Danfoss VLT HVAC Basic Drive FC 101 Design Manual page 14

Introduction to VLT® HVAC B...
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.
2.6.3 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%.
Illustration 2.3 describes the dependence of flow, pressure and
power consumption on RPM.
Q=Flow P=Power
Q =Rated flow P
1 1
Q =Reduced flow P
2 2
H=Pressure n=Speed regulation
H =Rated pressure n
1 1
H =Reduced pressure n
2 2
Table 2.4 The Laws of Proportionality
®
VLT HVAC Basic Drive Design Guide
A
SYSTEM CURVE
FAN CURVE
100 120 140 160 180
100 120 140 160 180
=Rated power
=Reduced power
=Rated speed
=Reduced speed
®
MG18C402 - VLT is a registered Danfoss trademark
100%
80%
Flow ~n
50%
25%
12,5%
50%
Illustration 2.3 Laws of Proportionally
Q 1 n 1
Flow :
=
Q 2 n 2
( )
H 1 n 1
2
Pressure :
=
H 2 n 2
( )
P 1 n 1
3
Power : =
P 2 n 2
2.6.4 Comparison of Energy Savings
The Danfoss frequency converter solution offers major
savings compared with traditional energy saving solutions.
This is because the frequency converter is able to control
fan speed according to thermal load on the system and
the fact that the frequency converter has a built-in facility
that enables the frequency converter to function as a
Building Management System, BMS.
Illustration 2.5 shows typical energy savings obtainable
with 3 well-known solutions when fan volume is reduced
to i.e. 60%.
As the graph shows, more than 50% energy savings can be
achieved in typical applications.
2
Pressure ~n
3
Power ~n
n
80% 100%
13
2 2