Articles
WATER USE FOR PAD AND FAN EVAPORATIVE COOLING OF A GREENHOUSE IN A SEMI-ARID CLIMATE
Article number
719_46
Pages
409 – 416
Language
English
Abstract
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.
Hydroponic greenhouse crop production greatly reduces irrigation water use; however, there is currently no information demonstrating water use of an evaporative cooling system.
This project investigated water use by a pad and fan (P&F) cooling system under semi-arid climate conditions.
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°C, 15% RH, 845 W m-2). One greenhouse had mature tomato plants (2.3 plants m-2) and the other had no plants.
Water use was primarily affected by air exchange rate.
The average water use by the P&F system was 0.145, 0.182, 0.265, 0.325, and 0.387 g m-2 s-1 for greenhouse air exchange rates of 0.017, 0.037, 0.051, 0.067, and 0.079 m³ m-2 s-1, respectively.
In the empty greenhouse, the lowest ventilation rate produced the highest average greenhouse air temperature (Tin=33.8°C) and lowest RH (40%). Tin and RH were nearly equal for the three highest air exchange rates.
In the greenhouse with plants, the lowest ventilation rate produced the highest Tin (31.1°C) but also the highest RH (69.4%). In general, RH decreased with increasing air exchange rate and the minimum Tin of 27.6°C (RH: 52%) was achieved at the middle air exchange rate (0.051 m³ m-2 s-1). It is believed that the lower cooling efficiency of the P&F system at higher ventilation rates caused a reduction in cooling.
However, the lower ventilation rates limited air exchange and effectively reduced cooling.
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.
Finally, when the air exchange rate was controlled to maintain the GH at 24°C/18°C 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.
Hydroponic greenhouse crop production greatly reduces irrigation water use; however, there is currently no information demonstrating water use of an evaporative cooling system.
This project investigated water use by a pad and fan (P&F) cooling system under semi-arid climate conditions.
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°C, 15% RH, 845 W m-2). One greenhouse had mature tomato plants (2.3 plants m-2) and the other had no plants.
Water use was primarily affected by air exchange rate.
The average water use by the P&F system was 0.145, 0.182, 0.265, 0.325, and 0.387 g m-2 s-1 for greenhouse air exchange rates of 0.017, 0.037, 0.051, 0.067, and 0.079 m³ m-2 s-1, respectively.
In the empty greenhouse, the lowest ventilation rate produced the highest average greenhouse air temperature (Tin=33.8°C) and lowest RH (40%). Tin and RH were nearly equal for the three highest air exchange rates.
In the greenhouse with plants, the lowest ventilation rate produced the highest Tin (31.1°C) but also the highest RH (69.4%). In general, RH decreased with increasing air exchange rate and the minimum Tin of 27.6°C (RH: 52%) was achieved at the middle air exchange rate (0.051 m³ m-2 s-1). It is believed that the lower cooling efficiency of the P&F system at higher ventilation rates caused a reduction in cooling.
However, the lower ventilation rates limited air exchange and effectively reduced cooling.
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.
Finally, when the air exchange rate was controlled to maintain the GH at 24°C/18°C 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.
Publication
Authors
N.C. Sabeh, G.A. Giacomelli, C. Kubota
Keywords
Cooling efficiency, ventilation rate, hydroponics, single-span greenhouse
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