Solar phase change heat storage cooperative control method and system

Abstract

The invention relates to the technical field of solar heat energy system control, and provides a solar phase change heat storage cooperative control method and system, which ensure that the thermal physical state of a material is accurately sensed by introducing a calibration mode; in the heat collection stage, according to the comparison between the actual melting time consumption of the phase change material and the reference melting time, the latent heat attenuation coefficient is dynamically calculated, the heat storage capacity attenuation is evaluated in real time, and misjudgment of heat storage saturation due to material performance reduction is avoided; in the heat release stage, based on the internal temperature of the heat storage unit and the water outlet temperature change of a user side, the supercooling degree of the phase change material is accurately determined, the crystallization characteristic of the phase change material is mastered in real time, and a basis is provided for supercooling intervention; and the system stores and updates the melting starting temperature, the latent heat attenuation coefficient and the supercooling degree in real time, and executes heat collection and heat release control according to the melting starting temperature, the latent heat attenuation coefficient and the supercooling degree. According to the method, the problem of inaccurate control caused by performance change of the phase-change material is solved, the utilization efficiency of solar heat energy and the stability of heat supply are remarkably improved, and energy waste is effectively avoided.

Description

Technical Field

[0001] This application relates to the field of solar thermal energy system control technology, and more specifically, to a solar phase change thermal storage coordinated control method and system. Background Technology

[0002] A typical solar thermal system usually includes a solar collector, a phase change energy storage unit to store heat, and a sophisticated coordinated control system. Such a system can efficiently capture solar heat and store it stably in the phase change material, releasing it when heat is needed.

[0003] Phase change energy storage materials (PCEs) utilize the property that a material absorbs or releases a large amount of heat when it undergoes a state change at a specific temperature to achieve high-density energy storage. However, when a system operates for a long time, the PCE undergoes countless cycles of incomplete melting and solidification. This repeated and incomplete state change leads to a "self-stratification" phenomenon in the PCE. Due to differences in density, melting point, and crystallization rate among its components, heavier components may slowly sink to the bottom under the influence of gravity, while lighter components may float to the top. This self-stratification causes the overall thermophysical properties of the material, especially the temperature at which its state change occurs and the amount of heat it can store, to become non-uniform within the energy storage unit, thus affecting its energy storage characteristics.

[0004] The system typically embeds temperature probes at specific heights within the phase change material (PCM). However, once the PCM undergoes delamination, the readings from these previously fixed temperature probes lose their representativeness for the average thermal state of the entire PCM. For example, if a temperature probe happens to be encased in a region of delamination with a lower melting point and easier melting, the material in the probe's region will reach the phase change temperature and melt faster than the material in most other parts of the PCM when the system begins heating the PCM unit. This means that even if most of the PCM is still in a solid state and has not yet completed heat storage, the probe may prematurely display a temperature plateau indicating phase change completion. When the system receives no longer representative local temperature data from these probes, it will make a fundamental misjudgment.

[0005] To address the aforementioned issues, existing technologies urgently need improvement. Summary of the Invention

[0006] This application discloses a solar phase change thermal storage synergistic control method, which aims to solve the problem of "self-stratification" phenomenon caused by long-term incomplete melting and solidification cycle of phase change thermal storage materials in existing solar thermal energy systems, which leads to temperature probe data distortion, causing the control system to misjudge the thermal storage saturation state, resulting in energy waste and insufficient heat supply.

[0007] The technical solution of this application is as follows: In a first aspect, this application discloses a solar phase change thermal storage synergistic control method, applied to a solar thermal energy system. The solar thermal energy system includes a solar collector and a phase change thermal storage unit for storing heat. The phase change thermal storage unit contains a phase change material. The method includes: When the outlet heat transfer medium temperature of the solar collector is higher than the internal temperature of the phase change thermal storage unit and reaches a preset temperature difference, the system enters the calibration mode and inputs heat to the phase change thermal storage unit at a preset power. At the same time, the system collects the temperature inside the phase change thermal storage unit to obtain the first temperature data. Based on the first temperature data, the system determines the melting start temperature of the current phase change material. During the heat collection stage, the actual melting time is determined based on the time it takes for the phase change material to go from the melting initiation temperature to the fully molten state, and a latent heat decay coefficient is determined based on the actual melting time and the reference melting time. During the heat release phase, the subcooling of the phase change material is determined based on the changes in the internal temperature of the phase change heat storage unit and the outlet water temperature at the user end. Store / update melting initiation temperature, latent heat decay coefficient, and subcooling; perform heat collection and release control based on melting initiation temperature, latent heat decay coefficient, and subcooling.

[0008] Furthermore, a latent heat decay coefficient is determined based on the actual melting time and the reference melting time, including: determining the ratio of the actual melting time to the reference melting time as the latent heat decay coefficient; the reference melting time is the time required from the initial melting temperature to complete melting at the time of manufacture; the initial melting temperature is the melting temperature set at the time of manufacture of the material. Heat collection and release are controlled based on the melting initiation temperature, latent heat decay coefficient, and subcooling, including: The current heat storage saturation time is determined by the product of the latent heat decay coefficient and the reference melting time; if the heating time continues until the current heat storage saturation time is reached after the phase change heat storage unit reaches the melting initiation temperature, then the heat storage is judged to be saturated. When the internal temperature of the phase change heat storage unit is lower than the melting initiation temperature and has not entered the heat release stage, if the supercooling exceeds a preset threshold, supercooling intervention measures are taken; the supercooling intervention measures include briefly starting the heat release circulation pump to generate fluid disturbance.

[0009] In some preferred embodiments, the melting initiation temperature of the current phase change material is determined based on the first temperature data, including: The instantaneous temperature rise rate is obtained by linear fitting of temperature data over a continuous short period of time in the first temperature data. The inflection point where the instantaneous temperature rise rate drops sharply from a high value to a low value and enters a stable period is identified. The temperature corresponding to this inflection point is determined as the melting start temperature of the phase change material.

[0010] Based on the above, this application further proposes that the method also includes: monitoring the internal temperature change of the phase change heat storage unit during the nighttime cooling process to capture the solidification initiation temperature of the phase change material; adjusting the power of the calibration mode and inputting heat into the phase change heat storage unit according to the solidification initiation temperature during the daytime calibration mode of the next day, and collecting temperature data of the phase change heat storage unit near the solidification initiation temperature; using the solidification initiation temperature as a reference, calculating the local average temperature rise rate by using sliding window least squares fitting, and when the average temperature rise rate is lower than a dynamic threshold for the first time and continues for a period of time, the temperature corresponding to the average temperature rise rate is confirmed as the melting initiation temperature of the current phase change material.

[0011] As an optional option, the dynamic threshold is 20%-30% of the average nighttime cooling rate during the previous night's nighttime cooling process.

[0012] This technical solution enables more flexible and adaptive identification of the melting initiation temperature through the setting of dynamic thresholds, further improving the accuracy of calibration.

[0013] In one embodiment, the supercooling of the phase change material is determined based on the change between the internal temperature of the phase change heat storage unit and the water temperature at the user end. This includes controlling the internal temperature of the phase change heat storage unit to continuously decrease to a first temperature so that the water temperature at the user end begins to rise steadily. The difference between the melting initiation temperature and the first temperature is then determined as the supercooling of the phase change material.

[0014] In another embodiment, the subcooling of the phase change material is determined based on the change between the internal temperature of the phase change thermal storage unit and the outlet water temperature at the user end, including: When the average internal temperature of the phase change heat storage unit enters the preset subcooling range, the crystallization state diagnosis mode is activated; the readings of multiple temperature probes inside the phase change heat storage unit are collected, and the temperature distribution uniformity is calculated. The control command heat exchange circulation pump operates in a preset pulse mode, generating fluid disturbance inside the phase change heat storage unit. Within a specific time period after the fluid disturbance is applied, the readings of all temperature probes inside the phase change heat storage unit are continuously collected and recorded, and the uniformity of temperature distribution after the disturbance is calculated. By comparing the difference in temperature distribution uniformity before and after the disturbance, it can be determined whether the phase change material in the phase change thermal storage unit has overcome supercooling and begun to crystallize effectively. Based on the judgment result, update the current crystallization state information of the phase change material, and record the average internal temperature of the phase change heat storage unit as the actual effective solidification initiation temperature. If the internal temperature of the phase change thermal storage unit is continuously reduced to the second temperature so that the water temperature at the user end begins to rise steadily, then the difference between the effective solidification initiation temperature and the second temperature is determined as the supercooling of the phase change material.

[0015] Based on the above, heat collection and release control are implemented according to the melting initiation temperature, latent heat decay coefficient, and subcooling. The method further includes: real-time monitoring of the energy conversion efficiency between the heat collected by the solar collector and the actual heat stored by the phase change thermal storage unit; real-time monitoring of the stability of the user-end water temperature and the duration of heat supply; evaluating the effectiveness of heat collection and release control based on the energy conversion efficiency, the stability of the water temperature, and the duration of heat supply; and dynamically adjusting the parameters of heat collection and release control based on the effectiveness evaluation results.

[0016] To enhance functionality, the system monitors the stability of the water temperature at the user's outlet and the duration of heat supply in real time. This includes: real-time monitoring of readings from multiple temperature sensors and flow sensors on the user's outlet water pipe; real-time calculation of the average temperature and temperature fluctuation range of the water at the user's outlet based on the readings from multiple temperature and flow sensors; recording the total duration of heat supply from start to finish; and comparing the average temperature, temperature fluctuation range, and total duration with a preset dynamic user demand range to assess the stability of the water temperature and the duration of heat supply.

[0017] Secondly, this application also discloses a solar phase change thermal storage co-control system applied to a solar thermal energy system. The solar thermal energy system includes a solar collector and a phase change thermal storage unit for storing heat. The phase change thermal storage unit contains a phase change material. The system includes: The calibration and determination module is used to enter calibration mode when the outlet heat transfer medium temperature of the solar collector is higher than the internal temperature of the phase change thermal storage unit and reaches a preset temperature difference. It inputs heat to the phase change thermal storage unit with a preset power and collects the temperature inside the phase change thermal storage unit to obtain the first temperature data. Based on the first temperature data, it determines the melting start temperature of the current phase change material. The latent heat decay determination module is used in the heat collection stage. It determines the actual melting time based on the time it takes for the phase change material to go from the melting start temperature to the fully molten state, and determines a latent heat decay coefficient based on the actual melting time and the reference melting time. The supercooling determination module determines the supercooling of the phase change material during the heat release stage based on the changes in the internal temperature of the phase change thermal storage unit and the outlet water temperature at the user end. The control module is used to store / update the melting start temperature, latent heat decay coefficient, and subcooling, and to perform heat collection and release control based on the melting start temperature, latent heat decay coefficient, and subcooling. Beneficial effects

[0018] The solar phase change thermal storage coordinated control method disclosed in this application effectively solves the problem of data distortion caused by the "self-stratification" of phase change materials in existing technologies by introducing a calibration mode, ensuring accurate perception of the actual thermophysical state of the phase change material. Furthermore, during the heat collection stage, this method dynamically determines the latent heat decay coefficient based on the actual melting time of the phase change material from the melting initiation temperature to the fully melted state, combined with a reference melting time. This allows the system to assess the decay of the phase change material's heat storage capacity in real time, avoiding misjudgments of heat storage saturation due to material performance degradation, thus preventing the collector from prematurely stopping heating before the heat storage unit is saturated, effectively avoiding energy waste. During the heat release stage, this method accurately determines the supercooling of the phase change material based on the changes in the internal temperature of the phase change thermal storage unit and the outlet water temperature at the user end, enabling the system to grasp the crystallization characteristics of the phase change material in real time. This provides an accurate basis for subsequent supercooling intervention, ensuring that heat can be effectively released when needed. Ultimately, by storing and updating the melting initiation temperature, latent heat decay coefficient, and supercooling in real time, and using this as a basis for heat collection and release control, this method enables precise and coordinated control of the solar thermal energy system. This not only overcomes the control inaccuracy problem caused by changes in the properties of phase change materials in existing technologies, significantly improving the utilization efficiency and heat supply stability of solar thermal energy, but also avoids energy waste caused by misjudgments. Thus, it effectively solves the technical problems raised in the background art and achieves unexpected technical results. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the steps of the solar phase change thermal storage synergistic control method disclosed in the embodiments of the present invention; Figure 2 This is a schematic diagram of the solar phase change thermal storage collaborative control system disclosed in an embodiment of the present invention. Detailed Implementation

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these embodiments belong; the terminology used herein and in the specification of the application is for the purpose of describing particular embodiments only and is not intended to limit these embodiments; the terms "comprising" and "having," and any variations thereof, in the specification of these embodiments and the foregoing drawings, are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification of these embodiments and the foregoing drawings are used to distinguish different objects, not to describe a particular order.

[0022] The implementation details of the technical solution in this embodiment are described in detail below: This application discloses a solar phase change thermal storage synergistic control method applied to a solar thermal energy system. The solar thermal energy system includes a solar collector and a phase change thermal storage unit for storing heat. The phase change thermal storage unit contains a phase change material, such as... Figure 1 As shown, the method includes: S101, in response to the outlet heat transfer medium temperature of the solar collector being higher than the internal temperature of the phase change heat storage unit and reaching a preset temperature difference, enter the calibration mode, input heat to the phase change heat storage unit with a preset power, and simultaneously collect the internal temperature of the phase change heat storage unit to obtain first temperature data; determine the melting start temperature of the current phase change material based on the first temperature data. S102, heat collection stage, the actual melting time is determined based on the time taken for the phase change material to go from the melting start temperature to the fully melted state, and a latent heat decay coefficient is determined based on the actual melting time and the reference melting time. S103, heat release stage: the supercooling of the phase change material is determined based on the change between the internal temperature of the phase change heat storage unit and the outlet water temperature at the user end. S104, store / update the melting initiation temperature, latent heat decay coefficient, and subcooling, and perform heat collection and heat release control based on the melting initiation temperature, latent heat decay coefficient, and subcooling.

[0023] The embodiments of this application aim to solve the problem of temperature probe data distortion and control system misjudgment caused by the "self-stratification" phenomenon of phase change thermal energy storage materials due to long-term cyclic use in existing solar thermal energy systems. After the phase change material undergoes self-stratification, the temperature data measured by the preset temperature probes in traditional phase change thermal energy storage systems may not accurately represent the average thermal state of the entire phase change thermal energy storage unit, leading to misjudgment by the phase change platform identification program and premature termination of the heating cycle, resulting in energy waste and insufficient heat supply. To address this, this application proposes a solar phase change thermal energy storage collaborative control method. This method dynamically calibrates key thermophysical parameters of the phase change material, including melting initiation temperature, latent heat decay coefficient, and supercooling, and performs heat collection and release control based on these real-time updated parameters, thereby ensuring the effective utilization of the phase change thermal energy storage unit and the stability of the heat supply.

[0024] Specifically, regarding entering calibration mode and initial data acquisition, a fixed temperature difference threshold can be set. For example, when the temperature of the heat transfer medium at the solar collector outlet is consistently 5°C higher than the internal temperature of the phase change thermal storage unit, the system is triggered to enter calibration mode. In this mode, a constant preset power, such as 2kW, can be used to input heat into the phase change thermal storage unit. Simultaneously, temperature data is continuously collected at a fixed sampling frequency, such as once every 10 seconds, using a temperature probe pre-embedded inside the phase change thermal storage unit to obtain the initial temperature data.

[0025] Regarding the determination of the melting initiation temperature of current phase change materials, it can be based on the collected initial temperature data. By manually observing the temperature-time curve, a plateau region where the temperature rise rate significantly slows down and tends to stabilize can be identified, and the starting temperature of this plateau region can be taken as the melting initiation temperature. Alternatively, a simple temperature threshold can be used. For example, when the internal temperature of the phase change thermal storage unit reaches a certain preset temperature that is close to the nominal melting point of the phase change material, it can be preliminarily identified as the melting initiation temperature.

[0026] During the heat collection phase, a lookup table based on historical operating data can be pre-established to determine the latent heat decay coefficient. Once the actual melting time is measured, the corresponding latent heat decay coefficient is obtained by consulting this table and considering the correspondence between the actual melting time and the baseline melting time. For example, if the actual melting time is longer than the baseline melting time, the latent heat decay coefficient may be set to a value less than 1, and vice versa. During the heat release phase, the subcooling of the phase change material can be determined by continuously monitoring the internal temperature of the phase change thermal storage unit and the user-end outlet water temperature. When the internal temperature of the phase change thermal storage unit continues to decrease and the user-end outlet water temperature begins to show a stable upward trend, the internal temperature of the phase change thermal storage unit at this time is recorded. The difference between the previously determined melting initiation temperature and this recorded temperature is taken as the subcooling of the phase change material. The aforementioned parameters, such as melting initiation temperature, latent heat decay coefficient, and subcooling, are stored in the system's non-volatile memory and can be updated periodically or triggered by specific events. Based on these real-time or recently updated parameters, the system can perform heat collection and heat release control. For example, in heat collection control, the operating strategy of the heat collector can be adjusted based on the updated melting onset temperature and latent heat decay coefficient to ensure that the heat input matches the actual heat storage capacity of the phase change material. In heat release control, the start-up and shutdown strategy of the heat release circulation pump can be adjusted based on the updated subcooling to optimize heat output and avoid heat release delays or inadequacies caused by subcooling.

[0027] Specifically, the method logic of this embodiment can be divided into the following five aspects: 1. Trigger condition judgment and calibration mode start-up: On clear days, when the system's main controller (e.g., an STM32F4-based microcontroller) detects that the temperature of the heat transfer medium at the solar collector outlet (obtained via a PT1000 platinum resistance temperature sensor installed at the collector outlet) is higher than the current temperature of the phase change material inside the storage tank (obtained via a PT1000 temperature sensor installed in the middle of the storage tank) by a preset temperature difference (e.g., 10 degrees Celsius), the system does not immediately enter the regular heat collection mode. Instead, the main controller initiates a brief "material state calibration mode." In this mode, the collector circulation pump (e.g., a DC brushless inverter water pump) is instructed to operate at a preset, stable power (e.g., controlled by a pulse width modulation (PWM) signal to operate at 80% of its rated power) for a fixed period of time (e.g., 10 minutes). This preset power and time period are determined during the initial system design to ensure that the phase change material is heated uniformly and that the temperature change curve is sufficiently characteristic.

[0028] 2. Real-time data acquisition and online determination of phase transition temperature: During "Material State Calibration Mode" operation, the main controller continuously acquires and records readings from multiple temperature probes inside the regenerator (e.g., three PT1000 temperature sensors distributed at different heights within the regenerator, or a single representative temperature probe) at a high frequency (e.g., once per second). This temperature data is converted into digital signals by an analog-to-digital converter (ADC) module and stored in the microcontroller's memory. The main controller then analyzes the acquired temperature rise curves during this period by calculating the rate of temperature change over time (dT / dt), for example, by linearly fitting five consecutive seconds of temperature data to obtain the instantaneous rate of temperature change. The controller then identifies the point where the rate of temperature rise begins to slow significantly (i.e., dT / dt suddenly drops from a high value to a low value and remains at a plateau for a period). The temperature value corresponding to this point is determined as the actual melting initiation temperature of the current phase change material. This newly determined temperature value (e.g., 48.5 degrees Celsius) will be immediately stored in the controller's non-volatile memory (e.g., EEPROM) as the latest reference for subsequent heat collection and dissipation decisions, replacing the previously inaccurate preset value.

[0029] 3. Dynamic assessment of latent heat decay: After completing the calibration mode and entering the normal heat collection mode, the main controller continuously monitors and records the total time elapsed from the start of melting (i.e., the temperature of the heat storage tank reaches the actual melting start temperature determined in step 2) to complete melting (i.e., the temperature curve starts to rise rapidly again, indicating the end of the phase change plateau period and the material enters the sensible heat rise stage). This time is precisely measured by an internal timer. The controller compares this actual time with the baseline melting time of the system in its initial healthy state (e.g., the time required for complete melting measured at the factory, assumed to be 120 minutes) to calculate a relative coefficient reflecting the current degree of latent heat decay. The calculation formula is: Latent heat decay coefficient = (Actual melting time / Baseline melting time). For example, if the actual time is 100 minutes, the latent heat decay coefficient is 100 / 120 ≈ 0.83. This coefficient will be used to adjust subsequent judgments on heat storage saturation. For example, if the system continues to heat for 83% of the baseline time after reaching the new phase change temperature, it is considered that the latent heat capacity of the current material has been fully utilized, thereby ensuring that the system can make full use of the heat collected by the collector and avoid insufficient heat storage due to material decay.

[0030] 4. Real-time measurement of subcooling: When the system first starts its heat release cycle in the evening or at night (e.g., when a user turns on a hot water tap and the heat release cycle pump starts working), the main controller records the temperature difference between when the internal temperature of the heat storage tank is below the actual phase change temperature determined in step 2 (e.g., below 48.5 degrees Celsius) and when the outlet water temperature at the user end (obtained by a PT1000 temperature sensor installed on the outlet water pipe) begins to steadily rise (marking that the phase change material has begun to effectively crystallize and release latent heat). This temperature difference is determined as the actual subcooling of the phase change material. For example, if the outlet water temperature only begins to steadily rise when the heat storage tank temperature drops to 45 degrees Celsius, then the subcooling is 48.5 - 45 = 3.5 degrees Celsius. The supercooling value will be immediately stored in the controller's non-volatile memory and used to guide the strategy adjustment in the subsequent heat release stage. For example, when the temperature of the heat storage tank is detected to be lower than the actual phase change temperature but heat release has not yet started, if the supercooling exceeds a certain threshold (e.g., 2 degrees Celsius), active intervention measures (such as briefly starting the heat release circulation pump to generate fluid disturbance) may be triggered to break the supercooling state and ensure that the latent heat can be released in time.

[0031] 5. Parameter Update and Decision Optimization: After each calibration and measurement, the main controller immediately updates its internal control logic with the newly determined actual phase change temperature, latent heat decay coefficient, and subcooling, overwriting the original preset values. This ensures that subsequent heat collection processes (e.g., determining when to stop heat collection to avoid overheating or insufficient heat storage, or adjusting the operation strategy of the heat collection circulation pump to adapt to the new phase change temperature) and heat release processes (e.g., determining when to start auxiliary heating or take subcooling intervention measures, or adjusting the flow rate of the heat release circulation pump to maintain a stable outlet water temperature) are based on the latest and most accurate physical state of the phase change material. This real-time adjustment ensures that the system can still provide heat energy efficiently and stably during long-term operation, even if the performance of the phase change material changes, significantly improving user experience and overall system energy efficiency.

[0032] Based on the above logical process, the system performs a "self-check" every morning when it first collects solar heat. During this brief "check," the system operates in a specific manner (e.g., the water pump runs at a fixed power for a period of time) and carefully observes the temperature change curve in the heat storage tank. By analyzing this curve, the system can accurately determine the phase change material's current true "temperature" (actual phase change temperature), "energy" (latent heat storage capacity), and "state" (supercooling), much like a doctor diagnoses an illness. If the phase change material experiences slight internal component separation due to long-term use, causing its actual melting temperature to drop from 50 degrees Celsius to 48 degrees Celsius, a traditional system might assume 50 degrees Celsius is the "full" state and stop heating at 48 degrees Celsius, resulting in insufficient heat collection. This solution, however, after discovering the actual melting temperature is 48 degrees Celsius through the "check," informs the controller of this new value. The controller then uses 48 degrees Celsius to determine if the material is "fully charged," ensuring sufficient heat collection. Similarly, if the system detects an increase in the supercooling of the material, it will know that it needs to be "actively" "awakened" during heat release to ensure that the heat can be released smoothly.

[0033] This application's solution effectively solves the parameter inaccuracy problem caused by the self-delamination of phase change materials in traditional systems by dynamically calibrating the key thermophysical parameters of the phase change material. Compared to existing technologies that rely on fixed or preset parameters for control, this application can obtain real-time information on the actual state of the phase change material, such as its true melting initiation temperature, latent heat decay rate, and supercooling characteristics. It is precisely because of the dynamic updating and precise control of these parameters that the control system can optimize the heat collection and release processes based on the current performance of the phase change material, rather than its factory-specified performance. Through this technical solution, energy waste caused by misjudging the heat storage state of the phase change thermal energy storage unit can be avoided, ensuring that the solar thermal energy system can maintain a highly efficient and stable heat supply during long-term operation, thereby significantly improving the overall energy utilization efficiency and reliability of the system.

[0034] This application further proposes a solar phase change thermal storage synergistic control method, which optimizes the determination of latent heat attenuation coefficient and the execution of heat collection and release control to improve the system's adaptability and reliability.

[0035] Specifically, a latent heat decay coefficient is determined based on the actual melting time and the reference melting time, including: determining the ratio of the actual melting time to the reference melting time as the latent heat decay coefficient. The reference melting time refers to the time required for the phase change material to completely melt from its initial melting temperature at the time of manufacture; the initial melting temperature is the melting temperature set at the time of manufacture.

[0036] The step of performing heat collection and release control based on the melting initiation temperature, latent heat decay coefficient, and subcooling includes: determining the current heat storage saturation time based on the product of the latent heat decay coefficient and the reference melting time; and determining that heat storage is saturated when the continuous heating time reaches the current heat storage saturation time after the phase change heat storage unit reaches the melting initiation temperature.

[0037] When the internal temperature of the phase change heat storage unit is lower than the melting initiation temperature and has not entered the heat release stage, if the supercooling exceeds a preset threshold, supercooling intervention measures are taken; the supercooling intervention measures include briefly starting the heat release circulation pump to generate fluid disturbance.

[0038] This application's solution introduces a dynamic determination mechanism for the latent heat decay coefficient, enabling real-time reflection of the performance degradation of phase change materials. The ratio of the actual melting time to the baseline melting time is used as the latent heat decay coefficient, allowing the system to quantify the actual changes in the material's latent heat capacity. It is precisely this introduction of a dynamic decay coefficient that makes it possible to determine the current heat storage saturation time during the heat collection stage by multiplying the latent heat decay coefficient by the baseline melting time. This achieves accurate judgment of the heat storage saturation state of the phase change heat storage unit, avoiding overcharging or undercharging due to material performance degradation. Furthermore, during the heat release stage, when the internal temperature of the phase change heat storage unit is lower than the melting initiation temperature and has not yet entered the heat release stage, if the supercooling exceeds a preset threshold, a brief activation of the heat release circulation pump generates fluid disturbance, effectively breaking the supercooled state of the phase change material, promoting rapid crystallization and releasing latent heat, ensuring a timely and effective supply of heat.

[0039] Through the above technical solution, this application can dynamically adjust the heat storage saturation judgment standard according to the actual performance degradation of the phase change material, thereby improving the heat collection efficiency and the accuracy of heat storage. At the same time, by introducing supercooling intervention measures, the supercooling problem that may occur in the phase change material during the heat release process is effectively solved, ensuring the stable release of heat and significantly improving the operational reliability and user experience of the solar thermal energy system.

[0040] In some preferred embodiments, a specific example is given below. Assume a phase change material is factory-set to have an initial melting point of 50°C and a baseline melting time of 4 hours. After the system has been running for a period, the actual melting time required for the phase change material to completely melt from the initial melting point is measured to be 5 hours using calibration mode. At this point, the latent heat decay coefficient will be calculated as 5 hours / 4 hours = 1.25. In subsequent heat collection processes, the system will adjust the current heat storage saturation time to 1.25 * 4 hours = 5 hours based on this latent heat decay coefficient. This means that even if the internal temperature of the phase change heat storage unit reaches the initial melting point, the system will continue heating until the heating time reaches 5 hours to ensure that the phase change material fully stores heat, thereby adapting to the decay of material properties.

[0041] For example, during the heat release phase, when the internal temperature of the phase change thermal storage unit drops to 40°C (below the melting initiation temperature of 50°C) but the water temperature at the user end does not rise steadily, and the system detects that the supercooling (e.g., the difference between the melting initiation temperature and the current internal temperature) exceeds a preset threshold (e.g., 5°C), it indicates that the phase change material is in a supercooled state. At this time, the system will automatically and briefly start the heat release circulation pump to create disturbance in the fluid inside the phase change thermal storage unit. This disturbance can effectively induce the phase change material to crystallize, causing it to rapidly release latent heat, thereby avoiding the problem of ineffective heat utilization due to supercooling and ensuring a continuous and stable supply of hot water to the user end.

[0042] Specifically, in the above-mentioned solar phase change thermal storage synergistic control method, the step of determining the melting initiation temperature of the current phase change material based on the first temperature data can be further refined as follows.

[0043] Determining the melting initiation temperature of the current phase change material based on the first temperature data includes: obtaining the instantaneous temperature rise rate based on linear fitting of temperature data over a continuous short period of time in the first temperature data, identifying the inflection point where the instantaneous temperature rise rate drops sharply from a high value to a low value and enters a stable period, and determining the temperature corresponding to the inflection point as the melting initiation temperature of the phase change material.

[0044] The first temperature data refers to the real-time temperature data inside the phase change thermal storage unit when a preset power of heat is input into the unit during calibration mode. Processing this temperature data aims to accurately identify the melting initiation point of the phase change material. Specifically, linear fitting is a mathematical method used to find the optimal linear relationship between a set of data points, thereby calculating the rate of temperature change over a continuous short period, i.e., the instantaneous temperature rise rate. By performing linear fitting on the temperature data over a continuous short period, data noise can be effectively smoothed, and the trend of temperature rise can be reflected more accurately.

[0045] Furthermore, identifying the inflection point where the instantaneous temperature rise rate abruptly drops from a high value to a low value and enters a plateau period is a crucial step in determining the melting initiation temperature. Before the phase change material begins to melt, its temperature rises rapidly with the input of heat, at which point the instantaneous temperature rise rate is high. When the phase change material reaches the melting initiation temperature and begins to absorb latent heat, its temperature rise rate slows significantly, or even remains constant under ideal conditions, causing the instantaneous temperature rise rate to drop sharply and tend to stabilize. This transition point from the high-temperature rise rate to the low-temperature rise rate is the inflection point, which precisely indicates the temperature at which the phase change material begins to melt.

[0046] This application's solution achieves accurate identification of the melting initiation temperature of phase change materials (PCMs) through refined analysis of internal temperature data within the PCM unit. In calibration mode, when heat is input into the PCM unit, the temperature of the PCM gradually increases. Before the material reaches its melting point, its temperature rises rapidly, exhibiting a high instantaneous temperature rise rate. Once the material begins to melt and absorb latent heat, its sensible temperature rise significantly slows down, causing the instantaneous temperature rise rate to suddenly drop from a relatively high value to a lower value, subsequently entering a relatively stable phase, as most of the heat is used for phase change rather than sensible temperature rise. By identifying this "inflection point" of the instantaneous temperature rise rate—the moment when the temperature rise rate changes significantly—the melting initiation temperature of the PCM can be accurately determined. This method effectively distinguishes between the sensible temperature rise stage and the phase change endothermic stage, thus overcoming the inaccurate judgment problems that may arise from temperature fluctuations or measurement errors in traditional methods.

[0047] The above technical solution enables the dynamic and precise determination of the melting initiation temperature of phase change materials (PCMs) based on actual operational data. This method avoids errors that may arise from relying on preset or factory parameters, and provides a more accurate real-time melting initiation temperature, especially when the performance of PCMs degrades over time or environmental conditions change. This provides a more reliable reference parameter for subsequent heat collection and release control, thereby optimizing the overall operating efficiency and stability of the solar thermal energy system. A precise melting initiation temperature helps to more accurately determine the heat storage saturation state of the PCM unit, avoiding overcharging or undercharging, thus improving thermal energy utilization efficiency and user experience.

[0048] In some embodiments described above in this application, a method is proposed to determine the melting initiation temperature of a phase change material by acquiring temperature data in calibration mode and based on the inflection point of the instantaneous temperature rise rate. However, in practical applications, the properties of a phase change material may change slightly over time, cycle number, or thermal history, which may prevent a single daytime calibration method from fully capturing these dynamic changes, thereby affecting the accuracy of the melting initiation temperature determination and the robustness of the control.

[0049] In response, this application further proposes a method for coordinated control of solar phase change thermal storage, which also includes: During the nighttime cooling process, the internal temperature change of the phase change thermal storage unit is monitored to capture the solidification initiation temperature of the phase change material; In the daytime calibration mode on the following day, the power of the calibration mode is adjusted according to the solidification initiation temperature, and heat is input into the phase change heat storage unit. Temperature data of the phase change heat storage unit near the solidification initiation temperature is also collected. Using the solidification initiation temperature as a benchmark, the local average temperature rise rate is calculated by sliding window least squares fitting. When the average temperature rise rate is lower than a dynamic threshold for the first time and remains so for a period of time, the temperature corresponding to the average temperature rise rate is identified as the melting initiation temperature of the current phase change material.

[0050] Specifically, during the nighttime cooling process, the system continuously monitors the temperature change trend inside the phase change thermal storage unit. By analyzing the temperature drop curve, the solidification initiation temperature when the phase change material transitions from a liquid to a solid state can be identified. This solidification initiation temperature is an important manifestation of the inherent properties of the phase change material and is correlated with the melting initiation temperature. For example, the solidification initiation temperature can be captured by observing a sudden slowdown or plateau in the rate of temperature drop.

[0051] Furthermore, when the daytime calibration mode is activated the following day, the system uses the solidification initiation temperature captured the previous night as a reference. Based on this solidification initiation temperature, the heating power of the calibration mode can be dynamically adjusted to ensure more accurate heat input, allowing the temperature of the phase change thermal storage unit to smoothly pass through the region near the solidification initiation temperature. Simultaneously, temperature data acquisition will focus on the vicinity of the solidification initiation temperature to obtain more refined and representative temperature change data.

[0052] To more accurately determine the melting initiation temperature of the current phase change material, this application employs a sliding window least squares fitting method. Specifically, using the solidification initiation temperature as a benchmark, a sliding window is applied to the collected temperature data, and least squares linear fitting is performed on the temperature data within the window to calculate the local average temperature rise rate. When this local average temperature rise rate first falls below a preset dynamic threshold and remains below it for a period of time, it indicates that the phase change material has begun to undergo a phase change, and the corresponding temperature is confirmed as the melting initiation temperature of the current phase change material. This dynamic threshold can be set according to actual application requirements.

[0053] This application's solution effectively addresses the limitations of traditional single-day calibration methods by introducing monitoring of the nighttime solidification process and combining it with the determination of the melting onset temperature during the next day. Specifically, the melting and solidification of phase change materials (PCMs) are two closely related aspects of their phase change process. By monitoring the nighttime solidification onset temperature, the true phase change characteristics of the PCM during cooling can be obtained. This solidification onset temperature reflects the current state of the PCM, including any potential long-term degradation or thermal history effects.

[0054] In the daytime calibration mode of the following day, the heating power and data acquisition range are adjusted based on the solidification initiation temperature. This allows the system to more accurately focus on the melting region of the phase change material, avoiding unnecessary heating and data acquisition in non-critical temperature areas, thus improving calibration efficiency and accuracy. Simultaneously, a sliding window least squares fitting method is used to calculate the local average temperature rise rate, combined with a dynamic threshold for judgment. Compared to simple instantaneous temperature rise rate inflection point identification, this method more effectively filters out noise, improving the robustness and accuracy of the melting initiation temperature determination. This approach better adapts to the subtle characteristic changes that may occur in phase change materials during actual operation, ensuring that the determined melting initiation temperature more closely reflects the material's true state.

[0055] Through the above technical solution, this application can significantly improve the accuracy and robustness of determining the melting initiation temperature of phase change materials. By considering the characteristics of phase change materials during solidification and feeding them back into the determination of the melting initiation temperature, the system can better adapt to the long-term degradation, thermal history effects, and environmental changes of phase change materials. Therefore, the determined melting initiation temperature is more accurate, providing more reliable parameters for subsequent heat collection and release control, thereby optimizing the overall operating efficiency and stability of the solar thermal energy system, extending the service life of the phase change thermal storage unit, and improving the stability and comfort of heat supply to users.

[0056] In some preferred embodiments, a specific example is given below. Suppose that one night, the solar thermal system enters a cooling state. The control system continuously monitors the temperature sensor readings inside the phase change thermal storage unit. As the temperature gradually decreases from 50°C to 45°C, the system observes a sudden slowdown in the rate of temperature decrease, and a brief temperature plateau appears around 43°C, indicating that the phase change material has begun to solidify. At this point, the system detects the solidification initiation temperature of the phase change material as 43°C.

[0057] The following morning, when the system prepares to enter calibration mode, it utilizes the 43°C solidification onset temperature captured the previous night. Based on this temperature, the control system dynamically adjusts the power of the heat input to the phase change thermal storage unit. For example, it adjusts the heating power to keep the temperature rise rate relatively stable within the 40°C to 46°C range, and densely collects temperature data within this range. Subsequently, the system applies a sliding window least-squares fit to the collected temperature data. For example, using a 5-minute sliding window, the average temperature rise rate within each window is calculated. Assuming the average overnight cooling rate was 0.5°C / min, the dynamic threshold can be set to 0.1°C / min. When the local average temperature rise rate first drops from a high value (e.g., 0.8°C / min) and remains below 0.1°C / min, the system identifies the corresponding temperature, such as 48°C, and confirms it as the current melting onset temperature of the phase change material. In this way, even if the properties of the phase change material change slightly change due to long-term use, the system can adaptively determine its accurate melting onset temperature, thereby ensuring the accuracy of subsequent heat collection and release control.

[0058] In some of the above embodiments, in order to more accurately determine the melting initiation temperature of the phase change material, this application proposes a method for setting a dynamic threshold.

[0059] Specifically, the aforementioned dynamic threshold is set to 20%-30% of the average cooling rate during the previous night's cooling process. This means that during the nighttime cooling process, the system continuously monitors the temperature changes inside the phase change thermal storage unit and calculates the average cooling rate during that period. When entering calibration mode the following day, the dynamic threshold used to identify the melting initiation temperature of the phase change material will no longer be a fixed value, but will be dynamically adjusted based on the actual cooling situation of the previous night, specifically taking a value between 20% and 30% of the average cooling rate during that night.

[0060] The proposed solution makes the identification process for the melting initiation temperature more adaptive by correlating a dynamic threshold with the average nighttime cooling rate during the previous night's cooling process. The average cooling rate during the nighttime cooling process reflects a combination of factors, including the current ambient temperature, system heat dissipation characteristics, and the thermophysical properties of the phase change material itself. By setting the dynamic threshold based on this cooling rate, the failure of a fixed threshold due to factors such as ambient temperature fluctuations, phase change material performance degradation, or changes in system heat loss can be effectively avoided. When the local average temperature rise rate first falls below this dynamic threshold and remains below it for a period of time, it can be more accurately determined that the phase change material has entered the melting stage, thus determining its melting initiation temperature. This adaptive threshold setting method allows the system to dynamically adjust the identification criteria for the melting initiation temperature according to changes in actual operating conditions and material state, improving the accuracy and robustness of the identification.

[0061] Through the above technical solutions, the determination of the melting initiation temperature of phase change materials becomes more precise and adaptive. This helps the system to more accurately grasp the actual thermodynamic state of the phase change material, thus providing more reliable parameter basis for subsequent heat collection and release control. Therefore, it can effectively avoid insufficient heat storage or overheating caused by inaccurate identification of the melting initiation temperature, further improving the operating efficiency and stability of the solar thermal energy system and extending the service life of the phase change heat storage unit.

[0062] Specifically, in the aforementioned solar phase change thermal storage synergistic control method, the supercooling of the phase change material can be precisely determined. Determining the supercooling of the phase change material based on the changes in the internal temperature of the phase change thermal storage unit and the user-end outlet water temperature includes: controlling the internal temperature of the phase change thermal storage unit to continuously decrease to a first temperature so that the user-end outlet water temperature begins to rise steadily; then, the difference between the melting initiation temperature and the first temperature is determined as the supercooling of the phase change material.

[0063] The first temperature refers to the temperature at which the internal temperature of the phase change thermal storage unit continuously decreases during the heat release process, and when it reaches a certain specific temperature point, the water temperature at the user end begins to show a stable and observable upward trend. This phenomenon indicates that the phase change material has overcome the supercooling state, begun to undergo effective crystallization and release latent heat, thus significantly affecting the hot water supply at the user end. The melting initiation temperature is the temperature at which the phase change material begins to melt during the heat absorption process, and is usually considered to be the ideal phase change temperature of the material. The difference between the melting initiation temperature and the first temperature is defined as the supercooling of the phase change material, which aims to quantify the degree to which the internal temperature of the phase change material is lower than the theoretical phase change temperature and has not undergone phase change (i.e., supercooling) during the actual heat release process.

[0064] This application's solution achieves precise quantification of the supercooling degree of the phase change material (PCM) by combining the temperature drop inside the PCM unit with the actual response of the user-end outlet water temperature. When the PCM is supercooled, its internal temperature is below the melting initiation temperature but it remains in a liquid state, unable to effectively release latent heat. Only when the supercooling is overcome, and the PCM begins to crystallize and release latent heat, can the PCM unit provide stable heat to the user end, resulting in a stable increase in the user-end outlet water temperature. Therefore, by monitoring this inflection point of the user-end outlet water temperature change, the actual temperature at which the PCM begins to effectively crystallize, i.e., the first temperature, can be deduced. Thus, the difference between the melting initiation temperature and the first temperature accurately reflects the degree of supercooling of the PCM, providing a key parameter for subsequent control strategies.

[0065] The above technical solution provides an intuitive and reliable method for determining the supercooling of phase change materials based on actual system response. This method avoids potential misjudgments that may arise from relying solely on internal temperature sensors. Instead, it combines the actual heat demand at the user end with the system output effect, making the determination of supercooling more practical and accurate. This provides more precise parameters for subsequent heat collection and dissipation control, thereby optimizing the overall operating efficiency and user experience of the solar thermal energy system and ensuring the stability and continuity of heat supply.

[0066] This application further proposes a method for determining the undercooling of a phase change material, which includes: When the average internal temperature of the phase change heat storage unit enters the preset subcooling range, the crystallization state diagnosis mode is activated; the readings of multiple temperature probes inside the phase change heat storage unit are collected, and the temperature distribution uniformity is calculated. The control command heat exchange circulation pump operates in a preset pulse mode, generating fluid disturbance inside the phase change heat storage unit. Within a specific time period after the fluid disturbance is applied, the readings of all temperature probes inside the phase change heat storage unit are continuously collected and recorded, and the uniformity of temperature distribution after the disturbance is calculated. By comparing the difference in temperature distribution uniformity before and after the disturbance, it can be determined whether the phase change material in the phase change heat storage unit has overcome supercooling and begun to crystallize effectively. Based on the judgment result, update the current crystallization state information of the phase change material, and record the average internal temperature of the phase change heat storage unit as the actual effective solidification initiation temperature. If the internal temperature of the phase change thermal storage unit is continuously reduced to a second temperature so that the water temperature at the user end begins to rise steadily, then the difference between the effective solidification initiation temperature and the second temperature is determined as the supercooling of the phase change material.

[0067] Specifically, when the average internal temperature of the phase change thermal storage unit enters a preset supercooled range, a crystallization state diagnostic mode is activated. This preset supercooled range can be understood as a temperature range below the theoretical solidification temperature of the phase change material, for example, it can be set to a range of 5°C to 15°C below the theoretical solidification temperature. The purpose is to promptly initiate diagnosis and intervention when the phase change material may be supercooled but has not yet fully solidified. Multiple temperature probes inside the phase change thermal storage unit can be arranged at different locations within the unit, for example, uniformly distributed along the height and radial directions, to obtain temperature distribution information within the phase change material. The uniformity of the temperature distribution can be measured by calculating statistical quantities such as the standard deviation, maximum temperature difference, or coefficient of variation of these temperature probe readings. The purpose is to assess the uniformity of the temperature field inside the phase change material, thereby indirectly reflecting its crystallization state.

[0068] The control command for the exothermic circulation pump operates in a preset pulse mode, generating fluid disturbance within the phase change thermal storage unit. This preset pulse mode can be understood as the circulation pump intermittently starting and stopping, for example, operating at a specific frequency and duty cycle. Its purpose is to provide additional nucleation sites for the phase change material or promote the growth of existing crystal nuclei through fluid flow and shear force, thereby helping it overcome supercooling. The specific time period following the application of the fluid disturbance, for example, can be set to several seconds to several minutes, to give the phase change material sufficient time to respond to the disturbance and begin crystallization. During this time period, readings from all temperature probes are continuously acquired and recorded, and the uniformity of the temperature distribution after the disturbance is calculated, aiming to capture the impact of the disturbance on the crystallization state of the phase change material.

[0069] In practical applications, by comparing the difference in temperature distribution uniformity before and after the disturbance, it is determined whether the phase change material (PCM) within the PCM thermal storage unit has overcome supercooling and begun effective crystallization. For example, if the temperature distribution uniformity significantly improves after the disturbance (e.g., the standard deviation decreases significantly), it indicates that the PCM has begun effective crystallization, because the heat released during crystallization will cause the temperature to tend towards uniformity. Based on the determination result, the current crystallization state information of the PCM is updated, and the average internal temperature of the PCM is recorded as the actual effective solidification initiation temperature. The effective solidification initiation temperature refers to the temperature at which the PCM actually begins to crystallize in large quantities and release latent heat after overcoming supercooling; its purpose is to provide a more accurate solidification reference point.

[0070] Furthermore, by controlling the internal temperature of the phase change thermal storage unit to continuously decrease to a second temperature so that the water temperature at the user end begins to rise steadily, the difference between the effective solidification initiation temperature and the second temperature is determined as the subcooling of the phase change material. The second temperature can be understood as the temperature at which the internal temperature of the phase change thermal storage unit decreases to a certain level, allowing the user end to stably obtain the required heat. Its purpose is to determine the subcooling in conjunction with the actual heating effect.

[0071] This application's solution introduces a crystallization state diagnostic mode, enabling proactive monitoring and intervention of supercooling in phase change materials (PCMs). Specifically, by initiating diagnostics within a preset supercooling range and utilizing multiple temperature probes to collect temperature distribution uniformity data, the crystallization state of the PCM can be assessed more precisely. When supercooling is detected, controlling the exothermic circulation pump to operate in a preset pulse mode generates fluid disturbance, effectively promoting the crystallization process of the PCM and helping it overcome supercooling. By comparing the difference in temperature distribution uniformity before and after the disturbance, it is possible to accurately determine whether the PCM has begun effective crystallization, thereby obtaining the actual effective solidification initiation temperature. Therefore, the supercooling calculated based on this effective solidification initiation temperature more accurately reflects the actual heat release capacity of the PCM, providing a more accurate basis for subsequent exothermic control.

[0072] Through the above technical solution, this application can more accurately diagnose the crystallization state of phase change materials and effectively overcome their supercooling phenomenon, thereby ensuring that the phase change materials can release latent heat in a timely and effective manner. This not only improves the heat release efficiency and stability of the phase change thermal storage unit, but also enables the system to more precisely control the heat release process, avoiding energy loss or insufficient heating caused by supercooling, thereby improving the operational reliability and user experience of the entire solar thermal energy system.

[0073] In some preferred embodiments, a specific example is given below. Assume a solar thermal system uses paraffin as the phase change material, with a theoretical solidification temperature of 50°C. During the heat release phase, when the average internal temperature of the phase change thermal storage unit drops to 45°C (a preset subcooling range), the system activates a crystallization state diagnostic mode. At this time, the system collects readings from multiple temperature probes inside the phase change thermal storage unit (e.g., five probes distributed at different heights and radial positions) and calculates the standard deviation of its temperature distribution, for example, 2°C, as an indicator of uniformity before disturbance. Subsequently, the heat release circulation pump is controlled to operate in a pulse mode, starting for 0.5 seconds and stopping for 1 second per second, for 30 seconds to generate a slight fluid disturbance in the phase change material. For a specific time period after the disturbance is applied (e.g., within one minute immediately after the disturbance ends), the system continuously collects and records the readings of all temperature probes and recalculates the standard deviation of the temperature distribution, for example, 0.5°C. Comparative analysis revealed a significant improvement in temperature distribution uniformity after perturbation (standard deviation decreased from 2℃ to 0.5℃), indicating that the phase change material (PCM) had successfully overcome supercooling and begun effective crystallization. At this point, the recorded average internal temperature of the PCM unit, for example, 48℃, was determined as the actual effective solidification initiation temperature. Subsequently, when the internal temperature of the PCM unit continued to decrease to 40℃, the user-end outlet water temperature began to rise steadily. The difference of 8℃ between 48℃ and 40℃ was then determined as the current supercooling of the PCM. In this way, the system can dynamically and accurately assess and manage the supercooling state of the PCM, ensuring efficient heat release.

[0074] This application further proposes a scheme for evaluating the control effect and dynamically adjusting parameters after implementing the above-mentioned heat collection and release control, to ensure long-term stable and efficient operation of the system. Specifically, after implementing heat collection and release control based on the above-mentioned melting initiation temperature, latent heat decay coefficient, and subcooling, the method further includes: Real-time monitoring of the energy conversion efficiency between the heat collected by the solar collector and the actual heat stored by the phase change thermal storage unit; real-time monitoring of the stability of the water temperature at the user end and the duration of heat supply; The effectiveness of the heat collection and release control is evaluated based on the energy conversion efficiency, the stability of the outlet water temperature, and the duration of the heat supply. Based on the effectiveness assessment results, the parameters for heat collection and heat release control are dynamically adjusted.

[0075] Specifically, real-time monitoring of the energy conversion efficiency between the heat collected by the solar collector and the actual heat stored by the phase change thermal storage unit refers to calculating the collected heat by measuring the flow rate of the heat transfer medium at the solar collector outlet and the inlet-outlet temperature difference, while estimating the stored heat by monitoring the internal temperature changes of the phase change thermal storage unit and the phase change enthalpy of the phase change material. The energy conversion efficiency can be calculated as the ratio of the heat stored in the phase change thermal storage unit to the heat collected by the solar collector, aiming to quantify the system's efficiency in absorbing and converting solar energy into usable heat energy. Real-time monitoring of the stability of the user-end outlet water temperature and the duration of heat supply refers to continuously acquiring temperature sensor readings on the user-end outlet water pipeline and recording the total duration of heat supply from start to finish. The stability of the outlet water temperature can be assessed by calculating its average value and fluctuation range, while the supply duration directly reflects the system's ability to meet user needs.

[0076] Furthermore, the effectiveness of heat collection and release control is evaluated based on the monitored energy conversion efficiency, the stability of the user-end water temperature, and the duration of heat supply. This evaluation process may involve comparing current performance indicators with preset benchmark values, historical data, or user demand ranges. For example, if the energy conversion efficiency remains below a certain threshold, or if the fluctuation of the user-end water temperature exceeds an acceptable range, it indicates that the current heat collection and release control strategy may be inadequate.

[0077] Therefore, based on the effectiveness assessment results, the parameters for heat collection and release control can be dynamically adjusted. These parameters may include, but are not limited to, the operating power and flow rate setting of the heat collection circulation pump, the charging and releasing temperature thresholds of the phase change thermal storage unit, and the start-stop logic or flow rate of the heat release circulation pump. Through this dynamic adjustment, the system can adaptively optimize its operating strategy to cope with environmental changes, material performance degradation, or fluctuations in user demand, thereby ensuring that the system always operates in an optimal state.

[0078] This application's solution overcomes the limitations of traditional control schemes by introducing a real-time monitoring, evaluation, and dynamic adjustment mechanism for the control effects of heat collection and release. By continuously monitoring energy conversion efficiency, the system can promptly detect and correct energy losses during heat collection and storage, ensuring efficient utilization of solar energy. Simultaneously, monitoring the stability of the user-end outlet water temperature and the duration of heat supply allows the system to directly respond to user needs, guaranteeing the comfort and reliability of heating. Through comprehensive evaluation of these key performance indicators, the system can identify shortcomings in the current control strategy and dynamically adjust parameters accordingly. This closed-loop feedback and optimization mechanism enables the heat collection and release control strategy to adaptively optimize itself based on changes in system operating status, environmental conditions, and the characteristics of the phase change material, thereby significantly improving the long-term operating efficiency, stability, and user satisfaction of the solar phase change thermal storage system.

[0079] As a specific implementation, suppose a solar phase change thermal storage system has been operating for several years. In the initial stage, the heat collection and release control parameters are set based on the characteristics of the new phase change material (such as melting onset temperature, latent heat decay coefficient, and subcooling). However, over time, the phase change material may experience slight performance degradation, or the efficiency of the solar collector may decrease slightly due to dust accumulation. In this case, without an additional feedback mechanism, the system may continue to operate according to the old parameters, leading to a gradual decrease in energy conversion efficiency and potentially affecting the stability of the user-end outlet water temperature, such as causing small fluctuations or a shortened heat supply duration.

[0080] The proposed solution allows the system to monitor in real time the energy conversion efficiency between the heat collected by the solar collector and the actual heat stored by the phase change thermal storage unit, as well as the stability of the user-end outlet water temperature and the duration of heat supply. When the system detects that the energy conversion efficiency is below a preset optimization threshold for several consecutive days (e.g., a 5% decrease from the initial efficiency) and the fluctuation range of the user-end outlet water temperature exceeds the normal range, the system will initiate an assessment of the effectiveness of the current heat collection and release control. The assessment results may indicate that the current collector temperature setpoint is insufficient to fully utilize solar energy, or that the operation strategy of the heat release circulation pump has failed to effectively mitigate outlet water temperature fluctuations.

[0081] Based on this assessment, the system will dynamically adjust the parameters for heat collection and release control. For example, the system may slightly increase the target outlet temperature of the solar collector to ensure that more heat is effectively collected; or adjust the operating frequency or flow rate of the heat release circulation pump to more precisely control the heat release rate of the phase change thermal storage unit, thereby stabilizing the outlet water temperature at the user end. This adaptive adjustment process requires no manual intervention, enabling the system to continuously optimize its performance and maintain efficient and stable operation even under material aging or changes in external conditions, thereby extending the service life of the phase change thermal storage system and improving overall economic benefits.

[0082] Specifically, in the aforementioned solar phase change thermal storage synergistic control method, the real-time monitoring of the stability of the user-end outlet water temperature and the duration of the heat supply may include the following steps: Real-time monitoring of readings from multiple temperature sensors and flow sensors on the user's water outlet pipeline; Based on the readings of the multiple temperature sensors and the flow sensor, the average temperature and temperature fluctuation range of the water outlet at the user end are calculated in real time; the total duration from the start to the end of the heat supply is recorded. The average temperature, the temperature fluctuation range, and the total duration are compared with a preset dynamic user demand range to evaluate the stability of the outlet water temperature and the duration of heat supply.

[0083] The user-end water outlet pipe can be equipped with multiple temperature sensors and at least one flow sensor. These sensors are used to acquire real-time temperature and flow information of the water outlet. For example, multiple temperature sensors can be arranged at different locations on the outlet pipe to capture local differences and overall trends in water temperature. The flow sensor is used to measure the amount of water flowing through the pipe.

[0084] Furthermore, after acquiring the readings from the multiple temperature sensors and the flow sensor, these data can be processed. Specifically, the average temperature of the water outlet at the user end can be obtained by averaging the readings from the multiple temperature sensors, while the temperature fluctuation range can be determined by calculating the difference or standard deviation between the highest and lowest temperatures. Simultaneously, the system records the entire time period from the start to the end of the heat supply to obtain the total duration of the heat supply.

[0085] Furthermore, the preset dynamic user demand range can be set according to actual application scenarios, user habits, or system design requirements. This range can include specific requirements or expected values ​​for the average outlet water temperature, temperature fluctuation range, and heat supply duration. By comparing the real-time calculated average temperature, temperature fluctuation range, and total duration with this preset range, the stability of the user-end outlet water temperature and the duration of heat supply can be quantitatively evaluated.

[0086] This application's solution, by deploying multiple temperature and flow sensors on the user-end water outlet pipeline, can comprehensively and in real-time acquire temperature and flow data of the user-end water. Through real-time calculation of this data, the average temperature and temperature fluctuations of the user-end water, as well as the duration of heat supply, can be accurately determined. This detailed data acquisition and analysis mechanism allows the system to objectively evaluate the quality and continuity of heat supply based on actual user demand ranges. Therefore, it ensures that the system not only provides heat, but also that the heat provided meets the user's actual needs in terms of temperature stability and duration, thus providing a reliable basis for subsequent control parameter adjustments.

[0087] The above technical solution enables refined monitoring and evaluation of the stability of the water temperature at the user end and the duration of heat supply. Compared to monitoring only a single temperature point or simple timing methods, this solution, by introducing multiple temperature and flow sensors and combining them with comprehensive calculations of average temperature, temperature fluctuation range, and total duration, can more comprehensively and accurately reflect the actual user experience. This effectively avoids user discomfort caused by large temperature fluctuations or insufficient supply time, significantly improves user satisfaction with the solar thermal energy system, and provides more precise feedback for dynamically adjusting the heat collection and release control parameters, thereby optimizing the overall system operating efficiency and user experience.

[0088] Furthermore, specific embodiments of this application also disclose a solar phase change thermal storage co-control system applied to a solar thermal energy system. The solar thermal energy system includes a solar collector and a phase change thermal storage unit for storing heat. The phase change thermal storage unit contains a phase change material, such as... Figure 2 As shown, the system includes: The calibration and determination module 201 is used to enter the calibration mode when the outlet heat transfer medium temperature of the solar collector is higher than the internal temperature of the phase change heat storage unit and reaches a preset temperature difference, and input heat to the phase change heat storage unit with a preset power, while collecting the internal temperature of the phase change heat storage unit to obtain first temperature data; and determine the melting start temperature of the current phase change material based on the first temperature data. The latent heat decay determination module 202 is used in the heat collection stage to determine the actual melting time based on the time taken for the phase change material to go from the melting start temperature to the fully melted state, and to determine a latent heat decay coefficient based on the actual melting time and the reference melting time. The supercooling determination module 203 determines the supercooling of the phase change material during the heat release stage based on the change between the internal temperature of the phase change heat storage unit and the outlet water temperature at the user end. The control module 204 is used to store / update the melting start temperature, latent heat decay coefficient, and subcooling, and to perform heat collection and heat release control based on the melting start temperature, latent heat decay coefficient, and subcooling.

[0089] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for coordinated control of solar phase change thermal storage, applied to a solar thermal energy system, the solar thermal energy system comprising a solar collector and a phase change thermal storage unit for storing heat, the phase change thermal storage unit containing a phase change material, characterized in that, The method includes: When the outlet heat transfer medium temperature of the solar collector is higher than the internal temperature of the phase change heat storage unit and reaches a preset temperature difference, the system enters calibration mode and inputs heat to the phase change heat storage unit at a preset power. At the same time, the system collects the internal temperature of the phase change heat storage unit to obtain first temperature data. Based on the first temperature data, the system determines the melting initiation temperature of the current phase change material. During the heat collection stage, the actual melting time is determined based on the time taken for the phase change material to reach a fully melted state from the melting initiation temperature, and a latent heat decay coefficient is determined based on the actual melting time and the reference melting time. During the heat release phase, the supercooling of the phase change material is determined based on the changes in the internal temperature of the phase change heat storage unit and the outlet water temperature at the user end. Store / update the melting initiation temperature, latent heat decay coefficient, and subcooling, and perform heat collection and release control based on the melting initiation temperature, latent heat decay coefficient, and subcooling.

2. The solar phase change thermal storage synergistic control method according to claim 1, characterized in that, Determining a latent heat decay coefficient based on the actual melting time and the reference melting time includes: determining the ratio of the actual melting time to the reference melting time as the latent heat decay coefficient; the reference melting time is the time required for complete melting from the initial melting temperature at the time of manufacture; the initial melting temperature is the melting temperature set at the time of manufacture of the material. The step of controlling heat collection and release based on the melting initiation temperature, latent heat decay coefficient, and subcooling includes: The current heat storage saturation time is determined by the product of the latent heat decay coefficient and the reference melting time; if the heating time continues until the current heat storage saturation time is reached after the phase change heat storage unit reaches the melting start temperature, then the heat storage is judged to be saturated. When the internal temperature of the phase change heat storage unit is lower than the melting initiation temperature and has not entered the heat release stage, if the supercooling exceeds a preset threshold, supercooling intervention measures are taken; the supercooling intervention measures include briefly starting the heat release circulation pump to generate fluid disturbance.

3. The solar phase change thermal storage synergistic control method according to claim 1, characterized in that, Based on the first temperature data, the melting initiation temperature of the current phase change material is determined, including: The instantaneous temperature rise rate is obtained by linear fitting of temperature data over a continuous short period of time in the first temperature data, and the inflection point where the instantaneous temperature rise rate drops sharply from a high value to a low value and enters a stable period is identified. The temperature corresponding to the inflection point is determined as the melting start temperature of the phase change material.

4. A method for coordinated control of solar phase change thermal storage according to any one of claims 1-3, characterized in that, The method further includes: During the nighttime cooling process, the internal temperature change of the phase change heat storage unit is monitored to capture the solidification initiation temperature of the phase change material; In the daytime calibration mode of the following day, the power of the calibration mode is adjusted according to the solidification initiation temperature, and heat is input to the phase change heat storage unit, and temperature data of the phase change heat storage unit near the solidification initiation temperature is collected. Using the solidification initiation temperature as a reference, the local average temperature rise rate is calculated by sliding window least squares fitting. When the average temperature rise rate is lower than a dynamic threshold for the first time and continues for a period of time, the temperature corresponding to the average temperature rise rate is confirmed as the melting initiation temperature of the current phase change material.

5. The solar phase change thermal storage synergistic control method according to claim 4, characterized in that, The dynamic threshold is 20%-30% of the average nighttime cooling rate during the previous night's cooling process.

6. The solar phase change thermal storage synergistic control method according to claim 1, characterized in that, The supercooling of the phase change material is determined based on the changes in the internal temperature of the phase change heat storage unit and the outlet water temperature at the user end. This includes controlling the internal temperature of the phase change heat storage unit to continuously decrease to a first temperature so that the outlet water temperature at the user end begins to rise steadily. The difference between the melting initiation temperature and the first temperature is then determined as the supercooling of the phase change material.

7. The solar phase change thermal storage synergistic control method according to claim 1, characterized in that, The subcooling of the phase change material is determined based on the change in internal temperature of the phase change thermal storage unit and the temperature of the water outlet at the user end, including: When the average internal temperature of the phase change heat storage unit enters the preset subcooling range, the crystallization state diagnosis mode is activated; the readings of multiple temperature probes inside the phase change heat storage unit are collected, and the temperature distribution uniformity is calculated. The control command heat exchange circulation pump operates in a preset pulse mode, generating fluid disturbance inside the phase change heat storage unit. Within a specific time period after the fluid disturbance is applied, the readings of all temperature probes inside the phase change heat storage unit are continuously collected and recorded, and the uniformity of temperature distribution after the disturbance is calculated. By comparing the difference in temperature distribution uniformity before and after the disturbance, it can be determined whether the phase change material in the phase change heat storage unit has overcome supercooling and begun to crystallize effectively. Based on the judgment result, update the current crystallization state information of the phase change material, and record the average internal temperature of the phase change heat storage unit as the actual effective solidification initiation temperature. If the internal temperature of the phase change thermal storage unit is continuously reduced to a second temperature so that the water temperature at the user end begins to rise steadily, then the difference between the effective solidification initiation temperature and the second temperature is determined as the supercooling of the phase change material.

8. A method for coordinated control of solar phase change thermal storage according to any one of claims 6-7, characterized in that, Based on the melting initiation temperature, latent heat decay coefficient, and subcooling, heat collection and release control are performed. The method then further includes: Real-time monitoring of the energy conversion efficiency between the heat collected by the solar collector and the actual heat stored by the phase change thermal storage unit; real-time monitoring of the stability of the water temperature at the user end and the duration of heat supply; The effectiveness of the heat collection and release control is evaluated based on the energy conversion efficiency, the stability of the outlet water temperature, and the duration of the heat supply. Based on the effectiveness assessment results, the parameters for heat collection and heat release control are dynamically adjusted.

9. The solar phase change thermal storage synergistic control method according to claim 8, characterized in that, The real-time monitoring of the stability of the water temperature at the user end and the duration of the heat supply includes: Real-time monitoring of readings from multiple temperature sensors and flow sensors on the user's water outlet pipeline; Based on the readings of the multiple temperature sensors and the flow sensor, the average temperature and temperature fluctuation range of the water outlet at the user end are calculated in real time; the total duration from the start to the end of the heat supply is recorded. The average temperature, the temperature fluctuation range, and the total duration are compared with a preset dynamic user demand range to evaluate the stability of the outlet water temperature and the duration of heat supply.

10. A solar phase change thermal storage co-control system, applied to a solar thermal energy system, the solar thermal energy system comprising a solar collector and a phase change thermal storage unit for storing heat, the phase change thermal storage unit containing a phase change material, characterized in that, The system includes: The calibration and determination module is used to enter calibration mode when the outlet heat transfer medium temperature of the solar collector is higher than the internal temperature of the phase change heat storage unit and reaches a preset temperature difference. It inputs heat to the phase change heat storage unit with a preset power and collects the internal temperature of the phase change heat storage unit to obtain first temperature data. Based on the first temperature data, it determines the melting start temperature of the current phase change material. The latent heat decay determination module is used in the heat collection stage to determine the actual melting time based on the time taken for the phase change material to go from the melting start temperature to the fully melted state, and to determine a latent heat decay coefficient based on the actual melting time and the reference melting time. The supercooling determination module, during the heat release stage, determines the supercooling of the phase change material based on the change between the internal temperature of the phase change heat storage unit and the outlet water temperature at the user end. The control module is used to store / update the melting initiation temperature, latent heat decay coefficient, and subcooling, and to perform heat collection and release control based on the melting initiation temperature, latent heat decay coefficient, and subcooling.

Images