JP5181828B2 - Heat pump water heater - Google Patents

Description

  The present invention relates to a heat pump water heater that uses hot water boiled using a heat pump.

  Conventionally, this type of heat pump water heater has a structure as shown in FIG. 6 (see, for example, Patent Document 1). FIG. 6 is a circuit configuration diagram of the heat pump water heater disclosed in Patent Document 1.

  In FIG. 6, the conventional heat pump water heater includes a heat pump unit 41 and a hot water storage unit 42. The heat pump unit 41 includes a compressor 1, a radiator 2, an expansion valve 3, and an evaporator 4. The heat pump cycle 5 is formed in an annular shape in this order.

  The hot water storage unit 42 also returns to the upper or lower part of the hot water storage tank 31 through the hot water storage tank 31, the circulation pump 32, the three-way valve 33, the lower part of the hot water storage tank 31, the circulation pump 32, the radiator 2, and the three-way valve 33. The boiling circuit 36 is configured. Further, 34 is a hot water mixing valve, 35 is a boiling temperature sensor, the hot water mixing valve 34 is provided in a mixing portion of the hot water piping 39 from the supply water piping 38 and the hot water storage tank 31, and the boiling temperature sensor 35 is radiating heat. It is equipped so that it may contact from the outer side of piping on the water side exit piping of the vessel 2.

  The operation of the conventional heat pump water heater configured as described above will be described below.

  When the boiling operation is started, the compressor 1 and the circulation pump 32 are appropriately started, the compressor 1 circulates the refrigerant in the heat pump cycle 5, and the circulation pump 32 circulates water in the boiling circuit 36. .

  In the heat pump cycle 5, the refrigerant is supplied to the radiator 2 after being made high temperature and high pressure in the compressor 1, and after heat is exchanged with water and radiated, the refrigerant is decompressed by the expansion valve 3 to become low temperature and low pressure. Then, it receives heat from the atmosphere and is supplied to the compressor 1 again.

  On the other hand, in the boiling circuit 36, water is supplied from the lower part of the hot water storage tank 31 to the radiator 2 by the circulation pump 32, and heat is exchanged with a high-temperature refrigerant to boil cold water into hot water. Depending on the boiling temperature, the flow path communicating with either the upper part or the lower part of the hot water storage tank 31 is selected by the three-way valve 33 and returned to the hot water storage tank 31. The three-way valve 33 is located at the lower part of the hot water storage tank 31 while the warming temperature is lower than the target boiling temperature by a certain temperature difference, such as immediately after starting the boiling operation or immediately after the defrosting operation. When the boiling temperature falls within a certain temperature difference with respect to the target boiling temperature, the flow path for returning to the upper part of the hot water storage tank 31 is selected.

  By operating the three-way valve 33 as described above, the lowering of the hot water temperature in the upper part due to the return of the intermediate hot water to the lower part of the hot water storage tank 31 is suppressed, and heat is stored in the hot water storage tank 31 when the boiling is completed. It works to increase the amount of heat.

However, when the medium temperature water is returned to the lower part of the hot water storage tank 31, the temperature of the cold water in the lower part of the hot water storage tank 31 rises, so that the boiling water supply temperature supplied to the radiator 2 rises and is heated by the heat pump cycle 5. Energy efficiency during operation is reduced. Therefore, from the viewpoint of improving the energy efficiency in the boiling operation, it is not a good idea to recirculate the medium-temperature water generated as described above to the lower part of the hot water storage tank 31, and only when heat storage using high-temperature hot water is necessary, It is reasonable to return the intermediate temperature water generated in the boiling operation to the lower part of the hot water storage tank 31.
JP 2003-279136 A

  However, since the flow path switching means such as the three-way valve 33 in the conventional heat pump water heater recirculates the generated medium temperature water to the lower part of the hot water storage tank 31 regardless of the necessity of heat storage with high temperature hot water, Each time the frost operation is performed, the boiling water supply temperature rises, and the energy efficiency during the heating operation by the heat pump cycle 5 is lowered.

  Further, in the heat pump water heater described in Patent Document 1, when the boiling temperature is equal to or higher than a certain temperature difference with respect to the target boiling temperature, the generated medium-temperature water is supplied again to the radiator via the bypass circuit. Therefore, there is no problem as described above. However, the energy efficiency when boiling the warm water once supplied to the radiator again through the bypass circuit is extremely low, and there is a problem that the amount of electric power consumed for the boiling operation increases.

  The present invention solves the above-mentioned problem, and in a time zone when there is no need for heat storage with high-temperature hot water, the generated medium-temperature water is returned to the lower part of the hot water storage tank 31 or supplied to the radiator again. An object of the present invention is to provide a heat pump water heater capable of suppressing a rise in the boiling water supply temperature and performing a boiling operation with high energy efficiency by returning to the upper part without performing the above operation.

In order to solve the above-described conventional problems, a heat pump water heater of the present invention includes at least a heat pump cycle including a compressor and a radiator to circulate the refrigerant, and a heated fluid heated by the refrigerant in the radiator. A hot water storage tank, a circulation pump for returning the heated fluid to the hot water storage tank through the radiator, an upper flow path communicating the heat radiator and a substantially upper portion of the hot water storage tank, the radiator and the hot water storage tank a lower channel and the flow channel switching means for switching the pre-SL upper channel the selected one of the lower flow path flow path communicating the substantially lower portion of were boiled in the radiator A boiling temperature detection means for detecting the boiling temperature of the fluid to be heated and a control means are provided. The control means detects the target boiling temperature and the boiling temperature detection means in the daytime period. When the temperature difference from the boiling temperature falls within a predetermined first predetermined value, the flow path switching means switches so as to select the upper flow path, and in the midnight time zone, the target boiling is When the temperature difference between the temperature and the boiling temperature detected by the boiling temperature detecting means is within a second predetermined value that is smaller than the first predetermined value, the flow path switching means is configured to cause the upper flow to change. In the time zone when there is no need for heat storage with hot hot water, the upper flow path communicating with the upper part of the hot water tank is selected to return the intermediate hot water to the upper side of the hot water tank. This suppresses the rise in the temperature of the chilled water in the lower part of the hot water storage tank, stores a large amount of heat in the hot water storage tank during the required time, and increases the number of times of boiling and defrosting operations. While maintaining a low degree, an effect that can be operated with high energy efficiency.

The heat pump water heater of the present invention stores a large amount of heat in the hot water storage tank in the required time zone by appropriately selecting whether the warm water is to be recirculated to the upper part or the lower part of the hot water storage tank depending on the time period. In addition, it is possible to obtain the effect that the boiling operation can be performed with high energy efficiency.

The first invention includes at least a heat pump cycle that includes a compressor and a radiator to circulate the refrigerant, a hot water storage tank that stores a heated fluid heated by the refrigerant in the radiator, and radiates the heated fluid to the heat. A circulation pump that recirculates to the hot water storage tank through a heater, an upper flow path that communicates the heat radiator and a substantially upper portion of the hot water storage tank, a lower flow path that communicates the heat radiator and a substantially lower portion of the hot water storage tank , a flow passage switching means for switching the flow path by selecting one of the previous SL upper channel and the lower channel, boiling detects the boiling temperature of the heated fluid is boiled by the heat radiator A temperature detecting means; and a control means, wherein the control means has a predetermined temperature difference between a target boiling temperature and a boiling temperature detected by the boiling temperature detecting means in a daytime period. 1's When it is within a certain value, the flow path switching means switches so as to select the upper flow path, and in the midnight time zone, the temperature of the target boiling temperature and the boiling temperature detected by the boiling temperature detection means When the difference falls within a second predetermined value having a temperature difference smaller than the first predetermined value, the flow path switching means switches so as to select the upper flow path .

Thus, in a time zone when there is no need for heat storage with hot hot water, the upper flow path communicating with the upper part of the hot water storage tank is selected to return the intermediate hot water to the upper side of the hot water storage tank. Suppresses the rise in temperature, stores a large amount of heat in the hot water storage tank in the required time zone, and keeps the boiling water supply temperature low even if the number of times of boiling operation and defrosting operation increases. There is an effect that it is possible to drive with energy efficiency.

In addition, during the daytime hours when the number of heating operations associated with the hot water supply load is high, it is possible to recirculate the medium temperature water to the upper part of the hot water storage tank to suppress the increase in the temperature of the boiling water supply, and to operate with high energy efficiency. it can.

In addition, during the midnight hours, the generated intermediate temperature water is returned to the lower part of the hot water storage tank so that the amount of heat stored in the hot water storage tank can be increased at the completion of midnight boiling, and the boiling operation can be performed with high energy efficiency. .

In the second aspect of the invention, in particular, the flow path switching means of the first aspect of the invention selects the upper flow path at the time of starting the compressor in the daytime period, and in the daytime period, after the compressor is started, The medium temperature water generated in the process of starting up the heat pump cycle is returned to the upper part of the hot water storage tank to suppress the rise in the temperature of the boiling water supply during the boiling operation, and the boiling operation can be performed with high energy efficiency. .

In the third aspect of the invention, in particular, the flow path switching means of the first aspect of the invention selects the upper flow path at the start of the circulation pump in the daytime period, and in the daytime period, after the boiling pump is started, The medium-temperature water generated during the startup process where the flow rate of water circulating in the boiling circuit is excessive is returned to the upper part of the hot water storage tank to suppress the rise in the temperature of the heated boiling water during the boiling operation. A boiling operation can be performed.

In the fourth invention, in particular, a refrigerant that can be in a supercritical state on the high pressure side is used as the refrigerant of the heat pump cycle of any one of the first to third inventions. Medium-temperature water generated during boiling operation at a high temperature that reaches ℃ is recirculated to the upper part of the hot water storage tank to suppress the rise in the boiling water supply temperature during boiling operation and perform boiling operation with high energy efficiency be able to.

In particular, the fifth invention uses carbon dioxide as the refrigerant of the heat pump cycle of the fourth invention, and can perform a boiling operation with high energy efficiency without risk of ignition or explosion of the refrigerant.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a configuration diagram of a heat pump water heater in the first embodiment of the present invention, and FIG. 2 is a flowchart showing a method for determining a flow path to be selected by a three-way valve of the heat pump water heater. In addition, about the same part as the said conventional heat pump water heater, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  First, based on FIG. 1, the structure of the heat pump water heater in this Embodiment is described.

  The heat pump water heater in the present embodiment includes a heat pump unit 21 and a hot water storage unit 22, and the heat pump unit 21 includes a compressor 1, a radiator 2, an expansion valve 3, and an evaporator 4. Are configured in this order to form a heat pump cycle 5.

  The hot water storage unit 22 includes a hot water storage tank 11 for storing the heated fluid boiled by the cooling heat of the refrigerant in the radiator 2, a circulation pump 12, a three-way valve 13, a three-way valve control means 14, and a three-way valve 13. A boiling circuit 16 that recirculates to the upper or lower portion of the hot water storage tank 11 is provided.

  The three-way valve 13 serves as a flow path switching unit that switches between an upper flow path 16 a communicating with the upper side of the hot water storage tank 11 and a lower flow path 16 b communicating with the lower side of the hot water storage tank 11.

  Reference numeral 14 denotes a three-way valve control means, and reference numeral 15 denotes a boiling temperature sensor serving as a boiling temperature detecting means.

  Next, the operation and action of the heat pump water heater in the present embodiment configured as described above will be described. When the boiling operation is started, the compressor 1 and the circulation pump 12 are started, the refrigerant circulates in the heat pump cycle 5 and the water circulates in the boiling circuit 16, and heat energy is transferred from the refrigerant to the water in the radiator 2. To produce hot water. Immediately after starting the boiling operation, the three-way valve 13 selects the lower flow path 16b communicating with the lower part of the hot water storage tank 11, but the boiling temperature detected by the boiling temperature sensor 15 is higher than a predetermined temperature. When it becomes higher, the three-way valve control means 14 switches the three-way valve 13 to select the upper flow path 16a communicating with the upper part of the hot water storage tank 11.

  A flowchart of the three-way valve control means 14 for determining the flow path selected by the three-way valve 13 is shown in FIG. As shown in FIG. 2, after the operation is started, the three-way valve 13 is switched so as to select the lower flow path 16 b communicating with the lower part of the hot water storage tank 11, and the current time is a daytime time zone or a midnight time. Check if it is a belt.

If the current time is daytime, the difference between the boiling temperature detected by the boiling temperature sensor 15 and the target boiling temperature is equal to or less than a first predetermined value (for example, 45 deg ) (for example, the target boiling). If the temperature is 70 ° C., it is determined whether or not the boiling temperature is 25 ° C. or more. If the temperature difference is 45 ° C., the three-way valve control means 14 connects the three-way valve 13 to the upper part of the hot water tank 11. Switch to the flow path 16a. On the other hand, if the current time is midnight, the difference between the boiling temperature detected by the boiling temperature sensor 15 and the target boiling temperature is equal to or less than a second predetermined value (for example, 15 deg ) (for example, the target boiling). When the raising temperature is 70 ° C., the three-way valve control means 14 switches the three-way valve 13 to the upper flow path 16 a communicating with the upper part of the hot water storage tank 11.

As described above, by operating way valve 13, in the daytime, the hot water in the temperature difference with respect to temperature boiling target is within 45 deg is returned to the hot water storage tank 11 top Therefore, an increase in the temperature of the cold water at the lower part of the hot water storage tank 11 is suppressed, an increase in the temperature of the boiling water supplied to the radiator 2 is suppressed, and the energy efficiency during the heating operation by the heat pump cycle 5 is improved.

On the other hand, in the midnight time zone, the medium temperature water whose boiling temperature is 15 deg or more with respect to the target boiling temperature is recirculated to the lower part of the hot water storage tank 11, and the temperature drop of the hot water in the upper part of the hot water storage tank 11 is suppressed. Thus, it is possible to increase the amount of heat stored in the hot water storage tank 11 when midnight boiling is completed.

  By doing so, a large amount of heat can be stored in the hot water storage tank 11 in a necessary time zone, and the energy efficiency during the boiling operation can be increased, thereby reducing the power consumption.

  According to the present embodiment, with the above configuration, when the boiling temperature reaches a predetermined temperature in the daytime and midnight hours, the flow path is switched so as to communicate from the lower part of the hot water storage tank 11 to the upper part. A three-way valve 13 is provided for setting the flow path switching temperature in the time zone higher than the flow path switching temperature in the daytime time zone, and in the daytime time zone, the hot water storage tank generates the medium-temperature water generated at the start of the boiling operation or after the defrosting operation. By returning to the upper part of 11 and returning the intermediate temperature water to the lower part of the hot water storage tank 11 in the late-night time zone, it is possible to achieve high energy efficiency during boiling operation while storing a large amount of heat in the required time zone. Play.

  In the present embodiment, the operation, action, and effect of the three-way valve 13 after the boiling operation is started until the boiling temperature reaches the target boiling temperature are described. The same effect can be obtained by operating the three-way valve 13 in the same way during the startup operation.

  As shown in FIG. 3, a three-way valve 13 includes a flow path communicating with the upper part of the hot water storage tank 11 and a flow path bypassing and communicating with a flow path for supplying boiling water to the radiator 2 from the lower part of the hot water storage tank 11. In the heat pump water heater as selected by the above, the same effect can be obtained by controlling by the three-way valve control means 14 as in the present embodiment.

(Embodiment 2)
FIG. 4 is a flowchart showing a method for determining a flow path to be selected by the three-way valve of the heat pump water heater in the second embodiment of the present invention. In addition, about the same part as the heat pump water heater in the said conventional and 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  As shown in FIG. 4, the heat pump water heater in the present embodiment is controlled by different control methods in the daytime time zone and the midnight time zone, and the other configuration is the heat pump water heater in the first embodiment. It is the same as the machine.

In FIG. 4, in the daytime period, the heat pump water heater starts operation, and the compressor 1 starts to circulate the refrigerant in the heat pump cycle 5. At the same time, the three-way valve 13 is controlled by the three-way valve control means 14. 11 is switched to the upper flow path 16a that communicates with the upper part.

On the other hand, in the midnight time zone, as in the conventional heat pump water heater and the heat pump water heater in the first embodiment, the boiling temperature detected by the boiling temperature sensor 15 is higher than the target boiling temperature. When the temperature difference falls within 15 deg (second predetermined value ), the three-way valve control means 14 switches the three-way valve 13 to the upper flow path 16 a communicating with the upper part of the hot water storage tank 11.

  By operating the three-way valve 13 as described above, the compressor 1 is started during the daytime period, and the medium-temperature water generated during the start-up process of the heat pump cycle is returned to the upper part of the hot water storage tank 11. 11 The rise in the cold water temperature at the bottom is suppressed, the rise in the boiling water supply temperature supplied to the radiator 2 is suppressed, and the energy efficiency during the boiling operation by the heat pump cycle 5 is improved.

On the other hand, in the midnight time zone, the medium temperature water whose boiling temperature is 15 deg or more with respect to the target boiling temperature is recirculated to the lower part of the hot water storage tank 11, and the temperature drop of the hot water in the upper part of the hot water storage tank 11 is suppressed. Thus, it is possible to increase the amount of heat stored in the hot water storage tank 11 when midnight boiling is completed.

  By doing so, a large amount of heat can be stored in the hot water storage tank 11 in a necessary time zone, and the energy efficiency during the boiling operation can be increased, thereby reducing the power consumption.

  According to the present embodiment, with the above configuration, in the daytime period, the flow path is switched so as to communicate from the lower part to the upper part of the hot water storage tank 11 when the compressor 1 is started, and in the late-night time period, the boiling temperature is increased. Is provided with a three-way valve 13 for switching the flow path when the temperature reaches or exceeds a predetermined flow path switching temperature, and in the daytime period, the medium-temperature water generated at the start of the boiling operation or the like is returned to the upper part of the hot water storage tank 11 to In this case, the medium-temperature water is returned to the lower part of the hot water storage tank 11 to produce a high energy efficiency during the boiling operation while storing a large amount of heat in a necessary time zone.

  As in the first embodiment, as shown in FIG. 3, the flow path communicates with the upper part of the hot water storage tank 11 and the flow path for supplying the boiling water supply from the lower part of the hot water storage tank 11 to the radiator 2. Even in a heat pump water heater in which the three-way valve 13 selects a flow path that bypasses and communicates, the same effect can be obtained by controlling the three-way valve control means 14 as in the present embodiment.

(Embodiment 3)
FIG. 5 is a flowchart showing a method for determining a flow path to be selected by the three-way valve of the heat pump water heater in the third embodiment of the present invention. In addition, about the same part as the heat pump water heater in the past and the said embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  The three-way valve 13 of the heat pump water heater in the present embodiment is controlled by the three-way valve control means 14 according to a different control method in the daytime time zone and the midnight time zone according to the flowchart as shown in FIG.

In FIG. 5, in the daytime period, the heat pump water heater starts operation, and the circulation pump 12 starts to circulate water to the boiling circuit 16, and at the same time, the three-way valve 13 is controlled by the three-way valve control means 14. The upper flow path 16 a communicating with the upper part of the hot water storage tank 11 is switched.

On the other hand, in the midnight time zone, the boiling temperature detected by the boiling temperature sensor 15 is equal to the target boiling temperature as in the conventional heat pump water heater and the heat pump water heater described in the first embodiment. When the temperature difference falls within 15 deg (second predetermined value ), the three-way valve control means 14 switches the three-way valve 13 to the upper flow path 16 a communicating with the upper part of the hot water storage tank 11.

  By operating the three-way valve 13 as described above, the circulation pump 12 is started in the daytime period, and the medium-temperature water generated in the rising process of the boiling circuit 16 and the heat pump cycle 5 is returned to the upper part of the hot water storage tank 11. Therefore, the rise of the cold water temperature at the lower part of the hot water storage tank 11 is suppressed, the rise of the boiling water supply temperature supplied to the radiator 2 is suppressed, and the energy efficiency during the heating operation by the heat pump cycle 5 is improved. .

On the other hand, in the midnight time zone, the medium temperature water whose boiling temperature is 15 deg or more with respect to the target boiling temperature is recirculated to the lower part of the hot water storage tank 11, and the temperature drop of the hot water in the upper part of the hot water storage tank 11 is suppressed. Thus, it is possible to increase the amount of heat stored in the hot water storage tank 11 when midnight boiling is completed.

  By doing so, a large amount of heat can be stored in the hot water storage tank 11 in a necessary time zone, and the energy efficiency during the boiling operation can be increased, thereby reducing the power consumption.

  According to the present embodiment, with the above configuration, the flow path is switched so as to communicate from the lower part to the upper part of the hot water storage tank 11 with the start of the circulation pump 12 in the daytime period, and the boiling temperature is increased in the midnight period. Is provided with a three-way valve 13 for switching the flow path when the temperature reaches or exceeds a predetermined flow path switching temperature, and in the daytime period, the medium-temperature water generated at the start of the heating operation or the like is returned to the upper part of the hot water storage tank 11 for midnight time. In the belt, the medium-temperature water is returned to the lower part of the hot water storage tank 11 to produce a high energy efficiency during the boiling operation while storing a large amount of heat in a necessary time zone.

  As in the first embodiment, as shown in FIG. 3, the flow path communicates with the upper part of the hot water storage tank 11 and the flow path for supplying the boiling water supply from the lower part of the hot water storage tank 11 to the radiator 2. Even in a heat pump water heater in which the three-way valve selects a flow path that bypasses and communicates, the same effect can be obtained by controlling the three-way valve control means 14 as in the present embodiment.

  In addition, if the refrigerant | coolant which can be in a supercritical state is used as a refrigerant | coolant of the heat pump cycle 5, it produces | generates at the time of the boiling operation in high temperature which makes a refrigerant | coolant a supercritical state and reaches the tapping temperature 90 degreeC. Thus, the warm water can be recirculated to the upper part of the hot water storage tank 11 to suppress the rise of the boiling water supply temperature during the boiling operation, and the boiling operation can be performed with high energy efficiency.

  In particular, when carbon dioxide is used as the refrigerant, boiling operation can be performed with high energy efficiency without risk of ignition or explosion of the refrigerant.

As described above, the hot water storage type heat pump water heater according to the present invention includes the flow path switching means for appropriately switching the flow path communicating with the substantially upper part and the substantially lower part of the hot water tank by a control method that varies depending on the time zone, When the large amount of heat needs to be stored, the medium temperature water generated in the lower part of the hot water storage tank is recirculated. While suppressing the rise in temperature of the raised feed water and making it possible to store a large amount of heat in the hot water storage tank during the required time, the heated feed water can be increased even if the number of times of the boiling operation and defrosting operation increases. This has the effect of suppressing the temperature rise and performing a boiling operation with high energy efficiency, and is useful for energy saving and prevention of hot water outflow of the heat pump water heater.

Configuration diagram of heat pump water heater in Embodiment 1 of the present invention The flowchart which shows the method of determining the flow path which the three-way valve of the heat pump water heater selects Configuration diagram showing another example of heat pump water heater The flowchart which shows the method of determining the flow path which the three-way valve of the heat pump water heater in Embodiment 2 of this invention selects. The flowchart which shows the method of determining the flow path which the three-way valve of the heat pump water heater in Embodiment 3 of this invention selects. Configuration diagram of conventional heat pump water heater

DESCRIPTION OF SYMBOLS 1 Compressor 2 Radiator 3 Expansion valve 4 Evaporator 5 Heat pump cycle 11 Hot water storage tank 12 Circulation pump 13 Three-way valve (flow path switching means)
14 Three-way valve control means 15 Boiling temperature sensor (boiling temperature detection means)
16 Boiling circuit 16a Upper flow path 16b Lower flow path 21 Heat pump unit 22 Hot water storage unit

Claims (5)

A heat pump cycle including at least a compressor and a radiator to circulate the refrigerant; a hot water storage tank for storing the heated fluid heated by the refrigerant in the radiator; and the hot water storage tank for passing the heated fluid through the radiator a circulation pump for recirculating the an upper passage communicating the substantially upper portion of the hot water storage tank and the radiator, and a lower passage communicating the substantially lower portion of the hot water storage tank and the radiator, before Symbol upper channel A flow path switching means for selecting one of the lower flow paths to switch the flow path, a boiling temperature detection means for detecting the boiling temperature of the heated fluid boiled by the radiator, and a control And the control means has a temperature difference between the target boiling temperature and the boiling temperature detected by the boiling temperature detecting means within a predetermined first predetermined value during daytime hours. Na And the flow path switching means switches so as to select the upper flow path, and in the midnight time zone, the temperature difference between the target boiling temperature and the boiling temperature detected by the boiling temperature detection means, The heat pump water heater according to claim 1, wherein when the temperature difference is within a second predetermined value that is smaller than the first predetermined value, the flow path switching means switches to select the upper flow path . 2. The heat pump water heater according to claim 1, wherein the flow path switching means selects the upper flow path when the compressor is started in the daytime time zone. The heat pump water heater according to claim 1, wherein the flow path switching means selects the upper flow path at the time of starting the circulation pump in the daytime time zone. The heat pump water heater according to any one of claims 1 to 3 , wherein a refrigerant that can be in a supercritical state on a high pressure side is used as a refrigerant of the heat pump cycle. The heat pump water heater according to claim 4 , wherein carbon dioxide is used as a refrigerant of the heat pump cycle.

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