New Barn Ventilation Details

I’m getting quite a few requests for ventilation details on new double-wide tunnel wean-finish or grow-finish facilities. In addition, I’ve reviewed the ventilation system as installed at quite a few sites in recent weeks. Unfortunately, the many builders and facility owners still undersize the attic inlet area and end up with higher electricity expense and tunnel curtains opening at colder outside temperatures that expected/desired.

Here are the design details that I use for soffit inlet sizing when double-wide tunnel barns are 102 x 196 in dimensioning.
• 8″ MINIMUM continuous south/east soffit with 8″ clearance at plate. The math becomes:

4-24″ fans (or 6-21″ or some combination) plus 1 36″ plus 1 52″ fan before going into tunnel mode in each room – this is often in the range of 50 cfm/pig or 62,000 cfm/room

 2 rooms = 124,000 cfm from attic
 196 ft long rooms
 124,000 cfm / 400 cfm/sqft soffit = 310 ft2 soffit inlet recommended
 310 ft2 / 196 ln feet = 1.58 ft wide soffit = 19” wide soffit opening

• If you have 8” of south/east soffit (0.67 ft wide), the air velocity when both rooms are in stage 4 ventilation and the north/west soffit is still closed becomes:

 124,000 cfm /(196 ln ft x 0.67 ft) = 950 fpm.

This adds 0.05 static pressure to the system due to the need to pull air this fast thru the soffit. This is more than we want/recommend, but I know I’m lucky if I can get 8” by the time insulation chutes are installed, etc.

• Fans sized on stage 1 so you can get to 2 cfm/pig range for starting single stocked weaned pigs. This may mean turning off one fan and turning off actuated inlets.

• Nothing other than bird netting (1” minimum opening) on soffit openings– no punched metal of any kind.

2 thoughts on “New Barn Ventilation Details

  1. What about pit fans?tunnel barn in last 3 stages should pit fans be left on or turned off?

  2. Whether to leave pit fans on or off at last stage of tunnel depends on the total fan capacity of the room, etc. For example, my design target is 1.7 air changes per minute for the total volume above the slats for 1200 head rooms. If your builder installs 5 – 50″ fans plus 2-36″ fans plus 4-24″ fans, the approximate total fan capacity as installed (this is less than 0.05 static pressure rated capacity to account for dirty shutters, pit plenums, etc) is about 145,000 cfm. If the barn is 50 x 196 with 8 ft ceiling, this is 78400 cubic ft of volume and you get 1.85 changes per minute with all fans operating.

    If on the other hand there are only 4-50″ fans installed, the total capacity is 122,300 cfm and now you’re at 1.56 changes per minute.

    In the first case you can turn off the pit fans while they are needed in the second to get the necessary exchange rate to limit heat buildup at the fan end of the room.

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