Solar energy-geothermal energy-valley electricity synergistic phase change heat storage and supply system and method

Abstract

The invention relates to a solar energy-geothermal energy-valley electricity synergistic phase change heat storage and supply system and method, and relates to the field of building heat supply. The system comprises an energy acquisition unit (a solar heat collector and a shallow buried pipe), a two-stage phase change heat storage unit (a high-temperature tank stores 40-60 DEG C heat energy to be directly supplied to a user, and a low-temperature tank takes ice-water as a heat source exclusive to a heat pump), a heat pump unit and a control unit. The method comprises the steps of time-sharing heat storage in a heating season (solar energy is charged into double tanks in the daytime, and valley electricity drives the heat pump to store heat at night) and step heat supply (high-temperature tank direct supply is preferentially adopted, and the heat pump supplements heat when the heat pump is insufficient); in non-heating seasons, solar energy accumulates heat across seasons through the buried pipes, and soil heat balance is maintained. The problems of low heat pump energy efficiency, heat energy waste, low buried pipe utilization rate and poor valley electricity utilization in the prior art are solved, the system energy efficiency is improved (the COP of the heat pump is larger than or equal to 3.5), the operation cost is reduced by more than 40%, and the system is suitable for medium-sized and large-sized building heating.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of building heating and multi-energy collaborative utilization, in particular to a phase change heat storage heating system and method for solar-geothermal energy-valley electricity collaboration. BACKGROUND

[0002] At present, there are mainly the following several typical systems or modes in the field of heating: Single solar heating system, traditional ground source heat pump system, conventional phase change heat storage system (usually using a single heat storage tank, or only used for storing heat energy of a single grade) and simple multi-energy complementary system. Although the simple multi-energy complementary system attempts to combine solar energy, geothermal energy, etc., it is often only a simple parallel or switching, lacking a set of intelligent collaboration and optimization operation strategy in time sequence and grade. The use of cheap valley electricity is usually limited to direct electric heating or heat supplement for the heat storage tank, and cannot be efficiently coupled with the heat pump.

[0003] The winter heating in northern China faces double challenges: on the one hand, according to the data of the Ministry of Ecology and Environment, PM2.5 pollution caused by scattered coal heating accounts for 30%-40% of the causes of winter smog, and clean replacement solutions are urgently needed; on the other hand, under the promotion of the "coal-to-electricity" and "coal-to-gas" policies, the limitations of single energy heating are highlighted - solar energy is affected by day and night / weather, and the heating stability is insufficient (in winter, the daily heating gap in areas with insufficient sunlight is 4-6 hours); electric heating relies on peak electricity, and the operation cost is 2-3 times higher than that of coal. Although the traditional "solar energy + ground source heat pump" system integrates renewable energy, it has the following defects: The mismatch of heat energy grade leads to the use of high-temperature solar energy for low-temperature heat source, with a smoke efficiency loss of more than 50%; the soil heat is unbalanced, with an annual average temperature drop of 2-3℃ / year; and the valley electricity utilization is inefficient, which is mostly direct electric heating. These defects restrict the system efficiency and economy. According to the 2025 report of the International Energy Agency (IEA), it is pointed out that the proportion of renewable energy in the field of building heating in China is only 18%, and the core obstacle is the "spatial and temporal mismatch of intermittent energy and stable load". The existing technology attempts to alleviate it through phase change heat storage, but is mostly limited to single heat storage tank (usually independent application of sensible heat / latent heat), and cannot realize the systematic integration of "time-sharing energy storage + grade classification + multi-energy collaboration". The closest solution in the existing technology is "solar energy assisted ground source heat pump + single heat storage tank", which has the problems of heat energy grade mismatch, soil heat imbalance, low valley electricity utilization efficiency, and insufficient adaptability of equipment parameters to commercial building scenes. SUMMARY

[0004] In view of the above problems, the technical problem to be solved by the present application is to provide a solar-geothermal energy-valley electricity collaborative phase change heat storage and supply system with innovative structural design and refined operation strategy, so that multiple energies are deeply coordinated in time sequence and grade, and finally a high-efficiency, stable, economical and sustainable heat supply system and method is constructed.

[0005] In order to solve the above technical problems, the present application provides the following technical scheme: The solar-geothermal energy-valley electricity collaborative phase change heat storage and supply system comprises an energy collection unit, a two-stage phase change heat storage unit, a heat pump unit, a control unit and an accessory component. The energy collection unit comprises a vacuum tube type solar collector and a shallow ground pipe. The solar collector is used for collecting solar energy and converting it into heat energy. The shallow ground pipe is used for extracting geothermal energy or realizing cross-season heat storage to maintain soil heat balance. The two-stage phase change heat storage unit comprises a high-temperature phase change heat storage tank and a low-temperature phase change heat storage tank. The high-temperature phase change heat storage tank is used for storing high-grade heat energy and directly supplying heat to the user side. The low-temperature phase change heat storage tank is used for storing low-grade heat energy and serving as a dedicated low-temperature heat source of the heat pump unit. The heat pump unit is used for upgrading low-grade heat energy into high-grade heat energy and can be driven to operate by valley electricity. The input end of the heat pump unit is in communication with the low-temperature phase change heat storage tank or the shallow ground pipe to obtain low-grade heat energy. The output end of the heat pump unit is in communication with the high-temperature phase change heat storage tank or the user side to output high-grade heat energy. The control unit is used for controlling the operation state of each unit according to temperature signals and time period signals. The accessory component is used for realizing heat energy transmission and medium isolation between units.

[0006] The accessory component comprises a plate heat exchanger with a heat exchange area of ≥50 square meters and a heat transfer coefficient of ≥2000 W / (square meter·℃). The accessory component comprises a heat preservation circulating pipeline with a heat preservation layer thickness of ≥50 mm and a thermal conductivity of ≤0.03 W / (m·℃).

[0007] When the temperature T3 of the low-temperature tank is greater than 0℃, the heat pump is preferentially controlled to take heat from the low-temperature tank. When the temperature T3 of the low-temperature tank is less than or equal to 0℃, the heat pump is controlled to take heat from the shallow ground pipe.

[0008] The high-temperature phase change heat storage tank is filled with a phase change material with a phase change temperature of 47-53℃, preferably C22 paraffin.

[0009] The phase change temperature of C22 paraffin is 47-53℃, and the operating temperature interval of the high-temperature tank designed by the system is 40-55℃. The low-temperature phase change heat storage tank uses ice-water as a phase change medium to store and release low-grade heat energy through latent heat released by ice freezing or latent heat absorbed by ice melting. The low-temperature tank is defined as T3 lasting for 1 hour ≤0℃ or ice completely melting (detected by a liquid level meter or a density sensor).

[0010] Preferably, the heat pump unit comprises an evaporator, a compressor, an expansion valve and a condenser, the evaporator is communicated with the low-temperature phase change heat storage tank or the shallow ground heat exchanger, and the condenser is communicated with the high-temperature phase change heat storage tank or the user side.

[0011] Preferably, the control unit comprises a temperature sensor, a water pump and a valve; the temperature sensor is used for detecting the solar collector outlet water temperature T1, the high-temperature phase change heat storage tank temperature T2, the low-temperature phase change heat storage tank temperature T3 and the shallow ground heat exchanger outlet water temperature T4; the water pump comprises P1 for solar collector circulation, P2 / P3 for shallow ground heat exchanger circulation, P4 / P5 for heat pump unit circulation and P6 for user side heat supply circulation; and the valve comprises V1-V11 for controlling the on-off of each circulation passage.

[0012] Preferably, the accessory components comprise a heat exchanger and a circulation pipeline; the heat exchanger is used for controlling the peak heat load of the collector side, preventing the instantaneous high temperature from exceeding the long-term tolerance limit of the shallow ground heat exchanger material, and playing a key protection role; and the circulation pipeline is used for connecting each unit to transmit heat energy carriers.

[0013] The application also provides a solar-geothermal energy-valley electricity collaborative phase change heat storage heating method applied to the system, which comprises a heating season operation step and a non-heating season operation step; the heating season operation step comprises a heat storage phase and a heat supply phase. The heat storage phase: the control unit controls the solar collector to store heat to the high-temperature phase change heat storage tank and the low-temperature phase change heat storage tank according to the time period and the temperature signal, controls the shallow ground heat exchanger to store heat to the low-temperature phase change heat storage tank, and controls the valley electricity driven heat pump unit to take heat from the low-temperature phase change heat storage tank or the shallow ground heat exchanger and store heat to the high-temperature phase change heat storage tank; The heat supply phase: the control unit preferentially controls the high-temperature phase change heat storage tank to directly supply heat to the user side according to the high-temperature phase change heat storage tank temperature, and controls the valley electricity driven heat pump unit to take heat from the low-temperature phase change heat storage tank or the shallow ground heat exchanger and supply heat to the user side when the high-temperature phase change heat storage tank temperature cannot meet the heat supply demand; The non-heating season operation step: the control unit controls the solar collector to realize cross-season heat storage through the shallow ground heat exchanger according to the temperature difference signal of the solar collector and the shallow ground heat exchanger, so as to maintain the soil heat balance.

[0014] Preferably, the heating season heat storage phase is executed according to the following time periods: 8:00-15:00: if T1-T2>8℃, start pump P1 and open valves V2 and V4, close V1 and V3, and the solar collector stores heat to the high-temperature phase change heat storage tank; if T1-T2<2℃, stop pump P1; 15:00-19:00: If T3≤0℃ and T1-T3>5℃, start P1 and open V2 and V3, and close V1 and V4. The solar collector stores heat in the low-temperature phase change storage tank. If T3>0℃ or T1-T3<2℃, close P1. 19:00-24:00: If T3≤0℃ and pump P4 is off, start pump P3; if T3>0℃, stop pump P3. 24:00-8:00: If T2 < 49℃, start the heat pump unit and pump P5, turn on V8 and turn off V9 and V10; if T2 > 55℃, turn off the heat pump and P5; during heat pump operation, if T3 > 0℃, start P4 and turn on V5 and turn off V7; if T3 < 0℃, turn on V7 and V6 and turn off V5.

[0015] Preferably, the heating season heating phase is implemented according to the following time periods: 8:00-24:00: If T2 > 40℃, start pump P6 and open V11; if T2 < 40℃, start the heat pump unit and P5, close P6, and simultaneously open V9 and V10 and close V8; during the operation of the heat pump unit, if T3 > 0℃, start P4 and open V5, close V7; if T3 < 0℃, open V7 and V6 and close V5. 24:00-8:00: Continuously start P6 and turn on V11 to provide heat to users.

[0016] Preferably, the non-heating season operation steps are as follows: when T1-T4 > 10℃, start pumps P1 and P2 and open valve V1, and close V2 and V6; when T1-T4 < 5℃, turn off pumps P1 and P2 to stop the heat storage cycle.

[0017] Compared to existing technologies that combine solar-assisted ground source heat pumps with single thermal storage, this invention provides a solar-geothermal-valley electricity synergistic phase change thermal storage heating system and method. Through its unique high- and low-temperature dual-stage phase change thermal storage structure and intelligent operation strategy, it achieves the following significant beneficial effects: 1. System architecture coupling high and low temperature two-stage phase change thermal storage with heat pump This invention innovatively constructs a composite energy system architecture integrating a high- and low-temperature dual-stage phase change thermal storage tank and a heat pump unit. The core of this architecture lies in using the high-temperature phase change thermal storage tank as a direct heating unit, while simultaneously designing the low-temperature phase change thermal storage tank as a dedicated, stable, low-temperature heat source for the heat pump. This structural design fundamentally solves the problem of reduced energy efficiency in traditional air-source or ground-source heat pumps due to large temperature fluctuations in the low-temperature heat source. By providing the heat pump with a high-quality, constant-temperature, and controllable low-temperature heat source, it ensures that the heat pump always operates within its high-efficiency range, thus laying the foundation for the efficient and stable operation of the entire system.

[0018] 2. System operation method for multi-energy complementation and thermal energy grade cascade utilization Based on the above system architecture, the present application proposes a set of multi-energy complementary and thermal energy grade cascade operation method. This method realizes the cooperation of "solar energy-geothermal energy-valley electricity" in time sequence and grade: during the day, solar energy is preferentially used to charge the high and low temperature heat storage tanks in cascade; at night, valley electricity is used to drive the heat pump to upgrade the low grade thermal energy and store it in the high temperature tank. At the energy release end, the system strictly follows the cascade principle of "high grade direct supply, low grade heat pump upgrade", and preferentially releases high temperature tank heat for direct heating, and when it is insufficient, the heat pump is used to extract stable heat source from the low temperature tank for heating. This method realizes the whole process grade matching of energy from the source to the end, and maximizes the energy storage density and the overall thermal efficiency of the system.

[0019] 3. High efficiency operation paradigm of heat pump based on valley electricity and low temperature phase change heat storage The present application creates a high efficiency operation paradigm of heat pump driven by night valley electricity. The core of this paradigm is that during the day, solar energy is preferentially used to store heat in the low temperature phase change heat storage tank; during the night valley electricity period, the heat pump is instructed to extract heat from the already stored low temperature phase change heat storage tank for heating users or charging the high temperature phase change heat storage tank. This method ingeniously combines cheap valley electricity with solar energy during the day, and through the medium of low temperature phase change heat storage tank, creates stable and efficient working conditions for the heat pump, making it feasible in terms of economy and efficiency to "generate high quality heat using valley electricity".

[0020] 4. The cascade utilization of solar energy can greatly improve the utilization efficiency of solar energy. High temperature heat is stored in the high temperature phase change heat storage tank during high temperature, and is used to melt the ice in the low temperature phase change heat storage tank during low temperature. At the same time, solar energy can realize cross-season heat storage by storing the collected heat in the ground pipe, solving the problem of soil heat balance.

[0021] 5. During the day, the heat pump unit does not work, and the outlet water temperature of the ground pipe is about 10℃, which can be used to melt the ice in the low temperature phase change heat storage tank during the day, and can be used as the low temperature heat source of the heat pump unit at night, greatly improving the utilization rate of the ground pipe.

[0022] 6. The roles of various energies in different time periods are fully utilized, solar energy and geothermal energy are maximized, the stability and safety of the system are ensured, and the pipe length of the ground pipe and the laying area of the solar energy can be minimized.

[0023] 7. During the day, solar energy and the heat stored by the ground source heat pump during the valley electricity period are fully utilized for heating, and during the night valley electricity period, the ground source heat pump and low temperature phase change heat storage + heat pump are used to supply heat to users and store heat in the high temperature tank, so that the heat pump unit does not run during peak electricity period, which can greatly reduce the operating cost.

[0024] 8. The low-temperature heat storage tank is filled with water, and the latent heat of water turning into ice is extracted as the low-temperature heat source of the heat pump. The advantage of large latent heat of water turning into ice is fully utilized. After night operation, the water in the low-temperature heat storage tank will turn into ice. During the day, the solar energy and the heat extracted from the ground heat exchanger during the low-temperature period are introduced into the low-temperature heat storage tank, which can greatly improve the utilization rate of solar energy and the ground heat exchanger. The large temperature difference between the solar energy and the ground heat exchanger and the low-temperature heat storage tank can also greatly improve the energy utilization efficiency of solar energy and geothermal energy.

[0025] The great advantage of the present application is that by structural innovation and strategic intelligent control, a variety of mature technologies are deeply coupled to produce a "1+1>2" synergistic effect. The core of the technical secret is not a single new component, but the system architecture of "high and low temperature two-stage phase change heat storage and forced coupling of heat pump", and the multi-energy complementary operation strategy based on time sequence and grade ladder.

[0026] Although there are disadvantages such as high initial cost and complex system, these disadvantages can be compensated in the whole life cycle of the project by the high energy efficiency, greatly reduced electricity bill and possible reduction of ground heat exchanger investment in the running stage. Therefore, the present application is particularly suitable for medium and large building heating projects which are sensitive to operating costs and pursue long-term energy saving benefits and stability. The "three-source coupling, two-stage heat storage and time sequence intelligent control" heating system and method proposed by the present application realizes the time and space translation and grade upgrading of renewable energy through architectural innovation and strategic optimization.

[0027] The solar-geothermal energy-valley electricity collaborative phase change heat storage heating system will be further described below in combination with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Fig. 1 is a structural schematic diagram of the solar-geothermal energy-valley electricity collaborative phase change heat storage heating system of the present application; Figure 2 Fig. 2 is a flow schematic diagram of the solar-geothermal energy-valley electricity collaborative phase change heat storage heating system of the present application. DETAILED DESCRIPTION

[0029] As Figure 1 and Figure 2As shown, it is a flow chart of a solar-geothermal energy-valley electricity collaborative phase change heat storage and heating system and method, mainly including a solar collector, a high-temperature phase change heat storage tank (C22 paraffin), a low-temperature phase change heat storage tank (ice-water), a shallow ground buried pipe, a heat pump unit, a water pump and related auxiliary components. In the heating season, when the solar radiation intensity is strong in the daytime, the solar collector is used to store heat in the high-temperature phase change heat storage tank and the low-temperature phase change heat storage tank, when the radiation intensity is weak at night, the buried pipe is used to store heat in the low-temperature phase change heat storage tank, and the low valley electricity is used to store heat in the high-temperature phase change heat storage tank by taking the low-temperature phase change heat storage tank or the shallow ground buried pipe as the low-temperature heat source of the heat pump unit, so as to meet the heating demand. In the non-heating season, the collector is used to store heat in the buried pipe to ensure the heat balance of the soil. So as to ensure high efficiency of the system when the shallow ground buried pipe is used as the low-temperature heat source.

[0030] I. The system physical whole implementation architecture of the present application is shown in detail in Figure 1 .

[0031] It is mainly divided into an energy collection area, a heat storage-heat pump area, a user area and a valve group control area, and the component composition, connection relationship and medium flow direction of each area are as follows: 1. Energy collection area It contains a vacuum tube type solar collector (heat collection area 1200 square meters) and a double U type shallow ground buried pipe (buried depth 120 m, pipe diameter De32, buried pipe number 90), which are connected to the heat exchanger through circulating pumps P1 (solar energy circulation, flow rate 25 m³ / h), P2 / P3 (ground buried pipe circulation, flow rate 20 m³ / h) respectively, and the circulating medium is glycol solution; the outlet of the solar collector is provided with a temperature sensor T1, and the outlet of the shallow ground buried pipe is provided with a temperature sensor T4.

[0032] 2. Heat storage-heat pump area It contains a low-temperature phase change heat storage tank (volume 15 m³, ice-water medium, provided with a temperature sensor T3), a high-temperature phase change heat storage tank (volume 9 m³, C22 paraffin filling amount 6.5 m³, provided with a temperature sensor T2) and a screw heat pump unit (rated heating capacity 1200 kW, valley electricity driving, standard working condition COP=3.8, suitable for 20,000 square meters of commercial complex heating load); the low-temperature tank is connected to the heat pump evaporator through circulating pump P4, and the high-temperature tank is connected to the heat pump condenser through circulating pump P5.

[0033] 3. User area It is communicated with the high-temperature tank through circulating pump P6 (flow rate 30 m³ / h), the pipeline is provided with valve V11 to control the on-off, the circulating medium is softened water, and floor heating heating on the user side is realized. When T2<40℃, start the heat pump, the heat pump unit takes heat from the low-temperature tank or the buried pipe, and supplies the user after being raised to 40-60℃.

[0034] 4. Valve group control area Electric valves V1-V11 are distributed at each pipeline node (V1 is the underground pipe-heat exchanger valve, V2-V4 are the solar-high temperature storage tank valves, V5-V7 are the low temperature tank-heat pump valves, V8-V10 are the heat pump-high temperature tank / user valves, and V11 is the high temperature tank-user valve), and are centrally controlled by a Siemens S7-1200 PLC with a valve response time of <15s.

[0035] 5. Medium flow direction: The heat energy collected in the energy harvesting area is transported to the thermal storage-heat pump area via circulating pumps, and after processing, it is distributed to the user area through the valve control area. For example: ethylene glycol solution. (1) Solar collector → P1 → heat exchanger → solar collector (2) Solar collector → P1 → V2 → V4 → High temperature tank → Solar collector (3) Solar collector → P1 → V2 → V3 → Solar collector (4) Heat exchanger → P2 → shallow buried pipe → heat exchanger (5) Shallow buried pipe → P3 → cryogenic tank → shallow buried pipe (6) Evaporator → P4 → Low Temperature Tank → Evaporator (7) Evaporator → P4 → V7 → Shallow buried pipe → Evaporator Softened water: (1) High-temperature tank → P6 → V11 → User (2) Condenser → P5 → V8 → Condenser II. The operation of this invention during the heating season is divided into a heat storage stage and a heating stage. Corresponding Appendix Figure 2 The specific control process for the "heat storage during the heating season" and "heat supply during the heating season" units is as follows: (I) Heat storage stage (divided into 4 periods)

[0036] (II) Heating Phase (divided into 2 time periods) 1. 8:00-24:00 (peak power period): When T2≥40℃, turn on V7 and V8, and supply the high temperature tank directly to the user; 2. 24:00-8:00 (Peak / Peak Electricity Period): When T2 < 40℃, the heat pump is started. The heat pump unit extracts heat from the low-temperature tank or underground pipe and raises it to 40-60℃ before supplying it to users.

[0037] (iii) Fault tolerance mechanism: When the temperature of the low-temperature tank is <0℃, the buried pipe will be automatically switched as the low-temperature heat source of the heat pump unit.

[0038] III. Operation and Control Procedures during the Non-Heating Season The present application executes the cross-season soil heat storage strategy in the non-heating season (May to September), and corresponds to the "non-heating season heat storage" unit, and the specific control process is as follows: Figure 2 The starting condition is that when the difference between the solar collector outlet water temperature T1 and the shallow ground buried pipe outlet water temperature T4 is greater than 10 DEG C, the circulating pumps P1 and P2 are started, the valve V1 is opened, and the valves V2 and V6 are closed, and the solar collector stores heat to the soil through the shallow ground buried pipe. The stopping condition is that when T1-T4 is less than 5 DEG C, the P1 and P2 are closed, and the heat storage cycle is stopped.

[0039] The running parameter is that the daily average heat storage of the solar collector to the soil in the non-heating season is 250 MJ, the annual average soil temperature is increased from 12 DEG C to 14 DEG C, and the soil heat balance improvement rate is maintained at 100%.

[0040] Four, actual project implementation case Taking a 20,000 square meter commercial complex heating project in Hebei as an example, the equipment selection and actual operation data of the system are as follows:

[0041] (1) Equipment selection and parameters

[0042] (2) Actual operation data in the heating season

[0043] (3) Non-heating season operation effectIn the non-heating season from May to September, the daily average heat storage of the solar collector to the soil is 250 MJ, the annual average soil temperature is increased from 12 DEG C to 14 DEG C, and the soil heat balance improvement rate is maintained at 100%, which is higher than that of the traditional ground source heat pump system (the annual average soil temperature is decreased by 1.5 DEG C per year), and lays a foundation for efficient heat source for the next year.

[0044] Five, engineering implementation innovation details The innovative design of the present application in the engineering implementation stage is as follows, which effectively reduces the initial investment and operation difficulty: 1. Buried pipe reuse design: in winter, as a heat pump low temperature source, in summer, as a solar cross-season heat storage channel, reducing the buried pipe length by 30%, saving 1.2 million yuan in cost in North China project.

[0045] 2. Prefabricated assembly: the double heat storage tanks, heat pump units and control boxes are designed as 6m x 3m x 2.8m prefabricated containers, the on-site installation period is shortened from 45 days to 15 days, and the on-site construction cost is greatly reduced.

[0046] Six, effect verification and analysis The economic, energy efficiency and environmental effect verification of the system in the actual project is as follows: 1. Economic effect​ Initial investment: Total investment of RMB 4.8 million, initial investment per unit area of ​​RMB 240 / ㎡ (RMB 20 / ㎡ higher than traditional ground source heat pump + single heat storage system, due to the cost of dual-stage heat storage and intelligent control).

[0047] Operating costs: The total electricity cost for the heating season (120 days) is 16,800 yuan, with an operating cost of 8.4 yuan / ㎡·season per unit area, while traditional electric heating requires about 30 yuan / ㎡.

[0048] Life cycle benefits: Over 6.48 million yuan in operating costs can be saved over the 15-year life cycle, offsetting the increase in initial investment.

[0049] The reduction of over 40% is compared with traditional ground source heat pump systems, and the reduction of 72% is compared with electric heating systems. The operating cost of traditional ground source heat pumps is 14 yuan / ㎡, while that of this system is 8.4 yuan / ㎡, resulting in a 40% reduction.

[0050] 2. Energy efficiency The heat pump's COP is consistently ≥3.5, a 25% improvement compared to traditional ground source heat pumps (COP≈2.8). The comprehensive utilization rate of solar energy in soil thermal storage during the non-heating season is 72%, the utilization rate of buried pipes is increased by 30%, and the overall thermal efficiency of the system exceeds 80%.

[0051] 3. Environmental benefits The average annual CO2 emission reduction is 39.8 tons (compared to natural gas heating), and the renewable energy share reaches 75%, which meets the requirements of the "dual carbon" policy and is in line with the industrial orientation of clean heating in winter in Hebei Province.

[0052] This invention mainly solves the following problems: 1) Two-stage phase change thermal energy storage architecture: Solving the problem of grade mismatch High-temperature tank (45-55℃): filled with C22 paraffin (latent heat of phase change 180kJ / kg), directly storing the medium-temperature heat energy of the solar collector (average daily heat storage 35-40MJ / ㎡), meeting the daytime heating needs of users at 40-50℃ (such as floor heating). Low-temperature tank (0℃ ice-water): A dedicated low-temperature heat source for heat pumps. The heat pump is driven by off-peak electricity at night (COP≥3.8) to utilize the latent heat of ice turning into water as the low-temperature heat source for the heat pump unit to store or supply heat to the high-temperature tank, avoiding the dependence of traditional heat pumps on fluctuating ground temperature (±5℃ fluctuation causes COP to fluctuate by 20%).

[0053] 2) Three-source timing coupling strategy: mitigating energy intermittency During the day: Solar energy is prioritized to heat the high-temperature tank (starting when T collector temperature > T high temperature + 8℃), and excess heat is used to melt the ice layer in the low-temperature tank (triggered when T low temperature < -2℃). Simultaneously, shallow ground temperature (10-15℃) is collected through buried pipes to replenish the low-temperature tank. Off-peak period: 0.3 yuan / kWh low price electricity driven heat pump, from the low temperature tank (ice-water phase change platform) stable heat, heat pump to high temperature tank storage, form "low price energy storage - high price release" economic cycle; Cross-seasonal thermal storage: non-heating season (May-September), solar energy through the buried pipe to the soil heat storage (temperature difference > 10 ℃ start), the average annual heat supplement 120-150 MJ / ㎡, maintain the average annual temperature fluctuation < 2 ℃ (solve the traditional ground source heat pump 10 years decay problem).

[0054] 3) Intelligent decision control system: dynamic matching load and electricity price Three-factor decision: based on real-time electricity price (peak electricity 1.2 yuan / kWh vs. valley electricity 0.3 yuan / kWh), heat storage state (high temperature tank > 55 ℃ stop pump), low temperature tank (< 0 ℃ start buried pipe auxiliary), automatically switch 7 operation modes (such as "solar direct supply + low temperature tank ice melting" "valley electricity heat pump + high temperature tank energy supplement"); Fault tolerance: when the low temperature tank temperature < 0 ℃, automatically switch the buried pipe as the low temperature heat source of the heat pump unit.

[0055] 4) Project implementation innovation: reduce initial investment and operation difficulty Buried pipe reuse design: in winter as a low temperature source of heat pump, in summer as a solar cross-seasonal heat storage channel, reduce the buried pipe length by 30% (this project saves 1.2 million yuan in cost); Unit assembly: double heat storage tank, heat pump unit, control box are designed as prefabricated container, the on-site installation period is shortened from 45 days to 15 days.

[0056] In view of the existing situation in the art, the present application is dedicated to solving the following core technical problems: 1. Intermittency and instability of renewable energy: Solar energy is affected by day and night cycle, and it is difficult to be used as a stable and reliable single heat source. The traditional non-phase change heat storage system has defects such as low heat storage density and large heat loss, resulting in high heat storage cost, and cannot guarantee the stable and continuous supply of heat in low irradiation period.

[0057] 2. Soil heat balance and energy efficiency decay of ground source heat pump: In the long-term operation of the traditional ground source heat pump, the imbalance between soil heat extraction and heat supplement causes temperature field deterioration, the temperature of the low temperature heat source of the heat pump decreases year by year, and the system energy efficiency decreases. In order to alleviate this problem, the number of buried pipes often needs to be increased, thereby increasing the initial investment and land occupation.

[0058] 3. Heat energy grade mismatch and low system efficiency: Solar energy, geothermal energy and other heat sources have different temperature grades, and user side demands are also different. The traditional system uses high-grade heat energy for low-grade demand or mixes different grade heat energy, resulting in waste of available energy and poor overall thermal efficiency. The temperature of the low-temperature heat source of the heat pump (such as air or buried pipe fluid) fluctuates greatly, hindering its continuous and efficient operation.

[0059] 4. High operating cost and lack of economic efficiency: Running a heat pump or electric heating equipment during peak electricity consumption period results in a sharp increase in electricity bills. The way to use cheap off-peak electricity is single and inefficient, which fails to fully realize its economic potential.

[0060] 5. Weak multi-energy coordination: There is a lack of intelligent operation strategy for dynamic management of energy input sequence, heat storage device charging and discharging time and heat energy grade cascade utilization.

[0061] In summary, the existing "solar-geothermal heat pump" system has not realized the three-dimensional depth coordination of time, space and grade due to the isolated development or simple superposition of energy technologies (solar energy, geothermal energy, heat storage and heat pump), which has bottlenecks in stability, efficiency, initial investment and operating cost. The present application solves the problems of intermittent renewable energy, soil heat imbalance and heat energy grade mismatch through innovative system architecture and intelligent coordination strategy, improves energy efficiency (heat pump COP≥3.5), reduces operating cost by more than 72%, and supports emission reduction targets. Through "two-stage phase change heat storage architecture + three-source time sequence coordination strategy + intelligent cascade control", the problems of low energy efficiency, high cost, poor stability and soil heat imbalance of existing heating technologies are systematically solved. Although there are limitations such as higher initial investment (9% higher than traditional systems) and complex control logic, more than 4 million yuan of operating cost can be saved within the full life cycle (15 years), and the environmental benefits are significant. Although there are challenges such as high initial investment and complex control, the full life cycle benefits can balance the initial investment, and it is suitable for medium and large-scale clean heating of buildings, and has wide application value.

[0062] The above-described embodiments are merely preferred embodiments of the present application and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the scope of protection determined by the claims of the present application.

Claims

1. A phase change thermal energy storage and heating system that integrates solar energy, geothermal energy, and off-peak electricity, characterized in that, include: Energy harvesting unit, two-stage phase change thermal storage unit, heat pump unit and control unit; The energy harvesting unit includes a solar collector and a shallow buried pipe. The solar collector is used to collect solar energy, and the shallow buried pipe realizes geothermal energy extraction and cross-seasonal soil heat balance. The dual-stage phase change thermal energy storage unit consists of a high-temperature tank and a low-temperature tank. The high-temperature tank stores high-grade thermal energy at 40-60℃ and supplies it directly to users. The low-temperature tank uses the latent heat of the ice-water phase change medium as the exclusive low-temperature heat source for the heat pump. The input end of the heat pump unit is selectively connected to the low-temperature tank or the shallow buried pipe, and the output end is selectively connected to the high-temperature tank or the user side. The control unit schedules the operation of the energy harvesting unit, the two-stage phase change thermal storage unit, and the heat pump unit based on temperature thresholds and time period signals.

2. The phase change thermal energy storage and heating system based on solar energy, geothermal energy, and off-peak electricity as described in claim 1, characterized in that, The high-temperature tank is filled with C22 paraffin with a phase change temperature of 47-53℃, and its heat storage density is about 125% higher than that of hot water with a temperature difference of 20℃. The low-temperature tank uses ice-water phase change medium, and its heat storage density is about 300% higher than that of hot water with a temperature difference of 20℃.

3. The phase change thermal energy storage and heating system based on solar energy, geothermal energy, and off-peak electricity as described in claim 1, characterized in that, The control unit is set with a cross-seasonal heat storage threshold: heat storage is started when the temperature difference between the solar collector and the buried pipe is >10℃ during the non-heating season, and stopped when the temperature difference is <5℃, so as to maintain the average annual soil temperature difference ≤2℃.

4. The phase change thermal energy storage and heating system based on solar energy, geothermal energy, and off-peak electricity as described in claim 1, characterized in that, The heat pump unit's evaporator is directly connected to the low-temperature tank. When the temperature of the low-temperature tank is >0℃, water-side circulation is started. When the temperature of the low-temperature tank is ≤0℃, the buried pipe is switched to extract heat, ensuring that the actual operating energy efficiency COP of the heat pump is stable at ≥3.

5.

5. A phase change thermal energy storage and heating system based on solar energy, geothermal energy, and off-peak electricity as described in claim 1, characterized in that, During off-peak hours in the heating season, the heat pump is prioritized to store heat in the high-temperature tank. The high-temperature tank starts when the temperature is below 49°C. During peak hours, only the high-temperature tank is used for direct supply or the residual heat from the low-temperature tank, reducing operating costs by more than 40%.

6. A phase change thermal energy storage and heating system based on solar energy, geothermal energy, and off-peak electricity as described in claim 5, characterized in that, The low-temperature tank uses the latent heat of the ice-water phase change as the core heat source of the heat pump unit. After the latent heat of the phase change in the tank is released, it automatically switches to a shallow buried pipe to provide a low-temperature heat source for the heat pump unit.

7. A phase change thermal energy storage and heating system based on solar energy, geothermal energy, and off-peak electricity as described in claim 6, characterized in that, The user side is equipped with zoned temperature control valves, providing independent heating for office areas and public areas to match the load fluctuation characteristics of commercial buildings.

8. A multi-energy synergistic phase change thermal energy storage and heating method, applied to any one of the systems of claims 1-7, comprising: Time-of-use heat storage: During the day, solar energy is prioritized to charge the high-temperature tank and low-temperature tank. At night, off-peak electricity drives the heat pump to extract heat from the low-temperature tank or underground pipes to store heat in the high-temperature tank or directly supply heat to users. Tiered heating: When the temperature of the high-temperature tank is ≥40℃, it is directly supplied to users; when the temperature is below 40℃, the heat pump is activated to boost the low-temperature heat energy. Cross-seasonal balance: When the temperature difference between the solar collector and the buried pipe is >10℃ during the non-heating season, heat storage is activated and stopped when the temperature difference is <5℃, maintaining the average annual soil temperature difference ≤2℃. The control logic is based on temperature thresholds and time period conditions. It schedules the start and stop of water pumps and valves and the operation status of heat pumps through the control unit, triggering unit switching.

9. The method according to claim 8, characterized in that, Heat storage during the heating season is divided into four stages: 8:00-15:00: When the temperature difference between the outlet water temperature T1 of the solar collector and the temperature T2 of the high-temperature tank is greater than 8℃, the solar energy will start storing heat in the high-temperature tank; when the difference is less than 2℃, it will stop. 15:00-19:00: When the temperature of the cryogenic tank T3 ≤ 0℃ and T1-T3 > 5℃, switch to solar energy to melt ice in the cryogenic tank; stop when T3 > 0℃ or T1-T3 < 2℃; 19:00-24:00: When the temperature of the cryogenic tank T3 is ≤0℃, switch the underground pipe to melt ice in the cryogenic tank; stop when T3 >0℃. 24:00-8:00: When the temperature of the high-temperature tank T2 is < 49℃, start the off-peak electricity heat pump to store heat in the high-temperature tank; stop when T2 > 55℃; This forms a time-series cycle of "daytime tiered energy storage - nighttime off-peak electricity efficiency improvement".

10. The method according to claim 8, characterized in that, A fault-tolerant mechanism is set up: when the temperature of the low-temperature tank is <0℃, the buried pipe is automatically switched as the low-temperature heat source of the heat pump unit to ensure the continuity of heating.

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