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30 TRG-TRC013-EN
notes
period two
Fan Types
Notice how the fan input-power lines cross the FC fan performance curves. If
the system resistance were to drop, the actual system resistance curve would
also drop, moving the operating point (A) to a higher airflow (B). At the same
time, the fan’s input power requirement would also rise, possibly overloading
the motor. Consequently, the FC fan is referred to as an “overloading” type of
fan.
As with all fan types, the FC fan can exhibit unstable operation, or surge.
However, since FC fans are used typically in low speed and low static-pressure
applications, many small FC fans can operate in surge without noticeable noise
and vibration.
Backward Inclined (BI) Fans
The second centrifugal fan design has blades that are slanted away from the
direction of wheel rotation. These backward inclined, or BI, fans operate at
higher speeds than FC fans.
airflow
airflow
static pressure
static pressure
actual system
resistance curve
actual system
actual system
resistance curve
resistance curve
surge
line
surge
surge
line
line
2 hp
2 hp
[1.5 kW]
[1.5 kW]
3 hp
3 hp
[2.2 kW]
[2.2 kW]
1 hp
1 hp
[0.75 kW]
[0.75 kW]
$
%
Figure 43
Backward Inclined Fan
Figure 44