Direct-current energy storage water heater and control method thereof

Abstract

The invention relates to the technical field of water heaters, particularly provides a direct-current water heater and a control method thereof, and aims to solve the problem that the burden of a user is increased or the income is reduced due to energy waste of an existing water heater. In order to achieve the purpose, the direct-current energy storage water heater comprises a plurality of water tanks, and at least two adjacent water tanks are communicated with each other; and the heater is arranged in the water tank. In addition, the number and the temperature of the water tanks needing heat storage are determined according to the heat using requirement of a user; all water in the water heater is not heated, so that energy required by energy storage can be saved, and a user can be more economical and more reasonable.

Description

Technical Field

[0001] The present invention relates to the technical field of water heaters, and in particular provides a direct current water heater and a control method thereof. Background Art

[0002] With the development of economy and technology, many households have been equipped with photovoltaic direct-flexible energy storage systems, but traditional photovoltaic direct-flexible energy storage systems are mostly single electric water heaters or single phase change systems for energy storage.

[0003] However, existing water heater energy storage systems often store energy based on the maximum capacity of the water heater and the user's desired temperature. This method results in a high heat requirement, which can lead to energy waste when water usage is low. This is especially true when the PV system's production capacity is low, requiring more utility power for heat storage, increasing the electricity burden. Even when the PV system is producing adequately, this reduces power upload, reducing user benefits.

[0004] Therefore, there is an urgent need for a DC energy storage water heater and a control method thereof to solve the above technical problems. Summary of the Invention

[0005] The present invention aims to solve the above technical problem, that is, to solve the problem that existing water heaters waste energy, resulting in increased burden on users or reduced benefits.

[0006] In a first aspect, the present invention provides a DC energy storage water heater, comprising:

[0007] A plurality of water tanks, at least two adjacent water tanks are connected to each other;

[0008] Heater: a heater is provided in the water tank.

[0009] In a specific embodiment of the above-mentioned DC energy storage water heater, a plurality of water tanks are arranged side by side up and down.

[0010] In a specific embodiment of the above-mentioned DC energy storage water heater, a first connecting pipe and a second connecting pipe are provided between two adjacent water tanks, a control valve is provided on the first connecting pipe, and a water pump is provided on the second connecting pipe. The water pump cooperates with the control valve to mix the water in the two adjacent water tanks.

[0011] In the specific implementation of the above-mentioned DC energy storage water heater, the gear position of each water tank is different, and the amount of heat stored in each water tank is different.

[0012] In a second aspect, the present invention provides a control method for the DC energy storage water heater as described above, the control method comprising the following steps:

[0013] According to the user's heating needs, determine the number and temperature of water tanks that need to store heat.

[0014] In a specific embodiment of the control method of the DC energy storage water heater, “determining the number and temperature of water tanks requiring heat storage according to the user's heat demand” includes:

[0015] Determine the heat demand based on the user's heat demand;

[0016] Determining the water tank that needs to store heat according to the heat demand;

[0017] The heat storage temperature of the water tank that needs to store heat is determined according to the heat demand and the maximum total heat storage of the water tank that needs to store heat.

[0018] In a specific embodiment of the control method of the DC energy storage water heater, “determining the heat storage temperature of the water tank that needs to store heat according to the heat demand and the maximum total heat storage of the water tank that needs to store heat” includes:

[0019] If the heat demand is less than the maximum total heat storage capacity of the water tank that needs to store heat, the water tank that needs to store heat is stored according to the required temperature of the heat demand or the temperature corresponding to the heat demand.

[0020] In a specific implementation of the control method for the above-mentioned DC energy storage water heater, if there are multiple water tanks participating in heat storage, and the required temperature for the heat demand is not greater than the temperature corresponding to the heat demand, heating is performed according to the temperature corresponding to the heat demand, and water is mixed in the multiple water tanks after heat storage and before heat use.

[0021] In a specific embodiment of the control method of the DC energy storage water heater, if the number of the water tanks participating in the heat storage is one, heat is stored in the water tank that needs heat storage according to the required temperature of the heat demand; and / or

[0022] If there are multiple water tanks involved in heat storage, and the required temperature of the heat demand is greater than the temperature corresponding to the heat demand, heating is performed according to the required temperature of the heat demand.

[0023] In a specific embodiment of the control method of the DC energy storage water heater, “determining the heat storage temperature of the water tank that needs to store heat according to the heat demand and the maximum total heat storage of the water tank that needs to store heat” further includes:

[0024] If the heat demand is equal to the maximum total heat storage capacity of the water tank that needs to store heat, heat storage is performed according to the maximum heat storage capacity of the water tank that needs to store heat.

[0025] When adopting the above technical solution, the DC energy storage water heater of the present invention includes multiple water tanks, phase change energy storage modules and heaters, at least two adjacent water tanks are interconnected, and the phase change energy storage modules and heaters are installed in the water tanks; moreover, the number and temperature of the water tanks that need to store heat are determined according to the user's heating demand; not all the water in the water heater is heated, which can save the energy required for energy storage and make it more economical for users. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0027] Figure 1 This is a schematic diagram of the structure of the DC energy storage water heater provided by the present invention. Figure 1 ;

[0028] Figure 2 This is a schematic diagram of the structure of the DC energy storage water heater provided by the present invention. Figure 2 ;

[0029] Figure 3 This is a flow chart of the main steps of the control method of the DC energy storage water heater provided by the present invention;

[0030] Figure 4 It is a flowchart of the detailed steps of the control method of the DC energy storage water heater provided by the present invention;

[0031] Figure 5 It is a flow chart of detailed steps for optimizing the energy storage mode of the DC energy storage water heater provided by the present invention.

[0032] List of reference numerals: 1. water tank; 2. phase change energy storage module; 3. first connecting pipe; 31. control valve; 4. second connecting pipe; 41. water pump; 5. third connecting pipe; 6. fourth connecting pipe. DETAILED DESCRIPTION

[0033] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0034] It should be noted that in the description of the present invention, terms such as "upper," "lower," "left," "right," "inner," and "outer" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. These terms are used solely for ease of description and are not intended to indicate or imply that the device or component described must have, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] Furthermore, it should be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "installed," "disposed," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to direct connections, indirect connections through an intermediate medium, or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0036] Existing water heater energy storage systems often store energy based on the maximum capacity of the water heater and the user's desired temperature. This method results in a high heat requirement, which can lead to energy waste when water usage is low. This is especially true when the photovoltaic system's production capacity is low, requiring more utility power for heat storage, increasing the electricity burden. Even when the photovoltaic system is producing adequately, this reduces power upload, reducing user benefits.

[0037] In order to solve the problem that existing water heaters waste energy, resulting in increased user burden or reduced benefits.

[0038] This embodiment discloses a DC energy storage water heater, which is equipped with a new energy system and an AC-DC module. The AC-DC module can convert AC power from a household power grid into DC power so that the DC energy storage water heater can be used directly.

[0039] A new energy system can specifically be a photovoltaic system, but it can also be a wind power system or a fuel cell system. The electricity generated by the photovoltaic system can be directly used by the user's DC home appliances or uploaded to the grid for revenue generation. Because the new energy system generates DC power, it can be directly used by DC home appliances. Specifically, it can be used directly by DC water heaters, DC rice cookers, DC refrigerators, DC wine cabinets, and DC washing machines. To enable the electricity generated by the new energy system to be uploaded to the grid, it must pass through a DC-to-AC converter. This converter is located between the new energy system and the grid, converting the DC power generated by the new energy system into AC power, which is then uploaded to the grid.

[0040] To save costs and installation space, a bidirectional converter replaces the DC-to-AC and AC-to-DC conversion modules. This new energy system also features an energy storage module, specifically a battery. This allows the battery to store the electricity generated by the new energy system when it cannot be consumed immediately. When the new energy system is unable to generate electricity, the energy storage module can discharge it for use by DC appliances. This discharge can occur during peak hours, saving users money on electricity bills.

[0041] like Figure 1As shown, the DC energy storage water heater includes an outer shell, multiple water tanks 1, a phase-change energy storage module 2, and a heater. The water tanks 1 are disposed within the outer shell. The multiple water tanks 1 can be individually molded and then installed within the outer shell. The multiple water tanks 1 can also be a single unit, separated by baffles. At least two adjacent water tanks 1 are interconnected.

[0042] A phase-change energy storage module 2 is provided in the water tank 1. When the new energy system is used to heat the water heater, the phase-change energy storage module 2 can store heat. When heat is needed, the phase-change energy storage module 2 can release heat to heat the water in the water tank 1 for the user to use. The phase-change energy storage module 2 is specifically a heat storage method that can be a passive heat storage mode, that is, heat is stored through the water in the water heater. Of course, an active heat storage mode can also be used for heat storage. Specifically, a heat exchange pipe can be provided in the phase-change energy storage module 2, and the heat generated by the new energy system flows through the heat exchange pipe to store heat in the phase-change energy storage module 2; or, the phase-change energy storage module 2 is directly connected to electricity, and when the new energy system generates electricity, it can be directly supplied to the phase-change energy storage module 2 for use in heat storage.

[0043] A heater is provided in the water tank 1, and the heater is used to heat the water in the water tank 1 for heat storage. The heater is an electric heating coil, and the phase change energy storage module 2 is specifically cylindrical. The electric heating coil is arranged around the phase change energy storage module 2, so that the electric heating coil can heat the water in the water tank 1 while also transferring heat to the phase change energy storage module 2, so that the phase change energy storage module 2 can store energy. The two methods of heat exchange pipes and electric heating coils can coexist. When the new energy system can generate enough heat, heat exchange pipes are used for energy storage. When enough electricity is generated, the phase change energy storage module 2 can be stored with the electric heating coil. When the new energy system cannot generate enough heat and electricity, the phase change energy storage module 2 can be stored with the electric heating coil during the valley period.

[0044] Multiple water tanks 1 are arranged side by side up and down, and a first connecting pipe 3 and a second connecting pipe 4 are provided between two adjacent water tanks 1. The first connecting pipe 3 is provided with a control valve 31, and the second connecting pipe 4 is provided with a water pump 41. The water pump 41 cooperates with the control valve 31 to mix the water in the two adjacent water tanks 1.

[0045] As a preferred embodiment, the number of water tanks 1 in this embodiment is two. They are connected by a first connecting pipe 3 and a second connecting pipe 4. In this connection mode, when the heat storage requirement is high (i.e., a large amount of electricity or heat generated by the new energy system needs to be absorbed) and the heat utilization requirement is low (the user requires less heat), both water tanks 1 are electrically heated according to the absorption requirement, slowly accumulating heat, and heat storage is completed after both water tanks 1 reach the heat storage temperature. If the heat storage amount is large and the time required is long, one water tank 1 is heated, and after reaching the temperature, the water pump 41 is turned on to circulate the heat, and heating is completed gradually according to the required absorption power. When the heat storage requirement is high and the heat utilization requirement is high, both water tanks 1 accumulate heat simultaneously, and heat storage is completed after reaching the temperature. When the heat storage requirement is low and the heat utilization requirement is high, heat storage is performed using mains electricity during off-peak hours, and heat storage is completed after reaching the target heat utilization. When the heat storage requirement is low and the heat utilization requirement is low, one water tank 1 uses the new energy system to store heat, and off-peak electricity heat storage is used for auxiliary purposes. Moreover, during the long-term heat storage process, in order to reduce heat loss, the circulation is started according to the temperature difference between the two water tanks 1 .

[0046] Regarding the connection mode of the water tank 1, it should be noted that although the connection is through a connecting pipe and the water is mixed by the water pump 41 in this embodiment, this is not a limitation of the present invention. Without departing from the principle of the present invention, in other embodiments, natural convection can be used to mix the water. Figure 2 As shown, the specific scheme is as follows: a third connecting pipe 5 and a fourth connecting pipe 6 are installed between the two water tanks 1. The top of the third connecting pipe 5 is located at the top of the upper water tank 1, and the fourth connecting pipe 6 is located at the bottom of the upper water tank 1. When heating a single water tank 1, due to the characteristics of thermal fluids, the heated water will flow downward. Therefore, if only the heater in the lower water tank 1 is turned on, the heated water in the lower water tank 1 will flow upward through the third connecting pipe 5 to the top of the upper water tank 1. The lower-temperature water in the upper water tank 1 will then flow through the fourth connecting pipe 6 to the lower water tank 1 for heating. However, this heating method is relatively slow. If only the heater in the lower water tank is turned on for heating, due to the heat flow characteristics, the hot water will not flow downward or will flow downward very slowly, resulting in an insignificant temperature change in the lower water tank 1. If the heaters in both water tanks 1 are turned on, dual water tank 1 heating can be achieved. Due to this limited heating mode, only the upper water tank 1 or both water tanks 1 will be heated during the heating process.

[0047] The gear position of each water tank 1 is different, and the heat stored in each water tank 1 is different. In this embodiment, the gear positions of the two water tanks 1 are different, but the water capacity is the same, which can ensure that the two water tanks 1 have different maximum heat storage capacities.

[0048] The DC energy storage water heater further includes a controller, which is configured to execute a control method for the DC energy storage water heater, comprising the following steps:

[0049] According to the user's heat demand, determine the quantity and temperature of the water tank 1 that needs heat storage. Not all water of the water heater is heated, can save the energy required for energy storage, can make the user more economically reasonable.

[0050] like Figure 3 As shown, "determining the number and temperature of the water tanks 1 required to store heat according to the user's heat demand" includes:

[0051] S1. Determine the heat demand, water consumption and heat demand temperature based on the user's heat demand; the heat demand is calculated from the water consumption and heat demand temperature using a thermodynamic formula.

[0052] S2. Determine the water tanks 1 that need to store heat according to the heat demand, and specifically determine which water tanks 1 need to participate in heat storage.

[0053] S3. Determine the heat storage temperature of the water tank 1 that needs to store heat according to the heat demand and the maximum total heat storage capacity of the water tank 1 that needs to store heat.

[0054] “Determining the heat storage temperature of the water tank 1 that needs to store heat based on the heat demand and the maximum total heat storage capacity of the water tank 1 that needs to store heat” specifically includes:

[0055] If the heat demand is less than the maximum total heat storage capacity of the water tank 1 that needs to store heat, the water tank 1 that needs to store heat is stored according to the required temperature of the heat demand or the temperature corresponding to the heat demand.

[0056] Specifically, if there are multiple water tanks 1 involved in heat storage, and the required temperature for heat demand is not greater than the temperature corresponding to the heat demand, heating is performed according to the temperature corresponding to the heat demand, and multiple water tanks 1 are mixed after heat storage and before heat use.

[0057] If the number of water tanks 1 involved in heat storage is one, heat is stored in the water tank 1 that needs heat storage according to the required temperature of the heat demand.

[0058] If there are multiple water tanks 1 involved in heat storage, and the required temperature for heat demand is greater than the temperature corresponding to the heat demand, heating is performed according to the required temperature for heat demand.

[0059] “Determining the heat storage temperature of the water tank 1 that needs to store heat based on the heat demand and the maximum total heat storage capacity of the water tank 1 that needs to store heat” specifically includes:

[0060] If the heat demand is equal to the maximum total heat storage capacity of the water tank 1 that needs to store heat, heat storage is performed according to the maximum total heat storage capacity of the water tank 1 that needs to store heat.

[0061] The various heat demands are explained using the heating conditions of the two water tanks 1 in this embodiment. The maximum gear of the upper water tank 1 is lower than the maximum gear of the lower water tank 1, that is, the maximum heat storage capacity of the upper water tank 1 is less than the maximum heat storage capacity of the lower water tank 1. The heat storage capacity design of the water tank 1 is generally designed according to the user's maximum heat demand, so the user's heat demand generally will not exceed the total maximum heat storage capacity of the two water tanks 1, so there will not be a situation where the user's heat demand is greater than the total maximum heat storage capacity of the two water tanks 1; even if the user's heat demand occasionally encounters such a situation, this application will not take it into consideration. Figure 4 As shown, the control method of the DC energy storage water heater specifically includes the following detailed steps:

[0062] S11. Obtain the user's heating demand.

[0063] S12. Determine the heat demand, water consumption, and heat demand temperature based on the user's heat demand; wherein the heat demand is calculated from the water consumption and heat demand temperature using a thermodynamic formula.

[0064] S13. Determine whether the heat demand is less than the maximum heat storage capacity of the upper water tank 1. If yes, proceed to step S14; if not, proceed to step S16.

[0065] S14, calculating the first temperature according to the heat demand and the water volume of the upper water tank 1; then proceeding to step S15.

[0066] S15. Determine whether the heat demand temperature is greater than the first temperature. If so, store heat in the upper water tank 1 according to the heat demand temperature. Since the heat demand temperature is less than the maximum heat storage capacity of the upper water tank 1, the heat demand temperature is less than the maximum heat storage temperature of the upper water tank 1. Therefore, storing heat in the lower water tank 1 according to the heat demand temperature can meet the user's heat demand.

[0067] S16: Determine whether the heat demand is equal to the maximum heat storage capacity of the upper water tank 1. If so, heat is stored in the upper water tank 1 according to the maximum heat storage capacity of the upper water tank 1, that is, heat is stored according to the maximum heat storage temperature of the upper water tank 1. If not, proceed to step S17.

[0068] S17, determine whether the heat demand is less than the maximum heat storage capacity of the lower water tank 1, if yes, proceed to step S18; if not, proceed to step S20.

[0069] S18. Calculate the second temperature based on the heat demand and the water volume in the lower water tank 1; then proceed to step S19.

[0070] S19: Determine whether the heat demand temperature is greater than the second temperature. If so, store heat in the lower water tank 1 according to the heat demand temperature. Since the heat demand temperature is less than the maximum heat storage capacity of the lower water tank 1, the heat demand temperature is less than the maximum heat storage temperature of the lower water tank 1. Therefore, storing heat in the lower water tank 1 according to the heat demand temperature can meet the user's heat demand.

[0071] S20: Determine whether the heat demand is equal to the maximum heat storage capacity of the lower water tank 1. If so, heat is stored in the lower water tank 1 according to the maximum heat storage capacity of the lower water tank 1, that is, heat is stored according to the maximum heat storage temperature of the lower water tank 1. If not, proceed to step S21.

[0072] S21. Determine whether the heat demand is less than the total maximum heat storage capacity of the two water tanks 1. If yes, proceed to step S22.

[0073] S22. Determine whether the required temperature for heat demand is greater than the temperature corresponding to the heat demand. If so, heat is performed according to the required temperature for heat demand; if not, heat is performed according to the temperature corresponding to the heat demand. After heat storage, multiple water tanks 1 mix water before heat use; specifically, open the control valve 31 and the water pump 41 to mix the water.

[0074] For the heat storage of the water heater, the electricity or heat generated by the new energy system is preferably used for heat storage. When the energy generated by the new energy system cannot meet the heat storage demand of the water heater, the mains electricity is used to store heat for the water heater during the valley period. Since the user's daily heat consumption is almost the same, or it is counted as a cycle per week, and the energy generated by the new energy system during this cycle is also predictable, especially in bad weather conditions, when the energy generated by the new energy system (photovoltaic system) is very little, heat can be stored in advance during the valley period based on the heat consumption for user use. Although heat storage during the valley period requires insulation, the heat storage can be carried out by using the heat stored in the phase change energy storage module 2, thereby avoiding the use of mains electricity for heat storage during the peak period, which can save the user's electricity costs in general.

[0075] Since off-peak periods last longer, calculating the total electricity price required for energy storage based on the start of the off-peak period may result in a higher total price. Calculating the total electricity price based on the end of the off-peak period may not be sufficient for energy storage. Therefore, optimizing the total electricity price required for energy storage can be used to find the most economically suitable off-peak energy storage method.

[0076] Specifically, the energy storage mode in the valley period is optimized based on the peak and valley electricity period and electricity price data of the previous day to obtain the optimal energy storage method. Figure 5 As shown, it specifically includes the following steps:

[0077] S21. Set the economic electricity price = the first total electricity price (the water heater calculates the first total electricity price of the peak period heat storage mode based on the heat usage time and the target temperature), and the energy storage time = the starting time of the valley period; after the optimal calculation, the normal economic electricity price should be lower than the first total electricity price, so the initial economic electricity price is assigned to the first total electricity price without affecting the subsequent calculations, and if the economic electricity price is greater than the first total electricity price after the optimal calculation, the water heater is not suitable for operation in the valley period heat storage mode at this time, and the economic electricity price will not be less than the first total electricity price, which is also convenient for subsequent judgment and calculation.

[0078] S22, obtaining a second total electricity price required for the water in the water tank 1 that needs to store energy to reach the target temperature from the energy storage moment, and a third total electricity price required for the water in the water tank 1 that needs to store energy to maintain the target temperature until the heat is used moment;

[0079] S23. Determine whether the sum of the second total electricity price and the third total electricity price is less than the economic electricity price; if yes, proceed to step S231; if not, proceed to step S232;

[0080] S231, set the economic electricity price = the second total electricity price + the third total electricity price, the optimal start time = the energy storage time, the energy storage time = the energy storage time + the preset duration, and proceed to step S24;

[0081] S232, charging time = charging time + preset duration, and proceed to step S24;

[0082] In this embodiment, the preset time length is preferably 5 minutes. Regarding the preset time length, it should be noted that although it is limited to 5 minutes in this embodiment, this is not a limitation of the present invention. Without departing from the principles of the present invention, those skilled in the art may also select 8 minutes, 10 minutes, or 15 minutes in other embodiments. Such selections do not deviate from the basic principles of the present invention and fall within the scope of protection of the present invention.

[0083] S24, determining whether the energy storage moment is within the valley period, if yes, proceeding to step S22, if not, proceeding to step S241;

[0084] S241. End the calculation of the valley period energy storage mode. In the valley period energy storage mode, the water heater starts to operate and store energy from the optimal start time.

[0085] By optimizing the calculation, the off-peak energy storage mode can be activated to cover all sections of the off-peak period, and the optimal activation time and, therefore, the optimal off-peak energy storage mode can be determined. By comparing the optimal off-peak energy storage mode with the traditional energy storage mode, the economic efficiency of the water heater can be optimized.

[0086] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A DC energy storage water heater, characterized in that: It includes: A plurality of water tanks (1), at least two adjacent water tanks (1) being connected to each other; A heater is provided in the water tank (1).

2. The DC energy storage water heater according to claim 1, characterized in that: A plurality of water tanks (1) are arranged side by side up and down.

3. The DC energy storage water heater according to claim 1, characterized in that: A first connecting pipe (3) and a second connecting pipe (4) are provided between two adjacent water tanks (1); a control valve (31) is provided on the first connecting pipe (3); a water pump (41) is provided on the second connecting pipe (4); the water pump (41) cooperates with the control valve (31) to mix the water in the two adjacent water tanks (1).

4. The DC energy storage water heater according to claim 3, characterized in that: The gear position of each water tank (1) is different, and the maximum heat stored in each water tank (1) is different.

5. A control method for a DC energy storage water heater according to any one of claims 1 to 4, characterized in that: The steps include: The number and temperature of the water tanks (1) required to store heat are determined according to the user's heat demand.

6. The control method of the DC energy storage water heater according to claim 3, characterized in that: "Determining the number and temperature of water tanks (1) required for heat storage based on the user's heat demand" includes: Determine the heat demand based on the user's heat demand; Determining the water tank (1) that needs to store heat based on the heat demand; The heat storage temperature of the water tank (1) that needs to store heat is determined based on the heat demand and the maximum total heat storage capacity of the water tank (1) that needs to store heat.

7. The control method of the DC energy storage water heater according to claim 6, characterized in that: “Determining the heat storage temperature of the water tank (1) that needs to store heat based on the heat demand and the maximum total heat storage capacity of the water tank (1) that needs to store heat” includes: If the heat demand is less than the maximum total heat storage capacity of the water tank (1) that needs to store heat, the water tank (1) that needs to store heat is stored according to the required temperature of the heat demand or the temperature corresponding to the heat demand.

8. The control method of the DC energy storage water heater according to claim 7, characterized in that: If there are multiple water tanks (1) involved in heat storage, and the required temperature for heat use is not greater than the temperature corresponding to the heat demand, heating is performed according to the temperature corresponding to the heat demand, and the multiple water tanks (1) are mixed after heat storage and before heat use.

9. The control method of the DC energy storage water heater according to claim 7, characterized in that: If the number of the water tanks (1) involved in the heat storage is one, heat is stored in the water tank (1) that needs heat storage according to the required temperature of the heat demand; and / or If there are multiple water tanks (1) involved in heat storage, and the required temperature of the heat demand is greater than the temperature corresponding to the heat demand, heating is performed according to the required temperature of the heat demand.

10. The control method of the DC energy storage water heater according to claim 7, characterized in that: “Determining the heat storage temperature of the water tank (1) that needs to store heat based on the heat demand and the maximum total heat storage capacity of the water tank (1) that needs to store heat” also includes: If the heat demand is equal to the maximum total heat storage capacity of the water tank (1) that needs to store heat, heat storage is performed according to the maximum heat storage capacity of the water tank (1) that needs to store heat.

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