Fans and energy
Use airflow, pressure, and efficiencies to estimate fan shaft power and electrical input.
Estimate air power, fan shaft BHP and electrical input kW from airflow, a matching pressure rise and actual efficiencies.
Air power measures the rate at which a fan supplies pressure energy to moving air. Operating airflow and matching pressure rise define that useful pressure-flow product. Fan efficiency connects air power to shaft power; motor and drive efficiencies then connect shaft power to electrical input. Each stage accounts for a different loss.
Pressure and efficiency must share the selected total or static basis. Mixing total pressure with static efficiency breaks the intended power balance. Efficiencies must also apply at the operating load: a peak catalog efficiency or motor rating does not automatically represent a part-load duty point. Enter percentages as shown by the fields.
P_air = Q × ΔP; P_shaft = P_air / η_fan; P_electric = P_shaft / (η_motor × η_drive)
Q = actual airflow; ΔP = pressure rise on the selected total/static basis; η = efficiency as a dimensionless fraction after conversion from the percentage fields. QΔP requires compatible physical units; the calculator converts CFM and in. w.g. before reporting shaft BHP and electrical kW.
Compare air, shaft, and electrical power to understand where the entered losses occur. W/CFM describes this duty point, while motor selection and electrical protection require additional information.
Inputs: Approximately 2,118.88 CFM at 2.007315 in. w.g., equivalent to 1 m³/s at 500 Pa; fan efficiency 65%, motor 92%, drive 97%.
Calculation: Air power is 500 W. Divide by 0.65 for shaft power, then by 0.92 and 0.97 for electrical input.
Result: Approximately 1.032 BHP at the shaft and 0.862 kW electrical input.
Use electrical input kW with operating hours. Shaft BHP describes the mechanical fan load and omits motor and drive losses.
Check the boundaries of the supplied efficiency data. Drive efficiency should account for losses that are not already included; counting the same loss twice inflates electrical demand.