| The conventional ON-OFF control of forced ventilation in agricultural greenhouse causes problems such as sudden change of internal temperature and uneven distribution of temperature fields. The work done in this thesis includes experimental study, CFD simulation of temperature in a greenhouse.A new technology to use the CFD simulation of the temperature field information to optimize the control decision and explore variable frequency drive in forced ventilation which can overcome problems in traditional way to achieve the purpose of energy saving.1. A experimental facility has been setup in a commercial production greenhouse. Detail on how to build experimental platform.Experimental platform for measuring wind speed of fan working, inside and outside the shade net’s shading rate and use the CFD simulation to the boundary conditions.And collect the wet curtain-fan system in the cooling process, the monitoring points within the greenhouse temperature stable and transit process. A summary and analysis of the final results of the experiment.2. On the basis of the experiment, a three-dimensional real scale geometric model of experimental greenhouse was designed by utilizing GAMBIT, the cooling process of forced ventilated greenhouse is simulated by combining with the standard k-sturbulence model. A comparison between experiment and the simulated was conducted to get more knowledge of internal temperature field contours and dynamic characteristics.3. By using the validated model in the experiment the effects on temperature fields by several important factors such as ventilation rate, air temperature of inlet and solar shading screen are studied.4. A new method of conducting variable ventilation in greenhouses is proposed and a new optimal control strategy of ventilation by CFD simulation results is designed. Based on these achievements a control system of forced ventilation by utilizing PLC and VFDs is described.
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