Hot water system

Abstract

To provide a technology capable of reducing a stratification range of an intermediate temperature stratification formed after finishing a tank sterilization operation.SOLUTION: A hot water supply system includes a hot water storage tank, a tank circulation passage, a tank circulation pump, a heat pump, and a controller. When a sterilization execution condition is established, the controller executes a tank sterilization operation in which the hot water is circulated between the hot water storage tank and the heat pump by the tank circulation pump, and the hot water is heated by the heat pump. The tank sterilization operation includes: preliminary heating processing for controlling the operation of the tank circulation pump and the heat pump so that the temperature of the hot water flowing out of the heat pump becomes a first target temperature; and main heating processing for controlling the operation of the tank circulation pump and the heat pump so that, after finishing the preliminary heating processing, the temperature of the hot water flowing out of the heat pump becomes a second target temperature higher than the first target temperature. The temperature increase width of the hot water in the main heating processing is smaller than the temperature increase width of the hot water in the preliminary heating processing.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a hot water supply system. [Background technology]

[0002] Patent Document 1 discloses a hot water supply system including a hot water storage tank in which hot water is stored, with a water supply path connected to the bottom and a hot water outlet path connected to the top, a tank circulation path connecting the bottom and top of the hot water storage tank, a tank circulation pump circulating the hot water stored in the bottom of the hot water storage tank to the top of the hot water storage tank via the tank circulation path, a heat pump provided midway along the tank circulation path for heating the hot water circulating through the tank circulation path, and a controller. The controller is configured to execute a tank sterilization operation in which the tank circulation pump circulates the hot water between the hot water storage tank and the heat pump and the hot water is heated by the heat pump when a predetermined sterilization implementation condition is met. The tank sterilization operation includes a preliminary heating process for controlling the operation of the tank circulation pump and the heat pump so that the temperature of the hot water flowing out of the heat pump becomes a first target temperature, and a main heating process for controlling the operation of the tank circulation pump and the heat pump so that the temperature of the hot water flowing out of the heat pump becomes a second target temperature higher than the first target temperature after the preliminary heating process is completed. The temperature rise of the hot water in the heat pump in the main heating process is equal to the temperature rise of the hot water in the heat pump in the preliminary heating process. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-094505 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a hot water supply system, if the hot water in a hot water storage tank is not used for a certain period of time, bacteria such as Legionella bacteria may grow in the water. For this reason, when a specified sterilization implementation condition is met, a tank sterilization operation must be performed to sterilize the hot water in the hot water storage tank. In the tank sterilization operation, the hot water in the hot water storage tank is heated to a temperature at which the above-mentioned bacteria can be sterilized (for example, a temperature of 60°C or higher). At this time, as in the hot water supply system of Patent Document 1, by boiling the hot water in the hot water storage tank in stages, the heat pump can be driven without placing an excessive load on the heat pump compressor.

[0005] However, as described above, if the tank sterilization operation is configured to boil the hot water in the hot water storage tank in stages, if the switching speed (temperature rise speed) when switching from the preliminary heating process to the main heating process is slow, the hot water will be heated to an incomplete temperature, resulting in intermediate temperature stratification in the hot water storage tank. If the range of the intermediate temperature stratification formed after the end of the tank sterilization operation is large, this may lead to problems such as insufficient sterilization effect. This specification provides a technology that can reduce the range of the intermediate temperature stratification formed after the end of the tank sterilization operation.

[0006] In this specification, the state in which a layer of hot water is piled up on top of a layer of low temperature water is called "temperature stratification." Also, the temperature stratification formed by water heated to an intermediate temperature is called "intermediate temperature stratification." And the ratio of the volume of the intermediate temperature stratification to the volume of the hot water storage tank is called the "stratification range of intermediate temperature stratification." [Means for solving the problem]

[0007] The hot water supply system disclosed in this specification includes a hot water storage tank having a water supply passage connected to a lower part and a hot water outlet passage connected to an upper part and storing hot water, a tank circulation passage connecting the lower part and upper part of the hot water storage tank, a tank circulation pump circulating the hot water stored in the lower part of the hot water storage tank to the upper part of the hot water storage tank via the tank circulation passage, a heat pump provided midway along the tank circulation passage and heating the hot water circulating through the tank circulation passage, and a controller. The controller is configured to execute a tank sterilization operation in which the tank circulation pump circulates the hot water between the hot water storage tank and the heat pump and the hot water is heated by the heat pump when a predetermined sterilization implementation condition is met. The tank sterilization operation includes a preliminary heating process in which the operation of the tank circulation pump and the heat pump is controlled so that the temperature of the hot water flowing out of the heat pump becomes a first target temperature, and a main heating process in which the operation of the tank circulation pump and the heat pump is controlled so that the temperature of the hot water flowing out of the heat pump becomes a second target temperature higher than the first target temperature after the preliminary heating process is completed. The temperature rise width of the hot water in the heat pump in the main heating process is smaller than the temperature rise width of the hot water in the heat pump in the preliminary heating process. In this specification, the temperature range between the water inlet temperature to the heat pump and the hot water outlet temperature from the heat pump in each process (preliminary heating process and main heating process) is referred to as the "temperature rise width".

[0008] Generally, the larger the temperature rise of the hot water when heating begins with a heat pump or when the temperature is switched, the slower the rise in temperature of the hot water will be, and the greater the amount of hot water heated to an incomplete temperature will be, leading to a larger stratification range of the intermediate temperature stratification that will be formed. According to the above configuration, by making the temperature rise range in the main heating process smaller than the temperature rise range in the preliminary heating process, the amount of hot water heated to an incomplete temperature in the main heating process can be reduced, and the stratification range of the intermediate temperature stratification that will be formed after the main heating process is completed (i.e., after the tank sterilization operation is completed) can be reduced.

[0009] In one or more embodiments, the controller is configured to stop the heat pump from heating the hot water when the temperature of the hot water flowing into the heat pump becomes equal to or higher than a threshold temperature during the main heating process, the threshold temperature being set to a temperature equal to or higher than the first target temperature and lower than the second target temperature.

[0010] In the main heating process of the tank sterilization operation, the hot water in the hot water storage tank is heated to a high second target temperature. Therefore, if the heating of hot water by the heat pump is continued until hot water of the second target temperature flows into the heat pump in the main heating process, the high-temperature hot water may flow in, causing an excessive load on the compressor of the heat pump and a decrease in the heating efficiency of the heat pump. In contrast, according to the above configuration, when hot water of a threshold temperature lower than the second target temperature flows in during the main heating process, the heating of hot water by the heat pump is stopped, so that the high-temperature hot water can be prevented from flowing into the heat pump. Therefore, the load on the compressor can be prevented from becoming excessive and the heating efficiency of the heat pump can be prevented from decreasing. Note that, since the hot water in the hot water storage tank is heated to the first target temperature in the preliminary heating process prior to the main heating process, if the threshold temperature is lower than the first target temperature, the heating operation of the hot water by the heat pump will stop immediately after the start of the main heating process, and the sterilization effect may be insufficient. According to the above configuration, the threshold temperature is set to a temperature equal to or higher than the first target temperature, so that it is possible to prevent the heat pump from stopping the heating operation of hot and cold water immediately after the start of the main heating process, thereby ensuring a sufficient sterilization effect.

[0011] In one or more embodiments, the tank sterilization operation further includes a hot water temperature equalization process in which the tank circulation pump is driven while the heat pump is stopped until a predetermined equalization end condition is satisfied. The controller is configured to execute the hot water temperature equalization process after the preliminary heating process ends and before the main heating process starts.

[0012] After the preliminary heating process is completed, hot water at a temperature lower than the first target temperature may be present at the bottom of the hot water storage tank, and hot water at a temperature higher than the first target temperature may be present at the top of the hot water storage tank. In this way, if the main heating process is started when the temperature of the hot water in the hot water storage tank is not uniform, the amount of hot water heated to an intermediate temperature in the main heating process increases, and the stratification range of the intermediate temperature stratification formed after the main heating process is completed may also increase. In the above configuration, after the preliminary heating process is completed and before the main heating process is started, the hot water in the hot water storage tank is stirred by the circulation of the tank circulation pump in the hot water storage temperature uniformization process, so that the temperature of the hot water in the hot water storage tank can be uniformed. Therefore, the amount of hot water heated to an intermediate temperature in the main heating process can be reduced, and the stratification range of the intermediate temperature stratification formed after the main heating process is completed (i.e., after the tank sterilization operation is completed) can be reduced.

[0013] In one or more embodiments, the hot water supply system further includes an outdoor air temperature sensor that detects an outdoor air temperature. The controller is configured to drive the heat pump at a first heating capacity when the temperature detected by the outdoor air temperature sensor is equal to or higher than a predetermined reference temperature, and to drive the heat pump at a second heating capacity lower than the first heating capacity when the temperature detected by the outdoor air temperature sensor is lower than the reference temperature, in the main heating process.

[0014] When the outside air temperature is low, if the heat pump heats hot water, frost may form on the evaporator of the heat pump. If frost forms on the evaporator while the heat pump is heating hot water, it is necessary to temporarily stop the heating of hot water by the heat pump and perform a defrosting operation. If a defrosting operation is performed during the main heating process, the amount of hot water heated to an incomplete temperature in the main heating process increases, and the stratification range of the intermediate temperature stratification formed after the main heating process is completed may also increase. In contrast, according to the above configuration, when the outside air temperature is low, the main heating process is performed with the heating capacity of the heat pump kept low. Therefore, it is possible to prevent frost from forming on the evaporator during the main heating process, and to prevent the occurrence of a situation in which the heating of hot water by the heat pump is temporarily stopped and a defrosting operation is performed. Therefore, it is possible to reduce the amount of hot water heated to an incomplete temperature in the main heating process and reduce the stratification range of the intermediate temperature stratification formed after the main heating process is completed (i.e., after the tank sterilization operation is completed). [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of a hot water supply system 2 according to first to third embodiments. [Diagram 2] 4 is a flowchart showing a process executed by a controller in the hot water supply system 2 according to the first embodiment. [Diagram 3] 1 is a diagram showing a schematic diagram of the change over time in the temperature of hot and cold water at the upper part of the tank 30 and the temperature of hot and cold water at the lower part of the tank 30 while the tank sterilization operation of Example 1 is being performed. FIG. [Figure 4] 10 is a flowchart showing a process executed by a controller in a hot water supply system 2 according to a second embodiment. [Diagram 5] 13 is a diagram showing a schematic diagram of the change over time in the temperature of hot and cold water at the upper part of the tank 30 and the temperature of hot and cold water at the lower part of the tank 30 while the tank sterilization operation of Example 2 is being performed. FIG. [Figure 6]11 is a flowchart showing a process executed by a controller in a hot water supply system 2 according to a third embodiment. [Figure 7] FIG. 11 is a diagram showing a schematic diagram of the change over time in the temperature of hot and cold water at the upper part of the tank 30 and the temperature of hot and cold water at the lower part of the tank 30 while the tank sterilization operation of Example 3 is being performed. [Figure 8] This is a diagram showing a schematic diagram of the change over time in the temperature of hot water at the top of the tank and the temperature of hot water at the bottom of the tank while a tank sterilization operation is being performed in the hot water supply system disclosed in Patent Document 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Example 1 As shown in FIG. 1, a hot water supply system 2 according to this embodiment includes an HP (heat pump) unit 4, a tank unit 6, and a burner unit 8.

[0017] The HP unit 4 includes a heat pump 10 that absorbs heat from outside air to heat hot and cold water. The heat pump 10 includes a compressor 11, a condenser 12, an expansion valve 14, and an evaporator 16. The compressor 11 pressurizes a refrigerant (e.g., a fluorocarbon-based refrigerant) to make it high temperature and high pressure. The condenser 12 cools the refrigerant by exchanging heat with hot and cold water that flows in from an HP forward pipe 26 and flows out to an HP return pipe 28. The expansion valve 14 decompresses the refrigerant to make it low temperature and low pressure. The evaporator 16 heats the refrigerant by exchanging heat with outside air. The heat pump 10 circulates the refrigerant through the compressor 11, the condenser 12, the expansion valve 14, and the evaporator 16 in this order, so that the evaporator 16 absorbs heat from the outside air and heats the hot and cold water.

[0018] The heat pump 10 also includes a defrost valve 19 and a defrost path 19a. The defrost path 19a is connected between the condenser 12 and the expansion valve 14 and between the expansion valve 14 and the evaporator 16, bypassing the expansion valve 14. The defrost valve 19 is normally closed and is opened when a defrosting operation, which will be described later, is performed.

[0019] A circulation pump 18 that flows hot water toward the condenser 12, and a supply thermistor 20 that detects the temperature of the hot water flowing through the HP supply pipe 26 are attached to the HP supply pipe 26. A return thermistor 22 that detects the temperature of the hot water flowing through the HP return pipe 28 is attached to the HP return pipe 28. The HP unit 4 further includes an outside air temperature thermistor 23 that detects the outside air temperature, and an HP controller 24 that controls the operation of each component of the HP unit 4.

[0020] The tank unit 6 includes a tank 30, a mixing valve 32, and a bypass control valve 34. The tank 30 is a sealed container that is covered with a heat insulating material on the outside and stores hot water inside. The capacity of the tank 30 in this embodiment is, for example, 100 liters. The HP forward pipe 26 is connected to the bottom of the tank 30, and the HP return pipe 28 is connected to the top of the tank 30. When the circulation pump 18 of the HP unit 4 is driven, hot water is sucked out from the bottom of the tank 30 and sent to the condenser 12 of the heat pump 10. The hot water heated by the heat pump 10 and heated to a high temperature is returned to the tank 30 from the top of the tank 30. When the hot water heated by the heat pump 10 flows into the tank 30, a temperature stratification is formed inside the tank 30, with a layer of high temperature hot water stacked on top of a layer of low temperature hot water. The tank 30 is equipped with an upper thermistor 36 that detects the temperature of the upper hot water and a lower thermistor 38 that detects the temperature of the lower hot water.

[0021] Tap water is supplied to the tank unit 6 via a water supply pipe 40. A pressure reducing valve 42 for reducing the water supply pressure and a water inlet thermistor 44 for detecting the water supply temperature are attached to the water supply pipe 40. The water supply pipe 40 branches into a tank water supply pipe 46 that communicates with the lower part of the tank 30 and a tank bypass pipe 48 that communicates with the mixing valve 32. Check valves 50 and 52 are attached to the tank water supply pipe 46 and the tank bypass pipe 48, respectively. A water-side water volume sensor 54 for detecting the flow rate of tap water flowing into the mixing valve 32 is attached to the tank bypass pipe 48. The upper part of the tank 30 and the mixing valve 32 are connected via a tank hot water outlet pipe 56. A check valve 58 and a hot water volume sensor 60 for detecting the flow rate of hot water from the tank 30 flowing into the mixing valve 32 are attached to the tank hot water outlet pipe 56.

[0022] The mixing valve 32 mixes the tap water flowing in from the tank bypass pipe 48 and the hot water from the tank 30 flowing in from the tank hot water outlet pipe 56, and sends the mixed water to a first hot water supply pipe 62. The mixing valve 32 is driven by a stepping motor, and adjusts the opening degree on the tank bypass pipe 48 side (opening degree on the water side) and the opening degree on the tank outlet pipe 56 side (opening degree on the hot water side). A mixing thermistor 64 that detects the temperature of the hot water sent out from the mixing valve 32 is attached to the first hot water supply pipe 62.

[0023] Hot water is supplied from tank unit 6 to hot water supply locations such as a kitchen, shower, and faucet via second hot water supply pipe 66. A hot water supply outlet thermistor 68 that detects the temperature of hot water supplied to the hot water supply location, and a check valve 70 are attached to second hot water supply pipe 66. The first hot water supply pipe 62 and second hot water supply pipe 66 are connected by a hot water supply bypass pipe 72. A bypass control valve 34 is attached to hot water supply bypass pipe 72.

[0024] The tank unit 6 further includes a tank controller 74 and a remote control 76 capable of communicating with the tank controller 74. The tank controller 74 controls the operation of each component of the tank unit 6. The remote control 76 accepts various operational inputs from the user via switches, buttons, etc. The remote control 76 also notifies the user of various pieces of information related to the settings and operation of the hot water supply system 2 by display and audio.

[0025] The burner unit 8 includes a burner 80, a heat exchanger 82, a bypass servo 84, a water volume servo 86, and a hot water filling valve 88. The burner 80 is a heat source that heats the hot water flowing through the heat exchanger 82 by burning gas. Hot water flows into the heat exchanger 82 from the first hot water supply pipe 62 of the tank unit 6 through a burner forward pipe 90. The hot water that has passed through the heat exchanger 82 flows out to the second hot water supply pipe 66 of the tank unit 6 through a burner return pipe 92. A water volume servo 86 that adjusts the flow rate of hot water flowing into the heat exchanger 82 is attached to the burner forward pipe 90. The burner forward pipe 90 and the burner return pipe 92 are connected through a burner bypass pipe 94. A bypass servo 84 is attached to the connection between the burner forward pipe 90 and the burner bypass pipe 94. The bypass servo 84 adjusts the flow rate of hot water flowing from the burner forward pipe 90 to the burner bypass pipe 94. A burner hot water thermistor 96 is attached to the burner return pipe 92, which detects the temperature of the hot water flowing out from the heat exchanger 82. A hot water filling pipe 98 branches off from the burner return pipe 92. A hot water filling valve 88 is attached to the hot water filling pipe 98. Hot water is filled into the bathtub, which is the hot water supply location, from the burner unit 8 via the hot water filling pipe 98. The burner unit 8 further includes a burner controller 100, which controls the operation of each component of the burner unit 8.

[0026] The HP controller 24 and the tank controller 74 are capable of communicating with each other. The tank controller 74 and the burner controller 100 are capable of communicating with each other. Therefore, the HP controller 24, the tank controller 74, and the burner controller 100 cooperate to perform control, so that the hot water supply system 2 can perform various operations such as a boiling operation and a hot water supply operation. Hereinafter, the HP controller 24, the tank controller 74, and the burner controller 100 are collectively referred to simply as controllers.

[0027] The main operations of the hot water supply system 2 will be described below.

[0028] (Boiling operation) In the boiling operation, the hot water supply system 2 drives the HP unit 4 to boil the hot water in the tank 30. The timing to start the boiling operation can be set from various viewpoints. For example, the controller may determine the start timing of the boiling operation so that the boiling of the hot water in the tank 30 ends just before the time when a large demand for hot water is expected to occur, based on the hot water supply performance up to the previous day. Alternatively, the user may instruct the boiling of the hot water in the tank 30 via the remote control 76, causing the controller to start the boiling operation.

[0029] When the boiling operation is started, the controller drives the compressor 11 to circulate the refrigerant through the compressor 11, condenser 12, expansion valve 14, and evaporator 16 in that order, and drives the circulation pump 18 to circulate hot water between the tank 30 and the condenser 12. As a result, the hot water sucked out from the bottom of the tank 30 is heated in the condenser 12 to a predetermined boiling temperature (e.g., 45°C) and returned to the top of the tank 30. When all the hot water in the tank 30 has been replaced with hot water heated to the boiling temperature, the controller ends the boiling operation.

[0030] (Hot water supply operation) In the hot water supply operation, hot water at the hot water supply setting temperature is supplied to the hot water supply location. In the hot water supply system 2 of this embodiment, for example, when the water volume (hot water supply volume) obtained by adding up the water volume detected by the water side water volume sensor 54 and the water volume detected by the hot water side water volume sensor 60 becomes equal to or greater than a predetermined value, the hot water supply operation is started.

[0031] When the hot water supply operation is started, the controller judges whether or not the tank 30 is out of hot water. In this embodiment, the controller judges that the tank 30 is out of hot water when the temperature detected by the upper thermistor 36 falls below the hot water supply setting temperature.

[0032] If the tank 30 is not out of hot water, the controller prohibits the combustion operation of the burner 80. The controller also adjusts the opening of the mixing valve 32 so that the temperature detected by the mixing thermistor 64 becomes the hot water supply set temperature. In this case, the high-temperature hot water supplied from the top of the tank 30 and the low-temperature tap water supplied from the water supply pipe 40 are mixed in the mixing valve 32 so as to become the hot water supply set temperature, and are supplied to the hot water supply location.

[0033] When the tank 30 runs out of hot water, the controller permits the burner 80 to operate. The controller also adjusts the opening of the mixing valve 32 so that the temperature detected by the mixing thermistor 64 is slightly lower than the hot water supply setting temperature. In this case, high-temperature hot water supplied from the top of the tank 30 and low-temperature tap water supplied from the tank bypass pipe 48 are mixed in the mixing valve 32, heated to the hot water supply setting temperature by the burner 80, and supplied to the hot water supply location.

[0034] For example, when the water volume (hot water volume) obtained by combining the water volume detected by the water side water volume sensor 54 and the hot water side water volume sensor 60 falls below a predetermined value, the controller prohibits the combustion operation of the burner 80 and terminates the hot water supply operation.

[0035] (Tank sterilization operation) The tank sterilization operation is an operation in which the hot water in the tank 30 is heated to a high temperature (e.g., 65°C) at which sterilization is possible when there is a risk of bacteria growing in the hot water in the tank 30. When a predetermined sterilization implementation condition is met, the controller drives the heat pump 10 and circulation pump 18 of the HP unit 4 to start the tank sterilization operation. An example of the predetermined sterilization implementation condition is when it is determined that the hot water in the upper part of the tank 30 has remained at a low temperature (e.g., a temperature of 60°C or lower) for a long period of time (e.g., 72 hours or more).

[0036] 2, when the tank sterilization operation is started, in S2, the controller determines whether the outside air temperature detected by the outside air temperature thermistor 23 is below a first reference temperature (e.g., 10°C). If the outside air temperature is below the first reference temperature (YES), the process proceeds to S4.

[0037] In S4, the controller sets the heating capacity of the heat pump 10 to the preliminary heating capacity (for example, 2.8 kW). After S4, the process proceeds to S6.

[0038] In S6, the controller executes circulatory heating of the hot water in the tank 30. The controller drives the compressor 11 of the heat pump 10 to circulate the refrigerant through the compressor 11, condenser 12, expansion valve 14, and evaporator 16 in that order, and drives the circulation pump 18 to circulate the hot water between the tank 30 and the condenser 12. As a result, the hot water sucked out from the bottom of the tank 30 is heated in the condenser 12 and returned to the top of the tank 30. At this time, the controller controls the capacity of the circulation pump 18 so that the temperature detected by the return thermistor 22 (HP return temperature) becomes a first target temperature (e.g., 45°C). After S6, the process proceeds to S8.

[0039] In S8, the controller determines whether the difference between the first target temperature and the temperature detected by lower thermistor 38 (the temperature of the hot and cold water at the bottom of tank 30) is equal to or less than a first predetermined value (e.g., 5°C). If the difference between the first target temperature and the temperature of the hot and cold water at the bottom of tank 30 exceeds the first predetermined value (if NO), processing returns to S6. If the difference between the first target temperature and the temperature of the hot and cold water at the bottom of tank 30 is equal to or less than the first predetermined value (if YES), processing proceeds to S10.

[0040] In S10, the controller sets the heating capacity of the heat pump 10 to a first main heating capacity (for example, 2.0 kW). After S10, the process proceeds to S12.

[0041] In S12, the controller executes circulatory heating of the hot water in the tank 30. The controller drives the compressor 11 of the heat pump 10 to circulate the refrigerant through the compressor 11, condenser 12, expansion valve 14, and evaporator 16 in that order, and drives the circulation pump 18 to circulate the hot water between the tank 30 and the condenser 12. As a result, the hot water sucked out from the bottom of the tank 30 is heated in the condenser 12 and returned to the top of the tank 30. At this time, the controller controls the capacity of the circulation pump 18 so that the HP return temperature detected by the return thermistor 22 becomes a second target temperature (for example, 65°C). After S12, the process proceeds to S14.

[0042] In S14, the controller determines whether the temperature detected by the forward thermistor 20 (HP forward temperature) is equal to or higher than a predetermined threshold temperature (e.g., 47°C). If the HP forward temperature is below the threshold temperature (if NO), the process returns to S12. If the HP forward temperature is equal to or higher than the threshold temperature (if YES), the controller stops driving the heat pump 10 and the circulation pump 18, and ends the process shown in FIG. 2.

[0043] If the outside air temperature is equal to or higher than the first reference temperature in S2 (if NO), the process proceeds to S20. In S20, the controller sets the heating capacity of the heat pump 10 to the normal heating capacity (for example, 2.4 kW). After S20, the process proceeds to S22.

[0044] In S22, the controller executes circulatory heating of the hot water in the tank 30. The controller drives the compressor 11 to circulate the refrigerant through the compressor 11, condenser 12, expansion valve 14, and evaporator 16 in that order, and drives the circulation pump 18 to circulate the hot water between the tank 30 and the condenser 12. As a result, the hot water sucked out from the bottom of the tank 30 is heated in the condenser 12 and returned to the top of the tank 30. At this time, the controller controls the capacity of the circulation pump 18 so that the HP return temperature detected by the return thermistor 22 becomes the second target temperature (similar to S12). After S22, the process proceeds to S24.

[0045] In S24, the controller judges whether the HP delivery temperature is equal to or higher than the threshold temperature (similar to S14). If the HP delivery temperature is lower than the threshold temperature (if NO), the process returns to S22. If the HP delivery temperature is equal to or higher than the threshold temperature (if YES), the controller stops driving the heat pump 10 and the circulation pump 18, and ends the process shown in FIG. 2.

[0046] In this embodiment, the processes from S4 to S8 in Fig. 2 are called "preliminary heating process", the processes from S10 to S14 in Fig. 2 are called "main heating process", and the processes from S20 to S24 in Fig. 2 are called "normal heating process".

[0047] For example, when the tank sterilization operation of this embodiment is started when the outside air temperature is 4°C, the controller judges YES in the process of S2 in Fig. 2 and executes the preliminary heating process and the main heating process in sequence. In this case, the temperature of the hot and cold water at the upper part of the tank 30 and the temperature of the hot and cold water at the lower part of the tank 30 each change as shown in Fig. 3. On the other hand, when a conventional tank sterilization operation is executed under the same conditions, the temperature of the hot and cold water at the upper part of the tank 30 and the temperature of the hot and cold water at the lower part of the tank 30 each change as shown in Fig. 8.

[0048] (Comparison with conventional technology) In the conventional tank sterilization operation shown in FIG. 8, the temperature rise of the hot water in the preliminary heating process is about 30° C., and the temperature rise of the hot water in the main heating process is also about 30° C. On the other hand, in the tank sterilization operation of this embodiment shown in FIG. 3, the temperature rise of the hot water in the preliminary heating process is about 40° C., and the temperature rise of the hot water in the main heating process is about 20° C. In the tank sterilization operation of this embodiment, unlike the conventional tank sterilization operation, the temperature rise of the hot water in the main heating process is smaller than the temperature rise of the hot water in the preliminary heating process. As a result, in the tank sterilization operation of this embodiment, the temperature of the hot water at the bottom of the tank 30 at the end of the main heating process (i.e., at the end of the tank sterilization operation) is about 10° C. higher than in the case of the conventional tank sterilization operation. In other words, in the tank sterilization operation of this embodiment, the temperature range of the intermediate temperature stratification formed after the end of the tank sterilization operation is reduced by about 10° C. compared to the case of the conventional tank sterilization operation.

[0049] In addition, in the tank sterilization operation of this embodiment, the temperature rise of the hot water in the main heating process can be reduced by about 10°C compared to the conventional tank sterilization operation. Therefore, in the tank sterilization operation of this embodiment, the amount of hot water heated to an intermediate temperature in the main heating process is relatively reduced, and the range of intermediate temperature stratification formed after the end of the tank sterilization operation is also relatively reduced.

[0050] As described above, in the tank sterilization operation of this embodiment, the effect of reducing the temperature width of intermediate temperature stratification and the effect of reducing the stratification range of intermediate temperature stratification are combined, thereby improving the sterilization effect of the tank sterilization operation compared to the conventional tank sterilization operation.

[0051] (Defrosting operation) When the heat pump 10 is driven in a situation where the outside air temperature is low, frost may form on the evaporator 16. When frost forms on the evaporator 16, the heat exchange rate with the outside air decreases, and the heating efficiency of the heat pump 10 decreases. Therefore, when the controller determines that frost has formed on the evaporator 16 while the heat pump 10 is heating the hot water in the tank 30, the controller interrupts the heating of the hot water in the tank 30 by the heat pump 10, stops the operation of the circulation pump 18, and executes a defrosting operation to defrost the evaporator 16. Specifically, the controller temporarily opens the defrost valve 19 to pass the high-temperature refrigerant discharged from the compressor 11 through the condenser 12, so that the refrigerant bypasses the expansion valve 14 and flows to the evaporator 16. As a result, the high-temperature refrigerant flows into the evaporator 16, and the evaporator 16 is defrosted.

[0052] (Corresponding relationship in Example 1) As described above, the hot water supply system 2 includes a tank 30 (an example of a hot water storage tank) in which hot water is stored, with a tank water supply pipe 46 (an example of a water supply path) connected to the bottom and a tank hot water outlet pipe 56 (an example of a hot water outlet path) connected to the top, an HP forward pipe 26 and an HP return pipe 28 (an example of a tank circulation path) connecting the bottom and top of the tank 30, a circulation pump 18 that circulates the hot water stored in the bottom of the tank 30 to the top of the tank 30 via the HP forward pipe 26 and the HP return pipe 28, a heat pump 10 that is provided between the HP forward pipe 26 and the HP return pipe 28 (an example of the middle of the tank circulation path) and heats the hot water flowing through the HP forward pipe 26 and the HP return pipe 28, and a controller. The controller is configured to execute a tank sterilization operation in which the circulation pump 18 circulates the hot water between the tank 30 and the heat pump 10 and the hot water is heated by the heat pump 10 when a predetermined sterilization implementation condition is met. The tank sterilization operation includes a preliminary heating process that controls the operation of the circulation pump 18 and the heat pump 10 so that the HP return temperature (an example of the temperature of hot water flowing out from the heat pump) becomes a first target temperature, and a main heating process that controls the operation of the circulation pump 18 and the heat pump 10 so that the HP return temperature becomes a second target temperature higher than the first target temperature after the preliminary heating process is completed. The temperature rise of the hot water in the heat pump 10 in the main heating process is smaller than the temperature rise of the hot water in the heat pump 10 in the preliminary heating process.

[0053] Generally, the larger the temperature rise of the hot water when heating begins or when the temperature is switched by the heat pump 10, the slower the rise in temperature of the hot water will be, and the greater the amount of hot water heated to an incomplete temperature will be, and the greater the range of intermediate temperature stratification that will be formed. According to the above configuration, by making the temperature rise in the main heating process smaller than the temperature rise in the preliminary heating process, the amount of hot water heated to an incomplete temperature in the main heating process can be reduced, and the range of intermediate temperature stratification that will be formed after the main heating process is completed (i.e., after the tank sterilization operation is completed) can be reduced.

[0054] In one or more embodiments, the controller is configured to stop heating of hot water by the heat pump 10 when the HP inlet temperature (an example of the temperature of hot water flowing into the heat pump) is equal to or greater than a threshold temperature during the main heating process. The threshold temperature is set to a temperature equal to or greater than the first target temperature and lower than the second target temperature.

[0055] In the main heating process of the tank sterilization operation, the hot water in the tank 30 is heated to a high second target temperature. For this reason, if the heat pump 10 continues to heat the hot water in the main heating process until hot water of the second target temperature flows into the heat pump 10, the high-temperature hot water may flow in, causing an excessive load on the compressor 11 of the heat pump 10 and a decrease in the heating efficiency of the heat pump 10. In contrast, according to the above configuration, when hot water of a threshold temperature lower than the second target temperature flows in during the main heating process, the heating of the hot water by the heat pump 10 is stopped, so that the flow of high-temperature hot water into the heat pump 10 can be prevented. For this reason, the load on the compressor 11 can be prevented from becoming excessive and the heating efficiency of the heat pump 10 can be prevented from decreasing. In addition, since the hot water in the tank 30 is heated to the first target temperature in the preliminary heating process prior to the main heating process, if the threshold temperature is below the first target temperature, the heating operation of the heat pump 10 will stop immediately after the start of the main heating process, which may result in insufficient sterilization effect. With the above configuration, the threshold temperature is set to a temperature equal to or higher than the first target temperature, so it is possible to prevent the heating operation of the heat pump 10 from stopping immediately after the start of the main heating process, and a sufficient sterilization effect can be ensured.

[0056] Example 2 The hot water supply system 2 of this embodiment has a similar configuration to the hot water supply system 2 of Example 1. In the hot water supply system 2 of this embodiment, when performing a tank sterilization operation, the controller executes the process shown in FIG. 4 instead of executing the process shown in FIG. 2. The process shown in FIG. 4 is common to the process shown in FIG. 2 with some exceptions. The following describes the differences between the process shown in FIG. 4 and the process shown in FIG. 2. Note that the same symbols are used for the common points between the two, and their description will be omitted.

[0057] 4, after S8, the process proceeds to S30. In S30, the controller stops driving the heat pump 10 and drives the circulation pump 18 to circulate hot and cold water between the tank 30 and the condenser 12. After S30, the process proceeds to S32.

[0058] In S32, the controller determines whether the difference between the temperature detected by the upper thermistor 36 (the temperature of the hot and cold water at the top of the tank 30) and the temperature detected by the lower thermistor 38 (the temperature of the hot and cold water at the bottom of the tank 30) is equal to or less than a second predetermined value (e.g., 2°C). If the difference between the temperature of the hot and cold water at the top of the tank 30 and the temperature of the hot and cold water at the bottom of the tank 30 exceeds the second predetermined value (if NO), processing returns to S30. If the difference between the temperature of the hot and cold water at the top of the tank 30 and the temperature of the hot and cold water at the bottom of the tank 30 is equal to or less than the second predetermined value (if YES), processing proceeds to S10.

[0059] In this embodiment, the processes from S4 to S8 in Fig. 4 are called "preliminary heating process". The processes from S30 and S32 in Fig. 4 are called "hot water temperature equalization process". The processes from S10 to S14 in Fig. 4 are called "main heating process". The processes from S20 to S24 in Fig. 4 are called "normal heating process".

[0060] For example, when the tank sterilization operation of this embodiment is started when the outside air temperature is 4°C, the controller judges YES in the process of S2 in Fig. 4 and executes the preliminary heating process, the stored hot water temperature equalization process, and the main heating process in that order. In this case, the temperature of the hot water in the upper part of the tank 30 and the temperature of the hot water in the lower part of the tank 30 change as shown in Fig. 5.

[0061] The tank sterilization operation of the second embodiment differs from the tank sterilization operation of the first embodiment in that it includes a hot water temperature equalization process. In the hot water temperature equalization process, the temperature stratification formed after the completion of the preliminary heating process is eliminated, so that the temperature of the hot water in the upper part of the tank 30 decreases and the temperature of the hot water in the lower part of the tank 30 increases.

[0062] (Corresponding relationship in Example 2) In one or more embodiments, the tank sterilization operation further includes a hot water temperature equalization process in which the circulation pump 18 is driven with the heat pump 10 stopped until the difference in temperature between the hot water at the top of the tank 30 and the hot water at the bottom of the tank 30 becomes equal to or less than a second predetermined value (an example of a predetermined equalization end condition being met). The controller is configured to execute the hot water temperature equalization process after the preliminary heating process ends and before the main heating process starts.

[0063] After the preliminary heating process is completed, hot water at a temperature lower than the first target temperature may be present in the lower part of the tank 30, and hot water at a temperature higher than the first target temperature may be present in the upper part of the tank 30. In this way, if the main heating process is started when the temperature of the hot water in the tank 30 is not uniform, the amount of hot water heated to an incomplete temperature in the main heating process increases, and the stratified range of the intermediate temperature stratification formed after the main heating process is completed may also increase. In the above configuration, after the preliminary heating process is completed and before the main heating process is started, the hot water in the tank 30 is stirred by the circulation of the circulation pump 18 in the hot water storage temperature equalization process, so that the temperature of the hot water in the tank 30 can be made uniform. Therefore, the amount of hot water heated to an incomplete temperature in the main heating process can be reduced, and the stratified range of the intermediate temperature stratification formed after the main heating process is completed (i.e., after the tank sterilization operation is completed) can be reduced.

[0064] Example 3 The hot water supply system 2 of this embodiment has a similar configuration to the hot water supply system 2 of Example 1. In the hot water supply system 2 of this embodiment, when performing a tank sterilization operation, the controller executes the process shown in FIG. 6 instead of executing the process shown in FIG. 2. The process shown in FIG. 6 is common to the process shown in FIG. 2 with some exceptions. The following describes the differences between the process shown in FIG. 6 and the process shown in FIG. 2. Note that the same symbols are used for the common points between the two, and their description will be omitted.

[0065] 6, after S8, the process proceeds to S40. In S40, the controller determines whether the outside air temperature detected by the outside air temperature thermistor 23 is below a second reference temperature (e.g., 5°C). If the outside air temperature is equal to or higher than the second reference temperature (NO), the process proceeds to S42.

[0066] In S42, the controller sets the heating capacity of the heat pump 10 to the first main heating capacity similar to S10 in Example 1. After S42, the process proceeds to S12.

[0067] In S40, if the outside air temperature is lower than the second reference temperature (YES), the process proceeds to S44. In S44, the controller sets the heating capacity of the heat pump 10 to the second main heating capacity (for example, 1.8 kW). After S44, the process proceeds to S12.

[0068] In this embodiment, the processes from S4 to S8 in Fig. 6 are called "preliminary heating process". The processes from S40 to S44 and S12 to S14 in Fig. 6 are called "main heating process". The processes from S20 to S24 in Fig. 6 are called "normal heating process".

[0069] For example, when the tank sterilization operation of this embodiment is started when the outside air temperature is 4°C, the controller judges YES in the process of S2 in Fig. 6 and executes the preliminary heating process and the main heating process in sequence. In addition, in the main heating process, the controller judges YES in the process of S40 in Fig. 6 and sets the heating capacity of the heat pump 10 to the second main heating capacity. In this case, the temperature of the hot water in the upper part of the tank 30 and the temperature of the hot water in the lower part of the tank 30 change as shown in FIG.

[0070] The tank sterilization operation of the third embodiment differs from the tank sterilization operation of the first embodiment in that the controller varies the heating capacity of the heat pump 10 in accordance with the outside air temperature in the main heating process. In a situation where the outside air temperature is low (i.e., a situation where frost is likely to form on the evaporator 16), the controller sets the heating capacity of the heat pump 10 in the main process to a second main heating capacity that is lower than the first main heating capacity. When the heat pump 10 is driven at the second main heating capacity, the temperature of the refrigerant flowing through the evaporator 16 is higher than when the heat pump 10 is driven at the first main heating capacity. For this reason, in the main heating process of the third embodiment, frost formation on the evaporator 16 is suppressed compared to the main heating process of the first embodiment.

[0071] (Corresponding relationship in Example 3) In one or more embodiments, the hot water supply system 2 further includes an outdoor air temperature thermistor 23 (an example of an outdoor air temperature sensor) that detects the outdoor air temperature. The controller is configured to drive the heat pump 10 at a first main heating capacity (an example of a first heating capacity) when the temperature detected by the outdoor air temperature thermistor 23 is equal to or higher than a second reference temperature (an example of a predetermined reference temperature) in the main heating process, and to drive the heat pump 10 at a second main heating capacity (an example of a second heating capacity) lower than the first main heating capacity when the temperature detected by the outdoor air temperature thermistor 23 is lower than the second reference temperature.

[0072] When the heat pump 10 heats hot water in a situation where the outdoor air temperature is low, frost may form on the evaporator 16 of the heat pump 10. If frost forms on the evaporator 16 while the heat pump 10 is heating hot water, it is necessary to temporarily stop the heating of hot water by the heat pump 10 and perform a defrosting operation. If a defrosting operation is performed during the execution of the main heating process, the amount of hot water heated to an incomplete temperature in the main heating process increases, and the stratification range of the intermediate temperature stratification formed after the main heating process is completed may also increase. In contrast, according to the above configuration, when the outdoor air temperature is low, the main heating process is performed with the heating capacity of the heat pump 10 kept low. Therefore, it is possible to prevent frost from forming on the evaporator 16 during the execution of the main heating process, and it is possible to prevent the occurrence of a situation where the heating of hot water by the heat pump 10 is temporarily stopped and a defrosting operation is performed. Therefore, it is possible to reduce the amount of hot water heated to an incomplete temperature in the main heating process and reduce the stratification range of the intermediate temperature stratification formed after the main heating process is completed (i.e., after the tank sterilization operation is completed).

[0073] (Modification) In the above embodiments 1 to 3, the configuration was described in which the sterilization implementation condition is that it is determined that the hot and cold water in the upper part of the tank 30 has remained at a low temperature for a long period of time. In another embodiment, the sterilization implementation condition may be that the time elapsed since the end of the most recent tank sterilization operation exceeds a predetermined time (e.g., 720 hours).

[0074] In the above first to third embodiments, the controller sequentially executes the preliminary heating process and the main heating process when the outside air temperature is below the first reference temperature (YES in the process of S2), and executes the normal heating process when the outside air temperature is equal to or higher than the first reference temperature (NO in the process of S2). In another embodiment, the controller may be configured to sequentially execute the preliminary heating process and the main heating process regardless of whether the outside air temperature is below the first reference temperature.

[0075] In the above-mentioned first to third embodiments, the tank sterilization operation includes a preliminary heating process and a main heating process, and the HP unit 4 circulates and heats the hot water in the tank 30 in two stages. In another embodiment, the tank sterilization operation may further include a heating process similar to the preliminary heating process, and the HP unit 4 may circulate and heat the hot water in the tank 30 in three stages. Specifically, the controller may be configured to drive the compressor 11 and the circulation pump 18 to circulate and heat the hot water in the tank 30 prior to the preliminary heating process, so that the hot water in the tank 30 has a temperature (e.g., 25°C) lower than the first target temperature. In yet another embodiment, the HP unit 4 may circulate and heat the hot water in the tank 30 in four or more stages.

[0076] In the above-mentioned first to third embodiments, the configuration in which the first target temperature is a predetermined temperature (45°C) has been described. In another embodiment, the tank sterilization operation may further include a process of specifying the first target temperature by the controller, and the first target temperature may be specified according to the operating conditions of the tank sterilization operation. Specifically, the controller may be configured to record the temperature of the hot water in the tank 30 at the start of the preliminary heating process (the temperature detected by the upper thermistor 36 or the temperature detected by the lower thermistor 38), and may specify the temperature obtained by adding a predetermined value (for example, 10°C) to the average value between the recorded temperature of the hot water in the tank 30 at the start of the preliminary heating process and the second target temperature as the first target temperature. In this case, the temperature rise of the hot water in the heat pump 10 in the main heating process is smaller than the temperature rise of the hot water in the heat pump 10 in the preliminary heating process by a value obtained by multiplying the predetermined value by two.

[0077] In the above first to third embodiments, a configuration has been described in which the controller stops driving the heat pump 10 when the HP delivery temperature becomes equal to or higher than the threshold temperature while the main heating process is being performed. In another embodiment, the controller may stop only the heating of hot water by the heat pump 10 without stopping the driving of the heat pump 10 when the HP delivery temperature becomes equal to or higher than the threshold temperature while the main heating process is being performed. The controller may immediately resume heating of hot water by the heat pump 10 when the HP delivery temperature subsequently falls below the threshold temperature.

[0078] In the above first to third embodiments, a configuration has been described in which the controller determines whether the HP delivery temperature is equal to or higher than a threshold temperature as a condition for stopping the heating of hot water by the heat pump 10. In another embodiment, the controller may be configured to determine whether the temperature of hot water in the lower part of the tank 30 is equal to or higher than a threshold temperature as a condition for stopping the heating of hot water by the heat pump 10.

[0079] In the above-mentioned first to third embodiments, the configuration in which the controller ends the tank sterilization operation simultaneously with the end of the main heating process has been described. In another embodiment, the controller may not be configured to end the tank sterilization operation simultaneously with the end of the main heating process. For example, the controller may be configured to further execute the hot water temperature equalization process described in the second embodiment after the end of the main heating process, and to end the tank sterilization operation after the hot water temperature equalization process is completed.

[0080] In the above second embodiment, a configuration has been described in which the controller continues to execute the hot water temperature equalization process until the difference between the temperature of the hot water in the upper part of the tank 30 and the temperature of the hot water in the lower part of the tank 30 becomes equal to or less than a second predetermined value (until the process of S32 in FIG. 4 becomes YES). In another embodiment, the controller may be configured to continue to execute the hot water temperature equalization process until a predetermined time has elapsed since the process was started.

[0081] In the above-described third embodiment, the controller may be configured to further execute the hot water temperature equalization process described in the second embodiment after the process of S8 shown in FIG. 6 and before the process of S40.

[0082] In the above Examples 1 to 3, the values ​​of the capacity of tank 30, the first reference temperature, the second reference temperature, the normal heating capacity, the preliminary heating capacity, the first main heating capacity, the second main heating capacity, the first predetermined value, the second predetermined value, and the threshold temperature may be changed as appropriate.

[0083] Although the embodiments have been described in detail above, they are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of the objectives itself has technical utility. [Explanation of symbols]

[0084] 2: Hot water system 4:HP unit 6:Tank unit 8: Burner unit 10: Heat pump 11: Compressor 12: Condenser 14: Expansion valve 16: Evaporator 18: Circulation pump 19: Defrost valve 19a: Defrost path 20: Forward thermistor 22: Return thermistor 23: Outside air temperature thermistor 24:HP Controller 26:HP Outlet Pipe 28:HP return pipe 30: Tank 32: Mixing valve 34: Bypass control valve 36: Upper thermistor 38: Lower thermistor 40: Water supply pipe 42: Pressure reducing valve 44: Water inlet thermistor 46: Tank water supply pipe 48: Tank bypass pipe 50: Check valve 52: Check valve 54: Water side water level sensor 56:Tank outlet pipe 58: Check valve 60: Hot water level sensor 62: First hot water pipe 64: Mixed thermistor 66: Second hot water pipe 68: Hot water outlet thermistor 70: Check valve 72: Hot water bypass pipe 74: Tank Controller 76: Remote control 80: Burner 82: Heat exchanger 84: Bypass servo 86: Water volume servo 88: Bath valve 90: Burner supply pipe 92: Burner return pipe 94: Burner bypass pipe 96: Burner hot water thermistor 98: Hot water pipe 100: Burner controller

Claims

1. a hot water storage tank having a water supply line connected to a lower portion and a hot water outlet line connected to an upper portion, in which hot water is stored; A tank circulation path connecting a lower portion and an upper portion of the hot water storage tank; A tank circulation pump that circulates the hot water stored in the lower part of the hot water storage tank to the upper part of the hot water storage tank through the tank circulation path; a heat pump provided in the tank circulation path and configured to heat the hot water flowing through the tank circulation path; A controller, The controller is configured to execute a tank sterilization operation in which, when a predetermined sterilization implementation condition is satisfied, the tank circulation pump circulates hot water between the hot water storage tank and the heat pump, and the heat pump heats the hot water, The tank sterilization operation is A preliminary heating process for controlling the operation of the tank circulation pump and the heat pump so that the temperature of the hot water flowing out from the heat pump becomes a first target temperature; a main heating process for controlling the operation of the tank circulation pump and the heat pump so that the temperature of the hot water flowing out of the heat pump becomes a second target temperature higher than the first target temperature after the completion of the preliminary heating process; A hot water supply system, wherein a temperature rise range of the hot water in the heat pump during the main heating process is smaller than a temperature rise range of the hot water in the heat pump during the preliminary heating process.

2. The controller is configured to stop heating the hot water by the heat pump when a temperature of the hot water flowing into the heat pump becomes equal to or higher than a threshold temperature during execution of the main heating process, The hot water supply system according to claim 1 , wherein the threshold temperature is set to a temperature equal to or higher than the first target temperature and lower than the second target temperature.

3. The tank sterilization operation further includes a hot water temperature equalization process in which the tank circulation pump is driven while the heat pump is stopped until a predetermined equalization end condition is satisfied, The hot water supply system according to claim 1 , wherein the controller is configured to execute the stored hot water temperature equalization process after the preliminary heating process is completed and before the main heating process is started.

4. Further comprising an outside air temperature sensor for detecting an outside air temperature, The controller, in the main heating process, When the temperature detected by the outside air temperature sensor is equal to or higher than a predetermined reference temperature, the heat pump is driven at a first heating capacity; 4. The hot water supply system of claim 1, wherein when the detected temperature of the outside air temperature sensor is lower than the reference temperature, the heat pump is configured to be driven at a second heating capacity lower than the first heating capacity.

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