Dynamic Thermal Environment And Heating Load Forecast For Solar Greenhouse

Solar greenhouses are mostly built in the northern regions of China,making a significant contribution to the supply of winter vegetables for urban residents.The solar greenhouse is a kind of passive agricultural facility construction that can realize the off-season production with the main enclosure of the heat storage wall,heat preservation roof,and transparent film.The heat removal and heat replenishment—— "cooling load and heating load",mainly depends on the dynamic characteristics of the greenhouse heat gain and loss.This dissertation is based on the experimental solar greenhouse of Shandong Jianzhu University(located at No.1000 Fengming Road,Licheng District,Jinan Shandong)and the " sixth-generation " solar greenhouse in Weifang(located in Hanting District,Weifang Shandong).Then,the outdoor temperature,the spatial distribution characteristics of air temperature inside,the surface temperature of the greenhouse's wall,the soil temperature,and solar radiation of the solar greenhouse w ere explored.Moreover,an analytical model for transmitted solar radiation was established based on the transparent curved surface of the experimental solar greenhouse of Shandong Jianzhu University,and the mathematical expression to calculate the equivalent reflected transmissivity of the experimental greenhouse curved surface was proposed.The experimental data were used to verify the incident solar radiation intensity transmitted from the transparent film.Next,based on the radiation model,the variation of the equivalent transmittance of the direct,scattered and reflected radiation are explored with the change of aspect ratios(height/span)of the greenhouse film,and the equivalent beam transmissivity is compared between the traditional simplified inclined planes and the actual curved surfaces of the experimental solar greenhouse.Then,the transmitted diffused radiation and the transmitted reflected radiation of the greenhouse under snow cover conditions in winter are focused.The results show that the contribution of the reflected radiation needs to be considered in the total radiation of the solar greenhouse film.Besides,by summarizing the method of the curved surface transmitted radiation,this approach can be applied to other transparent curved surfaces.The influence of the experimental solar greenhouse end effect on the light spot area was evaluated for the inner surface of the greenhouse envelope via the sun's perspective method.Then,the hourly variation characteristics of the spot area and the proportion of spot area on the inner wall under different lengths of the experimental greenhouse were compared.The results show that when the construction length of the greenhouse exceeds 60 m in the area of Jinan,the end effect of the greenhouse has negligible influence on the solar radiation shielding.Besides,the crops in the solar greenhouse may weaken solar radiation,which will affect the radiant heat flow received by the soil surface.In this study,a non-dimensional plant equivalent thermal resistance model is established by analogy with heat transfer and thermal resistance.The functional relationship between the equivalent thermal resistance and the leaf area index of the crop in the greenhouse and its extinction coefficient is analyzed.Besides,the changes in the ability of specific crops based on the " sixth-generation " solar greenhouse in Weifang to resist radiation penetration on sunny days are analyzed.Additionally,this thesis analyzes the heat transfer mechanism of the envelope structure with different boundary characteristics in the solar greenhouse.The Laplace transform method is selected to calculate the heat transfer of opaque enclosure structures such as greenhouse walls and soil,and this method was verified by the indoor air temperature of the experimental solar greenhouse situated at Shandong Jianzhu University.Moreover,the solar fraction expressions of the solar greenhouse were revised,taking tomatoes as an example,the hourly load variation characteristics are predicted under two given indoor air temperatures based on the experimental greenhouse of Shanjian University.The results showed that the heating load of the experimental greenhouse reached its peak value at 9:00 in the morning,and heat removal by ventilation was required between 11:00 and 15:00 during the daytime of a sunny day in winter.The heat loss from the solar greenhouse film was 51.36% and56.33% under two different indoor air conditions,respectively.Besides,this thesis also adopts two evaluation indicators,namely instantaneous loss efficiency and thermal load level,to compare the thermal environment of the solar greenhouses in Weifang and Jinan.The shortcomings of the two types of solar greenhouse were analyzed,which lay the foundation for optimizing the thermal environment of the solar greenhouse.