NATURAL VENTILATION PERFORMANCE OF A LARGE GREENHOUSE EQUIPPED WITH INSECT SCREENS

Natural ventilation performance is one of the key climate control parameters for Canary type greenhouses, which are rapidly expanding along the Atlantic coast in Morocco. The use of insect screens significantly reduces airflow and increases thermal gradients inside the greenhouse. The aim of this study was to analyze the natural ventilation performances in real cultural conditions of a large-scale Canary type tomato greenhouse (1.1 ha) equipped with insect screens on the vent openings. A global energy balance of the greenhouse was used, allowing for the determination of air exchange rates. The greenhouse ventilation performance was compared with those of other greenhouses types and discussed with respect to the improvement of greenhouse vent design, insect screen types, and ridge and crop row orientation. The results confirm the strong dependence of greenhouse ventilation rate on wind speed and ventilation opening location. In addition, results show a significant reduction of the ventilation rate compared with other greenhouse types: the insect screen reduced the greenhouse ventilation rate by 46%, and the tomato rows that were oriented perpendicular to the prevailing air movement through the greenhouse reduced the ventilation rate by 50%. From this analysis, practical improvements are proposed and discussed in the context of protected crop production in the coastal area of Morocco.