Study On Heat Collection Performance Of Snow-proof And Concentrating Flat Solar Collector

With the continuous development of clean energy,solar flat plate solar collectors are increasingly widely used in space heating,but there are problems of low heat collection efficiency and low heat collection amount when used in cold areas in winter.Adding a reflector to the collector to form a condensing collector can effectively solve this problem,but the existing reflector plate often needs to track the sun or frequently adjust the installation angle,which increases the cost and limits the wide application of the condensing collector in the field of space heating.In this paper,a reflector without sun-tracking is proposed to be installed on the flat plate collector,which can greatly reduce the use cost.This paper analyzes the operation characteristics of plate-type and parabolic-type reflectors fixed as reflectors without sun-tracking,and proposes a new reflector structure polyline-type reflector in order to overcome the shortcomings of the two.This paper makes a comparative study of the three reflectors by experimental and theoretical methods.The main work and results are as follows:According to the working characteristics of the reflector,a ray tracing model of the reflector,a collector model considering the influence of reflected light and a theoretical model such as an enhancement factor characterizing the action size of the reflector are established.The model takes into account complicated practical factors such as scattering,atmospheric transparency and reflected light loss,and can accurately calculate working conditions at any angle and at any time.Based on this model,through a large number of calculations,the reasonable design conditions and the optimal installation angle of each reflector are determined.On this basis,an experiment table was designed and built to study the effects of different reflector on the instantaneous efficiency,heat collection temperature and heat collection of the collector under different ambient temperatures and radiation illuminance,and the snow prevention effect of the reflectors in winter.The theoretical model established in this paper is verified by comparing the experimental data of heat collection with the theoretical calculation results.Based on the verified theoretical model,a comparative study was made on the condensation effect without sun-tracking of different reflectors in the whole year,and the operating performance of different reflectors under specific working conditions,seasonal working conditions and annual working conditions was analyzed.The following conclusions are drawn:The reflector designed according to the sun height angle at noon on the winter solstice as the design working condition can ensure the most unfavorable heat collection working condition in the whole winter,ensure higher heat collection in the coldest month,and meet the demand of users for heat supply load in winter.When the outdoor temperature is low or the radiation intensity is weak,the non-reflector collector may fail,and the condensing heat collector can still work efficiently,the heat collection efficiency can be increased by 15%-25%and the heat collection temperature can be increased by 10-15?.During the whole heating season,the heat collection of plate-type,polyline-type and parabolic-type reflector collectors increased by 16%,32%and 25%respectively compared with non-reflector collectors.The annual total collector increased by 11%,22%and 19%respectively.The loss of reflected light gradually decreases from early morning to noon,and decreases with the increase of the width-to-length ratio of the collector.When the width-to-length ratio is greater than 5,it is basically constant,and the daily average loss of the maximum reflected light throughout the year does not exceed 25%.The enhancement factor and loss rate of polyline-type reflector are between the two,so the comprehensive performance of polyline-type reflector is the best under complex and changeable working conditions.The reflector can effectively prevent the collector from losing its snow cover,and the snow melting speed after snow stops is much faster than that of the non-reflector collector.Under experimental conditions,the snow melting speed of the condensing collector is about 2.5 times that of the non-reflector collector.Part of the sunlight can be shielded in the strong radiation area near the summer solstice day,which can effectively prevent the heat collector from overheating in summer.Therefore,it is a feasible and effective approach for the space heating in severe cold regions to constitute a concentrating solar flat plate collector with free of sun-tracking by installing a fixed reflector.