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Water Use by Greenhouse Evaporative Cooling Systems in a Semi-Arid Climate

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  2007 ASAE Annual Meeting  074013.(doi:10.13031/2013.23054)
Authors:   Nadia C Sabeh, Gene A Giacomelli, Chieri Kubota
Keywords:   pad-and-fan, high-pressure-fog, ventilation, water use efficiency, controlled environment

Water availability is a common concern in semi-arid regions, such as Southern Arizona, USA, where greenhouse crop production is popular due to high solar radiation. Hydroponic greenhouse crop production greatly reduces irrigation water use; however, water use by evaporative cooling systems has never been quantified. This project investigated water use by two evaporative cooling systems: pad-and-fan (P&F) and high-pressure-fog (HPF) with fan ventilation and a central overhead line. Water use data were collected from a double-layer polyethylene film-covered greenhouse (28 x 9.8 x 6.3 m) with mature tomato plants (1.7 plants m-2) from 08:00 – 17:00 for each ventilation rate tested under semi-arid climate conditions (TOut,Avg=35°C, RHOut,Avg=10%, SolarAvg=900 W m-2). Total daily water use by P&F was 3.2, 6.4, 8.5, and 10.3 L m-2 for ventilation rates of 0.016, 0.034, 0.047, 0.061 m3 m-2 s-1, respectively. Total daily water use by the HPF system was 7.9, 7.4, and 9.3 L m-2 for fan ventilation rates of 0.01, 0.016, 0.034 m3 m-2 s-1, respectively. Total greenhouse WUE (water use efficiency) was calculated using hydroponic irrigation (4.5 L m-2) and evaporative cooling water use. Total WUE values were comparable to sprinkler-irrigated WUE (15-19 L m-2) and flood-irrigated WUE (< 12 L m-2). Using a “closed” hydroponic irrigation system would increase the WUE greatly and should be implemented to conserve water. Furthermore, HPF water use should decrease under natural ventilation.

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