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TRG-TRC013-EN 53
period four
Application Considerations
notes
System Static-Pressure Control
Fan capacity control requires a signal from a controller, which 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 the set point at that sensor location.
In the most common method for sensing and controlling system static
pressure, the static-pressure sensor is located in the supply duct system,
typically two-thirds of the distance between the supply fan outlet and the
critical terminal-unit inlet. The critical terminal unit is at the end of the supply
duct path that represents the largest total pressure drop.
The sensor is field-installed and the controller is set to maintain the pressure
corresponding to that location in the duct system at design airflow conditions.
In larger systems with many terminal units, determining the best sensor
location for all load conditions can be difficult—often determined by trial and
error or by using multiple sensors.
System Static-Pressure Control
VAV
VAV
terminal units
terminal units
supply
supply
fan
fan
static
static
pressure
pressure
sensor
sensor
controller
controller
Figure 77