Ventilation

Circulating Fans
Dairy free-stall barns and loose housing in the Midwest have typically been naturally ventilated. Many of these naturally ventilated barns have circulating fans that increase airflow past the animals on hot days to promote cooling. If fans are added, it is common to use high speed circulating fans however High Volume, Low-Speed (HVLS) fans are a newer technology which can reduce the energy cost for air circulation while maintaining or improving animal comfort.

Illustration 1: High-speed circulating fans in free-stall barn. Source: Scott Sanford.

Illustration 1: High-speed circulating fans in free-stall barn. Source: Scott Sanford.

High-Speed Circulating Fans
High-speed circulating fans can be used to increase the air velocity and reduce stagnation, Illustration 1. Increased air velocity helps animals give off heat during hot weather. It is common to install one or two rows of high-speed fans per group of animals in free-stall dairy barns; a row over each row of free-stalls and an optional row along the feed alley blowing over the animals’ backs. Usually, 36-inch or 48- to 50-inch fans are installed every 30 or 40 feet, respectively. The rule of thumb for fan spacing is 10 feet per foot of fan diameter.
The University of Illinois Bioenvironmental and Structural Systems (BESS) Laboratory tests circulating fans and reports their performance and energy efficiency. Circulating fans are rated for their thrust/power ratio, expressed as pounds force (lbf) per kilowatt (kW). A higher number indicates a more efficient conversion of electrical power to air movement. This makes it possible to easily compare fans of different design or from different manufacturers. Test results are available at the BESS lab web site. In general, the larger the fan, the more energy efficient it will be. Fan guards decrease energy efficiency by 15 percent or more but are necessary when fans are mounted within reach of animals or people. The air velocity directly downwind of a fan at five fan diameters is measured during testing. It is not a reliable predictor of the efficiency but is useful to determine the throw distance or downwind air velocity of different fans. Table 4 lists the recommended minimum ratings for selecting energy-efficient fans based on the fan test data from BESS Lab.

Table 4: Energy efficiency for high-speed circulating fans.Source: Compiled by Scott Sanford, Data Source: BESS Lab 2011

Table 4: Energy efficiency for high-speed circulating fans. Source: Compiled by Scott Sanford, Data Source: BESS Lab 2011

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