Environment: Ten steps to maintaining outstanding barn air quality Some tips to help you keep your mechanically ventilated barn

Friday, October 10, 2008

Air quality is becoming of increasing importance as we spend more time in our barns. Clean, fresh air also contributes greatly to the health of our pigs. The following 10 steps are intended to help you keep your mechanically ventilated barn an inviting place for you to work and for your pigs to grow.

1. Fresh air intakes servicing room air inlets. Although a ventilation system requires both intake and exhaust, the design and functioning of the building air intake and room air inlet is probably most critical. Openings must be provided to allow air into a building. These can be a louvered hole in the gable end of a barn, a screened slot in one or both soffits or an opening into a hallway.

It is most important that these be sized properly. The size of the opening should be based on an air speed of no more than 500 feet per minute. To size the opening(s), add the maximum capacity in cubic feet per minute of all fans being serviced by the inlet and divide by 500 to get the opening size in square feet. For instance, a 12-inch fan exhausting 1,000 cubic feet per minute would need a one-foot by two-foot opening (two square feet) to service it. To provide cooler intake air on hot summer days, any inlet ducts should be insulated or, if using the attic for an inlet, the roof should be white. Air can also be preheated in winter by passing it through a heat exchange system.

2. Room air inlets. Room air inlets can be manually controlled, controlled by a relatively simple weighted inlet, or automatically controlled by a powered fan controller. I feel that the inlet is the most critical part of the system. An inlet must provide enough fresh air at a correct and constant speed regardless of how many fans are operating. Any opening into a building providing air to an actual room inlet can also be initially sized, using an air speed of 500 feet per minute.

The orifice or louver responsible for jetting air across the ceiling should be adjusted to obtain an air speed of between 800-1,000 feet per minute in order to provide a high room entrance velocity, so the air will jet across the ceiling. This will assure proper mixing of the cold incoming air with the warm room air and prevent cold drafts on the pigs.   

It is extremely difficult to control inlets manually. To provide the correct air speed while avoiding drafts, inlets must respond to every change in fan speed. A weighted inlet is very effective and is relatively simple and inexpensive. Automatic systems incorporated into fan controllers work well, but they must be checked and adjusted periodically using an inexpensive static pressure gauge. Buildings should operate at between 1/10 and 1/8 of an inch of static pressure or vacuum.

3. Pen layout. Pen layout is critical in ensuring that a building or room is properly ventilated and in achieving good manuring habits.

Exhaust fans create a vacuum in a building and displace air in close proximity (within three to four feet) to the outside. If the room is airtight, if air inlets are sized and spaced properly and if the ceiling is perfectly smooth, this vacuum provided by the fans will pull air into the room through properly adjusted inlets and jet it approximately 15 feet across the ceiling before it starts to drop.

This slightly warmed but still rapidly moving air should drop preferably towards the back of the pen in the dunging area, or at least in an alley and then only if the animals have some protection from the draft.

This means that pens with solid or partially slatted floors shouldn't be much longer than 20-25 feet, or the preferred dunging area shouldn't be more than 20-25 feet from the inlet. This is not as important for barns with totally slatted floors, as pigs in these barns can move out of the way of drafts, and manuring habits are not as critical.

If on the other hand, the barn is equipped with two rows of discreet inlets (for example, two-foot by two-foot two-sided inlets over the centre of the pen) and the resting area is also in the centre of the pen under the inlet, then the pens can be longer.

4. Exhaust fans. Livestock buildings need a low rate of air exchange in winter primarily to control moisture accumulation, and higher rates during hot weather to control the temperature. The maximum summer ventilation rate is typically 17 times that of the minimum winter ventilation rate.

Choose fan sizes and thermostats so that the ventilation rate is changed in several steps. One rule of thumb is to double the ventilation rate at each step. Variable speed fans handle this nicely.

Preferably, fans should be placed in the ceiling or in groups spaced along a wall. If they are banked along a wall, the distance between banks of fans should not be more than 120 feet or twice the building width. They should also be at least 12 inches below the ceiling to avoid short-circuiting of inlet air if side air inlets are used. The poorest air quality occurs near an exhaust fan, so try to keep these groupings or fan banks to a minimum.

Fan output varies, so it is important to make sure your model's exhaust capacity has been calculated under a working condition of at least 1/10-inch static pressure. Always provide a minimum of at least four room air changes per hour. To calculate room air change add the total output of fans in the room in cubic feet per minute, calculate the cubic capacity of the room and divide the fan output into the total room volume.

If manure is to be stored beneath slatted floors for two weeks or more, most would agree that exhausting some air from below the floor level is beneficial. This could amount to the winter ventilation rate.

Fans must be protected from the wind. A 30 km/h (18 mph) wind blowing against a fan can reduce a fans output almost to zero. Hoods must extend away from a wall and preferably deflect exhaust air up or down. The hood should extend more than halfway down the building wall and be constructed at least six inches away from the wall to avoid back drafting.

Finally, fan blades must be kept clean to avoid a marked reduction in capacity.

5. Quality controls. Fan controllers are quite sophisticated these days and will generally perform well. Their temperature sensing probes, however, should be checked occasionally with a thermometer to be sure that they are reading the temperature as indicated by the controller and actual room temperature at pig level. Probes should be away from heat sources, away from inlets and doors, and should be in the centre of the area being monitored and as close to the animals as possible.

6. Supplemental heat. Most swine buildings need extra heat in order to keep the air fresh. If your barn is cold or if you notice on a cold night or day that the air in your building feels humid, or if the air has a high ammonia level, you probably need additional heat to allow a minimum amount of air exchange. Relative humidity should be maintained at between 60 and 80 per cent. Nurseries and farrowing rooms always need extra heat.

7. Insulation. The minimum insulation values should be R18 (RSI 3.5) in the walls, R 30 (RSI 5.3) in the ceiling and R 8 (RSI 1.4) around the perimeter of a foundation to at least 12 inches below grade.

8. Manure level. Always try to keep the manure level at least one foot below the slats to help avoid gasses entering the pig space.

9. Avoid overcrowding. The chart at the top of the page shows the minimum space requirements for hogs.

10. Clean buildings. Wet spilled feed or manure on floors can cause odour buildup and poor air quality. Keeping spilled feed cleaned up will help to keep barn air fresher.
A properly designed ventilation system, including well-designed air inlets, will go a long way in keeping floors clean and dry by providing a warm, draft-free sleeping area and a slightly draftier and cooler dunging area. Clean dry pens go a long way to keep barn air fresh. BP

Sam Bradshaw is environmental specialist with Ontario Pork