Study On The Temperature Adjustment And Operation Characteristics Of A Solar Heating Greenhouse With Inter-seasonal Thermal Energy Storage System

Solar greenhouse is an artificial constucture which provides suitable climate condition for crop growth.It features high heat transfer coefficient envelope and high heat leakage rate.Compared with conventional buildings,greenhouse structure has no heat storage capacity which leads small temperature difference between indoor and outdoor during winter time and results in uncapable of meeting the minimum temperature requirement of crops.During summer,accumulation of heat caused by"greenhouse effect"harms the planted crops in the other hand.Therefore,how to regulate the greenhouse indoor temperature is a vital task in Shanghai.Considering the climate features in Shanghai,two independent systems are employed to regulate greenhouse thermal environment:evaporative cooling system in summer and solar heating system with seasonal storage unit in winter.The work can be presented as follows:1.Based on the greenhouse heat balance model,thermal analysis is made to find out the most influential external environmental disturbance on the greenhouse indoor thermal condition.From the pointview of supply side,three types of heating structures were compared and the relevant parameters were investigated.Moreover,from the demand side viewpoint,heating fraction was taken as an index to evaluate the three heating types.Considering lower heating source temperature is required,the radiation heating for greenhouse application can be used in combination with the low grade solar energy.2.A seasonal heat storage system was designed,built and operated then.During the first year of operation,331.9 GJ heat was injected to the BTES and later 208.9 GJ was extracted.In the heating mode,the contribution of long-term and short-term heat storage units is influenced by weather conditions.According to the calculated daily averages,short-term heat storage took account for 49.4%of the greenhouse heat load while underground soil took the remained 50.6%.When using BTES as heat sourse,the greenhouse temperature is relatively stable.When the ambient temperature was-2 ~oC,10-13~oC was maintained indoor.3.According to the onsite experiment,a model of seasonal thermal storage heating system is set up.Parameters of supply side(including geometry of components and loop control strategy of subsystem)were investigated.Impact of each parameter on Solar Fraction and BTES efficiency are analysed and discussed.Total cost during life cycle time is taken as the objective function and optimization is run to get the minimum value of it.The result shows SF and BTES efficiency of the second year are 75.2%and 22.6%,respectively.Moreover,the performance of the system under different climatic conditions are compared and analysed.High solar fration value and low BTES efficiency in the same time indicate that short-term thermal storage tank alone can satisfy the heat load in that area,in which case no seasonal heat storage system is needed.In those areas where heat load is high while solar radiation amount is low,the heating subsystem is more relied on the underground storage unit since not much heat can be extracted from water tank.To improve the solar fraction and BTES efficiency,in addition to expansion of the parameters of supply-side components,reducing the heat transfer coeffiecient of building envelope is also a very effective way.4.By using a combination of inside and outside shadings together with the cooling system,greenhouse thermal environment can be regulated.The performence of wet pad-fan system in Shanghai is analyzed and the distribution of indoor temperature and humidity were studied.