Danfoss VLT AQUA Drive FC 202 Design Guide

2.1.3 Example of Energy Savings
As shown in Figure 2.2, the ow is controlled by changing
the pump speed, measured in RPM. By reducing the rated
speed by only 20%, the ow is also reduced by 20%. This
is because the ow is directly proportional to the speed.
The consumption of electricity, however, is reduced by up
to almost 50%.
If the system only has to supply a ow that corresponds to
100% a few days in a year, while the average is below 80%
of the rated ow for the remainder of the year, the energy
savings are even greater than 50%.
Figure 2.2 describes the dependence of
ow, pressure, and
power consumption on pump speed in RPM for centrifugal
pumps.
n
100%
50%
25%
12,5%
50% 100%
80%
80%
175HA208.10
Power ~n
3
Pressure ~n
2
Flow ~n
Figure 2.2 Anity Laws for Centrifugal Pumps
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
Assuming an equal eciency in the speed range.
Q=Flow
P=Power
Q
1
=Flow 1 P
1
=Power 1
Q
2
=Reduced ow P
2
=Reduced power
H=Pressure n=Speed regulation
H
1
=Pressure 1 n
1
=Speed 1
H
2
=Reduced pressure n
2
=Reduced speed
Table 2.1 Anity Laws
2.1.4
Valve Control versus Speed Control of
Centrifugal Pumps
Valve control
As the demand for process requirements in water systems
varies, the ow has to be adjusted accordingly. Frequently
used methods for ow adaptation are throttling or
recycling using valves.
A recycle valve that is opened too wide can cause the
pump to run at the end of the pump curve, with a high
ow rate at a low pump head. These conditions do not
only cause a waste of energy due to the high speed of the
pump, but can also lead to pump cavitation with resultant
pump damage.
Throttling the ow with a valve adds a pressure drop
across the valve (HP-HS). This can be compared with
accelerating and pulling the brake at the same time in an
attempt to reduce car speed. Figure 2.3 shows that
throttling makes the system curve turn from point (2) on
the pump curve to a point with signicantly reduced
eciency (1).
Product Overview
VLT
®
AQUA Drive FC 202
16 Danfoss A/S © 09/2014 All rights reserved. MG20N622
22

Danfoss VLT AQUA Drive FC 202 Specifications

General

Brand	Danfoss
Model	VLT AQUA Drive FC 202
Category	DC Drives
Language	English