VFD vs. damper
Control flow by throttling or by changing speed: power with damper, inlet guide vanes and drive, yearly savings and payback.
Simulator developed by José Geraldo da Silva Moreira · Energy-efficiency lab
Control flow by throttling or by changing speed?
Centrifugal fan or pump. Affinity laws: flow ∝ n, pressure ∝ n², power ∝ n³.
Outlet damper
kW
Inlet guide vanes (IGV)
kW
Drive (VFD)
kW
Savings VFD vs. damper
Power drawn (% of rated) vs. flow
Outlet damperIGVDrive (VFD)
What to watch
- At 70% flow the drive uses about a third of what the damper uses. The lower the average flow, the bigger the gain.
- With a high static share (a pump lifting water, a network with minimum pressure) the gain drops: the cube law applies to friction, not to static head.
- Typical targets: exhaust and combustion-air fans, cooling-water pumps, steel-shop dedusting.
Typical order-of-magnitude curves; the drive includes ≈3% losses.
Simplified teaching models with order-of-magnitude illustrative values. Do not use them for design or operating decisions without validation against plant data.