As the saying goes, “The only thing that is constant is change.” As we all know, change isn’t always good. But in this case, changes to codes and standards that incorporate the Fan Energy Index (FEI) will be great for both energy savings and fan quality.
The use of variable frequency drives (VFDs) or sheave changes on belt drive fans will adjust air performance. However, adjusting the pitch of the impeller may be the best option for inline axial fans having the adjustment capability.
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| Figure 1 - Axial fan with adjustable blades |
All three methods increase or slow airspeed but changing the blade pitch offers advantages over the other two methods. Changing the blade pitch requires no additional components. So long as the electrical amp draw of the new performance point is within the nameplate of the supplied motor, there is no need for sheaves or VFDs.
Before You Begin
If the actual applied fan’s electrical input power is more, the FEI is less than 1.00.
After determining the new required airflow performance point for the fan, contact your manufacturer’s local representative or use a computer selection program to determine the new pitch required. Note: if using the selection program, confirm the model (size, hub size, blade quantity) performance is identical to the unit in need of adjustment.
- Before adjusting the pitch, confirm that the new performance electrical amp draw does not exceed that on the motor nameplate
- Turn off all power before working on equipment
- To avoid flexing of blades during operation, keep the blades as close to a uniform pitch as possible
- Tighten each of the blades to the manufacturers recommended torque setting
The video below provides more detail to the steps required for adjusting blade pitch.
Fans
