A COMPARTIVE STUDY ON TWO DIFFERENT EVAPORATIVE COOLING SYSTEMS FOR PRODUCTING CUCUMBER CROP UNDER HOT-HUMID SUMMER CONDITIONS

The influence of greenhouse evaporative cooling systems (based on misting, and fan pads cooling systems) on the microclimatic conditions of greenhouse cucumber was studied and investigated in two fiberglass greenhouses combined with roof shading black net screen situated on the roof of the Agricultural Engineering Department, University of Mansoura. Measurements were executed during several days (122 days) in the hot summer of 2009; (G1) with a mist system operating 15 sec every 15 min., (G2) with a pad-fan system. In order to compare between the cooling systems, air temperatures and relative humidity inside and outside the greenhouses were measured and recorded. Experimental data revealed that the pad-fan cooling system was able to keep the air temperature within the greenhouse at rather low levels. The internal air temperature stayed 8.0°C below outside, even during hot afternoons (T_ao > 35°C). Whereas, the evaporative cooling using mist system kept the greenhouse air temperature above the set point temperature by an average of 4.9°C. Therefore, the internal air temperature stayed 4.2°C below outside. Due to the short length of the greenhouse (8 m), small temperature gradients (2.9°C) were observed from wet pads to extracting fan. The cooling system using fan-pad system inside the greenhouse (G2) was on the average more efficient than the misting system inside the greenhouse (G1) by 22.5% due to the cooling operation period for the greenhouse (2) was longer than that for the greenhouse (1), accordingly, the water temperature of cooling system (2) was lower than that in misting system (G1). The total fresh yield of cucumber crop per square meter for greenhouse (G1) and greenhouse (G2) was 3.805 and 5.491 kg/m², respectively. Therefore, the greenhouse (G2) produced 1.686 kg /m² (44.31%) more than the greenhouse (G1).