Abstract
When the transpiration of plants is low, the climate inside a greenhouse mainly results from a coupling of convective and radiative exchanges through the cover and ground. However up to now, this coupling has been hardly investigated through numerical techniques. A CFD model was thus implemented to investigate the airflow and temperature patterns inside a glasshouse during daytime, by solving simultaneously the radiative transfer and the energy equations. Simulations were carried out on a four-span compartmentalised glasshouse. The greenhouse was covered with a 4 mm thick horticulture glass and equipped with continuous roof vents. A two dimensional steady state CFD model was developed by using commercial software. The mathematical model solves the Navier-Stokes equations with the Boussinesq assumption and a k - epsilon turbulence model. Solar and atmospheric radiations are included by using a bi-band (distinguishing short and long wave length) radiation model. The analysis focuses not only on the ventilation rate but also on the heterogeneity of the climatic parameters in the canopy vicinity. The model was first partially validated by comparing measured and simulated temperatures inside the greenhouse and along the walls. Numerical predictions of the climate were then obtained for various ventilator configurations (windward only, leeward only and a combination of both). They offer a detailed view of the spatial velocity and temperature distributions and can be used as a tool to assess the characteristics of the ventilation process. The windward vent case generates the highest ventilation rate; nevertheless, the symmetric case ensures a better homogenization of the temperature and velocity. The best compromise between ventilation and homogenization of climatic parameters at the plant level is found by combining a windward roof vent for the windward span and symmetric roof vents for the rest of the greenhouse.
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