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TRG-TRC013-EN 21
period one
Fan Performance
notes
Reducing the fan speed causes the system resistance and fan performance
curves to intersect at E. The fan delivers the design airflow at a lower static
pressure, with less power required.
In these examples, it was possible to compensate for the inaccuracies in
estimated system resistance through fan speed adjustment. However, the
actual fan operating points fell at conditions other than intended. Therefore, it
may be wise to re-evaluate the fan selection. Possibly another fan size would
perform more efficiently at the revised system conditions.
A term commonly used to express the efficiency of a fan is static efficiency.
Static efficiency expresses the percentage of input power that is realized as
useful work in terms of static pressure.
The equation used to calculate static efficiency is:
where,
■ Airflow is in terms of cfm [m
3
/s]
■ Static pressure is in units of in. H
2
O [Pa]
■ Constant is 6,362 [982]
■ Input power is in units of hp [kW]
Static Efficiency
Static Efficiency (SE)
=
Power Out
Power In
Airflow × Static Pressure
Constant × Input Power
=
SE
SE
Figure 32
Static Efficiency (%)
Power Out
Power In
------------------------------
Airflow Static Pressure×
Constant Input Power×
---------------------------------------------------------------------
==