Refrigeration cycle equipment

Abstract

To downsize a refrigeration cycle device.SOLUTION: A refrigeration cycle device comprises a control unit (C) for controlling a refrigerant circuit (R) so that the pressure of a refrigerant compressed by a compression element (30) becomes equal to or higher than a critical pressure, and the pressure of the refrigerant decompressed by a first decompression valve (23) becomes lower than the critical pressure. The refrigerant circuit (R) includes: an inflow pipe (61) for sending the refrigerant decompressed by the first decompression valve (23), into a gas-liquid separator (50); a liquid outflow pipe (62) for sending a liquid refrigerant separated in the gas-liquid separator (50), to the side of second decompression valves (24 and 83); and an oil return flow passage (OP) for returning oil separated in the gas-liquid separator (50), to the compression element (30).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This disclosure relates to a refrigeration cycle device.

Background Art

[0002] The refrigeration cycle device described in Patent Document 1 includes a refrigerant circuit filled with carbon dioxide as a refrigerant. The refrigeration cycle device performs a refrigeration cycle in which the refrigerant is compressed by a compressor to a pressure equal to or higher than the critical pressure. In such a refrigeration cycle device, oil for lubricating the sliding part of the compressor is discharged from the compressor together with the refrigerant. Therefore, an oil separator for separating the oil in the refrigerant is provided on the discharge side of the compressor in the refrigerant circuit. The oil separated by the oil separator returns to the suction side of the compressor through an oil return pipe.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in a refrigeration device provided with an oil separator in a refrigerant circuit, miniaturization has been demanded.

[0005] An object of this disclosure is to miniaturize a refrigeration cycle device.

Means for Solving the Problems

[0006] The first embodiment relates to a refrigeration cycle device. The refrigeration cycle device comprises a refrigerant circuit (R) having a compression element (30), radiators (22, 83), a first pressure reducing valve (23), a gas-liquid separator (50), a second pressure reducing valve (24, 83), and evaporators (83, 22), and a control unit (C) that controls the refrigerant circuit (R) such that the pressure of the refrigerant compressed by the compression element (30) is equal to or greater than the critical pressure, and the pressure of the refrigerant reduced by the first pressure reducing valve (23) is less than the critical pressure. The refrigerant circuit (R) includes an inlet pipe (61) that sends the refrigerant depressurized by the first pressure reducing valve (23) into the gas-liquid separator (50), a liquid outlet pipe (62) that sends the liquid refrigerant separated in the gas-liquid separator (50) to the second pressure reducing valve (24, 83), and an oil return passage (OP) that returns the oil separated in the gas-liquid separator (50) to the compression element (30).

[0007] In the first embodiment, the first pressure reducing valve (23) reduces the pressure of the refrigerant to a pressure lower than the critical pressure. The reduced pressure of the refrigerant flows into the gas-liquid separator (50) through the inlet pipe (61). The gas-liquid separator (50) separates the refrigerant into gaseous refrigerant and liquid refrigerant. The gas-liquid separator (50) further separates oil from the refrigerant. Oil is more easily separated from subcritical refrigerant compared to critical refrigerant. The oil separated in the gas-liquid separator (50) returns to the compression element (30) through the oil return channel (OP).

[0008] The gas-liquid separator (50) also functions as an oil separator, which allows for a smaller refrigeration system.

[0009] In a second embodiment, the refrigerant circuit (R) has a gas introduction pipe (63) that sends the gaseous refrigerant separated in the gas-liquid separator (50) to the compression element (30).

[0010] In the second embodiment, the gaseous refrigerant separated in the gas-liquid separator (50) can be returned to the compression element (30) through the gas introduction pipe (63).

[0011] In the third embodiment, in the second embodiment, the oil return channel (OP) has oil inlets (O4, O5) into which oil from the gas-liquid separator (50) flows. The liquid outlet pipe (62) has a liquid inlet (O2) into which liquid refrigerant from the gas-liquid separator (50) flows. The oil inlets (O4, O5) are located lower than the liquid inlet (O2).

[0012] In the third embodiment, the oil inlets (O4, O5) are located lower than the liquid inlet (O2). In this configuration, oil, liquid refrigerant, and gaseous refrigerant tend to accumulate in the gas-liquid separator (50) in that order from the bottom to the top. Under normal operation, the density of oil is greater than the density of liquid refrigerant, and the density of liquid refrigerant is greater than the density of gaseous refrigerant. This prevents the oil in the gas-liquid separator (50) from flowing out into the liquid inlet (O2). As a result, it becomes easier to return the oil in the gas-liquid separator (50) to the compression element (30).

[0013] A fourth aspect is that, in the third aspect, the oil return passage (OP) has a first oil return pipe (64) and a second oil return pipe (65). The first oil return pipe (64) has a first oil inlet (O4) as an oil inlet. The second oil return pipe (65) has a second oil inlet (O5) as an oil inlet. The second oil inlet (O5) is located higher than the first oil inlet (O4).

[0014] In the fourth embodiment, when the oil level in the gas-liquid separator (50) rises, the oil at a relatively high position can be sent to the second oil return pipe (65) through the second oil inlet (O5). As a result, the oil in the gas-liquid separator (50) can be returned not only to the compression element (30) through the first oil return pipe (64), but also to the compression element (30) through the second oil return pipe (65).

[0015] The fifth aspect is the fourth aspect, wherein the second oil return pipe (65) is a gas inlet pipe (63). A gas inlet (O3) is formed at the end of the gas inlet pipe (63). The second oil inlet (O5) is located downstream of the gas inlet (O3) in the second oil return pipe (65) and connects the inside of the gas inlet pipe (63) to the inside of the gas-liquid separator (50).

[0016] In the fifth embodiment, the gaseous refrigerant separated in the gas-liquid separator (50) flows into the gas inlet (O3) of the second oil return pipe (65), which is a gas inlet pipe (63). This gaseous refrigerant is sent to the compression element (30) through the second oil return pipe (65). In addition, the oil separated in the gas-liquid separator (50) flows into the second oil inlet (O5). This oil returns to the compression element (30) through the second oil return pipe (65). In this way, the gas inlet pipe (63) also serves as an oil return passage.

[0017] The sixth embodiment is one of the first to fifth embodiments, wherein the refrigerant circuit (R) has an accumulator (26) positioned between the evaporator (83, 22) and the compression element (30). The oil return passage (OP) is located between the evaporator (83, 22) and the accumulator (26) in the refrigerant circuit (R), or is connected to the accumulator (26).

[0018] In the sixth embodiment, if the liquid refrigerant in the gas-liquid separator (50) flows into the oil return channel (OP), this liquid refrigerant can be stored in the accumulator (26). As a result, it is possible to suppress the intake of liquid refrigerant into the compression element (30), thereby avoiding so-called liquid compression.

[0019] The seventh embodiment is one of the first to sixth embodiments, wherein the compression element (30) includes a low-stage compression section (31) for compressing the refrigerant and a high-stage compression section (32) for compressing the refrigerant compressed in the low-stage compression section (31). The oil return passage (OP) includes a low-stage oil return pipe (66) for returning the oil separated in the gas-liquid separator (50) to the low-stage compression section (31) and a high-stage oil return pipe (67) for returning the oil separated in the gas-liquid separator (50) to the high-stage compression section (32).

[0020] In the seventh embodiment, the oil separated by the gas-liquid separator (50) can be returned to both the lower-stage compression section (31) and the higher-stage compression section (32).

[0021] The eighth aspect is that, in any one of the first to seventh aspects, the refrigerant is carbon dioxide, and the oil is polyalkylene glycol.

[0022] In the gas-liquid separator (50) of the eighth aspect, by setting carbon dioxide as the refrigerant to a subcritical state, polyalkylene glycol is particularly easily separated from the refrigerant.

Brief Description of the Drawings

[0023] [Figure 1] FIG. 1 is a piping system diagram of an air conditioner according to an embodiment. [Figure 2] FIG. 2 is a schematic configuration diagram showing a gas-liquid separator and the piping connected thereto. [Figure 3] FIG. 3 is a block diagram of main components of an air conditioner. [Figure 4] FIG. 4 is a diagram corresponding to FIG. 1 of Modification 1. [Figure 5] FIG. 5 is a diagram corresponding to FIG. 2 of Modification 1. [Figure 6] FIG. 6 is a diagram corresponding to FIG. 2 of Modification 2. [Figure 7] FIG. 7 is a diagram corresponding to FIG. 1 of Modification 3. [Figure 8] FIG. 8 is a diagram corresponding to FIG. 1 of Modification 4. [Figure 9] FIG. 9 is a diagram corresponding to FIG. 1 of other embodiments.

Modes for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below, and various modifications are possible without departing from the technical idea of the present disclosure. Since each drawing is for conceptually explaining the present disclosure, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for easy understanding.

[0025] The refrigeration cycle device of this disclosure constitutes an air conditioning device (10). The air conditioning device (10) adjusts the temperature of the air in the indoor space, which is the target space. The air conditioning device (10) of this embodiment performs both cooling and heating operations.

[0026] (1-1) Overall configuration of the air conditioning system As shown in Figure 1, the air conditioning system (10) includes an outdoor unit (20), an indoor unit (80), a liquid-side connecting pipe (2), and a gas-side connecting pipe (3). The outdoor unit (20) is installed outdoors, and the indoor unit (80) is installed indoors. In the air conditioning system (10), the outdoor unit (20) and the indoor unit (80) are connected to each other via the liquid-side connecting pipe (2) and the gas-side connecting pipe (3), thereby forming a refrigerant circuit (R). In the refrigerant circuit (R), a refrigeration cycle is performed by the circulation of refrigerant.

[0027] The outdoor unit (20) has an outdoor fan (21) and outdoor equipment installed in the refrigerant circuit (R). The outdoor equipment mainly includes a compression element (30), an outdoor heat exchanger (22), a first pressure reducing valve (23), a gas-liquid separator (50), and an outdoor expansion valve (24). The indoor unit (80) has an indoor fan (81) and indoor equipment installed in the refrigerant circuit (R). The indoor equipment mainly includes an indoor heat exchanger (82) and an indoor expansion valve (83).

[0028] (1-2) Details of the outdoor unit The outdoor equipment of the refrigerant circuit (R) includes a first pressure reducing valve (23) and a gas-liquid separator (50). The outdoor equipment further includes a four-way switching valve (25), a bridge circuit (B), and an accumulator (26).

[0029] The compression element (30) of this embodiment has a low-stage compressor (31), which is a low-stage compression section, and a high-stage compressor (32), which is a high-stage compression section. The low-stage compressor (31) compresses the low-pressure refrigerant in the refrigerant circuit (R) to an intermediate-pressure refrigerant and discharges the intermediate-pressure refrigerant. The high-stage compressor (32) compresses the intermediate-pressure refrigerant discharged from the low-stage compressor (31) to a high-pressure refrigerant and discharges the high-pressure refrigerant. An intake pipe (40) is connected to the intake side of the compression element (30) (more precisely, the low-stage compressor (31)). A discharge pipe (41) is connected to the discharge side of the compression element (more precisely, the high-stage compressor (32)). An intermediate pipe (42) is connected between the discharge side of the low-stage compressor (31) and the intake side of the high-stage compressor (32).

[0030] The outdoor heat exchanger (22) is a heat source side heat exchanger. The outdoor heat exchanger (22) exchanges heat between the refrigerant flowing inside it and the outdoor air transported by the outdoor fan (21).

[0031] The gas-liquid separator (50) is a sealed container. The gas-liquid separator (50) separates the refrigerant into gaseous refrigerant and liquid refrigerant. The gas-liquid separator (50) also has the function of separating oil from the refrigerant. The details of the gas-liquid separator (50) will be explained later.

[0032] The bridge circuit (B) has four pipes (P1, P2, P3, P4) and one check valve (CV) installed in each of these pipes (P1, P2, P3, P4). The check valve (CV) allows the flow of refrigerant in the direction indicated by the arrow in Figure 1 and prohibits the flow of refrigerant in the opposite direction.

[0033] One end of the inlet pipe (61) is connected to the connection point between the outlet end of the first pipe (P1) and the outlet end of the second pipe (P2). The other end of the inlet pipe (61) is connected to the gas-liquid separator (50). One end of the liquid outlet pipe (62) is connected to the connection point between the inlet end of the third pipe (P3) and the inlet end of the fourth pipe (P4). The other end of the liquid outlet pipe (62) is connected to the gas-liquid separator (50). The connection point between the inlet end of the second pipe (P2) and the outlet end of the fourth pipe (P4) is connected to the liquid side end (low temperature side end) of the outdoor heat exchanger (22) via the intermediate pipe (43). The connection point between the inlet end of the first pipe (P1) and the outlet end of the third pipe (P3) is connected to the liquid side end of the outdoor heat exchanger (22) via the liquid side connecting pipe (2).

[0034] The first pressure reducing valve (23) is installed in the inlet pipe (61). The first pressure reducing valve (23) is composed of an electronic expansion valve whose opening degree is variable. The first pressure reducing valve (23) reduces the pressure of high-pressure refrigerant above the critical pressure to an intermediate-pressure refrigerant below the critical pressure.

[0035] The outdoor expansion valve (24) is installed in the intermediate piping (43). The outdoor expansion valve (24) is composed of an electronic expansion valve with a variable opening. The outdoor expansion valve (24) constitutes a second pressure reducing valve that reduces the intermediate pressure refrigerant to a low pressure during heating operation.

[0036] The accumulator (26) is provided in the suction pipe (40). The accumulator (26) is a sealed container for storing liquid refrigerant. The accumulator (26) prevents the liquid refrigerant from being drawn into the compression element (30). The suction pipe (40) includes an upstream suction pipe (40a) on the upstream side of the accumulator (26) and a downstream suction pipe (40b) on the downstream side of the accumulator (26).

[0037] The four-way switching valve (25) is installed on the discharge side of the compression element (30). The four-way switching valve (25) switches between a first state (shown by the solid line in Figure 1) and a second state (shown by the dashed line in Figure 1). In the first state, the four-way switching valve (25) connects the discharge side of the compression element (30) to the gas side end of the outdoor heat exchanger (22), and simultaneously connects the suction side of the compression element (30) to the gas side end of the indoor heat exchanger (82). In the second state, the four-way switching valve (25) connects the discharge side of the compression element (30) to the gas side end of the indoor heat exchanger (82), and simultaneously connects the suction side of the compression element (30) to the gas side end of the outdoor heat exchanger (22).

[0038] During cooling operation, the four-way directional valve (25) in the refrigerant circuit (R) enters the first state, the outdoor heat exchanger (22) functions as a radiator, and the indoor heat exchanger (82) functions as an evaporator. During heating operation, the four-way directional valve (25) in the refrigerant circuit (R) enters the second state, the indoor heat exchanger (82) functions as a radiator, and the outdoor heat exchanger (22) functions as an evaporator.

[0039] (1-3) Details of the indoor unit The indoor heat exchanger (82) is a heat exchanger on the user side. The indoor heat exchanger (82) exchanges heat between the refrigerant flowing inside it and the outdoor air transported by the indoor fan (81).

[0040] The indoor expansion valve (83) is installed between the liquid-side end of the indoor heat exchanger (82) in the refrigerant circuit (R) and the liquid-side connecting pipe (2). The indoor expansion valve (83) is composed of an electronic expansion valve with a variable opening. The indoor expansion valve (83) constitutes a second pressure reducing valve that reduces the intermediate-pressure refrigerant to a low pressure during cooling operation.

[0041] (2) Refrigerants and oils The refrigerant circuit (R) is filled with carbon dioxide as the refrigerant. In the refrigerant circuit (R), a so-called supercritical cycle is performed in which the refrigerant compressed by the compression element (30) reaches a pressure above critical pressure. In the refrigerant circuit (R) of this embodiment, a two-stage compression / two-stage expansion type refrigeration cycle is performed.

[0042] The refrigerant contains oil as a refrigeration oil. The oil constitutes a lubricant that lubricates the sliding parts of the compression element (30). In this embodiment, the oil is PAG (polyalkylene glycol).

[0043] The solubility of PAG in carbon dioxide varies depending on the pressure and temperature of the carbon dioxide. When the pressure of carbon dioxide is above the critical pressure, in other words, when carbon dioxide is in a critical state, PAG dissolves more easily in carbon dioxide. Therefore, carbon dioxide and PAG become less likely to separate from each other. On the other hand, when the pressure of carbon dioxide is below the critical pressure, in other words, when carbon dioxide is in a subcritical state, PAG dissolves less easily in carbon dioxide. Therefore, carbon dioxide and PAG become more likely to separate from each other.

[0044] (3) Gas-liquid separator and its surrounding structure (3-1) Details of the gas-liquid separator As shown in Figure 2, the gas-liquid separator (50) is a hollow, sealed container that forms an internal space (S). The gas-liquid separator (50) is formed by a continuous cylindrical body (50a), a bottom (50b) formed below the body (50a), and a top (50c) formed above the body (50a). The gas-liquid separator (50) is installed outdoors. The gas-liquid separator (50) separates a gas-liquid two-phase refrigerant into gaseous refrigerant and liquid refrigerant.

[0045] Basically, subcritical carbon dioxide flows into the gas-liquid separator (50). As mentioned above, when carbon dioxide is in a subcritical state, PAG becomes less soluble in carbon dioxide. For this reason, oil is easily separated from the refrigerant in the gas-liquid separator (50). The gas-liquid separator (50) has the function of an oil separator that separates the refrigerant from the oil. Therefore, in the refrigerant circuit (R) of this embodiment, an oil separator is not provided on the discharge side (high-pressure line) of the compression element (30).

[0046] During normal operation of the air conditioning unit (10), oil, liquid refrigerant, and gaseous refrigerant accumulate in the internal space (S) from bottom to top. In other words, in the internal space (S), an oil layer (51), a liquid layer (52), and a gas layer (53), a gaseous refrigerant layer are formed in order from bottom to top.

[0047] (3-2) Details of the piping connected to the gas-liquid separator As shown in Figures 1 and 2, the refrigerant circuit (R) of this embodiment includes an inlet pipe (61), a liquid outlet pipe (62), a gas introduction pipe (63), and an oil return passage (OP). The oil return passage (OP) is the overall passage for returning the oil separated by the gas-liquid separator (50) back to the compression element (30). The oil return passage (OP) of this embodiment includes a first oil return pipe (64). These pipes are installed in the outdoor unit (20).

[0048] The inlet pipe (61) is a pipe that sends the refrigerant, which has been depressurized by the first pressure reducing valve (23), into the gas-liquid separator (50). In this embodiment, the inlet pipe (61) constitutes a flow path from the bridge circuit (B) to the gas-liquid separator (50). The inlet pipe (61) penetrates the top (50c) of the gas-liquid separator (50). The inlet pipe (61) has an outlet (O1) that allows the refrigerant to flow out into the gas-liquid separator (50). The outlet (O1) opens toward the internal space (S). The outlet (O1) faces downward.

[0049] The liquid outlet pipe (62) is a pipe for sending the liquid refrigerant separated in the gas-liquid separator (50) to the second pressure reducing valve (24, 83). In this embodiment, the liquid outlet pipe (62) constitutes a flow path from the gas-liquid separator (50) to the bridge circuit (B). The liquid outlet pipe (62) penetrates the body (50b) of the gas-liquid separator (50). The liquid outlet pipe (62) has a liquid inlet (O2) into which the refrigerant from the gas-liquid separator (50) flows. The liquid inlet (O2) opens toward the internal space (S). The liquid inlet (O2) faces downward.

[0050] The gas inlet pipe (63) is a pipe for sending the gaseous refrigerant separated in the gas-liquid separator (50) to the compression element (30). In this embodiment, the gas inlet pipe (63) sends the gaseous refrigerant to the suction side of the high-stage compressor (32). The outlet end of the gas inlet pipe (63) is connected to the intermediate pipe (42). The gas inlet pipe (63) penetrates the top (50c) of the gas-liquid separator (50). The gas inlet pipe (63) has a gas inlet (O3) into which the gaseous refrigerant from the gas-liquid separator (50) flows. The gas inlet (O3) is formed at the end of the gas inlet pipe (63). The gas inlet (O3) opens toward the internal space (S). The gas inlet (O3) faces downward.

[0051] The first oil return pipe (64) is a pipe for returning the oil separated in the gas-liquid separator (50) to the compression element (30). In this embodiment, the outlet end of the first oil return pipe (64) is connected to the suction pipe (40). Specifically, the outlet end of the first oil return pipe (64) is connected between the evaporators (83, 22) and the accumulator (26) in the refrigerant circuit (R). The evaporators (83, 22) here are the indoor heat exchanger (82) during cooling operation or the outdoor heat exchanger (22) during heating operation. The first oil return pipe (64) penetrates the bottom (50b) of the gas-liquid separator (50). The first oil return pipe (64) has a first oil inlet (O4) which serves as an oil inlet into which oil from the gas-liquid separator (50) flows. The first oil inlet (O4) opens toward the internal space (S). The first oil inlet (O4) faces upward. The first oil inlet (O4) and the bottom surface of the gas-liquid separator (50) (i.e., the top surface of the bottom (50b)) are approximately flush. In other words, the first oil inlet (O4) is formed at the bottom (50b) of the gas-liquid separator (50).

[0052] As shown in Figure 1, a first flow control valve (71) is provided in the gas inlet pipe (63). The first flow control valve (71) is, for example, an electronic expansion valve with a variable opening. A second flow control valve (72) is provided in the first oil return pipe (64). The second flow control valve (72) is, for example, an electronic expansion valve with a variable opening.

[0053] (3-3) Relationship between the height of the pipe opening Regarding the positional relationship of the heights of the openings of the inflow pipe (61), the liquid outflow pipe (62), the gas introduction pipe (63), and the first oil return pipe (64) in the internal space (S) of the gas-liquid separator (50), it will be described in detail while referring to FIG. 2.

[0054] In FIG. 2, the height position of the outflow port (O1) of the inflow pipe (61) is h1, the height position of the liquid inflow port (O2) of the liquid outflow pipe (62) is h2, the height position of the gas inflow port (O3) of the gas introduction pipe (63) is h3, and the height position of the opening of the first oil return pipe (64) is h4. In this embodiment, the relationship of h4 < h2 < h1 < h3 is satisfied. Here, the height position means altitude.

[0055] Specifically, in this embodiment, the first oil inflow port (O4) is at a position lower than the liquid inflow port (O2). The first oil inflow port (O4) is located near the bottom (50b) of the gas-liquid separator (50). The gas inflow port (O3) is at a position higher than the outflow port (O1). The gas inflow port (O3) is located near the top (50c) of the gas-liquid separator (50). The liquid inflow port (O2) is at a position lower than the outflow port (O1). The liquid inflow port (O2) is located closer to the lower part in the internal space (S), and the outflow port (O1) is located closer to the upper part in the internal space (S).

[0056] (4) Controller and Sensor As shown in FIG. 3, the air conditioner (10) has a control unit (C). The control unit (C) controls the refrigerant circuit (R). The control unit (C) has an outdoor control unit (C1) and an indoor control unit (C2). The outdoor control unit (C1) and the indoor control unit (C2) are configured to be able to communicate with each other wirelessly or by wire. The outdoor control unit (C1) and the indoor control unit (C2) include an MCU (Micro Controller Unit), an electric circuit, and an electronic circuit. The MCU includes a CPU (Central Processing Unit), a memory, and a communication interface. Various programs for the CPU to execute are stored in the memory.

[0057] The outdoor control unit (C1) is located in the outdoor unit (20). The outdoor control unit (C1) controls the rotational speed of the low-stage compressor (31), the rotational speed of the high-stage compressor (32), the rotational speed of the outdoor fan (21), the opening degree of the first pressure reducing valve (23), the opening degree of the outdoor expansion valve (24), the opening degree of the first flow control valve (71), the opening degree of the second flow control valve (72), the state of the four-way switching valve (25), etc. The indoor control unit (C2) is located in the indoor unit (80). The indoor control unit (C2) controls the rotational speed of the indoor fan (81), the opening degree of the indoor expansion valve (83), etc.

[0058] The air conditioning unit (10) has a plurality of sensors. The plurality of sensors include refrigerant-side sensors that detect the temperature and pressure of the refrigerant. The refrigerant-side sensors include a high-pressure sensor (44) and an intermediate-pressure sensor (45). The high-pressure sensor (44) is installed in the discharge pipe (41). The high-pressure sensor (44) detects the pressure of the refrigerant discharged from the compression element (30) (more precisely, the high-stage compressor (32)). The intermediate-pressure sensor (45) is installed, for example, in the liquid outlet pipe (62). The intermediate-pressure sensor (45) detects the pressure of the intermediate-pressure refrigerant after it has been reduced by the first pressure reducing valve (23) and before it is reduced by the second pressure reducing valve (24, 83).

[0059] (5) Operating The air conditioning unit (10) performs both cooling and heating operations. Figure 1 shows the refrigerant flow during cooling operation with solid arrows and the refrigerant flow during heating operation with dashed arrows.

[0060] During cooling and heating operations, the control unit (C) controls the refrigerant circuit (R) such that, in principle, the pressure of the refrigerant compressed by the compression element (30) is equal to or greater than the critical pressure, and the pressure of the refrigerant reduced by the first pressure reducing valve (23) is less than the critical pressure. Specifically, the control unit (C) controls the rotational speed of the low-stage compressor (31) and the high-stage compressor (32) so that the pressure of the refrigerant after compression by the compression element (30) is a predetermined pressure equal to or greater than the critical pressure. The pressure of the refrigerant after compression by the compression element (30) corresponds to the pressure detected by the high-pressure sensor (44). The control unit (C) controls the opening degree of the first pressure reducing valve (23) so that the pressure of the refrigerant after reduction by the first pressure reducing valve (23) is a predetermined pressure lower than the critical pressure. The pressure of the refrigerant after reduction by the first pressure reducing valve (23) corresponds to the pressure detected by the intermediate pressure sensor (45).

[0061] (5-1) Cooling operation During cooling operation, the control unit (C) operates the outdoor fan (21), the low-stage compressor (31), and the high-stage compressor (32), sets the four-way switching valve (25) to the first state, adjusts the opening of the first pressure reducing valve (23) and the indoor expansion valve (83), and fully opens the outdoor expansion valve (24).

[0062] The refrigerant compressed by the low-stage compressor (31) is further compressed by the high-stage compressor (32) to a pressure above critical. The refrigerant discharged from the compression element (30) is released into the outdoor air by the outdoor heat exchanger (22). The released refrigerant is then depressurized by the first pressure reducing valve (23). After depressurization, the refrigerant becomes a subcritical gas-liquid two-phase refrigerant at a pressure below critical. This refrigerant flows into the gas-liquid separator (50). In the gas-liquid separator (50), the refrigerant is separated into liquid refrigerant, gaseous refrigerant, and oil. The liquid refrigerant separated in the gas-liquid separator (50) is depressurized by the indoor expansion valve (83), and then evaporates by absorbing heat from the indoor air in the indoor heat exchanger (82). The evaporated refrigerant is then drawn into the low-stage compressor (31).

[0063] (5-2) Heating operation During heating operation, the control unit (C) operates the outdoor fan (21), the low-stage compressor (31), and the high-stage compressor (32), sets the four-way switching valve (25) to the second state, adjusts the opening of the first pressure reducing valve (23) and the outdoor expansion valve (24), and fully opens the indoor expansion valve (83).

[0064] The refrigerant compressed by the low-stage compressor (31) is further compressed to above the critical pressure by the high-stage compressor (32). The refrigerant discharged from the compression element (30) releases heat into the indoor air in the indoor heat exchanger (82). The refrigerant that has released heat is reduced in pressure by the first pressure reducing valve (23). After reduction in pressure, the refrigerant becomes a subcritical gas-liquid two-phase refrigerant at a pressure lower than the critical pressure. This refrigerant flows into the gas-liquid separator (50). In the gas-liquid separator (50), the refrigerant is separated into liquid refrigerant, gaseous refrigerant, and oil. The liquid refrigerant separated in the gas-liquid separator (50) is reduced in pressure by the outdoor expansion valve (24), and then evaporates by absorbing heat from the indoor air in the outdoor heat exchanger (22). The evaporated refrigerant is drawn into the low-stage compressor (31).

[0065] (5-3) Gas introduction operation During cooling and heating operations, a gas introduction operation is performed to send the gaseous refrigerant in the gas-liquid separator (50) to the compression element (30). During the gas introduction operation, the control unit (C) opens the first flow control valve (71) to a predetermined opening. The gaseous refrigerant in the gas layer (53) of the gas-liquid separator (50) flows out into the gas introduction pipe (63) and passes through the first flow control valve (71). This refrigerant is then drawn into the high-stage compressor (32) via the intermediate piping (42).

[0066] (5-4) Oil return operation During cooling and heating operations, an oil return operation is performed to return the oil in the gas-liquid separator (50) to the compression element (30). During the oil return operation, the control unit (C) opens the second flow control valve (72) to a predetermined opening. The oil in the oil layer (51) of the gas-liquid separator (50) flows out into the first oil return pipe (64) and passes through the second flow control valve (72). This oil flows out into the upstream suction pipe (40a), passes through the accumulator (26), and is then drawn into the low-stage compressor (31). As a result, the sliding parts of the low-stage compressor (31) can be lubricated. Since oil flows out of the low-stage compressor (31) along with the refrigerant, this oil can also be returned to the high-stage compressor (32). As a result, the sliding parts of the high-stage compressor (32) can be lubricated.

[0067] If liquid refrigerant from the liquid layer (52) leaks into the first oil return pipe (64), this liquid refrigerant can be captured by the accumulator (26). This prevents the liquid refrigerant from being directly drawn into the lower stage compressor (31), thus avoiding so-called liquid compression in the compression element (30).

[0068] Since the first oil return pipe (64) is connected to the suction side of the low-stage compressor (31), a sufficient differential pressure can be ensured between the inlet and outlet sides of the first oil return pipe (64). Therefore, the oil in the gas-liquid separator (50) can be reliably returned to the compression element (30).

[0069] The temperature of the oil in the gas-liquid separator (50) is lower than, for example, the temperature of the high-pressure refrigerant. Therefore, by sending the low-temperature oil in the gas-liquid separator (50) to the compression element (30), the compression efficiency of the compression element (30) can be improved compared to, for example, returning the oil in the high-pressure refrigerant to the compression element (30).

[0070] (6) Characteristics (6-1) Issues related to oil separators Conventional air conditioning systems sometimes include an oil separator on the high-pressure side of the refrigerant circuit (e.g., the discharge pipe) to return oil contained in the refrigerant discharged from the compression element back to the compression element. On the other hand, when a refrigeration cycle is performed in the refrigerant circuit to a pressure above critical pressure, it was necessary to increase the wall thickness of the oil separator to ensure its pressure resistance. As a result, the oil separator could become, for example, larger, heavier, or more expensive.

[0071] Therefore, in this embodiment, the oil separator is omitted from the refrigerant circuit (R), and the gas-liquid separator (50) is equipped with an oil separation function, thereby enabling a miniaturization of the refrigeration cycle device (air conditioning device (10)).

[0072] (6-2) Effects of the Embodiment (6-2-1) The control unit (C) controls the refrigerant circuit (R) such that the pressure of the refrigerant compressed by the compression element (30) is equal to or greater than the critical pressure, and the pressure of the refrigerant reduced by the first pressure reducing valve (23) is less than the critical pressure. The refrigerant circuit (R) includes an inlet pipe (61) that sends the refrigerant reduced by the first pressure reducing valve (23) into the gas-liquid separator (50), a liquid outlet pipe (62) that sends the liquid refrigerant separated in the gas-liquid separator (50) to the second pressure reducing valve (24, 83), and an oil return channel (OP) that returns the oil separated in the gas-liquid separator (50) back to the compression element (30).

[0073] In this configuration, a subcritical refrigerant can be stored in the gas-liquid separator (50), making it easier to separate oil from the refrigerant. The oil separated in the gas-liquid separator (50) returns to the compression element (30) through the oil return channel (OP). Therefore, the sliding parts of the compression element (30) can be lubricated with oil without providing an oil separator in the refrigerant circuit (R).

[0074] In addition, the oil in the gas-liquid separator (50) is at a lower temperature than, for example, the oil in the high-pressure refrigerant. Therefore, compared to returning the oil from the high-pressure side to the compression element (30), lower-temperature oil can be returned to the compression element (30). Consequently, the compression efficiency of the compression element (especially the low-stage compressor (31) in this embodiment) can be improved.

[0075] (6-2-2) The first oil inlet (O4) of the oil return passage (OP) (more precisely, the first oil return pipe (64)) is located lower than the liquid inlet (O2) of the liquid outlet pipe (62). This prevents oil near the bottom (50b) of the gas-liquid separator (50) from flowing into the liquid outlet pipe (62). As a result, insufficient oil lubrication of the compression element (30) can be suppressed.

[0076] In addition, it is possible to prevent the liquid refrigerant in the gas-liquid separator (50) from flowing out into the first oil return pipe (64). As a result, it is possible to prevent a decrease in the amount of liquid refrigerant sent to the evaporators (83, 22).

[0077] (6-2-3) The oil return channel (OP) (more precisely, the first oil return pipe (64)) is connected between the evaporator (83, 22) and the accumulator (26) in the refrigerant circuit (R). Therefore, if liquid refrigerant in the gas-liquid separator (50) flows into the oil return channel (OP), this liquid refrigerant can be stored in the accumulator (26). As a result, it is possible to suppress the intake of liquid refrigerant into the compression element (30), thereby avoiding so-called liquid compression.

[0078] (6-2-4) The refrigerants are carbon dioxide and polyalkylene glycol. With these refrigerant and oil combinations, oil is easily separated from the refrigerant, especially when the refrigerant is brought to a subcritical state in the gas-liquid separator (50). Therefore, the oil separation rate in the gas-liquid separator (50) can be improved.

[0079] (7) Variant The above-described embodiment may also have the following modified configuration. The differences from the above embodiment will be explained below.

[0080] (7-1) Variation 1 As shown in FIGS. 4 and 5, the oil return passage (OP) of the first modification has the same first oil return pipe (64) as that of the embodiment and a second oil return pipe (65). The first oil return pipe (64) and the second oil return pipe (65) are pipes for returning the oil separated in the gas-liquid separator (50) to the compression element (30). The second oil return pipe (65) penetrates, for example, the body portion (50a) of the gas-liquid separator (50). The second oil return pipe (65) has a second oil inlet (O5) as an oil return port into which the oil in the gas-liquid separator (50) flows. The second oil inlet (O5) opens toward the internal space (S). The second oil inlet (O5) faces downward. The outflow end of the second oil return pipe (65) is connected to the suction pipe (40). Specifically, the outflow end of the second oil return pipe (65) is connected between the evaporators (83, 22) and the accumulator (26) in the refrigerant circuit (R).

[0081] Let the height position of the second oil inlet (O5) of the second oil return pipe (65) be h5. In the first modification, the relationship h4 < h5 < h2 < h1 < h3 is satisfied. The second oil inlet (O5) is at a higher position than the first oil inlet (O4). The second oil inlet (O5) is at a lower position than the liquid inlet (O2). A third flow rate control valve (73) is provided in the second oil return pipe (65). The second flow rate control valve (72) is, for example, an electronic expansion valve with a variable opening degree.

[0082] In the gas-liquid separator (50), the densities of the oil and the refrigerant change according to the temperature of the refrigerant or oil inside. For example, when the temperature of the refrigerant or oil is 20°C, in the internal space (S), from bottom to top, the oil, liquid refrigerant, and gas refrigerant accumulate in this order. On the other hand, when the temperature of the refrigerant or oil is extremely low (e.g., -20°C), the density of the liquid refrigerant may become greater than the density of the oil. In this case, in the internal space (S), from bottom to top, the liquid refrigerant, oil, and gas refrigerant accumulate in this order. Therefore, in the internal space (S), the oil layer (51) and the liquid layer (52) may be reversed vertically.

[0083] In the modified example 1, a second oil return pipe (65) is connected to the gas-liquid separator (50), and the second oil inlet (O5) is located higher than the first oil inlet (O4). Therefore, if the oil layer (51) and the liquid layer (52) are reversed vertically, the oil in the oil layer (51) can be returned to the compression element (30) through the second oil return pipe (65).

[0084] Specifically, in Modification 1, when the first condition is met, the control unit (C) closes the second flow control valve (72), which is an on-off valve, and opens the third flow control valve (73), which is an on-off valve. As a result, the oil in the oil layer (51) above the liquid layer (52) can be returned to the compression element (30) through the second oil return pipe (65). On the other hand, by closing the second flow control valve (72), it is possible to prevent the liquid refrigerant in the liquid layer (52) below the oil layer (51) from flowing through the second oil return pipe (65).

[0085] The first condition is a predetermined condition under which the oil layer (51) and the liquid layer (52) may be reversed. The first condition is a condition indicating that the temperature of the refrigerant in the gas-liquid separator (50) is lower than a predetermined temperature. Specifically, the first condition includes the fact that the outside air temperature is lower than a predetermined temperature at the time of starting operation of the air conditioning system (10).

[0086] In Modification 1, the outlet end of the second oil return pipe (65) may be connected to the downstream portion of the second flow control valve (72) in the first oil return pipe (64). In this configuration, a portion of the piping of both can be shared between them.

[0087] In modified example 1, the second oil inlet (O5) may be located higher than the liquid inlet (O2).

[0088] (7-2) Modification 2 In the modified example 2 shown in Figure 6, the gas inlet pipe (63) also serves as the second oil return pipe (65) in the modified example 1. The gas inlet pipe (63) has a first piping section (63a), a second piping section (63b), and a third piping section (63c).

[0089] The first piping section (63a) penetrates through the top (50c) of the gas-liquid separator (50). The first piping section (63a) is a vertical pipe extending in the vertical direction. The first piping section (63a) extends to near the bottom (50b) of the gas-liquid separator (50). One end of the second piping section (63b) is continuous with the lower end of the first piping section (63a). The second piping section (63b) is formed in a U shape. The third piping section (63c) is continuous with the other end of the second piping section (63b). The third piping section (63c) is a vertical pipe extending in the vertical direction. The third piping section (63c) extends from near the bottom (50b) of the gas-liquid separator (50) to near the top (50c) of the gas-liquid separator (50). A gas inlet (O3) is formed at the end of the third piping section (63c), specifically, at the upper end. The gas inlet (O3) opens toward the internal space (S). The gas inlet (O3) faces upward.

[0090] A second oil inlet (O5) is formed in the peripheral wall (63d) of the gas introduction pipe (63). The second oil inlet (O5) has the same function as the second oil inlet (O5) in the first modification. The second oil inlet (O5) is located on the downstream side of the gas inlet (O3) in the gas introduction pipe (63). In other words, the second oil inlet (O5) is formed in the middle of the gas introduction pipe (63) inside the gas-liquid separator (50). The second oil inlet (O5) communicates the internal space (S) of the gas-liquid separator (50) with the inside of the gas introduction pipe (63).

[0091] When the height position of the second oil inlet (O5) is h5, in the second modification as well, the relationship h4 < h5 < h2 < h1 < h3 is satisfied. Here, strictly speaking, the height position h5 of the second oil inlet (O5) is the height position of the lower end of the second oil inlet (O5).

[0092] In Modification 2, when the oil layer (51) and the liquid layer (52) are inverted vertically, the oil from the oil layer (51) can be allowed to flow into the second oil inlet (O5). In this case, the oil that flows into the second oil inlet (O5) returns to the compression element (30) through the gas introduction pipe (63). Thus, in Modification 2, the gas introduction pipe (63) constitutes the second oil return pipe (65), thus reducing the number of parts. In Modification 2, when the first condition is met, the control unit (C) closes the second flow control valve (72), which is an on-off valve, and opens the first flow control valve (71), which is an on-off valve.

[0093] (7-3) Modified example 3 The oil return channel (OP) of the modified example 3 shown in Figure 7 has a low-stage oil return pipe (66) and a high-stage oil return pipe (67). The low-stage oil return pipe (66) returns the oil separated in the gas-liquid separator (50) to the low-stage compressor (31). The high-stage oil return pipe (67) returns the oil separated in the gas-liquid separator (50) to the high-stage compressor (32).

[0094] The inlet end of the low-stage oil return pipe (66) is connected to the gas-liquid separator (50). The outlet end of the low-stage oil return pipe (66) is connected to the suction pipe (40), which is the suction side of the low-stage compressor (31). The inlet end of the high-stage oil return pipe (67) is connected to the gas-liquid separator (50). The outlet end of the high-stage oil return pipe (67) is connected to the intermediate piping (42), which is the suction side of the high-stage compressor (32). The oil inlet of the low-stage oil return pipe (66) and the oil inlet of the high-stage oil return pipe (67) may be at the same height, or they may be at different heights, for example, as with the first oil return pipe (64) and the second oil return pipe (65) in Modification 1.

[0095] A fourth flow control valve (74) is provided in the lower-stage oil return pipe (66), and a fifth flow control valve (75) is provided in the higher-stage oil return pipe (67). The fourth flow control valve (74) and the fifth flow control valve (75) are, for example, electronic expansion valves with variable opening degrees.

[0096] When the control unit (C) opens the fourth flow control valve (74) to a predetermined opening, the oil in the gas-liquid separator (50) is returned to the low-stage compressor (31) through the low-stage oil return pipe (66). When the control unit (C) opens the fifth flow control valve (75) to a predetermined opening, the oil in the gas-liquid separator (50) is returned to the high-stage compressor (32) through the high-stage oil return pipe (67). When the control unit (C) opens both the fourth flow control valve (74) and the fifth flow control valve (75) to a predetermined opening, the oil in the gas-liquid separator (50) is returned to both the low-stage compressor (31) and the high-stage compressor (32).

[0097] In modified example 3, the oil return channel (OP) may have one main return pipe connected to the gas-liquid separator (50), and two branching oil return pipes, a lower-stage oil return pipe (66) and a higher-stage oil return pipe (67), from the outlet end of the main return pipe.

[0098] (7-4) Modification 4 As shown in Figure 8, the refrigerant circuit (R) of the modified example 4 has an oil separator (90). The oil separator (90) is installed in the discharge pipe (41). The oil separator (90) is made up of a sealed container. The oil separator (90) separates oil from the refrigerant compressed by the compression element (30). In this example, the compression element (30) has a low-stage compressor (31) and a high-stage compressor (32) connected in series. More precisely, the oil separator (90) is installed on the discharge side of the high-stage compressor (32) in the refrigerant circuit (R).

[0099] The refrigerant circuit (R) of Modified Example 4 has a discharge-side oil return passage (91). One end (inlet end) of the discharge-side oil return passage (91) is connected to an oil separator (90), and the other end (outlet end) of the discharge-side oil return passage (91) is connected to a suction pipe (40). In this example, the other end of the discharge-side oil return passage (91) is connected to a downstream suction pipe (40b) downstream of the accumulator (26). The other end of the discharge-side oil return passage (91) may be connected to an upstream suction pipe (40a) upstream of the accumulator (26). The accumulator (26) may be omitted in the refrigerant circuit (R) of Modified Example 4. A discharge-side oil return valve (92) is provided in the discharge-side oil return passage (91). The discharge-side oil return valve (92) in this example is a flow control valve, but it may also be an on / off valve.

[0100] In the modified example 4, the discharge-side oil return valve (92) is opened, allowing the oil separated by the oil separator (90) to be returned to the compression element (30) via the suction pipe (40). Specifically, the oil separated by the oil separator (90) is returned to the low-stage compressor (31) via the suction pipe (40).

[0101] In the modified example 4, the subcritical refrigerant can be stored in the gas-liquid separator (50), making it easier to separate oil from the refrigerant. The oil separated in the gas-liquid separator (50) returns to the compression element (30) through the oil return channel (OP). Therefore, in the refrigerant circuit (R) of the modified example 4, the gas-liquid separator (50) takes over the function of oil return of the oil separator (90), allowing the oil separator (90) to be miniaturized, and furthermore, the refrigeration cycle device (air conditioning device (10)) to be miniaturized.

[0102] In modified example 4, the other end of the discharge-side oil return passage (91) may be directly connected to the compression chamber of the low-stage compressor (31). The other end of the discharge-side oil return passage (91) may be connected to the intermediate piping (42) between the low-stage compressor (31) and the high-stage compressor (32), or it may be directly connected to the compression chamber of the high-stage compressor (32). When returning the oil from the oil separator (90) to the intermediate piping (42) or the compression chamber of the high-stage compressor (32), it is preferable for the control unit (C) to fully close the first flow control valve (71).

[0103] In Modification 4, two branch passages may be provided on the other end of the discharge-side oil return passage (91), with one connected to the suction side or compression chamber of the low-stage compressor (31) and the other to the suction side or compression chamber of the high-stage compressor (32). In this case, it is preferable to provide a discharge-side oil return valve in each branch passage. With this configuration, the oil separated by the oil separator (90) can be selectively returned to the low-stage compressor (31) and the high-stage compressor (32).

[0104] (8) Other embodiments As shown in Figure 9, the compression element (30) may consist of a single-stage compressor (33). The air conditioning unit (10) in this example performs a single-stage compression / two-stage expansion refrigeration cycle. Oil from the oil return pipe (e.g., first oil return pipe (64)) is sent to the suction side of the single-stage compressor (33).

[0105] The compression element (30) may be composed of a single two-stage compression compressor having a low-stage compression mechanism which is the low-stage compression section and a high-stage compression mechanism which is the high-stage compression section.

[0106] The oil return channel (OP) may return the oil in the gas-liquid separator (50) directly to the compression chamber of the compression mechanism of the low-stage compressor (31), or directly to the compression chamber of the compression mechanism of the high-stage compressor (32), or directly to the compression chamber of the compression mechanism of the single-stage compressor (33).

[0107] The oil return channel (OP) may return the oil in the gas-liquid separator (50) to the downstream side of the accumulator (26) in the suction pipe (40). The oil return channel (OP) may also return the oil in the gas-liquid separator (50) directly to the accumulator (26). In other words, the outlet end of the oil return channel (OP) may be directly connected to the accumulator (26).

[0108] The inlet pipe (61), liquid outlet pipe (62), gas introduction pipe (63), first oil return pipe (64), second oil return pipe (65), lower-stage oil return pipe (66), and upper-stage oil return pipe (67) do not necessarily have to pass through the gas-liquid separator (50). In this case, the ends (O1~O5) of these pipes are formed in the gas-liquid separator (50).

[0109] The refrigerant circuit (R) may be configured in which the gas introduction pipe (63) is omitted.

[0110] In the embodiment described above, the outlet end of the gas inlet pipe (63) is connected to the intermediate pipe (42). However, the outlet end of the gas inlet pipe (63) may be connected to the oil return passage (OP). Specifically, the outlet end of the gas inlet pipe (63) may be connected to the downstream side of the second flow control valve (72) in the first oil return pipe (64) or to the downstream side of the third flow control valve (73) in the second oil return pipe (65). Furthermore, the outlet end of the gas inlet pipe (63) may be connected to the suction pipe (40). In this case, the outlet end of the gas inlet pipe (63) may be connected to the upstream suction pipe (40a) or to the downstream suction pipe (40b).

[0111] The refrigerant circuit (R) may have an oil separator on the discharge side of the compression element (30). In this case as well, the gas-liquid separator (50) also functions as an oil separator, so the oil separator on the discharge side of the compression element (30) can be made smaller, and the refrigeration cycle device (air conditioning device (10)) can be made smaller.

[0112] The refrigerant may be anything other than carbon dioxide, such as a natural refrigerant.

[0113] The oil contained in the refrigerant may be POG (polyol ester) or PVE (polyvinyl ether).

[0114] The outdoor equipment of the refrigerant circuit (R) may include, for example, four on-off valves, two three-way valves, or one four-way valve instead of the bridge circuit (B). The air conditioning unit (10) may not have a four-way switching valve (25) and may perform only cooling operation or only heating operation. In this case, the bridge circuit (B) is omitted.

[0115] The refrigerant circuit (R) may have electromagnetic valves or capillary tubes instead of the flow control valves provided in the oil return pipe.

[0116] The refrigeration cycle equipment may include a cooling system for cooling the interior of a container or trailer, a heat pump unit for generating chilled or hot water, and a water heater for storing the generated hot water in a tank.

[0117] While embodiments and modifications have been described above, it will be understood that a variety of changes in form and details are possible without departing from the spirit and scope of the claims. Furthermore, the embodiments, modifications, and other embodiments described above may be combined or substituted as appropriate, as long as they do not impair the functions covered by this disclosure.

[0118] The designations "1st," "2nd," "3rd," etc., mentioned above are used to distinguish between the terms to which these designations are attached, and do not limit the number or order of those terms. [Industrial applicability]

[0119] As described above, this disclosure is useful for refrigeration cycle systems. [Explanation of Symbols]

[0120] 10. Refrigeration cycle system (air conditioning system) 22,83 Heat sink 23. First pressure reducing valve 24,83 Second pressure reducing valve 26 Accumulator 30 compression elements 31. Lower-stage compressor (lower-stage compression section) 32. High-stage compressor (high-stage compression section) 50 Gas-liquid separator 61 Inflow pipe 62 Liquid outflow pipe 63 Gas inlet pipe 83,22 Evaporator C control section O2 liquid inlet O3 gas inlet O4 No. 1 Oil Inlet O4,O5 Oil inlet O5 2nd oil inlet R Refrigerant circuit

Claims

1. A refrigerant circuit (R) having a compression element (30), radiators (22, 82), a first pressure reducing valve (23), a gas-liquid separator (50), a second pressure reducing valve (24, 83), and evaporators (82, 22), The system includes a control unit (C) that controls the refrigerant circuit (R) such that the pressure of the refrigerant compressed by the compression element (30) is equal to or greater than the critical pressure, and the pressure of the refrigerant reduced by the first pressure reducing valve (23) is less than the critical pressure. The aforementioned refrigerant circuit (R) is An inlet pipe (61) that sends the refrigerant, which has been depressurized by the first pressure reducing valve (23), into the gas-liquid separator (50), A liquid outlet pipe (62) sends the liquid refrigerant separated in the gas-liquid separator (50) to the second pressure reducing valve (24, 83), The gas-liquid separator (50) includes an oil return channel (OP) that returns the oil separated in the gas-liquid separator (50) to the compression element (30), The refrigerant circuit (R) has a gas introduction pipe (63) that sends the gas refrigerant separated in the gas-liquid separator (50) to the compression element (30), The oil return channel (OP) has oil inlets (O4, O5) into which oil from the gas-liquid separator (50) flows. The liquid outlet pipe (62) has a liquid inlet (O2) into which the liquid refrigerant in the gas-liquid separator (50) flows. The oil inlets (O4, O5) are located at a lower position than the liquid inlet (O2), The oil return passage (OP) comprises a first oil return pipe (64) and a second oil return pipe (65). The first oil return pipe (64) has a first oil inlet (O4) as the oil inlet, The second oil return pipe (65) has a second oil inlet (O5) as the oil inlet, The second oil inlet (O5) is located at a higher position than the first oil inlet (O4), The second oil return pipe (65) is the gas introduction pipe (63), A gas inlet (O3) is formed at the end of the gas introduction pipe (63). The second oil inlet (O5) is located downstream of the gas inlet (O3) in the second oil return pipe (65) and connects the inside of the gas introduction pipe (63) to the inside of the gas-liquid separator (50). Refrigeration cycle device.

2. A refrigerant circuit (R) having a compression element (30), radiators (22, 82), a first pressure reducing valve (23), a gas-liquid separator (50), a second pressure reducing valve (24, 83), and evaporators (82, 22), The system includes a control unit (C) that controls the refrigerant circuit (R) such that the pressure of the refrigerant compressed by the compression element (30) is equal to or greater than the critical pressure, and the pressure of the refrigerant reduced by the first pressure reducing valve (23) is less than the critical pressure. The aforementioned refrigerant circuit (R) is An inlet pipe (61) that sends the refrigerant, which has been depressurized by the first pressure reducing valve (23), into the gas-liquid separator (50), A liquid outlet pipe (62) sends the liquid refrigerant separated in the gas-liquid separator (50) to the second pressure reducing valve (24, 83), The gas-liquid separator (50) includes an oil return channel (OP) that returns the oil separated in the gas-liquid separator (50) to the compression element (30), The compression element (30) is A lower-stage compression section (31) for compressing the refrigerant, It includes a high-stage compression section (32) that compresses the refrigerant compressed in the low-stage compression section (31), The aforementioned oil return channel (OP) is A low-stage oil return pipe (66) returns the oil separated in the gas-liquid separator (50) to the low-stage compression section (31), The gas-liquid separator (50) has a high-stage oil return pipe (67) that returns the oil separated in the gas-liquid separator (50) to the high-stage compression section (32). Refrigeration cycle device.

3. The refrigerant is carbon dioxide, and the oil is polyalkylene glycol. A refrigeration cycle apparatus according to claim 1 or 2.

4. The refrigerant circuit (R) includes an oil separator (90) that separates oil from the refrigerant compressed by the compression element (30). A refrigeration cycle apparatus according to claim 1 or 2.

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