Poultry House Ventilation Fan CFM Sizing Guide
Engineering guidelines and mathematical formulas for sizing exhaust fans, cooling pads, and static pressure boundaries.
Scientific Overview
Proper ventilation in commercial poultry houses is critical to remove metabolic moisture, carbon dioxide, ammonia, and excess heat. For broiler and layer flocks, ventilation transitions from 'Minimum Ventilation' (controlling air quality during brooding) to 'Tunnel Ventilation' (creating high wind velocity to cool birds during hot weather). This guide details the mathematics used by agricultural engineers to design ventilation systems.
Minimum Ventilation vs. Tunnel Ventilation
Minimum Ventilation: Operated on an ON/OFF timer cycle. Its goal is to bring in fresh air and remove moisture/ammonia without chilling young chicks. It relies on side wall inlets directed upwards towards the ceiling where heat accumulates.
Tunnel Ventilation: Operated continuously when house temperatures exceed target levels. Large exhaust fans at one end of the house pull air through evaporative cooling pads at the opposite end, creating a 'wind chill' cooling effect for the birds.
Sizing Tunnel Fans (CFM Calculation)
To calculate the total fan capacity (in CFM - Cubic Feet per Minute) required for tunnel cooling, we use the cross-sectional area of the poultry house and the target air velocity:
Example Calculation: A standard broiler house is 40 ft wide, has an average height of 8 ft, and requires a target wind velocity of 600 ft/min (approx 3.0 m/s) to cool mature broilers.
- Cross-Sectional Area = 40 ft × 8 ft = 320 sq ft
- Required CFM = 320 sq ft × 600 ft/min = 192,000 CFM
- If using 50-inch exhaust fans rated at 24,000 CFM at 0.10" static pressure: 192,000 ÷ 24,000 = 8 fans
Sizing Evaporative Cooling Pads
Evaporative cooling pads are sized to prevent excessive static pressure drop. The air velocity through standard 6-inch thick paper pads should not exceed 400 ft/min:
Using the previous example of 192,000 CFM:
- Required Pad Area = 192,000 CFM ÷ 400 ft/min = 480 sq ft
- If the pads are 5 ft high: 480 sq ft ÷ 5 ft = 96 linear feet of pad (installed as 48 ft on each side wall at the intake end).
Poultry House Ventilation Fan CFM Sizing Guide — Frequently Asked Questions
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