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14 TRG-TRC013-EN
notes
period one
Fan Performance
Finally, using the measurements from the dynamometer and the fan laws,
curves can be calculated and plotted to represent the fan’s power consumption
at each operating condition.
When most fans approach the blocked-tight static-pressure condition,
instability is encountered. This condition is known as surge.
Surge occurs when the quantity of air being moved by the fan falls below the
amount necessary to sustain the existing static-pressure difference between the
inlet and outlet sides of the fan. When this occurs, the pressurized air flows
backward through the fan wheel, instantaneously reducing the pressure at the
fan outlet. This surge of air enables the fan to re-establish the proper direction
of airflow. The resulting fluctuation in airflow and static pressure within the fan
and ductwork can result in excessive noise, vibration, and possibly damage to
the fan.
airflow
airflow
static pressure
static pressure
2 hp
2 hp
[1.5 kW]
[1.5 kW]
3 hp
3 hp
[2.2 kW]
[2.2 kW]
0.5 hp
0.5 hp
[0.37 kW]
[0.37 kW]
1 hp
1 hp
[0.75 kW]
[0.75 kW]
input power
input power
Input Power
Figure 20
Fan Surge
high
high
pressure
pressure
low
low
pressure
pressure
fan
fan
Figure 21