Posted by Dr. Sara Hooge on June 22 2009 13:52
Ideal barn
- Protection from the elements for workers.
- All-in-all-out and filled within 2 weeks. Barn should be able to be cleaned/disinfected between groups.
- Sidewall – 14 ft.
- Cement – 3 ft
- Two roll type curtains. The bottom –8 ft and rolls up and the top curtain – 2 ft and rolls down.
- Width – 40-50 feet
- Open ridge
- Eaves on both sides to prevent water coming in the sides.
- Control the microenvironment of each calf to allow for low total airborne bacterial counts within pens.
- Solid panels separating calves on 3 or 4 sides (limited to 20 inches high).
- Calf pens 8' x 4'
- Sufficient bedding to reduce calf heat loss (wood shavings or non-straw recommended). Recommend tiling underneath the barn to allow for proper drainage of water.
- Alleys should be at least 16 inches in width.
- Positive-pressure ventilation system. Goal is to provide fresh air to each calve's environment.
- Reliable.
- Fabric or polyethylene vent tubing.
- Holes punched to exit at 800 fpm. Hole size ranges from .5 to 3 inches.
- Fan with a hood to protect it from snow covering and rain.
- Great way to supplement current natural or negative pressure ventilation systems.
General ventilation guidelines
- Minimal winter ventilation rate = 15 cfm/calf or 4 air changes/hour in the building.
- Minimal hot weather ventilation rate = 100 cfm/calf
- Air should enter at 600-800 fpm – adequate mixing of air.
Approach to designing a positive-pressure supplemental system
- Determine minimal winter ventilation rate for the building.
- Base on maximum number of calves in the barn.
- Example: 70 calves need 1050 cfm.
- Determine number of distribution ducts required
- Width 36' – one duct
- Width > 40' – two ducts
- Calculate cross-sectional area of the ducts.
- Determine diameter of fan.
- A = pr2 . Example: 22 inch fan the A = 3.14 (112) = 380 in2
- Calculate are needed for air to leave the duct at high speeds and still be able to distribute air along the entire duct.
- Identify the fan speed. Divide the fan speed by the goal of 800 fpm. 2000/800 = 2.5 ft2.
- This is the total area that should be distributed among the holes within the duct.
- Recommend holes at least 2 inches to increase the distance the air moves.