Danfoss VLT AQUA Drive Series User Manual

2.7.3 Example of Energy Savings
As can be seen from the figure (the laws of proportionality), 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
The figure below 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
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 Example with Varying Flow over 1 Year
The example below is calculated on the basis of pump characteristics ob-
tained from a pump datasheet.
The result obtained shows energy savings in excess of 50% at the given
flow distribution over a year. The pay back period depends on the price
per kwh and price of frequency converter. In this example it is less than
a year when compared with valves and constant speed.
Energy savings
P
shaft
=P
shaft output
Flow distribution over 1 year
2 Introduction to VLT AQUA Drive VLT
®
AQUA Drive Design Guide
16 MG.20.N5.02 - VLT
®
is a registered Danfoss trademark
2

Danfoss VLT AQUA Drive Series Specifications

General

Brand	Danfoss
Model	VLT AQUA Drive Series
Category	Media Converter
Language	English