Phase change heat storage system of medium-deep geothermal system and cascade heating method of phase change heat storage system

Abstract

The invention discloses a phase-change heat storage system of a middle-deep layer geothermal system and a cascade heating method of the phase-change heat storage system, and belongs to the technical field of coupling utilization of middle-deep layer geothermal energy and solar energy, in a device, a solar heat collection unit is connected with a middle-deep layer geothermal heat exchanger, and the middle-deep layer geothermal heat exchanger is buried underground; the middle-deep layer geothermal heat exchanger comprises a shallow layer section and a deep layer section, the shallow layer section is sleeved with the annular sleeve type phase change heat storage layer, the shallow layer section is filled with phase change materials, and the phase change materials are used for conducting heat buffering and heat efficient low-temperature-difference storage in the heat exchange process. The circulating control system is respectively connected with the solar heat collection unit, the middle-deep layer geothermal heat exchanger and the annular sleeve type phase change heat storage layer; the circulation control system is used for controlling flowing and temperature adjustment of a medium in the system. The cascade coupling of solar energy and medium-deep geothermal energy can be effectively realized, the thermal stability and the energy storage and utilization efficiency of the system are improved, and the cascade coupling system can be suitable for a park multi-energy complementary heat supply system.

Description

Technical Field

[0001] This invention belongs to the field of medium-deep geothermal and solar energy coupling utilization technology, specifically relating to a phase change thermal storage system for medium-deep geothermal systems and its cascade heating method. Background Technology

[0002] Currently, in the integrated utilization of medium-deep geothermal and solar energy, medium-deep geothermal energy has significant advantages in district heating and industrial heating due to its higher temperature, better stability, and stronger sustainability. Solar energy, as a clean and renewable energy source, can further improve the overall energy utilization rate and operational economy of the system when coupled with geothermal energy. However, solar energy has significant intermittency, fluctuations, and unpredictability; direct coupling into the geothermal system can easily lead to disturbances in the geothermal field, degradation of thermal storage performance, and system instability.

[0003] Current solar-geothermal coupling technologies mostly employ methods such as ground-based thermal storage tanks, increasing heat exchange area, or installing intermediate heat exchangers. These methods may have several problems: ground-based thermal storage tanks suffer from significant heat loss and require a large footprint; simply increasing the heat exchange area cannot effectively address the time mismatch between heat load and temperature; and intermediate heat exchangers increase system complexity and heat transfer temperature difference losses. Especially in the shallow geothermal range (0-200 meters), where the ground temperature is low and significantly affected by surface climate, current methods struggle to achieve efficient pre-buffering and cascade heating of the deep geothermal medium, and cannot effectively mitigate the thermal shock caused by solar energy fluctuations. Therefore, overall, current integrated utilization of mid-to-deep geothermal and solar energy does not easily achieve effective cascade coupling of solar energy and mid-to-deep geothermal energy, the system's thermal storage efficiency and stability are insufficient, and the lifespan and energy utilization rate of geothermal reservoirs need further improvement. Summary of the Invention

[0004] This invention provides a phase change thermal storage system for medium-deep geothermal systems and its cascade heating method. The purpose is to solve the problems that are currently difficult to effectively achieve cascade coupling of solar energy and medium-deep geothermal energy in the integrated utilization of medium-deep geothermal and solar energy, the thermal storage efficiency and stability of the system are not high enough, and the lifespan and energy utilization rate of geothermal reservoirs need to be further improved.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a phase change thermal energy storage system for a medium-deep geothermal system, comprising a medium storage section, a medium-deep geothermal heat exchanger, a solar collector unit, and a circulation path formed by an annular shell-and-tube phase change thermal energy storage layer, wherein: The medium storage section stores the medium that can circulate in the circulation path; the solar collector unit is connected to the inlet of the medium-deep geothermal heat exchanger for primary heating of the medium; The medium-deep geothermal heat exchanger is buried underground. The medium-deep geothermal heat exchanger includes a shallow section and a deep section arranged from top to bottom, which are used for medium-deep geothermal heat exchange. The annular shell-type phase change heat storage layer is installed in the shallow section. The interior of the shallow section is filled with phase change material, which is used for thermal buffering and high-efficiency low-temperature differential storage during the heat exchange process. It also includes a circulation control system, which is connected to the solar collector unit, the medium-deep geothermal heat exchanger and the annular shell-and-tube phase change heat storage layer respectively; the circulation control system is used to control the flow and temperature regulation of the medium between the solar collector unit and the medium-deep geothermal heat exchanger.

[0006] In some embodiments, the annular shell-type phase change thermal storage layer includes an outer tube, an inner tube, and an annular cavity; the outer tube is made of corrosion-resistant metal material, with an insulation layer attached to the inner wall, and is in direct contact with the surrounding strata; the inner tube is attached to the outer wall of the medium-deep geothermal heat exchanger; the annular cavity is located between the outer tube and the inner tube, and the phase change material is filled in the annular cavity.

[0007] Furthermore, phase change materials include paraffin-based, hydrated salt-based, or fatty acid-based materials.

[0008] Furthermore, the annular sleeve-type phase change thermal storage layer is uniformly arranged along the shallow section, and thermally conductive fins are also provided between the outer and inner tubes. The thermally conductive fins are used to enhance the heat exchange efficiency between the outer and inner tubes and the phase change material.

[0009] In some implementations, the solar thermal collector unit includes a solar collector and a heat collection circulation pump; the medium is heated by the solar collector and then enters a medium-deep geothermal heat exchanger for heat exchange.

[0010] In some embodiments, the circulation control system includes a temperature sensor, a flow sensor, an electric valve, and a control unit, wherein the control unit is electrically connected to the temperature sensor, the flow sensor, and the electric valve, respectively. The control unit can automatically adjust the circulation flow and heating mode based on solar irradiance, medium temperature, and ground temperature data.

[0011] In some implementations, the outlet of the medium-deep geothermal heat exchanger is equipped with a heat pump unit, and the medium storage section is also connected to an external heating unit via a plate heat exchanger.

[0012] This invention also provides a cascade heating method for a phase change thermal storage system in a medium-deep geothermal system, which is based on the aforementioned phase change thermal storage system in a medium-deep geothermal system, and includes the following steps: S1. When there is sufficient solar radiation, start the solar thermal collector unit to heat the medium in the first stage; S2. The heated medium enters the medium-deep geothermal heat exchanger. When it flows through the shallow section, some of the heat is transferred to the annular shell-and-tube phase change heat storage layer, where it is absorbed and stored by the phase change material. S3. The medium continues to flow through the deep section and exchanges heat with the annular sleeve-type phase change thermal storage layer in the deep section to achieve heat cascade transfer. S4. When solar radiation is insufficient or at night, the phase change material releases the stored heat to preheat the medium entering the deep section and maintain the heat supply stability of the phase change thermal storage system. S5. The circulating control system monitors temperature, flow rate, and solar energy status in real time, and dynamically adjusts the medium flow rate, heating mode, and thermal storage layer working status to achieve seasonal heat balance and system energy efficiency control.

[0013] Furthermore, it also includes seasonal operating modes, which include summer and winter modes; among which: In summer mode, the solar thermal collector is the main heating element, and the heat generated after operation is stored in the phase change material of the shallow section of the medium-deep geothermal heat exchanger in order to reduce the heat load discharged to the deeper underground layers. In winter mode, the solar thermal collectors provide auxiliary heating, while the phase change material releases stored heat, working in conjunction with deep geothermal energy to increase the heating temperature.

[0014] Furthermore, in S5, the temperature change of the phase change material is monitored in real time to determine the heat storage / release state and phase change process of the phase change material; Based on the thermal storage status, user load, and weather forecast, the heating power and medium circulation speed of the solar thermal collector are predictively adjusted. It also supports access to remote monitoring platforms, enabling data visualization, fault diagnosis, and remote control of operational strategies.

[0015] The present invention discloses a phase change thermal storage system for a medium-deep geothermal system and its cascade heating method, which has the following beneficial effects.

[0016] This invention discloses a phase change thermal storage system for medium-deep geothermal systems. The system architecture is relatively reasonable, convenient, and easy to implement: only an annular casing thermal storage layer is added outside the shallow section of the existing medium-deep geothermal heat exchanger, requiring no large-scale ground engineering modifications, making construction convenient and suitable for both new and renovation projects. Utilizing the high latent heat storage characteristics of phase change materials, it effectively buffers fluctuations in solar energy input, achieving temporary heat storage in the shallow section and cascaded heat transfer in the deep section. This efficient thermal buffering and cascaded utilization enhance the system's thermal stability. This invention reduces drastic fluctuations in the geothermal field caused by intermittent solar energy, which helps maintain the thermal balance of the geothermal reservoir, extends its service life, increases the solar energy contribution rate, and improves system energy efficiency and geothermal reservoir lifespan. Furthermore, by integrating sensors and a control system, this invention can automatically adjust the operating strategy based on real-time data and predictive information, achieving efficient and stable system operation, and has significant engineering practical value. Attached Figure Description

[0017] The accompanying drawings are provided to further understand the invention and constitute a part of this invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] Figure 1 This is a schematic diagram of the overall structure of a phase change thermal storage system for a medium-deep geothermal system according to the present invention. Figure 2 This is a schematic diagram showing the structural details of the annular sleeve-type phase change thermal storage layer in a phase change thermal storage system of a medium-deep geothermal system according to the present invention.

[0019] Among them, 1. Medium-deep geothermal heat exchanger, 2. Annular shell-and-tube phase change thermal storage layer, 3. Solar collector, 4. Heat pump unit, 5. Temperature sensor, 6. Electric valve, 7. Heat collection circulation pump, 8. Hot water storage tank, 9. Heating circulation pump, 10. Plate heat exchanger, 11. User side, 12. Control unit, 13. Outer pipe, 14. Inner pipe, 15. Phase change material, 16. Thermal conductive fins, 17. Flow sensor. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0022] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0023] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0024] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0025] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0026] How to provide a system with a reasonable structure, simple construction, high thermal storage efficiency, and effective cascade coupling of solar energy and medium-deep geothermal energy to improve the overall stability of the system, extend the life of geothermal reservoirs, and improve energy utilization?

[0027] like Figure 1 As shown, the present invention discloses a phase change thermal storage system for a medium-deep geothermal system, comprising a medium storage section, a medium-deep geothermal heat exchanger 1, a solar collector unit, and a circulation path formed by an annular sleeve-type phase change thermal storage layer 2, wherein: The medium storage section stores the medium that can circulate in the circulation path; the solar thermal collector unit is connected to the inlet of the medium-deep geothermal heat exchanger 1 for primary heating of the medium; The medium-deep geothermal heat exchanger 1 is buried underground; the medium-deep geothermal heat exchanger 1 includes a shallow section and a deep section arranged from top to bottom, which are used for medium-deep geothermal heat exchange; the annular sleeve-type phase change heat storage layer 2 is sleeved in the shallow section, and the interior of the shallow section is filled with phase change material 15, which is used for thermal buffering and high-efficiency low temperature difference storage during the heat exchange process. It also includes a circulation control system, which is connected to the solar collector unit, the medium-deep geothermal heat exchanger 1 and the annular shell-and-tube phase change heat storage layer 2 respectively; the circulation control system is used to control the flow and temperature regulation of the medium between the solar collector unit and the medium-deep geothermal heat exchanger 1.

[0028] In a phase change thermal storage system of a medium-deep geothermal system, an annular sleeve-type phase change thermal storage layer 2 is set in the shallow section of the medium-deep geothermal heat exchanger 1, and combined with primary heating and intelligent control of solar energy, the heat of the medium is transferred in stages, buffered, stored and released on demand, thereby effectively mitigating the adverse effects of intermittent solar energy and improving the system's operational stability and overall energy efficiency.

[0029] In some embodiments, the present invention provides a phase change thermal energy storage system for a medium-deep geothermal system. The medium-deep geothermal heat exchanger 1 adopts a U-shaped or coaxial sleeve structure. When buried underground, the medium-deep geothermal heat exchanger 1 is generally buried at a depth greater than 1500 meters to extract deep geothermal energy. The shallow section of the medium-deep geothermal heat exchanger 1 is generally selected at a depth of 0-200 meters underground. The medium storage section can be a hot water storage tank 8, and the medium can be water or antifreeze. The solar collector unit includes a solar collector 3 and a collector circulation pump 7, used for primary heating of the circulating medium. An annular sleeve-type phase change thermal energy storage layer 2 is sleeved outside the shallow section of the annular sleeve-type phase change thermal energy storage layer.

[0030] Furthermore, the annular sleeve-type phase change thermal storage layer 2 of the present invention consists of an outer tube 13, an inner tube 14, and an annular cavity between them. The outer tube 13 is in direct contact with the annular sleeve-type phase change thermal storage layer 2 and can be made of corrosion-resistant metal; the inner tube 14 is tightly attached to the outer wall of the medium-deep geothermal heat exchanger 1 to ensure good thermal contact. The annular sleeve-type phase change thermal storage layer 2 is uniformly arranged along the shallow section, and heat-conducting fins 16 are also provided between the outer tube 13 and the inner tube 14. Alternatively, the thickness of the annular cavity can be 30-200 cm, and the heat-conducting fins 16 are used to enhance heat exchange efficiency. At the same time, expanded graphite and other materials are added to the phase change material 15 to enhance heat dissipation. The interior of the annular cavity is filled with phase change material 15 with a suitable phase change temperature, which is used to absorb or release heat during the heat exchange process, playing the role of thermal buffering and short-term heat storage. The circulation control system consists of a temperature sensor 5, a flow sensor 17, an electric valve 6, and a control unit 12, and is used to automatically adjust the system operating conditions based on real-time operating data.

[0031] The solar thermal collector unit of this invention heats the circulating medium to a temperature 15-35 degrees Celsius higher than the shallow geothermal temperature. The heated medium first flows through the shallow section, where some of the heat is absorbed and stored by the phase change thermal storage layer. The remaining heat flows with the medium into the deeper section for further heat exchange. The circulation control system of this invention has multi-mode operation logic, which can automatically switch operating modes and optimize control parameters according to solar irradiance, medium temperature, user load, and seasonal characteristics.

[0032] In some embodiments, the circulation control system of the present invention includes a temperature sensor 5, a flow sensor 17, an electric valve 6, and a control unit 12, which is electrically connected to the temperature sensor 5, the flow sensor 17, and the electric valve 6, respectively. It also includes a plate heat exchanger 10 and a heat pump unit 4. The medium storage section is connected to the user side 11 of an external heating unit via the plate heat exchanger 10. The heat pump unit 4 is located at the outlet of the medium-deep geothermal heat exchanger 1. The heat pump unit 4 enhances the thermal energy grade of the lower-temperature geothermal fluid extracted from deep geological structures, bringing it to a high temperature level suitable for direct use in building heating, industrial production, etc. Valves, a heating circulation pump 9, and temperature sensors 5 are installed in the pipeline between the hot water storage tank 8 and the plate heat exchanger 10. Temperature sensors 5 are also installed in the pipeline between the plate heat exchanger 10 and the user side 11 to provide real-time monitoring data to the control unit 12.

[0033] The solar collector 3 of this invention is connected to the inlet of the medium-deep geothermal heat exchanger 1 via a pipeline, which is equipped with a heat collection circulation pump 7 and an electric valve 6. Multiple temperature sensors 5 are configured and arranged at key nodes, including the outlet of the solar collector 3, the inlet of the annular sleeve-type phase change thermal storage layer 2, the outer wall of the annular sleeve-type phase change thermal storage layer 2, and the outlet on the user side of the external heating unit. A heat pump unit 4 is installed at the outlet of the medium-deep geothermal heat exchanger 1 for heat exchange.

[0034] like Figure 2 As shown in the figure, in one embodiment, in the annular sleeve-type phase change heat storage layer 2 of the present invention, the outer tube 13 is made of 304 stainless steel, the inner tube 14 is closely attached to the outer wall of the medium-deep geothermal heat exchanger 1, and the annular cavity is filled with paraffin-based phase change material 15 with a phase change temperature of 60 degrees Celsius. In order to enhance heat exchange, a number of axially distributed copper heat-conducting fins 16 are welded between the outer tube 13 and the inner tube 14.

[0035] This invention also provides a cascade heating method for a phase change thermal storage system in a medium-deep geothermal system, based on the phase change thermal storage system of the medium-deep geothermal system, comprising the following steps: S1. When there is sufficient solar radiation, start the solar thermal collector unit to heat the medium in the first stage; S2. The heated medium enters the medium-deep geothermal heat exchanger 1. When it flows through the shallow section, some of the heat is transferred to the annular shell-type phase change heat storage layer 2, where it is absorbed and stored by the phase change material 15. S3. The medium continues to flow through the deep section and exchanges heat with the annular sleeve-type phase change thermal storage layer 2 in the deep section to achieve heat transfer in stages. S4. When solar radiation is insufficient or at night, the phase change material 15 releases the stored heat to preheat the medium entering the deep section and maintain the heat supply stability of the phase change thermal storage system. S5. The circulating control system monitors temperature, flow rate, and solar energy status in real time, and dynamically adjusts the medium flow rate, heating mode, and thermal storage layer working status to achieve seasonal heat balance and system energy efficiency control.

[0036] The cascade heating method of this invention involves a solar collector unit heating the circulating medium in the first stage; after heating, the medium enters the shallow section of the medium-deep geothermal heat exchanger 1, where the annular shell-type phase change thermal storage layer 2 absorbs and stores some of the heat; the medium continues to enter the deep section, exchanging heat with the deep geothermal storage layer to achieve cascade utilization of heat; when solar energy is insufficient, the phase change thermal storage layer releases the stored heat to preheat the medium; and the intelligent control system enables real-time adjustment of operating parameters and optimization of seasonal strategies.

[0037] The present invention discloses a cascade heating method for a phase change thermal storage system of a medium-deep geothermal system, including a seasonal operation mode, which includes a summer mode and a winter mode. In the summer mode, the solar thermal collector is the main heating unit, and the heat after operation is stored in the phase change material 15 of the shallow section of the medium-deep geothermal heat exchanger 1, so as to reduce the heat load to the deep underground layer. In winter mode, the solar thermal collector unit provides auxiliary heating, and the phase change material 15 releases stored heat to work in conjunction with deep geothermal energy to increase the heating temperature.

[0038] In some specific embodiments, during summer operation, when solar energy is abundant during the day, the control unit 12 activates the solar thermal collection mode. The circulating medium (water / antifreeze) is heated from 30 degrees Celsius to 55 degrees Celsius by the solar collector 3, and then enters the geothermal heat exchanger 1. Flowing through the shallow section, some heat (approximately the heat corresponding to a temperature difference of 10-15 degrees Celsius) is transferred to the phase change material 15 through the inner tube 14 and fins 16. The material absorbs heat and melts, temporarily storing excess solar energy in the shallow strata. The medium carrying the remaining heat continues to descend to the deeper section, where it exchanges heat with the deep geothermal reservoir, further increasing its temperature. Finally, it is supplied to users or used for domestic hot water via the plate heat exchanger 10. At night or on cloudy or rainy days, solar thermal collection stops. At this time, the phase change material 15 in the shallow section gradually solidifies and releases heat, preheating the medium entering the deeper section, thereby maintaining a stable heating temperature and reducing the direct extraction load on the deep geothermal reservoir.

[0039] In some specific embodiments, during summer operation, when solar irradiance is weak, the control unit 12 activates auxiliary heating and thermal energy storage release modes. The solar collector 3 can still provide a certain temperature rise, while the annular sleeve-type phase change thermal storage layer 2 continuously releases the heat stored in summer, jointly preheating the medium. The preheated medium receives geothermal heating in the deeper layers, ensuring that the outlet temperature meets heating requirements, such as above 45 degrees Celsius. In this mode, the phase change thermal storage system of the present invention significantly reduces dependence on deep geothermal energy, improving heating security and energy utilization efficiency.

[0040] Furthermore, in the step heating method of the phase change thermal storage system of the medium-deep geothermal system of the present invention, in S5, the temperature change of the phase change material 15 is monitored in real time to determine the thermal storage / heat release state and phase change process of the phase change material 15. Based on the thermal storage status, user load, and weather forecast, the heating power and medium circulation speed of the solar thermal collector can be predictively adjusted; and remote monitoring platform access can be supported to realize data visualization, fault diagnosis, and remote control of operation strategies.

[0041] Specifically, the operating logic of the control system of the cascade heating method of the present invention is as follows: The control unit 12 continuously receives data from each temperature sensor 5 and flow sensor 17, and, in conjunction with weather forecasts and user load predictions, executes the following logic: If the solar irradiance is higher than the set threshold and the user load is lower than the heating capacity, the heat storage priority mode will be entered, and the circulation flow rate will be appropriately increased to promote the transfer of heat to the heat storage layer. If solar energy is insufficient and the temperature of the thermal storage layer is higher than the temperature of the medium, the heat release auxiliary mode is entered, and the electric valve 6 is controlled to adjust the flow path to make full use of the thermal storage. Operating parameters are preset according to seasonal characteristics, such as focusing on heat storage in summer and heat release and auxiliary heating in winter; The phase change thermal energy storage system of this invention supports remote monitoring. Operation and maintenance personnel can view real-time data, adjust set values, and receive fault alarms through the platform.

[0042] In some embodiments, the stepped heating method of the present invention is specifically performed according to the following steps: 1) System initialization: Read current temperature, irradiance, load, and other parameters; determine if solar energy is sufficient; if so, proceed to 2); otherwise, proceed to 5). 2): Start the primary solar heating and adjust the circulation pump and valves to the optimal thermal storage condition; 3): The heating medium flows through the shallow section, and the phase change heat storage layer absorbs and stores part of the heat; 4): The medium enters the deep section for geothermal heat exchange, completing the cascade transfer of heat; 5): Determine if the thermal storage layer has usable heat. If so, proceed to 6); otherwise, proceed to 7). 6): Activate the heat storage layer to release heat and preheat the medium; 7): Switch to pure geothermal or auxiliary heating mode; 8) Dynamically adjust operating strategies based on seasons, weather, and load forecasts; 9) Continuously monitor and regulate to achieve continuous optimization of system operation.

[0043] In some practical applications, the phase change thermal energy storage system of this invention was implemented in a multi-energy complementary heating demonstration project in a certain park. The measured data after testing showed that the system's heating temperature fluctuation was reduced by about 40% compared with the traditional coupling system; the overall efficiency of solar and geothermal coupling was improved by more than 25%; the heat loss in the shallow section was reduced by 20%, and the deep geothermal extraction was reduced by 15%; the system has good seasonal adaptability, and the effects of heat storage in summer and heat release in winter are relatively significant.

[0044] It should be noted that the above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Anyone skilled in the art can readily implement the present invention according to the description and above. Any modifications, alterations, and variations made based on the disclosed technical content are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A phase change thermal storage system for a medium-deep geothermal system, characterized in that, The circulation path includes a medium storage section, a medium-deep geothermal heat exchanger (1), a solar collector unit, and an annular shell-and-tube phase change thermal storage layer (2), wherein: The medium storage section stores a medium that can circulate in the circulation path; the solar thermal collector unit is connected to the inlet of the medium-deep geothermal heat exchanger (1) for primary heating of the medium; The medium-deep geothermal heat exchanger (1) is buried underground; the medium-deep geothermal heat exchanger (1) includes a shallow section and a deep section arranged from top to bottom, which are used for medium-deep geothermal heat exchange; the annular sleeve-type phase change heat storage layer (2) is sleeved on the shallow section, and the interior of the shallow section is filled with phase change material (15), which is used for thermal buffering and high-efficiency low temperature difference storage during the heat exchange process; It also includes a circulation control system, which is connected to the solar thermal collector, the medium-deep geothermal heat exchanger (1) and the annular shell-type phase change heat storage layer (2) respectively; the circulation control system is used to control the flow and temperature regulation of the medium between the solar thermal collector and the medium-deep geothermal heat exchanger (1).

2. The phase change thermal storage system of the medium-deep geothermal system according to claim 1, characterized in that, The annular sleeve-type phase change thermal storage layer (2) includes an outer tube (13), an inner tube (14), and an annular cavity; the outer tube (13) is made of corrosion-resistant metal material, with an insulation layer attached to the inner wall, and is in direct contact with the surrounding strata; the inner tube (14) is attached to the outer wall of the medium-deep geothermal heat exchanger (1); the annular cavity is located between the outer tube (13) and the inner tube (14), and the phase change material (15) is filled in the annular cavity.

3. The phase change thermal storage system of the medium-deep geothermal system according to claim 2, characterized in that, The phase change material (15) includes paraffin-based, hydrated salt, or fatty acid-based materials.

4. The phase change thermal storage system of the medium-deep geothermal system according to claim 2, characterized in that, The annular sleeve-type phase change thermal storage layer (2) is uniformly arranged along the shallow section. A heat-conducting fin (16) is also provided between the outer tube (13) and the inner tube (14). The heat-conducting fin (16) is used to enhance the heat exchange efficiency between the outer tube (13) and the inner tube (14) and the phase change material (15).

5. The phase change thermal storage system of the medium-deep geothermal system according to claim 1, characterized in that, The solar thermal collector unit includes a solar collector (3) and a heat collection circulation pump (7); the medium is heated by the solar collector (3) and then enters the medium-deep geothermal heat exchanger (1) for heat exchange.

6. The phase change thermal storage system of the medium-deep geothermal system according to claim 1, characterized in that, The circulation control system includes a temperature sensor (5), a flow sensor (17), an electric valve (6), and a control unit (12), wherein the control unit (12) is electrically connected to the temperature sensor (5), the flow sensor (17), and the electric valve (6), respectively. The control unit (12) can automatically adjust the circulation flow and heating mode based on solar irradiance, medium temperature and ground temperature data.

7. The phase change thermal storage system of the medium-deep geothermal system according to claim 1, characterized in that, The outlet of the medium-deep geothermal heat exchanger (1) is equipped with a heat pump unit (4), and the medium storage section is also connected to an external heating unit through a plate heat exchanger (10).

8. A cascade heating method for a phase change thermal storage system in a medium-deep geothermal system, characterized in that, This is based on the phase change thermal storage system of the medium-deep geothermal system described in any one of claims 1-7, and includes the following steps: S1. When there is sufficient solar radiation, start the solar thermal collector unit to heat the medium in the first stage; S2. The heated medium enters the medium-deep geothermal heat exchanger (1). When it flows through the shallow section, some of the heat is transferred to the annular shell-type phase change heat storage layer (2), where it is absorbed and stored by the phase change material (15). S3. The medium continues to flow through the deep section and exchanges heat with the annular sleeve-type phase change thermal storage layer (2) in the deep section to achieve heat transfer in stages. S4. When solar radiation is insufficient or at night, the phase change material (15) releases the stored heat to preheat the medium entering the deep section and maintain the heat supply stability of the phase change heat storage system. S5. The circulating control system monitors temperature, flow rate, and solar energy status in real time, and dynamically adjusts the medium flow rate, heating mode, and thermal storage layer working status to achieve seasonal heat balance and system energy efficiency control.

9. The cascade heating method for a phase change thermal storage system in a medium-deep geothermal system according to claim 8, characterized in that, It also includes seasonal operating modes, which include summer mode and winter mode; wherein: In the summer mode, the solar thermal collector unit is the main heating element, and the heat after operation is stored in the phase change material (15) of the shallow section of the medium-deep geothermal heat exchanger (1) in order to reduce the heat load to the deep underground layer. In the winter mode, the solar thermal collector unit provides auxiliary heating, and the phase change material (15) releases stored heat to work in conjunction with the deep geothermal layer to increase the heating temperature.

10. The cascade heating method for a phase change thermal storage system in a medium-deep geothermal system according to claim 8, characterized in that, In S5, the temperature change of the phase change material (15) is monitored in real time to determine the heat storage / heat release state and phase change process of the phase change material (15); Based on the thermal storage status, user load, and weather forecast, the heating power and medium circulation speed of the solar thermal collector are predictively adjusted. It also supports access to remote monitoring platforms, enabling data visualization, fault diagnosis, and remote control of operational strategies.

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