Design And Photothermal Performance Of A Façade-embedded Compound Parabolic Concentrator

With the continuous development of society and science,people’s requirements for life and living environment are getting higher and higher,which has led to a rapid increase in building energy consumption.Meanwhile,the continuous increase in building energy consumption has put a severe test on the use of traditional energy sources and global warming.Among them,domestic and industrial heating account for a large proportion of building energy consumption.In order to meet the heating demand,renewable energy such as solar energy has gradually attracted people’s attention and favor with its good environmentally friendly performance.Solar energy has been developed and utilized due to its large total volume,wide distribution,easy access and pollution-free advantages.Combining solar energy utilization technology with modern buildings is the effective way to alleviate the pressure on building energy consumption.Therefore,it is a general trend to apply it to the building field to alleviate the problem of building energy consumption.Based on the compound parabolic concentrator(CPC),a facade embedded compound parabolic concentrator solar collector(FE-CPC-SC)is proposed,which is suitable for the building facade and can meet the thermal energy requirements of the building.The physical model,optical model,heat transfer model and annual light collection of the facade embedded compound parabolic concentrator(FE-CPC)were constructed and evaluated through a closed-loop photo-thermal conversion experiment under outdoor conditions for the photo-thermal performance.The main conclusions are as follows:(1)Based on the law of light reflection,the numerical expression of CPC with circular absorber was derived by analytic geometry method.Then the physical model of FE-CPC is proposed and designed by combining with the characteristics of the south-facing facade for building and the variation of solstice solar altitude.In addition,the optical simulation of FE-CPC is performed via MCRT method,and its beam radiation model is constructed.The peak value of beam radiation optical efficiency for FE-CPC at four different latitudes is about 72.18%,69.69%,69.12% and 68.69%,respectively.The average beam radiation optical efficiency in the range of the acceptable angle is 50.91%,51.82%,52.12% and 53.37%,respectively.(2)According to the principle of energy conservation,the one-dimensional steady-state photo-thermal conversion numerical model of FE-CPC-SC is built,and the theoretical numerical solution of FE-CPC-SC is obtained through calculation in C language program.In addition,the numerical model of photo-thermal conversion is verified by an outdoor photo-thermal conversion experimental of FE-CPC-SC(built in Kunming)with a maximum uncertainty of about 10.24%,but the parameters of outdoor experiments are greatly affected by environmental factors.(3)The numerical model of photo-thermal conversion established can accurately predict the operating performance of FE-CPC-SC under daily conditions.Through the combination of experiment and theory,it is concluded that the experimental and theoretical values of the FE-CPC-SC vacuum tube inlet and outlet temperature are in good agreement.The maximum relative error(RE)between the experimental and theoretical values of the vacuum tube outlet temperature is 6.72%.In addition,the experimental value of photo-thermal conversion efficiency is in good agreement with the theoretical value,and the relative error is between-12.5% and 10.8%.(4)Based on the data of the typical meteorological year(TMY),the performance of FE-CPC-SC at four different latitudes in capturing sunlight is evaluated.The results show that the solar radiation capture by FE-CPC-SC is affected by the solar azimuths,and the performance of capturing solar radiation for FE-CPC-SC in winter is better than that in summer,which is consistent with the actual heat demand.Moreover,the ratio of the solar radiation absorbed and converted by FE-CPC-SC on the facade to the total radiation reaching the horizontal surface is 29.99%,27.56%,30.70% and 17.45%.And the average efficiency useful energy of obtained by the actual converted solar radiation in the four areas is about 50.31%.