Performance of a fog system for cooling greenhouses

An evaporative cooling system for greenhouses based on spraying water in very fine droplets (in the fog-size range) without wetting the foliage, is proposed. The combination of ventilation and evaporation flow rates was determined as a function of solar radiation and the ambient climate conditions in order to provide the desired climate conditions. This cooling system can provide a wide range of desired temperatures and relative humidities in greenhouses during most months of the year in Israel with only a minor influence on the radiation level inside the greenhouse. A mathematical model was established to characterize the system, followed by the installation of an experimental system in a semi-commercial greenhouse. The ventilation and evaporation flow rates obtained from the experimental system were in accordance with those obtained from the mathematical model. The fog system provided more uniform temperature and humidity conditions than a pad-and-fan system under similar conditions. (C) 1999 Silsoe Research Institute.