2.7.5 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.
Flow distribution over 1 year
P
shaft
=P
shaft output
500
[h] t
1000
1500
2000
200
100
300
[m
3
/h]
400
Q
175HA210.11
Table 2.6 Energy Savings
175HA209.11
60
50
40
30
20
10
H
s
0
100
200
300
400
(mwg)
B
C
A
750rpm
1050rpm
1350rpm
1650rpm
0
10
20
30
(kW)
40
50
60
200
100
300
(
m
3
/h
)
(
m
3
/h
)
400
750rpm
1050rpm
1350rpm
1650rpm
P
shaft
C
1
B
1
A
1
Illustration 2.13 Example with Varying Flow
m
3
/
h
Distri-
bution
Valve regulation
Frequency converter
control
% Hours Power Consumption Power Consumptio
n
A
1
-B
1
kWh
A
1
-C
1
kWh
350
5
438
42,5
18.615
42,5
18.615
300 15 1314
38,5
50.589
29,0
38.106
250 20 1752
35,0
61.320
18,5
32.412
200 20 1752
31,5
55.188
11,5
20.148
150 20 1752
28,0
49.056
6,5
11.388
100 20 1752
23,0
40.296
3,5
6.132
Σ
100 8760
275.064
26.801
Table 2.7 Consumption
2.7.6 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) utilising
the built-in PID control.
2.7.7 Cos
φ
Compensation
Generally speaking, the VLT
®
HVAC Drive has a cos
φ
of 1
and provides power factor correction for the cos
φ
of the
motor, which means that there is no need to make
allowance for the cos
φ
of the motor when sizing the
power factor correction unit.
2.7.8 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
, a frequency converter does
not consume more than rated current.
Introduction to VLT® HVAC D...
Design Guide
22
Danfoss A/S © Rev. 06/2014 All rights reserved.
MG11BC02
2
2
