Danfoss VLT HVAC Basic Drive FC 100 Series Design Manual page 14

Introduction to VLT HVAC Ba...
2.5.5 Example with Varying Flow over 1
Year
The example below is calculated on the basis of 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
Flow distribution over 1 year
H
(mwg)
s
60
50
B
40
30
20
C
10
750rpm
0 100 200
P
(kW)
shaft
60
50
40
30
B 1
20
10
1050rpm
C 1
750rpm
0 100 200
VLT HVAC Basic Drive Design Guide
A
1650rpm
1350rpm
1050rpm
( 3 )
m /h
300 400
A 1
1650rpm
1350rpm
( 3 )
300 400 m /h
®
MG.18.C2.02 - VLT is a registered Danfoss trademark
Distribution Valve regulation
m 3 /
h
% Hours Power Consumptio
A -
1
B
1
350 5 438 42.5 18,615
300 15 1314 38.5 50,589
250 20 1752 35.0 61,320
200 20 1752 31.5 55,188
150 20 1752 28.0 49,056
100 20 1752 23.0 40,296
Σ
100 8760 275,064
2.5.6 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, thereby 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) utilizing
the built in PI control.
2.5.7 Star/Delta Starter or Soft-starter not
Required
When larger motors are started, it is necessary in many
countries to use equipment that limits the start-up current.
In more traditional systems, a star/delta starter or soft-
starter is widely used. Such motor starters are not required
if a frequency converter is used.
As illustrated in the figure below, a frequency converter
does not consume more than rated current.
800
700
600
500
400
300
200
100
1
0
0 12,5
Frequency converter
control
Power Consumptio
n n
kWh 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
4
3
2
25 37,5 50Hz
Full load
& speed
13
2 2