Direct cooling with stir fans and sprinklers.

By Austin Baker, Ventilation Director, Hog Slat Inc. 

The summer performance of curtain-sided, naturally ventilated buildings can be improved by utilizing a combination of stir fans and a sprinkler system to reduce animal heat stress.

Pigs feel a cooling effect as high-velocity air from the stir fans moves across their body.  By wetting the pig's skin, we increase the cooling effect as the air evaporates the water removing heat from the animal.

For direct cooling to work efficiently, the pig's skin should be thoroughly wetted and then allowed to dry completely.  The wetting and drying cycle is a critical part of the process.  If the pigs are continuously wet, the humidity rises which in turn reduces the amount of cooling by evaporation.

Choose nozzles that produce coarse droplets vs. a fine mist.  Large drops fall quickly thoroughly wetting the pigs while a fine mist hangs in the air increasing humidity.  The control system should include an adjustable timer enabling the system to operate for two to four minutes every 15 to 30 minutes after reaching the temperature set point.

For optimum cooling, strive for an air velocity of 300 fpm at pig level.  The effective thrust of a fan is 2X (in feet) of its diameter.

For example:

18" fan - 36'

20" fan - 40'

24" fan - 48'

We show typical layouts for 40' x 200' finishing building with both a racetrack and cross-staggered patterns.  Angle the fans in the racetrack pattern at about 20° towards the middle.

Stir fans also do an effective job circulating stratified air during colder weather.   Low winter ventilation rates decrease air movement in the building creating a 5 to 10-degree temperature difference from floor to ceiling.  By slowing the stir fans down to a minimum speed, a gentle circulation pattern mixes the layered air.  Forcing the warmer air to the floor reduces heating costs and results in drier slats.   Tilt the fans towards the ceiling and monitor airflow at floor level being aware that movement greater than 50 fpm can feel like a draft to the pigs.