Ventilate Barns in Winter
Lingying Zhao
  

Ventilate Barns in Winter 
Winter is here. As the outdoor temperature drops, we tend to close our buildings to keep them warm and save energy. Sealing a barn will result in high moisture levels and poor indoor air quality because animal facilities generate moisture levels and poor indoor air quality because animal facilities generate moisture, dust, odor, toxic gases and airborne bacteria.

Poor indoor air quality affects human and animal health. High levels of indoor moisture and corrosive gases promote deterioration of building materials. Ventilation plays an important role in maintaining a comfortable and healthy indoor environment. Properly ventilating animal buildings in winter can be a challenge.

Why ventilate? 
Ventilation is an intentional air exchange, which introduces fresh air in and exhausts stale air out of an enclosed space. Failure of a ventilation system can result in death caused by asphyxiation (lack of oxygen and increased carbon dioxide), heat prostration, poisoning from harmful gases or a combination of these.

The goal is to maintain animal comfort and health. Specifically, the ventilation system must:

• Maintain the indoor temperature within the comfort zone of your animals,

• Provide adequate fresh air,

• Distribute air evenly without creating drafts, and

• Dilute and exhaust moisture, odor and gases.

In summer, ventilation is the primary economical way to remove excessive heat build-up around animals. In winter, ventilation is the primary way to remove moisture, gas and odor emissions.

Animals needs
Animals have lived for centuries on the open range, but that doesn't mean they like temperature extremes. Different animals have different comfort zones, and they are quite different from humans. For example, a temperature range of 50 to 70 degrees F is best for horses, with 55 degrees being ideal. Dairy cows and beef cattle prefer 40 to 60 degrees and hogs like 50 to 70 F. However, most of us humans prefer a warmer temperature, 69 to 79 F. In animal barns set the temperature based on animal needs, not yours.

Critical winter ventilation requirement
In winter, bringing in fresh cold air and exhausting stale warm air are both in conflict with in maintaining a comfortable temperature.  However, animals need fresh air continuously.

The ventilation rate for keeping safe air quality is called minimum ventilation. Bringing in fresh air in winter often requires supplemental heat to  maintain a comfortable temperature. Balancing minimum ventilation and supplemental heating is critical for producing healthy animals economically.

Minimum ventilation requirements vary by animal species, numbers, weight and age. For example, per 1,000 pounds of animal, horses need 25 cubic feet per minute (cfm) air exchange, hogs need 10 to 14 cfm and cows need 36 cfm.

Ensure ventilation without drafts
A well-designed ventilation system must operate properly to supply the right amount of air to the right place. For worker safety, animal safety and welfare, and business profitability, producers are advised to check ventilation systems regularly, especially in winter. Two things need to be checked: is the ventilation rate adequate, and is the fresh air distributed as designed without causing any draft on the animals.

Ventilation systems can be classified as nature, mechanical or a combination. Natural ventilation systems move air by wind and thermal buoyancy through air inlets and outlets (vents, windows, doors, eave and ridge slots, etc.).

Mechanical ventilation systems move air by pressure differences created by fans through air inlets and/or outlets under the control of electronic controllers. 

Natural ventilation systems are most efficient and economical for mature animals. Mechanical ventilation systems can meet special needs more precisely.

For a naturally ventilated barn, eave inlets should be opened to the standard 1 inch per 10 feet of building width on both sides of the building, and the ridge opening (also 1 inch per 10 feet pf building width) should be unblocked. Drafts should be minimized by patching curtain holes, reducing gaps at the ends of curtains and sealing around doors to eliminate small gaps. To prevent condensation on the structure surfaces, insulate the roof to at least R-6.

For a mechanically ventilated barn, at least on fan needs to run continuously and deliver the minimum ventilation rate. The building should be sealed to ensure air enters only through designed air inlets rather than through "leaks." The static pressure of a barn needs to be checked to ensure enough inlet openings and that fans are running correctly. Provide at least 1 square foot of inlet area of every 400 cfm of continuous air exchange provided by the exhaust fans. The control of air inlets needs to be checked to prevent small openings, which will result in insufficient fresh air locally, and fix large openings, which will result in drafts on the animals. Walls and ceilings need to be insulated and protected with a vapor barrier on the warm side of the insulation to prevent condensation within the walls. 

For complete information on winter ventilation, get a copy of "Heating, Cooling and Tempering Air for Livestock Housing," MWPS-34. It can purchased online at http://www.mwpshq.org or by calling 800-562-3618, or by sending an email to mwps@iastate.edu.

 

Lingying Zhao, assistant professor and Extension agricultural engineer; can be reached at zhao.119@osu.edu.