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2.5 Advantages
2.5.1 Why use a Frequency Converter for
Controlling Fans and Pumps?
A frequency converter takes advantage of the fact that
centrifugal fans and pumps follow the laws of propor-
tionality for such fans and pumps. For further information
see
2.5.3 Example of Energy Savings .
2.5.2 The Clear Advantage - Energy Savings
The very clear advantage of using a frequency converter
for controlling the speed of fans or pumps lies in the
electricity savings.
When comparing with alternative control systems and
technologies, a frequency converter is the optimum energy
control system for controlling fan and pump systems.
SYSTEM CURVE
FAN CURVE
PRESSURE%
130BA780.10
A
B
C
0
20
40
60
80
100
120
20 40 60 80 100 120 140 160 180
VOLUME%
Illustration 2.1 The graph is showing fan curves (A, B and C) for
reduced fan volumes.
120
100
80
60
40
20
0
20 40 60 80 100 120 140 160 180
120
100
80
60
40
20
0 20 40 60 80 100 120 140 160 180
Voume %
Voume %
INPUT POWER %
PRESSURE %
SYSTEM CURVE
FAN CURVE
A
B
C
130BA781.10
ENERGY
CONSUMED
Illustration 2.2 When using a frequency converter to reduce fan
capacity to 60% - more than 50% energy savings may be
obtained in typical applications.
2.5.3 Example of Energy Savings
As shown in Illustration 2.3 , the flow is controlled by
changing the RPM. By reducing the speed only 20% from
the rated speed, the flow is also reduced by 20%. This is
because the flow is directly 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 that corresponds to 100% a few days in a year, while
the average is below 80% of the rated flow for the
remainder of the year, the amount of energy saved is even
more than 50%.
The laws of proportionality
Illustration 2.3 describes the dependence of flow, pressure and
power consumption on RPM.
Q = Flow
P = Power
Q
1
= Rated flow P
1
= Rated power
Q
2
= Reduced flow P
2
= Reduced power
H = Pressure n = Speed regulation
H
1
= Rated pressure n
1
= Rated speed
H
2
= Reduced pressure n
2
= Reduced speed
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