Consumptive Water Use of Evaporative Pads

Abstract

Dairies are using evaporative pads to cool air in tunnel ventilated facilities. However, additional information is needed to ensure adequate water is available to meet the demands of the evaporative pad system. The objective of this study was to determine the water usage of an evaporative pad. Consumptive water usage by evaporative pads was measured during 7 days of a 3-week period at a Kansas (KS) dairy and a 2-day period at a North Dakota (ND) dairy. Water meters were installed between the water hydrants and evaporative pads at each dairy and monitored. Data was recorded every 30 minutes during 5 hrs at the KS site and 15 minutes during 1 to 2.5 hrs at the ND site. Ratio of pad area to cow equaled 0.45 m2 (4.8 ft2) and 0.42 m2 (4.5 ft2) per cow at the KS and ND sites, respectively. Air velocities through the pads were 0.5 m/s (1.2 mph), 0.9 m/s (2.1 mph), and 1.4 m/s (3.2 mph) at the ND dairy and 1.5 m/s (3.3 mph) at the KS dairy. During the study period in KS, the temperature humidity index ranged from 78 to 86 and water usage varied from 2.6 L/min (0.7 gpm) to 17.6 L/min (4.7 gpm). Average pad efficiency equaled 62%. Water usage averaged 0.2 L/min/m2 (0.3 gal/hr/ft2) of pad when airflow rate was 1.5 m/s (3.3 mph) to 1.6 m/s (3.6 mph). At the ND dairy, the water usage averaged 0.07 L/min/m2 (0.1 gal/hr/ft2), 0.20 L/min/m2 (0.3 gal/hr/ft2) and 0.26 L/min/m2 (0.38 gal/hr/ft2) of pad for the low, medium, and high airflow rates, respectively. The temperature humidity index inside the freestall building equaled 65, 72.5, and 71 for the low, medium, and high airflow study periods. Pad efficiency averaged 93, 86, and 81% from the low to high airflow rates. Similar to pad efficiencies at the KS site, efficiency increased as the outdoor air temperature decreased.