Calculate air velocity and friction pressure drop for rectangular and circular HVAC ducts. Uses the Darcy-Weisbach equation with real material roughness values. SI units.
Enter duct dimensions and airflow to calculate velocity and pressure drop.
Aspect ratio limit: Keep width:height ratio ≤ 5:1 for reliable results. Above this ratio, pressure drop calculations become unreliable.
Enter duct diameter and airflow to calculate velocity and pressure drop.
Pressure drop calculated using: ΔP/L = f × (1/D) × (ρV²/2), where f is the Darcy friction factor, D is hydraulic diameter, ρ is air density (1.2 kg/m³), and V is velocity.
Friction factor solved iteratively using the Colebrook-White equation: 1/√f = −2 log(ε/3.7D + 2.51/Re√f), applied for turbulent flow (Re > 4000).
For rectangular ducts, the equivalent circular diameter is: De = 1.30 × (a×b)^0.625 / (a+b)^0.25. This allows circular duct friction equations to be applied to rectangular sections.
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