Cooling is an essential part of greenhouse climate control in warm climates. There are three types of cooling technique: natural ventilation, evaporative cooling and mechanical cooling. Natural ventilation can only be applied when the outside temperature does not exceed 35°C and the average daily temperature is not higher than 22°C. Above these temperatures, production will be negatively affected. Evaporative cooling can be applied when the dew-point temperature of the outside air is less than these limits. These methods of cooling work effectively in arid regions, though the water consumption is high. The third method of cooling demands a cold surface to remove the latent and sensible heat from the greenhouse. This method has been applied in the current research. This method allows optimal control of the greenhouse climate in terms of temperature and humidity, but also in terms of carbon dioxide concentration. The amount of cooling capacity required depends on the amount of solar radiation being absorbed in the greenhouse and the convective heat transfer from outside, provided the outside temperature is higher than the greenhouse air temperature. The experiment showed that roughly 50% of the solar radiation has to be cooled from the greenhouse in order to maintain its temperature. Sixty per cent of the heat being absorbed in the greenhouse is transformed into latent heat through the transpiration of the crop. The system was able to maintain the preset temperature and humidity for the greenhouse air.
- Energy use