Danfoss VLT Series Design Manual page 18

2. Introduction to VLT HVAC Drive
2.7.4. Example with varying flow over 1 year
The example below is calculated on the basis of pump characteristics obtained from a pump da-
tasheet. (45 kW). The same examples of calculations can be used in the case of fan characteristics.
2
The result obtained is savings in excees of 50% at the
given flow distribution over a year, corresponding to 8,760 hours.
Typically, the example calculated below results in a pay-back period of one year - depending on
the price per kWh and the price of the frequency converter.
Pump characteristics
m 3
350
300
250
200
150
100
Σ
18
/h Distribution
% Hours
5 438
15 1314
20 1752
20 1752
20 1752
20 1752
100 8760
MG.11.B2.02 - VLT
Energy savings
This figure compares power control via
valves and without speed control with
pressure control via a frequency convert-
er.
P =P
shaft shaft output
Flow distribution over 1 year
Valve regulation
Power Consumption
A - B kWh
1 1
42,5 18.615
38,5 50.589
35,0 61.320
31,5 55.188
28,0 49.056
23,0 40.296
275.064
®
is a registered Danfoss trademark
®
VLT HVAC Drive Design Guide
Frequency converter control
Power Consumption
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