EP4692674A1

EP4692674A1 - Refrigeration cycle device

Info

Publication number: EP4692674A1
Application number: EP24780298.6A
Authority: EP
Inventors: Ryo Takaoka
Original assignee: Fujitsu General Ltd
Current assignee: Fujitsu General Ltd
Priority date: 2023-03-29
Filing date: 2024-03-26
Publication date: 2026-02-11
Also published as: JP2024141183A; CN120898104A; JP7647786B2; WO2024204186A1; AU2024247996A1

Abstract

A refrigerant circuit (9) where a compressor (4), a utilization-side heat exchanger (6) configured to function as a condenser, an expansion valve (7), and a heat-source-side heat exchanger (8) configured to function as an evaporator are connected by a pipe; a discharge superheat degree calculation device (26) configured to calculate the discharge superheat degree of a refrigerant; a heating device (11) configured to heat the compressor; and a control device (25) configured to control the opening degree of the expansion valve, the compressor, and the heating device are provided, and the control device is configured to heat the compressor by the heating device when the discharge superheat degree has fallen below the predetermined discharge-superheat-degree lower limit value and the opening degree of the expansion valve has become equal to or less than the predetermined opening degree.

Description

Technical Field

The present invention relates to a refrigeration cycle device.

Background Art

As a refrigeration cycle device, a hot water supply device is known which has a refrigerant circuit where a compressor, a condenser, an expansion valve, and an evaporator are connected by a pipe and a control device and in which the control device controls the opening degree of the expansion valve such that the discharge superheat degree, which is the superheat degree of a refrigerant discharged from the compressor, reaches a target discharge superheat degree and the supercooling degree, which is a target supercooling degree of a refrigerant flowing out of the condenser, reaches a target supercooling degree (e.g., PTL 1). In the device of PTL 1, the control device controls the opening degree of the expansion valve such that the enthalpy difference in the condenser is set within a target range, so that the hot water supply device can exhibit the required capability.
At this time, to suppress a decrease in the reliability of the compressor due to liquid compression, it is conceivable to control the opening degree of the expansion valve with the discharge superheat degree when the refrigerant flowing out of the evaporator has the superheat degree of 0 and the dryness of 1 as a target value (target discharge superheat degree).
On the other hand, when the discharge superheat degree of the refrigerant is low, the refrigerant solubility in a refrigeration oil increases and the reliability of the compressor decreases. Therefore, the lower limit value of the discharge superheat degree at which the reliability of the compressor does not decrease is set as the specification for the compressor.

Citation List

Patent Literature

PTL 1: JP 2018-4128 A

Summary of Invention

Technical Problem

Under given operating conditions, the target discharge superheat degree sometimes falls below the lower limit value. In such a case, the control device controls the opening degree of the expansion valve to be small such that the target discharge superheat degree becomes equal to or more than the lower limit value. Particularly under operating conditions in which the circulation amount of the refrigerant circulating through the refrigerant circuit is small, the suction superheat degree of the refrigerant sucked into the compressor gently increases and even when the control device controls the opening degree of the expansion valve to be minimum, there is a risk that the target discharge superheat degree does not reach the lower limit value.
When a refrigerant having a small specific heat ratio, such as R290, is used, the enthalpy increase amount in a compression process is smaller than that of a refrigerant having a large specific heat ratio. Therefore, the suction superheat degree required for the discharge superheat degree to exceed the lower limit value becomes relatively high, posing a risk that the target discharge superheat degree falls below the lower limit value. In low differential pressure operation in which a difference between the suction pressure and the discharge pressure of the compressor is small, the enthalpy increase amount in the compression process becomes further smaller, posing a risk that the target discharge superheat degree falls below the lower limit value.
Thus, the present invention has been made for solving such a problem. It is an object of the present invention to provide a refrigeration cycle device in which the target discharge superheat degree does not fall below the lower limit value of a compressor specification and which can suppress the decrease in the reliability of the compressor.

Solution to Problem

One aspect of the invention is a refrigeration cycle device including: a refrigerant circuit where a compressor, a utilization-side heat exchanger configured to function as a condenser, an expansion valve, and a heat-source-side heat exchanger configured to function as an evaporator are connected by a pipe; a discharge superheat degree calculation device configured to calculate the discharge superheat degree of a refrigerant; a heating device configured to heat the compressor; and a control device configured to control the opening degree of the expansion valve, the compressor, and the heating device, in which the control device is configured to control the opening degree of the expansion valve such that the discharge superheat degree reaches the predetermined target discharge superheat degree and heat the compressor by the heating device when the discharge superheat degree has fallen below the predetermined discharge-superheat-degree lower limit value and the opening degree of the expansion valve has become equal to or less than the predetermined opening degree.

Advantageous Effects of Invention

According to the refrigeration cycle device of the present invention, the target discharge superheat degree does not fall below the lower limit value of a compressor specification and the decrease in the reliability of the compressor can be suppressed.

Brief Description of Drawings

FIG. 1 is a circuit diagram illustrating a heat pump-type heating device of a first embodiment as a heat pump cycle device of the present invention;
FIG. 2 is a refrigerant circuit illustrating an outdoor unit of the heat pump-type heating device;
FIG. 3 is the Mollier Diagram related to the refrigerant circuit in FIG. 2;
FIG. 4 is a control flow showing a control method of the heat pump-type heating device of the first embodiment;
FIG. 5 is the Mollier Diagram of the refrigerant circuit when a compressor performs low differential pressure operation;
FIG. 6 is the Mollier Diagram of the refrigerant circuit when a refrigerant having a low specific heat ratio is used;
FIG. 7 is a circuit diagram illustrating a heat pump-type heating device of a second embodiment; and
FIG. 8 is a control flow showing a control method of the heat pump-type heating device of the second embodiment.

Description of Embodiments

Next, embodiments according to the present invention are described with reference to the drawings. The embodiments described below exemplify devices or methods for embodying the technical idea of the present invention. The technical idea of the present invention does not specify the materials, shapes, structures, arrangement, and the like of constituent components to the materials, shapes, structures, arrangement, and the like described below. The technical idea of the present invention can be variously altered in the technical scope defined by claims.

(First embodiment)

FIG. 1 is a circuit diagram of a heat pump-type heating device 1 of a first embodiment as the refrigeration cycle device of the present invention.
The heat pump-type 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 utilization-side heat exchanger 6 exchanging heat between water and a refrigerant, an expansion valve 7, and an outdoor heat exchanger 8 are sequentially connected, forming 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 a refrigerant circulates. An outdoor fan 10 blowing the outdoor air to the outdoor heat exchanger 8 is also provided.
The compressor 4 is provided with a belt heater 11 heating a casing of the compressor 4. The belt heater 11 corresponds to the heating device in the present invention.
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 detecting the temperature of a 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 detecting the temperature of a 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 detecting the temperature of a refrigerant flowing into the outdoor heat exchanger 8. On the discharge side of the compressor 4, a discharge pressure sensor 18 detecting the discharge pressure of a refrigerant and a discharge temperature sensor 19 detecting the discharge temperature of a refrigerant are further provided.
As the refrigerant circulating through the refrigerant circuit 9 of the outdoor unit 2, R290 (propane) having a specific heat ratio of 1.3 or less, for example, is used. A refrigerant having a specific heat ratio larger than 1.3 (e.g., R32) may also be acceptable.
The indoor unit 3 is configured to be supplied with water that has been subjected to heat exchange with a refrigerant by the utilization-side heat exchanger 6 of the outdoor unit 2. The utilization-side heat exchanger 6, a hot water circulation pump 20, and an indoor heat exchanger 21 exchanging heat between water and the indoor air are sequentially connected, forming a water circulation path 22. The outlet of water of the utilization-side heat exchanger 6 is provided with a temperature sensor (not illustrated) detecting the outlet temperature of water. The indoor unit 3 is further provided with an indoor fan 23 blowing air that has been subjected to heat exchange by the indoor heat exchanger 21 to a room.
The heat pump-type heating device 1 of the first embodiment includes a control device 25 performing drive control of the four-way valve 5 and the hot water circulation pump 20, opening degree control of the expansion valve 7, drive control of the compressor 4, and energization control of the belt heater 11. Into the control device 25, a condenser outlet temperature of a refrigerant is input from the condenser outlet refrigerant-temperature sensor 15 and an evaporator outlet temperature is input from the evaporator outlet refrigerant-temperature sensor 16.
When the heat pump-type heating device 1 of the first embodiment starts operation, the control device 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 device 25 has a built-in microcomputer storing a program performing the control specific to this embodiment and switches the four-way valve 5 when the circulation direction of a refrigerant is reversed in defrosting operation.
Next, the state of the refrigerant of the refrigerant circuit 9 in the outdoor unit 2 is described with reference to FIGS. 2 and 3. As the reference points of the refrigerant circuit 9 in FIG. 2, a point A indicates a point between the compressor 4 and the condenser (corresponding to the utilization-side heat exchanger 6, hereinafter referred to as a condenser 6), a point B indicates a point between the condenser 6 and the expansion valve (corresponding to the expansion valve 7, hereinafter referred to as the expansion valve 7), a point C indicates a point between the expansion valve 7 and the evaporator (corresponding to the outdoor heat exchanger 8, hereinafter referred to as an evaporator 8), and a point D indicates a point between the evaporator 8 and the compressor 4.
The state of the refrigerant from the point A to the point D or between each point changes according to the following processes (1) to (8) as illustrated by the Mollier Diagram in FIG. 3. (1) The refrigerant in a compression process (between the points D and A) is compressed by the compressor 4, and both the pressure (vertical axis) and the temperature increase, so that the refrigerant becomes high-temperature and 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 a cooling process (between the points A and B) exchanges heat with water flowing through a water circulation path 22 (dissipating heat to water) in the condenser 6 to be a high-pressure supercooled liquid through each of the states of superheated vapor, saturated vapor, wet vapor, and saturated liquid while the pressure is kept constant. (4) The refrigerant that has flowed out of the condenser 6 (point B) is a high-pressure liquid-phase refrigerant in a supercooled state. (5) The refrigerant in an expansion process (between the points B and C) expands by the expansion valve 7, and both the pressure (vertical axis) and the temperature decrease, so that the refrigerant becomes wet vapor. (6) The refrigerant that has flowed out of the expansion valve 7 (point C) is a low-pressure two-phase refrigerant in a liquid-rich (= high liquid phase ratio) state. (7) The refrigerant in an evaporation process (between the points C and D) exchanges heat (absorbs heat) with the ambient air in the evaporator 8 to be low-pressure superheated vapor through each of the states of wet vapor and saturated vapor while the pressure is kept constant. (8) The refrigerant that has flowed out of the evaporator 8 (point D) is a low-pressure gas-phase refrigerant in a superheated state.
A difference between the refrigerant temperature at the point A and the saturated gas temperature at a point E on the saturated vapor line where the pressure is the same as that at the point A in FIG. 3 is the superheat degree of the refrigerant that has been discharged from the compressor 4 and is also referred to as a discharge superheat degree of the refrigerant. A difference between the refrigerant temperature at the point B and the saturated liquid temperature at a point F in FIG. 3 on the saturated liquid line where the pressure is the same as that at the point B is the supercooling degree of the refrigerant.
The discharge superheat degree of the refrigerant in the Mollier Diagram in FIG. 3 is a target value (target discharge superheat degree) when the refrigerant that has flowed out of the evaporator 8 (point D) is on the saturated vapor line (suction superheat degree = 0 and dryness = 1). The target discharge superheat degree at this time varies according to the values of the condensation temperature (pressure) and the evaporation temperature (pressure).
Herein, in the specification for the compressor 4, the lower limit value (discharge-superheat-degree lower limit value) of the discharge superheat degree at which the reliability of the compressor 4 is not reduced is set. The discharge-superheat-degree lower limit value of the compressor 4 is set to 10°C, for example.
The control device 25 of the heat pump-type heating device 1 has a discharge superheat degree calculation device 26 and a target discharge superheat degree calculation device 27 as illustrated in FIG. 1.
The discharge superheat degree calculation device 26 calculates the current discharge superheat degree of the refrigerant. As a specific calculation method, the discharge superheat degree is calculated depending on a difference between the discharge temperature of the refrigerant detected by the discharge temperature sensor 19 and the saturated vapor temperature of the saturated vapor line in the Mollier Diagram of the refrigerant illustrated in FIG. 3, i.e., the condensation temperature (converted from the discharge pressure of the refrigerant detected by discharge pressure sensor 18).
The target discharge superheat degree calculation device 27 calculates the target discharge superheat degree by substituting the condensation temperature of the refrigerant converted from the detection value of the discharge pressure sensor 18 and the evaporation temperature of the refrigerant detected by the evaporator inlet refrigerant-temperature sensor 17 into an arithmetic expression stored in advance in the control device 25. The target discharge superheat degree is the target value (target discharge superheat degree) when the refrigerant that has flowed out of the evaporator 8 (point D) is on the saturated vapor line (suction superheat degree = 0 and dryness = 1). The discharge superheat degree calculation device 26 and the target discharge superheat degree calculation device 27 are realized by software that is made to function by the control device 25.
Next, FIG. 4 is a control flow showing the control of the expansion valve 7 and the energization control of the belt heater 11 in the operation of the heat pump-type heating device 1. Before the control method is started, a determination switch Sc is supposed to be set to "0".
First, in Step ST1 in FIG. 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, which are input into the control device 25, are read. Next, in Step ST2, the discharge superheat degree calculation device 26 calculates the current discharge superheat degree. Next, in Step ST3, the target discharge superheat degree calculation device 27 calculates the target discharge superheat degree.
Next, in Step ST4, the control device 25 subtracts the target discharge superheat degree from the current discharge superheat degree and controls the opening degree of the expansion valve 7 according to the subtraction result. More specifically, when the subtraction result is positive, the control device 25 controls the opening degree of the expansion valve 7 to be large, and when the subtraction result is negative, the control device 25 controls the opening degree of the expansion valve 7 to be small.
Next, in Step ST5, the control device 25 determines whether the target discharge superheat degree falls below the discharge-superheat-degree lower limit value (e.g., 10°C).
In the determination in Step ST5, when the target discharge superheat degree falls below the discharge-superheat-degree lower limit value (Step ST5: YES), the process proceeds to Step ST6, and when the target discharge superheat degree is equal to or more than the discharge-superheat-degree lower limit value (Step ST5: NO), the process proceeds to Step ST9.
In Step ST6 to which the process proceeds when the determination in Step ST5 is YES, the control device 25 determines whether the opening degree of the expansion valve 7 is the minimum opening degree. The fact that the opening degree of the expansion valve 7 is the minimum opening degree corresponds to the fact that the opening degree of the expansion valve is the predetermined opening degree in the present invention. In the determination in Step ST6, when the opening degree of the expansion valve 7 is the minimum opening degree (Step ST6: YES), the process proceeds to Step ST7, and when the opening degree of the expansion valve 7 is not the minimum opening degree (Step ST6: NO), the process returns to Step ST1.
In Step ST7 to which the process proceeds when the opening degree of the expansion valve 7 is the minimum opening degree, the energization 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 a target discharge superheat degree in heating (> discharge-superheat-degree lower limit value) and the output of the belt heater is adjusted such that the discharge superheat degree reaches the target discharge superheat degree in heating. Next, in Step ST8, the determination switch Sc is set to "1", and then the process returns to Step ST1.
On the other hand, in Step ST9 to which the process proceeds when the determination in Step ST5 is NO, it is determined whether the current discharge superheat degree is equal to or more than the target discharge superheat degree. In the determination in Step ST9, when the current discharge superheat degree is equal to or more than the target discharge superheat degree (Step ST9: YES), the process proceeds to Step ST10 and when the current discharge superheat degree falls below the target discharge superheat degree (Step ST9: NO), the process returns to Step ST1.
In Step ST10, it is determined whether the determination switch Sc is "1". In the determination in Step ST10, when the determination switch Sc is "1" (Step ST10: YES), the process proceeds to Step ST11 and when the determination switch Sc is not "1" (Step ST10: NO), the process returns to Step ST1.
In Step ST11, the determination switch Sc is set to "0". Next, in Step ST12, the control device 25 stops the energization control of the belt heater 11. Thereafter, the control in FIG. 4 is ended.
Herein, there is a risk that the target discharge superheat degree does not reach the discharge-superheat-degree lower limit value (e.g., 10°C) in the specification for the compressor 4 when the heat pump-type heating device 1 is in operation.
More specifically, FIG. 5 illustrates the Mollier Diagram of the heat pump-type heating device 1 when the compressor 4 is performing low differential pressure operation. In low load operation or heating operation under a high outdoor air temperature of the heat pump-type heating device 1, the circulation amount of the refrigerant circulating through the refrigerant circuit 9 decreases, resulting in the low differential pressure operation in which a difference between the suction pressure and the discharge pressure of the compressor 4 is small. In such low differential pressure operation, the discharge superheat degree becomes relatively small in value even in a state in which the refrigerant suctioned into the compressor 4 is on the saturated vapor line (suction superheat degree = 0 and dryness = 1). Therefore, even when the control device 25 controls the opening degree of the expansion valve 7 to be minimum, the target discharge superheat degree becomes small in value (e.g., 8°C), posing a risk that the target discharge superheat degree does not reach the discharge-superheat-degree lower limit value.
FIG. 5 illustrates the Mollier Diagram of the heat pump-type heating device 1 when a R32 refrigerant having a relatively high specific heat ratio is used as the refrigerant, while FIG. 6 illustrates the Mollier Diagram of the heat pump-type heating device 1 when R290 (propane) having a low specific heat ratio as in the refrigerant in this embodiment is used. When R290 is used, the enthalpy increase amount in the compression process is smaller than that of a refrigerant having a large specific heat ratio. Therefore, the suction superheat degree required for the discharge superheat degree to exceed the lower limit value is relatively high, so that the target discharge superheat degree falls below the lower limit value. Therefore, even when the control device 25 controls the opening degree of the expansion valve 7 to be minimum, the target discharge superheat degree becomes small in value (e.g., 8°C), posing a risk that the target discharge superheat degree does not reach the discharge-superheat-degree lower limit value.
In contrast thereto, in the control illustrated in FIG. 4, when the target discharge superheat degree does not reach the discharge-superheat-degree lower limit value (Step ST5: YES) and when the opening degree of the expansion valve 7 is the minimum opening degree (Step ST6: YES), the energization control of the belt heater 11 is performed (Step ST7), thereby warming the casing of the compressor 4. By warming the casing of the compressor 4 by the belt heater 11, the target discharge superheat degree can be increased to be equal to or more than the discharge-superheat-degree lower limit value and the decrease in the reliability of the compressor 4 can be suppressed.
Herein, when the control is performed with the discharge-superheat-degree lower limit value as the target value, the opening degree of the expansion valve 7 is merely adjusted when the discharge superheat degree has fallen below the discharge-superheat-degree lower limit value due to load variations, and the current discharge superheat degree cannot be controlled. Thus, in this embodiment, the target discharge superheat degree in heating is set, the target discharge superheat degree in heating which is a high target discharge superheat degree allowing changes in the discharge superheat degree due to load variations, and the control is performed by comparing the target discharge superheat degree and the discharge-superheat-degree lower limit value with each other, thereby achieving fine control of the discharge superheat degree by the expansion valve 7.
Further, the belt heater 11 warms the casing of the compressor 4, so that the temperature of a refrigeration oil increases and the refrigerant solubility in the refrigeration oil decreases, and therefore the decrease in the reliability of the compressor 4 can be further suppressed.
Further, the utilization-side heat exchanger 6 of the heat pump-type heating device 1 is a water-refrigerant heat exchanger exchanging heat between water and a refrigerant. Hot water supply operation under a high outdoor air temperature tends to result in the low differential pressure operation of the compressor 4. However, the decrease in the reliability of the compressor 4 can be suppressed by performing the control illustrated in FIG. 4 to increase the target discharge superheat degree to be equal to or more than the discharge-superheat-degree lower limit value.
Even when R290 (propane) having a relatively low specific heat ratio is used, the decrease in the reliability of the compressor 4 can be suppressed by performing the control illustrated in FIG. 4 to increase the target discharge superheat degree to be equal to or more than the discharge-superheat-degree lower limit value.

(Second embodiment)

Next, FIG. 7 is a circuit diagram of the heat pump-type heating device 1 of a second embodiment as the refrigeration cycle device of the present invention. FIG. 7 is different in the configuration from the circuit diagram of the heat pump-type heating device 1 of the first embodiment illustrated in FIG. 1 in that the control device 25 includes a supercooling degree calculation device 32 and a target supercooling degree extraction device 33 besides the discharge superheat degree calculation device 26 and the target discharge superheat degree calculation device 27.
FIG. 8 is a control flow showing the control of the expansion valve 7 and the energization control of the belt heater 11 in the operation of the heat pump-type heating device 1 of the second embodiment. A different point of the control flow in FIG. 8 from subcooling control processing illustrated in FIG. 4 is that the control flow includes expansion valve opening degree processing by the supercooling degree in Step ST20 in place of Step ST4 illustrated in FIG. 4.
The expansion valve opening degree processing by the supercooling degree in Step ST20 is described below.
First, the supercooling degree calculation device 32 calculates the current supercooling degree. As a specific calculation method, the saturated liquid temperature (condensation temperature) of the saturated liquid line in the Mollier Diagram of the refrigerant illustrated in FIG. 3 is calculated based on the discharge pressure of the refrigerant detected by the discharge pressure sensor 30. Then, the supercooling degree calculation device 32 calculates the current supercooling degree 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 the saturated liquid temperature.
The target supercooling degree extraction device 33 stores a target supercooling degree table. In the target supercooling degree table, a target supercooling degree according to the condensing pressure state and the rotational speed (unit: rps) of the compressor 4 is set. The target supercooling degree extraction device 33 determines the condensing pressure state of the pressure value (condensing pressure) detected by the discharge pressure sensor 30 and extracts the target supercooling degree from the target supercooling degree table based on the current rotational speed of the compressor 4.
Then, the control device 25 subtracts the target supercooling degree extracted by the target supercooling degree extraction device 33 from the current supercooling degree calculated by the supercooling degree calculation device 32. Then, the control device 25 performs control to increase the opening degree of the expansion valve 7 when the result of subtracting the target supercooling degree from the current supercooling degree is positive and performs control to reduce the opening degree of the expansion valve 7 when the result of subtracting the target supercooling degree from the current supercooling degree is negative.
The second embodiment can also suppress the decrease in the reliability of the compressor 4 by increasing the target discharge superheat degree to be equal to or more than the discharge-superheat-degree lower limit value as with the first embodiment.
Then, in the expansion valve opening degree processing by the supercooling degree in Step ST20 in FIG. 8, the target supercooling degree is extracted from the target supercooling degree table allowing the condensing pressure and the rotational speed of the compressor 4, the target supercooling degree is subtracted from the current supercooling degree, and the opening degree control of the expansion valve 7 is performed according to the subtraction result, and therefore fine discharge superheat degree control can be performed by the expansion valve 7.
Further, the enthalpy difference is ensured in the utilization-side heat exchanger 6 (condenser), and therefore highly efficient heat pump cycle operation with an improved COP (Coefficient of Performance) can be performed.

Reference Signs List

1: heat pump-type heating device
2: outdoor unit
3: indoor unit
4: compressor
5: four-way valve
6: utilization-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 device
26: discharge superheat degree calculation device
27: target discharge superheat degree calculation device
30: discharge pressure sensor
31: discharge temperature sensor
32: supercooling degree calculation device
33: target supercooling degree extraction device

Claims

A refrigeration cycle device comprising:
a refrigerant circuit where a compressor, a utilization-side heat exchanger configured to function as a condenser, an expansion valve, and a heat-source-side heat exchanger configured to function as an evaporator are connected by a pipe;

a discharge superheat degree calculation device configured to calculate a discharge superheat degree of a refrigerant;

a heating device configured to heat the compressor; and

a control device configured to control an opening degree of the expansion valve, the compressor, and the heating device, wherein

the control device is configured to heat the compressor by the heating device when the discharge superheat degree has fallen below a predetermined discharge-superheat-degree lower limit value and the opening degree of the expansion valve has become equal to or less than a predetermined opening degree.
The refrigeration cycle device according to claim 1, wherein the control device is configured to continue the heating of the compressor by the heating device until the discharge superheat degree becomes equal to or more than the discharge-superheat-degree lower limit value.
The refrigeration cycle device according to claim 1 or 2, wherein the utilization-side heat exchanger is a water-refrigerant heat exchanger configured to exchange heat between water and the refrigerant.
The refrigeration cycle device according to claim 1 or 2, wherein the control device is configured to control the opening degree of the expansion valve such that the discharge superheat degree reaches a predetermined target discharge superheat degree.
The refrigeration cycle device according to claim 1 or 2, comprising:
a supercooling degree calculation device configured to calculate a supercooling degree of the refrigerant, wherein

the control device is configured to control the opening degree of the expansion valve such that the supercooling degree reaches a predetermined target supercooling degree.
The refrigeration cycle device according to claim 1 or 2, wherein the predetermined opening degree is a minimum opening degree of the expansion valve.
The refrigeration cycle device according to claim 1 or 2, wherein the heating device is a belt heater configured to warm a casing of the compressor.
The refrigeration cycle device according to claim 1 or 2, wherein the refrigerant has a specific heat ratio of 1.3 or less.