Filter
Top Products
66 TRG-TRC014-EN
notes
period four
Fan Modulation
The optimized static-pressure control method combines the location-
related benefits of fan outlet control with operating cost savings that exceed
those of supply duct static-pressure control. A single static-pressure sensor is
located at the fan outlet, and the controller dynamically adjusts the static-
pressure set point based on the position of the modulating devices in the VAV
terminal units.
The DDC/VAV controllers know the position of their individual air-modulation
devices and, because they are pressure independent, they will modulate to
maintain the required airflow. The building automation system (BAS)
continually polls the VAV terminal units looking for the most-open VAV damper.
The controller resets the static-pressure set point so that at least one VAV
terminal, the one requiring the highest inlet pressure, is nearly wide open.
The result is that the supply fan generates only enough static pressure to get
the required flow through this “critical” terminal unit.
This method allows the sensor to be factory-installed and-tested. Because the
pressure sensor is at the fan outlet, it can also serve as the duct high-pressure
sensor. If the terminal units use DDC controls, the system-level
communications are already in place, making this the lowest-cost, highest
energy savings strategy.
Optimized Static-Pressure Control
damper
damper
positions
positions
communicating
communicating
BAS
BAS
fan speed or
fan speed or
inlet vane position
inlet vane position
VAV
VAV
terminal
terminal
units
units
supply
supply
fan
fan
static
static
pressure
pressure
sensor
sensor
sensor located
at fan outlet
Figure 93