JPWO2017158782A1 - Heat pump water heater - Google Patents

Abstract

A heat pump water heater having a refrigerant circuit in which carbon dioxide circulates and a hot water supply circuit, wherein water flowing through the hot water supply circuit and the carbon dioxide flowing through the refrigerant circuit exchange heat with a first heat exchanger, The circuit has a compressor, a refrigerant flow path of the first heat exchanger, an expansion valve, and a second heat exchanger, and the hot water supply circuit has a water flow path and a tank of the first heat exchanger, The heat pump water heater includes a first sensor that detects a temperature of the carbon dioxide discharged from the compressor, a second sensor that detects a temperature of water flowing into the water flow path of the first heat exchanger, A third sensor for detecting the temperature of the water flowing out of the water flow path of the first heat exchanger, and the expansion valve has an opening set so that a difference between the first value and a target value is reduced. , The first value is the value detected by the third sensor and the value of the first sensor. The target value is a smaller value when the detection value of the second sensor is the first temperature than when the second temperature is lower than the first temperature. .

Description

  The present invention relates to a heat pump water heater having a refrigerant circuit and a hot water supply circuit using carbon dioxide as a refrigerant, and exchanging heat between water flowing through the hot water supply circuit and carbon dioxide flowing through the refrigerant circuit.

  Conventionally, in a heat pump water heater having a refrigerant circuit using an HC (hydrocarbon) refrigerant and a hot water supply circuit, the temperature difference between the discharge temperature from the compressor and the tapping temperature from the hot water heat exchanger is COP (Coefficient A technique for controlling the opening degree of the expansion valve has been proposed so that the target value is maximized (of performance: coefficient of performance) (see, for example, Patent Document 1).

JP2012-233626A (Claim 1, page 9)

  One type of refrigerant circulating in the refrigerant circuit is carbon dioxide. Carbon dioxide has a merit that it is nonflammable and has a low global warming potential, but has a characteristic that the pressure in the refrigerant circuit is higher than that of hydrocarbon refrigerant. Patent Document 1 discloses that in a heat pump water heater using a hydrocarbon-based refrigerant, the temperature difference between the refrigerant discharge refrigerant temperature and the tapping temperature is such that the COP (Coefficient of Performance) is maximized. However, the control adopted in Patent Document 1 cannot be applied to a heat pump water heater using carbon dioxide. This is because, as described above, since carbon dioxide has a high pressure in the refrigerant circuit, the high pressure exceeds the design pressure when the target temperature difference between the discharge refrigerant temperature and the tapping temperature is determined so that COP is maximized. In this case, the heat pump operation cannot be continued and the hot water supply is stopped. In addition, when the temperature of the water heated by carbon dioxide is high, the high pressure of carbon dioxide tends to increase, and management of the high pressure is important. For this reason, in the heat pump water heater using carbon dioxide, the technique which can suppress the raise of a high voltage | pressure and can perform the stable hot water supply driving | operation was desired.

  The present invention has been made against the background of the above-described problems, and provides a heat pump water heater using carbon dioxide as a refrigerant that can suppress a rise in high pressure and perform a stable hot water supply operation. .

  The heat pump water heater of the present invention has a refrigerant circuit and a hot water supply circuit in which carbon dioxide circulates, and a heat pump in which water flowing through the hot water supply circuit and the carbon dioxide flowing through the refrigerant circuit exchange heat with a first heat exchanger. In the hot water supply device, the refrigerant circuit includes a compressor, a refrigerant flow path of the first heat exchanger, an expansion valve, and a second heat exchanger, and the hot water supply circuit includes the first heat exchanger. The heat pump water heater has a water flow path and a tank, and the heat pump water heater detects the temperature of the carbon dioxide discharged from the compressor, and the temperature of water flowing into the water flow path of the first heat exchanger And a third sensor for detecting the temperature of water flowing out of the water flow path of the first heat exchanger, and the expansion valve has a difference between the first value and the target value. The opening is set so as to decrease, and the first value is the third set. The target value is a difference between the detected value of the first sensor and the detected value of the first sensor, and the target value is a second temperature lower than the first temperature when the detected value of the second sensor is the first temperature. This is a smaller value than the case of.

  ADVANTAGE OF THE INVENTION According to this invention, in the heat pump water heater provided with the refrigerant circuit which uses a carbon dioxide as a refrigerant | coolant, the raise of the high voltage | pressure of the refrigerant | coolant discharged from a compressor can be suppressed, and the stable hot water supply operation can be performed.

1 is a circuit configuration diagram of a heat pump water heater according to Embodiment 1. FIG. 3 is a functional block diagram of the heat pump water heater according to Embodiment 1. FIG. 3 is a flowchart relating to control of a refrigerant circuit of the heat pump water heater according to the first embodiment. It is an example of the relationship figure of the water inlet temperature of the heat pump water heater which concerns on Embodiment 1, and target temperature difference. It is another example of the relationship figure of the water inlet temperature of the heat pump water heater which concerns on Embodiment 1, and target temperature difference. 6 is a configuration diagram of an accumulator according to Embodiment 2. FIG. It is a functional block diagram of the heat pump water heater according to the second embodiment.

  A heat pump water heater according to an embodiment of the present invention will be described with reference to the drawings. In each drawing, the relative dimensional relationship or shape of each component may differ from the actual one.

Embodiment 1 FIG.
FIG. 1 is a circuit configuration diagram of the heat pump water heater according to the first embodiment. The heat pump water heater 100 includes a refrigerant circuit 10 in which carbon dioxide as a refrigerant circulates, and a hot water supply circuit 20. The refrigerant circuit 10 and the hot water supply circuit 20 are thermally connected in the first heat exchanger 12 which is a water refrigerant heat exchanger, and the refrigerant circulating in the refrigerant circuit 10 and the water circulating in the hot water supply circuit 20 are first connected. 1 Heat exchange is performed by the heat exchanger 12.

  The refrigerant circuit 10 includes a compressor 11 that compresses and discharges the refrigerant, a refrigerant flow path 12a of the first heat exchanger 12 through which the refrigerant discharged from the compressor 11 passes, an expansion valve 13 that decompresses the refrigerant, The second heat exchanger 14 is configured to be annularly connected by the refrigerant pipe 18 in this order. The compressor 11 is driven by a driving device including, for example, an inverter-controlled DC brushless motor, and has a function of making the pressure and temperature of refrigerant discharged from the compressor 11 variable. The expansion valve 13 has a structure in which the opening degree of the valve can be adjusted, and has a function of changing the decompression state of the refrigerant passing therethrough. In the present embodiment, an accumulator 15, which is a container for storing excess refrigerant, is connected to the downstream side of the second heat exchanger 14 and the upstream side of the compressor 11. The second heat exchanger 14 is an air heat exchanger that performs heat exchange between the refrigerant circulating in the refrigerant circuit 10 and the outside air. A blower 16 that blows outside air to the second heat exchanger 14 is installed around the second heat exchanger 14.

  The discharge part of the compressor 11 is provided with a first sensor 17 that is a temperature sensor that detects the temperature of the refrigerant discharged from the compressor 11. The 1st sensor 17 is a temperature sensor which detects the temperature of a refrigerant directly or indirectly via piping.

  The hot water supply circuit 20 is configured by connecting a tank 21 for storing water and a water flow path 12 b of the first heat exchanger 12 by a water circulation pipe 25. The water circulation pipe 25 is provided with a pump 22 for sending water, and the water is circulated in the hot water supply circuit 20 by operating the pump 22. One end of the water circulation pipe 25 is connected to the lower part of the tank 21, and the other end of the water circulation pipe 25 is connected to the upper part of the tank 21, so that the relatively low temperature water in the lower part of the tank 21 is subjected to the first heat exchange. The tank 12 is heated and flows into the tank 21 from the upper part of the tank 21.

  A water supply pipe 26 different from the water circulation pipe 25 is connected to the lower part of the tank 21, and water from the water supply source is stored in the tank 21 through the water supply pipe 26. A hot water supply pipe 27 different from the water circulation pipe 25 is connected to the upper part of the tank 21, and relatively high-temperature water in the upper part of the tank 21 is supplied to, for example, a bathtub. In addition, the piping structure which concerns on the water supply to the tank 21 and the tapping from the tank 21 is an example, and this invention is not limited by these piping structures.

A second sensor 23, which is a temperature sensor that detects the temperature of water flowing into the first heat exchanger 12, is provided at the inlet of the water flow path 12 b of the first heat exchanger 12. In addition, a third sensor 24 that is a temperature sensor that detects the temperature of water flowing out of the first heat exchanger 12 is provided at the outlet of the water flow path 12 b of the first heat exchanger 12. Water inlet temperature T _wi detected by the second sensor 23 is a temperature of the water before being heated in the first heat exchanger 12, the water outlet temperature T _wo detected by the third sensor 24, the first The temperature of the water after being heated by the heat exchanger 12. A 2nd sensor and a 3rd sensor are temperature sensors which detect the temperature of water directly or indirectly through piping.

  The heat pump water heater 100 includes an outside air temperature detection device 28 that is a temperature sensor. The outside air temperature detection device 28 is installed in a place where the outside air temperature around the heat pump water heater 100 can be measured.

  FIG. 2 is a functional block diagram of the heat pump water heater according to the first embodiment. The heat pump water heater 100 includes a control device 30 that performs overall control, and the control device 30 includes a memory 31. The control device 30 receives the output of the first sensor 17, the second sensor 23, the third sensor 24, and the outside air temperature detection device 28, information from the operating means operated by the user, and the like. The control device 30 controls the operation of these actuators by issuing commands to the compressor 11, the expansion valve 13, the blower 16, and the pump 22 based on these input information. Specifically, the control device 30 controls the operating state of the compressor 11 so as to adjust the pressure and temperature of the refrigerant to be discharged by controlling the frequency of the drive device of the compressor 11. In addition, the control device 30 controls the opening degree of the expansion valve 13 so that the refrigerant reaches the target decompression state in the expansion valve 13. Further, the control device 30 controls the operating states of the blower 16 and the pump 22.

  The control device 30 is configured by dedicated hardware or a CPU (also referred to as a central processing unit, a central processing device, a processing device, an arithmetic device, a microprocessor, a microcomputer, or a processor) that executes a program stored in the memory 31. The

  When the control device 30 is dedicated hardware, the control device 30 is, for example, a single circuit, a composite circuit, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination thereof. Applicable. Each functional unit realized by the control device 30 may be realized by individual hardware, or each functional unit may be realized by one piece of hardware.

  When the control device 30 is a CPU, each function executed by the control device 30 is realized by software, firmware, or a combination of software and firmware. Software and firmware are described as programs and stored in the memory 31. The CPU implements each function of the control device 30 by reading and executing the program stored in the memory 31. Here, the memory 31 is, for example, a nonvolatile or volatile semiconductor memory such as a RAM, a ROM, a flash memory, an EPROM, or an EEPROM.

  Note that part of the functions of the control device 30 may be realized by dedicated hardware, and part of it may be realized by software or firmware. Further, in FIG. 2, the control of the respective actuators is illustrated as being controlled by the control device 30, but the control device 30 does not necessarily have to be physically configured as illustrated. That is, the specific form of distribution and integration of the control device 30 is not limited to the illustrated one, and all or a part thereof is functionally or physically distributed in arbitrary units according to various loads or usage conditions. Alternatively, they can be integrated.

  An outline of the hot water supply operation of the heat pump water heater 100 will be described. When the frequency-controlled compressor 11 is operated, the compressed refrigerant is discharged from the compressor 11. The high-temperature and high-pressure refrigerant discharged from the compressor 11 flows into the refrigerant flow path 12a of the first heat exchanger 12. On the other hand, in the hot water supply circuit 20, the pump 22 is driven, and the water in the tank 21 flows into the water flow path 12 b of the first heat exchanger 12 through the water circulation pipe 25 by the action of the pump 22. The high-temperature and high-pressure refrigerant passing through the refrigerant flow path 12a and the water passing through the water flow path 12b are heat-exchanged in the first heat exchanger 12, and the refrigerant whose temperature has decreased and the high-temperature water whose temperature has increased respectively. Outflow from the first heat exchanger 12. The high-temperature water whose temperature has risen in the first heat exchanger 12 flows into the tank 21 through the water circulation pipe 25.

  The refrigerant whose temperature has decreased due to heat exchange with water in the first heat exchanger 12 flows into the expansion valve 13. The refrigerant flowing into the expansion valve 13 is depressurized to a state corresponding to the opening degree of the expansion valve 13, and becomes a low-pressure refrigerant and flows into the second heat exchanger 14. The refrigerant flowing into the second heat exchanger 14 exchanges heat with the outside air in the process of passing through the second heat exchanger 14, and the temperature rises. The operation state of the blower 16 is controlled in order to obtain a desired heat exchange amount between the outside air and the refrigerant. The refrigerant whose temperature has risen due to heat exchange with the outside air in the second heat exchanger 14 is sucked into the compressor 11 via the accumulator 15. The control device 30 monitors the high-pressure side refrigerant pressure output from the first sensor 17, and temporarily stops the hot water supply operation when the high-pressure side refrigerant pressure exceeds the upper limit value determined at the time of design. It is configured.

  Next, details of operation control of the refrigerant circuit 10 in the hot water supply operation of the heat pump water heater 100 will be described. FIG. 3 is a flowchart relating to the control of the refrigerant circuit of the heat pump water heater according to the first embodiment.

(S1)
The control device 30 determines the drive frequency of the compressor 11 and operates the compressor 11 at the determined drive frequency. Specifically, the control device 30 determines the drive frequency of the compressor 11 based on the outside air temperature T _a output from the outside air temperature detector 28 and the water inlet temperature T _wi output from the second sensor 23. To do. If the outside air temperature T _a is lower than is higher, the driving frequency of the compressor 11 is set high. Further, when the water inlet temperature _Twi is low, the drive frequency of the compressor 11 is determined to be higher than when the water inlet temperature _Twi is high. For example, previously obtained by test etc. correspondence table between a combination and the driving frequency of the compressor 11 with the outside air temperature T _a and the water inlet temperature T _wi, stores the correspondence table in the memory 31, the controller 30 memory The drive frequency can be determined based on the correspondence table stored in 31. Instead of determining the driving frequency based on such a correspondence table, the control unit 30 applies a predetermined operation expression the detected outside air temperature T _a and the water inlet temperature T _wi, the drive frequency May be determined.

(S2)
Controller 30 sets the target temperature difference [Delta] T _{_t} is a target value of the temperature difference between the discharged refrigerant temperature _{T ro} and the target water outlet temperature _{T wo_t.} Here, the target water outlet temperature _{Two_t} is set based on a predetermined temperature of water stored in the tank 21. Discharged refrigerant temperature T _ro, as the temperature of the water heated by the refrigerant in the first heat exchanger 12 becomes equal to the target water outlet temperature T _{Wo_t,} as higher temperatures only margin allowance with respect to the target water outlet temperature T _{Wo_t} Is set. The value for the margin is the target temperature difference _{ΔT_t} . Target temperature difference [Delta] T _{_t} In step S2, the value corresponding to the target water outlet temperature _{T Wo_t} is set. For example, it can be stored in advance in the memory 31 a correspondence table between the target water outlet temperature T _{Wo_t} and the target temperature difference [Delta] T _{_t.}

(S3)
The control device 30 corrects the target temperature difference _{ΔT_t} set in step S2. Specifically, when the water inlet temperature T _wi output from the second sensor 23 is the first temperature V ₁ , the control device 30 is the second temperature V ₂ (where V ₁ > V). ₂₎ than, so that the target temperature difference [Delta] T _{_t} is a small value, it corrects the target temperature difference [Delta] T _{_t.} That is, even in the target water outlet temperature T _{Wo_t} the same, depending on the water inlet temperature T _wi with different target temperature difference [Delta] T _{_t,} than when the water inlet temperature T _wi is large is small, the target temperature difference Let _{ΔT_t} be a small value.

FIG. 4 is an example of a relationship diagram between the water inlet temperature and the target temperature difference of the heat pump water heater according to the first embodiment. 4, as the larger the water inlet temperature T _wi target temperature difference [Delta] T _{_t} decreases, shows an example of varying the correction value of the target temperature difference [Delta] T _{_t} stepwise. In addition to the example shown in FIG. 4, the threshold value of the water inlet temperature T _wi advance one determined, when the water inlet temperature T _wi exceeds the threshold value, subtracting a predetermined correction value from the target temperature difference [Delta] T _{_t} Thus, the target temperature difference _{ΔT_t} may be corrected.

FIG. 5 is another example of a relationship diagram between the water inlet temperature and the target temperature difference of the heat pump water heater according to the first embodiment. As shown in FIG. 5, in the correction of the target temperature difference [Delta] T _{_t,} in addition to the water inlet temperature T _wi, may be adjusted to the correction value in accordance with the ambient temperature T _a. Specifically, when the outside air temperature T _a is high (T _a = β ° C.), the target temperature difference _{ΔT_t} is made smaller than when it is low (T _a = α ° C.). The higher the ambient temperature T _a, is less heat radiation amount of water in the hot water supply circuit 20. Therefore, when the outside air temperature T _a is greater by reducing the target temperature difference [Delta] T _{_t,} it is possible to obtain a desired water outlet temperature T _wo.

(S4)
The control device 30 determines that the temperature difference ΔT between the discharged refrigerant temperature T _ro detected by the first sensor 17 and the water outlet temperature T _wo detected by the third sensor 24 becomes the target temperature difference _{ΔT_t} corrected in step S3. The opening degree of the expansion valve 13 is controlled so as to approach.

While the operation of Step S4 is being performed, the pump 22 operates to allow water from the lower portion of the tank 21 to pass through the water flow path 12b of the first heat exchanger 12, and in the process, the water is heated by the refrigerant and heated. The water is returned from the upper part of the tank 21 into the tank 21. In this way, the hot water boiled in the tank 21 is stored. The rotation speed of the pump 22 is controlled so that the output value of the third sensor 24 becomes the target water outlet temperature _{Two_t} . Since the opening degree of the expansion valve 13 is controlled so that the target temperature difference _{ΔT_t} is obtained in step S4, that is, the heating capacity in the heat pump cycle is maintained constant, the water speed is adjusted by adjusting the rotation speed of the pump 22. The outlet temperature _Two can be ensured.

(S5)
The control device 30 continuously performs the process of step S4 until the boiling is completed. When a predetermined amount of hot water at the target temperature is accumulated in the tank 21, the controller 30 determines that the boiling is completed and ends the operation.

As described above, according to the present embodiment, the opening degree of the expansion valve 13 is controlled so that the difference between the temperature difference ΔT between the discharge refrigerant temperature _Tro and the water outlet temperature _Two and the target temperature difference _{ΔT_t} becomes small. Is done. The value of the target temperature difference _{ΔT_t} is set to be smaller when the water inlet temperature T _wi is the first temperature than when the second temperature is smaller than the first temperature. Is done. For this reason, when the water inlet temperature T _wi is high, the opening degree of the expansion valve 13 is controlled so that the degree of superheat of carbon dioxide, which is a refrigerant, is lower than when the water inlet temperature T _wi is low. The amount of liquid refrigerant increases. When the amount of the liquid refrigerant in the accumulator 15 increases, an increase in the high pressure of the refrigerant discharged from the compressor 11 is suppressed. As described above, the control device 30 temporarily stops the hot water supply operation when the refrigerant pressure on the high pressure side exceeds the upper limit value determined at the time of design, but according to the present embodiment, an excessive increase in the refrigerant pressure is suppressed. Thus, the hot water supply operation can be continued stably, and a highly reliable heat pump water heater 100 can be obtained. The first value of the present invention corresponds to the temperature difference ΔT in the present embodiment.

Embodiment 2. FIG.
In the present embodiment, a modified example of the first embodiment will be described. In the first embodiment described above have been described to correct the target temperature difference [Delta] T _{_t} based on water inlet temperature T _wi, in the present embodiment, the control of the minimum value of the target temperature difference [Delta] T _{_t} corrected explain. The present embodiment is realized by adding a configuration to the first embodiment, and the following description will focus on differences from the first embodiment.

  FIG. 6 is a configuration diagram of the accumulator according to the second embodiment. As shown in FIG. 6, the piping of the refrigerant circuit 10 is inserted in the upper part and the lower part of the accumulator 15, respectively, the refrigerant flows into the accumulator 15 from the upper pipe, and the gas refrigerant flows out from the lower pipe. It is a configuration. As shown in FIG. 1, the refrigerant flowing out of the accumulator 15 is sucked into the compressor 11.

  The accumulator 15 is provided with a liquid level gauge 19 for detecting the liquid level of the liquid refrigerant in the accumulator 15. The liquid level gauge 19 is not particularly limited in its specific configuration as long as it has a function of detecting the liquid level of the liquid refrigerant. For example, any type such as a magnet float type, a capacitance type, and an ultrasonic type may be used. Can be used.

  FIG. 7 is a functional block diagram of the heat pump water heater according to the second embodiment. As shown in FIG. 7, the liquid level gauge 19 is communicably connected to the control device 30, and an output from the liquid level gauge 19 is input to the control device 30.

Operation control regarding the heating capability of water in the refrigerant circuit 10 of the heat pump water heater 100 is performed in the same manner as that shown in FIG. That is, the target temperature difference [Delta] T _{_t} between the discharge refrigerant temperature Tro and the target water outlet temperature _{T Wo_t} is corrected based on the water inlet temperature _{T wi.} Then, the temperature difference [Delta] T between the detected discharge refrigerant temperature T _ro water outlet temperature T _wo is, so that the target temperature difference [Delta] T _{_t} the corrected opening degree of the expansion valve 13 is controlled.

Here, also in the present embodiment, the value of the target temperature difference _{ΔT_t} is corrected so as to be smaller as the water inlet temperature T _wi is higher, but the liquid level in the accumulator 15 is set to a threshold value by the liquid level gauge 19. Is detected, the downward correction of the target temperature difference _{ΔT_t} is not performed. That is, when the level gauge 19 detects a threshold value, the control device 30 maintains the current value of the target temperature difference _{ΔT_t at} a current value or a value larger than the current value regardless of the detected value of the water inlet temperature T _wi. To do.

As described above, in the present embodiment, until the liquid refrigerant amount in the accumulator 15 reaches the threshold value, the control device 30 performs the correction to decrease the target temperature difference _{ΔT_t} as the water inlet temperature T _wi is higher. As in the first embodiment, the increase in the pressure of the refrigerant discharged from the compressor 11 can be suppressed. Further, when the amount of liquid refrigerant in the accumulator 15 exceeds the threshold value, the control device 30 does not perform correction for reducing the target temperature difference _{ΔT_t,} and therefore, it is possible to prevent an insufficient amount of refrigerant circulating in the refrigerant circuit 10.

  DESCRIPTION OF SYMBOLS 10 Refrigerant circuit, 11 Compressor, 12 1st heat exchanger, 12a Refrigerant flow path, 12b Water flow path, 13 Expansion valve, 14 2nd heat exchanger, 15 Accumulator, 16 Blower, 17 1st sensor, 18 Refrigerant piping, 19 Liquid Level Meter, 20 Hot Water Supply Circuit, 21 Tank, 22 Pump, 23 Second Sensor, 24 Third Sensor, 25 Water Circulation Pipe, 26 Water Supply Pipe, 27 Hot Water Supply Pipe, 28 Outside Air Temperature Detection Device, 30 Control Device, 31 Memory , 100 Heat pump water heater.

The heat pump water heater of the present invention has a refrigerant circuit and a hot water supply circuit in which carbon dioxide circulates, and a heat pump in which water flowing through the hot water supply circuit and the carbon dioxide flowing through the refrigerant circuit exchange heat with a first heat exchanger. In the hot water supply device, the refrigerant circuit includes a compressor, a refrigerant flow path of the first heat exchanger, an expansion valve, and a second heat exchanger, and the hot water supply circuit includes the first heat exchanger. The heat pump water heater has a water flow path and a tank, and the heat pump water heater detects the temperature of the carbon dioxide discharged from the compressor, and the temperature of water flowing into the water flow path of the first heat exchanger A second sensor for detecting the temperature, a third sensor for detecting the temperature of the water flowing out of the water flow path of the first heat exchanger, a downstream side of the second heat exchanger of the refrigerant circuit and the compressor. An accumulator provided upstream, and the accumulator A liquid level gauge for detecting the liquid level of carbon dioxide in the Yumureta, and a control unit, the expansion valve opening degree is set such that the difference between the first value and the target value is reduced, the first Is the difference between the detection value of the third sensor and the detection value of the first sensor, and the target value is the first value when the detection value of the second sensor is the first temperature. than if a small second temperature than the temperature, Ri smaller der, the control device, the target value, as compared with the case when the detected value of the second sensor is large is small, a small value The control device does not correct the target value to be a small value regardless of the detection value of the second sensor in a state where the detection value of the liquid level meter exceeds a threshold value. /> Is.

Claims (3)

A heat pump water heater having a refrigerant circuit and a hot water supply circuit in which carbon dioxide circulates, wherein water flowing through the hot water supply circuit and the carbon dioxide flowing through the refrigerant circuit exchange heat with a first heat exchanger,
The refrigerant circuit includes a compressor, a refrigerant flow path of the first heat exchanger, an expansion valve, and a second heat exchanger.
The hot water supply circuit has a water flow path and a tank of the first heat exchanger,
The heat pump water heater is
A first sensor for detecting a temperature of the carbon dioxide discharged from the compressor;
A second sensor for detecting a temperature of water flowing into the water flow path of the first heat exchanger;
A third sensor for detecting the temperature of water flowing out of the water flow path of the first heat exchanger,
The opening of the expansion valve is set so that the difference between the first value and the target value is reduced, and the first value is the difference between the detection value of the third sensor and the detection value of the first sensor. The target value is smaller when the detection value of the second sensor is the first temperature than when the second temperature is lower than the first temperature. The heat pump water heater according to claim 1, wherein the target value is a smaller value when the outside air temperature is high than when the target temperature is low. An accumulator provided downstream of the second heat exchanger and upstream of the compressor of the refrigerant circuit;
A liquid level gauge for detecting the liquid level of carbon dioxide in the accumulator;
A control device that corrects the target value so that the target value is smaller when the detection value of the second sensor is larger than when it is smaller;
The control device does not perform correction to make the target value a small value regardless of the detection value of the second sensor when the detection value of the liquid level meter exceeds a threshold value. The heat pump water heater described in 1.

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