Teitel, M., Agricultural Engineering Institute, Agricultural Research Organization, Volcani Center, P.O.B. 6, Bet Dagan, 50250, Israel
Barak, M., Agricultural Engineering Institute, Agricultural Research Organization, Volcani Center, P.O.B. 6, Bet Dagan, 50250, Israel
Zhao, Y., Faculty of Mechanical and Electrical Engng, Jiaxing University, 56# Yuexiu Road, Jiaxing 314001 Zhejiang, China

Experiments were done in a four span greenhouse in which pepper was grown, to compare between roof plus side and roof-alone ventilation. The effects of the resistance to air flow through the roof and side vents, on the microclimate and ventilation rate were studied. The resistance of the roof vents to airflow was changed by changing the screen installed on them, while the resistance of the side vents was changed by varying the area of these openings without changing the screen mounted on them. It was shown that in small commercial greenhouses, a combination of roof and side vents can be more efficient in reducing temperature and humidity than a roof-alone ventilation system, when the airflow resistance of the side vents is low. In such a case, the type of screen mounted on the roof vents (i.e. the resistance of the roof vents) has little effect on the microclimate within the enclosure.