Research On Temporal And Spatial Variation Of Air Temperature Prediction Model In Protected Environment Based On CFD

The environmental control technologies of protected agriculture plays an important role to obtain the agricultural products with high quality.The greenhouse technology has become the important direction of protected agriculture development because of its characteristics of high yield and high quality.How to make reasonable control schemes of greenhouse air temperature is the key to improve the greenhouse production efficiency and reduce the energy consumption.This paper took the large multi-span plastic greenhouse in southern region of Jiangsu as the research object,established a temporal and spatial variation of air temperature prediction model in greenhouse based on the computational fluid dynamics(CFD)modeling method and meteorology forecast information.Then combined with the measured data to verify this model and analyzed the prediction results.The main research contents are as follows:(1)This study simplified the greenhouse thermal environment reasonably and established the CFD mathematical model.The buoyancy lift of natural convection was disposed by using the Boussinesq hypothesis.The turbulence transfer was described by the k-? turbulence model,and dealt with the near-wall region using the standard wall function.The DO radiation model was used to simulate the radiation heat transfer in the greenhouse.Using the finite volume method to discrete differential equations and separate method for solving discrete equations.(2)The greenhouse experimental environment and relevant experiment plan was built according to the actual situation of greenhouse.This study did the experimental measurement under the conditions of natural ventilation and fan-pan cooling system in summer and the conditions of insulation curtain folded or unfolded in winter,then analyzed the indoor climate data to provide the reference basis for the establishment and validation of the prediction model.(3)Based on the CFD modeling method and meteorology forecast information,this stody proposed a new temporal and spatial variation of air temperature prediction model in greenhouse through improving the classical CFD model.Adjusted the model parameters,this paper established the temporal and spatial variation of air temperature prediction model in summer by introduced the influence of outdoor temperature,the fan-pad cooling system and solar radiation while the prediction model in winter was established by introduced the influence of outdoor temperature,solar radiation and insulation curtain.Then using the prediction model to forecast the spatial and temporal distribution of air temperature in greenhouse under different control measures.(4)The measured data were compared with the predicted data to validate and analyze the predicted results.The results showed that the predicted values match the measured values.The root mean square error is within 1.2 ?,the maximum relative error is less than 6%,the average relative error is within 4%in summer test and The root mean square error is within 1 ?,the maximum relative error is less than 16%,the average relative error is within 12%.The prediction model can accurately predict the spatial and temporal variation of air temperature inside the greenhouse under different ventilations.According to the results,the spatial distribution of indoor air temperature exits obvious gradient phenomenon.Compared with natural ventilation,the cooling effect of fan-pad cooling system is better,the indoor air temperature can be kept at a lower level by implementing continued fan-pad cooling measure.The spatial distribution of indoor air temperature is evener in winter.The indoor air temperature is significantly higher than outdoor air temperature during the daytime.During the night with insulation curtain unfolded,the cooling trend of crop areas is slowed down.The greenhouse environment meet the demand of the growth of crops.