Photovoltaic-photothermal integrated water heater heating performance test method

Abstract

This invention discloses a method for testing the heating performance of a photovoltaic-thermal integrated water heater, relating to the field of water heater testing. The photovoltaic-thermal integrated water heater includes a hot water storage tank and a photovoltaic-thermal integrated module. The testing method includes: circulating water at a temperature not lower than 20°C in the hot water storage tank at a flow rate of 400L / h to 600L / h; determining the effective inlet temperature of the hot water storage tank as the inlet temperature if the temperature change at the inlet does not exceed 1°C within at least 5 minutes; starting the heating mode of the photovoltaic-thermal integrated water heater, stopping heating after 8 hours, and shielding the photovoltaic-thermal integrated module; starting the mixing pump located in the hot water storage tank to mix the water in the tank and obtaining the effective outlet temperature of the hot water storage tank; determining the daily heat gain value based on the effective inlet and outlet temperatures. This invention has the advantage of improving testing accuracy.

Description

Technical Field

[0001] This invention relates to the field of water heater testing technology, and specifically to a method for testing the heating performance of a photovoltaic-thermal integrated water heater. Background Technology

[0002] With the widespread application of photovoltaic (PV) and solar thermal water heaters in the renewable energy sector, performance evaluation technology has become a key factor restricting the industry's development. Existing testing systems have significant limitations in environmental simulation, data acquisition, and efficiency assessment, making it difficult for test results to accurately reflect actual operating conditions. For example, initial conditions (such as the temperature of the hot water tank and the inlet cold water temperature) lack precise control, resulting in large parameter fluctuations and a lack of unified standards, leading to poor data comparability between different test batches or devices. Dynamic monitoring capabilities are insufficient, relying solely on low-frequency sampling or key node recordings, failing to capture transient changes during heat output and thus failing to comprehensively reflect the system's thermal response characteristics. Furthermore, existing methods generally ignore heat loss factors such as insulation loss and pipe heat dissipation during the heat output process, resulting in inflated heat output rate calculations that fail to accurately reflect performance under actual usage scenarios.

[0003] The aforementioned problems collectively lead to low reliability and poor data comparability in the performance test results of photovoltaic thermal water heaters, making it difficult to meet the needs of product design optimization and market access certification. There is an urgent need to establish standardized and high-precision testing methods to scientifically evaluate the system's heat output performance. Summary of the Invention

[0004] This invention aims to address one of the technical problems in related technologies to a certain extent. To this end, this invention provides a method for testing the heating performance of a photovoltaic-thermal integrated water heater, which has the advantage of improving test accuracy.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for testing the heating performance of a photovoltaic-thermal integrated water heater, wherein the photovoltaic-thermal integrated water heater includes a hot water storage tank and a photovoltaic-thermal integrated module, and the testing method includes:

[0007] Water at a temperature of not less than 20℃ is used to circulate water in the hot water storage tank at a flow rate of 400L / h to 600L / h.

[0008] If the temperature change at the inlet of the hot water storage tank is no greater than 0.1℃ within at least 5 minutes, the inlet temperature is determined as the effective inlet temperature of the hot water storage tank.

[0009] The heating mode of the photovoltaic-thermal integrated water heater is activated, and heating is stopped after 8 hours. The photovoltaic-thermal integrated module is then shielded.

[0010] Start the mixing pump located in the hot water storage tank to mix the water in the hot water storage tank and obtain the effective outlet temperature of the hot water storage tank.

[0011] The daily heat gain value is determined based on the effective inlet temperature and the effective outlet temperature; wherein, the daily heat gain value is one of the performance indicators of heating performance.

[0012] By circulating water at a temperature no lower than 20℃ and ensuring the inlet temperature of the hot water storage tank fluctuates within ±0.1℃ over 5 minutes, a consistent water temperature at the start of heating is guaranteed, eliminating the impact of initial temperature differences on test results. Furthermore, a mixing pump draws water from the bottom of the storage tank to the top for circulation, avoiding measurement errors caused by temperature stratification. The inlet water flow rate is set to 400L / h~600L / h to prevent uneven water temperature distribution or changes in heat exchange efficiency due to excessive flow fluctuations, further ensuring the stability of test conditions. In addition, the average temperature over 5 minutes is used as the water temperature at the start and end of heating, avoiding the influence of instantaneous temperature fluctuations on the results. Strict control of each step reduces errors caused by operational differences, improving the accuracy of test results.

[0013] Optionally, obtaining the effective outlet temperature of the hot water storage tank includes:

[0014] The outlet temperature of the hot water storage tank is continuously acquired. If the outlet temperature of the hot water storage tank changes by no more than 0.1℃ within at least 5 minutes, the outlet temperature is determined as the effective outlet temperature of the hot water storage tank.

[0015] The formula for calculating the daily calorie gain is shown in formula (1):

[0016] (1)

[0017] Where c pw The specific heat capacity of water at constant pressure, t e For the effective outlet temperature, t b The effective inlet temperature is denoted by m, which represents the total mass of water in the storage tank, expressed in kilograms (Kg).

[0018] Optionally, the heating mode includes a photovoltaic heating mode, a solar thermal heating mode, and a photovoltaic-solar integrated heating mode; wherein, the solar thermal heating mode includes any one of photovoltaic short-circuit condition, photovoltaic open-circuit condition, and photovoltaic load condition;

[0019] When the heating mode is photovoltaic heating mode, activating the heating mode of the photovoltaic-thermal integrated water heater includes: connecting the photovoltaic-thermal integrated module to an electric heater;

[0020] When the heating mode is solar thermal heating mode, the process of activating the heating mode of the photovoltaic-thermal integrated water heater includes: connecting the positive and negative cables of the photovoltaic-thermal integrated module under photovoltaic short-circuit conditions; disconnecting the positive and negative terminals of the photovoltaic-thermal integrated module under photovoltaic open-circuit conditions; and connecting the positive and negative terminals of the photovoltaic-thermal integrated module to a pure resistance module under photovoltaic load conditions, and immersing the pure resistance module in a constant temperature water tank.

[0021] When the heating mode is photovoltaic-thermal heating mode, starting the heating mode of the photovoltaic-thermal integrated water heater includes: connecting the photovoltaic-thermal integrated component to the electric heating and connecting the direct photovoltaic heating circulation pipeline.

[0022] Optionally, the performance indicators also include a daily solar irradiance of 5 kWh / m² on the surface of the photovoltaic-thermal integrated module. 2 The nominal daily heat gain per unit photovoltaic installation area is calculated using the formula shown in formula (2):

[0023] (2)

[0024] Where H represents the daily solar irradiance on the surface of the photovoltaic-thermal integrated module, in kWh / m². 2 A represents the area of ​​the light-receiving surface of the photovoltaic-thermal integrated module, in square meters (㎡).

[0025] Optionally, the performance indicators also include a daily solar irradiance of 5 kWh / m² on the surface of the photovoltaic-thermal integrated module. 2 The nominal daily heat gain per unit photovoltaic installation capacity is calculated using the formula shown in formula (3):

[0026] (3)

[0027] Where H represents the daily solar irradiance on the surface of the photovoltaic-thermal integrated module, in kWh / m². 2 P peak The measured value of the photovoltaic installation capacity is expressed in watts (W).

[0028] Optionally, obtaining the effective outlet temperature of the hot water storage tank includes:

[0029] Water of different temperatures is continuously injected into the inlet of the hot water storage tank, and hot water in the hot water storage tank is discharged from the outlet of the hot water storage tank at a constant flow rate. The temperature of the discharged water is measured at least once every second until the volume of the discharged water is greater than three times the volume of the hot water storage tank and the temperature difference between the discharged water and the inlet water is less than 1°C. The temperatures of the discharged water are determined as multiple effective outlet temperatures.

[0030] The formula for calculating the daily calorie gain is shown in formula (4):

[0031] (4)

[0032] Where T1 is the temperature of the inlet water, T2 is the effective outlet water temperature, and C is the specific heat capacity of water at constant pressure. The mass flow rate of the water at the outlet is expressed in kilograms per second (kg / s).

[0033] Optionally, after starting the heating mode of the photovoltaic-thermal integrated water heater, heating is stopped after 8 hours, and the photovoltaic-thermal integrated module is shielded, the process then includes:

[0034] The cumulative photovoltaic power generation during the heating period is obtained using an electricity meter. Based on the daily heat gain value and the cumulative photovoltaic power generation, the heating efficiency of the photovoltaic-thermal integrated water heater is determined. The calculation formula for the heating efficiency of the photovoltaic-thermal integrated water heater is shown in formula (5):

[0035] (5)

[0036] Among them, E PV The cumulative photovoltaic power generation is mentioned above.

[0037] Optionally, it may also include, subsequently:

[0038] After adjusting the water temperature in the hot water storage tank to 65℃±3℃, turn off any power heating mode.

[0039] Cold water at a temperature of 15℃±2℃ is continuously injected into the inlet of the hot water storage tank, and hot water is continuously discharged from the outlet of the hot water storage tank.

[0040] After 15 seconds of starting drainage, the inlet and outlet temperatures are measured every 5 seconds. Drainage is stopped when the outlet temperature is 20°C lower than the maximum outlet temperature.

[0041] Obtain the average influent temperature, average discharge temperature, and total discharge mass during the drainage period;

[0042] The hot water output rate is determined based on the average inlet water temperature, the average outlet water temperature, and the total mass of the outlet water.

[0043] Optionally, the formula for calculating the hot water output rate is as shown in formula (6):

[0044] (6)

[0045] Where m is the total mass of the drainage, t p The average drainage temperature, t cThe average inlet water temperature is m. p The mass of the water released is in kilograms (kg), and m is the total mass of the water in the storage tank, in kilograms (Kg).

[0046] Optionally, before starting the mixing pump located in the hot water storage tank, mixing the water in the hot water storage tank, and obtaining the effective outlet temperature of the hot water storage tank, the following steps are included:

[0047] Stop injecting water into the inlet of the hot water storage tank.

[0048] Optionally, before circulating water from the hot water storage tank at a temperature not lower than 20°C at a flow rate of 400L / h to 600L / h, the following steps are included:

[0049] Clean the surface of the photovoltaic-thermal integrated module and completely cover the photovoltaic-thermal integrated module.

[0050] These features and advantages of the present invention will be disclosed in detail in the following specific embodiments and accompanying drawings. The preferred embodiments or means of the present invention will be shown in detail in conjunction with the accompanying drawings, but are not intended to limit the technical solutions of the present invention. In addition, each of these features, elements and components appearing in the following text and drawings is a plurality of, and different symbols or numbers are used for convenience of representation, but all represent parts with the same or similar construction or function. Attached Figure Description

[0051] The present invention will be further described below with reference to the accompanying drawings:

[0052] Figure 1 This is a schematic diagram of a test method flow according to an embodiment of the present invention;

[0053] Figure 2 This is a connection diagram of the photovoltaic heating performance testing system in the above embodiments;

[0054] Figure 3 Drainage curve of another embodiment of the present invention Figure 1 :

[0055] Figure 4 Drainage curves of the above embodiments Figure 2 .

[0056] The components include: 1. Photovoltaic-thermal integrated module; 2. Power grid supply; 3. Hot water storage tank; 4. Electric heater; 5. Controller; 6. Three-way valve; 7. Bypass water pump; 8. Hot water storage tank inlet temperature sensor; 9. Hot water storage tank outlet temperature sensor; 10. Total radiation meter; 11. Outdoor temperature sensor; and 12. Indoor temperature sensor. Detailed Implementation

[0057] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described are intended to explain the present invention and should not be construed as limiting the invention.

[0058] The terms "an embodiment," "example," or "trademark" used in this specification refer to a particular feature, structure, or characteristic described in connection with the embodiment itself that may be included in at least one embodiment disclosed in this patent. The phrase "in an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0059] This invention provides a method for testing the heating performance of a photovoltaic-thermal integrated water heater, wherein the photovoltaic-thermal integrated water heater includes a hot water storage tank and a photovoltaic-thermal integrated module, such as... Figure 1 As shown, the test method includes:

[0060] In step S110, water with a temperature not lower than 20°C is used to circulate water in the hot water storage tank at a flow rate of 400L / h to 600L / h.

[0061] In step S120, if the temperature change of the inlet water of the hot water storage tank is not greater than 0.1°C within at least 5 minutes, the inlet water temperature is determined as the effective inlet water temperature of the hot water storage tank.

[0062] In step S130, the heating mode of the photovoltaic-thermal integrated water heater is started, heating is stopped after 8 hours, and the photovoltaic-thermal integrated module is shielded.

[0063] In step S140, the mixing pump located in the hot water storage tank is started to mix the water in the hot water storage tank and obtain the effective outlet temperature of the hot water storage tank.

[0064] In step S150, the daily heat gain value is determined based on the effective inlet temperature and the effective outlet temperature; wherein, the daily heat gain value is one of the performance indicators of heating performance.

[0065] By circulating water at a temperature no lower than 20℃ and ensuring the inlet temperature of the hot water storage tank fluctuates within ±0.1℃ over 5 minutes, a consistent water temperature at the start of heating is guaranteed, eliminating the impact of initial temperature differences on test results. Furthermore, a mixing pump draws water from the bottom of the storage tank to the top for circulation, avoiding measurement errors caused by temperature stratification. The inlet water flow rate is set to 400L / h~600L / h to prevent uneven water temperature distribution or changes in heat exchange efficiency due to excessive flow fluctuations, further ensuring the stability of test conditions. In addition, the average temperature over 5 minutes is used as the water temperature at the start and end of heating, avoiding the influence of instantaneous temperature fluctuations on the results. Strict control of each step reduces errors caused by operational differences, improving the accuracy of test results.

[0066] The requirements for the test object and the test environment during the testing process are as follows:

[0067] 1. During the test, the photovoltaic-thermal integrated water heater will operate in heating mode and will not shut down the photovoltaic heating function when the temperature of the water in the storage tank reaches the maximum protection temperature value of photovoltaic heating.

[0068] 2. The test period must include at least one full day, and the test time period must be from 4 hours before local noon to 4 hours after local noon;

[0069] III. During the testing period, the daily solar irradiance on the surface of the photovoltaic-thermal integrated module was 4.5 kWh / m². 2 ~6kWh / m 2 Within the range;

[0070] IV. The hot water storage tank was placed indoors, and the water temperature in the tank was 20.0℃±1.0℃ at the start of the test; the average temperature of the environment where the hot water storage tank was located during the test was within the range of 15℃~30℃.

[0071] 5. Install each component of the photovoltaic water heater according to the manufacturer's instructions;

[0072] VI. The photovoltaic-thermal integrated modules shall be installed on the mounting brackets provided by the manufacturer, or installed at the installation angle specified by the manufacturer.

[0073] 7. Connect the photovoltaic water heater to the photovoltaic heating performance testing system;

[0074] The photovoltaic heating performance testing system includes a photovoltaic-thermal integrated module 1, grid power supply 2, hot water storage tank 3, electric heater 4, controller 5, three-way valve 6, bypass water pump 7, hot water storage tank inlet temperature sensor 8, hot water storage tank outlet temperature sensor 9, total radiation meter 10, outdoor temperature sensor 11, and indoor temperature sensor 12, with connection methods as follows: Figure 2 As shown.

[0075] 8. The total radiation meter measures the solar irradiance on the plane where the photovoltaic-thermal integrated module is located;

[0076] 9. The horizontal distance between the outdoor temperature sensor and the photovoltaic-thermal integrated module shall not exceed 3m, and the horizontal distance between the indoor temperature sensor and the hot water storage tank shall not exceed 3m.

[0077] Optionally, obtaining the effective outlet temperature of the hot water storage tank includes:

[0078] The outlet temperature of the hot water storage tank is continuously acquired. If the outlet temperature of the hot water storage tank changes by no more than 1°C within at least 5 minutes, the outlet temperature is determined as the effective outlet temperature of the hot water storage tank.

[0079] The formula for calculating the daily calorie gain is shown in formula (1):

[0080] (1)

[0081] Where c pw The isobaric specific heat capacity of water should be determined based on the average water temperature before and after startup, and is expressed in kilojoules per kilogram per degree Celsius [kJ / (kg‧℃)]. e For the effective outlet temperature, t b The effective inlet temperature is denoted by m, which represents the total mass of water in the storage tank, expressed in kilograms (Kg).

[0082] The water at the bottom of the hot water storage tank is pumped to the top and circulated for at least 5 minutes by a mixing pump to ensure that the water temperature in the tank is evenly distributed and to avoid measurement errors caused by temperature stratification. The water temperature fluctuation during the mixing process does not exceed ±0.1℃, which further ensures the accuracy of temperature measurement.

[0083] Optionally, the heating mode includes a photovoltaic heating mode, a solar thermal heating mode, and a photovoltaic-solar integrated heating mode; wherein, the solar thermal heating mode includes any one of photovoltaic short-circuit condition, photovoltaic open-circuit condition, and photovoltaic load condition;

[0084] When the heating mode is photovoltaic heating mode, activating the heating mode of the photovoltaic-thermal integrated water heater includes: connecting the photovoltaic-thermal integrated module to an electric heater;

[0085] When the heating mode is solar thermal heating mode, the process of activating the heating mode of the photovoltaic-thermal integrated water heater includes: connecting the positive and negative cables of the photovoltaic-thermal integrated module under photovoltaic short-circuit conditions; disconnecting the positive and negative terminals of the photovoltaic-thermal integrated module under photovoltaic open-circuit conditions; and connecting the positive and negative terminals of the photovoltaic-thermal integrated module to a pure resistance module under photovoltaic load conditions, and immersing the pure resistance module in a constant temperature water tank.

[0086] When the heating mode is photovoltaic-thermal heating mode, starting the heating mode of the photovoltaic-thermal integrated water heater includes: connecting the photovoltaic-thermal integrated component to the electric heating and connecting the direct photovoltaic heating circulation pipeline.

[0087] The resistance value of the pure resistance module is determined based on the electric heating resistor configured in the photovoltaic-thermal integrated water heater. Immersing the pure resistance module in a constant-temperature water bath maintains a constant resistance value. Testing the water heater under various heating modes improves the comprehensiveness of the heating performance evaluation of the photovoltaic-thermal integrated water heater.

[0088] Optionally, the performance indicators also include a daily solar irradiance of 5 kWh / m² on the surface of the photovoltaic-thermal integrated module. 2 The nominal daily heat gain per unit photovoltaic installation area is calculated using the formula shown in formula (2):

[0089] (2)

[0090] Where H represents the daily solar irradiance on the surface of the photovoltaic-thermal integrated module, in kWh / m². 2 A represents the area of ​​the light-receiving surface of the photovoltaic-thermal integrated module, in square meters (㎡).

[0091] In one optional embodiment, the performance indicators also include a daily solar irradiance of 5 kWh / m² on the surface of the photovoltaic-thermal integrated module. 2 The nominal daily heat gain per unit photovoltaic installation capacity is calculated using the formula shown in formula (3):

[0092] (3)

[0093] Where H represents the daily solar irradiance on the surface of the photovoltaic-thermal integrated module, in kWh / m². 2 P peak The measured value of the photovoltaic installation capacity is expressed in watts (W).

[0094] Optionally, obtaining the effective outlet temperature of the hot water storage tank includes:

[0095] Water of different temperatures is continuously injected into the inlet of the hot water storage tank, and hot water in the hot water storage tank is discharged from the outlet of the hot water storage tank at a constant flow rate. The temperature of the discharged water is measured at least once every second until the volume of the discharged water is greater than three times the volume of the hot water storage tank and the temperature difference between the discharged water and the inlet water is less than 1°C. The temperatures of the discharged water are determined as multiple effective outlet temperatures.

[0096] The formula for calculating the daily calorie gain is shown in formula (4):

[0097] (4)

[0098] Where T1 is the temperature of the inlet water, T2 is the effective outlet water temperature, and C is the specific heat capacity of water at constant pressure. The mass flow rate of the water at the outlet is expressed in kilograms per second (kg / s).

[0099] By frequently measuring the temperature of the drainage, in order to plot... Figure 3 The drainage curve shown can more accurately describe the change in water temperature over time. f(T) is obtained through quadratic fitting of the drainage curve. By combining the drainage curve with the actual solar energy received by the solar system at different inlet water temperatures (T1), the actual solar energy received can be obtained. Furthermore, as... Figure 4 As shown, by setting the temperature line, you can also obtain the total volume and total heat value of the hot water that the user can actually use.

[0100] In one optional embodiment, after the photovoltaic-thermal integrated water heater is activated and heated for 8 hours, heating is stopped and the photovoltaic-thermal integrated module is shielded, the process then includes:

[0101] The cumulative photovoltaic power generation during the heating period is obtained using an electricity meter. Based on the daily heat gain value and the cumulative photovoltaic power generation, the heating efficiency of the photovoltaic-thermal integrated water heater is determined. The calculation formula for the heating efficiency of the photovoltaic-thermal integrated water heater is shown in formula (5):

[0102] (5)

[0103] Among them, E PV The cumulative photovoltaic power generation is mentioned above.

[0104] Optionally, it may also include, subsequently:

[0105] After adjusting the water temperature in the hot water storage tank to 65℃±3℃, turn off any power heating mode.

[0106] Cold water at a temperature of 15℃±2℃ is continuously injected into the inlet of the hot water storage tank, and hot water is continuously discharged from the outlet of the hot water storage tank.

[0107] After 15 seconds of starting drainage, the inlet and outlet temperatures are measured every 5 seconds. Drainage is stopped when the outlet temperature is 20°C lower than the maximum outlet temperature.

[0108] Obtain the average influent temperature, average discharge temperature, and total discharge mass during the drainage period;

[0109] The hot water output rate is determined based on the average inlet water temperature, the average outlet water temperature, and the total mass of the outlet water.

[0110] Before testing, turn off the power and heating mode to ensure a consistent water temperature in the tank at the start of the test, eliminating the impact of initial condition differences on the test results. Continuously drain water until the water temperature is 20°C below the maximum drain temperature to ensure the test covers the entire heat output process and avoid performance underestimation due to stopping water draining too early.

[0111] In addition, the drainage flow rate can be controlled by a valve installed at the outlet of the hot water storage tank. When the drainage volume is no more than 10L, the drainage flow rate is 2L / min; when the drainage volume is between 10L and 50L, the drainage flow rate is 5L / min; when the drainage volume is between 50L and 200L, the drainage flow rate is 10L / min; when the drainage volume is greater than 200L, 5% of the nominal capacity of the hot water storage tank is discharged per minute.

[0112] In one alternative embodiment, the formula for calculating the hot water output rate is as shown in formula (6):

[0113] (6)

[0114] Where m is the total mass of the drainage, t p The average drainage temperature, t c The average inlet water temperature is m. p The mass of the water released is in kilograms (kg), and m is the total mass of the water in the storage tank, in kilograms (Kg).

[0115] Optionally, before starting the mixing pump located in the hot water storage tank, mixing the water in the hot water storage tank, and obtaining the effective outlet temperature of the hot water storage tank, the following steps are included:

[0116] Stop injecting water into the inlet of the hot water storage tank.

[0117] Before starting the test, stop the water circulation and disconnect the bypass circuit to ensure that the water flows completely through the main circulation system and avoid abnormal flow or temperature caused by the bypass circuit.

[0118] Optionally, before circulating water from the hot water storage tank at a temperature not lower than 20°C at a flow rate of 400L / h to 600L / h, the following steps are included:

[0119] Clean the surface of the photovoltaic-thermal integrated module and completely cover the photovoltaic-thermal integrated module.

[0120] Before testing, the photovoltaic-thermal integrated module was completely shaded to avoid interference from photovoltaic power generation on the initial water temperature.

[0121] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A method for testing the heating performance of a photovoltaic-thermal integrated water heater, wherein the photovoltaic-thermal integrated water heater comprises a hot water storage tank and a photovoltaic-thermal integrated module, characterized in that, The testing method includes: Water at a temperature of not less than 20℃ is used to circulate water in the hot water storage tank at a flow rate of 400L / h to 600L / h. If the temperature change at the inlet of the hot water storage tank is no greater than 0.1℃ within at least 5 minutes, the inlet temperature is determined as the effective inlet temperature of the hot water storage tank. The heating mode of the photovoltaic-thermal integrated water heater is activated, and heating is stopped after 8 hours. The photovoltaic-thermal integrated module is then shielded. Start the mixing pump located in the hot water storage tank to mix the water in the hot water storage tank and obtain the effective outlet temperature of the hot water storage tank. The daily heat gain value is determined based on the effective inlet temperature and the effective outlet temperature; wherein, the daily heat gain value is one of the performance indicators of heating performance.

2. The method for testing the heating performance of a photovoltaic-thermal integrated water heater according to claim 1, characterized in that, The method of obtaining the effective outlet temperature of the hot water storage tank includes: The outlet temperature of the hot water storage tank is continuously acquired. If the outlet temperature of the hot water storage tank changes by no more than 0.1℃ within at least 5 minutes, the outlet temperature is determined as the effective outlet temperature of the hot water storage tank. The formula for calculating the daily calorie gain is shown in formula (1): （1） Where c pw The specific heat capacity of water at constant pressure, t e For the effective outlet temperature, t b For effective inlet water temperature.

3. The method for testing the heating performance of a photovoltaic-thermal integrated water heater according to claim 2, characterized in that, The heating modes include photovoltaic heating mode, solar thermal heating mode, and integrated photovoltaic and solar thermal heating mode; wherein, solar thermal heating mode includes any one of photovoltaic short-circuit condition, photovoltaic open-circuit condition, and photovoltaic load condition; When the heating mode is photovoltaic heating mode, the heating mode for activating the photovoltaic-thermal integrated water heater includes: Connect the photovoltaic-thermal integrated module to an electric heater; When the heating mode is a solar thermal heating mode, the heating mode for activating the integrated photovoltaic and solar thermal water heater includes: Under photovoltaic short-circuit conditions, connect the positive and negative cables of the photovoltaic-thermal integrated module; In the case of photovoltaic circuit failure, disconnect the positive and negative electrodes of the photovoltaic-thermal integrated module; Under photovoltaic load conditions, the positive and negative terminals of the photovoltaic-thermal integrated module are connected to the pure resistor module, and the pure resistor module is immersed in a constant temperature water bath. When the heating mode is photovoltaic-thermal heating mode, the heating mode for activating the integrated photovoltaic-thermal water heater includes: Connect the photovoltaic-thermal integrated module to the electric heater and connect the direct solar heating circulation pipeline.

4. The method for testing the heating performance of a photovoltaic-thermal integrated water heater according to claim 3, characterized in that, The performance indicators also include a daily solar irradiance of 5 kWh / m² on the surface of the photovoltaic-thermal integrated module. 2 The nominal daily heat gain per unit photovoltaic installation area is calculated using the formula shown in formula (2): （2） Where H represents the daily solar irradiance on the surface of the photovoltaic-thermal integrated module, in kWh / m². 2 .

5. The method for testing the heating performance of a photovoltaic-thermal integrated water heater according to claim 3, characterized in that, The performance indicators also include a daily solar irradiance of 5 kWh / m² on the surface of the photovoltaic-thermal integrated module. 2 The nominal daily heat gain per unit photovoltaic installation capacity is calculated using the formula shown in formula (3): （3） Where H represents the daily solar irradiance on the surface of the photovoltaic-thermal integrated module, in kWh / m². 2 .

6. The method for testing the heating performance of a photovoltaic-thermal integrated water heater according to claim 1, characterized in that, The method of obtaining the effective outlet temperature of the hot water storage tank includes: Water of different temperatures is continuously injected into the inlet of the hot water storage tank, and hot water in the hot water storage tank is discharged from the outlet of the hot water storage tank at a constant flow rate. The temperature of the discharged water is measured at least once every second until the volume of the discharged water is greater than three times the volume of the hot water storage tank and the temperature difference between the discharged water and the inlet water is less than 1°C. The temperatures of the discharged water are determined as multiple effective outlet temperatures. The formula for calculating the daily calorie gain is shown in formula (4): （4） Where T1 is the temperature of the inlet water, and T2 is the effective outlet water temperature.

7. The method for testing the heating performance of a photovoltaic-thermal integrated water heater according to any one of claims 2 to 6, characterized in that, After activating the heating mode of the photovoltaic-thermal integrated water heater and heating for 8 hours, heating is stopped, and the photovoltaic-thermal integrated module is shielded. The process then includes: The cumulative photovoltaic power generation during the heating period is obtained using an electricity meter. Based on the daily heat gain value and the cumulative photovoltaic power generation, the heating efficiency of the photovoltaic-thermal integrated water heater is determined. The calculation formula for the heating efficiency of the photovoltaic-thermal integrated water heater is shown in formula (5): （5） Among them, E PV The cumulative photovoltaic power generation is mentioned above.

8. The method for testing the heating performance of a photovoltaic-thermal integrated water heater according to claim 1, characterized in that, Following that, it also includes: After adjusting the water temperature in the hot water storage tank to 65℃±3℃, turn off any heating mode. Cold water at a temperature of 15℃±2℃ is continuously injected into the inlet of the hot water storage tank, and hot water is continuously discharged from the outlet of the hot water storage tank. After 15 seconds of starting drainage, the inlet and outlet temperatures are measured every 5 seconds. Drainage is stopped when the outlet temperature is 20°C lower than the maximum outlet temperature. Obtain the average influent temperature, average discharge temperature, and total discharge mass during the drainage period; The hot water output rate is determined based on the average inlet water temperature, the average outlet water temperature, and the total mass of the outlet water.

9. The method for testing the heating performance of a photovoltaic-thermal integrated water heater according to claim 8, characterized in that, The formula for calculating the hot water output rate is shown in formula (6): （6） Where m is the total mass of the drainage, t p The average drainage temperature, t c The average inlet water temperature is denoted as .

10. The method for testing the heating performance of a photovoltaic-thermal integrated water heater according to claim 1, characterized in that, Before circulating water from the hot water storage tank at a temperature not lower than 20°C at a flow rate of 400L / h to 600L / h, the following steps are included: Clean the surface of the photovoltaic-thermal integrated module and completely cover the photovoltaic-thermal integrated module.

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