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58 TRG-TRC014-EN
notes
period four
Fan Modulation
The system static pressure controller senses this higher pressure and sends a
signal to the supply fan to reduce capacity. Modulating the fan capacity results
in a new fan performance curve and the system balances at an operating point
(B) along the fan modulation curve, bringing the system static pressure back
down to the set point.
Fan Modulation Methods
The four methods commonly used to modulate fan capacity are: discharge
dampers, inlet vanes, fan-speed control, and variable-pitch blade control.
We will examine these now.
Discharge dampers match the static pressure supplied by the fan with the
static pressure required by the system. They accomplish this by adding static-
pressure loss to the system a little bit downstream of the fan.
Fan Modulation Methods
▲ Discharge dampers
▲ Inlet vanes
▲ Fan-speed control
▲ Variable-pitch blade control
Figure 80
Discharge Dampers
discharge
discharge
dampers
dampers
supply
supply
fan
fan
Figure 81