Hot water supply system

Abstract

This technology provides a way to reduce the waiting time for hot water when internal heating control is performed in a hot water supply system. [Solution] The hot water supply system comprises a hot water storage tank, an internal heat source device positioned in the middle or upper region inside the hot water storage tank, a first temperature sensor for detecting the temperature of water below the internal heat source device inside the hot water storage tank, a second temperature sensor for detecting the temperature of water above the internal heat source device inside the hot water storage tank, a circulation path connecting the lower and upper parts of the hot water storage tank, a heat pump for heating the water flowing through the circulation path with the heat of a refrigerant, a circulation pump for sending the water stored in the hot water storage tank from the lower part of the tank to the upper part of the tank via the circulation path, and a control unit. The control unit is configured to perform internal heating control, which operates the internal heat source device to heat the water stored in the hot water storage tank while the heat pump is stopped.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a hot water supply system.

Background Art

[0002] Patent Document 1 discloses a hot water supply system including a hot water storage tank for storing water to be supplied to a predetermined hot water supply location, an internal heat source device disposed in a lower region inside the hot water storage tank for heating the water stored in the hot water storage tank, a first temperature sensor for detecting, as a first detected temperature, the temperature of water below the internal heat source device inside the hot water storage tank, a second temperature sensor for detecting, as a second detected temperature, the temperature of water above the internal heat source device inside the hot water storage tank, a circulation path connecting the lower and upper portions of the hot water storage tank, a heat pump provided in the circulation path for heating the water flowing through the circulation path by the heat of a refrigerant, a circulation pump for sending the water stored in the hot water storage tank from the lower portion of the hot water storage tank to the upper portion of the hot water storage tank via the circulation path, and a control unit. The control unit is configured to be capable of executing internal heating control for operating the internal heat source device to heat the water stored in the hot water storage tank in a state where the operation of the heat pump is stopped. The control unit starts the internal heating control when the first detected temperature is equal to or higher than a predetermined reference temperature, and then ends the internal heating control when a predetermined time has elapsed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] If the heat pump is operated when the temperature of the water flowing from the hot water storage tank into the heat pump (i.e., the temperature detected as the first detection temperature) is high, there is a risk that the pressure of the refrigerant flowing into the heat pump's compressor will become excessively high. Therefore, in order to suppress excessive pressure on the compressor, the hot water supply system of Patent Document 1 is configured to perform internal heating control (i.e., stop the operation of the heat pump and instead operate an internal heat source device to heat the water in the hot water storage tank) when the first detection temperature is above a predetermined reference temperature.

[0005] Conventional hot water supply systems are configured to send water from the top of a hot water storage tank to the hot water supply location. Therefore, in order to provide hot water to the hot water supply location quickly, it is desirable to heat the water at the top of the hot water storage tank quickly. However, in the hot water supply system of Patent Document 1, the internal heat source device is located in the lower region inside the hot water storage tank. Therefore, when the internal heating control, which heats the water using the internal heat source device, is being performed, the water at the top of the hot water storage tank cannot be heated quickly. For this reason, in the hot water supply system of Patent Document 1, when internal heating control is performed, the time until hot water is supplied to the hot water supply location (also called the waiting time for hot water) may become longer. This specification provides a technology that can shorten the waiting time for hot water when internal heating control is performed in a hot water supply system. [Means for solving the problem]

[0006] In a first aspect of this technology, the hot water supply system may include: a hot water storage tank for storing water to be supplied to a predetermined hot water supply location; an internal heat source device positioned in an intermediate or upper region inside the hot water storage tank for heating the water stored in the hot water storage tank; a first temperature sensor for detecting the temperature of water below the internal heat source device inside the hot water storage tank as a first detection temperature; a second temperature sensor for detecting the temperature of water above the internal heat source device inside the hot water storage tank as a second detection temperature; a circulation path connecting the lower and upper parts of the hot water storage tank; a heat pump provided in the circulation path for heating the water flowing through the circulation path by the heat of a refrigerant; a circulation pump for sending the water stored in the hot water storage tank from the lower part of the hot water storage tank to the upper part of the hot water storage tank via the circulation path; and a control unit. The control unit may be configured to perform internal heating control, which involves operating the internal heat source device to heat the water stored in the hot water storage tank while the operation of the heat pump is stopped. The control unit may be configured to perform a first process in which it starts the internal heating control when the first detected temperature is equal to or greater than a predetermined first reference temperature and the second detected temperature is less than a first lower threshold temperature, and then terminates the internal heating control when the second detected temperature becomes equal to or greater than a first upper threshold temperature which is higher than the first lower threshold temperature.

[0007] According to the above configuration, the internal heat source device is positioned in the middle or upper region inside the hot water storage tank (i.e., positioned above the internal heat source device described in Patent Document 1). Therefore, even when internal heating control is performed in the hot water supply system, the water at the top of the hot water storage tank can be heated quickly. This reduces the waiting time for hot water when internal heating control is performed in the hot water supply system.

[0008] In a second aspect of this technology, in the first embodiment, the control unit may perform the internal heating control in the first process with the circulation pump stopped.

[0009] Normally, hot water heated by the internal heat source moves to the top of the hot water storage tank by thermal convection. Therefore, the water at the bottom of the hot water storage tank (specifically, the water below the internal heat source inside the hot water storage tank) is relatively cold. If the circulation pump is operated while the water is being heated by the internal heat source, there is a risk that the cold water at the bottom of the hot water storage tank will be sent to the top of the tank via the circulation path. As a result, it may take longer to heat the water at the top of the hot water storage tank to the desired temperature, potentially increasing the waiting time for hot water. With the above configuration, since the circulation pump does not operate when the water is being heated by the internal heat source, the water at the top of the hot water storage tank can be heated to the desired temperature in a shorter time compared to when the circulation pump is operating. This further reduces the waiting time for hot water.

[0010] In a third aspect of the present technology, in the first or second aspect described above, the control unit may be configured to further perform a second process in which the internal heating control is started when the first detected temperature is equal to or greater than a predetermined second reference temperature and the second detected temperature is less than a second lower threshold temperature, and the internal heating control is terminated when the first detected temperature becomes equal to or greater than a second upper threshold temperature which is higher than the second lower threshold temperature.

[0011] In the first process, when the first detected temperature exceeds the first upper threshold temperature (i.e., when the water above the internal heat source is heated to a certain extent), the internal heating control terminates. Therefore, when the control unit is made to execute the first process, the internal heating control may terminate before the water at the bottom of the hot water storage tank is heated. However, in some cases, it is desirable to heat the water at the bottom of the hot water storage tank as well through the internal heating control. With the above configuration, the control unit can execute a second process separate from the first process. In the second process, the internal heating control is executed until the first detected temperature exceeds the second upper threshold temperature (i.e., until the water below the internal heat source is heated to a certain extent). Therefore, by making the control unit execute the second process, the water at the bottom of the hot water storage tank, as well as the water at the top of the tank, can be heated through the internal heating control.

[0012] In a fourth aspect of this technology, in the third aspect described above, the control unit may perform the internal heating control while operating the circulation pump in the second process.

[0013] Normally, hot water heated by the internal heat source moves to the top of the hot water storage tank by thermal convection. As a result, the water at the bottom of the hot water storage tank (specifically, the water below the internal heat source) is relatively cold. With the above configuration, when the water is being heated by the internal heat source, the circulation pump operates, sending the cold water at the bottom of the hot water storage tank to the top of the tank via the circulation path. This allows the cold water and hot water inside the hot water storage tank to be actively mixed, and the water inside the hot water storage tank can be heated evenly throughout.

[0014] In a fifth aspect of this technology, in the first to fourth embodiments described above, a fluorocarbon refrigerant may be used as the refrigerant of the heat pump.

[0015] Because fluorocarbon refrigerants have high thermal conductivity, using them as refrigerants in heat pumps can improve the operating efficiency of the heat pump. However, heat pumps using fluorocarbon refrigerants tend to have a low water temperature when the water is heated to its limit (also called the upper heating limit temperature). For example, the upper heating limit temperature of a heat pump using fluorocarbon refrigerants is 66°C. Therefore, if the water in the hot water storage tank is agitated for any reason, the temperature of the water in the storage tank may become uniform, resulting in an overall temperature that is neither too high nor too low. Specifically, this "intermediate temperature" refers to a temperature that is slightly insufficient to supply hot water to the hot water supply point, and at which heating by the heat pump could result in excessive pressure being applied to the compressor. With the above configuration, if the water in the hot water storage tank is at an overall temperature that is neither too high nor too low, internal heating control can be performed by an internal heat source device to heat the water in the storage tank. This allows the water in the storage tank to be heated to a temperature sufficient to supply hot water to the hot water supply point without heating by the heat pump. Therefore, the above configuration eliminates the problem that arises when using a fluorocarbon refrigerant in a heat pump (i.e., the water temperature in the hot water storage tank remains at an intermediate temperature overall). [Brief explanation of the drawing]

[0016] [Figure 1] This diagram schematically shows the configuration of the hot water supply system 100 according to the embodiment. [Figure 2] This is a flowchart of the first boiling-related processing performed by the controller of the hot water supply system 100 according to the embodiment. [Figure 3] This figure shows the temperature distribution of the water in the tank 30 after it has been heated by the heat pump 17 in the hot water supply system 100 according to the embodiment. [Figure 4] This figure shows the temperature distribution of the water in the tank 30 when the water temperature in the tank 30 is at an intermediate temperature overall, according to the hot water supply system 100 of the embodiment. [Figure 5]In the hot water supply system 100 according to the embodiment, it is a diagram showing the temperature distribution of the water in the tank 30 after heating the water in the tank 30 by the electric heater 39 without operating the circulation pump 18. [Figure 6] It is a flowchart of the second boiling-related process executed by the controller of the hot water supply system 100 according to the embodiment. [Figure 7] In the hot water supply system 100 according to the embodiment, it is a diagram showing the temperature distribution of the water in the tank 30 after heating the water in the tank 30 by the electric heater 39 while operating the circulation pump 18.

Mode for Carrying Out the Invention

[0017] (Example; Hot water supply system 100) As shown in FIG. 1, the hot water supply system 100 includes an HP (heat pump) unit 4 and a tank unit 6.

[0018] (HP unit 4) The HP unit 4 uses electric power to absorb heat from the outside air and heat water. The HP unit 4 includes a heat pump 17 including a compressor 10, a condenser 12, an expansion valve 14, a fan 15, and an evaporator 16. The heat pump 17 circulates a refrigerant (for example, a fluorocarbon refrigerant) in the order of the compressor 10, the condenser 12, the expansion valve 14, and the evaporator 16 to absorb heat from the outside air and heat water. The compressor 10 pressurizes the refrigerant to a high temperature and high pressure. The condenser 12 cools the refrigerant by heat exchange with water. HP forward paths 19 and HP return paths 21 are connected to both ends of the water flow path of the condenser 12, respectively. The expansion valve 14 depressurizes the refrigerant to a low temperature and low pressure. The fan 15 sends outside air into the evaporator 16. The evaporator 16 heats the refrigerant by heat exchange with the outside air sent from the fan 15. The HP unit 4 further includes a circulation pump 18 that circulates water through the condenser 12, an incoming thermistor 20 that detects the temperature of the water flowing into the condenser 12, a return thermistor 22 that detects the temperature of the water flowing out of the condenser 12, and an HP controller 24 that controls the operation of each component of the HP unit 4.

[0019] (Tank unit 6) The tank unit 6 includes a tank 30. The tank 30 is a sealed container with its outer side covered by heat insulation material and stores water inside. The capacity of the tank 30 in this embodiment is, for example, 100 liters. In FIG. 1, regions A, B, C, D, E, and F are defined so as to equally divide the total height of the tank 30 (i.e., the distance from the top to the bottom of the tank 30). Regions A and B are also called upper regions. Regions C and D are also called intermediate regions. Regions E and F are also called lower regions.

[0020] The tank unit 6 further includes a tank forward path 31 and a tank return path 33 for circulating the water in the tank 30 to the condenser 12 of the HP unit 4. The upstream end of the tank forward path 31 is connected to the region F (i.e., the lower region) of the tank 30. The downstream end of the tank forward path 31 is connected to the upstream end of the HP forward path 19. The upstream end of the tank return path 33 is connected to the downstream end of the HP return path 21. The downstream end of the tank return path 33 is connected to the region A (i.e., the upper region) of the tank 30. When the circulation pump 18 of the HP unit 4 is driven, the water in the lower region of the tank 30 is sent to the condenser 12 through the tank forward path 31 and the HP forward path 19. The water heated to a high temperature by the condenser 12 is returned to the upper region of the tank 30 through the HP return path 21 and the tank return path 33. When the water heated by the HP unit 4 flows into the tank 30, a temperature stratification (see FIG. 3) in which a layer of high-temperature water is stacked on top of a layer of low-temperature water is formed inside the tank 30.

[0021] The tank unit 6 is supplied with tap water from a water source (not shown), such as a public water supply, via a water supply route 40. The downstream end of the water supply route 40 is connected to area F (i.e., the lower area) of the tank 30. Hot water is also supplied from the tank unit 6 to hot water supply locations (not shown), such as kitchens, showers, and faucets, via a hot water supply route 60. The upstream end of the hot water supply route 60 is connected to area A (i.e., the upper area) of the tank 30. When the hot water supply system 100 supplies hot water, high-temperature water is sent from the upper area of ​​the tank 30 to the hot water supply route 60, and low-temperature water flows from the water supply route 40 into the lower area of ​​the tank 30.

[0022] The tank unit 6 further comprises an intermediate thermistor 37, a lower thermistor 38, and an electric heater 39. The intermediate thermistor 37 is located in region C and detects the temperature of the water in region C. The intermediate thermistor 37 is located, for example, at a distance equivalent to 45% of the total height of the tank 30 from the top of the tank 30. The lower thermistor 38 is located in region F and detects the temperature of the water in region F. The lower thermistor 38 is located, for example, at a distance equivalent to 90% of the total height of the tank 30 from the top of the tank 30. In another example, the lower thermistor 38 may be located in the tank supply path 31 (see Figure 1) connected to region F. The electric heater 39 is located in region D. The electric heater 39 is located, for example, at a distance equivalent to 50% of the total height of the tank 30 from the top of the tank 30. The electric heater 39 generates heat when power is supplied to it. The tank unit 6 can heat the water in the tank 30 by operating the electric heater 39.

[0023] The tank unit 6 further includes a tank controller 74 that controls the operation of each component of the tank unit 6. The tank controller 74 can communicate with the HP controller 24 and also with a remote control 99 operated by the user. The remote control 99 is installed, for example, indoors. The remote control 99 accepts various input operations from the user via switches, buttons, etc. The remote control 99 also informs the user of various information regarding the settings and operation of the hot water supply system 100 through displays and voice.

[0024] The HP controller 24, the tank controller 74, and the remote control 99 are all equipped with a control unit such as a CPU, ROM, and RAM, and a storage unit such as an EEPROM. The control unit executes various processes according to the program stored in the storage unit. The hot water supply system 100 can perform various operations such as boiling by the coordinated control of the HP controller 24, the tank controller 74, and the remote control 99. Hereafter, the HP controller 24, the tank controller 74, and the remote control 99 will be collectively referred to simply as the controller.

[0025] (Boiling operation) During boiling operation, the hot water supply system 100 operates either the heat pump 17 or the electric heater 39 to heat the water in the tank 30 (specifically, the water in the upper region) to a boiling set temperature (e.g., 55°C) set by the user via the remote control 99. Boiling operation is performed, for example, when a predetermined boiling start time arrives, when a user inputs a command to start boiling operation into the remote control 99, when a large amount of hot water flows out of the tank 30 due to filling the bathtub, or when the temperature of the water in the tank 30 drops. The following describes a series of processes (referred to as boiling-related processes) performed by the controller in relation to boiling operation, which is performed when the temperature of the water in the tank 30 drops. The controller repeatedly performs boiling-related processes while the power is on.

[0026] (First boiling-related process: Figure 2) In S2, the controller determines whether the temperature detected by the lower thermistor 38 (also called the lower detected temperature) is above a predetermined HP operation prohibition temperature (e.g., 40°C). If the lower detected temperature is below the HP operation prohibition temperature (NO), the process proceeds to S4.

[0027] In S4, the controller allows the heat pump 17 to operate. Specifically, the controller allows the heat pump 17 to operate until the process reaches S14 (i.e., when the operation of the heat pump 17 is prohibited). After S4, the process proceeds to S6.

[0028] In S6, the controller determines whether the temperature detected by the intermediate thermistor 37 (also called the intermediate detection temperature) is less than a predetermined HP heating start temperature (e.g., 45°C). The HP heating start temperature is, for example, the temperature obtained by subtracting a predetermined temperature (e.g., 10°C) from the boiling point set temperature. If the intermediate detection temperature is equal to or greater than the HP heating start temperature (NO), the process returns to S2. If the intermediate detection temperature is less than the HP heating start temperature (YES), the process proceeds to S8.

[0029] In S8, the controller starts the operation of the heat pump 17 and the circulation pump 18. Specifically, the controller drives the compressor 10 and fan 15 of the heat pump 17 to circulate the refrigerant in the order of compressor 10, condenser 12, expansion valve 14, and evaporator 16, and also drives the circulation pump 18 to circulate water between the tank 30 and the condenser 12. As a result, the water drawn from the bottom of the tank 30 is heated in the condenser 12 through heat exchange with the refrigerant and returned to the top of the tank 30. At this time, the controller controls the output of the heat pump 17 and the circulation pump 18 so that the temperature of the water returned to the top of the tank 30 reaches the boiling point set temperature (for example, 55°C). After S8, the process proceeds to S10.

[0030] In S10, the controller determines whether the lower detection temperature (i.e., the temperature detected by the lower thermistor 38) is equal to or greater than a predetermined HP heating termination temperature (e.g., 45°C). The HP heating termination temperature is, for example, the temperature obtained by adding a predetermined temperature (e.g., 5°C) to the aforementioned HP operation prohibition temperature. If the lower detection temperature is less than the HP heating termination temperature (NO), the process repeats S10. While S10 is repeatedly executed, the water in the tank 30 is heated by the heat pump 17, so the lower detection temperature will eventually become equal to or greater than the HP heating termination temperature. If the lower detection temperature becomes equal to or greater than the HP heating termination temperature (YES), the process proceeds to S12.

[0031] In S12, the controller terminates the operation of the heat pump 17 and the circulation pump 18. This ends the heating of the water in the tank 30 by the heat pump 17. After S12, the process returns to S2.

[0032] If the lower detection temperature in S2 is above the HP operation prohibition temperature (NO), the process proceeds to S14. In S14, the controller prohibits the operation of the heat pump 17. Specifically, the controller prohibits the operation of the heat pump 17 until the process reaches S4 (i.e., when the operation of the heat pump 17 is permitted). After S14, the process proceeds to S16.

[0033] In S16, the controller determines whether the intermediate detection temperature (i.e., the temperature detected by the intermediate thermistor 37) is less than a predetermined heater heating start temperature (e.g., 45°C). The heater heating start temperature is, for example, the temperature obtained by subtracting a predetermined temperature (e.g., 10°C) from the boiling set temperature. If the intermediate detection temperature is equal to or greater than the heater heating start temperature (NO), the process returns to S2. If the intermediate detection temperature is less than the heater heating start temperature (YES), the process proceeds to S18.

[0034] In S18, the controller starts the operation of the electric heater 39. Specifically, the controller energizes the electric heater 39 to start heating the water in the tank 30. When the electric heater 39 starts operating, the water near the electric heater 39 (i.e., region D) is heated first. The water heated by the electric heater 39 moves to the upper part of the tank 30 (i.e., regions A, B, and C) by thermal convection. Therefore, when the electric heater 39 is operating, the water below the electric heater 39 (i.e., the water in regions E and F) is not heated, while the water above the electric heater 39 (i.e., the water in regions A, B, C, and D) is heated. After S18, the process proceeds to S20.

[0035] In S20, the controller determines whether the intermediate detection temperature (i.e., the temperature detected by the intermediate thermistor 37) is equal to or greater than a predetermined heater heating completion temperature (e.g., 55°C). The heater heating completion temperature is higher than the heater heating start temperature mentioned above. The heater heating completion temperature is set to, for example, the same value as the boiling point setting temperature. If the intermediate detection temperature is less than the heater heating completion temperature (NO), the process repeats S20. While S20 is repeatedly executed, the water in the tank 30 is heated by the electric heater 39, so the intermediate detection temperature eventually becomes equal to or greater than the heater heating completion temperature. If the intermediate detection temperature becomes equal to or greater than the heater heating completion temperature (YES), the process proceeds to S22.

[0036] In S22, the controller terminates the operation of the electric heater 39. This ends the heating of the water in the tank 30 by the electric heater 39. After S22, the process returns to S2.

[0037] (Advantages of the first boiling-related treatment) According to the first boiling-related process, if the temperature of the lower region of the tank 30 (i.e., the temperature detected as the lower detection temperature) is such that heating by the heat pump 17 will not cause excessive pressure on the compressor 10 (for example, less than 40°C), then heating of the water in the tank 30 by the heat pump 17 (i.e., processes S8, S10, and S12) is performed. In this case, a temperature stratification as shown in Figure 3 is formed inside the tank 30. However, if the water in the tank 30 is stirred for some reason, the temperature of the water in the tank 30 may become uniform, resulting in an overall temperature that is neither too high nor too low, as shown in Figure 4. Specifically, the temperature of the water in the tank 30 may be such that it is slightly too low to supply to the hot water supply point, and heating by the heat pump 17 will cause excessive pressure on the compressor 10 (for example, between 40°C and 50°C). According to the first boiling-related process, in this case, the water in the tank 30 is not heated by the heat pump 17, but instead the water in the tank 30 is heated by the electric heater 39 (i.e., processes S18, S20, and S22). As a result, as shown in Figure 5, the water in the tank 30 (specifically, the water in areas A, B, C, and D) can be heated to a temperature sufficient to supply hot water to the hot water supply location (for example, 50°C or higher) without heating by the heat pump 17.

[0038] (Second boiling-related process: Figure 6) The controller may perform the second boiling-related process shown in Figure 6 instead of the first boiling-related process shown in Figure 2. The process shown in Figure 6 differs from the process shown in Figure 2 in that it operates the circulation pump 18 to agitate the water in the tank 30 when heating the water in the tank 30 with the electric heater 39. Specifically, the process shown in Figure 6 replaces S20 and S22 of the process shown in Figure 2 with S32, S34, S36, S38, S40, and S42. Below, we will explain the processes S32, S34, S36, S38, S40, and S42 of the process shown in Figure 6, and the other processes will be denoted by the same reference numerals as in Figure 2, and their explanations will be omitted.

[0039] In the process shown in Figure 6, after S18, the process proceeds to S32. In S32, the controller determines whether the intermediate detection temperature (i.e., the temperature detected by the intermediate thermistor 37) is equal to or greater than the boiling set temperature (for example, 55°C). If the intermediate detection temperature is less than the boiling set temperature (NO), the process repeats S32. While S32 is repeatedly executed, the water in the tank 30 is heated by the electric heater 39, so the intermediate detection temperature eventually becomes equal to or greater than the boiling set temperature. If the intermediate detection temperature becomes equal to or greater than the boiling set temperature (YES), the process proceeds to S34.

[0040] In S34, the controller starts the circulation pump 18. When the circulation pump 18 is operating, the cold water drawn from the bottom of the tank 30 is returned to the top of the tank 30 and mixes with the hot water at the top of the tank 30. After S34, the process proceeds to S36.

[0041] In S36, the controller determines whether the intermediate detection temperature is below a predetermined circulation termination temperature (e.g., 50°C). Due to the operation of the circulation pump 18 started in S34, the cold water and hot water in the tank 30 mix, which may result in the intermediate detection temperature falling below the circulation termination temperature. If the intermediate detection temperature falls below the circulation termination temperature (YES), the process proceeds to S38.

[0042] In S38, the controller stops the operation of the circulation pump 18. By stopping the operation of the circulation pump 18, the cold water drawn from the bottom of the tank 30 is returned to the top of the tank 30, preventing the temperature of the hot water at the top of the tank 30 from dropping any further. After S38, the process returns to S32.

[0043] If the intermediate detection temperature in S36 is equal to or greater than the circulation end temperature (NO), the process proceeds to S40. In S40, the controller determines whether the lower detection temperature (i.e., the temperature detected by the lower thermistor 38) is equal to or greater than the heater heating end temperature (e.g., 55°C). If the lower detection temperature is less than the heater heating end temperature (NO), the process returns to S36. Subsequently, the processes from S32 to S40 are repeatedly executed, and the water in the tank 30 is heated by the electric heater 39, so the lower detection temperature will eventually become equal to or greater than the heater heating end temperature. If the lower detection temperature becomes equal to or greater than the heater heating end temperature (YES), the process proceeds to S42. In S42, the controller terminates the operation of the electric heater 39 and the circulation pump 18. After S42, the process returns to S2.

[0044] (Advantages of the second boiling-related treatment) According to the second boiling-related process, the circulation pump 18 operates when the electric heater 39 heats the water in the tank 30, so that the cold water and hot water inside the tank 30 are actively mixed. As a result, as shown in Figure 7, not only the water above the electric heater 39 but also the water below the electric heater 39 can be heated.

[0045] (modified version) (See Figure 1) The hot water supply system 100 may also include a heat source other than the electric heater 39 (for example, a burner that burns fuel) as an internal heat source device located inside the tank 30. In the example where a burner is used as the internal heat source device, a heat exchanger through which a heat transfer medium flows may be placed inside the tank 30. The burner may heat the water in the tank 30 via the heat transfer medium.

[0046] (See Figure 1) Instead of being located in region D, the electric heater 39 may be located in any of regions A, B, or C. In this case, the position of the intermediate thermistor 37 may be changed to be located above the electric heater 39.

[0047] In the process shown in Figure 2 (or the process shown in Figure 6), the return thermistor 22 may be used instead of the intermediate thermistor 37 as the temperature sensor for detecting water above the electric heater 39. Specifically, in steps S6, S16, and S2 of the process shown in Figure 2 (or the process shown in Figure 6), the controller may refer to the temperature detected by the return thermistor 22 instead of the temperature detected by the intermediate thermistor 37.

[0048] In the process shown in Figure 2 (or the process shown in Figure 6), instead of the lower thermistor 38, the supply thermistor 20 may be used as the temperature sensor for detecting water below the electric heater 39. Specifically, in steps S2, S10, and S32 of the process shown in Figure 2 (or the process shown in Figure 6), the controller may refer to the temperature detected by the supply thermistor 20 instead of the temperature detected by the lower thermistor 38.

[0049] The refrigerant used in the heat pump 17 may be a refrigerant other than a fluorocarbon refrigerant (for example, propane or carbon dioxide).

[0050] (Correspondence) In this embodiment, the hot water supply system 100 is an example of a "hot water supply system". The tank 30 is an example of a "hot water storage tank". Regions A and B are examples of "upper regions". Regions C and D are examples of "intermediate regions". Regions E and F are examples of "lower regions". The tank supply path 31, HP supply path 19, HP return path 21, and tank return path 33 are examples of "circulation paths". The heat pump 17 is an example of a "heat pump". The circulation pump 18 is an example of a "circulation pump". The electric heater 39 is an example of an "internal heat source device". The lower thermistor 38 is an example of a "first temperature sensor". The lower detected temperature is an example of a "first detected temperature". The intermediate thermistor 37 is an example of a "second temperature sensor". The intermediate detected temperature is an example of a "second detected temperature". The controller is an example of a "control unit". The HP operation prohibition temperature is an example of a "first reference temperature" and a "second reference temperature". The heater heating start temperature is an example of the "first lower threshold temperature" and the "second lower threshold temperature". The heater heating end temperature is an example of the "first upper threshold temperature" and the "second upper threshold temperature". Operating the electric heater 39 is an example of "internal heating control". The first boiling-related process is an example of the "first process". The second boiling-related process is an example of the "second process".

[0051] The technical elements described herein or in the drawings demonstrate technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated herein or in the drawings can achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness in itself. [Explanation of Symbols]

[0052] 4: HP unit, 6: Tank unit, 10: Compressor, 12: Condenser, 14: Expansion valve, 15: Fan, 16: Evaporator, 17: Heat pump, 18: Circulation pump, 19: HP supply path, 20: Supply thermistor, 21: HP return path, 22: Return thermistor, 24: HP controller, 30: Tank, 31: Tank supply path, 33: Tank return path, 37: Intermediate thermistor, 38: Lower thermistor, 39: Electric heater, 40: Water supply path, 60: Hot water supply path, 74: Tank controller, 99: Remote control, 100: Hot water supply system

Claims

1. A hot water storage tank for storing water to be supplied to designated hot water outlets, An internal heat source device is located in the intermediate or upper region inside the hot water storage tank and heats the water stored in the hot water storage tank. A first temperature sensor detects the temperature of the water located below the internal heat source device inside the hot water storage tank as the first detected temperature, A second temperature sensor detects the temperature of water located above the internal heat source device inside the hot water storage tank as the second detected temperature, A circulation path connecting the lower and upper parts of the hot water storage tank, A heat pump is provided in the aforementioned circulation path and heats the water flowing through the circulation path by the heat of the refrigerant, A circulation pump that sends the water stored in the hot water storage tank from the bottom of the hot water storage tank to the top of the hot water storage tank via the circulation path, It includes a control unit, The control unit is configured to perform internal heating control, which involves operating the internal heat source device while the heat pump is stopped to heat the water stored in the hot water storage tank. A hot water supply system in which the control unit is configured to perform a first process, in which the internal heating control is started when the first detected temperature is equal to or greater than a predetermined first reference temperature and the second detected temperature is less than a first lower threshold temperature, and the internal heating control is then terminated when the second detected temperature becomes equal to or greater than a first upper threshold temperature which is higher than the first lower threshold temperature.

2. The hot water supply system according to claim 1, wherein the control unit performs the internal heating control with the circulation pump stopped during the first process.

3. The hot water supply system according to claim 1, wherein the control unit is configured to perform a second process in which it starts the internal heating control when the first detected temperature is equal to or greater than a predetermined second reference temperature and the second detected temperature is less than a second lower threshold temperature, and then terminates the internal heating control when the first detected temperature becomes equal to or greater than a second upper threshold temperature which is higher than the second lower threshold temperature.

4. The hot water supply system according to claim 3, wherein the control unit performs the internal heating control while operating the circulation pump in the second process.

5. The hot water supply system according to any one of claims 1 to 4, wherein a fluorocarbon refrigerant is used as the refrigerant of the heat pump.

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