Arbel, A., Inst. of Agricultural Engineering, Agricultural Research Organization, Volcani Center, P. O. Box 6, Bet Dagan 50250, Israel
Barak, M., Inst. of Agricultural Engineering, Agricultural Research Organization, Volcani Center, P. O. Box 6, Bet Dagan 50250, Israel
Shklyar, A., Inst. of Agricultural Engineering, Agricultural Research Organization, Volcani Center, P. O. Box 6, Bet Dagan 50250, Israel

This work focuses on the operational characterisation of a fogging system in combination with forced ventilation for cooling greenhouses. This cooling system was installed and operated according to the following scheme: high-pressure spray nozzles with the highest possible uniformity of distribution, fans at both ends of the greenhouse (north and south) placed at ground level, roof openings and two side openings (east and west). The results obtained revealed that inside the greenhouse air temperature and relative humidity of 28°C and 80%, respectively, were maintained during the summer at midday. Furthermore, the results obtained revealed generally high uniformity of the climatic conditions (the same magnitude of temperature measurements error - ± 0.5°C), within the greenhouse, in the lengthwise (north-south) and vertical directions. In contrast to that, there was significant variation across the width of the greenhouse (east-west), which arose as a result of wind action; however, under the conditions of a greenhouse with developed plants or with the windward openings closed, uniform conditions were obtained. It must be concluded that in order to obtain completely uniform climatic conditions throughout the volume of the greenhouse, it is desirable to install fans in all four sides. Such an arrangement may make possible: uniform climatic conditions within the desired range, even in the summer months; good control over the climatic conditions through reduction of the influence of the wind; operation of the greenhouse by means of a relatively simple control system; the establishment of greenhouses in large units and, consequently, better exploitation of the land area and significant reduction in the cost per unit area of the structure. © 2003 Silsoe Research Institute. All rights reserved. Published by Elsevier Science Ltd.