Cooling Effectiveness of High-Volume Low-Speed Fans Versus Conventional Fans in a Free-Stall Dairy Barn in Hot, Humid Conditions1

High-volume low-speed (HVLS) fans use less energy and are quieter than conventional high-speed fans; however, data on the cooling effectiveness of these fans in a dairy free-stall barn in a hot, humid climate is limited. A 4-row free-stall dairy barn located in Tifton, Georgia was fitted with 2 redundant mechanical cooling systems. The first system utilized 0.9-m diameter high-speed cooling fans installed over the feeding area and over the free stalls 6 m apart (conventional system). Each fan was equipped with 4 high-pressure mister nozzles. The second system utilized 7.3-m diameter HVLS fans installed over the center drive-through aisle at 18-m spacing (HVLS system). Evaporative cooling was provided with the same nozzles used in the conventional system. Misters were automatically turned on for both systems when relative humidity was below 85% and temperature was above 24°C. Two groups of 64 cows each were cooled randomly by one system or the other during 2 tests conducted in 2004 and 2005. Four cows within each group were fitted with vaginal temperature probes to monitor the deep body temperature every 5 min on 4 consecutive d. Temperature and relative humidity inside the barn were also recorded every 5 min. Air speeds in the barn were measured with each system operating separately. Observed air speeds were lower for the HVLS system (0 to 8.1 km/h) than for the conventional system (0 to 13 km/h), although air speed was more evenly distributed with the HVLS system. Body temperature was 0.2°C higher (P < 0.01) with HVLS fans compared with the conventional system. These results indicate that the HVLS fans were less effective at cooling cows than the conventional system under extremely hot, humid conditions.