HVAC & Ventilation
Fan Power & System Curve
Calculate fan shaft power and electrical input power based on air flow, total pressure and fan/motor efficiency.
Units:
Fan laws: if speed doubles, flow doubles, pressure quadruples, power increases 8×. Variable speed drives (VFD) save enormous energy: 50% speed = 12.5% of full-load power.
P_shaft = Q × ΔP_total / η_fan | P_elec = P_shaft / η_motor
Input
Air flow Q iVolume flow rate in m³/s. Divide m³/h by 3600.
m³/s
Total pressure ΔP iTotal system pressure (static + dynamic) in Pascal. Typical HVAC systems: 200–800 Pa.
Pa
Fan efficiency η_fan iFan total efficiency at operating point. Centrifugal: 60–82%, Axial: 55–78%. See fan curve.
%
Motor efficiency η_motor iMotor efficiency. IE2: 85–93%, IE3: 87–95%.
%
Result
Air power P_air [W]
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Shaft power P_shaft [W]
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Electrical power P_elec [W]
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Electrical power P_elec [kW]
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Annual energy cost (4000h) [€/yr]
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