Hot water system

Abstract

The utility model relates to a hot water system which comprises a gas water heater, and the gas water heater is provided with a water inlet and a domestic hot water outlet. The hot water system further comprises a heat storage type water tank, the heat storage type water tank is provided with a hot water inlet, a water return port, a hot water outlet and a cold water inlet, and a water inlet of the gas water heater is in fluid communication with the water return port of the heat storage type water tank through a domestic hot water return pipeline. A domestic hot water outlet of the gas water heater is in fluid communication with a hot water inlet of the heat storage type water tank through a domestic hot water outlet pipeline, a hot water outlet of the heat storage type water tank is in fluid communication with a domestic hot water terminal through a hot water supply pipeline, and a cold water inlet of the heat storage type water tank is in fluid communication with a water source through a water inlet pipeline. The hot water system further comprises an instant heating type electric heater located at the domestic hot water using terminal in the path of the hot water supply pipeline. By means of the hot water system, hot water with the temperature as constant as possible can be rapidly and stably provided.

Description

Technical Field

[0001] The present application relates to a hot water system for providing hot water with a temperature that is as constant as possible. Background Art

[0002] In modern life, water heaters are essential for comfortable living. Usually, water heaters can provide people with hot water for washing or bathing. In addition, for areas with cold winters but no central heating, such as most southern regions of China, it is also very common to use water heaters to provide heating water on a household basis.

[0003] According to the different energy sources used, the water heaters commonly used in the market include gas water heaters, solar water heaters and electric water heaters. However, these water heaters have their own defects and limitations.

[0004] Gas water heaters can continuously prepare hot water, but they often cannot provide hot water at a constant temperature. In particular, when the water pressure is unstable, the prepared hot water often becomes hot and cold, which is particularly uncomfortable for bathing. In addition, gas water heaters do not have a heat storage tank and are often installed in the kitchen far away from the bathroom for safety reasons. Therefore, it takes a long time to drain the cold water in the water pipe and provide hot water at the right temperature, which wastes a lot of water resources in the process.

[0005] Although solar water heaters are energy-efficient, they must be installed outdoors and require sufficient sunshine hours, so they are only widely used in some rural areas, and lack the conditions for widespread use of solar water heaters in cities. Moreover, the heating time of solar water heaters is very slow, and it takes several days to fully heat the water in the water tank. In addition, solar water heaters are completely dependent on the weather. When there are continuous rainy days, they often cannot provide hot water for use. And depending on the volume of the water tank, the hot water it can provide at one time is limited, so it is obviously unable to meet the heating needs.

[0006] Electric water heaters can be divided into storage type electric water heaters and instant electric water heaters. Storage type electric water heaters cannot provide hot water that meets the requirements immediately. It takes a very long time to heat the water in the entire water tank at one time. And depending on the volume of the water tank, the hot water that can be provided at one time is limited. Therefore, when there are many family members, it cannot meet the needs of all people, let alone the need for circulating heating water. Although instant electric water heaters can quickly prepare hot water, their power is usually very high, especially for high-power instant electric water heaters that can provide bathing water. In order to provide enough water for bathing, their power is usually as high as 5Kw or more. When they run continuously for a long time, they will cause a huge burden on the home power grid, which often leads to other electrical appliances being unable to be used at the same time when the capacity of the home power grid is limited. The water output of the commonly used small instant electric water heater (also called small kitchen treasure) is relatively small. Although its power is not that high, it cannot meet the requirements of bathing at all. Utility Model Content

[0007] One aspect of the present application is to provide a hot water system, the hot water system comprising a gas water heater, the gas water heater having a water inlet and a domestic hot water outlet. The hot water system also comprises a thermal storage water tank, the thermal storage water tank having a hot water inlet, a return water inlet, a hot water outlet and a cold water inlet, wherein the water inlet of the gas water heater is fluidly connected to the return water inlet of the thermal storage water tank via a domestic hot water return water pipeline, the domestic hot water outlet of the gas water heater is fluidly connected to the hot water inlet of the thermal storage water tank via a domestic hot water outlet pipeline, the hot water outlet of the thermal storage water tank is fluidly connected to the domestic hot water water terminal via a hot water supply pipeline, and the cold water inlet of the thermal storage water tank is fluidly connected to a water source via a water inlet pipeline, wherein the hot water system also comprises an instant electric heater located at the domestic hot water water terminal in the path of the hot water supply pipeline, so that the hot water from the hot water outlet of the thermal storage water tank flows through the instant electric heater and reaches the domestic hot water water terminal. Optionally, when the temperature of the water flowing through the instant electric heater is lower than a target temperature, the instant electric heater can heat the water flowing through the instant electric heater to the target temperature.

[0008] Here, the gas water heater can be a conventional gas water heater already available on the market. Such a conventional gas water heater does not have a heat storage water tank as described above, so it cannot prepare hot water for use in advance, but must start burning and preparing hot water by opening a domestic hot water water terminal such as a faucet or a shower when using hot water. However, such a gas water heater must wait for a certain period of time before preparing hot water with a stable temperature, and before that, the cold water residing in the pipeline between the gas water heater and the domestic hot water water terminal must be emptied. In addition, when the water pressure is unstable, the water temperature of the hot water prepared by the gas water heater will also fluctuate. In the hot summer weather, the prepared hot water often overheats. All of the above lead to poor user experience. In order to improve this, the gas water heater is equipped with a heat storage water tank as described above, so that a certain amount of hot water can be prepared in advance before the water is actually used. Before the pre-prepared hot water is consumed and the water temperature in the water tank is too low due to the injection of cold water, the gas water heater has long been able to prepare hot water with a stable temperature to replenish the heat storage water tank. Thus, hot water that meets the requirements can be continuously provided. Moreover, due to the presence of the thermal storage water tank, even if the water pressure is unstable, the temperature of the hot water will not fluctuate, especially avoiding the risk of scalding due to overheating of the water temperature in summer. By arranging an instant electric heater in the path of the hot water supply pipeline at the domestic hot water water terminal, even if the hot water supply pipeline between the thermal storage water tank and the domestic hot water water terminal is long, the cold water resident in the hot water supply pipeline can be instantly heated by the instant electric heater, thereby further accelerating the water output speed of the hot water. Optionally, the instant electric heater can be integrated into the domestic hot water water terminal. As a result, there is no longer a pipeline for resident cold water between the instant electric heater and the domestic hot water water terminal, thereby further accelerating the water output speed of the hot water, and truly achieving instant hot water. Since the instant electric heater needs to heat a very small amount of water or only needs to heat the water to a very low temperature, it does not need to have a very high power on the one hand, and does not need to work continuously on the other hand, thereby not placing too much burden on the household power grid, and will not affect the normal use of other electrical appliances.

[0009] According to one embodiment of the present application, the hot water system also includes: a temperature sensor, which can measure the water temperature in the thermal storage water tank; a circulation pump located in the path of the domestic hot water return pipeline or in the path of the domestic hot water outlet pipeline; and a controller, which can control the gas water heater and the circulation pump according to the water temperature measured by the temperature sensor, wherein when the water temperature measured by the temperature sensor is lower than the target temperature and the difference between the target temperature and the water temperature measured by the temperature sensor exceeds a preset first threshold, the controller sends a heat demand to the gas water heater and starts the circulation pump, thereby pumping water out of the thermal storage water tank and re-pumping it into the thermal storage water tank after being heated by the gas water heater, and when the water temperature measured by the temperature sensor is higher than the target temperature and the difference between the water temperature measured by the temperature sensor and the target temperature exceeds a preset second threshold, the controller cancels the heat demand sent to the gas water heater, the gas water heater stops heating, and then the controller cuts off the circulation pump. Through this implementation, the gas water heater is not started immediately to replenish hot water for the thermal storage water tank when water is used, but the gas water heater is started to circulate and heat the hot water in the thermal storage water tank only when the water temperature of the hot water in the thermal storage water tank is lower than the target temperature by a certain amount. This avoids frequent starting of the gas water heater. At this time, although the water temperature of the hot water in the thermal storage water tank may be slightly lower than the target temperature due to the injection of cold water or heat loss, the instant electric heater at the domestic hot water terminal can easily further heat the flowing hot water to the target temperature.

[0010] According to another embodiment of the present application, the hot water system further includes: two temperature sensors, wherein the first temperature sensor is capable of measuring the water temperature at the hot water inlet in the thermal storage water tank, and the second temperature sensor is capable of measuring the water temperature at the return water outlet in the thermal storage water tank; a circulating pump located in the path of the domestic hot water return pipeline or in the path of the domestic hot water outlet pipeline; and a controller, wherein the controller is capable of controlling the gas water heater and the circulating pump according to the water temperature measured by the temperature sensor, wherein when the water temperature measured by the first temperature sensor is lower than the target temperature and the target temperature When the difference between the water temperature measured by the first temperature sensor and the target temperature exceeds a preset first threshold, the controller sends a heat demand to the gas water heater and starts the circulation pump, thereby pumping water out of the thermal storage water tank and re-pumping it into the thermal storage water tank after heating by the gas water heater. When the water temperature measured by the second temperature sensor is higher than the target temperature and the difference between the water temperature measured by the second temperature sensor and the target temperature exceeds a preset second threshold, the controller cancels sending the heat demand to the gas water heater, the gas water heater stops heating, and then the controller cuts off the circulation pump. In a thermal storage water tank, the water temperature in the thermal storage water tank may be uneven due to the injection of cold water. The temperature at the hot water inlet of the thermal storage water tank is usually the highest, while the temperature at the return water outlet of the thermal storage water tank is usually lower than the temperature at the hot water inlet of the thermal storage water tank. In particular, if the return water port of the thermal storage water tank is closer to the cold water inlet of the thermal storage water tank and farther from the hot water inlet of the thermal storage water tank, the temperature difference between the water temperature at the hot water inlet of the thermal storage water tank and the water temperature at the return water port of the thermal storage water tank is greater. By setting two temperature sensors, the start and stop of the gas water heater and the start and stop of the circulation pump can be better controlled. When the start of the gas water heater and the circulation pump is controlled according to the water temperature at the hot water inlet of the thermal storage water tank, it can be ensured that the hot water in the thermal storage water tank is fully utilized, and the gas water heater and the circulation pump will not be started too frequently due to the injection of cold water. When the heat demand for the gas water heater is canceled and the circulation pump is cut off according to the water temperature at the return water port of the thermal storage water tank, the gas water heater and the circulation pump will not be cut off in advance when the water in the thermal storage water tank is not fully and evenly heated. The above measures can enable the heat storage water tank to fully exert its heat storage capacity, reduce the start and stop times of the gas water heater, and save the energy consumption of the circulation pump.

[0011] Optionally, the controller can calculate the rate of increase of the water temperature measured by the first temperature sensor and the temperature difference between the water temperature measured by the first temperature sensor and the water temperature measured by the second temperature sensor after starting the circulation pump, wherein when the rate of increase of the water temperature measured by the first temperature sensor is lower than a preset third threshold value and the temperature difference between the water temperature measured by the first temperature sensor and the water temperature measured by the second temperature sensor is lower than a preset fourth threshold value, the controller can control the circulation pump to reduce the flow rate of the circulation pump. Optionally, the circulation pump is a variable frequency circulation pump, and the controller can adjust the flow rate of the circulation pump by adjusting the frequency of the circulation pump. Through the above measures, the water injection speed is reduced, thereby reducing the possibility of upper and lower convection mixing in the thermal storage water tank, and effectively reducing the influence of the injection of cold water or hot water on the temperature stratification inside the thermal storage water tank. In addition, due to the reduction of the flow rate, the heat load of the gas water heater can be reduced, so that the outlet water temperature of the gas water heater is guaranteed.

[0012] Optionally, the hot water system further comprises a proportional mixing valve located in the path of the domestic hot water outlet pipeline, and the hot water from the domestic hot water outlet of the gas water heater can flow from the first inlet of the proportional mixing valve to the hot water inlet of the thermal storage water tank via the outlet of the proportional mixing valve, and the domestic hot water return pipeline is fluidly connected to the second inlet of the proportional mixing valve via a bypass pipeline. Optionally, the proportional mixing valve is an electric proportional mixing valve, and when the water temperature measured by the first temperature sensor exceeds the target temperature, the controller can control the proportional mixing valve so that the opening of the first inlet of the proportional mixing valve is reduced, while the opening of the second inlet of the proportional mixing valve is increased. In this way, hot water with a water temperature of the target temperature can be directly injected into the thermal storage water tank.

[0013] Optionally, the gas water heater is a dual-purpose boiler for heating and hot water and also has a heating water outlet and a heating water return port. The heating water outlet of the gas water heater is connected to the heating water inlet fluid of the heating terminal equipment via a heating water outlet pipeline, and the heating water return port of the gas water heater is connected to the heating water outlet fluid of the heating terminal equipment via a heating water return pipeline.

[0014] Optionally, the hot water system further comprises a cabinet, in which the gas water heater, the thermal storage water tank and the controller are arranged, thereby making the hot water system more beautiful and allowing for more flexible arrangement of the hot water system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The following will further describe the embodiments of the present application in detail in conjunction with the accompanying drawings, but those skilled in the art will appreciate that these drawings are only used for the purpose of explaining the embodiments and should not be used as a limitation on the scope of the present application. The accompanying drawings show:

[0016] Figure 1 is a schematic diagram of a hot water system according to an embodiment of the present application. DETAILED DESCRIPTION

[0017] Figure 1 FIG. 1 is a schematic diagram of a hot water system 100 according to an embodiment of the present application. The hot water system 100 is used to provide hot water with a temperature as constant as possible. Figure 1 As shown, the hot water system 100 includes a gas water heater 1, which can prepare hot water with a water temperature higher than or equal to a target temperature. Here, the target temperature refers to a temperature that makes the user feel comfortable using water. The user can flexibly set the target temperature according to different personal preferences and different water temperature requirements in different seasons. Figure 1 In the embodiment shown, the gas water heater 1 is a dual-purpose heating and hot water boiler and has a water inlet, a domestic hot water outlet, a heating water outlet and a heating water return. The hot water system 100 also includes a thermal storage water tank 2, which has a hot water inlet, a return, a hot water outlet and a cold water inlet, wherein the water inlet of the gas water heater 1 is fluidly connected to the return port of the thermal storage water tank 2 via a domestic hot water return pipeline 21, the domestic hot water outlet of the gas water heater 1 is fluidly connected to the hot water inlet of the thermal storage water tank 2 via a domestic hot water outlet pipeline 12, the hot water outlet of the thermal storage water tank 2 is fluidly connected to the domestic hot water water terminal 3 via a hot water supply pipeline 23, and the cold water inlet of the thermal storage water tank 2 is fluidly connected to the water source via a water inlet pipeline 20. The heating water outlet of the gas water heater 1 is in fluid communication with the heating water inlet of the heating terminal device 7 via the heating water outlet pipeline 17, and the heating water return port of the gas water heater 1 is in fluid communication with the heating water outlet of the heating terminal device 7 via the heating water return pipeline 71. It should be noted that the gas water heater 1 may also be a conventional gas water heater that only provides domestic hot water but not heating water. In this case, the gas water heater 1 only has a water inlet and a domestic hot water outlet but no heating water outlet and heating water return port.

[0018] Here, the hot water system 100 can be fluidly connected to multiple domestic hot water terminals 3 as needed, but Figure 1 Only one domestic hot water terminal 3 is shown as an example. The domestic hot water terminal 3 can be, for example, a faucet in a kitchen or toilet, or a shower head in a bathroom.

[0019] The hot water system 100 further includes an instant electric heater 4 located at the domestic hot water terminal 3 in the path of the hot water supply pipeline 23, so that the hot water from the hot water outlet of the thermal storage water tank 2 flows through the instant electric heater 4 and reaches the domestic hot water terminal 3. Therefore, when the temperature of the water flowing through the instant electric heater 4 is lower than the target temperature, the instant electric heater 4 can heat the water flowing through the instant electric heater 4 to the target temperature. In one embodiment, the instant electric heater 4 can be integrated into the domestic hot water terminal 3, so that there is no cold water pipeline between the instant electric heater 4 and the domestic hot water terminal 3, thereby further accelerating the water output speed of hot water, and truly achieving instant hot water use.

[0020] The hot water system 100 further includes a temperature sensor, which can measure the water temperature in the thermal storage water tank 2. Figure 1 In the embodiment shown, two temperature sensors are provided, wherein the first temperature sensor 8 can measure the water temperature at the hot water inlet of the thermal storage water tank 2, and the second temperature sensor 9 can measure the water temperature at the return water outlet of the thermal storage water tank 2. Of course, only one temperature sensor can also be provided. Figure 1 In the illustrated embodiment, the hot water system 100 further comprises a circulation pump 5 located in the path of the domestic hot water outlet pipeline 12. Alternatively, the circulation pump 5 may also be located in the path of the domestic hot water return pipeline 21.

[0021] The hot water system 100 also has a controller (not shown in the figure), which can control the gas water heater 1 and the circulation pump 5 according to the water temperature measured by the temperature sensor. In the case where there is only one temperature sensor, when the water temperature measured by the temperature sensor is lower than the target temperature and the difference between the target temperature and the water temperature measured by the temperature sensor exceeds a preset first threshold, the controller sends a heat demand to the gas water heater 1 and starts the circulation pump 5, so that the water in the thermal storage water tank 2 is pumped out and re-pumped into the thermal storage water tank 2 after being heated by the gas water heater 1. When the water temperature measured by the temperature sensor is higher than the target temperature and the difference between the water temperature measured by the temperature sensor and the target temperature exceeds a preset second threshold, the controller cancels the heat demand sent to the gas water heater 1, the gas water heater 1 stops heating, and then the controller cuts off the circulation pump 5. Figure 1In the case where there are two temperature sensors as shown in the figure, when the water temperature measured by the first temperature sensor 8 is lower than the target temperature and the difference between the target temperature and the water temperature measured by the first temperature sensor 8 exceeds a preset first threshold value, the controller sends a heat demand to the gas water heater 1 and starts the circulation pump 5, thereby pumping out the water in the thermal storage water tank 2 and re-pumping it into the thermal storage water tank 2 after being heated by the gas water heater 1, and when the water temperature measured by the second temperature sensor 9 is higher than the target temperature and the difference between the water temperature measured by the second temperature sensor 9 and the target temperature exceeds a preset second threshold value, the controller cancels sending the heat demand to the gas water heater 1, the gas water heater 1 stops heating, and then the controller cuts off the circulation pump 5.

[0022] Here, the first threshold is also called the start hysteresis, and the second threshold is also called the stop hysteresis. The first threshold and the second threshold may be the same or different. The smaller the first threshold and the second threshold are, the higher the frequency of the start and stop of the circulation pump and the gas water heater, but the lower the water temperature fluctuation in the thermal storage water tank. The larger the first threshold and the second threshold are, the lower the frequency of the start and stop of the circulation pump and the gas water heater, but the greater the water temperature fluctuation in the thermal storage water tank. Usually, the first threshold and the second threshold can be selected as 1K, 2K or 3K, for example. Of course, the first threshold and the second threshold are not limited to the above exemplary values, and can also be adjusted by the user according to actual conditions and preferences.

[0023] Optionally, the controller can calculate the rate of increase of the water temperature measured by the first temperature sensor 8 and the temperature difference between the water temperature measured by the first temperature sensor 8 and the water temperature measured by the second temperature sensor 9 after starting the circulation pump 5, wherein when the rate of increase of the water temperature measured by the first temperature sensor 8 is lower than a preset third threshold value and the temperature difference between the water temperature measured by the first temperature sensor 8 and the water temperature measured by the second temperature sensor 9 is lower than a preset fourth threshold value, the controller can control the circulation pump 5 to reduce the flow rate of the circulation pump 5. The circulation pump 5 can be, for example, a variable frequency circulation pump, and the controller can adjust the flow rate of the circulation pump 5 by adjusting the frequency of the circulation pump 5. However, the circulation pump 5 can also be other known types of pumps, which can adjust the flow rate of the pump, for example, by adjusting the speed of the pump, adjusting the blade angle of the pump, adjusting the opening of the inlet and outlet valves of the pump, or by other means.

[0024] It should be noted that the third threshold value represents the critical value of the rate of increase of the water temperature at the hot water inlet in the thermal storage water tank after the gas water heater is started, and the fourth threshold value represents the critical value of the difference between the water temperature at the hot water inlet in the thermal storage water tank and the water temperature at the return port, which is related to the water capacity of the thermal storage water tank, the heating power of the gas water heater, etc. Taking a 24kW heating and hot water dual-purpose furnace and a 100L water tank as an example, 5 minutes after a new heating cycle starts, if the temperature rise of the first temperature sensor 8 does not exceed 5°C and the temperature difference between the temperature measured by the first temperature sensor 8 and the temperature measured by the second temperature sensor 9 is within 2K, for example, the flow rate of the circulation pump 5 is reduced.

[0025] exist Figure 1 In the illustrated embodiment, the hot water system 100 further includes a proportional mixing valve 6 located in the path of the domestic hot water outlet pipeline 12, wherein the proportional mixing valve 6 has two inlets and one outlet, wherein hot water from the domestic hot water outlet of the gas water heater 1 can flow from the first inlet of the proportional mixing valve 6 via the outlet of the proportional mixing valve 6 to the hot water inlet of the thermal storage water tank 2, and the domestic hot water return pipeline 21 is fluidly connected to the second inlet of the proportional mixing valve 6 via the bypass pipeline 26.

[0026] exist Figure 1 In the illustrated embodiment, the proportional water mixing valve 6 is an electric proportional water mixing valve. When the water temperature measured by the first temperature sensor 8 exceeds the target temperature, the controller can control the proportional water mixing valve 6 so that the opening of the first inlet of the proportional water mixing valve 6 is reduced, while the opening of the second inlet of the proportional water mixing valve 6 is increased.

[0027] exist Figure 1 In the illustrated embodiment, the hot water system 100 further comprises a cabinet 10, and the gas water heater 1, the thermal storage water tank 2 and the controller are all arranged in the cabinet 10. This makes the hot water system more beautiful and can be arranged more flexibly.

[0028] The above is only an exemplary implementation of the present application, and the protection scope of the present application is not limited to the above implementation. All technical solutions under the concept of the present application belong to the protection scope of the present application. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present application should also be regarded as the protection scope of the present application.

Claims

1. A hot water system (100), the hot water system (100) comprising a gas water heater (1), the gas water heater (1) having: water inlets; and Domestic hot water outlet, It is characterized in that The hot water system (100) further comprises a heat storage water tank (2), wherein the heat storage water tank (2) comprises: Hot water inlet; return water outlet; Hot water outlet; as well as Cold water inlet, The water inlet of the gas water heater (1) is fluidly connected to the water return port of the thermal storage water tank (2) via a domestic hot water return pipe (21); the domestic hot water outlet of the gas water heater (1) is fluidly connected to the hot water inlet of the thermal storage water tank (2) via a domestic hot water outlet pipe (12); the hot water outlet of the thermal storage water tank (2) is fluidly connected to the domestic hot water terminal (3) via a hot water supply pipe (23); and the cold water inlet of the thermal storage water tank (2) is fluidly connected to a water source via a water inlet pipe (20). The hot water system (100) further comprises an instant electric heater (4) located at the domestic hot water terminal (3) in the path of the hot water supply pipeline (23), so that hot water from the hot water outlet of the thermal storage water tank (2) flows through the instant electric heater (4) and reaches the domestic hot water terminal (3).

2. The hot water system (100) according to claim 1, characterized in that: The hot water system (100) further comprises: a temperature sensor capable of measuring the water temperature in the thermal storage water tank (2); a circulation pump (5) located in the path of the domestic hot water return pipeline (21) or located in the path of the domestic hot water outlet pipeline (12); and a controller capable of controlling the gas water heater (1) and the circulation pump (5) according to the water temperature measured by the temperature sensor, When the water temperature measured by the temperature sensor is lower than the target temperature and the difference between the target temperature and the water temperature measured by the temperature sensor exceeds a preset first threshold, the controller sends a heat demand to the gas water heater (1) and starts the circulation pump (5), thereby pumping water out of the thermal storage water tank (2) and re-pumping the water into the thermal storage water tank (2) after being heated by the gas water heater (1); and when the water temperature measured by the temperature sensor is higher than the target temperature and the difference between the water temperature measured by the temperature sensor and the target temperature exceeds a preset second threshold, the controller cancels sending the heat demand to the gas water heater (1), the gas water heater (1) stops heating, and then the controller cuts off the circulation pump (5).

3. The hot water system (100) according to claim 1, characterized in that: The hot water system (100) further comprises: Two temperature sensors, wherein the first temperature sensor (8) is capable of measuring the water temperature at the hot water inlet of the thermal storage water tank (2), and the second temperature sensor (9) is capable of measuring the water temperature at the water return outlet of the thermal storage water tank (2); a circulation pump (5) located in the path of the domestic hot water return pipeline (21) or located in the path of the domestic hot water outlet pipeline (12); and a controller capable of controlling the gas water heater (1) and the circulation pump (5) according to the water temperature measured by the temperature sensor, When the water temperature measured by the first temperature sensor (8) is lower than the target temperature and the difference between the target temperature and the water temperature measured by the first temperature sensor (8) exceeds a preset first threshold, the controller sends a heat demand to the gas water heater (1) and starts the circulation pump (5), thereby pumping water out of the thermal storage water tank (2) and pumping the water back into the thermal storage water tank (2) after heating by the gas water heater (1); and when the water temperature measured by the second temperature sensor (9) is higher than the target temperature and the difference between the water temperature measured by the second temperature sensor (9) and the target temperature exceeds a preset second threshold, the controller cancels sending the heat demand to the gas water heater (1), the gas water heater (1) stops heating, and then the controller cuts off the circulation pump (5).

4. The hot water system (100) according to claim 3, characterized in that: The controller is capable of calculating the rate of increase of the water temperature measured by the first temperature sensor (8) and the temperature difference between the water temperature measured by the first temperature sensor (8) and the water temperature measured by the second temperature sensor (9) after starting the circulation pump (5), wherein when the rate of increase of the water temperature measured by the first temperature sensor (8) is lower than a third preset threshold value and the temperature difference between the water temperature measured by the first temperature sensor (8) and the water temperature measured by the second temperature sensor (9) is lower than a fourth preset threshold value, the controller is capable of controlling the circulation pump (5) so as to reduce the flow rate of the circulation pump (5).

5. The hot water system (100) according to claim 4, characterized in that: The circulation pump (5) is a variable frequency circulation pump, and the controller can adjust the flow rate of the circulation pump (5) by adjusting the frequency of the circulation pump (5).

6. The hot water system (100) according to claim 3, characterized in that: The hot water system (100) further comprises a proportional water mixing valve (6) located in the path of the domestic hot water outlet pipeline (12), and hot water from the domestic hot water outlet of the gas water heater (1) can flow from the first inlet of the proportional water mixing valve (6) via the outlet of the proportional water mixing valve (6) to the hot water inlet of the thermal storage water tank (2), and the domestic hot water return pipeline (21) is fluidly connected to the second inlet of the proportional water mixing valve (6) via a bypass pipeline (26).

7. The hot water system (100) according to claim 6, characterized in that: The proportional water mixing valve (6) is an electric proportional water mixing valve. When the water temperature measured by the first temperature sensor (8) exceeds the target temperature, the controller can control the proportional water mixing valve (6) so that the opening of the first inlet of the proportional water mixing valve (6) decreases, while the opening of the second inlet of the proportional water mixing valve (6) increases.

8. The hot water system (100) according to any one of claims 1 to 7, characterized in that: When the temperature of the water flowing through the instant electric heater (4) is lower than the target temperature, the instant electric heater (4) is capable of heating the water flowing through the instant electric heater (4) to the target temperature.

9. The hot water system (100) according to any one of claims 1 to 7, characterized in that: The instant electric heater (4) is integrated into the domestic hot water terminal (3).

10. The hot water system (100) according to any one of claims 1 to 7, characterized in that: The gas water heater (1) is a dual-purpose boiler for heating and hot water and also has a heating water outlet and a heating water return port. The heating water outlet of the gas water heater (1) is connected to the heating water inlet fluid of the heating terminal device (7) via a heating water outlet pipeline (17), and the heating water return port of the gas water heater (1) is connected to the heating water outlet fluid of the heating terminal device (7) via a heating water return pipeline (71).

11. The hot water system (100) according to any one of claims 1 to 7, characterized in that: The hot water system (100) further comprises a cabinet (10), in which the gas water heater (1), the thermal storage water tank (2) and the controller are all arranged.

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