Danfoss VLT HVAC Basic Drive FC 100 Series Design Manual page 12

Introduction to VLT HVAC Ba...
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 2.4.3 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.
100
80
B
60
40
C
20
0 20 40 60 80
VOLUME%
Illustration 2.1 The graph is showing fan curves (A, B and C) for
reduced fan volumes.
VLT HVAC Basic Drive Design Guide
A
SYSTEM CURVE
FAN CURVE
100 120 140 160 180
®
MG.18.C2.02 - VLT is a registered Danfoss trademark
120
100
80
B
60
40
C
20
0
20 40 60 80
Voume %
120
100
80
60
40
ENERGY
20
CONSUMED
0 20 40 60 80
Voume %
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
Q = Rated flow
1
Q = Reduced flow
2
H = Pressure
H = Rated pressure
1
H = Reduced
2
pressure
A
SYSTEM CURVE
FAN CURVE
100 120 140 160 180
100 120 140 160 180
P = Power
P = Rated power
1
P = Reduced power
2
n = Speed regulation
n = Rated speed
1
n = Reduced speed
2
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2 2