Specifications
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 2.10 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
Table 2.5 Abbreviations Used in Equation
n
100%
50%
25%
12,5%
50% 100%
80%
80%
175HA208.10
Power ~n
3
Pressure ~n
2
Flow ~n
Illustration 2.10 The Dependence of Flow, Pressure and Power
Consumption on RPM
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
2.7.4
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 2.12
shows typical energy savings obtainable
with 3 well-known solutions when fan volume is reduced
to i.e. 60%.
Illustration 2.12 shows more than 50% energy savings can
be achieved in typical applications.
130BA782.10
Discharge
damper
Less energy savings
IGV
Costlier installation
Maximum energy savings
Illustration 2.11 The 3 Common Energy Saving Systems
130BA779.11
0 60 0 60 0 60
0
20
40
60
80
100
Discharge Damper Solution
IGV Solution
VLT Solution
Energy consumed
Energy consumed
Energy consumed
Input power %
Volume %
Illustration 2.12 Discharge dampers reduce power
consumption somewhat. Inlet Guide Vans offer a 40%
reduction but are expensive to install. The Danfoss frequency
converter solution reduces energy consumption with more
than 50% and is easy to install.
Introduction to VLT® HVAC D... Design Guide
MG11BC02 Danfoss A/S © Rev. 06/2014 All rights reserved. 21
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