Refrigeration cycle device

Abstract

A refrigerant circuit (C1) of a refrigeration cycle device (100) includes: a compressor (1); a first gas-liquid separator (3) disposed on a discharge port side of the compressor (1); a condenser (5) through which a gas refrigerant discharged from the first gas-liquid separator (3) passes; a pressure reducing device (6) for reducing the pressure of the refrigerant that has passed through the condenser (5); and an evaporator (7) through which the refrigerant of which the pressure has been reduced by the pressure reducing device (6) passes. The refrigeration cycle device (100) further comprises: a bypass flow passage (P0) that branches from a branching portion (B1) between the compressor (1) and the first gas-liquid separator (3) and merges at a first merging portion (J1) between the first gas-liquid separator (3) and the condenser (5); a first liquid flow passage (P1) that connects a second merging portion (J2) between the evaporator (7) and the compressor (1) to a liquid discharge port of the first gas-liquid separator (3); and a first flow rate adjusting device (9) that is disposed in the first liquid flow passage (P1) and that is configured to be capable of adjusting the flow rate of fluid flowing through the first liquid flow path (P1).

Description

Refrigeration Cycle Equipment

[0001] The present disclosure relates to a refrigeration cycle device.

[0002] Some refrigeration cycle systems that use refrigerants are equipped with an oil return mechanism to prevent a shortage of refrigerant oil in the compressor. The oil return mechanism separates the refrigerant oil discharged from the compressor together with the refrigerant using a gas-liquid separator and returns it to the compressor.

[0003] An example of this type of oil return mechanism is disclosed in Japanese Patent Laid-Open Publication No. 2016-138677 (Patent Document 1).

[0004] JP 2016-138677 A

[0005] The refrigeration oil sealed in the compressor of a refrigeration cycle device circulates through the refrigerant circuit together with the refrigerant and accumulates in various components such as the heat exchanger and piping. In air conditioners such as packaged air conditioners and building air conditioners, the difference in the amount of oil remaining is greater when the extension piping is short or long compared to room air conditioners. For this reason, an amount of refrigeration oil is sealed in the compressor so that there is no shortage of oil even when the extension piping is long. Furthermore, as disclosed in Japanese Patent Laid-Open Publication No. 2016-138677 (Patent Document 1), a gas-liquid separator is installed in the compressor's discharge piping to increase the amount of oil returned in order to avoid oil shortage in the compressor.

[0006] However, if the amount of refrigerant oil to be charged is designed to match the length of the extension pipe, the amount of refrigerant oil that exceeds the amount that can be held in the compressor will be left over if the extension pipe is short. Furthermore, since the amount of refrigerant required varies depending on the operating state (cooling or heating) and the length of the pipe, if the amount of refrigerant charged is uniformly set to the same, excess refrigerant may be generated. The following problems arise from the excess refrigerant and refrigerant oil.

[0007] When excess oil increases, the flow rate of refrigeration oil flowing into the gas-liquid separator increases, causing the gas-liquid separator to overflow, increasing the amount of oil circulating in the refrigerant circuit and resulting in a decrease in performance. Furthermore, when the refrigerant flow rate is high, the increased flow rate causes the separated refrigeration oil to re-spray, further reducing the amount of oil that the gas-liquid separator can store, causing it to overflow sooner.

[0008] When the amount of excess refrigerant increases, even under operating conditions where the required amount of refrigerant is small and performance is good, the performance of the refrigeration cycle device decreases due to the excessive circulation of refrigerant.

[0009] The refrigeration cycle device of the present disclosure is intended to solve the above-mentioned problems, and aims to suppress a decrease in performance of the refrigeration cycle device.

[0010] The present disclosure relates to a refrigeration cycle apparatus, the refrigeration cycle apparatus including: a refrigerant circuit through which a refrigerant circulates; a compressor disposed in the refrigerant circuit; a first gas-liquid separator disposed on a discharge port side of the compressor in the refrigerant circuit; a condenser through which gas refrigerant discharged from the first gas-liquid separator passes in the refrigerant circuit; a pressure reducing device configured to reduce the pressure of the refrigerant that has passed through the condenser in the refrigerant circuit; an evaporator through which the refrigerant decompressed by the pressure reducing device passes in the refrigerant circuit; a bypass flow path branching from a branching portion between the compressor and the first gas-liquid separator in the refrigerant circuit and joining a first junction between the first gas-liquid separator and the condenser in the refrigerant circuit; a first liquid flow path connecting a second junction between the evaporator and the compressor in the refrigerant circuit and a liquid discharge port of the first gas-liquid separator; and a first flow control device disposed in the first liquid flow path and configured to adjust the flow rate of a fluid flowing in the first liquid flow path.

[0011] According to the refrigeration cycle device of the present disclosure, the amount of refrigerant circulated and the amount of refrigerating machine oil returned can be adjusted, thereby suppressing a decrease in performance of the refrigeration cycle device.

[0012] 10 is an overall configuration diagram of a refrigeration cycle apparatus 100 of embodiment 1. It is a Mollier diagram showing the state of refrigerant in the refrigeration cycle apparatus shown in FIG. 1. It is a flowchart for explaining a first example of control of the flow rate control device 9. It is a flowchart for explaining a second example of control of the flow rate control device 9. It is an overall configuration diagram of a refrigeration cycle apparatus 200 of embodiment 2. It is a Mollier diagram showing the state of refrigerant in the refrigeration cycle apparatus shown in FIG. 5. It is a diagram (T-xy diagram) showing the gas-liquid equilibrium composition in a gas-liquid separator. It is an overall configuration diagram of a refrigeration cycle apparatus 300 of embodiment 3. It is a Mollier diagram showing the state of refrigerant in the refrigeration cycle apparatus shown in FIG. 8. It is an overall configuration diagram of a refrigeration cycle apparatus 300A of a modified example of embodiment 3. It is a diagram showing the flow of refrigerant and refrigerating machine oil during normal operation. It is a diagram showing the flow of refrigerant and refrigerating machine oil during variable operation. It is a flowchart for explaining control of a switching valve 16.

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. While multiple embodiments will be described below, it is anticipated from the beginning that the configurations described in each embodiment will be appropriately combined. Note that identical or corresponding parts in the drawings will be designated by the same reference numerals, and their description will not be repeated.

[0014] Embodiment 1. Fig. 1 is an overall configuration diagram of a refrigeration cycle apparatus 100 according to embodiment 1. Note that Fig. 1 functionally illustrates the connection relationships and arrangement of the devices in the refrigeration cycle apparatus, and does not necessarily illustrate the physical spatial arrangement.

[0015] The refrigeration cycle apparatus 100 shown in Fig. 1 includes an outdoor unit 20 and an indoor unit 30. The outdoor unit 20 and the indoor unit 30 are connected by extension pipes 41, 42. In this embodiment, the outdoor unit 20 operates as a cold source that discharges heat outdoors.

[0016] The outdoor unit 20 includes a compressor 1, a gas-liquid separator 3, a condenser 5, an outdoor fan (not shown), a pressure reducing device 6, and a flow rate adjusting device 9. The indoor unit 30 includes an evaporator 7 and an indoor fan (not shown).

[0017] The refrigerant flow path of the outdoor unit 20 runs from a refrigerant inlet through the compressor 1, gas-liquid separator 3, condenser 5, and pressure reducing device 6 in this order to a refrigerant outlet of the outdoor unit 20. The refrigerant flow path of the outdoor unit 20, together with the evaporator 7 of the indoor unit 30, is configured to form a refrigerant circuit C1 through which the refrigerant circulates.

[0018] The outdoor unit 20 of the refrigeration cycle apparatus 100 further includes a bypass flow path P0 and a liquid flow path P1. The bypass flow path P0 branches from a branch point B1 between the compressor 1 and the gas-liquid separator 3 in the refrigerant circuit C1 and merges into a junction J1 between the gas-liquid separator 3 and the condenser 5 in the refrigerant circuit C1. The liquid flow path P1 connects a junction J2 between the evaporator 7 and the compressor 1 in the refrigerant circuit C1 with a liquid outlet of the gas-liquid separator 3. The flow rate control device 9 is disposed in the liquid flow path P1 and is configured to be able to adjust the flow rate of the fluid. The liquid flow path P1 is also called an oil return path.

[0019] The pressure reducing device 6 may be, for example, a thermal expansion valve or an electronic expansion valve.

[0020] The compressor 1 compresses the refrigerant that has joined at the joining point J2 in the refrigerant circuit C1, and discharges the refrigerant to the branch point B1.

[0021] The outdoor unit 20 further includes a control device 50. The compressor 1 is configured to adjust its operating rotation speed in accordance with a control signal from the control device 50. By adjusting the operating rotation speed of the compressor 1, the amount of refrigerant circulating is adjusted, and the refrigeration capacity of the refrigeration cycle apparatus 100 can be adjusted. Various types of compressors 1 can be used, and for example, a scroll type, a rotary type, a screw type, or the like can be used.

[0022] The condenser 5 condenses the refrigerant discharged from the compressor 1 and passed through the gas-liquid separator 3, and sends it to the pressure reducing device 6. The condenser 5 is configured so that the high-temperature, high-pressure gas refrigerant discharged from the compressor 1 exchanges heat with outside air. Through this heat exchange, the refrigerant that has released heat condenses and changes to a liquid phase. A fan (not shown) supplies outside air with which the refrigerant exchanges heat to the condenser 5. The refrigerant pressure on the discharge side of the compressor 1 can be adjusted by adjusting the rotation speed of the fan.

[0023] The evaporator 7 is configured so that heat exchange occurs between the refrigerant, which has been decompressed by passing through the pressure reducing device 6, and the indoor air. This heat exchange causes the refrigerant to evaporate and change into a gas phase. A fan (not shown) supplies the indoor air with which the refrigerant exchanges heat to the evaporator 7. The refrigerant pressure on the suction side of the compressor 1 can be adjusted by adjusting the rotation speed of the fan.

[0024] The control device 50 is configured to include a CPU (Central Processing Unit) 51, memory 52 (ROM (Read Only Memory) and RAM (Random Access Memory)), an input / output buffer (not shown) for inputting and outputting various signals, etc. The CPU 51 deploys a program stored in the ROM into the RAM, etc., and executes it. The program stored in the ROM is a program in which the processing procedures of the control device 50 are written. The control device 50 controls each device in the refrigeration cycle device 100 in accordance with these programs. This control is not limited to processing by software, but can also be processed by dedicated hardware (electronic circuitry).

[0025] The control device 50 controls the operating frequency of the compressor 1 based on the difference between the target temperature and the room temperature (indoor load). The control device 50 also controls the opening degree of the pressure reducing device 6 so that the degree of refrigerant superheat (suction SH) at the outlet of the evaporator 7 becomes the target value.

[0026] In the refrigeration cycle apparatus 100 shown in FIG. 1, a branch section B1 and a bypass flow path P1 are provided between the compressor 1 and the condenser 5, and the flow rate of the refrigerant flowing into the gas-liquid separator 3 is reduced by dividing the refrigerant into a path that passes through the gas-liquid separator 3 and a path that passes through the bypass flow path P1.

[0027] The flow of refrigerant and refrigeration oil will be described with reference to FIG. 1. The high-temperature, high-pressure gas refrigerant and a mixed liquid of liquid refrigerant and refrigeration oil discharged from compressor 1 flow into branch B1. Some of the refrigerant and refrigeration oil that flow into branch B1 pass directly through bypass flow path P0 to reach junction J1. The remainder flows into gas-liquid separator 3 at a refrigerant flow rate that is lower than the refrigerant flow rate discharged from compressor 1. This reduces re-entrainment of liquid within gas-liquid separator 3. The high-temperature, high-pressure gas refrigerant and mixed liquid that flow into gas-liquid separator 3 are separated into gas and liquid within gas-liquid separator 3. The high-pressure gas refrigerant separated within gas-liquid separator 3 flows into junction J1. A certain amount of the mixed liquid separated within gas-liquid separator 3 is stored in gas-liquid separator 3, and some passes through flow control device 9 and flows into junction J2.

[0028] Figure 2 is a Mollier diagram showing the state of the refrigerant in the refrigeration cycle system shown in Figure 1. In compressor 1, the refrigerant is compressed and becomes a high-temperature, high-pressure gas (a-b). In condenser 5, the refrigerant condenses through heat exchange with outside air (d-e). In pressure reducing device 6, the liquid refrigerant condensed in condenser 5 is reduced in pressure and changes to a two-phase state (ef). In evaporator 7, the refrigerant evaporates through heat exchange with indoor air (f-g). Note that the refrigerant flowing from gas-liquid separator 3 through liquid flow path P1 toward junction J2 is reduced in pressure (j-k) and then merges (a).

[0029] 3 is a flowchart for explaining a first example of control of the flow rate control device 9. The process of this flowchart is called from the main routine for control of the refrigeration cycle apparatus and executed every time a fixed time elapses. In the example shown in FIG. 3, the flow rate of the flow rate control device 9 is changed based on the operating frequency of the compressor 1.

[0030] First, in step S1, the control device 50 detects the frequency, and then in step S2, it is determined whether the frequency at the previous time is different from the currently detected frequency.

[0031] If the frequency is the same as the previous time (NO in S2), the opening degree of the flow rate adjusting device 9 is not changed and the processing of this flowchart is ended.

[0032] On the other hand, if the frequency is different from the frequency detected the previous time (YES in S2), it is determined in step S3 whether (current frequency / previous frequency) is greater than 1, i.e., whether the frequency has increased.

[0033] If the frequency has increased (YES in S3), the control device 50 increases the opening of the flow rate control device 9 in step S4. If the frequency has not increased (NO in S3), the control device 50 decreases the opening of the flow rate control device 9 in step S5. When the processing of step S4 or step S5 is completed, the processing from step S1 is repeated.

[0034] As shown in Figure 3, when the frequency of the compressor 1 increases, the opening of the flow control device 9 is also increased to increase the flow rate. This is because the circulation rate of the refrigerating machine oil in the refrigerant circuit can be maintained by maintaining the relationship between the inflow rate of oil into the gas-liquid separator 3 and the outflow rate of refrigerating machine oil from the gas-liquid separator 3. In other words, the inflow rate into the gas-liquid separator 3 is proportional to the refrigerant flow rate (frequency). On the other hand, the outflow rate is determined by the opening rate of the flow control device / (differential pressure), and is therefore proportional to the opening rate. From this relationship, it is appropriate to also increase the opening rate of the flow control device 9 when the frequency of the compressor 1 increases.

[0035] 4 is a flowchart illustrating a second example of the control of the flow control device 9. The process of this flowchart is called from the main routine for controlling the refrigeration cycle apparatus and executed at regular intervals. In the example shown in FIG. 4, the flow rate of the flow control device 9 is changed based on the differential pressure before and after the flow control device 9 (for example, between the discharge pressure or temperature and the suction pressure or temperature).

[0036] First, in step S11, the control device 50 detects the differential pressure before and after the flow rate control device 9. For example, the differential pressure can be detected from the discharge pressure or temperature and the suction pressure or temperature.

[0037] Subsequently, in step S12, it is determined whether the differential pressure at the previous time is different from the currently detected differential pressure.

[0038] If the differential pressure is the same as the previous time (NO in S12), the opening degree of the flow rate control device 9 is not changed and the processing of this flowchart is ended.

[0039] On the other hand, if a differential pressure different from the differential pressure detected at the previous time is detected (YES in S12), in step S13 it is determined whether (current differential pressure / differential pressure at the previous time) is greater than 1, i.e., whether the differential pressure has increased.

[0040] If the differential pressure has increased (YES in S13), the control device 50 decreases the opening of the flow control device 9 in step S14. If the differential pressure has not increased (NO in S13), the control device 50 increases the opening of the flow control device 9 in step S15. When the processing of step S14 or step S15 ends, the processing from step S11 is repeated.

[0041] In this way, the differential pressure is detected, and when the differential pressure becomes large, the opening of the flow rate control device 9 is controlled to decrease. The reason for this is that, although it is desired to maintain the oil circulation rate in the refrigerant circuit, when the high-low pressure difference changes, the outflow rate of refrigerating machine oil from the gas-liquid separator 3 changes.

[0042] As described above, according to the refrigeration cycle apparatus shown in the first embodiment, even if the flow rate of refrigerant discharged from the compressor 1 increases, the refrigerant flow rate to the gas-liquid separator 3 can be reduced to allow excess oil to be stored in the gas-liquid separator 3. This reduces the oil circulation rate in the refrigerant circuit, thereby improving the performance of the refrigeration cycle apparatus.

[0043] Second Embodiment Fig. 5 is a diagram showing the overall configuration of a refrigeration cycle device 200 according to a second embodiment.

[0044] The refrigeration cycle apparatus 200 shown in Fig. 5 has the same configuration as the refrigeration cycle apparatus 100 shown in Fig. 1 , except that it includes an outdoor unit 220 instead of the outdoor unit 20. The outdoor unit 220 further includes a heat exchanger 10 in addition to the configuration of the outdoor unit 20 shown in Fig. 1. The heat exchanger 10 includes a flow path 10A and a flow path 10B, and is configured to exchange heat between the refrigerant flowing through the flow path 10A and the refrigerant flowing through the flow path 10B. The flow path 10A is disposed in a refrigerant flow path extending from the branching point B1 toward the refrigerant inlet of the gas-liquid separator 3. The flow path 10B is disposed in a refrigerant flow path extending from the junction J2 toward the suction port of the compressor 1.

[0045] The other configurations of the refrigeration cycle apparatus 200 are similar to those of the refrigeration cycle apparatus 100 shown in FIG. 1, and therefore description thereof will not be repeated.

[0046] In the heat exchanger 10, heat is exchanged between a high-temperature, low-flow refrigerant flowing from the branch point B1 into the flow path 10A and a low-temperature, high-flow refrigerant flowing from the evaporator into the flow path 10B. The high-temperature, low-flow refrigerant has a reduced quality factor and flows out of the flow path 10A into the gas-liquid separator 3. This refrigerant is separated into gas and liquid in the gas-liquid separator 3, and the liquid is stored in the gas-liquid separator while the gas is discharged to the junction J1, allowing excess refrigerant to be stored in the gas-liquid separator 3.

[0047] The flow of refrigerant and refrigeration oil will be described with reference to FIG. 5 . The high-temperature, high-pressure gas refrigerant and the mixed liquid of liquid refrigerant and oil discharged from compressor 1 reach branch B1, where a portion flows directly into junction J1. The remainder flows into high-temperature side flow path 10A of heat exchanger 10, located midway toward gas-liquid separator 3, at a refrigerant flow rate lower than the refrigerant flow rate discharged from compressor 1. The refrigerant flowing through flow path 10A passes through evaporator 7 and exchanges heat with refrigerant flowing through low-temperature side flow path 10B. The refrigerant that passed through flow path 10A condenses through heat exchange and becomes a mixture of refrigerant, gas refrigerant, and refrigeration oil, which then flows into gas-liquid separator 3. The high-temperature, high-pressure gas refrigerant and the mixed liquid that flowed into gas-liquid separator 3 are separated within gas-liquid separator 3. The high-pressure gas refrigerant then flows into junction J1. Some of the mixed liquid is stored in gas-liquid separator 3, and a portion passes through flow control device 9 and flows into junction J2.

[0048] Figure 6 is a Mollier diagram showing the state of the refrigerant in the refrigeration cycle device shown in Figure 5. In compressor 1, the refrigerant is compressed and becomes a high-temperature, high-pressure gas (a-b). In condenser 5, the refrigerant condenses through heat exchange with outside air (d-e). In pressure reducing device 6, the liquid refrigerant condensed in condenser 5 is reduced in pressure and changes to a two-phase state (ef). In evaporator 7, the refrigerant evaporates through heat exchange with indoor air (f-g). The above is the same as in Figure 2.

[0049] By providing the heat exchanger 10, the refrigerant (bi) flowing from the branching section B1 to the gas-liquid separator 3 exchanges heat with the refrigerant (ha) flowing from the junction J2 to the compressor 1.

[0050] The refrigerant that flows into the gas-liquid separator 3 is cooled and becomes a two-phase gas-liquid refrigerant, and is separated into a gas state (j) and a liquid state (k). The gas state refrigerant (j) discharged from the gas-liquid separator 3 merges with the refrigerant (c) flowing through the bypass flow path (d) and is condensed in the condenser 5. The liquid state refrigerant (k) discharged from the gas-liquid separator 3 flows through the liquid flow path P2, is decompressed by the flow rate control device 9, becomes a two-phase state (l), merges with the refrigerant (g) that has passed through the evaporator 7, and becomes a two-phase state (h). Thereafter, superheat is imparted in the heat exchanger 10, and becomes a gas refrigerant (a), which is then drawn into the compressor 1.

[0051] In the refrigeration cycle apparatus of the second embodiment, the heat exchanger 10 is provided to condense a portion of the refrigerant sent to the gas-liquid separator 3. This makes it easier to store excess refrigerant in the gas-liquid separator 3, and by adjusting the amount of stored refrigerant to be appropriate for the operating and installation conditions, the performance of the refrigeration cycle apparatus can be improved.

[0052] <Modification of Second Embodiment> As a modification of the second embodiment, a non-azeotropic refrigerant mixture is used in the refrigeration cycle apparatus 200 shown in Fig. 5. Examples of the non-azeotropic refrigerant mixture include R454B, R454C, and R407C.

[0053] In the case of non-azeotropic refrigerant mixtures, the composition of the excess refrigerant may change, causing changes in the circulating composition. In the case of non-azeotropic refrigerant mixtures, if excess refrigerant with a high composition ratio of low-boiling point refrigerant is stored in a refrigerant container, the composition ratio of high-boiling point refrigerant in the refrigerant circuit will increase, resulting in a decrease in performance.

[0054] Figure 7 is a diagram (T-xy diagram) showing the vapor-liquid equilibrium composition in the vapor-liquid separator. Under the condition of constant pressure P, the vertical axis of Figure 7 represents temperature T, and the horizontal axis represents mass fraction X. Mass fraction X = 0 indicates that only low-boiling-point refrigerant is present, and mass fraction X = 100 indicates that only high-boiling-point refrigerant is present. X １Ｌ indicates the ratio of low boiling point refrigerant to the liquid refrigerant, and X ２Ｌ indicates the ratio of high boiling point refrigerant to the liquid refrigerant. １Ｇ indicates the ratio of low boiling point refrigerant to gas refrigerant, and X ２Ｇ indicates the percentage of high boiling point refrigerant in the gas refrigerant.

[0055] The gas refrigerant (b) discharged from the compressor 1 is cooled by the heat exchanger 10, lowering its temperature and transitioning to a two-phase state (i). This refrigerant is a mixture of a gaseous refrigerant (j) and a liquid refrigerant (k).

[0056] When a non-azeotropic refrigerant mixture is used, the high-temperature, low-flow refrigerant flowing through the flow path 10A of the heat exchanger 10 is condensed, and the composition ratio of the condensed liquid becomes high in the high-boiling-point refrigerant (k). The mass fraction X of the high-boiling-point refrigerant in the liquid composition is X ２Ｌ (=100-X １Ｌ Therefore, a large amount of high boiling point refrigerant can be stored in the gas-liquid separator 3 that subsequently flows in. On the other hand, the mass fraction X of the low boiling point refrigerant in the refrigerant (j) having the gas composition separated in the gas-liquid separator 3 is X １Ｇ (=100-X ２Ｇ As a result, the composition ratio of the refrigerant circulating through the refrigerant circuit C1 becomes higher with respect to the low boiling point refrigerant.

[0057] For example, a refrigerant such as R454C is a mixture of R32 and R1234yf. Although R32 has a low boiling point, it has a large enthalpy difference on the Mollier diagram, making it superior in performance to R1234yf. Therefore, by storing mainly liquid refrigerant (R1234yf) in the gas-liquid separator 3, the composition of the R32 circulating refrigerant increases, increasing the theoretical COP.

[0058] In the first modification of the second embodiment, the composition ratio of the refrigerant circulating through each component is set to a state in which the low-boiling-point refrigerant is at a high ratio, thereby improving the performance of the refrigeration cycle device.

[0059] Third Embodiment In a third embodiment, another gas-liquid separator is further added. Fig. 8 is an overall configuration diagram of a refrigeration cycle apparatus 300 according to the third embodiment.

[0060] A refrigeration cycle apparatus 300 shown in Fig. 8 includes an outdoor unit 320 instead of the outdoor unit 20 in the configuration of the refrigeration cycle apparatus 100 shown in Fig. 1. The outdoor unit 320 further includes a heat exchanger 13, a gas-liquid separator 14, and a flow rate control device 15 in addition to the configuration of the outdoor unit 20 shown in Fig. 1. The gas-liquid separator 14 is inserted between the gas discharge port of the gas-liquid separator 3 and the junction J1.

[0061] The gas-liquid separator 14 discharges the gas refrigerant after gas-liquid separation to the junction J1. The gas-liquid separator 14 also flows the liquid after gas-liquid separation to the junction J3 via the liquid flow path P2. The flow rate control device 15 is disposed in the liquid flow path P2 and controls the flow rate of the liquid passing through.

[0062] The heat exchanger 13 includes a flow path 13A and a flow path 13B, and is configured so that the refrigerant flowing through the flow path 13A exchanges heat with the refrigerant flowing through the flow path 13B. The flow path 13A is disposed in a refrigerant flow path extending from the gas outlet of the gas-liquid separator 3 toward the gas-liquid separator 14. The flow path 13B is disposed in a refrigerant flow path extending from the junction J3 toward the junction J2.

[0063] The other configuration of the refrigeration cycle apparatus 300 is similar to the configuration of the refrigeration cycle apparatus 100 shown in FIG. 1, and therefore description thereof will not be repeated.

[0064] In the heat exchanger 13, heat is exchanged between the high-temperature, low-flow rate refrigerant discharged from the gas-liquid separator 3 and the low-temperature, high-flow rate refrigerant flowing from the junction J3 to the junction J2. The high-temperature, low-flow rate refrigerant has a reduced quality fraction and flows out of the flow path 13A into the gas-liquid separator 14. This refrigerant is separated into gas and liquid in the gas-liquid separator 14, and the liquid refrigerant is stored in the gas-liquid separator 14 while the gas refrigerant is discharged to the junction J1, allowing the excess refrigerant to be stored in the gas-liquid separator 14.

[0065] With this configuration, the excess oil can be stored mainly in the gas-liquid separator 3, and the excess refrigerant can be stored mainly in the gas-liquid separator 14.

[0066] The flow of the refrigerant and refrigeration oil will be described with reference to Figure 8. The high-temperature, high-pressure gas refrigerant and the mixture of liquid refrigerant and oil discharged from the compressor 1 reach the branching point B1, where a portion of the refrigerant flows directly to the junction point J1, and the remainder flows toward the gas-liquid separator 3 at a refrigerant flow rate that is lower than the refrigerant flow rate discharged from the compressor 1.

[0067] The high-temperature, high-pressure gas refrigerant and the mixed liquid that flow into the gas-liquid separator 3 are separated in the gas-liquid separator 3. A certain amount of the separated mixed liquid is stored in the gas-liquid separator 3, and a portion of it passes through the flow control device 9 and flows into the junction J2. Meanwhile, the high-pressure gas refrigerant separated in the gas-liquid separator 3 flows through the high-temperature side flow path 13A of the heat exchanger 13. On the other hand, the low-temperature, low-pressure refrigerant that has passed through the evaporator 7 flows through flow path 13B. The gas refrigerant that passes through flow path 13A exchanges heat with the low-temperature side refrigerant that passes through flow path 13B, and a portion of it is condensed. The gas refrigerant and mixed liquid (including the condensed liquid) that have passed through flow path 13A flow into the gas-liquid separator 14. The high-temperature, high-pressure gas refrigerant and mixed liquid that flow into the gas-liquid separator 14 are separated in the gas-liquid separator 14. The separated high-pressure gas refrigerant flows into the confluence J1, and a certain amount of the separated mixed liquid is stored in the gas-liquid separator 14, and a portion of it passes through the flow control device 15 and flows into the confluence J3.

[0068] Fig. 9 is a Mollier diagram showing the state of the refrigerant in the refrigeration cycle device shown in Fig. 8. The Mollier diagram shown in Fig. 9 shows state changes that are a combination of Fig. 2 and Fig. 6.

[0069] The flow rate adjusting devices 9 and 15 are basically controlled in the same way as in FIG. 3 or FIG.

[0070] 5, when the amount of inflowing oil is high, the oil concentration of the liquid stored in the gas-liquid separator 3 is determined by the local oil concentration calculated from the dryness fraction of the refrigerant and the oil circulation rate. When a mixture with a high dryness fraction and a high oil circulation rate flows into the gas-liquid separator 3, almost no liquid refrigerant can be stored in the gas-liquid separator 3, reducing its effectiveness.

[0071] According to the third embodiment, two gas-liquid separators are provided, so that both excess oil and excess refrigerant can be stored, thereby improving performance.

[0072] <Modification of Third Embodiment> FIG. 10 is a diagram showing the overall configuration of a refrigeration cycle apparatus 300A according to a modification of the third embodiment.

[0073] A refrigeration cycle apparatus 300A shown in Fig. 10 has the same configuration as the refrigeration cycle apparatus 300 shown in Fig. 8, except that it has an outdoor unit 320A instead of the outdoor unit 320. The outdoor unit 320A further has a switching valve 16 arranged midway through the bypass flow path P0, in addition to the configuration of the outdoor unit 320 shown in Fig. 8. When the switching valve 16 is opened, the bypass flow path P0 is communicated, and when the switching valve 16 is closed, the bypass flow path P0 is closed. An on-off valve, a solenoid valve, an expansion valve, or the like can be used as the switching valve 16.

[0074] The other parts of the configuration of the refrigeration cycle apparatus 300A are similar to the configuration of the refrigeration cycle apparatus 300 shown in FIG. 8, and therefore description thereof will not be repeated.

[0075] Fig. 11 is a diagram showing the flow of refrigerant and refrigeration oil during normal operation. Fig. 12 is a diagram showing the flow of refrigerant and refrigeration oil during variable operation. In Fig. 11 and Fig. 12, solid arrows indicate the flow of refrigerant, and dashed arrows indicate the flow of refrigeration oil.

[0076] During normal operation shown in Fig. 11, the switching valve 16 is open, and the refrigerant and refrigeration oil circulate as in the third embodiment. In contrast, during fluctuation operation shown in Fig. 12, the switching valve 16 is closed. During fluctuation operation shown in Fig. 12, the high-temperature, high-pressure gas refrigerant and mixed liquid (liquid refrigerant + oil) discharged from the compressor 1 flow into the branching section B1, but because the switching valve 16 is closed, all of the refrigerant and mixed liquid flow into the gas-liquid separator 3. The high-temperature, high-pressure gas refrigerant and mixed liquid that flow into the gas-liquid separator 3 are separated into the gas refrigerant and the mixed liquid within the gas-liquid separator 3. The separated mixed liquid is stored to a certain extent within the gas-liquid separator 3, and a portion of it passes through the flow control device 9 and flows to the junction J2.

[0077] The mixed liquid that has not been completely separated from the high-pressure gas refrigerant in the gas-liquid separator 3 flows into the high-temperature side flow path 13A of the heat exchanger 13. The mixed liquid that has flowed into the flow path 13A exchanges heat with the low-temperature low-pressure refrigerant that has flowed out of the evaporator 7 and is passing through the flow path 13B.

[0078] After heat exchange, the gas refrigerant and mixed liquid flowing into the gas-liquid separator 14 are separated in the gas-liquid separator 14. The high-pressure gas refrigerant separated in the gas-liquid separator 14 flows into the junction J1. A certain amount of the mixed liquid separated in the gas-liquid separator 14 is stored in the gas-liquid separator 14, and a portion of it passes through the flow rate control device 15 and flows into the junction J3.

[0079] 13 is a flowchart for explaining the control of the switching valve 16. The process of this flowchart is called from the main routine for controlling the refrigeration cycle apparatus and executed every time a predetermined time elapses.

[0080] First, in step S31, the control device 50 detects an operation signal (or compressor operation) and determines whether the compressor 1 is operating. If the compressor 1 is not operating (NO in S31), the processing of this flowchart ends. On the other hand, if the compressor 1 is operating (YES in S31), the control device 50 detects the operation mode and determines whether the operation mode is normal operation in step S32.

[0081] For example, the control device 50 determines that the operating mode is not normal operation when the fluctuation value of the compressor operating frequency is greater than a reference value, when the mode is switched from heating to cooling or defrosting operation, when there is an unstable period from startup until a certain time has passed, or when the degree of superheat of the refrigerant discharged from compressor 1 is lower than the target value.

[0082] If the operation mode is normal operation in step S32 (YES in S32), the control device 50 opens the switching valve 16 in step S33. On the other hand, if the operation mode is not normal operation (variable operation) in step S32 (NO in S32), the control device 50 closes the switching valve 16 in step S34.

[0083] When the process of step S33 or step S34 is completed, the process from step S31 is executed again after a certain time has elapsed.

[0084] In this way, by providing the switching valve 16 in the bypass flow path P0 and routing the entire refrigerant flow through two gas-liquid separators during variable operation such as startup or compressor frequency fluctuation, separation efficiency during variable operation is improved, thereby increasing the amount of oil returned to the compressor and improving reliability during variable operation.

[0085] (Summary) Hereinafter, the present embodiment will be summarized with reference to the drawings again.

[0086] (Item 1) The present disclosure relates to a refrigeration cycle apparatus 100 including a refrigerant circuit through which a refrigerant circulates. The refrigeration cycle apparatus 100 shown in FIG. 1 includes a refrigerant circuit C1 including a compressor 1, a first gas-liquid separator 3, a condenser 5, a pressure reduction device 6, and an evaporator 7. The refrigeration cycle apparatus 100 further includes a bypass flow path P0, a first liquid flow path P1, and a first flow control device 9. The first gas-liquid separator 3 is disposed on the discharge port side of the compressor 1 in the refrigerant circuit C1. Gas refrigerant discharged from the first gas-liquid separator 3 in the refrigerant circuit C1 passes through the condenser 5. The pressure reduction device 6 reduces the pressure of the refrigerant that has passed through the condenser 5 in the refrigerant circuit C1. The refrigerant that has been depressurized by the pressure reduction device 6 in the refrigerant circuit C1 passes through the evaporator 7. The bypass flow path P0 branches off from a branch point B1 in the refrigerant circuit C1 between the compressor 1 and the first gas-liquid separator 3, and merges into a first junction J1 in the refrigerant circuit C1 between the first gas-liquid separator 3 and the condenser 5. The first liquid flow path P1 connects a second junction J2 in the refrigerant circuit C1 between the evaporator 7 and the compressor 1, to a liquid outlet of the first gas-liquid separator 3. The first flow control device 9 is disposed in the first liquid flow path P1, and is configured to be able to adjust the flow rate of the fluid flowing through the first liquid flow path P1.

[0087] With this configuration, even if the refrigerant flow rate discharged from the compressor 1 increases, the refrigerant flow rate to the gas-liquid separator 3 can be reduced by the bypass flow path P0, preventing the liquid from being re-entrained, and excess oil can be stored in the gas-liquid separator 3. This reduces the oil circulation rate in the refrigerant circuit C1, thereby improving the performance of the refrigeration cycle device.

[0088] (Section 2) As shown in Figure 5, the refrigeration cycle device described in Section 1 further includes a heat exchanger 10 configured to exchange heat between the refrigerant flowing from the branching section B1 toward the refrigerant inlet of the first gas-liquid separator 3 and the refrigerant flowing from the second merging section J2 toward the suction port of the compressor 1.

[0089] With this configuration, the dryness of the refrigerant flowing into the gas-liquid separator 3 is reduced, allowing excess refrigerant to be stored in the gas-liquid separator 3, and an appropriate amount of refrigerant to circulate depending on the operating and installation conditions, thereby further improving the performance of the refrigeration cycle device.

[0090] (Clause 3) The refrigerant circulating through the refrigerant circuit C1 of the refrigeration cycle device described in clause 1 is a non-azeotropic refrigerant mixture.

[0091] By adopting such a configuration, the composition ratio of the refrigerant circulating through each component can be made high with low boiling point refrigerant, thereby improving the performance of the refrigeration cycle device.

[0092] (Item 4) As shown in FIG. 8 , the refrigeration cycle apparatus described in item 1 further includes a second gas-liquid separator 14, a second liquid flow path P2, a second flow control device 15, and a heat exchanger 13. The second gas-liquid separator 14 is connected in series with the first gas-liquid separator 3 in the refrigerant circuit C1 between the branching point B1 and the first junction J1. The second liquid flow path P2 allows liquid discharged from the second gas-liquid separator 14 to flow to a third junction J3 provided in the refrigerant circuit C1 between the second junction J2 and the evaporator 7. The second flow control device 15 is disposed in the second liquid flow path P2 and is configured to adjust the flow rate of the fluid flowing through the second liquid flow path P2. The heat exchanger 13 is configured to exchange heat between the refrigerant flowing from the gas outlet of the first gas-liquid separator 3 toward the refrigerant inlet of the second gas-liquid separator 14 and the refrigerant flowing from the third junction J3 toward the second junction J2.

[0093] By using this configuration, excess oil can be stored in the first gas-liquid separator and excess refrigerant can be stored in the second gas-liquid separator, so that both excess oil and excess refrigerant can be stored, thereby improving the performance of the refrigeration cycle device.

[0094] (Item 5) As shown in FIG. 10 , the refrigeration cycle apparatus described in item 4 further includes a third flow control device (switching valve 16) that is provided in the bypass flow path P0 and is configured to be able to adjust the amount of refrigerant passing through the bypass flow path P0.

[0095] By adopting this configuration, the discharged refrigerant is passed through two gas-liquid separators during variable operation such as startup, thereby increasing the total gas-liquid separation efficiency and increasing the amount of oil returned to compressor 1, thereby improving the reliability of the refrigeration cycle device during variable operation.

[0096] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims.

[0097] 1 Compressor, 3, 14 Gas-liquid separator, 5 Condenser, 6 Pressure reducing device, 7 Evaporator, 8, 10, 13 Heat exchanger, 9, 15 Flow control device, 10A, 10B, 13A, 13B, P0, P1, P2 Flow path, 16 Switching valve, 20, 220, 320, 320A Outdoor unit, 30 Indoor unit, 41, 42 Extension piping, 50 Control device, 51 CPU, 52 Memory, 100, 200, 300, 300A Refrigeration cycle device, B1 Branch section, C1 Refrigerant circuit, J1, J2, J3 Confluence section.

Claims

1. A refrigeration cycle apparatus comprising a refrigerant circuit through which a refrigerant circulates, the refrigerant circuit including: a compressor; a first gas-liquid separator disposed on a discharge port side of the compressor in the refrigerant circuit; a condenser through which gas refrigerant discharged from the first gas-liquid separator in the refrigerant circuit passes; a pressure reducing device which reduces the pressure of the refrigerant which has passed through the condenser in the refrigerant circuit; and an evaporator through which the refrigerant depressurized by the pressure reducing device passes in the refrigerant circuit, the refrigeration cycle apparatus further comprising: a bypass flow path which branches off from a branching portion between the compressor and the first gas-liquid separator in the refrigerant circuit and merges into a first junction between the first gas-liquid separator and the condenser in the refrigerant circuit; a first liquid flow path which connects a second junction between the evaporator and the compressor in the refrigerant circuit and a liquid discharge port of the first gas-liquid separator; and a first flow control device disposed in the first liquid flow path and configured to be able to adjust a flow rate of a fluid flowing through the first liquid flow path.

2. The refrigeration cycle device of claim 1, further comprising a heat exchanger configured to exchange heat between the refrigerant flowing from the branching portion toward the refrigerant inlet of the first gas-liquid separator and the refrigerant flowing from the second junction portion toward the suction port of the compressor.

3. A refrigeration cycle device according to claim 1, wherein the refrigerant circulating through the refrigerant circuit is a non-azeotropic refrigerant mixture.

4. The refrigeration cycle apparatus according to claim 1, further comprising: a second gas-liquid separator connected in series with the first gas-liquid separator between the branching portion and the first junction in the refrigerant circuit; a second liquid flow path for flowing liquid discharged from the second gas-liquid separator to a third junction provided in the refrigerant circuit between the second junction and the evaporator; a second flow control device disposed in the second liquid flow path and configured to be able to adjust the flow rate of fluid flowing in the second liquid flow path; and a heat exchanger configured to exchange heat between the refrigerant flowing from the gas discharge port of the first gas-liquid separator toward the refrigerant inlet of the second gas-liquid separator and the refrigerant flowing from the third junction to the second junction.

5. The refrigeration cycle apparatus according to claim 4, further comprising a third flow rate control device provided in the bypass flow passage and configured to be able to adjust the amount of refrigerant passing through the bypass flow passage.

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