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TRG-TRC013-EN 7
period one
Fan Performance
notes
This build-up of static pressure results in reduced air velocity (velocity pressure)
and therefore a reduction in the airflow delivered by the fan.
Notice that the hinged vane has moved toward a more vertical position. The
reduced velocity pressure on the face of the vane causes it to move to a more
neutral position.
Finally, when the damper is closed fully, airflow stops and no velocity pressure
exists in the ductwork. All of the usable fan energy is now being converted to
static pressure. The pressure on the back side of the vane equals the pressure
on the face of the vane and it assumes the neutral (vertical) position.
Both velocity and static pressures can be determined using the inclined
manometer. Static pressure is measured directly by inserting a probe through
the duct wall with its open end perpendicular to air movement. In this position
only the outward, or static, pressure within the duct is sensed.
damper
damper
fully closed
fully closed
Velocity Pressure vs. Static Pressure
Figure 11
Measuring Static Pressure
inclined
inclined
manometer
manometer
Figure 12