Trane TRG-TRC014-EN Optimized Static-PressureControl, Fan Modulation, period four, sensor located

period four

Fan Modulation

notes

Optimized Static-Pressure Control

sensor located		damper
at fan outlet	static	positions
	pressure
supply	sensor

fan	VAV
communicating	terminal
	units

BAS

fan speed or inlet vane position

Figure 93

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.

66 TRG-TRC014-EN