IMPROVING THE GREENHOUSES MACROCLIMATE OF HOT AND HUMID REGIONS BY MODIFIED EVAPORATIVE COOLING SYSTEM

Abstract

In hot and humid regions such as around the Equator, coastal areas and Mediterranean basin, crop growth in greenhouses during hot and humid summer is almost impossible because of the excess temperatures accumulated inside causing plant stress and welt. The aim of this experimental work was to investigate the effects of a developed evaporative cooling system on the greenhouse macroclimate and productivity of tomato crop. Two similar gable-even-span greenhouses were utilized at EL-Sabahia Horticultural Research Station, Alexandria (as a Costal region), to produce tomato crop during the summer seasons of 2014 and 2015. Each greenhouse was equipped with a complete evaporative cooling system. One of them was modified (MECS) by obstruct the humid ambient air by a granule silica gel sieve. Whereas it absorbs the excess moisture of ambient air prior to passing through the cooling pads. The other one used the traditional fan-pad evaporative cooling system, (FPECS). The obtained results illustrated that, the averages air temperature after leaving the cooling pad, greenhouse air temperatures, relative humidity, efficiency and vapor pressure deficit were (21.6-28.2 o C), (29.2-33.4 o C), (65.2-71.4%), (89.2-62.1%) and (1.39-1.50 kPa) for MECS and FPECS greenhouses, respectively. The maximum greenhouse temperature decreased below the outside temperature by 2.9 o C for MECS while, it increased by 1.6 o C over it for FPECS. The percentages increase in early yield, number of fruit per plant, fruit weight, total yield per plant and total yield per feddan were 14.07, 9.43, 8.00, 18.15 and 18.13%, respectively for MECS greenhouse over FPECS greenhouse in 2014 season, while they were 12.41, 12.98, 7.90, 22.06 and 21.97%, respectively in 2015 season.