Danfoss VLT FC51 Design Manual page 16

Safety and Conformity
2.7.5 Example with Varying Flow over 1
Year
2 2
This example 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 price of
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 2.6 Flow Distribution over 1 Year
14
®
VLT Micro Drive FC 51 Design Guide
(mwg)
60
50
40
30
20
10
0
(kW)
60
50
40
30
20
10
0
Illustration 2.7 Energy
m 3 /
h
%
350 5
300 15
250 20
200 20
150 20
100 20
Σ
100 8760
Table 2.5 Result
MG02K302 - Rev. 2013-12-03
H
s
B
C
1050rpm
750rpm
100 200
P
shaft
B 1
1050rpm
C 1
750rpm
100 200
Distri- Valve regulation
bution
Hours Power Consump-
tion
A - B kWh
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
1350rpm
( 3 )
m /h
300 400
A 1
1650rpm
1350rpm
( )
300 400 m 3 /h
Frequency converter
control
Power Consump-
tion
A - 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