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54 TRG-TRC013-EN
notes
period four
Application Considerations
Another method of static-pressure control, the optimized static-pressure
control method, positions a single static-pressure sensor near the fan outlet.
The static-pressure controller dynamically adjusts the static-pressure set point
based on the position of the modulating dampers, or valves, in the VAV terminal
units.
The DDC/VAV controller in each terminal unit modulates its valve to maintain
the airflow required by the zone thermostat and keeps track of the valve
position. 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 damper (the one requiring the
highest inlet pressure) is nearly wide open. The result is that the supply fan
generates only enough static pressure to ensure the required airflow through
this “critical” terminal unit.
Since the pressure sensor is near the fan outlet, this method allows the sensor
to be factory-installed and tested. It can also serve as the duct high-pressure
sensor. If the terminal units use DDC controls, and the system-level
communications are already in place, this control method provides the highest
energy savings at the lowest cost.
Optimized Static-Pressure Control
static
static
pressure
pressure
sensor
sensor
communicating BAS
communicating BAS
supply
supply
fan
fan
VAV terminal units
VAV terminal units
Figure 78