ISHS Acta Horticulturae 614: VI International Symposium on Protected Cultivation in Mild Winter Climate: Product and Process Innovation
TEMPERATURE AND HUMIDITY GRADIENTS IN FAN VENTILATED GREENHOUSES UNDER TWO COOLING MODES |
| Authors: | M. Teitel, M. Barak, Y. Zhao |
| Keywords: | Greenhouse cooling, transpiration, fan, pad |
| Abstract:
Cooling of the greenhouse environment is considered a challenge in many warm-climate countries. Finding the limits of cooling offered by fan ventilation only (mode I) and comparing them with the performance of a fan and pad system (mode II) may improve climate control, increase crop quality/production, reduce energy costs and improve the economics of greenhouse production. Experiments were done in a greenhouse equipped with a fan and pad system in which pepper was grown to a height of about 3 m. Temperature and humidity gradients along the greenhouse and as functions of height were measured in each of the above-mentioned cooling modes, applying two ventilation rates in each mode. The effects of the ventilation rate on the gradients and on the heat fluxes within the greenhouse were examined. It is shown that in mode I the air temperature within the greenhouse was most of the days lower than ambient temperature with a very small effect of the ventilation rate on the temperature difference between inside and outside the greenhouse. The main temperature gradient, in this mode of operation, was observed in the vertical direction from bottom to top and its absolute value decreased with an increase in ventilation rate. A similar behavior was observed with the specific humidity within the greenhouse. In mode II the air temperature inside the greenhouse was lower than that obtained with mode I and was all the days lower than ambient temperature. Contrary to mode I, in mode II, the ventilation rate affected the temperature difference between inside and outside the greenhouse; decreasing the air temperature further as the ventilation rate increased. In both modes of operation (I and II), the specific humidity within the greenhouse was always higher than ambient specific humidity, with higher values observed in mode II, as expected. Similar to the temperature gradients, the largest gradients in specific humidity in mode II were observed in the vertical direction and they decreased when the ventilation rate increased. | |
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