Research On The Design Of Variable Inclination Active Solar Heating System And Its Application Effect In Chinese Solar Greenhouse

Providing the necessary heating measures for greenhouse during the cold season is an important part of greenhouse production,and solar energy,as a renewable and clean energy source,has advantages that cannot be replaced by traditional fossil energy sources.The application of solar heating technology in greenhouse can meet the heating needs of greenhouse at night in winter and provide a good growing environment for greenhouse crops.For the problems existing in current solar collectors,such as limited heat collection capacity,occupied arable land area and shading,the following two aspects of the study were developed:Designed a vacuum tube solar collector,investigated the influence of collector inclination angle,tube spacing and insulation material on the performance of vacuum tube solar collector,and carried out optimization of vacuum tube solar collector according to the research results;The application effect of vacuum tube solar collector was verified,and a set of a variable inclination active solar heating system was designed,researched on the performance of a variable inclination active solar heating system combined with the actual greenhouse production,analysis of its heat collection,heat collection efficiency and energy utilization efficiency and other parameters changes,studied the effect of a variable inclination active solar heating system on the microclimate and plant growth indicators of the Chinese solar greenhouse,in order to solve the winter heating needs of the Chinese solar greenhouse and the limitations of existing heat collection devices.The main conclusions are as follows:（1）Different installation angles and tube spacings have direct effects on the heat collection performance of vacuum tube solar collector.When the installation angle was 50°,the performance of the vacuum tube solar collector was the best among the three installation angles（30°,40°,50°）,which can make the water temperature in the collector reached 47.4℃on average;When the tube spacing was 20 mm,the heat collection of vacuum tube solar collector was 369.6 MJ,which was the largest of the three tube spacings（10 mm,20 mm,30 mm）.Insulation material only affects the size of heat dissipation from the tank of vacuum tube solar collector,and plays an indirect role in the performance of vacuum tube solar collector.Considering the heat loss coefficient,anti-aging performance and cost,rubber insulation cotton is most suitable as the thermal insulation material for the tank of vacuum tube solar collector.（2）The application results of variable inclination active solar heating system in Chinese solar greenhouse show that,on a typical sunny day,the heat collection of this system was 7.6MJ/m²,and its heat collection per unit time was 1.9 MJ·(m^-2·h^-1),which had a good heat collection performance,the heat release of the system at night was 5.1 MJ/m²,and the energy utilization fficiency was 85.1%.The system adopted intermittent operation mode,the energy saving rate was 77.9～84.0%,and the performance coefficient COP reached 5.2 on average,so the system had remarkable energy saving effect.The flow rate and solar radiation have an impact on the performance of the variable inclination active solar heating system.With the increased of the flow rate,the heat collection efficiency of the system showed a trend of increasing first and then decreasing,and when the flow rate was 5.4 L/min,the system heat collection efficiency was the largest,reaching 61.4%;As the solar radiation increased,the heat collection efficiency of the system first increased and then tended to level off,after the solar radiation increased to 10.5 MJ/m²,the solar radiation has less influence on the heat collection efficiency of the system.（3）Variable inclination active solar heating system can improve greenhouse climate conditions and promote greenhouse crop growth.The greenhouse was heated by the system,which increased the night air temperature of the greenhouse by an average of 2.2°C,the crop root substrate temperature by 3.3℃,the relative humidity of the greenhouse air was reduced by 21.1%,the plant height and leaf area of tomato plants were higher than control greenhouse,and the relative chlorophyll content of tomato plants increased by 15.6%.