Simulation of climatic conditions in full-scale greenhouse fitted with insect-proof screens

Abstract

Air flow, temperature and humidity patterns were simulated in a large-scale Moroccan type tomato-greenhouse (5600 m 2) equipped with insect-proof nets. The fundamental calculation of climatic conditions is based on computational fluid dynamics, which uses the mass, momentum and energy conservation equations. The airflow in the crop cover together with the insect-proof nets were described by means of the porous medium approach proposed by Darcy and modified by Forcheimer. A commercial software package was used to obtain the numerical solutions using discrete finite volumes. Three-dimensional simulations were performed for the stationary regime and the turbulent transfers as described by the k– e turbulence model. The computer fluid dynamics (CFD) code was also customized in order to simulate, within each element of the crop cover, the sensible and latent heat exchanges between the air and the crop (assimilated to the solid matrix of the porous medium). Results show that air flow penetrates into the greenhouse through the windward end, it then follows a spiral trajectory, through the crop cover where it is warmed and humidified before rising over the crop and escaping through the leeward part of the roof vents. A reverse flow is also observed near the leeward end of the greenhouse. These simulations were later validated with respect to air exchange rate measurements and a good agreement was observed between measured and simulated ventilation rates. This model was used later to analyze the effects of insect-proof nets with finer threads on the inside climate and the results show a significant increase of temperature and humidity induced by the anti- thrips and anti- aphids nets.