Improved performance of partly pit exhaust systems in pig housing

Abstract. Commercial chemical or biological air cleaning systems are capable to remove more than 90 % of the ammonia in exhaust air from mechanical ventilated pig housing, but it is costly to install cleaning systems large enough to treat the large amount of air needed in warm periods. Introduction of partly pit ventilations systems where the first 10 % of ventilation capacity is expelled through local exhaust located in the pit beneath the slatted floor can reduce pollutant concentration in the room, and simultaneously remove a large part of the pollutants in the small amount of expelled air from the pit. In addition this creates the preconditions for installing cost effective cleaning system that treats only the air expelled from the pit. CFD studies has shown that even though 10 % of ventilation capacity is expelled from the pit there still are significant amount of air moving up through the slats and that observation indicates that changes in pen or pit design potentially may lead to improved performance of partly pit ventilation systems. One option is to reduce the openings of the slatted floor, but this may have a negative consequence of accumulated urine and manure on the floor and can therefor potentially increase the total ammonia emission. Another option is to place plates (or curtains) in the pit to reduce the air movement beneath the slats, and the effects of this method are investigated in this study. The study includes CFD and full scale measurement, and shows that plates or curtains in the pit significantly can improve the performance of a partly pit ventilation system.