Effect Of Environmental Factors On Thermal Performance Of Flat Plate Solar Collector

Flat plate solar collector(FPC)is getting higher installed capacity in China due to its better safety performance and advantage of integrating with buildings.Normally,environmental factors,such as dust deposition,rainfall and wind will not be considered when calculating the thermal performance of FPC,which results in a big difference between calculation and operation.To study effect of environmental factors on thermal performance of FPC,following theoretical and experimental studies have been carried out:Firstly,based on analysis of the structure and working principle of FPC,main influence of environmental factors on heat transfer process has been summarized,and the heat transfer model of FPC is developed.Comparing with the performance test results of FPC sample under different conditions,the maximum deviation of collector's efficiency between simulation and testing is 0.023,and the relative deviation is 4.9%,which verifies the accuracy of the heat transfer model of FPC.Secondly,an artificial environment experiment system including artificial sky and solar simulator is designed and built.Using this system,a series of experiments have been performed to explore the influence of wind speed and dust deposition on the efficiency of FPC.Both experimental and simulated results show similar conclusions:(1)Wind speed has more significant effect on the heat loss coefficient,and the variation curve of thermal performance is similar to a right-side-opened parabola;(2)The heat loss coefficient would increase by more than 16% when wind speed increases from 0 to 4 m/s;(3)The effect of dust deposition on the intercept efficiency is approximately linear,and the intercept efficiency would decline by 42.2% when transmittance of the dust layer decreases from 1 to 0.5;(4)Wind speed also has effect on the intercept efficiency and dust deposition has slight effect on the heat loss coefficient.Thirdly,with a 12-month experiment in Beijing,the correlation of environmental factors,such as dust deposition and rainfall,on cover transmittance have been summarized.The maximum deviation between calculation and experiment is 6.42%.Combined with the correlation and the influence of the dust deposition and wind speed,a correction method for thermal efficiency curve is proposed.Compared with the simulated results under different conditions,the maximum deviation of intercept efficiency is 2.3%,and the maximum deviation of heat loss coefficient is 4.6%.This correction method could simplify and support the design of solar thermal system with FPC.Finally,an annual performance prediction model considering the influence of dust deposition,rainfall,wind and inclination angles has been established.Results show that the heat gain could decline by 19.2% in Beijing because of little rain in winter.Based on the analysis of the FPC system performance under different rainfall conditions,the recommendations on the cleaning and maintenance strategies for different solar thermal systems have been proposed in order to improve the operation performance.