| As a technology of building energy conservation and comprehensive utilization of renewable energy,building integrated photovoltaic(BIPV)will have a certain impact on building energy consumption while taking into account solar power generation.In this paper,microencapsulated phase change material suspension(MPCMS)is combined with traditional BIPV system to construct BIPV-MPCMS system,MPCMS is used to adjust the operating temperature of photovoltaic modules and the temperature of system backplane,so as to improve the photoelectric conversion efficiency of photovoltaic modules and reduce indoor thermal disturbance.This study not only expands the application form of PV in traditional buildings,but also provides a theoretical basis for the application of MPCMS in BIPV.In this paper,two kinds of microcapsule phase change particles TH-ME25 and TH-ME32 with different phase change temperatures,the capsule material is melamine resin and the core material is paraffin are selected.The suspension with mass fraction of 5%,10% and 20% is prepared by using deionized water as the base solution,and its physical parameters are tested experimentally and analyzed theoretically.The results show that the thermal conductivity of MPCMS increases with the increase of temperature in the phase transition temperature range,but after the phase transition process,the thermal conductivity of liquid paraffin is lower than that of solid paraffin,and the thermal conductivity will decrease to a certain extent;For the same MPCMS,the thermal conductivity decreases with the increase of mass fraction,and the overall density increases with the increase of mass fraction;The rectangular equivalent model is used to calculate the specific heat capacity of the suspension,the results show that in the nonphase transition temperature range,the specific heat capacity decreases with the increase of mass fraction,while the specific heat capacity increases with the increase of mass fraction when phase transition occurs;In order to improve the stability of the system,0.2% xanthan gum was added to the deionized water during the preparation of MPCMS,so the viscosity of the suspension basically remains unchanged in the working temperature range and can be regarded as a fixed value.The experimental platform of BIPV system and BIPV-MPCMS system was built in Nanjing area to test the system performance.The results show that on May 24,2021,MPCMS25 can maintain the temperature reduction trend of BIPV system components for 9.5h,and the maximum temperature can be reduced by 8.8℃.The temperature of the backplane decreased by 9.75 h,the maximum decrease was 11.1℃,and the peak temperature of the module is delayed by 114 minutes,and the peak temperature of the backplane is delayed by 125 minutes.At the same time,the maximum output power of the module is increased by 4.48%,and the photoelectric conversion efficiency is increased by a maximum of 4.8%;From June 23 to June 25,2021,the peak temperature differences between the BIPV-MPCMS32 system and the BIPV system backplane were 9.82°C,9.69°C,and 7.73°C,respectively,and the peak operating temperature differences for PV modules were 4.91°C,4.04°C,and 3.08°C.The optimized durations for the operating temperature of the PV modules are 8.23 h,7.07 h and6.1h respectively,and the optimum durations for the backplane temperature are 11 h,11.32 h and 8.85 h respectively,and the output power and photoelectric conversion efficiency are also improved to a certain extent.And comparing and analyzing the operating results of the system,it can be seen that the optimization effect of MPCMS on the heat transfer performance and power generation performance of the BIPV system is positively correlated with the solar radiation intensity of the day.Analyze the heat and mass transfer mechanism of the system,build a numerical heat transfer-power generation calculation model,and verify its accuracy.The results show that the simulation results are basically the same as the experimental data,the root mean square error of both is controlled within 1.5,and the correlation coefficient can reach more than 0.98,which proves that the calculation model has high accuracy.The model will be used to carry out optimization research and performance analysis of the system later.The results show that: with the increase of the mass fraction of microcapsule particles in the MPCMS,the temperature fluctuation of the system backplane decreases,the peak temperature decreases,and the same effect can be achieved by increasing the thickness of the MPCMS layer of the system.The simulation shows that the optimal thickness of the MPCMS layer is 40 mm,which can reduce the peak temperature of the backplane of the BIPV system by 12.71℃,the time lag of the peak temperature is 119 min,and the indoor heat gain is reduced.38.00%,and the power generation efficiency is up to 2.84% higher;Under the premise of ensuring the completion of the phase transition,changing the phase transition temperature of the suspension and keeping other parameters unchanged has little effect on the system performance.Under the same outdoor conditions,the difference between the peak temperature of the backplane of MPCMS25 and MPCMS32 is only 0.42°C.Finally,the BIPV-MPCMS system with a mass fraction of 20% and a phase transition temperature of 25°C was used to simulate the performance of the representative cities in the five climatic regions of my country under the meteorological conditions of the summer solstice and the spring equinox.The results show that the heat transfer of the system can be reduced by more than 30% during the simulation period,and the trend of the peak temperature reduction of the backplane can basically exceed 10℃.However,the energy saving effect of BIPV-MPCMS is more significant in regions with higher solar radiation intensity and milder climate. |
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