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64 TRG-TRC014-EN
notes
period four
Fan Modulation
System Static-Pressure Control
Each of these fan-capacity control methods requires a signal from a controller
that monitors static pressure, using a sensor located somewhere in the supply-
duct system. This controller compares the sensed pressure to a set point and
modulates the fan capacity to maintain a set point at that sensor location.
There are three common methods for sensing and controlling system static
pressure. They are: fan outlet static-pressure control, supply duct static-
pressure control, and optimized static-pressure control.
For the fan outlet static-pressure control method, the static pressure
sensor is mounted near the outlet of the main supply fan. The controller is set
to maintain the static pressure required at design flow.
The appeal of this method is that the sensor can be factory-installed and tested,
resulting in greater reliability and no field installation cost. If fire dampers are
Controlling System Static Pressure
▲ Fan outlet static-pressure control
▲ Supply duct static-pressure control
▲ Optimized static-pressure control
Figure 90
Fan Outlet Static-Pressure Control
VAV
VAV
terminal units
terminal units
supply
supply
fan
fan
static
static
pressure
pressure
sensor
sensor
sensor located
at fan outlet
Figure 91