Specifications
2.7 Advantages
2.7.1 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 applications. For further information, see
2.7.3 Example of Energy Savings.
2.7.2 The Clear Advantage - Energy Savings
The 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.
120
100
80
60
40
20
0
20 40 60 80 100 120 140 160 180
120
100
80
60
40
20
0204060 80 100 120 140 160 180
Voume %
Voume %
INPUT POWER %PRESSURE %
SYSTEM CURVE
FAN CURVE
A
B
C
130BA781.10
ENERGY
CONSUMED
Illustration 2.3 Energy Saved with Reduced Fan Capacity
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 2.4 Fan Curves for Reduced Fan Volumes.
2.7.3 Example of Energy Savings
As seen in Illustration 2.5, the flow is controlled by
changing the RPM. Reducing the speed only 20% from the
rated speed also reduces the flow by 20%. The flow is
directly proportional to the RPM. The consumption of
electricity, however, is reduced by 50%.
If the system only runs at 100% flow a few days per year,
while the average is below 80% of the rated flow, the
amount of energy saved is even more than 50%.
Illustration 2.5 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 control
H
1
= Rated pressure n
1
= Rated speed
H
2
= Reduced pressure n
2
= Reduced speed
Table 2.3 Laws of Proportionality
Flow:
Q
1
Q
2
=
n
1
n
2
Pressure:
H
1
H
2
=
(
n
1
n
2
)
2
Power:
P
1
P
2
=
(
n
1
n
2
)
3
Introduction VLT® HVAC Drive FC 102 Design Guide
MG16C102 - Rev. 2013-08-20 19
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