A new indirect type heat accumulating water tank

Abstract

The application provides a novel indirect heat storage water tank. The water tank mainly comprises an upper heat storage chamber and a lower heat exchange chamber, which are communicated through a vertical pipe and a controllable circulation hole. The core is a three-layer sleeve pipe type coil heat exchanger arranged in the lower chamber, which is filled with solar heat working medium, user domestic water and switchable working medium from inside to outside. By changing the working medium in the outermost pipe, the heat exchange state between the internal pipe and the water tank can be actively controlled. The application also provides a stage-by-stage working method: in the initial heat storage stage, the heat exchanger is in the heat insulation mode, and the solar heat is used to quickly heat the domestic water; after reaching the set temperature, the heat exchanger is switched to the heat exchange mode to heat the lower water; after the temperature of the lower water is increased, the circulation hole is opened to drive the hot water to rise to the upper chamber for storage, so that the water temperature stratification is efficiently established and maintained. The application realizes the unification of fast heat supply, controllable heat exchange and efficient stratified heat storage, and improves the system response speed and energy utilization efficiency.

Description

Technical Field

[0001] This invention relates to the field of solar thermal utilization and energy storage technology, specifically to an indirect hot water storage tank with efficient heat exchange and flexible control functions for use in solar water heating systems or other waste heat recovery systems. Background Technology

[0002] A typical solar water heating system mainly consists of a collector, a hot water storage tank, circulation pipes, and a control unit. For a long time, the industry and research have focused on improving the photothermal conversion efficiency of the collectors, and significant progress has been made. However, as the system's "energy warehouse," the hot water storage tank is a key component of the solar heating system, connecting the collector to the heating terminal and playing a role in heat storage and exchange. Its performance often determines the overall system's heat collection efficiency and user experience. However, traditional hot water storage tanks have revealed many problems in long-term use, such as a lack of intelligent control strategies based on user habits, making optimal energy management and conservation impossible; limited heat exchange area of ​​heat exchange elements, limiting heat exchange efficiency; when heat exchange is not needed or insulation is required, the coils remain in contact with the water in the tank, causing unnecessary heat loss or reverse heat dissipation; the water temperature in the tank tends to become uniform due to circulation and mixing, making it difficult to achieve an optimal match between high-temperature heat storage and on-demand heat extraction, reducing the system's effective heat storage capacity and operational flexibility. While existing technologies employ jacketed water tanks or external panels, these solutions are complex in structure, costly, and fail to fundamentally address the issues of uncontrollable heat exchange and easily disrupted thermal storage temperature stratification. Therefore, there is an urgent need for a novel indirect hot water storage tank with high heat exchange efficiency, the ability to actively control the heat exchange process, and the capacity to effectively maintain thermal storage temperature stratification, thereby improving the overall energy efficiency and practicality of solar energy systems. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide an indirect hot water storage tank with a novel structure, controllable heat exchange, and the ability to achieve efficient heat storage and stable heat extraction.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A novel indirect hot water storage tank includes: a lower heat exchange chamber and an upper heat storage chamber, wherein the volume of the upper heat storage chamber is larger than that of the lower heat exchange chamber; at least one three-layer shell-and-tube heat exchanger is installed in the lower heat exchange chamber; the three-layer shell-and-tube heat exchanger includes: an innermost pipe for circulating solar thermal working fluid; a middle pipe for circulating domestic water; and an outermost pipe whose internal working fluid is switchable to control the heat exchange state between the innermost and middle pipes and the water in the tank; the lower heat exchange chamber and the upper heat storage chamber are connected by a riser, the top of which extends to near the top of the upper heat storage chamber; at least four small holes are respectively provided at the bottom of the upper heat storage chamber and the top of the lower heat exchange chamber for circulating water between the upper heat storage chamber and the lower heat exchange chamber.

[0005] Optionally, the working fluid inside the outermost pipe can be switched between air and a high heat transfer fluid. When air flows through the outermost pipe, the innermost pipe and the intermediate pipe are insulated from the water in the tank. When a high heat transfer fluid flows through the outermost pipe, the innermost pipe and the intermediate pipe exchange heat with the water in the tank.

[0006] Optionally, the solar thermal working fluid is a 50% concentration propylene glycol aqueous solution.

[0007] Optionally, a temperature sensor is provided at the outlet of the middle casing to monitor the water temperature. When the water temperature reaches a set threshold, the working medium in the outermost casing is switched or the water is circulated upward to the upper heat storage chamber through the riser.

[0008] Optionally, the top end of the riser is located below and near the top of the liquid level in the upper heat storage chamber.

[0009] Optionally, the orifice diameter of the water circulation in the water tank chamber is 40-50mm, which is used to form a slow circulating water flow, reduce the temperature mixing of the water in the upper and lower chambers, and control the water circulation between the upper heat storage chamber and the lower heat exchange chamber by switching the orifice.

[0010] Optionally, the water tank includes a control system for controlling the switching of the working fluid in the outermost pipe according to user needs or system operating conditions. The working principle and beneficial effects of the novel indirect hot water storage tank of this invention are: controllable heat exchange: by switching the working fluid in the outermost flow channel of the three-layer casing, it is possible to actively and precisely control when solar heat is released into the water tank and when domestic water absorbs heat from the tank. This avoids unnecessary heat dissipation during non-water usage periods caused by the continuous heat exchange of traditional coils, greatly improving system controllability and energy-saving effects.

[0011] 2. High-efficiency temperature-stratified heat storage: During operation, solar heat first heats the local water in the lower heat exchange chamber. When the water temperature at this location rises to the set value, the hot water, due to its lower density, slowly rises through the riser to the top of the upper heat storage chamber. Simultaneously, the relatively cooler water at the bottom of the upper chamber slowly flows into the lower heat exchange chamber through small holes at the bottom to replenish it. This process forms a natural circulation based on temperature difference, continuously "pumping" heat to the upper chamber for storage, and in the process, establishing and maintaining a temperature gradient stratification from top to bottom, causing high-temperature hot water to accumulate at the top. When users draw water, cold water enters from the bottom, first exchanging heat with the lower heat exchange chamber and coils, preferentially utilizing the low-temperature waste heat, thereby maximizing the preservation of the high-temperature water stored at the top, improving heat storage efficiency and user experience.

[0012] 3. Compact Structure and High-Efficiency Integration: The heat exchange, heat storage, and temperature control functions are integrated into a single water tank, resulting in a compact structure. The three-layer sleeve design increases the heat exchange area within a limited space, while simultaneously enabling independent and controllable heat exchange for two fluids (solar working fluid and domestic water). Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the overall structure of the indirect hot water storage tank described in this invention.

[0014] Figure 2 This is a front cross-sectional schematic diagram of the indirect hot water storage tank described in this invention.

[0015] Figure 3 This is a schematic diagram of the cross-sectional structure of the three-layer shell-and-tube heat exchanger described in this invention.

[0016] Figure 4 for Figure 3 A schematic diagram of each layer of the three-layer sleeve coil.

[0017] Attached reference numerals: 1. Upper heat storage chamber of the water tank; 2. Lower heat exchange chamber of the water tank; 3. Riser connecting the upper and lower chambers; 4. Small water circulation hole; 5. Three-layer shell-and-tube heat exchanger; 6. Outlet direction of solar working fluid and domestic water; 7. Inlet direction of solar working fluid and domestic water; 501. Innermost layer pipe (solar working fluid flow channel); 502. Middle layer pipe (domestic water flow channel); 503. Outermost layer pipe (control flow channel) Detailed Implementation

[0018] like Figure 1As shown, the novel indirect hot water storage tank provided by this invention is divided into an upper heat storage chamber 1 and a lower heat exchange chamber 2 by an insulating partition. The two chambers are hydraulically connected through a riser pipe 3 and a small circulation hole 4 at the bottom. The upper end of the riser pipe 3 is close to the top end cap of the heat storage chamber 1, and the lower end is connected to the bottom of the heat exchange chamber 2. The small circulation hole 4 has a small diameter (e.g., 40 mm) and mainly serves to slowly replenish water, avoiding forced convection that could disrupt stratification.

[0019] like Figure 3 As shown, the core heat exchange component is a three-layer coaxial coil heat exchanger 5, which consists of three coaxially mounted metal round tubes (such as copper or stainless steel tubes) coiled into a spiral or serpentine shape and fixedly installed in the lower heat exchange chamber 2. The inlet and outlet of the innermost pipe 501 are connected to the solar collector circulation loop. The inlet and outlet of the middle pipe 502 are connected to the user's domestic water supply network. The two ends of the outermost pipe 503 are connected to an external small working fluid switching device, which controls the charging and discharging of the working fluid.

[0020] A key and optimized operating process of this invention is as follows: First stage: Rapid response mode. When the system starts, the working fluid in the outermost pipe 503 is controlled to be air, and the circulation hole 4 is closed. At this time, the three-layer shell heat exchanger 5 is in "insulation mode." High-temperature heat transfer fluid (such as propylene glycol solution) from the solar collector flows into the innermost pipe 501. Due to the outer insulation, heat is efficiently confined inside the shell, mainly transferred to the domestic water flowing in the middle pipe 502. The core of this stage is rapid response to user needs, ignoring the need for water tank heat storage. Solar heat is concentrated to raise the domestic water outlet temperature to a set value (e.g., 45°C) that the user can directly use in the shortest possible time. This solves the problem of slow initial hot water production in traditional heat storage systems.

[0021] Phase Two: High-Efficiency Heat Storage Mode. When the domestic water outlet temperature reaches the first set threshold, i.e., the temperature required by the user, the control system issues a command. The working medium in the outermost pipe 503 is switched to a high thermal conductivity working medium, and the heat exchange chamber participates in heat exchange; the circulation hole 4 remains closed. At this time, the heat from the solar working medium in the innermost pipe 501 is efficiently transferred to the water in the lower heat exchange chamber 2 through the high thermal conductivity working medium, starting to rapidly heat the lower small volume of water. Because the circulation hole 4 is closed, the upper large volume heat storage chamber 1 does not participate in this process, avoiding heat dissipation and allowing the lower water temperature to rise rapidly.

[0022] The third stage: stratified heat storage mode. When the water temperature in the lower heat exchange chamber 2 is heated to the second set threshold, such as 65-80℃, to store high-grade heat energy, the control system activates again, opening the circulation hole 4. The high-temperature water in the lower heat exchange chamber 2, due to its lower density, begins to rise naturally through the riser 3 to the top of the upper heat storage chamber 1 and accumulates. Simultaneously, the relatively cooler water at the bottom of the upper chamber slowly flows into the lower chamber through the opened circulation hole 4 for replenishment and reheating. This natural circulation based on temperature difference continuously "pumps" and stores high-temperature water in the upper part of the tank, thereby establishing and maintaining a stable, top-to-bottom temperature stratification throughout the tank. This stratified structure allows for the maximum preservation of limited high-grade heat energy.

[0023] The beneficial effects of this optimized process can be summarized as follows: Extremely fast user response: The first stage directly and quickly heats domestic water, shortening the waiting time for hot water. High and orderly heat storage efficiency: Through phased control of "isolation first, then lower part, then global," precise and efficient heat transfer is achieved from "immediate use" to "small-capacity rapid heat storage" and then to "large-capacity high-temperature stratified heat storage," avoiding energy waste and quality degradation. Significant stratification effect: By controlling the opening timing of the circulation holes, global circulation is only initiated when the local (lower) water temperature is sufficiently high. This strengthens the formation and stability of temperature stratification, significantly improving the effective heat storage capacity and usability of the water tank.

[0024] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A novel indirect hot water storage tank, characterized in that, include: The lower heat exchange chamber and the upper heat storage chamber have a larger volume than the lower heat exchange chamber. At least one three-layer shell-and-tube heat exchanger is provided in the lower heat exchange chamber. The three-layer coaxial coil heat exchanger includes: an innermost pipe for circulating solar thermal working fluid; a middle pipe for circulating domestic water; and an outermost pipe with a switchable working fluid to control the heat exchange state between the innermost and middle pipes and the water in the tank. The lower heat exchange chamber and the upper heat storage chamber are connected by a riser, the top of which extends to near the top of the upper heat storage chamber. The bottom of the upper heat storage chamber and the top of the lower heat exchange chamber are each provided with at least four small holes to allow water to circulate between the upper heat storage chamber and the lower heat exchange chamber.

2. The indirect hot water storage tank according to claim 1, characterized in that, The working fluid inside the outermost pipe can switch between air and a high heat transfer fluid. When air flows through the outermost pipe, the innermost pipe and the middle pipe are insulated from the water in the tank. When a high heat transfer fluid flows through the outermost pipe, the innermost pipe and the middle pipe exchange heat with the water in the tank.

3. The indirect hot water storage tank according to claim 1 or 2, characterized in that, The solar thermal working fluid is a 50% concentration propylene glycol aqueous solution.

4. The indirect hot water storage tank according to claim 1, characterized in that, A temperature sensor is installed at the outlet of the intermediate layer pipe to monitor the water temperature. When the water temperature reaches a set threshold, the working medium in the outermost layer pipe is switched or the water is circulated upward to the upper heat storage chamber through the riser.

5. The indirect hot water storage tank according to claim 1, characterized in that, The top of the riser is located below the liquid level in the upper heat storage chamber and close to its top.

6. The indirect hot water storage tank according to claim 1, characterized in that, The small holes at the bottom of the upper heat storage chamber and the top of the lower heat exchange chamber have a diameter of 40-50mm. They are used to form a slow circulating water flow, reduce the temperature mixing of the water in the upper and lower chambers, and control the water circulation between the upper heat storage chamber and the lower heat exchange chamber by switching the small holes.

7. The indirect hot water storage tank according to claim 1, characterized in that, It also includes a control system for controlling the switching of the working medium in the outermost pipe according to user needs or system operating conditions.

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