Calculations for a Twin-Lobe Blower

revolutions per minute and volume of rotary lobe blower equals volume. this simplified but blower manufactures have volume calculations for every frame size.

Performance curves published by blower manufacturers can indicate this relationship.

Formula for IHP is P₁*Q₁*((P₂/P₁)ⁿ)-1)/n where P₁ and P₂ are inlet and outlet absolute pressures, Q₁ = actual inlet flow, n = polytropic exponent, usual figure 0.23.

Shaft power (BHP) is IHP/η where η = compressor efficiency. For this sort of blower efficiency usually 60 - 65%, depending on size.

Power in watt if SI units used. I usually put pressures in kPa, then power in kW if flow in m³/s. I assume watt/kW is OK, and ref to HP is for historic reasons. If not you need to convert or work in FPS units, and divide by 550.