Ventilation · Sizing

Tunnel Ventilation Sizing: Fan Count, Wind Speed and Static Pressure

Tunnel ventilation is sized on bird-zone wind speed, not total fan count. This guide gives the sizing methodology commercial buyers can use to challenge a supplier proposal — with a worked example.

Wind-speed target
Fan selection
Static pressure loss
Worked example

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Project references

Visual scope of ventilation · sizing

The sizing target: bird-zone wind speed

Commercial broiler houses target 2.0–3.0 m/s air velocity through the bird zone at peak stocking and design temperature. Higher velocity gives more wind chill (up to 8°C effective temperature reduction at 3.0 m/s), lower velocity leaves birds heat-stressed. Sizing must deliver this velocity across the full cross-section.

Cross-section defines total airflow

Total airflow (m³/h) = cross-section area (m²) × target velocity (m/s) × 3,600. Example: 15 m wide × 3.0 m clear ceiling = 45 m² × 3.0 m/s × 3,600 = 486,000 m³/h. Add 15% margin for static-pressure loss and duct effects: 560,000 m³/h total fan capacity.

Fan selection and count

Commercial tunnel fans (137 cm / 54" diameter) deliver 40,000–45,000 m³/h at 25 Pa static pressure. Divide total capacity by per-fan flow: 560,000 / 42,000 ≈ 14 fans. Round up to 14 fans in the example. Fans installed in end-wall in one bank, or split across gable and side depending on house length.

Static pressure loss

Inlets, evap-cooling pads, deflectors and ductwork add pressure loss. Total system SP typically 25–40 Pa. Fans must be selected on their flow-at-that-SP curve, not free-air rating. A fan rated 50,000 m³/h at 0 Pa may deliver only 38,000 m³/h at 30 Pa — the number that matters.

Worked example: 120 m × 15 m broiler house, 35,000 birds

Cross-section 45 m² × 3.0 m/s wind speed × 3,600 = 486,000 m³/h. Add 15% margin = 560,000 m³/h. Install 14 × 137cm fans at 42,000 m³/h @ 30 Pa. Inlet area 18 m² at 2.5 m/s inlet velocity = 162,000 m³/h natural, plus fans. Evap pads 60 m² sized at 1.5 m/s face velocity = 324,000 m³/h. This delivers ~2.5 m/s bird-zone velocity with pads engaged in hot weather. Cross-check with the ventilation calculator.

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FAQ

Common questions

Is 3.0 m/s always the right target?

For heavy broilers in hot climates, yes. For layers and light birds it can be 1.5–2.0 m/s. For turkeys, 2.5–3.5 m/s. Match to species and stocking density.

What if my house is shorter than 90 m?

Tunnel effectiveness drops below 90 m house length — wind chill and velocity uniformity suffer. Consider cross ventilation instead for houses < 80 m.

Are 137 cm fans always best?

Highest flow per fan and lowest fan count. Smaller 122 cm or 91 cm fans are used in narrower houses or where end-wall real estate is limited.

Do I need static-pressure control?

Yes. Any commercial tunnel house needs pressure-controlled inlets that open/close automatically to maintain 20–35 Pa. Fixed inlets guarantee poor mixing.

Does FeedMatch review ventilation designs?

We connect buyers with independent poultry engineering consultants for design peer-review — recommended above USD 500k equipment CAPEX.