International Conference “Passive and Low Energy Cooling 1003 for the Built Environment”, May 2005, Santorini, Greece Effect of vent configuration and insect screen on greenhouse microclimate T. Bartzanas, N. Katsoulas and C. Kittas Department of Agriculture Crop Production and Rural Environment, University of Thessaly, Greece T. Boulard INRA-URIH 400, Sophia Antipolis, France M. Mermier INRA d'Avignon; Unité de Bioclimatologie, Site Agroparc, France ABSTRACT In this paper the effect of insect screens and vent configuration of a tunnel greenhouse culti- vated with a tomato crop on airflow, tempera- ture and humidity patterns was numerically ana- lyzed using a commercial computational fluid dynamics (CFD) code. The numerical model was firstly validated against experimental data, which were carried out in an arch plastic cov- ered greenhouse with continuous side openings. The three components of air velocity and the spatial distribution of air temperature and hu- midity were measured using a sonic anemome- ter and fast response sensors respectively. After the good agreement between experimental and numerically obtained results the code was used for parametric studies concerning the effect of different insect screens and vent configuration on the inside climate. Data from the experi- ments were used to define proper and realistic boundary conditions in the numerical model. A gradual increase of air temperature and humid- ity and a decrease of air velocity were observed as the porosity of the tested insect screen was reduced. It was found that vent configuration affects the ventilation rate and the climate dis- tribution inside the greenhouse. 1. INTRODUCTION Natural ventilation of a greenhouse is a complex process, which depends on the greenhouse char- acteristics (number, location and geometry of windows, area of leaks, etc.) as well as on the external ambient conditions. The role of natural ventilation is predominant in Mediterraneans’ region greenhouses, which are rudimentary equipped and natural ventilation is usually the only climate control system (Baille, 2004). Re- cently the occurrence of resistance to pesticides in several greenhouses key pests, the necessity to reduce environmental problems associated with the use of pesticides and the consumers’ demands for residue-free products increase the incorporation of insect screens in the ventilation openings. However, insect screens can consid- erably reduce the ventilation rate, since they act as an extra barrier on the air movement. Several studies on natural ventilation were based on estimations of a global air exchange rate using tracer gas measurements (Fernandez and Bailey, 1992, Boulard and Draoui 1995, Kittas et al., 1996) and simulations of a homo- geneous air temperature from energy balance models (Kindelan, 1980, Wang and Deltour, 1996). Direct estimates of the airflow through the ventilation openings have also been carried out by the measurement of pressure difference in several greenhouses (Kittas et al., 1996). More recently, sonic anemometry was used to measure airflow patterns in greenhouse ventila- tion openings (Boulard et al., 1997, Wang, 1998). The resistance of insect screens has been in- vestigated using the approach of Bernoulli with experimentally determined discharge coeffi- cients (Montero et al., 1997, Munoz et al., 1999). Another approach has been based on the flow through porous media using the Forchheimer equation (Miguel, 1998, Bailey et al., 2003). However none of the above methods allows improving the greenhouse vents’ design. This is