JP7542579B2 - Refrigeration Cycle Equipment - Google Patents

Description

This disclosure relates to a refrigeration cycle device.

In recent years, two-stage compression refrigeration cycles have been adopted to improve the performance of refrigerators and air conditioners. The two compressors used in this system are filled with lubricating oil, but if the oil level in one of the compressors becomes low, that compressor may break down. For this reason, it is necessary to keep the amount of oil in the two compressors constant.

Patent Document 1 discloses a two-stage compression refrigeration cycle device equipped with an oil-equalizing mechanism that keeps the oil in the low-stage compressor and the high-stage compressor equal. The oil-equalizing mechanism includes an oil storage tank, a first oil-equalizing pipe that connects the oil storage tank to the low-stage compressor, and a second oil-equalizing pipe that connects the oil storage tank to the high-stage compressor, and each oil-equalizing pipe is provided with a valve. By opening and closing the valve, oil from the oil storage tank is supplied to each compressor, and excess oil from each compressor is returned to the oil storage tank.

The interval between valve opening and closing is important when adjusting the amount of oil using this valve. When controlling by time, it is difficult to set an appropriate time due to the various conditions. If the interval between valve opening and closing is long, it takes a long time to supply oil to each compressor, and if the interval between valve opening and closing is short, there is a risk that the supply of oil to each compressor will be interrupted midway.

The above problem could be solved by detecting the amount of oil and opening and closing the valves, but a special device is required to detect the amount of oil in the compressors. Even if the amount of oil could be detected, if there was a shortage of oil in both compressors at the same time, opening both valves would only supply oil to the low-stage compressor, and not to the high-stage compressor. For these reasons, there is a risk that the refrigeration cycle device will not be able to maintain a constant amount of oil in each compressor.

JP 2015-68565 A

The objective of this disclosure is to provide a refrigeration cycle device that can keep the amount of oil in the low-stage compressor and the high-stage compressor constant.

The refrigeration cycle device disclosed herein includes an oil storage tank for storing oil, a low-stage compressor and a high-stage compressor for compressing a refrigerant, a supply unit for supplying oil from the oil storage tank to the low-stage compressor, a first pipe for overflowing excess oil from the low-stage compressor to supply it to the high-stage compressor, and a second pipe for overflowing excess oil from the high-stage compressor back to the oil storage tank.

With this configuration, excess oil in each compressor can be overflowed and returned to the oil storage tank. In addition, the low-stage compressor is supplied with oil from the oil storage tank by the supply unit, and the high-stage compressor is supplied with overflowed oil from the low-stage compressor. This makes it possible to keep the amount of oil in each of the low-stage compressor and high-stage compressor constant.

FIG. 1 is a configuration diagram of an air conditioner according to a first embodiment. FIG. 1 is a diagram showing the flow of oil in an air conditioner according to a first embodiment; FIG. 13 is a diagram showing the flow of oil in an air conditioner according to a second embodiment. FIG. 13 is a configuration diagram of an air conditioner according to another embodiment.

[First embodiment]
Hereinafter, a first embodiment of an air conditioner 1, which is an example of a refrigeration cycle device, will be described with reference to Figures 1 and 2. In each figure (including Figure 3), the dimensional ratios in the figure do not necessarily match the actual dimensional ratios, and the dimensional ratios between the figures do not necessarily match. The air conditioner 1 is a room air conditioner, a packaged air conditioner, a multi-air conditioner for buildings, etc. In addition, the refrigeration cycle device can also be used as a refrigerator, etc.

Figure 1 is a diagram showing the refrigeration cycle of the air conditioner 1 according to the first embodiment. The dashed arrows in Figure 1 indicate the flow of oil, the solid arrows indicate the flow of refrigerant during cooling operation, and the dotted arrows indicate the flow of refrigerant during heating operation.

As shown in FIG. 1, the air conditioner 1 is a device that performs air conditioning such as cooling and heating. The air conditioner 1 includes a heat source unit 2 (e.g., an outdoor unit) that supplies heat, and a utilization unit 3 (e.g., an indoor unit) that performs heating and cooling using the heat. The heat source unit 2 and utilization unit 3 are connected via refrigerant pipes L8 and L9. The number of heat source units 2 and utilization units 3 is not limited to one each, and may be multiple.

The heat source unit 2 (air conditioner 1) comprises an oil storage tank 4, a low-stage compressor 5, an intermediate cooler 6, a high-stage compressor 7, a four-way valve 8, a heat source heat exchanger 9, a heat source fan 10, a heat source expansion valve 11 which is a pressure reducing device on the heat source unit 2 side, a gas-liquid separator 12, and multiple check valves 13. The utilization unit 3 (air conditioner 1) comprises a utilization expansion valve 14 which is a pressure reducing device on the utilization unit 3 side, a utilization heat exchanger 15, and a utilization fan 16. The four-way valve 8 shown in Figure 1 is in a state during cooling operation.

The oil storage tank 4 is a tank in which oil (also called refrigeration oil or lubricating oil) is stored. The oil in the oil storage tank 4 is supplied to the low-stage compressor 5 by a supply unit 20 (see FIG. 2) described later. The oil in the low-stage compressor 5 returns to the oil storage tank 4 via the high-stage compressor 7. It is preferable that the amount of oil that can be stored in the oil storage tank 4 is greater than the maximum oil amount of each of the compressors 5 and 7.

In this embodiment, the oil storage tank 4 is connected to the refrigerant pipe L1 through which low-pressure refrigerant flows, and separates and temporarily stores liquid refrigerant from the refrigerant in a gas-liquid two-phase state. This makes it possible to prevent the liquid refrigerant from flowing to the low-stage compressor 5. The liquid refrigerant temporarily stored in the oil storage tank 4 becomes gas refrigerant in the oil storage tank 4 and is sucked into the low-stage compressor 5. The low-pressure refrigerant means the refrigerant that has passed through the heat source side heat exchanger 9 or the user side heat exchanger 15 and has not yet been sucked into the low-stage compressor 5. The refrigerant pipe L1 may be directly connected to the low-stage compressor 5 without passing through the oil storage tank 4.

The compressor is a two-stage compressor that compresses the refrigerant in two stages using a low-stage compressor 5 and a high-stage compressor 7. The compressors 5, 7 are, for example, reciprocating compressors, rotary compressors, screw compressors, scroll compressors, etc. The inside of each compressor 5, 7 is filled with oil. In this embodiment, the inside of each compressor 5, 7 is filled with oil evenly, but this is not limited to this.

The intermediate cooler 6 is disposed between the low-stage compressor 5 and the high-stage compressor 7. The intermediate-pressure gas refrigerant compressed by the low-stage compressor 5 is cooled by the intermediate cooler 6 and further compressed by the high-stage compressor 7. A cooling fan 6a is disposed near the intermediate cooler 6. The intermediate cooler 6 exchanges heat between the refrigerant flowing therein and the air on the heat source side (e.g., outdoors) sent in by the cooling fan 6a. The air conditioner 1 may be configured without the intermediate cooler 6.

The four-way valve 8 is a valve that switches the flow path of the refrigerant depending on the operating mode of the air conditioner 1. The four-way valve 8 switches the flow path of the refrigerant pipe L4. Refrigerant compressed by the high-stage compressor 7 flows through the refrigerant pipe L4. The four-way valve 8 switches the flow path of the refrigerant pipe L4 to the heat source side heat exchanger 9 side during cooling operation (solid arrow in Figure 1), and to the user side heat exchanger 15 side during heating operation (dotted arrow in Figure 1).

The heat source side heat exchanger 9 exchanges heat between the refrigerant flowing inside it and the heat source side air sent in from the heat source side fan 10. The heat source side fan 10 is a fan that sends the heat source side air to the heat source side heat exchanger 9, and is located near the heat source side heat exchanger 9.

The heat source side expansion valve 11 is a valve that reduces the pressure of the refrigerant condensed in the condenser (one of the heat source side heat exchanger 9 and the utilization side heat exchanger 15). The liquid refrigerant reduced in pressure by the heat source side expansion valve 11 is directed toward the evaporator (the other of the heat source side heat exchanger 9 and the utilization side heat exchanger 15). The utilization side expansion valve 14 has the same function as the heat source side expansion valve 11.

In the gas-liquid separator 12, the refrigerant in a two-phase gas-liquid state is separated into gas and liquid. The liquid refrigerant separated in the gas-liquid separator 12 flows to the heat source side heat exchanger 9 via the heat source side expansion valve 11 during heating operation, and flows to the user side heat exchanger 15 via the user side expansion valve 14 during cooling operation. The gas refrigerant separated in the gas-liquid separator 12 is sucked into the high-stage compressor 7 through the refrigerant piping L3. This reduces the amount of gas refrigerant compressed in the low-stage compressor 5, and reduces the power consumption of the low-stage compressor 5.

The refrigerant pipe L6 connecting the gas-liquid separator 12 and the heat source side expansion valve 11 is provided with a plurality (two) of check valves 13. In addition, the refrigerant pipe L7 connecting the gas-liquid separator 12 and the user side expansion valve 14 is provided with a plurality (two) of check valves 13. The plurality (four) of check valves 13 are referred to as first to fourth check valves 13a to 13d, respectively.

The first check valve 13a is arranged in the refrigerant pipe L6a from the heat source side expansion valve 11 toward the gas-liquid separator 12 so that the gas-liquid separator 12 side is the outflow side. The second check valve 13b is arranged in the refrigerant pipe L7a from the gas-liquid separator 12 toward the utilization side expansion valve 14 side so that the utilization side expansion valve 14 side is the outflow side. The third check valve 13c is arranged in the refrigerant pipe L7b from the utilization side expansion valve 14 side toward the gas-liquid separator 12 so that the gas-liquid separator 12 side is the outflow side. The fourth check valve 13d is arranged in the refrigerant pipe L6b from the gas-liquid separator 12 toward the heat source side expansion valve 11 side so that the heat source side expansion valve 11 side is the outflow side.

During cooling operation, the refrigerant in a two-phase gas-liquid state flowing from the heat source side expansion valve 11 flows into the gas-liquid separator 12 through the first check valve 13a. The liquid refrigerant separated in the gas-liquid separator 12 flows into the user side expansion valve 14 through the second check valve 13b on the low pressure side. During heating operation, the refrigerant in a two-phase gas-liquid state flowing from the user side expansion valve 14 flows into the gas-liquid separator 12 through the third check valve 13c. The liquid refrigerant separated in the gas-liquid separator 12 flows into the heat source side expansion valve 11 through the fourth check valve 13d on the low pressure side. This allows the gas-liquid separator 12 to separate the refrigerant in a two-phase gas-liquid state into gas and liquid in both cooling operation and heating operation.

The user-side heat exchanger 15 exchanges heat between the refrigerant flowing inside it and the air on the user side (e.g., indoors) sent in from the user-side fan 16. The user-side fan 16 is a fan that sends the air on the user side to the user-side heat exchanger 15, and is located near the user-side heat exchanger 15.

The refrigerant is a carbon dioxide refrigerant, but is not limited to this. For example, the refrigerant may be other types of refrigerants, such as fluorocarbon-based refrigerants or hydrocarbon-based refrigerants. Carbon dioxide refrigerants also include mixed refrigerants that are a mixture of carbon dioxide and other substances.

The solid arrows in Figure 1 indicate the flow of refrigerant during cooling operation. During cooling operation of the air conditioner 1, the refrigerant discharged from the high-stage compressor 7 flows through the four-way valve 8 into the heat source heat exchanger 9, where it is condensed by dissipating heat to air or water through heat exchange. The high-pressure gas refrigerant discharged from the high-stage compressor 7 becomes high-pressure liquid refrigerant through heat exchange in the heat source heat exchanger 9. As the high-pressure liquid refrigerant passes through the heat source expansion valve 11, it is reduced in pressure according to the opening of the heat source expansion valve 11.

The greater the opening of the heat source side expansion valve 11, the less the pressure is reduced, and the smaller the opening of the heat source side expansion valve 11, the greater the pressure reduction. During cooling operation, the heat source side expansion valve 11 may be fully open. The liquid refrigerant reduced in pressure by the heat source side expansion valve 11 flows to the utilization unit 3 via the gas-liquid separator 12 and the refrigerant pipe L8.

The low-pressure liquid refrigerant (or gas-liquid two-phase refrigerant) that flows into the utilization unit 3 is further reduced in pressure as it passes through the utilization side expansion valve 14, and flows into the utilization side heat exchanger 15. The low-pressure gas-liquid two-phase refrigerant that flows into the utilization side heat exchanger 15 absorbs heat by exchanging heat with the indoor air to cool the room, and evaporates to become low-pressure gas refrigerant. The low-pressure gas refrigerant flows into the heat source unit 2 via the refrigerant piping L9, and flows into the low-stage compressor 5 via the four-way valve 8 and the oil storage tank 4. The gas refrigerant discharged from the low-stage compressor 5 flows into the high-stage compressor 7 via the intermediate cooler 6.

The dotted arrows in Figure 1 indicate the flow of refrigerant during heating operation. During heating operation of the air conditioner 1, the refrigerant discharged from the high-stage compressor 7 flows to the utilization unit 3 via the four-way valve 8 and the refrigerant pipe L9. The high-pressure gas refrigerant that flows into the utilization unit 3 exchanges heat with the outside indoor air in the utilization side heat exchanger 15, dissipating heat, and heating is performed. Through heat exchange in the utilization side heat exchanger 15, the high-pressure gas refrigerant dissipates heat and condenses to become high-pressure liquid refrigerant. When the high-pressure liquid refrigerant passes through the utilization side expansion valve 14, it is reduced in pressure depending on the opening of the utilization side expansion valve 14. Note that the utilization side expansion valve 14 may also be fully open.

The refrigerant that has passed through the user-side expansion valve 14 flows to the heat source unit 2 via the refrigerant pipe L8. The liquid refrigerant that has flowed to the heat source unit 2 is further decompressed according to the opening degree when passing through the heat source-side expansion valve 11 via the gas-liquid separator 12, and flows into the heat source-side heat exchanger 9. The low-pressure gas-liquid two-phase refrigerant that has flowed into the heat source-side heat exchanger 9 absorbs heat from the external air or water and evaporates. As a result, the low-pressure gas-liquid two-phase refrigerant becomes a low-pressure gas refrigerant. The low-pressure gas refrigerant flows into the low-stage compressor 5 via the four-way valve 8 and the oil storage tank 4. The gas refrigerant discharged from the low-stage compressor 5 flows into the high-stage compressor 7 via the intermediate cooler 6.

Next, the oil piping of the oil storage tank 4, the low-stage compressor 5, and the high-stage compressor 7 will be described with reference to FIG. 2. FIG. 2 is a diagram showing the flow of oil in the air conditioner 1 according to the first embodiment. In FIG. 2, the dashed arrows indicate the flow of oil, and the solid arrows indicate the flow of refrigerant.

As shown in FIG. 2, the air conditioner 1 includes a supply section 20 that supplies (allows the oil OL in) the oil storage tank 4 to the low-stage compressor 5, a first pipe 21 that allows the excess oil OL in the low-stage compressor 5 to overflow and supply (allows the oil OL in) to the high-stage compressor 7, and a second pipe 22 that allows the excess oil OL in the high-stage compressor 7 to overflow and return to the oil storage tank 4. With this configuration, the excess oil OL in the low-stage compressor 5 and the high-stage compressor 7 can be overflowed and returned to the oil storage tank 4. In addition, the low-stage compressor 5 is supplied with oil OL from the oil storage tank 4, and the high-stage compressor 7 is supplied with oil OL that has overflowed from the low-stage compressor 5. This allows the amount of oil in each of the compressors 5 and 7 to be kept constant. As a result, it is possible to prevent the oil OL from being biased to one of the compressors 5 and 7 and the other from being insufficient.

The supply unit 20 includes a third pipe 201 that supplies (flows into) the oil OL and gas refrigerant in the oil storage tank 4 to the low-stage compressor 5, and a U-shaped tube 202 arranged inside the oil storage tank 4. One end 202a of the U-shaped tube 202 is connected to the third pipe 201, and the other end 202b opens inside the oil storage tank 4. The U-shaped tube 202 includes not only a tube formed in a U shape, but also a V-shaped tube or a tube with an angular portion that is approximately U-shaped.

The U-shaped tube 202 has a through hole 202c provided below the other end 202b. With this configuration, when the oil level of the oil OL stored in the oil storage tank 4 is located above the through hole 202c, the oil OL penetrates into the inside of the U-shaped tube 202. At that time, the oil OL that penetrates into the inside of the U-shaped tube 202 is supplied to the low-stage compressor 5 by the gas refrigerant flowing from the other end 202b of the U-shaped tube 202 toward the low-stage compressor 5. The through hole 202c is preferably provided on the lower end side of the U-shaped tube 202. The flow rate of oil supplied to the low-stage compressor 5 can be adjusted by the position, size, number, etc. of the through holes 202c.

The first piping 21 includes a first overflow pipe 211. The first overflow pipe 211 is disposed inside the low-stage compressor 5. In this embodiment, the first overflow pipe 211 is inserted from the side of the low-stage compressor 5 and disposed inside the low-stage compressor 5 at an incline with respect to the vertical direction. The first overflow pipe 211 is bent inside the low-stage compressor 5. Note that the first overflow pipe 211 is not limited to this, and may be configured, for example, as a straight pipe inserted from the bottom of the low-stage compressor 5 and disposed along the vertical direction inside the low-stage compressor 5.

The first pipe 21 is preferably connected to at least one of the refrigerant pipe L2 through which the gas refrigerant compressed by the low-stage compressor 5 flows (is discharged) and the refrigerant pipe L3 through which the gas refrigerant separated by the gas-liquid separator 12 (see FIG. 1) flows. As a result, the oil discharged from the first overflow pipe 211 is supplied (flows into) the high-stage compressor 7 by the flow of the gas refrigerant. In this embodiment, the first pipe 21 is connected to both the refrigerant pipe L2 and the refrigerant pipe L3. Note that the first pipe 21 does not have to be connected to the refrigerant pipe L2 and the refrigerant pipe L3. In this case, a transport means (e.g., a pump, etc.) is required to transport the oil in the first pipe 21 to the high-stage compressor 7.

One end of the refrigerant pipe L2 is connected to the top of the low-stage compressor 5, and the other end is connected to the first pipe 21 or the refrigerant pipe L3. An intermediate cooler 6 is provided in the middle of the refrigerant pipe L2. One end of the refrigerant pipe L3 is connected to the gas-liquid separator 12, and the other end is connected to the first pipe 21 or the refrigerant pipe L2.

The second pipe 22 is connected to the oil storage tank 4. In this embodiment, the second pipe 22 is connected to the oil storage tank 4 via the refrigerant pipe L1, but is not limited to this. For example, the second pipe 22 may be connected directly to the oil storage tank 4.

The second piping 22 includes a second overflow pipe 221. The second overflow pipe 221 is disposed inside the high-stage compressor 7. In this embodiment, the second overflow pipe 221 is inserted from the side of the high-stage compressor 7 and disposed inside the high-stage compressor 7 at an incline with respect to the vertical direction. The second overflow pipe 221 is bent inside the high-stage compressor 7. Note that the second overflow pipe 221 is not limited to this, and may be, for example, a straight pipe inserted from the bottom of the high-stage compressor 7 and disposed along the vertical direction inside the high-stage compressor 7. The oil discharged from the second overflow pipe 221 flows (returns) to the low-pressure oil storage tank 4 due to the pressure difference.

In this embodiment, the shape and size of the second overflow pipe 221 are substantially the same as the shape and size of the first overflow pipe 211, but are not limited to this.

The second pipe 22 is preferably provided with a fixed resistor 222 that reduces the oil flow rate. This allows the pressure in the second pipe 22 to be reduced, and prevents gas refrigerant from entering the second overflow pipe 221. The fixed resistor 222 is, for example, a capillary tube.

The refrigerant pipe L4 through which the gas refrigerant compressed by the high-stage compressor 7 flows (discharges) has one end connected to the top of the high-stage compressor 7 and the other end connected to the four-way valve 8 (see Figure 1).

[Second embodiment]
Next, a second embodiment of the air conditioner 1, which is an example of a refrigeration cycle device, will be described with reference to Fig. 3. Descriptions of configurations similar to those of the first embodiment will be omitted, and differences will be mainly described. Configurations already described in the first embodiment are given the same reference numerals. Fig. 3 is a diagram showing the flow of oil in the air conditioner 1 according to the second embodiment. In Fig. 3, dashed arrows indicate the flow of oil, and solid arrows indicate the flow of refrigerant.

As shown in FIG. 3, the air conditioner 1 includes a refrigerant pipe L5 through which the refrigerant compressed by the high-stage compressor 7 flows (discharges), and an oil separator 23 connected to the refrigerant pipe L5. The oil separator 23 separates oil from the gas refrigerant flowing through the refrigerant pipe L5, for example, by gravity. In this embodiment, the refrigerant pipe L5 is connected to the oil separator 23 via the second pipe 22. The oil separator 23 is disposed between the high-stage compressor 7 and the oil storage tank 4. Note that the refrigerant pipe L5 and the second pipe 22 may be connected to the oil separator 23 separately, for example. Also, the second pipe 22 may not be connected to the oil separator 23, for example.

It is preferable that the oil separator 23 is empty of oil inside. This prevents the oil in the oil separator 23 from being stirred up by the gas refrigerant and flowing into the heat source side heat exchanger 9 (user side heat exchanger 15) together with the gas refrigerant. The fixed resistor 222 is disposed closer to the oil storage tank 4 than the oil separator 23. If the amount of oil returned by the fixed resistor 222 is made greater than the amount of oil supplied to the low stage compressor 5 in the supply section 20, the oil separator 23 will always be empty of oil.

One end of the refrigerant pipe L5 is connected to the top of the high-stage compressor 7, and the other end is connected to the second pipe 22 on the high-stage compressor 7 side of the oil separator 23. This allows the oil discharged from the second overflow pipe 221 to flow into the oil separator 23 by the flow of the refrigerant. In this embodiment, one end of the refrigerant pipe L4 is connected to the top of the oil separator 23, and the other end is connected to the four-way valve 8.

[1]
As described above, the refrigeration cycle apparatus of the present disclosure comprises an oil storage tank 4 in which oil is stored, a low-stage compressor 5 and a high-stage compressor 7 which compress the refrigerant, a supply section 20 that supplies oil from the oil storage tank 4 to the low-stage compressor 5, a first pipe 21 through which excess oil from the low-stage compressor 5 overflows and supplies it to the high-stage compressor 7, and a second pipe 22 through which excess oil from the high-stage compressor 7 overflows and is returned to the oil storage tank 4.

With this configuration, excess oil in the low-stage compressor 5 and high-stage compressor 7 can be overflowed and returned to the oil storage tank 4. In addition, the low-stage compressor 5 is supplied with oil from the oil storage tank 4, and the high-stage compressor 7 is supplied with overflowed oil from the low-stage compressor 5. This allows the amount of oil in each of the compressors 5 and 7 to be kept constant.

[2]
In the above refrigeration cycle device of [1], the oil storage tank 4 is connected to a refrigerant pipe L1 through which a low-pressure refrigerant flows, and the supply unit 20 includes a third pipe 201 that supplies the oil and refrigerant (gas refrigerant) in the oil storage tank 4 to the low-stage compressor 5, and a U-shaped tube 202 arranged in the oil storage tank 4, wherein one end 202a of the U-shaped tube 202 is connected to the third pipe 201 and the other end 202b opens in the oil storage tank 4, and the U-shaped tube 202 is preferably configured to have a through hole 202c provided below the other end 202b.

According to this configuration, when the oil level of the oil stored in the oil storage tank 4 is located above the through hole 202c, the oil penetrates into the inside of the U-shaped tube 202. At that time, the oil in the U-shaped tube 202 is supplied to the low-stage compressor 5 by the gas refrigerant flowing from the other end 202b of the U-shaped tube 202 toward the low-stage compressor 5. As a result, when the oil filled in each compressor 5, 7 is insufficient, that is, when oil is accumulated in the oil storage tank 4, oil can be supplied to each compressor 5, 7, and a shortage of oil in each compressor 5, 7 can be prevented.

[3]
It is preferable that the refrigeration cycle device of the above [1] or [2] is configured to include a refrigerant pipe L5 through which the refrigerant compressed by the high-stage side compressor 7 flows, and an oil separator 23 connected to the refrigerant pipe L5.

With this configuration, the oil stirred up by the gas refrigerant can be separated in the oil separator 23. This makes it possible to prevent oil from entering the heat source side heat exchanger 9 or the user side heat exchanger 15.

[4]
In the refrigeration cycle device of any one of the above items [1] to [3], the refrigerant is preferably carbon dioxide refrigerant.

With this configuration, the environmental impact can be reduced by using carbon dioxide refrigerant, which has a low global warming potential (GWP). In addition, by using multiple compressors 5, 7, the performance of carbon dioxide refrigerant, which requires a larger amount of energy than fluorocarbon refrigerants (e.g., R32), can be ensured.

The refrigeration cycle device is not limited to the configuration of the above-mentioned embodiment, nor is it limited to the above-mentioned effects. Furthermore, the refrigeration cycle device can of course be modified in various ways without departing from the spirit of the present invention. For example, it is of course possible to arbitrarily select one or more of the configurations, methods, etc. of the various modified examples described below and adopt them in the configurations, methods, etc. of the above-mentioned embodiment.

(A) In this embodiment, the supply unit 20 is configured to include a U-shaped tube 202, but is not limited to this. For example, the supply unit 20 may be configured to include a supply pump that supplies oil to the low-stage compressor 5 without including a U-shaped tube 202. In such a configuration, a refrigerant pipe that supplies refrigerant to the low-stage compressor 5 and an oil pipe that supplies oil are provided separately.

(B) In this embodiment, the air conditioner 1 is configured to include a gas-liquid separator 12, but is not limited to this. For example, as shown in FIG. 4, the air conditioner 1 may be configured to include an economizer 17 (also called a subcooler 17). In such a configuration, the air conditioner 1 does not include a gas-liquid separator 12 and a check valve 13.

The economizer 17 is disposed in the same position as the gas-liquid separator 12 in FIG. 1. That is, the economizer 17 is disposed in the middle of the refrigerant piping that connects the heat source side expansion valve 11 and the user side expansion valve 14, and is connected to the refrigerant piping L3. The refrigerant piping L10 that connects the heat source side expansion valve 11 and the economizer 17 is connected to the refrigerant piping L11 that is connected to the economizer 17. The refrigerant piping L11 is provided with a bypass expansion valve 18 that reduces the pressure of the refrigerant flowing through the refrigerant piping L11.

The refrigerant flowing in from one of the refrigerant pipes L8, L10 is supercooled by the economizer 17 and flows to the other. Then, the refrigerant flowing from the refrigerant pipe L10 to the refrigerant pipe L11 is depressurized by the bypass expansion valve 18 and flows into the economizer 17. As a result, heat is exchanged between the refrigerant flowing in from one of the refrigerant pipes L8, L10 and the refrigerant depressurized by the bypass expansion valve 18, and the refrigerant depressurized by the bypass expansion valve 18 becomes a gas refrigerant and flows into the high-stage compressor 7 through the refrigerant pipe L3.

1...Air conditioner (refrigeration cycle device), 2...Heat source unit, 3...Utilization unit, 4...Oil storage tank, 5...Low stage compressor, 6...Intermediate cooler, 6a...Cooling fan, 7...High stage compressor, 8...Four-way valve, 9...Heat source heat exchanger, 10...Heat source fan, 11...Heat source expansion valve, 12...Gas-liquid separator, 13...Check valve, 14...Utilization expansion valve, 15...Utilization heat exchanger, 16...Utilization fan, 17...Economizer, 18...Bypass expansion valve, 20...Supply section, 201...Third pipe, 202...U-shaped pipe, 202c...Through hole, 21...First pipe, 211...First overflow pipe, 22...Second pipe, 221...Second overflow pipe, 222...Fixed resistor, 23...Oil separator

Claims (5)

an oil storage tank in which oil is stored;
a low-stage compressor and a high-stage compressor for compressing a refrigerant;
a supply unit that supplies oil from the oil storage tank to the low-stage compressor;
a first pipe through which excess oil from the low-stage compressor is allowed to overflow and supplied to the high-stage compressor;
a second pipe through which excess oil of the high-stage compressor is allowed to overflow and returned to the oil storage tank ;
the first piping includes a first overflow pipe disposed inside the low-stage compressor,
the second piping includes a second overflow pipe disposed inside the high-stage compressor,
A refrigeration cycle apparatus , wherein the first overflow pipe and/or the second overflow pipe is inclined with respect to a vertical direction . The refrigeration cycle apparatus according to claim 1 , wherein the first overflow pipe and/or the second overflow pipe is bent inside the compressor. The oil storage tank is connected to a refrigerant pipe through which a low-pressure refrigerant flows,
the supply unit includes a third pipe that supplies the oil and the refrigerant in the oil storage tank to the low-stage compressor, and a U-shaped pipe that is disposed inside the oil storage tank;
The U-shaped tube has one end connected to the third pipe and the other end opening in the oil storage tank,
The refrigeration cycle apparatus according to claim 1 , wherein the U-shaped tube has a through hole provided below the other end. a refrigerant pipe through which the refrigerant compressed by the high-stage compressor flows;
The refrigeration cycle apparatus according to claim 1 , further comprising an oil separator connected to the refrigerant pipe. The refrigeration cycle device according to any one of claims 1 to 4 , wherein the refrigerant is a carbon dioxide refrigerant.