Generally fan manufacturers use two ways to mention fan efficiency: mechanical efficiency and static efficiency. Both measures indicate how well the fan converts horsepower into flow and pressure.
The equation for determining mechanical efficiency is:
The static efficiency equation is the same except that the outlet velocity pressure is not added to the fan static pressure
Drive motor kW may be measured by a load analyzer. This kW multiplied by motor efficiency gives the shaft power to the fan.
Payback of energy saving options
Experience from the past has shown that implementing energy saving options in fans are highly profitable with payback of investment of less than 3 years.
Table 2: Payback of investment of energy saving options for fans
| Options | Estimated Payback Period |
|---|---|
| Operate the fans at best efficiency points | <1 year |
| Adopt VFD for capacity control in place of other options | 1 - 2 years |
| Adopt FRP blades in place of metallic blades | < 1 years |
| Avoid in leakages and out leakages in fan systems | < 1 year |
| Adopt proper duct sizes for pressure drop reductions | < 1 years |
| Adopt high efficiency fans | 2 - 3 years |
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