Filter
Top Products
TRG-TRC014-EN 53
period four
Fan Modulation
notes
plot performance on the basis of the static pressure component only.
Performance curves published for some packaged air handlers will include the
effects of the dampers, filters, and coils that are in the unit. In this case, the
static pressure capacity of the fan must be able to overcome the rest of the
static pressure losses in the system (supply duct, terminal units, diffusers and
grilles, and so forth).
To deliver 24,000 cfm [11.3 m
3
/s] of air, this example fan, running at 1,000 rpm,
generates 2.7 in. H
2
O [672.5 Pa] of static pressure.
System Resistance Curve
The system resistance curve is a plot of the pressure drop, in terms of static
pressure, that the system (including the supply ductwork, duct fittings, terminal
units, diffusers and return grilles, coils, filters, dampers, and so forth) creates
over a range of airflows. When the airflow in a system increases, the resistance
also increases because more friction is experienced.
When delivering 15,000 cfm [7.1 m
3
/s], this example system creates 1.05 in.
H
2
O [261.5 Pa] of static pressure resistance.
System Resistance Curve
airflow
airflow
static pressure
static pressure
24,000 cfm
24,000 cfm
[11.3 m
[11.3 m
3
3
/s]
/s]
2.7 in. H
2.7 in. H
2
2
O
O
[672.5 Pa]
[672.5 Pa]
system
resistance
curve
system
system
resistance
resistance
curve
curve
15,000 cfm
15,000 cfm
[7.1 m
[7.1 m
3
3
/s]
/s]
1.05 in. H
1.05 in. H
2
2
O
O
[261.5 Pa]
[261.5 Pa]
1
,
0
0
0
r
p
m
1
,
0
0
0
r
p
m
Figure 73