Heat pump device

Abstract

To improve efficiency by maintaining a good gas-liquid two-phase intermediate-pressure refrigerant supply to the internal heat exchanger. [Solution] The heat pump device (1) is configured with a low-stage compressor (11), a high-stage compressor (12), a condenser (13), an internal heat exchanger (17) for cooling the high-pressure refrigerant condensed by the condenser, a high-stage expansion valve (V1) for depressurizing and expanding the high-pressure refrigerant condensed by the internal heat exchanger to an intermediate pressure, a gas-phase side outlet (P43) of a gas-liquid separator (14) for separating the gas-liquid two-phase refrigerant from the high-stage expansion valve, and an intermediate pipe (L7) connecting the discharge port (P12) of the low-stage compressor and the suction port (P21) of the high-stage compressor. The device further includes a liquid return pipe (L8) that branches off from the high-stage expansion pipe (L5) on the internal heat exchanger side of the high-stage expansion valve and merges with the intermediate pipe on the gas-liquid separator side of the internal heat exchanger, and a liquid return expansion valve (V3) provided in the liquid return pipe for depressurizing and expanding the high-pressure refrigerant condensed by the internal heat exchanger to a gas-liquid two-phase refrigerant.

Description

Technical Field

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[0001] The present invention relates to a heat pump device, and more particularly to a heat pump device having a two-stage compression type.

Background Art

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[0006] A heat pump device according to one embodiment of the present invention includes an evaporator that evaporates a low-pressure refrigerant with heat recovered from a heat source water, a low-stage compressor that compresses the low-pressure refrigerant to an intermediate pressure, a high-stage compressor that compresses the intermediate-pressure refrigerant to a high pressure, a condenser that condenses the high-pressure refrigerant and heats the heating medium, an internal heat exchanger that cools the high-pressure refrigerant condensed by the condenser, and the high-pressure refrigerant condensed by the internal heat exchanger By increasing or decreasing the valve opening A heat pump device with a two-stage compression-two-stage expansion cycle, comprising: a high-stage expansion valve that depressurizes and expands to the intermediate pressure; a gas-liquid separator that separates the gas-liquid two-phase refrigerant from the high-stage expansion valve into gas and liquid phases; an intermediate pipe connecting the gas-phase side outlet of the gas-liquid separator to the discharge port of the low-stage compressor and the suction port of the high-stage compressor; and a low-stage expansion valve that depressurizes and expands the liquid-phase intermediate-pressure refrigerant introduced from the liquid-phase side outlet of the gas-liquid separator to reduce pressure, wherein the internal heat exchanger heats the intermediate-pressure refrigerant flowing through the intermediate pipe with the high-pressure refrigerant condensed by the condenser, the high-stage expansion valve is provided in the high-stage expansion pipe connected from the internal heat exchanger to the gas-liquid separator, and a liquid return pipe that branches off from the high-stage expansion valve in the high-stage expansion pipe on the internal heat exchanger side and merges with the intermediate pipe on the gas-liquid separator side of the internal heat exchanger, and provided in the liquid return pipe, By increasing or decreasing the valve opening A liquid return expansion valve that depressurizes and expands the high-pressure refrigerant condensed by the internal heat exchanger to convert it into a gas-liquid two-phase refrigerant. The system further comprises: a pressure sensor that detects the pressure of the intermediate-pressure refrigerant heated in the internal heat exchanger in the intermediate piping; a temperature sensor that detects the temperature of the intermediate-pressure refrigerant; and a control unit that controls the valve opening of the liquid return expansion valve based on the detection results of the pressure sensor and the temperature sensor. The control unit calculates the saturation temperature from the pressure value detected by the pressure sensor, calculates the degree of superheating from the saturation temperature and the temperature value detected by the temperature sensor, and compares the degree of superheating with a preset target value. If the degree of superheating is greater than the target value, the control unit controls the valve opening of the liquid return expansion valve to increase; and if the degree of superheating is less than the target value, the control unit controls the valve opening of the liquid return expansion valve to decrease. It is characterized by the following. [Effects of the Invention]

[0007] According to the present invention, the liquid return expansion valve described above can ensure a differential pressure between the liquid return pipe and the intermediate piping. This allows for good maintenance of the gas-liquid two-phase intermediate pressure refrigerant introduced into the internal heat exchanger, thereby improving efficiency. [Brief explanation of the drawing]

[0008] [Figure 1] This is a circuit diagram showing the configuration of a heat pump device according to an embodiment. [Figure 2] This is a PH diagram of a heat pump device according to an embodiment. [Figure 3] This is a circuit diagram showing the configuration of a heat pump device according to the first modified example. [Figure 4] This is a circuit diagram showing the configuration of a heat pump device according to the second modified example. [Modes for carrying out the invention]

[0009] The heat pump device according to the embodiment will be described below with reference to the attached drawings. Note that the present invention is not limited to the embodiments described below, and can be modified as appropriate without changing its essence. In the following figures, some components may be omitted for the sake of explanation.

[0010] Figure 1 is a circuit diagram showing the configuration of a heat pump device according to an embodiment. As shown in Figure 1, the heat pump device 1 has a two-stage compression, two-stage expansion heat pump cycle configuration comprising a compressor 10, a condenser 13, a high-stage expansion valve V1, a gas-liquid separator 14, a low-stage expansion valve V2, and an evaporator 15.

[0011] The compressor 10 includes a low-stage compressor 11 that compresses low-pressure refrigerant to an intermediate pressure and a high-stage compressor 12 that compresses intermediate-pressure refrigerant to a high pressure. In this embodiment, the discharge port P12 of the low-stage compressor 11 and the suction port P21 of the high-stage compressor 12 are connected by a compressor connection pipe L1. The low-stage compressor 11 and the high-stage compressor 12 may be separate components or an integrated unit. Furthermore, the low-stage compressor 11 and the high-stage compressor 12 may be connected by a common drive shaft. The compressor 10 may also be a scroll-type compressor.

[0012] The evaporator 15 evaporates the low-pressure refrigerant using heat recovered from waste hot water H, which is a heat source water constantly introduced via the hot water circulation path 2. The condenser 13 condenses the high-pressure refrigerant to heat the water to be heated W, which is the heating medium. The heat pump device 1 recovers heat from waste hot water H, such as factory wastewater, in the evaporator 15, and uses the recovered heat to heat the water to be heated W in the condenser 13 to generate steam. The generated steam is sent to steam utilization equipment such as drying equipment and sterilization equipment.

[0013] The refrigerant outlet P52 of the evaporator 15 and the inlet P11 of the low-stage compressor 11 are connected by evaporation piping L3. The discharge port P22 of the high-stage compressor 12 and the refrigerant inlet P31 of the condenser 13 are connected by compression piping L4. The refrigerant outlet P32 of the condenser 13 and the refrigerant inlet P41 of the gas-liquid separator 14 are connected by high-stage expansion piping L5. The liquid-phase outlet P42 of the gas-liquid separator 14 and the refrigerant inlet P51 of the evaporator 15 are connected by low-stage expansion piping L6. The gas-phase outlet P43 of the gas-liquid separator 14 and the connection port P10 on the compressor connection piping L1, which is between the discharge port P12 of the low-stage compressor 11 and the inlet P21 of the high-stage compressor 12, are connected by intermediate piping L7.

[0014] The heat pump device 1 further includes an internal heat exchanger 17 that cools the high-pressure refrigerant condensed by the condenser 13 into a liquid phase. The internal heat exchanger 17 performs heat exchange between the high-pressure refrigerant flowing from the condenser 13 through the high-stage expansion pipe L5 and the intermediate-pressure refrigerant flowing from the gas-phase outlet P43 of the gas-liquid separator 14 through the intermediate pipe L7. In other words, the internal heat exchanger 17 heats the intermediate-pressure refrigerant flowing through the intermediate pipe L7 with the high-pressure refrigerant condensed by the condenser 13.

[0015] In the internal heat exchanger 17, the high-temperature side flow path 17a forms part of the high-stage expansion piping L5, and the low-temperature side flow path 17b in the internal heat exchanger 17 forms part of the intermediate piping L7. Therefore, the high-stage expansion piping L5 is provided to connect from the internal heat exchanger 17 to the gas-liquid separator 14. Due to the heat exchange in the internal heat exchanger 17, the high-pressure refrigerant flowing through the high-stage expansion piping L5 changes state from a gas-liquid two-phase to a liquid phase, and the intermediate-pressure refrigerant flowing through the intermediate piping L7 changes state from a gas-liquid two-phase to a gas phase.

[0016] The high-stage expansion valve V1 is provided in the high-stage expansion pipe L5, and decompresses and expands the high-pressure refrigerant that has become a liquid phase condensed by the internal heat exchanger 17 through the condenser 13 to an intermediate pressure at which it becomes a gas-liquid two-phase state.

[0017] The gas-liquid separator 14 separates (gas-liquid separation) the gas-liquid two-phase intermediate-pressure refrigerant introduced from the high-stage expansion valve V1 into the refrigerant inlet P41 into a gas phase and a liquid phase. The liquid-phase intermediate-pressure refrigerant flowing through the low-stage expansion pipe L6 from the liquid-phase side outlet P42 of the gas-liquid separator 14 is introduced into the low-stage expansion valve V2 provided in the low-stage expansion pipe L6. The low-stage expansion valve V2 decompresses and expands the liquid-phase intermediate-pressure refrigerant to a low pressure at which it becomes a gas-liquid two-phase state. The gas-liquid two-phase low-pressure refrigerant decompressed and expanded by the low-stage expansion valve V2 is introduced into the evaporator 15 and heated, and its state changes from a gas-liquid two-phase state to a gas phase.

[0018] Here, the heat pump device 1 further includes a liquid return pipe L8 and a liquid return expansion valve V3 provided in the liquid return pipe L8.

[0019] One end of the liquid return pipe L8 is connected to the high-stage side connection point P81 on the side of the internal heat exchanger 17 rather than the high-stage expansion valve V1 in the high-stage expansion pipe L5, and the liquid return pipe L8 is provided so as to branch from the high-stage expansion pipe L5 at the high-stage side connection point P81. The other end of the liquid return pipe L8 is connected to the intermediate connection point P82 on the side of the gas-liquid separator 14 rather than the internal heat exchanger 17 in the intermediate pipe L7, and the liquid return pipe L8 is provided so as to merge into the intermediate pipe L7 at the intermediate connection point P82.

[0020] The liquid return expansion valve V3 decompresses and expands the high-pressure refrigerant introduced into the liquid return pipe L8. More specifically, the liquid return expansion valve V3 decompresses and expands the liquid-phase high-pressure refrigerant that has been condensed by the internal heat exchanger 17 through the condenser 13 and branches from the high-stage expansion pipe L5 into the liquid return pipe L8 to an intermediate pressure at which it becomes a gas-liquid two-phase state.

[0021] At the intermediate connection point P82 of the intermediate pipe L7, the refrigerant that becomes a gas-liquid two-phase after being decompressed and expanded by the liquid return expansion valve V3 from the liquid return pipe L8 is merged with the intermediate-pressure refrigerant in the gas phase flowing through the intermediate pipe L7 from the gas-phase side outlet P43 of the gas-liquid separator 14. After such merging, the refrigerant in the intermediate pipe L7 becomes an intermediate pressure of gas-liquid two-phase and is heated by the internal heat exchanger 17, and at the connection port P10 on the compressor connection pipe L1, it merges with the intermediate-pressure refrigerant compressed by the low-stage compressor 11 and is introduced into the high-stage compressor 12.

[0022] The heat pump device 1 further includes a pressure sensor 21 and a temperature sensor 22 attached to the intermediate pipe L7, and a control unit 23 that performs overall control of the heat pump device 1.

[0023] The pressure sensor 21 detects the pressure of the intermediate-pressure refrigerant that is heated by the internal heat exchanger 17 in the intermediate pipe L7 and introduced into the low-stage compressor 11. The temperature sensor 22 detects the temperature of the intermediate-pressure refrigerant that is heated by the internal heat exchanger 17 in the intermediate pipe L7 and introduced into the low-stage compressor 11. The pressure sensor 21 and the temperature sensor 22 output the detection results to the control unit 23.

[0024] The control unit 23 includes, in addition to a processor that executes various processes, a memory that stores various parameters, programs, etc. The control unit 23 is connected to the pressure sensor 21, the temperature sensor 22, and each expansion valve V1 to V3. The control unit 23 has a function of controlling the valve opening degree of the liquid return expansion valve V3 based on the detection results of the pressure sensor 21 and the temperature sensor 22, and a function of controlling the valve opening degree of the high-stage expansion valve V1 based on the detection result of the pressure sensor 21. Each of the expansion valves V1 to V3 is an electronic expansion valve that can change the opening degree according to a given command.

[0025] Next, the actual operating conditions of the heat pump device 1 will be described using the P-H diagram of FIG. 2. FIG. 2 is a P-H diagram of the heat pump device according to the embodiment.

[0026] As shown in Figure 2, from point X3 to point X4, the intermediate pressure (PM) refrigerant (intermediate pressure refrigerant) is compressed by the high-stage compressor 12 to produce high-pressure (PH) refrigerant (high-pressure refrigerant), which is then introduced into the condenser 13. Subsequently, from point X4 to point X5, the high-pressure refrigerant is cooled by heat dissipation condensation in the condenser 13 and the internal heat exchanger 17, and undergoes a state change from the gas phase to the liquid phase via a gas-liquid two-phase process.

[0027] Next, between points X5 and X6, the high-pressure liquid refrigerant is depressurized and expanded by the high-stage expansion valve V1, becoming an intermediate-pressure refrigerant in two phases (gas and liquid) and introduced into the gas-liquid separator 14. Between points X6 and X7, the intermediate-pressure refrigerant is separated into liquid by the gas-liquid separator 14. Then, between points X7 and X8, the intermediate-pressure liquid refrigerant discharged from the liquid-phase outlet P42 of the gas-liquid separator 14 is depressurized and expanded by the low-stage expansion valve V2.

[0028] The depressurized expansion of the low-stage expansion valve V2 generates low-pressure (PL) refrigerant (low-pressure refrigerant), which is introduced into the evaporator 15. From point X8 to point X1, the low-pressure refrigerant is heated and evaporated by the evaporator 15, changing from a gas-liquid two-phase system to a gas phase. Then, from point X1 to point X2, the low-pressure refrigerant, now in the gas phase, is compressed by the low-stage compressor 11 to generate intermediate-pressure refrigerant, which is introduced into the high-stage compressor 12.

[0029] Here, at point X6, the intermediate-pressure refrigerant is separated into liquid and gas phases by the gas-liquid separator 14 as described above. Also, from point X5 to point X6, the high-pressure liquid-phase refrigerant is depressurized and expanded by the high-stage expansion valve V1 as described above, and also depressurized and expanded by the liquid return expansion valve V3. Then, at point Y, which is between point X6 and point X3, the gas-liquid two-phase intermediate-pressure refrigerant that has been depressurized and expanded by the liquid return expansion valve V3 is merged with the gas-separated intermediate-pressure refrigerant by the gas-liquid separator 14 in the intermediate piping L7 (see dashed arrow in Figure 2). Also, from point Y to point X3, the intermediate-pressure refrigerant generated by the merger is heated by the internal heat exchanger 17 and changes state from gas-liquid two-phase to gas phase.

[0030] Here, the intermediate pressure (PM) in the heat pump cycle shown in Figure 2 is adjusted by the control unit 23 controlling the valve opening of the high-stage expansion valve V1. This adjustment is performed by pre-setting a target value for the intermediate pressure and storing it in the control unit 23. During the operation of the heat pump device 1, the pressure sensor 21 detects the intermediate pressure of the refrigerant in the intermediate piping L7, and the control unit 23 compares the detected value with the target value. In this comparison, for example, if the detected intermediate pressure is lower than the target value, the control unit 23 controls the valve opening of the high-stage expansion valve V1 to increase, thereby raising the intermediate pressure of the refrigerant in the high-stage expansion piping L5, the gas-liquid separator 14, and the internal heat exchanger 17.

[0031] From point X2 to point X3, the gaseous intermediate-pressure refrigerant generated in the low-stage compressor 11 merges with the gas-liquid two-phase intermediate-pressure refrigerant introduced from the intermediate piping L7, and the degree of superheating of the gaseous intermediate-pressure refrigerant introduced into the high-stage compressor 12 decreases. The degree of superheating of the intermediate-pressure refrigerant at point X3 changes according to the specific enthalpy of the refrigerant that merges from the intermediate piping L7 into the compressor connection piping L1. This specific enthalpy changes depending on the weight ratio of the gaseous and liquid phases in the gas-liquid two-phase refrigerant that is depressurized and expanded in the liquid return expansion valve V3 and merges from the liquid return pipe L8 into the intermediate piping L7. More specifically, as the weight ratio of the liquid phase increases, the temperature and degree of superheating of the refrigerant decrease, and the specific enthalpy also decreases. Conversely, as the weight ratio of the liquid phase decreases, the temperature and degree of superheating of the refrigerant increase, and the specific enthalpy also increases.

[0032] Therefore, the degree of superheating of the intermediate-pressure refrigerant introduced into the high-stage compressor 12 is adjusted by controlling the valve opening of the liquid return expansion valve V3 by the control unit 23. This adjustment is performed by pre-setting a target value for the degree of superheating and storing it in the control unit 23. During the operation of the heat pump device 1, the intermediate pressure and temperature of the refrigerant in the intermediate piping L7 are detected by the pressure sensor 21 and the temperature sensor 22. The control unit 23 calculates the saturation temperature from the pressure value detected by the pressure sensor 21, and calculates the degree of superheating from the saturation temperature and the temperature value detected by the temperature sensor 22. Next, the calculated degree of superheating and the target value are compared in the control unit 23. In this comparison, for example, if the calculated degree of superheating is greater than the target value, the control unit 23 controls the valve opening of the liquid return expansion valve V3 to increase the weight ratio of the liquid phase of the intermediate-pressure refrigerant. As a result, the specific enthalpy of the refrigerant flowing from the intermediate piping L7 to the compressor connection piping L1 is reduced, and the degree of superheating of the intermediate-pressure refrigerant introduced into the high-stage compressor 12 is reduced.

[0033] According to the above embodiment, the liquid return expansion valve V3 ensures a differential pressure between the refrigerants in the liquid return pipe L8 and the intermediate pipe L7, which merge at the intermediate connection point P82. This allows for a good maintenance of the weight ratio of the gas phase and liquid phase in the gas-liquid two-phase intermediate pressure refrigerant introduced into the internal heat exchanger 17. Therefore, the gas injection effect that lowers the specific enthalpy at the intake port P21 of the high-stage compressor 12 can be effectively utilized, and the ratio of the compression amount of the low-stage compressor 11 to the compression amount of the high-stage compressor 12 can be brought closer to the optimal value. As a result, the COP (Coefficient of Performance, cycle efficiency) of the heat pump device 1 can be improved, leading to higher efficiency.

[0034] Furthermore, as described above, by controlling the valve opening of the liquid return expansion valve V3, the degree of superheating of the intermediate-pressure refrigerant introduced into the high-stage compressor 12 can be optimally controlled. This allows the gas injection effect to be better utilized, improving the COP of the heat pump device 1 and increasing its efficiency.

[0035] Furthermore, by controlling the degree of superheating of the intermediate-pressure refrigerant and simultaneously controlling the valve opening of the high-stage expansion valve V1 as described above, the intermediate pressure of the refrigerant can be controlled to approach the target pressure value. This allows the compression ratios of the low-stage compressor 11 and the high-stage compressor 12 to be set to target values, thereby improving the COP of the heat pump device 1 and increasing its efficiency.

[0036] Furthermore, the control of the superheating degree and pressure value of the intermediate-pressure refrigerant can be performed independently by the liquid return expansion valve V3 and the high-stage expansion valve V1, making it possible to operate the heat pump device 1 with both the superheating degree and intermediate pressure under optimal conditions. This avoids a situation where bringing one condition close to the optimal value makes the other condition uncontrollable, thereby improving the COP of the heat pump device 1 and increasing its efficiency.

[0037] It should be noted that the present invention is not limited to the embodiments described above, and can be implemented with various modifications. In the embodiments described above, the size, shape, orientation, etc., shown in the accompanying drawings are not limited thereto, and can be appropriately modified within the scope that allows the present invention to exert its effects. Furthermore, it can be implemented with appropriate modifications as long as it does not deviate from the scope of the objectives of the present invention.

[0038] For example, the heat pump device 1 in the above embodiment may be modified to the configuration of the first modified example shown in Figure 3 or the second modified example shown in Figure 4.

[0039] In the first modified example shown in Figure 3, an intermediate expansion valve V4 is added to the intermediate piping L7 between the gas phase outlet P43 and the intermediate connection point P82 of the gas-liquid separator 14 in the above embodiment.

[0040] In the second modified example shown in Figure 4, the position of the high-stage expansion valve V1 in the high-stage expansion piping L5 in the above embodiment is changed to be between the internal heat exchanger 17 and the high-stage side connection point P81. In addition, in the second modified example, a middle-stage expansion valve V4 is added and installed on the intermediate piping L7 between the intermediate connection point P82 and the internal heat exchanger 17 in the above embodiment.

[0041] In the first and second modified examples, the pressure of the intermediate-pressure refrigerant flowing through the intermediate pipe L7 can be controlled by adjusting the valve opening of the intermediate expansion valve V4, and the pressure of the high-pressure refrigerant can be controlled by adjusting the valve opening of the high-pressure expansion valve V1.

[0042] Furthermore, in order to improve efficiency in the above embodiment, heat exchangers and the like may be added. For example, a heat exchanger may be provided to exchange heat between the refrigerant flowing through the low-stage expansion pipe L6 and the refrigerant flowing through the evaporation pipe L3, or a subcooler may be provided in series with the condenser 13. [Explanation of Symbols]

[0043] 1: Heat pump device 10: Compressor 11: Low-stage compressor 12: High-stage compressor 13: Condenser 14: Gas-liquid separator 15: Evaporator 17: Internal heat exchanger 21: Pressure sensor 22: Temperature sensor 23: Control Unit L5: High-stage expansion piping L7: Intermediate piping L8:Liquid return pipe P12:Discharge port P21: Inlet P42:Liquid phase side outlet P43: Gas phase outlet V1: High-stage expansion valve V2: Low-stage expansion valve V3: Liquid return expansion valve V4: Mid-stage expansion valve

Claims

1. An evaporator that evaporates a low-pressure refrigerant using heat recovered from the heat source water, A low-stage compressor for compressing the low-pressure refrigerant to an intermediate pressure, A high-stage compressor that compresses intermediate-pressure refrigerant to high pressure, A condenser that condenses a high-pressure refrigerant to heat the heating medium, An internal heat exchanger for cooling the high-pressure refrigerant condensed by the condenser, A high-stage expansion valve that reduces the pressure of the high-pressure refrigerant condensed by the internal heat exchanger to the intermediate pressure by increasing or decreasing the valve opening, A gas-liquid separator for separating the gas-liquid two-phase refrigerant from the aforementioned high-stage expansion valve, An intermediate pipe connecting the gas phase outlet of the gas-liquid separator to the discharge port of the low-stage compressor and the suction port of the high-stage compressor, A heat pump system with a two-stage compression-two-stage expansion cycle, comprising a low-stage expansion valve that reduces the pressure of the liquid-phase intermediate-pressure refrigerant introduced from the liquid-phase side outlet of the gas-liquid separator to a low pressure, The internal heat exchanger heats the intermediate-pressure refrigerant flowing through the intermediate piping with the high-pressure refrigerant condensed by the condenser. The aforementioned high-stage expansion valve is provided in the high-stage expansion piping that connects the internal heat exchanger to the gas-liquid separator. A liquid return pipe that branches off from the high-stage expansion valve in the high-stage expansion piping on the internal heat exchanger side, and merges with the gas-liquid separator side of the intermediate piping on the internal heat exchanger side, A liquid return expansion valve is provided in the liquid return pipe, and by increasing or decreasing the valve opening, the high-pressure refrigerant condensed by the internal heat exchanger is depressurized and expanded to become a gas-liquid two-phase refrigerant. The intermediate piping includes a pressure sensor for detecting the pressure of the intermediate pressure refrigerant heated by the internal heat exchanger and a temperature sensor for detecting the temperature of the intermediate pressure refrigerant. The system further comprises a control unit that controls the valve opening of the liquid return expansion valve based on the detection results of the pressure sensor and the temperature sensor, The control unit is characterized by calculating the saturation temperature from the pressure value detected by the pressure sensor, calculating the degree of superheating from the saturation temperature and the temperature value detected by the temperature sensor, and comparing the degree of superheating with a preset target value, controlling the valve opening of the liquid return expansion valve to increase if the degree of superheating is greater than the target value, and controlling the valve opening of the liquid return expansion valve to decrease if the degree of superheating is less than the target value.

2. The heat pump device according to claim 1, characterized in that the control unit controls the valve opening degree of the high-stage expansion valve based on the detection result of the pressure sensor.

3. The heat pump device according to claim 1, characterized in that an intermediate expansion valve for controlling the pressure of the intermediate-pressure refrigerant flowing through the intermediate pipe is provided on the intermediate pipe.

4. The heat pump device according to claim 3, characterized in that the intermediate expansion valve is provided on the intermediate piping between the gas phase outlet of the gas-liquid separator and the intermediate connection point where the liquid return pipe joins the intermediate piping.

5. The heat pump device according to claim 3, characterized in that the intermediate expansion valve is provided on the intermediate piping between an intermediate connection point where the liquid return pipe joins the intermediate piping and the internal heat exchanger.

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