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TRG-TRC014-EN 61
period four
Fan Modulation
notes
Fan-speed control modulates fan capacity by varying the speed of rotation.
This is commonly accomplished using a variable-speed drive on the fan motor.
In response to reduced airflow and rising system static pressure, adjustable
fan-speed control produces a system/fan interaction that is similar to that
produced by inlet vane control.
By reducing the fan speed, the performance curve for the fan shifts downward,
and the airflow and resulting static pressure decrease until the operating point
(B) balances along the fan modulation curve.
Fan-Speed Control
variable
variable
-
-
speed drive
speed drive
supply
supply
fan
fan
Figure 85
Fan-Speed Control
airflow
airflow
static pressure
static pressure
A
B
design system
design system
resistance curve
resistance curve
actual system
actual system
resistance curve
resistance curve
1
,
0
0
0
r
p
m
1
,
0
0
0
r
p
m
VAV system
VAV system
modulation curve
modulation curve
9
0
0
r
p
m
9
0
0
r
p
m
8
0
0
r
p
m
8
0
0
r
p
m
Figure 86