| China is rich in solar energy resources,but with hot summers and cold winters,there are significant seasonal changes in the climate,which limits the promotion and development of solar greenhouses.In winter,the solar greenhouse cannot maintain the normal growth of crops inside the greenhouse solely based on its own heat storage capacity,and additional heat sources need to be added to provide heating for the greenhouse.In summer,due to the high outdoor temperature,without any cooling measures taken,the temperature inside the greenhouse can reach 60 ℃,which affects the normal growth of crops.At this time,it is necessary to cool the greenhouse.Common greenhouse heating and cooling methods have problems such as high energy consumption and environmental pollution.Therefore,in response to the problems faced by the development of solar greenhouses,this study proposes to use a combination of solar spectral selective transmission film and solar cross seasonal heat storage energy configuration in solar greenhouses,achieving both summer cooling and winter heating in a single system.However,the transmittance of the solar spectral selective transmission film in the visible light region and the reflectance in the near-infrared region often cannot be achieved simultaneously.Therefore,this study optimizes the design from three aspects: the selection of coating materials,coating structure and coating thickness to obtain the optimal coating combination.Prepare a solar spectral selective transmission film through simulation and experimental methods and measure its transmittance in the visible and near-infrared regions of solar radiation.Then,through theoretical calculations and dynamic hourly simulation calculations,a cross seasonal heat storage system for the solar greenhouse is established.Finally,by conducting numerical simulation calculations on the established solar greenhouse model,the temperature field distribution maps of the solar greenhouse under different seasons and operating conditions were obtained.By analyzing the temperature field differences between the solar spectral selective transmission membrane greenhouse and the ordinary film greenhouse,the impact mechanism of the combination of solar spectral selective transmission membrane and cross season heat storage system on the thermal environment of the solar greenhouse was explored,providing a basis for the optimization design of the solar greenhouse.The main research conclusions are as follows:(1)TFCalc software was used to simulate the preparation of solar spectral selective transmission films.The coating materials were copper and silicon nitride,and the coating structure was a five layer structure of(DMDMDMD).When the thickness of the coating materials was 40,12,80,15 and 40 nm,the film had ideal transmittance and reflectivity.The simulation analysis shows that the transmittance of the film in the visible light area is 89.4%,and the reflectance in the near infrared area is 83.5%.The data of the simulation coating are prepared by using a multi target Magnetron sputtering coating instrument.The film samples prepared in the experiment are tested by using a full energy spectrophotometer and a Fourier transform infrared spectrometer.The experimental data show that the transmittance of the film in the visible light area is 86.8%,and the reflectance in the near infrared area is 88.7%,The results obtained by the software are basically consistent.(2)Through theoretical and EQUEST dynamic simulation,the thermal load of the solar greenhouse is calculated.The theoretical calculated thermal load is 37.28 KW,and the dynamic simulated thermal load is 35.46 KW.Based on the dynamic simulated thermal load value,the equipment for cross season heat storage is selected and a cross season heat storage system for the solar greenhouse is established.Under the premise of meeting the heating demand of the greenhouse,energy can be saved.(3)The temperature field of solar greenhouses under different seasons and operating conditions was simulated using FLUENT software.The research results showed that in summer,without ventilation,the room temperature of greenhouses using solar spectral selective transmission membranes was 9℃ and 3℃ lower than that of control greenhouses(which were ordinary single-layer membrane greenhouses and ordinary double-layer membrane greenhouses,respectively).Under natural ventilation,the greenhouse using solar spectral selective transmission membrane is 6℃ and 3℃ lower than the control greenhouse,respectively.In the transitional season,consider a single heating mode(north wall heat dissipation and buried pipe heat dissipation).To meet the growth conditions of crops in the greenhouse and avoid energy waste,only a single heating mode can be activated.In winter,greenhouses using solar spectral selective transmission membranes have room temperatures5℃ and 2℃ higher than control greenhouses,respectively. |
