GE AF-600 FP Design And Installation Manual page 63

Application Set-up Examples
Figure 6.4 The graph is showing fan curves (A, B and C) for
reduced fan volumes.
6 6
Figure 6.5 When using a adjustable frequency drive to reduce
fan capacity to 60%, more than 50% energy savings may be
obtained in typical applications.
6.3.3 Example of Energy Savings
As can be seen from the figure (the laws of propor-
tionality), the flow is controlled by changing the RPM. By
reducing the rated speed by only 20%, the flow is also
reduced by 20%. This is because the flow is directly
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AF-600 FP Design and Installation Guide
proportional to the RPM. The consumption of electricity,
however, is reduced by 50%.
If the system in question only needs to be able to supply a
flow corresponding to 100% a few days each year, while
the average is below 80% of the rated flow for the
remainder of the year, the amount of energy saved is even
greater than 50%.
Figure 6.6 describes the dependency of flow, pressure and
power consumption on RPM.
Figure 6.6 The laws of proportionality
Flow
:
Pressure
Power
DET-768A
Q n
1 1
=
Q n
2 2
( )
H n
2
1 1
: =
H n
2 2
( )
P n
3
1 1
: =
P n
2 2
Q = Flow
Q = Rated flow
1
Q = Reduced flow
2
H = Pressure
H = Rated pressure
1
H = Reduced pressure
2
P = Power
P = Rated power
1
P = Reduced power
2
n = Speed regulation
n = Rated speed
1
n = Reduced speed
2