Predicted Effects of Roof Vent Combinations on the Climate Distribution in a Glasshouse Considering Radiative and Convective Heat Transfers P.E. Bournet and S.A. Ould Khaoua UMR SAGAH A_462, Institut National d’Horticulture 2, rue Le Nôtre 49045 Angers France Keywords: CFD modelling, sky and solar radiation, inside climate heterogeneity 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 ε − 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. INTRODUCTION The temperature in a greenhouse results from convective and radiative exchanges through the surfaces of its different components (e.g. crop leaves, cover, ground surface, heating pipe etc.). Most of the short wavelength (i.e. solar) radiation reaches the ground which warms up and re-emits an infrared radiation which is absorbed by the glass. The glass then re-emits an infrared radiation towards the ground and the atmosphere, which leads to an increase of the temperature inside the greenhouse. Warming is however limited by thermal conductive transfers through the ground and mostly by convective exchanges towards the outside. In most of CFD studies of full-scale greenhouse climate, the effect of solar and thermal radiations was taken into account by setting specific wall temperatures (inferred from measurements for instance). However very few studies have been conducted by solving the radiative transfer equation coupled to the convective transfer equations (Lee and Short, 1998; Lee and Short, 2000; Montero et al., 2005). Nevertheless, none of these studies appeared to include both the interchange of short and long wavelength radiation between the sky and the greenhouse cladding, and between greenhouse structural elements. 925 Proc. IS on Greensys2007 Eds.:S. De Pascale et al. Acta Hort. 801, ISHS 2008