Comparison of High Volume Low Speed (HVLS) vs. Conventional Fans in a Free Stall Dairy Barn in a Hot Humid Climate

Abstract

High-volume low-speed (HVLS) fans have been used to ventilate a number of dairy free-stall barns. These large fans use less energy and run much more quietly than conventional high-speed fans. This report addresses the cooling effectiveness of these fans in a dairy free stall barn located in a hot, humid climate. A four-row free-stall dairy barn located in Tifton, Georgia was fitted with two redundant ventilation systems. System one utilized 0.9-m (3-ft) diameter high-speed cooling fans installed over the feeding fence and over the free stalls 6 m (20 ft) apart. Each fan was equipped with 4 high-pressure mister nozzles. System two utilized 7.3-m (20-ft) diameter HVLS fans installed over the center drive-through aisle at 18-m (60-ft) spacing. Controls were installed so that two groups of 64 cows each could be cooled by one system or the other. Vaginal temperature probes were installed in four cows in each group to monitor the deep body temperature. Temperature and RH inside the barn and cow temperature were recorded every 5 minutes. The tests were run for a total of six days with ventilation systems alternated among groups. Misters were automatically turned on for both systems when relative humidity was below 85% and temperature was above 24 oC. Wind speeds in the barn were measured with each system operating separately. Observed wind speeds were significantly lower for the HVLS system (0 to 8.1 km/h) than for the high-speed fan system (0 to 13 km/h), although wind speed is more evenly distributed with the HVLS system. Body temperature was approximately 0.2 oC (0.4 oF) higher for cows cooled by the HVLS fans compared with conventional high-speed fans. These results indicate that the HVLS fans did not provide adequate air flow to cool cows as effectively as the high-speed fans under extremely hot, humid conditions.