Air Duct Friction Loss Formula

Equation for calculate air duct friction loss is,

Friction Loss = (0.109136 * q^1.9 ) / (d^5.02)
Friction Loss per 100 Feet = (0.109136 * q^1.9 ) / (d^5.02)*(l/100)

Where,
q = Air Volume Flow
d = Equivalent Duct Diameter
l = Duct Length