Aspects of CFD Modelling of a Fan and Pad Evaporative Cooling System in Greenhouses

Abstract

A methodology approach to simulate, by means of computational fluid dynamics (CFD) tools, a greenhouse equipped with a fan and pad evaporative cooling system is presented. Using the main aspects of evaporative cooling systems, in terms of heat and mass transfer, the flow and boundary conditions of the simulation model are identified taking into account both the external and internal climatic conditions. The crop (tomato) was simulated using the equivalent porous medium approach by the addition of a momentum source term. The temperature and humidity of incoming air and the operational characteristics of fans were specified to set up the CFD model. Numerical analysis was based on the Reynolds-averaged Navier-Stokes equations in conjunction with the realizable k-epsilon turbulence model. The finite-volume method (FVM) was used to solve the governing equations. The 3D full scale model was solved in several differencing schemes of various orders in order to examine its accuracy. This simulation approach was used to identify the critical parameters of microclimate of a greenhouse and the regions where these have to be measured during the experimental processes. The simulation model was validated against experimental data based on the air temperature inside the greenhouse at twenty three points for three ventilation rates. These results showed good qualitative agreement in which the influence of the different airflow rates on greenhouse microclimate, indicated that the proper choice of ventilation rate is a crucial factor in order to improve the efficiency of evaporative cooling systems in greenhouses.