Many of the readers of my blog have tunnel ventilated wean-finish or grow-finish facilities. Others have seen these type of facilities and have questions about how they function in terms of meeting the heat removal needs of growing pigs. A common question I get asked – how much temperature variation is ‘normal’ for these facilities?
For readers unfamiliar with tunnel ventilated barns, these facilities use ceiling inlets for relatively uniform air distribution within the room of the facility for the lower stages of ventilation. Often times there are enough fans and ceiling inlets to accommodate 45-54 cfm/pig of ventilation capacity.
Once higher amounts of air exchange are required to remove heat produced by the growing pig, a curtain opens at one end of the relatively long and narrow room (often 50 ft x 196 ft or 40 x 240) as an additional air inlet to the room with exhaust fans at the opposite end of the room pulling the air across the pigs on its way to being exhausted by the fans. As more fans come on to increase the amount of air exchanged the curtain opens further and in most cases the ceiling inlets close so little if any solar heated air from the attic is pulled into the animal space. When the ventilation system reaches maximum capacity, 100% of the incoming air enters at one end of the room via the tunnel curtain opening with it being exhausted at the other end of the room.
Most ventilation experts size maximum ventilation rates with the expectation that during warm/hot weather the temperature of the air at the exhaust fans is no more than 2-3F warmer than the temperature of the incoming air (ambient). It is generally felt that it is not economical to install additional fan capacity to lower temperature variation below this target.