News Page
January 27, 1997
Reducing ventilation in a naturally ventilated dairy barn during frigid winter weather might seem like a good way to keep the barn warmer. But this strategy could be a disaster, says Kevin Janni, biosystems engineer with the University of Minnesota's Extension Service.
"Some dairy producers who have uninsulated, naturally ventilated free-stall barns are thinking about tightening them up and closing the eave inlets to keep the barns warmer," says Janni. "The barns may seem too cold and drafty for the cows. However, barns of this type are designed to be cold--within a few degrees of the outside air temperature."
Janni says closing eave inlets will create wet, damp conditions and lead to respiratory health problems in the cows. Wet, damp conditions will be evidenced by fog, condensation or frost on building surfaces, and high humidities.
"At 30 degrees F, a 1,100-pound dairy cow will give off about 20 pounds of water vapor per day through respiration and losses through its skin as sweat," says Janni. "This moisture must be removed by ventilating air. It can take a ventilating rate of 170 cubic feet per minute per cow to remove it."
Closing eave inlets restricts the ventilating rate and causes moisture to accumulate in the barn, the Minnesota engineer points out. As moisture accumulates it will begin to condense on cold surfaces and, if the surfaces are below freezing, frost will form.
"In severe cold weather and during blizzard conditions, eave inlets can be partially closed to reduce airflow and the amount of snow blowing into the barn," says Janni. "According to Midwest Plan Service, the minimum inlet opening during severe cold weather is one-half inch for each 10 feet of building width. (There should be an inlet on each long side of the building.) When normal winter weather returns, eave inlets should be reopened to the standard one inch per 10 feet on both sides of the building.
"Of course, eave inlet adjustments are much easier if the inlets have been designed to be adjusted. Boards on hinges are the most common type of adjustable eave inlets."
Janni says cows need a dry, draft-free resting area. Drafty conditions at cow level can be reduced by patching curtain holes, minimizing gaps at the ends of curtains, and sealing around doors to eliminate small gaps where the wind blows through.
"Avoid the temptation to keep uninsulated, naturally ventilated free-stall barns too warm," Janni concludes. "They were designed to be cold, and dairy cows do quite well in cold temperatures when they are dry, protected from wind, and properly fed and watered."
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Source: Kevin Janni, (612) 625-3108
Editor: Joseph Kurtz, EDS, (612)
625-3168, pkurtz@extension.umn.edu