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60 TRG-TRC014-EN
notes
period four
Fan Modulation
Inlet vanes modulate the capacity of a fan by “pre-swirling” the air in the
direction of fan wheel rotation before it enters the wheel.
By changing the angle of air entry into the fan, the modulating inlet vanes
lessen the ability of the fan wheel to “bite” the air. This reduces the airflow
capacity which, in turn, reduces the power consumption and the ability to
generate static pressure.
This illustrates how inlet vanes control the fan operating point so that it tracks
the desired modulation curve in response to reduced airflow and rising system
static pressure.
By closing the inlet vanes, the performance curve for the fan shifts downward.
The airflow and resulting static pressure fall until the operating point balances
along the fan modulation curve (B).
Inlet Vanes
inlet
inlet
vanes
vanes
supply
supply
fan
fan
Figure 83
Inlet Vanes
airflow
airflow
static pressure
static pressure
A
B
design system
design system
resistance curve
resistance curve
actual system
actual system
resistance curve
resistance curve
inlet vane
inlet vane
position (%)
position (%)
100%
100%
90%
90%
80%
80%
Figure 84