Engineering Notes Index

Engineering Notes
Winter 1995-96

Winter Ventilation Checklist

Larry D. Jacobson, Extension Engineer

This winter's early cold weather has magnified indoor air quality concerns inside many of the state's pig confinement facilities. High moisture levels and poor overall air quality are common complaints in both mechanically and naturally ventilated buildings. Some of the newer curtain sided" finishing barns are experiencing problems because producers are still learning how to manage them during extremely cold temperatures.

Remember, even though subzero temperatures exist outside, a pig building still needs to have a small but continuous air exchange to control moisture and maintain acceptable indoor air quality. This is true whether the barn is mechanically or naturally ventilated. If the building contains pigs under 120 lbs, you may need supplemental heat (furnace or heater) during extreme cold weather to maintain room temperatures greater than 60F. An alternative is to provide some type of radiant heat (heat mats, infrared heaters, and/or a hover) which creates a warm floor and/or a warmer microenvironment for the pigs. This is especially beneficial in naturally ventilated facilities where trying to add heat with a furnace is not economical.

If you have a mechanically ventilated barn (includes the newer "curtain style" finishing facilities), use the following checklist in preparing your unit for cold weather:

• At least one ventilation fan runs continuously and delivers from 2 (nursery) up to 10 (finishing) cfm per pig. The fan or fans delivering this air exchange should be single speed, or if variable speed, the speed should never be lower than half the fan's maximum. This improves the fan's ability to overcome wind forces.

   

• The building should be as tight as possible, with air entering only through designed air inlets rather than through undesigned "leaks." Provide at least 1 sq. ft of inlet area for every 400 cfm of continuous air exchange provided by the exhaust fans. These inlets should take air from the attic or adjacent rooms or hallways rather than directly from outside to reduce wind effects on the inlets. Attics and hallways, in turn, need to have intakes which will allow fresh air to enter those spaces. Remember, there must be some way for air to enter the building if you want to remove moisture and other air contaminants with the exhaust fans.

   

• Walls and ceilings need to be insulated and protected with a vapor retarder (sheet of plastic) on the warm side of the insulation to prevent condensation within the walls. R-values in the mid-teens for the walls and in the mid-twenties for the ceiling are adequate for pig buildings. Because curtain barns cannot meet these insulation requirements for the walls, wet and sometime frosted (during extreme cold) curtains will need to be tolerated.

Facilities which are naturally ventilated also need to have continuous ventilation, but need to be managed differently from mechanically ventilated buildings. Follow this checklist if your building is naturally ventilated (no fans) during winter:

• Make sure there is adequate outlet (ridge opening or chimneys) area. For modified environment buildings (pig grow-finishing and sow gestation), provide at least 1 inch of continuous ridge opening per 10 ft of building width. Watch for frosting at the outlets and clear excessive ice and frost build up periodically to maintain this amount of opening.

   

• The building shell should be as tight as possible, making sure that air only enters through designed air inlets. During subzero temperatures, air should only enter on leeward (typically the south or east) sides of naturally ventilated buildings. Temperature controlled curtains or vents are the most common inlets. However, curtains or vents must be adjusted to provide a small but permanent opening so that even though the room temperature is below the setpoint, some air is continuously moving through the building. If this is not done and there are few cracks or leaks in the barn, insufficient air exchange will result in high humidity and poor air quality. Also, without this minimum amount of sidewall inlet area in a naturally ventilated barn, air often enters the ridge or outlet at one end of the barn and exits at the other end creating a reverse or downward air flow plus a large temperature variation down the length of the building.

   

• A naturally ventilated pig barn also needs to be insulated, especially on the underside of the roof, to prevent condensation and frosting. R-values of at least 6 to 8 should be provided under the roof or in the sloping ceiling.

In summary, during extremely cold conditions, a minimum and continuous (no timer controlled fans) air exchange needs to be provided in pig buildings to control moisture and maintain minimum indoor air quality. This is true for both mechanically and naturally ventilated structures. Unfortunately, this air exchange rate during subzero outside temperatures, will result in lower room temperatures for pigs under 120 lbs. How cold the room gets will depend on the size of pigs, ventilation rate, and insulation level. Supplemental heat can be added to maintain the room temperature. Or radiant heat or hovers can be incorporated into pens to create a warmer microenvironment for the pigs, especially in naturally ventilated barns.

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