Heat pump water heater

Abstract

To provide a heat pump water heater that performs a discharge temperature lowering operation for lowering a discharge temperature of a compressor from a time immediately before completion of defrosting.SOLUTION: A heat pump water heater (1) includes: a heat pump unit (4); a hot water storage unit (3) having a hot water storage tank (2) that stores hot water heated by the heat pump unit (4); and control means for controlling a hot water storage operation for storing hot water in the hot water storage tank (2) and a defrosting operation for removing frost adhered to an evaporation heat exchanger. The heat pump water heater is configured to stop inflow of hot water from the hot water storage tank (2) to a condensation heat exchanger, stop a fan of the evaporation heat exchanger and perform the defrosting operation by circulating a refrigerant by expanding an opening of an expansion valve when frost is formed on the evaporation heat exchanger during the hot water storage operation. When an outlet temperature of the evaporation heat exchanger satisfies a predetermined condition indicating a time immediately before the completion of defrosting, a discharge temperature lowering operation for lowering a discharge temperature from the compressor is performed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heat pump water heater that uses hot water heated by a heat pump unit and stored in a hot water storage tank for hot water supply. [Background technology]

[0002] Heat pump water heaters have been widely used for a long time. These systems operate by storing hot water heated by a heat pump unit in a hot water storage tank, and then use the stored water for hot water supply. The heat pump unit is composed of a compressor, a condensing heat exchanger, an expansion valve, and an evaporating heat exchanger, all connected by a refrigerant circuit.

[0003] Heat pump units are highly energy efficient, but their limited heating capacity makes it difficult to heat water instantaneously. Therefore, heat pump water heaters operate in a hot water storage mode to store the amount of heat needed for hot water supply in a hot water storage tank. At this time, the heat pump water heater predicts the time of hot water supply (hot water supply) and the amount of heat needed, for example, based on past hot water supply history, and operates in a hot water storage mode to store the amount of heat needed by the predicted hot water supply time.

[0004] In hot water storage operation, a refrigerant absorbs heat from outside air in an evaporative heat exchanger, compresses the refrigerant, and uses the heat of the compressed refrigerant to heat hot water in a condensing heat exchanger. When the outside air temperature is low, the moisture contained in the outside air that has absorbed heat and cooled down condenses, making it more likely to form frost on the evaporative heat exchanger. Since frost on the evaporative heat exchanger prevents it from absorbing heat from the outside air, when frost is detected, a defrosting operation is performed to remove the frost.

[0005] This defrosting operation is performed by stopping the flow of hot water from the hot water storage tank to the condensing heat exchanger and circulating the refrigerant with the expansion valve opened to a larger degree.

[0006] Incidentally, Patent Document 1 describes that when returning from defrosting operation to normal operation, in order to prevent a drop in the temperature of the hot water in the hot water storage tank, the circulation pump is delayed relative to the return operation of the expansion valve to return to the specified capacity.

[0007] Furthermore, Patent Document 2 describes that a recovery operation is performed to prevent a drop in the temperature of hot water in the hot water storage tank before restarting the heat storage operation after the defrosting operation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 3737357 [Patent Document 2] Patent No. 7211512 Summary of the Invention [Problem to be solved by the invention]

[0009] Patent documents 1 and 2 address the issue that when hot water storage operation is performed to store hot water at a temperature of 80°C or higher in the hot water storage tank, the temperature of the hot water in the condensing heat exchanger drops during defrosting operation, and when normal operation is resumed, low-temperature water flows into the hot water storage tank.

[0010] In contrast, when defrosting is performed during hot water storage operation in which the hot water temperature stored in the hot water storage tank is approximately 65°C, the circulation of hot water to the condensing heat exchanger is stopped, and as the refrigerant heated by the compressor of the heat pump unit passes through the condensing heat exchanger, it heats the stagnant water, which may result in high-temperature hot water being discharged when normal operation is resumed. Furthermore, if the refrigerant temperature is lowered during the defrosting operation to prevent the accumulated water from becoming too hot, the amount of heat supplied to the evaporative heat exchanger decreases, lengthening the defrosting time.

[0011] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a heat pump hot water supply system that performs a discharge temperature reduction operation in which the discharge temperature of the compressor is reduced immediately before the end of defrosting. [Means for solving the problem]

[0012] The heat pump water heater of claim 1 is a heat pump water heater comprising a heat pump unit constructed by connecting a compressor, a condensing heat exchanger, an expansion valve, and an evaporative heat exchanger by a refrigerant circuit, a hot water storage unit having a hot water storage tank for storing hot water heated by the heat pump unit, and a control means for controlling the hot water storage operation for storing hot water in the hot water storage tank and the defrosting operation for removing frost from the evaporative heat exchanger, and is configured so that when frost forms on the evaporative heat exchanger during hot water storage operation, the flow of hot water from the hot water storage tank to the condensing heat exchanger is stopped, the fan of the evaporative heat exchanger is stopped, the opening of the expansion valve is increased to circulate the refrigerant and perform the defrosting operation, and when the outlet temperature of the evaporative heat exchanger satisfies a predetermined condition indicating that defrosting is about to end, a discharge temperature reduction operation is performed to lower the discharge temperature from the compressor.

[0013] According to the above configuration, when the outlet temperature of the evaporative heat exchanger satisfies a predetermined condition indicating that defrosting is about to end, discharge temperature reduction operation is performed to lower the discharge temperature from the compressor, thereby reducing the temperature of the high-temperature accumulated water in the condenser heat exchanger and preventing the occurrence of high-temperature hot water discharge. Moreover, since discharge temperature reduction operation is performed just before the defrosting is about to end, the defrosting time is not prolonged.

[0014] The heat pump water heater of claim 2 is characterized in that, in the invention of claim 1, the discharge temperature lowering operation is performed by lowering the rotation speed of the compressor by a predetermined rotation speed. According to the above configuration, the discharge temperature decreasing operation is performed by decreasing the rotation speed of the compressor by a predetermined rotation speed, so that the discharge temperature decreasing operation can be performed with simple control.

[0015] A heat pump water heater according to a third aspect of the present invention is the heat pump water heater according to the first or second aspect of the present invention, characterized in that the opening of the expansion valve is increased during the discharge temperature decreasing operation compared to during the defrosting operation. According to the above configuration, the expansion valve is not fully opened during defrosting operation but is opened just short of fully opened, and the opening of the expansion valve is increased during the discharge temperature reduction operation compared to during defrosting operation, thereby enabling the discharge temperature of the compressor to be reduced. [Effects of the Invention]

[0016] As described above, the present invention provides various functions and effects. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a configuration diagram of a heat pump hot water heater according to an embodiment of the present invention. [Figure 2] FIG. 2 is a configuration diagram of the heat pump unit of FIG. 1. [Figure 3] 10 is a flowchart showing the contents of a defrosting operation. [Figure 4] 4 is a time chart showing a change in refrigerant temperature at the outlet of the evaporative heat exchanger during a defrosting operation. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, the mode for carrying out the present invention will be described based on examples. [Example]

[0019] First, the configuration of a heat pump hot water heater 1 of the present invention will be described. As shown in Fig. 1, the heat pump water heater 1 has a hot water storage unit 3 equipped with a hot water storage tank 2, a heat pump unit 4 which is a main heat source unit, and, for example, a combustion-type auxiliary heat source unit 5. In this heat pump water heater 1, the heat pump unit 4 heats hot water from the hot water storage tank 2 to a predetermined target hot water storage temperature, and performs a hot water storage operation in which the heated hot water is returned to the hot water storage tank 2 for storage.

[0020] The auxiliary heat source unit 5 supplies hot water from the hot water tap 6 at the set hot water supply temperature, for example as shown by the arrow HW, by heating the hot water discharged from the hot water storage unit 3 according to its temperature, or without heating, depending on the temperature, to the hot water tap 6. Specifically, if the hot water storage tank 2 contains hot water at a temperature that can be supplied at the set hot water supply temperature, the hot water is supplied without heating by the auxiliary heat source unit 5. If the hot water storage tank 2 does not contain hot water at a temperature that can be supplied at the set hot water supply temperature, the hot water is heated by the auxiliary heat source unit 5 and supplied.

[0021] Next, the hot water storage unit 3 will be described. A supply passage 8 equipped with a hot water pump 7 is connected to the bottom of the hot water storage tank 2 of the hot water storage unit 3 in order to supply hot water from the hot water storage tank 2 to the heat pump unit 4. A return passage 9 is connected to the top of the hot water storage tank 2 in order to return the hot water heated by the heat pump unit 4 to the hot water storage tank 2. A switching valve 10 is disposed midway along the return passage 9 to switch the hot water flow path. A return branch passage 9a branched off from the return passage 9 at this switching valve 10 is connected to a portion of the supply passage 8 upstream of the hot water pump 7.

[0022] A return temperature sensor 9b is disposed upstream of the switching valve 10 in the return passage 9, which detects the temperature of the hot water heated by the heat pump unit 4. For example, immediately after the heat pump unit 4 is started, if the temperature detected by the return temperature sensor 9b is lower than a predetermined hot water set temperature, the switching valve 10 can be switched from the hot water storage tank 2 side to the return branch passage 9a side, and the hot water can be circulated without being returned to the hot water storage tank 2 until it can be heated sufficiently.

[0023] A water supply passage 11, which supplies clean water indicated by arrow CW, is connected to the bottom of the hot water storage tank 2. A hot water outlet passage 12, which allows hot water in the hot water storage tank 2 to be discharged from the hot water storage unit 3, is connected to the top of the hot water storage tank 2. A mixing valve 14 is provided midway along the hot water outlet passage 12, and a water supply branch passage 11a, which branches off midway along the water supply passage 11, is connected to the mixing valve 14. The hot water from the hot water storage tank 2 and the clean water from the water supply branch passage 11a are mixed by the mixing valve 14 and discharged from the hot water storage unit 3.

[0024] The hot water storage tank 2 is provided with a plurality of hot water temperature sensors 2a-2d arranged at predetermined intervals in the vertical direction, which can detect the temperature of the hot water stored in the hot water storage tank 2 and the amount of hot water stored at that temperature, i.e., the amount of stored hot water heat. In order to prevent the temperature of the stored hot water from dropping, heat insulating material (not shown) is provided to cover the hot water temperature sensors 2a-2d and the hot water storage tank 2.

[0025] A water supply temperature sensor 11b is disposed in the water supply passage 11 to detect the temperature of clean water (water supply temperature) flowing through the water supply passage 11. A hot water outlet flow rate sensor 12a, a tank hot water outlet temperature sensor 12b, and a hot water outlet temperature sensor 12c are disposed in the hot water outlet passage 12. The hot water outlet flow rate sensor 12a detects the hot water outlet flow rate from the hot water storage unit 3. The tank hot water outlet temperature sensor 12b detects the temperature of the hot water that is discharged from the hot water storage tank 2 and supplied to the mixing valve 14. The hot water outlet temperature sensor 12c detects the temperature of the hot water that is discharged from the hot water storage unit 3 (hot water outlet temperature).

[0026] The downstream end of the hot water outlet passage 12 is connected to the water supply port 5a of the auxiliary heat source unit 5, and a hot water passage 16 is connected to the hot water supply port 5b of the auxiliary heat source unit 5. The hot water passage 16 is connected to a hot water supply destination such as a hot water tap 6 in the kitchen or a bathroom faucet or shower (not shown).

[0027] The hot water storage unit 3 has a hot water storage unit control unit 18 (control means) that controls the temperature adjustment of the hot water discharged from the hot water storage unit 3. The hot water storage unit control unit 18 drives the heat pump unit 4 and the hot water storage pump 7 to control the hot water storage operation in which hot water heated to a target hot water storage temperature by the heat pump unit 4 is stored from the top of the hot water storage tank 2. The hot water storage heat quantity of the hot water storage tank 2 is calculated by the hot water storage unit control unit 18 based on, for example, the temperatures detected by the hot water storage temperature sensors 2a to 2d.

[0028] When the hot water outlet flow rate sensor 12a detects a flow rate equal to or greater than a predetermined flow rate, the hot water storage unit control unit 18 adjusts the mixing ratio of the mixing valve 14 to dispense hot water. The mixing ratio is adjusted based on the temperatures detected by the feed water temperature sensor 11b and the tank hot water outlet temperature sensor 12b so that the temperature detected by the outlet hot water temperature sensor 12c becomes the predetermined hot water outlet temperature. The hot water storage unit control unit 18 learns and stores various operational histories and, for example, uses the hot water outlet history to control the hot water storage operation according to the user's usage pattern.

[0029] An operation remote control 19, which allows the user to set, for example, the hot water supply setting temperature, is connected to the hot water storage unit control unit 18 and the auxiliary heat source unit 5. A plurality of operation remote controls 19 may be connected, and the operation remote control 19 corresponding to the hot water storage unit 3 may be connected to the hot water storage unit control unit 18, and the operation remote control corresponding to the auxiliary heat source unit 5 may be connected to the auxiliary heat source unit 5.

[0030] Next, the heat pump unit 4 will be described. 2, the heat pump unit 4 is configured by connecting a compressor 21, a condensing heat exchanger 22, an expansion valve 23 (expansion means), and an evaporative heat exchanger 24 via a refrigerant circuit 25. The refrigerant sealed in the refrigerant circuit 25 circulates, passing through the compressor 21, the condensing heat exchanger 22, the expansion valve 23, and the evaporative heat exchanger 24 in that order, before returning to the compressor 21. The refrigerant circuit 25 is provided with a discharge temperature sensor 26 that detects the temperature of the refrigerant discharged from the compressor 21, and an evaporative heat exchanger outlet temperature sensor 27 that detects the refrigerant temperature at the outlet of the evaporative heat exchanger 24.

[0031] The heat pump unit 4 includes a blower fan 28 that circulates outside air through the evaporative heat exchanger 24, a heat pump unit control unit 29 that controls the heat pump unit 4 based on commands from the hot water storage unit control unit 18, and an outside air temperature sensor 30 that detects the outside air temperature. The heat pump unit control unit 29 acquires the temperatures detected by the discharge temperature sensor 26, the evaporative heat exchanger outlet temperature sensor 27, and the outside air temperature sensor 30, communicates with the hot water storage unit control unit 18 via a communication line 29a, and controls the operating speed of the compressor 21, the opening of the expansion valve 23, and the air flow rate of the blower fan 28.

[0032] In hot water storage operation, the compressor 21 supplies the compressed, high-temperature, high-pressure refrigerant to the condensing heat exchanger 22. In the condensing heat exchanger 22, hot water supplied from the hot water storage tank 2 by the hot water storage pump 7 is heated to a target hot water storage temperature by heat exchange with the high-temperature refrigerant and returned to the hot water storage tank 2. The high-pressure refrigerant, whose temperature has been lowered and partially liquefied by the heat exchange in the condensing heat exchanger 22, is sent to the expansion valve 23.

[0033] Expansion valve 23 is, for example, an electrically operated control valve whose throttle amount can be changed. When refrigerant passes through expansion valve 23, it rapidly expands and becomes colder than the outside air, and is sent to evaporation heat exchanger 24. The refrigerant then absorbs heat from the circulating outside air in evaporation heat exchanger 24, vaporizing and raising its temperature, and returns to compressor 21, where it is compressed again to a high temperature and high pressure, and is then supplied to condensation heat exchanger 22. By using this heat pump cycle to store hot water, the amount of heat required to dispense hot water is stored in hot water storage tank 2.

[0034] Next, the hot water storage operation and the defrosting operation that may be performed during this hot water storage operation will be described. When the hot water storage operation is started, hot water storage of the required amount of heat based on the hot water storage prediction is started, the heat pump unit 4 is operated, and the hot water storage pump 7 is driven. In the heat pump unit 4, the blower fan 28 is driven, the compressor 21 is driven at a predetermined operating speed, the expansion valve 23 is opened to a predetermined degree to cause the refrigerant in the refrigerant circuit 25 to flow, and the hot water supplied from the hot water storage tank 2 is heated in the condensing heat exchanger 22.

[0035] In cold seasons, when frost forms on the evaporative heat exchanger 24, it becomes difficult for the refrigerant to absorb heat from the outside air, and the refrigerant temperature at the outlet of the evaporative heat exchanger 24 drops. Therefore, when the refrigerant temperature at the outlet of the evaporative heat exchanger 24 falls below the frost determination temperature, a defrosting operation is initiated to remove frost from the evaporative heat exchanger 24. During a long period of hot water storage operation when the outside air temperature is low, frost formation on the evaporative heat exchanger 24 and a defrosting operation to remove the frost may be repeated.

[0036] This defrosting operation will be described based on the flowchart of FIG. 3. In the figure, Si (i = 1, 2, ···) represents each step. This flowchart is pre-stored in the hot water storage unit control unit 18. When the defrosting operation is started, at S1, the rotational speed of the compressor 21 is switched to the defrosting rotational speed (for example, 70 Hz), the opening degree of the expansion valve 23 is switched to the defrosting opening degree (for example, 90% opening degree), and the blower fan 28 and the hot water pump 7 are stopped.

[0037] Next, at S2, the outside air temperature To is read from the outside air temperature sensor 30, the evaporative heat exchanger outlet temperature Tv is read from the evaporative heat exchanger outlet temperature sensor 27, and based on the outside air temperature To and the evaporative heat exchanger outlet temperature Tv read from the sensor and stored in the memory during the hot water storage operation, (To - Tv) = A during the hot water storage operation is calculated.

[0038] Next, at S3, in order to determine whether a predetermined condition indicating immediately before the end of defrosting is satisfied, it is determined whether the temperature difference (To - Tv) between the outside air temperature To and the evaporative heat exchanger outlet temperature Tv is equal to or greater than a set value B (where B > A). As the defrosting progresses, the evaporative heat exchanger outlet temperature Tv gradually increases. Before immediately before the end of defrosting, (To - Tv) < B, so the determination at S3 is No, and thus it returns from S3 to S2. When it is immediately before the end of defrosting, (To - Tv) ≧ B, and the process proceeds from S3 to S4.

[0039] At S4, in order to lower the refrigerant temperature in the heat pump unit 4 and reduce the temperature of the retained water in the condenser heat exchanger 22, as a discharge temperature lowering operation, the rotational speed of the compressor 21 is reduced from, for example, 70 Hz to 60 Hz, and the opening degree of the expansion valve 23 is expanded to, for example, 100%.

[0040] Next, at S5, in order to determine whether the defrosting operation has ended, it is determined whether the evaporative heat exchanger outlet temperature Tv is equal to or higher than a predetermined temperature C (for example, 20°C). While the determination is No, S5 is repeated, and when the determination becomes Yes, the process proceeds to S6. In S6, the defrosting operation is terminated and the hot water storage operation is resumed, so that the rotation speed of the compressor 21 is switched to the hot water storage rotation speed, the expansion valve 23 is switched to the hot water storage opening (for example, 20% opening), the blower fan 28 and the hot water storage pump 7 are restarted, and then this control is terminated.

[0041] FIG. 4 shows a time chart of the evaporative heat exchanger outlet temperature Tv during defrosting operation. After defrosting starts, the refrigerant temperature gradually rises. When the condition (To-Tv)≧B is satisfied, it is determined that the defrosting is about to end, and as a control to lower the refrigerant temperature as described above, the rotation speed of the compressor 21 is reduced and the opening of the expansion valve 23 is increased.

[0042] The operation and effects of the heat pump hot water supply device 1 will be described. When the outlet temperature Tv of the evaporative heat exchanger 24 satisfies a predetermined condition indicating that defrosting is about to end, discharge temperature reduction operation is performed to lower the discharge temperature from the compressor 21, thereby reducing the temperature of the high-temperature accumulated water in the condenser heat exchanger 22 and preventing the occurrence of high-temperature hot water discharge. Moreover, since the discharge temperature reduction operation is performed just before the defrosting is about to end, the defrosting time is not prolonged.

[0043] Since the discharge temperature decreasing operation is performed by decreasing the rotation speed of the compressor 21 by a predetermined rotation speed, the discharge temperature decreasing operation can be performed with simple control.

[0044] During the discharge temperature lowering operation, the opening degree of the expansion valve 23 is increased compared to during the defrosting operation, so that the discharge temperature of the compressor 21 can be lowered.

[0045] In addition, a person skilled in the art can implement the present invention in a form in which various modifications are added to the above-described embodiment without departing from the spirit of the present invention, and the present invention includes such modifications. [Explanation of symbols]

[0046] 1: Heat pump water heater 2: Hot water tank 3: Hot water storage unit 4: Heat pump unit 18: Hot water storage unit control unit 21: Compressor 22: Condensing heat exchanger 23: Expansion valve 24: Evaporative heat exchanger 25: Refrigerant circuit 28: Fan 29: Heat pump unit control unit

Claims

1. A heat pump water heater comprising a heat pump unit configured by connecting a compressor, a condensing heat exchanger, an expansion valve, and an evaporative heat exchanger by a refrigerant circuit, a hot water storage unit having a hot water storage tank for storing hot water heated by the heat pump unit, and control means for controlling a hot water storage operation for storing hot water in the hot water storage tank and a defrosting operation for removing frost from the evaporative heat exchanger, This heat pump water heater is configured to perform defrosting operation when frost forms on the evaporative heat exchanger during hot water storage operation by stopping the flow of hot water from the hot water storage tank to the condensing heat exchanger, stopping the fan of the evaporative heat exchanger, and increasing the opening of the expansion valve to circulate the refrigerant, and when the outlet temperature of the evaporative heat exchanger satisfies a predetermined condition indicating that defrosting is about to end, perform discharge temperature reduction operation to lower the discharge temperature from the compressor.

2. 2. The heat pump hot water supply apparatus according to claim 1, wherein the discharge temperature lowering operation is performed by lowering the rotation speed of the compressor by a predetermined rotation speed.

3. 3. The heat pump hot water supply apparatus according to claim 1, wherein the opening degree of the expansion valve is increased during the discharge temperature decreasing operation compared to during the defrosting operation.

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