Web-based estimation model of natural ventilation efficiency in greenhouses using 3D computational fluid dynamics

In this work a model to estimate the efficiency of natural ventilation in a commercial twin-span greenhouse is presented. A numerical simulation approach was adopted using the theory of three-dimensional computational fluid dynamics (CFD). With this approach, it was able to generate three-dimensional patterns for temperature and airspeed inside the greenhouse, using specific boundary conditions. The CFD simulation was applied to an empty twin-span greenhouse with a floor area of 980 m with low density polyethylene cover and two side continuous opening and one roof opening. The simulation assumed a sunny summer day with four different airspeeds vertical to the long side of the greenhouse and three different temperature values. Temperature and airspeed data of the entire greenhouse environment were generated by means of CFD simulation and the obtained results were of high accuracy. Each span of the greenhouse was then notionally divided into ten blocks. Average values of the CFD-generated data were used for the parameters estimation of each block. Interpolation was used on the average values of temperature and airspeed of each block to estimate values at different boundary conditions than those that were used during the CFD simulation. This model, which has very low computational demands in comparison with the original CFD simulation model, is incorporated into a web-based application for real-time predictive modeling of temperature and air speed patterns of the greenhouse environment. The web system consists of three main components: the user interface the interpolation process and the output interface.