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56 TRG-TRC014-EN
notes
period four
Fan Modulation
Fan Modulation Curve
The fan modulation curve illustrates the static pressure requirement of the
VAV system over the range of airflows. This requirement consists of a fixed
component and a variable component.
The VAV system requires a minimum amount of static pressure to properly
operate the terminal-unit modulation devices and diffusers. This static pressure
is the fixed component.
The second component of this static pressure curve is variable. This is the
amount of static pressure required to overcome the system pressure losses due
to the ducts, fittings, coils, filters, and so forth, at various airflows. These losses
vary with changes to the system airflow.
This curve describes the fan modulation needed to balance the static pressure
that is required to offset these variable system losses (demand) with the static
pressure produced by the fan (supply).
Fan Modulation Curve
sensor
sensor
set point
set point
VAV system
VAV system
modulation curve
modulation curve
airflow
airflow
static pressure
static pressure
Figure 77