This project investigated water use by a pad and fan (P&F) cooling system under semi-arid climate conditions. Hydroponic greenhouse crop production greatly reduces irrigation water use however, there is currently no information demonstrating water use of an evaporative cooling system.

Finally, when the air exchange rate was controlled to maintain the GH at 24☌/18☌ during day and night, water use by the P&F cooling system (14.8 L m -2 day -1) was greater than the tomato irrigation system (8.9 L m -2 day -1) assuming 100% drainage recovery, which is typical for many high-technology greenhouse facilities.Ībstract = 'Water availability is a common concern in semi-arid regions, such as Southern Arizona, USA, where more greenhouses are operating due to high solar radiation. If a higher pad cooling efficiency could be maintained at high ventilation rates, a cooler air temperature and higher relative humidity may be achieved, though water use would increase. However, the lower ventilation rates limited air exchange and effectively reduced cooling. It is believed that the lower cooling efficiency of the P&F system at higher ventilation rates caused a reduction in cooling. In general, RH decreased with increasing air exchange rate and the minimum T in of 27.6☌ (RH: 52%) was achieved at the middle air exchange rate (0.051 m 3 m -2 s -1). In the greenhouse with plants, the lowest ventilation rate produced the highest T in (31.1☌) but also the highest RH (69.4%). T in and RH were nearly equal for the three highest air exchange rates. In the empty greenhouse, the lowest ventilation rate produced the highest average greenhouse air temperature (T in=33.8☌) and lowest RH (40%). Water use was primarily affected by air exchange rate. One greenhouse had mature tomato plants (2.3 plants m -2) and the other had no plants. Data were collected for two physically identical, side-by-side, double-layer polyethylene film-covered arched-roof greenhouses (28 m x 9.8 m x 6.3 m) during summer conditions (38.5☌, 15% RH, 845 W m -2). Water availability is a common concern in semi-arid regions, such as Southern Arizona, USA, where more greenhouses are operating due to high solar radiation.

Fan and pad system greenhouse