Refrigeration Cycle Equipment

Abstract

To provide a refrigeration cycle device in which a target discharge overheat degree is not lower than a lower limit value of a compressor specification, and degradation of reliability of a compressor can be prevented.SOLUTION: A refrigeration cycle device includes: a refrigerant circuit 9 in which a compressor 4, a use-side heat exchanger 6 functioned as a condenser, and a heat source-side heat exchanger 8 functioned as an expansion valve 7 and an evaporator, are connected by piping; discharge overheat degree calculation means 26 for calculating a discharge overheat degree of the refrigerant; heating means 11 for heating the compressor; and control means 25 for controlling an opening of the expansion valve, the compressor and the heating means. The control means heats the compressor by the heating means when the discharge overheat degree is lower than a predetermined lower limit of the discharge overheat degree, and the opening of the expansion valve becomes a prescribed opening or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a refrigeration cycle device. [Background technology]

[0002] A known refrigeration cycle device is a hot water supply device that has a refrigerant circuit in which a compressor, a condenser, an expansion valve, and an evaporator are connected by piping, and a control means, in which the control means controls the opening of the expansion valve so that the discharge superheat degree, which is the superheat degree of the refrigerant discharged from the compressor, becomes a target discharge superheat degree, and so that the subcooling degree of the refrigerant flowing out from the condenser becomes a target subcooling degree (for example, Patent Document 1). In the device of Patent Document 1, the control means controls the opening of the expansion valve so that the enthalpy difference in the condenser is set within a target range, allowing the hot water supply device to demonstrate the required capacity.

[0003] At this time, in order to suppress the deterioration of the compressor reliability due to liquid compression, it is possible to control the opening degree of the expansion valve by setting the discharge superheat degree when the refrigerant flowing out of the evaporator has a superheat degree of 0 and a dryness degree of 1 as a target value (target discharge superheat degree). On the other hand, if the discharge superheat of the refrigerant is low, the solubility of the refrigerant in the refrigeration oil increases, reducing the reliability of the compressor. Therefore, a lower limit of the discharge superheat at which the reliability of the compressor does not decrease is set as a compressor specification. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-4128 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, under certain operating conditions, the target discharge superheat may fall below the lower limit, in which case the control means controls the opening of the expansion valve to be small so that the target discharge superheat is equal to or greater than the lower limit. In particular, under operating conditions where the amount of refrigerant circulating through the refrigerant circuit is small, the suction superheat of the refrigerant sucked into the compressor increases slowly, and even if the control means controls the opening of the expansion valve to the minimum, the target discharge superheat may not reach the lower limit. In addition, when using a refrigerant with a small specific heat ratio, such as R290, the increase in enthalpy during the compression process is smaller than that of a refrigerant with a large specific heat ratio. Therefore, the suction superheat required to make the discharge superheat degree exceed the lower limit becomes relatively high, and the target discharge superheat degree may fall below the lower limit. During low differential pressure operation, where the difference between the suction pressure and discharge pressure of the compressor is small, the increase in enthalpy during the compression process becomes even smaller, and the target discharge superheat degree may fall below the lower limit.

[0006] Therefore, the present invention has been made to solve such problems, and aims to provide a refrigeration cycle device in which the target discharge superheat does not fall below the lower limit of the compressor specifications and a decrease in compressor reliability can be suppressed. [Means for solving the problem]

[0007] One aspect of the invention is a refrigeration cycle device comprising a refrigerant circuit in which a compressor, a utilization side heat exchanger functioning as a condenser, an expansion valve, and a heat source side heat exchanger functioning as an evaporator are connected by piping, a discharge superheat calculation means for calculating a discharge superheat of the refrigerant, a heating means for heating the compressor, and a control means for controlling the opening of the expansion valve and the compressor and the heating means, wherein the control means controls the opening of the expansion valve so that the discharge superheat becomes a predetermined target discharge superheat, and heats the compressor by the heating means when the discharge superheat falls below a predetermined discharge superheat lower limit and the opening of the expansion valve becomes equal to or lower than a predetermined opening. Effect of the Invention

[0008] According to the refrigeration cycle device of the present invention, the target discharge superheat degree does not fall below the lower limit value of the compressor specifications, and deterioration in the reliability of the compressor can be suppressed. [Brief description of the drawings]

[0009] [Figure 1] 1 is a circuit diagram showing a heat pump heating device according to a first embodiment of the present invention as a heat pump cycle device. [Diagram 2] 1 is a refrigerant circuit showing an outdoor unit of a heat pump heating device. [Diagram 3] FIG. 3 is a Mollier diagram of the refrigerant circuit of FIG. 2. [Figure 4] 4 is a control flow diagram showing a control method for the heat pump heating device of the first embodiment. [Diagram 5] FIG. 4 is a Mollier diagram of the refrigerant circuit when the compressor performs low differential pressure operation. [Figure 6] FIG. 2 is a Mollier diagram of a refrigerant circuit when a refrigerant with a low specific heat ratio is used. [Figure 7] FIG. 5 is a circuit diagram showing a heat pump heating device according to a second embodiment. [Figure 8] 6 is a control flow diagram showing a control method for a heat pump heating device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Next, an embodiment of the present invention will be described with reference to the drawings. The embodiments shown below are examples of devices and methods for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not specify the materials, shapes, structures, arrangements, etc. of the components to be described below. The technical idea of ​​the present invention can be modified in various ways within the technical scope defined by the claims.

[0011] (First embodiment) FIG. 1 is a circuit diagram of a heat pump heating device 1 according to a first embodiment of the refrigeration cycle device of the present invention. The heat pump heating device 1 of the first embodiment has an outdoor unit 2 and an indoor unit 3. In the outdoor unit 2, a compressor 4, a four-way valve 5, a user-side heat exchanger 6 that exchanges heat between water and a refrigerant, an expansion valve 7, and an outdoor heat exchanger 8 are connected in sequence to form a refrigerant circuit 9. The outdoor heat exchanger 8 corresponds to the heat source-side heat exchanger of the present invention. The four-way valve 5 switches the direction in which the refrigerant circulates. An outdoor fan 10 that blows outside air to the outdoor heat exchanger 8 is also provided. The compressor 4 is provided with a belt heater 11 for heating the housing of the compressor 4. The belt heater 11 corresponds to the heating means in the present invention.

[0012] When the utilization side heat exchanger 6 functions as a condenser, a refrigerant outlet of the utilization side heat exchanger 6 is provided with a condenser outlet refrigerant temperature sensor 15 that detects the temperature of the refrigerant that has passed through the utilization side heat exchanger 6. When the outdoor heat exchanger 8 functions as an evaporator, a refrigerant outlet of the outdoor heat exchanger 8 is provided with an evaporator outlet refrigerant temperature sensor 16 that detects the temperature of the refrigerant that has passed through the outdoor heat exchanger 8. When the outdoor heat exchanger 8 functions as an evaporator, a refrigerant inlet of the outdoor heat exchanger 8 is provided with an evaporator inlet refrigerant temperature sensor 17 that detects the temperature of the refrigerant flowing into the outdoor heat exchanger 8. In addition, a discharge pressure sensor 18 that detects the discharge pressure of the refrigerant and a discharge temperature sensor 19 that detects the discharge temperature of the refrigerant are provided on the discharge side of the compressor 4.

[0013] For example, R290 (propane) having a specific heat ratio of 1.3 or less is used as the refrigerant circulating through the refrigerant circuit 9 of the outdoor unit 2. Note that a refrigerant having a specific heat ratio of more than 1.3 (for example, R32) may also be used. The indoor unit 3 is configured to be supplied with water that has undergone heat exchange with the refrigerant in the utilization-side heat exchanger 6 of the outdoor unit 2, and the utilization-side heat exchanger 6, a hot water circulation pump 20, and an indoor heat exchanger 21 that exchanges heat between the water and the indoor air are connected in sequence to form a water circulation path 22. A temperature sensor (not shown) that detects the outlet temperature of the water is provided at the water outlet of the utilization-side heat exchanger 6. The indoor unit 3 is also provided with an indoor fan 23 that blows the air that has undergone heat exchange in the indoor heat exchanger 21 into the room.

[0014] The heat pump heating device 1 of the first embodiment is equipped with a control means 25 which controls the operation of the four-way valve 5 and the hot water circulating pump 20, controls the opening of the expansion valve 7, controls the operation of the compressor 4, and controls the energization of the belt heater 11. In addition, the control means 25 receives an input of the condenser outlet temperature of the refrigerant from the condenser outlet refrigerant temperature sensor 15 and an input of the evaporator outlet temperature from the evaporator outlet refrigerant temperature sensor 16. When the heat pump heating device 1 of the first embodiment starts operating, the control means 25 drives the hot water circulation pump 20 to circulate water between the utilization side heat exchanger 6 and the indoor heat exchanger 21. The control means 25 has a built-in microcomputer that stores a program for performing control specific to this embodiment, and switches the four-way valve 5 when reversing the refrigerant circulation direction during defrosting operation.

[0015] Next, the state of the refrigerant in the refrigerant circuit 9 in the outdoor unit 2 will be described with reference to Figures 2 and 3. As reference points of the refrigerant circuit 9 in Figure 2, point A indicates between the compressor 4 and the condenser (corresponding to the utilization side heat exchanger 6; hereinafter referred to as the condenser 6), point B indicates between the condenser 6 and the expansion valve (corresponding to the expansion valve 7; hereinafter referred to as the expansion valve 7), point C indicates between the expansion valve 7 and the evaporator (corresponding to the outdoor heat exchanger 8; hereinafter referred to as the evaporator 8), and point D indicates between the evaporator 8 and the compressor 4.

[0016] The state of the refrigerant from point A to point D or between each point changes according to the following processes (1) to (8) as shown in the Mollier diagram of FIG. 3. (1) The refrigerant in the compression process (between points D and A) is compressed by the compressor 4, and both the pressure (vertical axis) and temperature rise to become high-temperature, high-pressure superheated vapor. (2) The refrigerant discharged from the compressor 4 (point A) is a high-pressure gas-phase refrigerant in a superheated state. (3) The refrigerant in the cooling process (between points A and B) exchanges heat with the water flowing through the water circulation path 22 in the condenser 6 (dissipates heat to the water), and becomes a high-pressure supercooled liquid while maintaining a constant pressure through the states of superheated vapor, saturated vapor, wet vapor, and saturated liquid. (4) The refrigerant flowing out from the condenser 6 (point B) is a high-pressure liquid-phase refrigerant in a supercooled state. (5) The refrigerant in the expansion process (between points B and C) expands by the expansion valve 7, and both the pressure (vertical axis) and temperature drop to become wet vapor. (6) The refrigerant (point C) flowing out of the expansion valve 7 is a low-pressure two-phase refrigerant in a liquid-rich state (= high liquid phase ratio). (7) The refrigerant in the evaporation process (between points C and D) exchanges heat (absorbs heat) with the surrounding air in the evaporator 8, and while the pressure remains constant, it becomes low-pressure superheated steam after passing through the wet vapor and saturated vapor states. (8) The refrigerant (point D) flowing out of the evaporator 8 is a low-pressure gas-phase refrigerant in a superheated state.

[0017] The difference between the refrigerant temperature at point A in Fig. 3 and the saturated gas temperature at point E on the saturated vapor line at the same pressure as point A is the superheat degree of the refrigerant discharged from the compressor 4, which is also called the discharge superheat degree of the refrigerant. Also, the difference between the refrigerant temperature at point B in Fig. 3 and the saturated liquid temperature at point F on the saturated liquid line at the same pressure as point B is the subcooling degree of the refrigerant. The discharge superheat of the refrigerant in the Mollier diagram in Fig. 3 is set as a target value (target discharge superheat) when the refrigerant (point D) flowing out of the evaporator 8 is on the saturated vapor line (suction superheat = 0 and dryness = 1). The target discharge superheat at this time varies depending on the values ​​of the condensation temperature (pressure) and evaporation temperature (pressure). Here, a lower limit value of the discharge superheat degree (lower limit value of the discharge superheat degree) that does not reduce the reliability of the compressor 4 is set in the specifications of the compressor 4. The lower limit value of the discharge superheat degree of the compressor 4 is set to, for example, 10°C.

[0018] The control means 25 of the heat pump heating device 1 has a discharge superheat degree calculation means 26 and a target discharge superheat degree calculation means 27, as shown in FIG. The discharge superheat degree calculation means 26 calculates the current discharge superheat degree of the refrigerant. A specific calculation method is to calculate the difference between the discharge temperature of the refrigerant detected by the discharge temperature sensor 19 and the saturated vapor temperature on the saturated vapor line in the Mollier diagram of the refrigerant shown in Fig. 3, that is, the condensation temperature (calculated from the discharge pressure of the refrigerant detected by the discharge pressure sensor 18).

[0019] Further, the target discharge superheat degree calculation means 27 calculates the target discharge superheat degree by substituting the refrigerant condensation temperature converted from the detection value of the discharge pressure sensor 18 and the refrigerant evaporation temperature detected by the evaporator inlet refrigerant temperature sensor 17 into an arithmetic expression stored in advance in the control means 25. The target discharge superheat degree is a target value (target discharge superheat degree) when the refrigerant (point D) flowing out from the evaporator 8 is on the saturated vapor line (suction superheat degree=0 and dryness fraction=1). The discharge superheat degree calculation means 26 and the target discharge superheat degree calculation means 27 are realized by software operated by the control means 25.

[0020] Next, Fig. 4 is a control flow showing the control of the expansion valve 7 and the power supply control of the belt heater 11 during operation of the heat pump heating device 1. Note that it is assumed that the determination switch Sc is set to "0" before starting this control method. 4, the condenser outlet temperature of the refrigerant detected by the condenser outlet refrigerant temperature sensor 15 and the evaporator outlet temperature of the refrigerant detected by the evaporator outlet refrigerant temperature sensor 16 are read in the control means 25. Next, in step ST2, the discharge superheat degree calculation means 26 calculates the current discharge superheat degree. Next, in step ST3, the target discharge superheat degree calculation means 27 calculates the target discharge superheat degree.

[0021] Next, in step ST4, the control means 25 subtracts the target discharge superheat from the current discharge superheat, and controls the opening degree of the expansion valve 7 according to the subtraction result. That is, when the subtraction result is positive, the opening degree of the expansion valve 7 is controlled to be increased, and when the subtraction result is negative, the opening degree of the expansion valve 7 is controlled to be decreased. Next, in step ST5, the control means 25 judges whether or not the target discharge superheat degree is below a lower limit value of the discharge superheat degree (for example, 10° C.). If it is determined in step ST5 that the target discharge superheat degree is below the lower limit of the discharge superheat degree (step ST5: YES), the process proceeds to step ST6. If the target discharge superheat degree is equal to or greater than the lower limit of the discharge superheat degree (step ST5: NO), the process proceeds to step ST9.

[0022] In step ST6, which is reached if the determination in step ST5 is YES, the control means 25 determines whether the opening of the expansion valve 7 is the minimum opening. Note that the opening of the expansion valve 7 being the minimum opening corresponds to the opening of the expansion valve being a predetermined opening in the present invention. If the determination in step ST6 is that the opening of the expansion valve 7 is the minimum opening (step ST6: YES), the process proceeds to step ST7, and if the opening of the expansion valve 7 is not the minimum opening (step ST6: NO), the process returns to step ST1.

[0023] In step ST7, which is performed when the opening degree of the expansion valve 7 is at the minimum opening degree, the power supply control of the belt heater 11 is performed. At this time, the target value of the discharge superheat degree is changed from the target discharge superheat degree calculated in step ST3 to the target discharge superheat degree during heating (>discharge superheat degree lower limit value), and the output of the belt heater is adjusted so that the discharge superheat degree becomes the target discharge superheat degree during heating. Next, in step ST8, the decision switch Sc is set to "1" and then the process returns to step ST1. On the other hand, in step ST9, which is performed if the determination in step ST5 is NO, it is determined whether the current discharge superheat degree is equal to or higher than the target discharge superheat degree. If the determination in step ST9 is that the current discharge superheat degree is equal to or higher than the target discharge superheat degree (step ST9: YES), the process proceeds to step ST10, and if the current discharge superheat degree is lower than the target discharge superheat degree (step ST9: NO), the process returns to step ST1.

[0024] In step ST10, it is determined whether or not the decision switch Sc is "1." If it is determined in step ST10 that the decision switch Sc is "1" (step ST10: YES), the process proceeds to step ST11, and if the decision switch Sc is not "1" (step ST10: NO), the process returns to step ST1. In step ST11, the decision switch Sc is set to "0." Next, in step ST12, the control means 25 stops the power supply control of the belt heater 11. After that, the control in FIG. 4 is ended. Here, when the heat pump heating device 1 is in operation, there is a risk that the target discharge superheat degree will not reach the lower limit of the discharge superheat degree in the compressor 4 specifications (for example, 10° C.).

[0025] That is, Fig. 5 shows the Mollier diagram of the heat pump heating device 1 when the compressor 4 is operating at a low differential pressure. During low load operation of the heat pump heating device 1 or heating operation under high outdoor air temperature, the amount of refrigerant circulating through the refrigerant circuit 9 decreases, and the compressor 4 operates at a low differential pressure with a small difference between the suction pressure and the discharge pressure. During such low differential pressure operation, even if the refrigerant sucked into the compressor 4 is on the saturated vapor line (suction superheat degree = 0 and dryness fraction = 1), the discharge superheat degree becomes a relatively small value. Therefore, even if the control means 25 controls the opening degree of the expansion valve 7 to the minimum, the target discharge superheat degree becomes a small value (e.g., 8°C), and there is a risk that the discharge superheat degree lower limit value will not be reached.

[0026] 5 shows the Mollier diagram of the heat pump heating device 1 when the refrigerant used is R32 refrigerant with a relatively high specific heat ratio, but FIG. 6 shows the Mollier diagram of the heat pump heating device 1 when the refrigerant used is R290 (propane) with a low specific heat ratio as in this embodiment. When R290 is used, the increase in enthalpy during the compression process is smaller than that of a refrigerant with a large specific heat ratio. Therefore, the suction superheat required for the discharge superheat to exceed the lower limit becomes relatively high, and the target discharge superheat falls below the lower limit. Therefore, even if the control means 25 controls the opening of the expansion valve 7 to the minimum, the target discharge superheat becomes a small value (e.g., 8°C), and there is a risk that the lower limit of the discharge superheat will not be reached.

[0027] 4, when the target discharge superheat does not reach the lower limit of the discharge superheat (step ST5: YES) and the opening of the expansion valve 7 is at the minimum opening (step ST6: YES), the belt heater 11 is energized (step ST7) to heat the housing of the compressor 4. By heating the housing of the compressor 4 with the belt heater 11, the target discharge superheat is increased to or above the lower limit of the discharge superheat, and a decrease in the reliability of the compressor 4 can be suppressed.

[0028] Here, if control is performed using the lower limit value of the discharge superheat as a target value, when the discharge superheat falls below the lower limit value due to load fluctuation, the current discharge superheat cannot be controlled by simply adjusting the opening of the expansion valve 7. Therefore, in this embodiment, a high target discharge superheat during heating is set, which is a high target discharge superheat that anticipates changes in the discharge superheat due to load fluctuation, and control is performed by comparing the target discharge superheat with the lower limit value of the discharge superheat, thereby enabling fine control of the discharge superheat by the expansion valve 7. In addition, since the belt heater 11 warms the housing of the compressor 4, the temperature of the refrigeration oil increases and the solubility of the refrigerant in the refrigeration oil decreases, so that the deterioration of the reliability of the compressor 4 can be further suppressed.

[0029] In addition, the user-side heat exchanger 6 of the heat pump heating device 1 is a water-refrigerant heat exchanger that exchanges heat between water and a refrigerant. During hot water supply operation at high outdoor temperatures, the compressor 4 is likely to operate at a low differential pressure. However, by performing the control shown in FIG. 4 to raise the target discharge superheat to or above the lower limit of the discharge superheat, it is possible to suppress deterioration in the reliability of the compressor 4. In addition, even if R290 (propane) having a low specific heat ratio is used, the deterioration of the reliability of the compressor 4 can be suppressed by performing the control shown in FIG. 4 to increase the target discharge superheat to or above the lower limit of the discharge superheat.

[0030] Second embodiment Next, Fig. 7 is a circuit diagram of a heat pump heating device 1 of a second embodiment as a refrigeration cycle device of the present invention. The configuration of Fig. 7 differs from the circuit diagram of the heat pump heating device 1 of the first embodiment shown in Fig. 1 in that the control means 25 includes a subcooling degree calculation means 32 and a target subcooling degree extraction means 33 in addition to the discharge superheat degree calculation means 26 and the target discharge superheat degree calculation means 27. 8 is a control flow showing the control of the expansion valve 7 and the power supply control of the belt heater 11 during operation of the heat pump heating device 1 of the second embodiment. The control flow in FIG. 8 differs from the subcooling control process shown in FIG. 4 in that the control flow in FIG. 8 includes an expansion valve opening process based on the degree of subcooling in step ST20 instead of step ST4 shown in FIG. The expansion valve opening degree processing based on the degree of subcooling in step ST20 will be described below.

[0031] First, the subcooling degree calculation means 32 calculates the current degree of subcooling. In particular, the calculation method calculates the saturated liquid temperature (condensation temperature) of the saturated liquid line in the Mollier diagram of the refrigerant shown in Fig. 3 based on the discharge pressure of the refrigerant detected by the discharge pressure sensor 30. Then, the subcooling degree calculation means 32 calculates the current degree of subcooling by subtracting the temperature of the refrigerant that has passed through the utilization side heat exchanger 6, detected by the condenser outlet refrigerant temperature sensor 15, from this saturated liquid temperature. The target subcooling degree extraction means 33 stores a target subcooling degree table. The target subcooling degree table sets a target subcooling degree according to the condensing pressure state and the rotation speed (unit: rps) of the compressor 4. The target subcooling degree extraction means 33 determines the condensing pressure state of the pressure value (condensing pressure) detected by the discharge pressure sensor 30, and extracts a target subcooling degree from the target subcooling degree table based on the current rotation speed of the compressor 4.

[0032] Then, the control means 25 subtracts the target subcooling degree extracted by the target subcooling degree extraction means 33 from the current subcooling degree calculated by the subcooling degree calculation means 32. Then, when the result of subtracting the target subcooling degree from the current subcooling degree is positive, the control means 25 controls the opening degree of the expansion valve 7 to be larger, and when the result of subtracting the target subcooling degree from the current subcooling degree is negative, the control means 25 controls the opening degree of the expansion valve 7 to be smaller.

[0033] In the second embodiment, similarly to the first embodiment, the target discharge superheat degree is increased to or above the lower limit of the discharge superheat degree, thereby making it possible to suppress a decrease in reliability of the compressor 4. In the expansion valve opening process based on the degree of subcooling in step ST20 of Figure 8, the target degree of subcooling is extracted from a target degree of subcooling table that takes into account the condensation pressure and the rotation speed of the compressor 4, the target degree of subcooling is subtracted from the current degree of subcooling, and the opening of the expansion valve 7 is controlled according to the subtraction result, thereby enabling the expansion valve 7 to perform fine-tuned control of the discharge superheat degree. Furthermore, since the enthalpy difference is ensured in the utilization side heat exchanger 6 (condenser), a highly efficient heat pump cycle with improved COP (Coefficient Of Performance) can be operated. [Explanation of symbols]

[0034] 1. Heat pump heating system 2 Outdoor unit 3 Indoor unit 4. Compressor 5. Four-way valve 6 User side heat exchanger 7 Expansion valve 8 Outdoor heat exchanger 9 Refrigerant circuit 10 Outdoor fan 11 Belt heater 15 Condenser outlet refrigerant temperature sensor 16 Evaporator outlet refrigerant temperature sensor 17 Evaporator inlet refrigerant temperature sensor 18 Discharge pressure sensor 19 Discharge temperature sensor 20 Hot water circulation pump 21 Indoor heat exchanger 22 Water circulation path 23 Indoor fan 25 Control Means 26 Discharge superheat degree calculation means 27 Target discharge superheat degree calculation means 30 Discharge pressure sensor 31 Discharge temperature sensor 32 Supercooling degree calculation means 33 Target supercooling degree extraction means

Claims

1. a refrigerant circuit in which a compressor, a utilization-side heat exchanger functioning as a condenser, an expansion valve, and a heat source-side heat exchanger functioning as an evaporator are connected by piping; A discharge superheat degree calculation means for calculating a discharge superheat degree of the refrigerant; A heating means for heating the compressor; A control means for controlling the opening degree of the expansion valve, the compressor, and the heating means, The control means a heating means for heating the compressor when the discharge superheat degree falls below a lower limit value that does not reduce reliability of the compressor and when the opening degree of the expansion valve becomes a minimum opening degree.

2. 2. The refrigeration cycle apparatus according to claim 1, wherein the control means continues heating the compressor by the heating means until the discharge superheat degree becomes equal to or greater than the lower limit of the discharge superheat degree.

3. 3. The refrigeration cycle apparatus according to claim 1, wherein the utilization side heat exchanger is a water-refrigerant heat exchanger that exchanges heat between water and the refrigerant.

4. The control means controlling an opening degree of the expansion valve so that the discharge superheat degree becomes a predetermined target discharge superheat degree; 3. The refrigeration cycle device according to claim 1 or 2.

5. A subcooling degree calculation means for calculating a subcooling degree of the refrigerant is provided, The control means controlling an opening degree of the expansion valve so that the degree of subcooling becomes a predetermined target degree of subcooling; 3. The refrigeration cycle device according to claim 1 or 2.

6. 3. The refrigeration cycle apparatus according to claim 1, wherein the heating means is a belt heater for heating a housing of the compressor.

7. 3. The refrigeration cycle device according to claim 1, wherein the refrigerant has a specific heat ratio of 1.3 or less.

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