Trane TRG-TRC014-EN manual Supply Duct Static-PressureControl, Fan Modulation, period four

period four

Fan Modulation

notes

included in the supply duct, this method ensures that the sensor is on the fan side of the damper so that the duct is protected from high pressures. Also, depending on the layout of the duct system, this method may eliminate the need for multiple duct-mounted sensors. It is not, however, as energy efficient as the other methods.

Supply Duct Static-Pressure Control

sensor located

2/3 down supply duct

static	VAV
pressure
	terminal units
sensor

supply fan

Figure 92

For the supply duct static-pressure control method, the static pressure sensor is located somewhere in the supply duct system. Typically the location of the sensor, and consequently the set point of the controller, is 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 and requiring multiple sensors. Field installation and adjustment of one or possibly several duct pressure sensors increases installation cost. Without factory testing, reliability may also suffer compared to the fan outlet method previously discussed. However, using this method typically allows for fan energy savings compared to the fan outlet method.

TRG-TRC014-EN 65