A Control Method Of Energy Saving For The Greenhouses Based On Model Optimized Prediction And Computational Fluid Dynamics Analysis

Agricultural greenhouses are used to grow crop for better quality and protect them against natural environnmental effects,such as high or low temperature.It is necessary for energy consumption to maintain a suitable temperature for crop production in the greenhouses,especially in cold winter and hot summer.Large amount of energy consumption for crop growth in the greenhouse has been the key problem for agricultural greenhouse development and promotion rapidly.Thus,the energy savings for greenhouse is an important issue.The thesis proposes a modeling methodology for energy prediction model(EPM)of greenhouses,a design method for greenhouse cooling/heating of computational fluid dynamics(CFD)and a CFD-EPM-based control method of greenhouse for saving energy consumption to maintain suitable indoor temperature and better system performance.In chapter 1:The history and latest progress of researches on the methods for prediction energy consumption in the greenhouse,CFD modeling for the greenhouse and control methods of greenhouse for energy savings are reviewed.The research backgrounds and significances of the thesis are analyzed,and the research contents and general framework are pointed out.In chapter 2:According to the non-linear and multi-factor coupling for energy flux process of greenhouses,The physical model of greenhouses energy demand is built up,and the uncertain parameters of model is reduced to improve the convergence speed for identification by using the sensitivity analysis of the Sobol’ method.Adaptive hybrid particle swarm optimization and genetic algorithms(APSO-GA)is presented to improve the prediction performance of greenhouse energy demand with more accuracy and time cost.The cooling experiments in a Venlo-style greenhouse are performed to prove the model and algorithms.In chapter 3:According to the physical characters of the heating process in a semi-closed greenhouse,the energy consumption model of greenhouse is improved.Combined with a self-accelerating PSO and GA(SPSO-GA),the energy forecasting model can be reliable to estimate the energy consumption of semi-closed greenhouse.The heating experiments were conducted in a semi-closed greenhouse located in Shanghai city to verify the extensive applicability of MOP.The developed model for energy consumption can act as a tool to design the cooling/heating load and manage the greenhouse energy for financial and energy savings.In chapter 4:The properties of air fluid dynamic inside the greenhouse are analyzed,and the source-terms of mass,momentum and energy for crop canopy effect are deduced from Darcy-Forchheimer equation of the porous medium.The standard k-ε turbulent model is applied to develop a 3D unsteady model of greenhouse with the fan-pad evaporative cooling system.By simulating the distribution of air flow and temperature under different parameters of greenhouse length,evaporative pad area and fan velocity,the relationships between the fan-pad parameters and greenhouse cooling performance are revealed.A CFD-based design method for fan-pad cooling system in the greenhouse is proposed to configure the reasonable evaporative pad area and the fan in terms of the greenhouse construction.In chapter 5:The heat load of greenhouse is calculated for open-loop surface water source heat pump system(SWSHPS)by using EPM.Based on the low-Reynolds number turbulence model of Lam-Bremhorst,a CFD model of heating greenhouse is built up to optimize the fan coil units(FCU)layout indoor.A novel design method for the heating system of greenhouse based on the CFD and EPM is presented.The SWSHPS for greenhouse is conducted to validate the proposed methods with respect to its heating performance.In chapter 6:A control method of greenhouse heating using CFD and energy prediction model(EPM)is proposed for energy savings and system performance.According to the heating efficiency and temperature uniformity,the priorities of each FCU loop can be predicted to generate a database with priorities for control system.EPM is used to predict and optimize the energy demand of the greenhouse online.Combined with the priorities of FCU loops from CFD simulations offline,the CFD-EPM based heating control system of greenhouse with SWSHPS are developed.Experiment results show the CFD-EPM-based method can improve system performance with more accurate temperature,more rapid responses and lower energy consumption.In chapter 7:The research contents and innovations of the thesis are summarized,and the future work of related research issues is prospected.