ISHS Acta Horticulturae 287: II International Symposium on Protected Cultivation of Vegetables in Mild Winter Climates
THE ENVIRONMENT IN EVAPORATIVELY COOLED GREENHOUSES |
| Author: | B.J. BAILEY |
| Abstract:
Regions with mild winter climates often experience high summer temperatures which limit the effective production period of greenhouse crops. If the high external air temperatures are associated with low absolute humidities, evaporative cooling can provide an effective way of reducing the thermal and water stresses on greenhouse plants, and thus allow the growing season to be extended. A simulation model was used with meteorological data recorded at ICARDA (Aleppo, Syria) to predict the temperatures and vapour pressure deficits obtained in greenhouses with fan and pad cooling. The temperature of the air entering the greenhouse from the cooling pad depends on the external dry and wet bulb temperatures and on the efficiency of the pad. Inside the greenhouse the gradient in temperature between the cooling pad and the air extract fans is influenced by the extent of crop cover, the amount of external shading and the type of greenhouse cladding. Compared to an unshaded, single plastics film clad greenhouse with no crop, the temperature gradient was reduced by 50% when full crop cover was present, a further 45% reduction was obtained with 50% external shading, and using double cladding provided an additional reduction of 20%. The results showed that in a partially cropped greenhouse the plants should be positioned near the cooling pad. Shading was shown to be very effective in reducing the cooling requirement but it also reduced the photosynthetically active radiation. The value of a double cover increased as the ventilation temperature was lowered as it reduced the conductive transfer of heat into the house. | |
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