the heat sink and the heat absorber. The second expansion valve 54 is located in the second refrigerant circuit 50 between the second connection part P2 and the second compressor 52 (the inlet 52s of the second compressor 52). The first injection passage 60 connects the third connection part P3 to the injection port 20i of the first compressor 20. The third connection part P3, which is the connection part between the first injection passage 60 and the first refrigerant circuit 10, is located between the second connection part P2 and the inlet 52s of the second compressor 52.

[0150] In this air conditioner 100, by injecting a portion of the refrigerant flowing through the second refrigerant circuit 50 into the first compressor 20, it is possible to improve the capacity and efficiency of the air conditioner 100 while suppressing the need to increase the size of the first compressor 20.

[0151] In particular, in this embodiment, the third connection part P3 is positioned in the second refrigerant circuit 50 between the second expansion valve 54 and the suction port 52s of the second compressor 52. With this configuration, the pressure of the injected refrigerant can be accurately controlled to an appropriate value by controlling the rotational speed of the second compressor 52, making it easier to improve the efficiency of the air conditioner 100.

[0152] (3-2) In the air conditioner 100, the injection port 20i of the first compressor 20 may be positioned above the third connection part P3.

[0153] In this configuration, the occurrence of a malfunction in which liquid refrigerant accumulated in the first injection channel 60 (refrigerant that has entered the first injection channel 60 and condensed) flows into the first compressor 20 from the injection port 20i can be suppressed.

[0154] (3-3) The air conditioner 100 may have a first valve 62 installed in the first injection passage 60. By closing the first valve 62 when the air conditioner 100 or the second compressor 52 is stopped, the accumulation of oil and refrigerant in the first injection passage 60 can be suppressed.

[0155] Furthermore, the air conditioner 100 has a temperature sensor 12, which is an example of a first sensor for detecting the temperature of the refrigerant discharged from the first compressor 20, and the opening degree of the first valve 62 may be controlled based on the detection result of the temperature sensor 12. With this configuration, an appropriate amount of refrigerant can be injected into the first compressor 20.

[0156] For example, in the air conditioner 100, if the temperature detected by the temperature sensor 12 is lower than a first value (a predetermined value), the opening degree of the first valve 62 is controlled to be smaller. In this case, by appropriately setting the first value, the occurrence of wet operation in the first compressor 20 can be suppressed.

[0157] (3-4) In the air conditioner 100, the flow path length L1 between the refrigerant outlet 56o of the economizer heat exchanger 56 that leads to the second compressor 52 and the third connection part P3 may be shorter than the flow path length L2 between the third connection part P3 and the inlet 52s of the second compressor 52.

[0158] This configuration reduces the pressure loss in the suction pipe 51a of the second refrigerant circuit 50, thereby improving the performance of the air conditioner 100.

[0159] (3-5) In the air conditioner 100, the second expansion valve 54 may be closed before the second compressor 52 is stopped.

[0160] In the air conditioner 100, the accumulation of refrigerant and oil between the second expansion valve 54 and the second compressor 52, and in the first injection passage 60 can be suppressed. As a result, it is possible to suppress liquid refrigerant from being drawn into the second compressor 52 when the second compressor 52 is restarted, and to suppress the injection of excess refrigerant into the first compressor 20.

[0161] (3-6) The air conditioner 100 may have a pressure sensor 53 or a temperature sensor 53'. The pressure sensor 53 or temperature sensor 53' is an example of a third sensor in the claims that detects a physical quantity correlated with the suction pressure of the second compressor 52.

[0162] Furthermore, if the pressure corresponding to the physical quantity detected by the pressure sensor 53 or temperature sensor 53' is greater than a predetermined value (the fourth value in the claims, for example, the target evaporation pressure), the opening degree of the second expansion valve 54 may be controlled to be small.

[0163] Such control may be performed, for example, when the second compressor 52 is operating under high load (for example, when the rotational speed of the second compressor 52 is at its maximum value).

[0164] This configuration helps to prevent wet operation of the second compressor 52 and the injection of excess refrigerant into the first compressor 20.

[0165] (3-7) The air conditioner 100 may have a bypass passage 70 and a check valve 72, as an example of a second valve in the claims, which is located in the bypass passage 70. The bypass passage 70 connects a fourth connection P4 and a connection Pa. The fourth connection P4 is located between the heat absorber and the suction port 20s of the first compressor 20. For example, in this embodiment, the fourth connection P4 is located in the suction pipe 11a of the first refrigerant circuit 10. The connection Pa is located in the second refrigerant circuit 50 between the second expansion valve 54 and the suction port 52s of the second compressor 52. The check valve 72 allows the flow of refrigerant from the fourth connection P4 to the connection Pa when the second compressor 52 is operated while the first compressor 20 is stopped (in other words, in the second compressor-only operation mode). The check valve 72 does not allow the flow of refrigerant from the connection Pa to the fourth connection P4.

[0166] In the air conditioner 100, by providing a bypass flow path 70, when the required capacity of the air conditioner 100 decreases, a refrigeration cycle using only the second compressor 52 can be performed, enabling efficient operation according to the required capacity of the air conditioner 100.

[0167] Furthermore, the second valve in the claims, which is located in the bypass flow path 70, may not be a check valve 72, but rather a solenoid valve or an electric valve controlled by the control unit 8, which is opened when the operating mode of the air conditioner 100 is the second compressor-only operation mode (and closed in the simultaneous operation mode or the first compressor-only operation mode).

[0168] (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.

[0169] (4-1) Variation 1A In the above embodiment, the second connection part P2 is positioned between the radiator and the economizer heat exchanger 56 in the direction of refrigerant flow. However, as shown in Figure 9, the second connection part P2 may be positioned between the economizer heat exchanger 56 and the first expansion valve 28 (downstream of the economizer heat exchanger 56) in the direction of refrigerant flow.

[0170] (4-2) Modification 1B In addition to the configuration of the above embodiment, the air conditioner 100 may further have a configuration for injecting a portion of the refrigerant flowing through the second pipe 11d of the first refrigerant circuit 10 into the refrigerant that is being compressed by the compression mechanism (not shown) of the second compressor 52.

[0171] Specifically, the air conditioner 100 may further include a second injection passage 80, an expansion valve 82 as an example of a fourth expansion valve in the claims, and an economizer heat exchanger 84, as shown in Figure 10. The second injection passage 80 connects a fifth connection P5 to the injection port 52i of the second compressor 52. The fifth connection P5 is positioned between the radiator and the second connection P2 in the direction of refrigerant flow. The expansion valve 82 is positioned in the second injection passage 80. The economizer heat exchanger 84 is positioned between the expansion valve 82 and the injection port 52i of the second compressor 52. In the economizer heat exchanger 84, heat exchange occurs between the refrigerant flowing from the expansion valve 82 to the injection port 52i of the second compressor 52 and the refrigerant flowing from the fifth connection P5 to the heat absorber (to the second connection P2).

[0172] With this configuration, the air conditioner 100 can achieve even more efficient operation.

[0173] (4-3) Modification 1C In the above embodiment, the case described was that the air conditioner 100 is a device capable of both cooling and heating operations, and has an operating mode in which both the first compressor 20 and the second compressor 52 are operated during both cooling and heating operations. However, the invention is not limited to this. For example, if the air conditioner 100 is a device capable of both cooling and heating operations, and it is possible to meet the required capacity by operating only the first compressor 20 or the second compressor 52 during either the cooling or heating operation, then the air conditioner does not need to have an operating mode in which both the first compressor 20 and the second compressor 52 are operated during that operation.

[0174] (4-4) Modification 1D In the above embodiment, the air conditioner 100 has three operating modes, but is not limited thereto. For example, the air conditioner 100 does not have to have at least one of the first compressor-only operating mode and the second compressor-only operating mode as an operating mode.

[0175] If the air conditioner 100 does not have a second compressor-only operation mode as an operating mode, the bypass passage 70 does not need to be provided.

[0176] (4-5) Modification 1E In the above embodiment, the first compressor 20 is a scroll compressor and the second compressor 52 is a rotary compressor, but the type of compressor is not limited to the above type. For example, the first compressor 20 may be a scroll compressor with a first design compression ratio, and the second compressor 52 may be a scroll compressor with a second design compression ratio smaller than the first design compression ratio.

[0177] (4-6) Modification 1F In the above embodiment, the example is described using a case where there is one unit each of the first compressor 20, the second compressor 52, the heat source heat exchanger 24, and the utilization heat exchanger 30 included in the air conditioner 100, but it is not limited to this. The number of these devices can be selected as appropriate.

[0178] <Second Embodiment> An air conditioner 100 according to a second embodiment of the refrigeration cycle device of this disclosure will be described with reference to the drawings.

[0179] The air conditioner 100A of the second embodiment is similar in many respects to the air conditioner 100 of the first embodiment. In the description of the air conditioner 100A, the same reference numerals are used for components that are the same as those of the air conditioner 100, and explanations are omitted unless particularly necessary.

[0180] Air conditioner 100A differs from air conditioner 100 mainly in the following ways.

[0181] As shown in Figure 11, the second refrigerant circuit 50 of the air conditioner 100A has a gas-liquid separation flash tank 56a (flash tank economizer) that spans between the first refrigerant circuit 10 and the second refrigerant circuit 50, instead of an economizer heat exchanger 56. The flash tank 56a is located at the second connection point P2 between the radiator and the heat absorber. In particular, the flash tank 56a is located at the second connection point P2 between the radiator and the first expansion valve 28 in the direction of refrigerant flow. The second refrigerant circuit 50 extends from the second connection point P2, which is located at the outlet of the gaseous refrigerant of the flash tank 56a, to the first connection point P1.

[0182] Furthermore, a third expansion valve 36 may be positioned between the radiator and the flash tank 56a in the refrigerant flow direction in the first refrigerant circuit 10. The third expansion valve 36 is, for example, an electronically controlled expansion valve with a variable opening, and its opening is controlled by the control unit 8. By providing the third expansion valve 36, the liquid refrigerant and gaseous refrigerant can be separated in an appropriate ratio, and the required amount of gaseous refrigerant can be secured in the flash tank 56a.

[0183] Furthermore, as in this embodiment, when using CO2 refrigerant, the refrigerant flowing through the second pipe 11d is a supercritical refrigerant, and there is a possibility that the liquid refrigerant and gaseous refrigerant will not separate in the flash tank 56a. However, by providing the third expansion valve 36, the liquid refrigerant and gaseous refrigerant can be separated in the flash tank 56a.

[0184] For example, in the case of cooling operation in simultaneous operation mode, the refrigerant cooled by the radiator (heat source heat exchanger 24) is depressurized by the third expansion valve 36 (see point e in Figure 12; point e in Figure 12 indicates the state of the refrigerant at point e in Figure 11, and the same applies to other symbols in Figure 12), separated into gaseous refrigerant and liquid refrigerant, and then flows into the flash tank 56a. The gaseous refrigerant in the flash tank 56a flows into the second refrigerant circuit 50 (from the second connection part P2), passes through the second expansion valve 54, and flows to the inlet 52s of the second compressor 52. In addition, a portion of the refrigerant flowing through the second refrigerant circuit 50 flows into the first injection passage 60 from the third connection part P3 and is injected into the injection port 20i of the first compressor 20. The liquid refrigerant in the flash tank 56a is sent to the heat absorber via the first expansion valve 28.

[0185] Even when a flash tank 56a is used instead of the economizer heat exchanger 56, as in the air conditioner 100A, the refrigeration effect can be greatly increased. Furthermore, in the air conditioner 100A, the amount of high-pressure refrigerant discharged from the first compressor 20 can be increased by injecting the intermediate-pressure refrigerant in the refrigeration cycle of the first compressor 20 through the first injection passage 60, thereby improving the capacity of the air conditioner 100.

[0186] Also, in the air conditioner 100A, the third connection part P3 may be arranged such that the flow path length L1' between the outlet of the refrigerant (second connection part P2) heading to the second compressor 52 in the flash tank 56a and the third connection part P3 is shorter than the flow path length L2' between the third connection part P3 and the suction port 52s of the second compressor 52 (in FIG. 1, for convenience of drawing, the length of the part indicated by "L2'" is shorter than the length of the part indicated by "L1'", but actually, it is preferable that L1' < L2'). In this way, among the suction pipe 51a, the flow path length L1' between the outlet (second connection part P2) of the flash tank 56a through which a relatively large amount of refrigerant flows and the third connection part P3 is made shorter than the flow path length L2' between the third connection part P3 and the suction port 52s of the second compressor 52 through which a relatively small amount of refrigerant flows (the refrigerant branching from the refrigerant flowing between the outlet of the flash tank 56a and the third connection part P3 to the first injection flow path 60 from the third connection part P3 decreases). By doing so, the pressure loss in the suction pipe 51a can be suppressed, and the performance of the air conditioner 100 can be improved.

[0187] The first refrigerant circuit 10 may include a sensor 14 as an example of a second sensor that is arranged between the flash tank 56a and the first expansion valve 28 in the flow direction of the refrigerant and detects a physical quantity correlated with pressure. Here, the expression that the sensor 14 is arranged between the flash tank 56a and the first expansion valve 28 includes the case where the sensor 14 is arranged on the flash tank 56a. The sensor 14 may be a sensor that measures pressure or a sensor that measures temperature. The control unit 8 that receives the measurement result of the sensor 14 can also grasp the pressure from the temperature when the physical quantity measured by the sensor 14 is temperature.

[0188] And when the pressure corresponding to the physical quantity detected by the sensor 14 is greater than the second value (target value), the control unit 8 controls the opening degree of the second expansion valve 54 to be larger (increases the opening degree of the second expansion valve 54), and when the pressure corresponding to the physical quantity detected by the sensor 14 is smaller than the third value (≤ the second value), the control unit 8 controls the opening degree of the second expansion valve 54 to be smaller (decreases the opening degree of the second expansion valve 54). By being configured in this way, the optimization of the pressure in the flash tank 56a can be achieved.

[0189] (1) Features The air conditioner 100A also has the same features as (3-1) to (3-3), (3-5) to (3-7) described in (3) Features of the first embodiment.

[0190] Furthermore, the 100A air conditioner has the following features:

[0191] (1-1) The air conditioner 100A is equipped with a flush tank 56a located at the second connection point P2.

[0192] In the air conditioner 100A, refrigerant can be stored in the flash tank 56a according to the load, making it easy to adjust the amount of refrigerant flowing through the first injection passage 60.

[0193] (1-2) The air conditioner 100A is equipped with a third expansion valve 36 located between the radiator and the flash tank 56a.

[0194] The air conditioner 100A can separate liquid refrigerant and gaseous refrigerant in appropriate proportions in the flash tank 56a by the third expansion valve 36.

[0195] (1-3) In the air conditioner 100A, the flow path length L1' between the flash tank 56a and the third connection part P3 is shorter than the flow path length L2' between the third connection part P3 and the intake port 52s of the second compressor 52.

[0196] In the air conditioner 100A, the performance of the air conditioner 100A can be improved by reducing the pressure loss in the second refrigerant circuit 50.

[0197] (1-4) The air conditioner 100A includes a sensor 14 as an example of a second sensor in the claims. The sensor 14 is located between the flush tank 56a and the first expansion valve 28. The sensor 14 detects a physical quantity correlated with pressure.

[0198] Furthermore, if the pressure corresponding to the physical quantity detected by sensor 14 is greater than the second value, the opening degree of the second expansion valve 54 is controlled to be larger. If the pressure corresponding to the physical quantity detected by sensor 14 is smaller than the third value (which is less than or equal to the second value), the opening degree of the second expansion valve 54 is controlled to be smaller.

[0199] This configuration allows for the optimization of the pressure inside the flash tank 56a.

[0200] (2) Variant A modified version of the air conditioner 100A of the above embodiment will now be described. Note that the following modifications can be combined as appropriate.

[0201] First, the air conditioner 100A may further have a configuration for injecting a portion of the refrigerant flowing through the second pipe 11d of the first refrigerant circuit 10 into the refrigerant that is being compressed by the compression mechanism (not shown) of the second compressor 52, similar to the modification 1B of the first embodiment.

[0202] Furthermore, if the air conditioner 100A is a device capable of both cooling and heating operations, it is not necessary to have an operating mode in which both the first compressor 20 and the second compressor 52 are operated for either the cooling or heating operation, as shown in Modification 1C of the first embodiment.

[0203] Furthermore, the modified examples 1D and 1E of the first embodiment may also be applied to the air conditioner 100A.

[0204] In addition, the air conditioner 100A may be configured as follows:

[0205] (2-1) Modification example 2A In the above embodiment of the air conditioner 100A, the third connection part P3 is located downstream of the second expansion valve 54, and as shown in Figure 12, the case in which the pressure of the refrigerant injected into the injection port 20i of the first compressor 20 and the pressure of the refrigerant supplied to the second compressor 52 are substantially the same is described.

[0206] However, the configuration is not limited to this, and the third connection P3 may be positioned between the second connection P2 and the second expansion valve 54, as shown in Figure 13. In other words, the gaseous refrigerant from the flash tank 56a may flow into the first injection passage 60 from the third connection P3 without passing through the second expansion valve 54.

[0207] Furthermore, an electronic expansion valve is used for the first valve 62, and the control unit 8 adjusts the opening degree of the first valve 62 as appropriate, so that a refrigerant at a pressure different from the refrigerant pressure supplied to the second compressor 52 (see point f' in Figure 14; point f in Figure 14 indicates the state of the refrigerant at point f in Figure 13, and the same applies to other symbols in Figure 14) is injected into the injection port 20i of the first compressor 20.

[0208] In this configuration, the suction pressure of the second compressor 52 and the pressure of the refrigerant injected into the first compressor 20 can be set to different values, and by adjusting each to an appropriate value, the operation can be optimized.

[0209] (2-2) Modification 2B As shown in Figure 15, the air conditioner 100A may also be provided with an economizer heat exchanger 56 between the radiator and the third expansion valve 36 in the refrigerant flow direction in the first refrigerant circuit 10, and between the second expansion valve 54 and the suction port 52s of the second compressor 52 in the refrigerant flow direction in the second refrigerant circuit 50. The refrigerant flowing from the radiator to the flash tank 56a may be heat-exchanged with the refrigerant flowing from the second connection point P2 (the outlet of the gaseous refrigerant in the flash tank 56a) toward the third connection point P3, thereby further cooling the refrigerant flowing from the radiator to the flash tank 56a (and further toward the heat absorber).

[0210] <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]

[0211] 10 1st refrigerant circuit 12. Temperature sensor (first sensor) 14. Sensor (Second Sensor) 20. First Compressor 20i Injection Port 24 Heat source heat exchanger (radiator, heat absorber) 28. First expansion valve 30 Heat exchanger used (heat absorber, heat radiator) 36. Third expansion valve 50 Second refrigerant circuit 52 Second Compressor 52a Accumulator 52i Injection Port 52s inlet 53 Pressure sensor (third sensor) 53' Temperature sensor (third sensor) 54. Second expansion valve 56 Economizer heat exchanger (1st heat exchanger) 56a Flush Tank 56o exit 60 First injection channel 62 First valve 70 Bypass channel 72 Second valve 80 Second injection channel 82. Fourth expansion valve 84 Economizer heat exchanger (second heat exchanger) 100 Air conditioners (refrigeration cycle devices) 100A Air Conditioner (Refrigeration Cycle System) L1 flow path length L1' Flow channel length L2 flow path length L2' flow path length P1 First connection section P2 Second connection section P3 Third Connection Section P4 Fourth Connection Section P5 Fifth Connection Section [Prior art documents] [Patent Documents]

[0212] [Patent Document 1] European Patent No. 2203693

Claims

1. A first refrigerant circuit (10) includes a first compressor (20), radiators (24, 30), a first expansion valve (28), and heat absorbers (30, 24), A second refrigerant circuit (50) includes a first connection (P1) between the first compressor and the heat sink, a second connection (P2) between the heat sink and the heat absorber, a second compressor (52) disposed between the heat sink and the heat absorber, and a second expansion valve (54) disposed between the second connection and the second compressor. A first injection passage (60) connects the third connection (P3) between the second connection and the suction port (52s) of the second compressor, and the injection port (20i) of the first compressor, A refrigeration cycle device (100, 100A) equipped with the following.

2. The third connection portion is positioned between the second expansion valve and the intake port of the second compressor. The refrigeration cycle apparatus according to claim 1.

3. The injection port of the first compressor is positioned above the third connection portion. The refrigeration cycle apparatus according to claim 1.

4. The first compressor is a scroll compressor, and the second compressor is a rotary compressor having an accumulator (52a). The third connection is located upstream of the accumulator of the second compressor. The refrigeration cycle apparatus according to claim 3.

5. The system further comprises a first valve (62) installed in the first injection channel, The refrigeration cycle apparatus according to claim 1.

6. The system further includes a first sensor (12) for detecting the temperature of the refrigerant discharged from the first compressor, The opening degree of the first valve is controlled based on the detection result of the first sensor. The refrigeration cycle apparatus according to claim 5.

7. If the temperature detected by the first sensor is lower than a first value, the opening degree of the first valve is controlled to be small. The refrigeration cycle apparatus according to claim 6.

8. The system further includes a first heat exchanger (56) positioned between the second expansion valve and the intake port of the second compressor, in which the refrigerant flowing from the second expansion valve to the intake port of the second compressor and the refrigerant flowing from the radiator to the heat absorber exchange heat. The refrigeration cycle apparatus according to claim 1.

9. The flow path length (L1) between the refrigerant outlet (56o) of the first heat exchanger toward the second compressor and the third connection is shorter than the flow path length (L2) between the third connection and the inlet of the second compressor. The refrigeration cycle apparatus according to claim 8.

10. The system further comprises a flash tank (56a) located at the second connection point. The refrigeration cycle apparatus according to claim 1.

11. The system further includes a third expansion valve (36) positioned between the heat sink and the flash tank. The refrigeration cycle apparatus according to claim 10.

12. The first injection channel is further provided with a first valve (62) located in the first injection channel, The third connection is positioned between the flash tank and the second expansion valve. The refrigeration cycle apparatus according to claim 11.

13. The flow path length (L1') between the flash tank and the third connection is shorter than the flow path length (L2') between the third connection and the intake port of the second compressor. The refrigeration cycle apparatus according to claim 10.

14. The system further includes a second sensor (14) positioned between the flash tank and the first expansion valve, which detects a physical quantity correlated with pressure. The refrigeration cycle apparatus according to claim 10.

15. When the pressure corresponding to the physical quantity detected by the second sensor is greater than the second value, the opening degree of the second expansion valve is controlled to be larger. When the pressure corresponding to the physical quantity detected by the second sensor is smaller than a third value less than or equal to the second value, the opening degree of the second expansion valve is controlled to be small. The refrigeration cycle apparatus according to claim 14.

16. Before the second compressor stops, the second expansion valve is closed. The refrigeration cycle apparatus according to claim 2.

17. The system further includes a third sensor (53, 53') that detects a physical quantity correlated with the suction pressure of the second compressor, When the pressure corresponding to the physical quantity detected by the third sensor is greater than the fourth value, the opening degree of the second expansion valve is controlled to be smaller. The refrigeration cycle apparatus according to claim 1.

18. A bypass passage (70) connects the second expansion valve and the inlet of the second compressor, and the fourth connection point (P4) between the heat absorber and the inlet of the first compressor, A second valve (72) is arranged in the bypass passage, Furthermore, When the operation of the first compressor is stopped and the second compressor is operated, the second valve allows the flow of refrigerant. The refrigeration cycle apparatus according to claim 1.

19. A second injection channel (80) connects a fifth connection (P5) positioned between the heat sink and the second connection, and the injection port of the second compressor. A fourth expansion valve (82) is arranged in the second injection passage, A second heat exchanger (84) is positioned between the fourth expansion valve and the injection port (52i) of the second compressor, and the refrigerant flowing from the fourth expansion valve to the injection port of the second compressor and the refrigerant flowing from the fifth connection to the heat absorber exchange heat. It also has, The refrigeration cycle apparatus according to claim 1.

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