Underground cross-season composite heat storage system based on phase change ball accumulation

Abstract

This invention discloses an underground cross-seasonal composite thermal energy storage system based on phase change sphere stacking, belonging to the field of thermal energy storage technology. The system includes a heat collection unit, a heat storage unit, a heat release unit, a heat supply unit, and a phase change composite thermal energy storage body (6) buried underground. The phase change composite thermal energy storage body (6) is filled with water (61) and stacked with phase change thermal energy storage spheres (62) encapsulating composite phase change materials. Multiple non-connected and staggered temperature-layering partitions (63) are set along the height direction to divide the internal space into thermal energy storage zones with different phase change temperatures. Preferably, the high phase change temperature thermal energy storage spheres (62) are arranged in the lower part of the thermal energy storage body (6). This invention achieves high thermal energy storage density, stable heat release temperature, land space reuse, and low heat loss through sensible heat-latent heat composite storage, multi-stage heat transfer enhancement, and flexible operation mode switching. It is suitable for cross-seasonal clean heating of renewable energy sources such as solar energy and geothermal energy.

Description

Technical Field

[0001] This invention relates to the field of thermal energy storage technology, specifically to an underground cross-seasonal composite thermal storage system based on phase change sphere stacking. Background Technology

[0002] To address global climate change and energy structure transformation, clean heating from renewable energy sources, such as solar and geothermal energy, is receiving increasing attention. However, renewable energy sources are characterized by significant intermittency and instability, resulting in a mismatch between their energy supply and the continuous, stable demand for heat. Transseasonal thermal storage technology is key to resolving this contradiction.

[0003] Currently, mainstream interseasonal thermal storage technologies mainly include sensible thermal storage and latent thermal (phase change) thermal storage. Sensible thermal storage technologies (such as large underground aquifer thermal storage, geothermal pipe thermal storage, or water tank thermal storage) are relatively mature, but their low thermal density results in huge system volume and land area, and the outlet temperature continues to drop during the heat release process, affecting the efficiency of energy-consuming equipment. Although phase change thermal storage technology has the potential for high thermal density and stable heat release temperature, it faces two major challenges: first, the phase change material itself has poor thermal conductivity, resulting in a slow heat storage / release rate; second, when applied on a large scale, internal heat transfer deteriorates, making it difficult to reconcile the contradiction between high thermal density and high heat release power.

[0004] Existing improvement solutions mostly focus on single aspects such as material modification, packaging structure optimization, or system layout adjustment. There is a lack of a cross-seasonal thermal storage system solution that can organically integrate multi-level enhancement methods and systematically solve comprehensive problems such as thermal storage density, heat release power, temperature stability, and floor space. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems by providing a high-performance underground cross-seasonal composite thermal storage system based on phase change sphere stacking that can integrate multi-stage heat transfer enhancement, achieve efficient and compact thermal storage, has flexible operation modes and is easy to utilize underground space.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] The present invention discloses a cross-seasonal underground composite thermal storage system based on phase change sphere stacking, comprising a heat collection unit, a heat storage unit, a heat release unit, a heat supply unit, and a phase change composite thermal storage body. The heat collection unit includes a heat collector, a pump A, a high-temperature side of a heat exchanger A, and corresponding connecting pipelines. The outlet of the heat collector is connected to the high-temperature side inlet of the heat exchanger A, the high-temperature side outlet of the heat exchanger A is connected to the inlet of the pump A, and the outlet of the pump A is connected to the inlet of the heat collector.

[0008] The thermal storage unit includes a low-temperature side of heat exchanger A, pump B, valve A, valve D and corresponding connecting pipelines. The outlet of the low-temperature side of heat exchanger A is connected to the inlet of pump B, the outlet of pump B is connected to the inlet of valve A, the outlet of valve A is connected to the bottom inlet of phase change composite thermal storage body through thermal storage circulation pipeline, the top outlet of phase change composite thermal storage body is connected to the inlet of valve D through pipeline, and the outlet of valve D is connected to the low-temperature side inlet of heat exchanger A.

[0009] The heat release unit includes a pump C, a valve C, a high-temperature side of a heat exchanger B, a valve F, and corresponding connecting pipes. The heat release circulation pipe is led out from the bottom outlet of the phase change composite heat storage body and connected to the inlet of the pump C. The outlet of the pump C is connected to the inlet of the valve C. The outlet of the valve C is connected to the high-temperature side inlet of the heat exchanger B. The high-temperature side outlet of the heat exchanger B is connected to the inlet of the valve F. The outlet of the valve F extends through a pipe and is connected to the top inlet of the phase change composite heat storage body.

[0010] The heating unit includes a low-temperature side of heat exchanger B, pump D, heat users and corresponding connecting pipelines. The outlet of the low-temperature side of heat exchanger B is connected to the inlet of pump D, the outlet of pump D is connected to the inlet of heat users, and the outlet of heat users is connected to the inlet of the low-temperature side of heat exchanger B.

[0011] The phase change composite thermal storage body is provided with multiple temperature-layered partitions along its height direction, dividing the internal space into multiple thermal storage zones; different thermal storage zones are arranged with phase change thermal storage balls with different phase change temperatures; the temperature-layered partitions do not penetrate the entire cross-section of the phase change composite thermal storage body in the horizontal direction, and the extension starting positions of adjacent partitions are staggered.

[0012] The aforementioned transseasonal underground composite thermal storage system based on phase change sphere stacking includes, from the inside out, a waterproof layer, an insulation layer, and a structural layer in the outer shell of the phase change composite thermal storage body, which is filled with water.

[0013] The above-mentioned cross-seasonal underground composite thermal storage system based on phase change sphere stacking includes: phase change thermal storage spheres (internally encapsulated with composite phase change material composed of phase change substrate and high thermal conductivity skeleton material).

[0014] The above-mentioned cross-seasonal underground composite thermal storage system based on phase change sphere stacking includes: a first branch pipeline branching off from the main pipeline between the outlet of pump B and the inlet of valve A, a valve B being installed on the branch pipeline, and the outlet of valve B being connected to the pipeline between the outlet of valve C and the high-temperature side inlet of heat exchanger B.

[0015] The above-mentioned cross-seasonal underground composite thermal storage system based on phase change sphere stacking includes: a second branch pipeline is branched off from the main pipeline between the high-temperature side outlet of heat exchanger B and the inlet of valve F. Valve E is installed on this branch pipeline, and the outlet of valve E is connected to the pipeline between the outlet of valve D and the low-temperature side inlet of heat exchanger A.

[0016] The above-mentioned cross-seasonal underground composite thermal storage system based on phase change sphere stacking includes a thermal storage zone corresponding to a phase change thermal storage sphere with a higher phase change temperature, which is arranged in the lower middle part of the phase change composite thermal storage body.

[0017] The aforementioned transseasonal underground composite thermal storage system based on phase change sphere stacking includes a thermal storage circulation pipe interface and a heat release circulation pipe interface extending into the phase change composite thermal storage body, which are arranged at a certain distance in the horizontal direction inside the thermal storage body.

[0018] Compared with the prior art, the present invention has the following beneficial effects, as can be seen from the above technical solution:

[0019] 1. High heat storage density and stable output temperature: This invention utilizes water as the sensible heat storage medium inside a phase change composite heat storage body, while simultaneously stacking a large number of phase change heat storage spheres encapsulating composite phase change materials. This achieves composite storage of the sensible heat of the water medium and the latent heat of the phase change material, significantly improving the heat storage capacity per unit volume compared to a single sensible heat storage method. Furthermore, since the temperature of the phase change material remains essentially constant during the phase change process of heat storage / release, the heat output to the heating unit through heat exchanger B during the heat release stage maintains a stable temperature, overcoming the shortcomings of continuous temperature changes in traditional sensible heat storage / release methods and significantly improving the efficiency of energy-consuming equipment.

[0020] 2. Save land and realize space reuse: The present invention buries the phase change composite thermal storage body underground as a whole, and the main body of the system does not occupy the surface area, so that the surface above the thermal storage body can be restored to other uses such as parking lots and green spaces, realizing the composite utilization of underground space and surface land resources, and effectively solving the engineering problem of large-scale thermal storage systems occupying a large area.

[0021] 3. Multi-scale synergistic heat transfer enhancement: This invention systematically enhances heat transfer performance from three levels, synergistically resolving the contradiction between heat storage density and heat release power in large-scale thermal storage. These levels are: material level (composite phase change material composed of a high thermal conductivity framework material and a phase change substrate), structural level (encapsulating the composite phase change material into phase change thermal storage spheres, significantly increasing the heat exchange area per unit volume), and system level (by setting multiple non-through staggered temperature stratification baffles along the height direction, guiding the fluid to form a tortuous flow path within the thermal storage body, and arranging phase change thermal storage spheres with different phase change temperatures according to different thermal storage zones to form temperature gradients, achieving efficient heat storage and retrieval within the entire volume of the thermal storage body).

[0022] 4. Flexible and Efficient Operation Modes: This invention establishes independent heat storage and heat release circulation pipelines, along with a first branch pipeline with valve B and a second branch pipeline with valve E, creating a controllable coupling relationship between the heat collection unit, heat storage unit, heat release unit, and heating unit. By controlling the opening and closing of each valve, various operation modes such as pure heat storage, pure heat release, and simultaneous storage and release can be flexibly implemented to optimally adapt to different seasonal and load demands, significantly improving the system's overall annual utilization efficiency.

[0023] 5. Achieving High-Temperature Thermal Storage and Optimizing Thermal Management: This invention concentrates the thermal storage zones of high-temperature phase change thermal storage spheres in the lower middle part of the phase change composite thermal storage body. It directly utilizes the hydrostatic pressure generated by the underground depth, allowing the water in the lower region of the storage body to remain liquid at temperatures exceeding the atmospheric boiling point (e.g., 100°C to 120°C), achieving safe storage of high-grade heat. Simultaneously, this "hot at the bottom, cold at the top" temperature distribution keeps the temperature of the top region of the storage body, which is the main heat dissipation surface, lower, significantly reducing heat loss to the surrounding environment through the top of the storage body. Furthermore, addressing the potential for natural convection mixing due to density inversion in this layout, this invention utilizes a built-in non-through staggered temperature stratification baffle and a porous media structure formed by the stacking of phase change thermal storage spheres. Under forced convection conditions, this effectively guides the orderly flow of fluid, primarily through forced convection, significantly suppressing the destructive effect of natural convection on thermal stratification. The synergistic effect of these technical features ensures the stable maintenance of internal temperature stratification and extremely low long-term heat loss during long-term thermal storage. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the system structure of the present invention.

[0025] Marked in the image:

[0026] 1. Heat collector; 2. Pump A; 3. Heat exchanger A; 4. Pump B; 5. Valve A; 6. Phase change composite thermal storage body; 7. Valve D; 8. Valve B; 9. Heat exchanger B; 10. Valve E; 11. Valve F; 12. Pump C; 13. Valve C; 14. Pump D; 15. Heat user; 16. Ground; 61. Water; 62. Phase change thermal storage ball; 63. Temperature stratification partition; 64. Shell; 65. Thermal storage circulation pipeline; 66. Heat release circulation pipeline. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below with reference to the accompanying drawings.

[0028] Example 1:

[0029] See Figure 1The present invention discloses a cross-seasonal underground composite thermal storage system based on phase change sphere stacking, comprising a heat collection unit, a heat storage unit, a heat release unit, a heat supply unit, and a phase change composite thermal storage body (6), wherein:

[0030] The heat collection unit includes a heat collector 1, a pump A2, a high-temperature side of a heat exchanger A3, and corresponding connecting pipes. The outlet of the heat collector 1 is connected to the high-temperature side inlet of the heat exchanger A3, the high-temperature side outlet of the heat exchanger A3 is connected to the inlet of the pump A2, and the outlet of the pump A2 is connected to the inlet of the heat collector 1, thus forming an independent closed heat collection loop.

[0031] The heat storage unit includes a low-temperature side of heat exchanger A3, pump B4, valve A5, valve D7 and corresponding connecting pipes to form a heat storage cycle. The outlet of the low-temperature side of heat exchanger A3 is connected to the inlet of pump B4, the outlet of pump B4 is connected to the inlet of valve A5, the outlet of valve A5 is connected to the bottom inlet of phase change composite heat storage body 6 through heat storage cycle pipe 65, the top outlet of phase change composite heat storage body 6 is connected to the inlet of valve D7 through a pipe, and the outlet of valve D7 is connected back to the low-temperature side inlet of heat exchanger A3.

[0032] The heat release unit includes a pump C12, a valve C13, a high-temperature side of a heat exchanger B9, a valve F11, and corresponding connecting pipes, forming a heat release cycle. The heat release cycle pipe 66 extends from the bottom outlet of the phase change composite heat storage body 6 and connects to the inlet of the pump C12. The outlet of the pump C12 connects to the inlet of the valve C13. The outlet of the valve C13 connects to the high-temperature side inlet of the heat exchanger B9. The high-temperature side outlet of the heat exchanger B9 connects to the inlet of the valve F11. The outlet of the valve F11 extends through a pipe and connects to the top inlet of the phase change composite heat storage body 6.

[0033] The heating unit includes the low-temperature side of heat exchanger B9, pump D14, heat user 15, and corresponding connecting pipelines, forming a heating cycle. The outlet of the low-temperature side of heat exchanger B9 is connected to the inlet of pump D14, the outlet of pump D14 is connected to the inlet of heat user 15, and the outlet of heat user 15 is connected back to the low-temperature side inlet of heat exchanger B9.

[0034] To enhance system operational flexibility and facilitate mode switching and heat distribution, a branch pipeline is branched off from the main pipeline between the outlet of pump B4 and the inlet of valve A5. Valve B8 is installed on this branch pipeline, and its outlet connects to the pipeline between the outlet of valve C13 and the high-temperature inlet of heat exchanger B9. Similarly, a branch pipeline is branched off from the main pipeline between the high-temperature outlet of heat exchanger B9 and the inlet of valve F11. Valve E10 is installed on this branch pipeline, and its outlet connects to the pipeline between the outlet of valve D7 and the low-temperature inlet of heat exchanger A3.

[0035] The phase change composite thermal storage body 6, which is the core component, is buried below ground level 16. Its outer shell 64 includes a waterproof layer, a thermal insulation layer and a structural layer from the inside out. The waterproof layer is used to prevent leakage of internal media, the thermal insulation layer is used to reduce heat loss from the thermal storage body to the surrounding soil, and the structural layer is used to withstand soil pressure and internal load.

[0036] The phase change composite thermal energy storage body 6 is filled with water 61 as the heat transfer fluid and sensible heat storage medium, and has a large number of phase change thermal energy storage balls 62 stacked inside. The phase change thermal energy storage balls 62 are encapsulated with composite phase change material, which is composed of a high thermal conductivity material (such as metal foam or expanded graphite) as a skeleton or substrate and a phase change substrate, thereby obtaining high thermal energy storage density and good thermal conductivity.

[0037] To optimize heat matching and heat exchange efficiency during the heat storage / release process, multiple temperature-layering baffles 63 are installed along the height of the phase change composite thermal storage body 6. These baffles divide the internal space into multiple heat storage zones, each containing phase change thermal storage balls 62 with different phase change temperatures, thus forming a continuous temperature gradient along the height. The number, relative positions, and phase change temperature ranges of the heat storage zones can be configured according to system design requirements. The temperature-layering baffles 63 do not penetrate the entire cross-section of the phase change composite thermal storage body 6 in the horizontal direction, and the extension positions of adjacent baffles are staggered. This structure forces the flowing water to change its flow direction, forming a tortuous flow path, thereby greatly enhancing the convective heat transfer between the fluid and the phase change thermal storage balls 62, ensuring that heat is uniformly and efficiently stored and extracted within the large thermal storage body.

[0038] To further optimize heat exchange and prevent localized "thermal short circuits" between the heat storage and release cycles, the heat storage circulation pipes 65, which extend into the phase change composite heat storage body 6 and connect to the bottom inlet and top outlet respectively, and the heat release circulation pipes 66, which connect to the bottom outlet and top inlet respectively, should be arranged at a certain distance in the horizontal direction inside the heat storage body. Preferably, the openings of the two sets of pipes have a large distance between them on the horizontal projection plane, for example, close to opposite side walls of the heat storage body. This arrangement helps guide the working fluid to form a more uniform and sufficient flow path inside the heat storage body, ensuring efficient heat storage and extraction throughout the entire volume of the heat storage body, thereby improving the overall energy efficiency of the system.

[0039] Preferably, phase change thermal storage spheres 62 with high phase change temperatures (e.g., above 90°C) are concentrated in the lower middle part of the phase change composite thermal storage body 6 to form a high-temperature thermal storage zone. This design is based on two main considerations: first, to fully utilize the hydrostatic pressure generated by the underground depth, allowing the water 61 in this area to remain liquid at temperatures exceeding the atmospheric boiling point (e.g., 100°C to 120°C), thus achieving high-grade heat storage; second, to form a "hot at the bottom, cold at the top" temperature layout, as the temperature in the top region is lower, significantly reducing heat loss through the top of the thermal storage body—the main heat dissipation surface closest to the low-temperature environment—fundamentally improving the system's insulation characteristics. Although this layout is not the most stable in terms of temperature gradient, the present invention effectively guides the orderly flow of fluid, mainly through forced convection, through the built-in non-through staggered temperature stratification baffles and the porous medium formed by the stacking of phase change spheres, and significantly suppresses natural convection mixing that may be caused by density inversion. These measures work synergistically to ensure stable temperature stratification and extremely low long-term heat loss within the thermal storage body.

[0040] Work mode:

[0041] By controlling the opening and closing of valves A5, B8, C13, D7, E10, and F11, and in conjunction with the corresponding circulating pumps (pump A2, pump B4, pump C12, and pump D14), this invention can flexibly adapt to different seasons and load requirements, achieving multiple efficient operating modes. The table below lists the valve status under five typical operating modes:

[0042] Table 1. Correspondence between valve status and operating conditions in typical system working modes.

[0043] Mode Name Corresponding to typical working conditions Valve A(5) Valve B(8) Valve C(13) Valve D(7) Valve E(10) Valve F(11) Core Functions and Instructions Mode 1: Pure thermal storage In summer, there is strong radiation and no demand for heating. open close close open close close All the collected heat is stored in the heat storage body. Mode 2: Independent operation of heat storage and heat release Special scheduling requirements open close open open close open The heat storage and heat release cycles are physically independent and run in parallel. Mode 3: Direct heat supply and heat storage Early winter or transitional season, with sunshine and partial load. open Partially open close open open close Heat collection is distributed as follows: a portion is supplied directly, and the remainder is stored. The heat storage element is only charged. Mode 4: Direct Heat Supply In late autumn or early winter, on cold days, the demand for heating is high, and heat storage is not required. close open close close open close All the heat collected is directly supplied for heating, and the heat storage body is completely isolated. Mode 5: Combined heating In the depths of winter or during periods of severe cold, there is insufficient sunlight and a high load. close open open close open open The heat storage medium primarily releases heat, supplemented by heat collection. Valve E must be open to close the circulation on the heat collection side. Mode 6: Pure heat release Nighttime, continuous rainy days close close open close close open It relies entirely on the heat stored in the heat storage body for heating.

[0044] Note: In Table 1, "Open" indicates that the valve is open, "Closed" indicates that the valve is closed, and "Partially Open" indicates that the opening degree is adjusted according to heat distribution requirements. By adjusting the valve opening degree, heat distribution and flow in the coupled loop can be precisely controlled. Pumps not mentioned in each mode are controlled according to the start-up and shutdown requirements of their respective cycles.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A transseasonal underground composite thermal storage system based on phase change sphere stacking, comprising a heat collection unit, a heat storage unit, a heat release unit, a heat supply unit, and a phase change composite thermal storage body (6), characterized in that: The heat collection unit includes a heat collector (1), a pump A (2), a high-temperature side of a heat exchanger A (3) and corresponding connecting pipes. The outlet of the heat collector (1) is connected to the high-temperature side inlet of the heat exchanger A (3), the high-temperature side outlet of the heat exchanger A (3) is connected to the inlet of the pump A (2), and the outlet of the pump A (2) is connected to the inlet of the heat collector (1). The heat storage unit includes a low-temperature side of heat exchanger A (3), pump B (4), valve A (5), valve D (7) and corresponding connecting pipes. The outlet of the low-temperature side of heat exchanger A (3) is connected to the inlet of pump B (4), the outlet of pump B (4) is connected to the inlet of valve A (5), the outlet of valve A (5) is connected to the bottom inlet of phase change composite heat storage body (6) through heat storage circulation pipe (65), the top outlet of phase change composite heat storage body (6) is connected to the inlet of valve D (7) through pipe, and the outlet of valve D (7) is connected to the low-temperature side inlet of heat exchanger A (3). The heat release unit includes a pump C (12), a valve C (13), a high-temperature side of a heat exchanger B (9), a valve F (11), and corresponding connecting pipes. The heat release circulation pipe (66) is led out from the bottom outlet of the phase change composite heat storage body (6) and connected to the inlet of the pump C (12). The outlet of the pump C (12) is connected to the inlet of the valve C (13). The outlet of the valve C (13) is connected to the high-temperature side inlet of the heat exchanger B (9). The high-temperature side outlet of the heat exchanger B (9) is connected to the inlet of the valve F (11). The outlet of the valve F (11) extends through a pipe and is connected to the top inlet of the phase change composite heat storage body (6). The heating unit includes a low-temperature side of heat exchanger B (9), pump D (14), heat user (15) and corresponding connecting pipes. The outlet of the low-temperature side of heat exchanger B (9) is connected to the inlet of pump D (14), the outlet of pump D (14) is connected to the inlet of heat user (15), and the outlet of heat user (15) is connected to the inlet of the low-temperature side of heat exchanger B (9). The phase change composite thermal storage body (6) has multiple temperature-layered partitions (63) arranged along its height direction to divide the internal space into multiple thermal storage zones; different thermal storage zones are arranged with phase change thermal storage balls (62) with different phase change temperatures; the temperature-layered partitions (63) do not penetrate the entire cross-section of the phase change composite thermal storage body (6) in the horizontal direction, and the extension starting positions of adjacent partitions are staggered.

2. The cross-seasonal underground composite thermal storage system based on phase change sphere stacking as described in claim 1, characterized in that: The outer shell (64) of the phase change composite thermal energy storage body (6) includes a waterproof layer, a thermal insulation layer and a structural layer from the inside to the outside, and is filled with water (61).

3. The cross-seasonal underground composite thermal storage system based on phase change sphere stacking as described in claim 1, characterized in that: The phase change thermal storage ball (62) is encapsulated with a composite phase change material composed of a phase change substrate and a high thermal conductivity skeleton material.

4. The cross-seasonal underground composite thermal storage system based on phase change sphere stacking as described in claim 1, characterized in that: A first branch pipe is branched off from the main pipeline between the outlet of pump B (4) and the inlet of valve A (5). A valve B (8) is installed on this branch pipe, and the outlet of valve B (8) is connected to the pipeline between the outlet of valve C (13) and the high-temperature side inlet of heat exchanger B (9). In the above-mentioned transseasonal underground composite thermal storage system based on phase change sphere stacking, a second branch pipe is branched off from the main pipeline between the high-temperature side outlet of heat exchanger B (9) and the inlet of valve F (11). A valve E (10) is installed on this branch pipe, and the outlet of valve E (10) is connected to the pipeline between the outlet of valve D (7) and the low-temperature side inlet of heat exchanger A (3).

5. The cross-seasonal underground composite thermal storage system based on phase change sphere stacking as described in claim 1, characterized in that: The heat storage zone corresponding to the phase change heat storage ball (62) with a higher phase change temperature is arranged in the lower middle part of the phase change composite heat storage body (6).

6. A transseasonal underground composite thermal storage system based on phase change sphere stacking as described in claim 1, wherein: The heat storage circulation pipe (65) interface and the heat release circulation pipe (66) interface that extend into the phase change composite heat storage body (6) are arranged at a certain distance in the horizontal direction inside the heat storage body.

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