Danfoss VLT AQUA Drive FC 202 Design Manual page 18

Introduction
100%
2 2
80%
Flow ~n
50%
25%
12,5%
Illustration 2.3 Dependence of Flow, Pressure and Power
consumption on RPM
Q 1 n 1
Flow :
=
Q 2 n 2
H 1
Pressure :
=
H 2
(
P 1 n 1
Power : =
P 2 n 2
2.7.4 Example with Varying Flow Over One
Year
Illustration 2.4 is calculated based on pump characteristics
obtained 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 the price of the
frequency converter. In this example, it is less than a year
when compared with valves and constant speed.
Energy savings
P =P
shaft shaft output
Illustration 2.4 Flow Distribution over 1 Year
16
VLT
Pressure ~n
3
Power ~n
50% 80%
( )
n 1
2
n 2
)
3
MG20Z102 - VLT
®
AQUA Drive FC 202 Design Guide
H
(mwg)
60
50
40
30
20
2
10
0
P
(kW)
shaft
n
100% 60
50
40
30
20
10
0
Illustration 2.5 Energy Savings in a Pump Application
3 Distri-
m /h
bution
%
350 5
300 15
250 20
200 20
150 20
100 20
Σ
100 8760
Table 2.5 Energy Savings - Calculation
2.7.5 Better Control
If a frequency converter is used for controlling the flow or
pressure of a system, improved control is obtained.
A frequency converter can vary the speed of the fan or
pump, obtaining variable control of flow and pressure.
Furthermore, a frequency converter can quickly adapt the
speed of the fan or pump to new flow or pressure
conditions in the system.
Simple control of process (flow, level, or pressure) utilising
the built-in PID control.
®
is a registered Danfoss trademark
s
B
1350rpm
C
1050rpm
750rpm
100 200 300
1350rpm
B 1
1050rpm
C 1
750rpm
100 200 300
Valve regulation Frequency converter
Hours Power Consump- Power
tion
A - B kWh A
1 1
438 42,5 18.615
1314 38,5 50.589
1752 35,0 61.320
1752 31,5 55.188
1752 28,0 49.056
1752 23,0 40.296
275.064
A
1650rpm
( 3 )
m /h
400
A 1
1650rpm
( )
400 m 3 /h
control
Consump-
tion
- C kWh
1 1
42,5 18.615
29,0 38.106
18,5 32.412
11,5 20.148
6,5 11.388
3,5 6.132
26.801