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46 TRG-TRC013-EN
notes
period three
Fan Capacity Control
Inlet Vanes
The next method of capacity control, inlet vanes, modulates a fan’s capacity
by “preswirling” the air in the direction of fan rotation before it enters the fan
wheel. By changing the air’s angle of entry into the fan, the modulating inlet
vanes lessen the ability of the fan wheel to “bite” the air. This reduces its
airflow capacity which, in turn, reduces its power consumption and its ability to
generate static pressure.
Inlet vanes actually alter fan performance, creating a new fan performance
curve with each vane position. Notice that with each increment of vane closing,
the power requirement becomes less. Therefore, with inlet vanes, fan energy
savings are realized any time the load drops below the design airflow.
Inlet vanes can, however, cause significant acoustical tones at part load when
applied to BI, AF, and vaneaxial fans.
Inlet Vanes
inlet
inlet
vanes
vanes
Figure 68
Inlet Vanes
airflow
airflow
static pressure
static pressure
inlet vane
inlet vane
position (%)
position (%)
input power
input power
80%
80%
90%
90%
100%
100%
Figure 69