University of Minnesota

Dairy Initiatives

Dairy

Department of Animal Science


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Don't Just Blow Hot Air

KEVIN JANNI
Department of Biosystems and Agricultural Engineering
University of Minnesota

Supplemental cooling fans can help boost production during hot weather. They do so by increasing air movement past cows' bodies, helping remove the heat they generate.

Where?
Supplemental cooling fans can be used in stall barns, close-up pens, and holding areas, as well as over feeding alleys and free stalls. For cooling fans to be effective, adequate air exchange must be provided through either ventilating fans or natural ventilation. Air exchange is needed to get the hot air out of the building. Little cooling is gained by blowing hot air.

How
For cooling fans to do much good, they should move air past the cows at a minimum of 200 to 400 feet per minute (2.2 to 4.5 mph). Some researchers in warmer climates have suggested higher velocities, but there is no consensus. Excessive air velocities are not economical and add little additional cooling benefit. As air temperature nears a cow's body temperature (around 102° F), increased air movement becomes less effective at cooling.

Axial Fans
Axial fans with diameters between 24 to 48 inches (2 to 4 feet) are commonly used as supplemental cooling fans. In free-stall barns these fans are mounted 10 to 12 feet above the floor at a slight downward tilt to blow air across the cows' backs. The fans are spaced at distances 10 times the fan diameter (e.g., every 20 feet for 2-foot-diameter fans). Properly oriented, high-quality fans operating at the recommended spacing should provide sufficient cooling.

Axial fan orientation is very important. If fans are pointed too high, little increased air velocity occurs at cow level. One approach is to use fans that have detectable velocities 20 to 40 feet away, and point them at the ground below the next fan. In free-stall barns, orient all fans to blow in one direction, preferably in the predominant summer wind direction.

Limited guidelines are available in the MidWest Plan Service (MWPS) Dairy Freestall Housing and Equipment handbook for selecting and installing axial cooling fans. Select energy-efficient fans with high airflow rates per electrical energy usage (cubic feet per minute per kilowatt hour) to minimize operating costs.

HVLS Fans
A new type of cooling fan being used in dairy facilities is the high volume low speed (HVLS) fan. These are fans with diameters ranging from 8 to 24 feet that move large volumes of air at much lower velocities than axial fans. They have 3/4 to 1 horsepower motors and speeds ranging from 50 to 120 revolutions per minute (RPM), depending on fan diameter.

HVLS fans are mounted like home ceiling fans and blow air toward the floor. As the air nears the floor it spreads out in all directions to provide cooling and mixing.

University of Wisconsin-Madison researchers are currently evaluating cooling effectiveness and air velocities in free-stall barns with HVLS fans. Additional research will be needed to determine mounting height and spacing specifications. Preliminary observations and comments are available at www.bbe.umn.edu/extens/ennotes/enaug01/hvls.htm.

Other Considerations
Poles, rough ceilings or joists in stall barns, walls, feed mangers, waterers, and other obstructions can block airflow, reducing the cooling effect. Locate and orient fans so there are minimal obstructions between the cooling fans and the animals to be cooled.

Wind in naturally ventilated buildings can decrease the cooling effect of both axial and HVLS fans. Wind can also impact HVLS fan flow. At low wind speeds, the effect is usually small and can be ignored. At high wind speeds, which usually increase ventilation, you can shut down the cooling fans to save energy. Be sure to turn the fans on again when wind speeds decrease.

The distance from a fan at which the air movement can no longer be detected is known as the fan's throw. No standards exist for measuring fan throw. Properly oriented fans with good throw can provide effective cooling.


Fan Safety Tips

  • Make sure fan wiring meets all National Electrical Codes (NEC) and local requirements.
  • Consider wiring the fans with a hook, cord, and plug to make it easier to remove the fan for maintenance.
  • Mount fans where they won't get in the way of people, animals, or equipment.
  • Screen or guard fans within reach of people or animals to prevent bodily injury.

D A I R Y    I n i t i a t i v e s    N E W S L E T T E R
Volume 11    Issue 2    Summer 2002