Specifications
2.7.5 Example with Varying Flow over 1
Year
Table 2.4 is 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
frequency converter. In this example, it is less than a year
when compared with valves and constant speed.
Energy savings
P
shaft
=P
shaft output
Table 2.4 Flow Distribution Over One Year
m
3
/h
Distribution Valve regulation Control
% Hours Power Consumption Power Consumption
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 2.5 Energy Savings Calculation
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
200100 300
(m
3
/h)
(
m
3
/h)
400
750rpm
1050rpm
1350rpm
1650rpm
P
shaft
C
1
B
1
A
1
Illustration 2.7 Energy Savings in a Pump Application
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, 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
Typically, the VLT
®
HVAC Drive has a cos φ of 1 and
provides power factor correction for the cos φ of the
motor, which means 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 Illustration 2.8, a frequency converter does
not consume more than rated current.
Introduction VLT® HVAC Drive FC 102 Design Guide
MG16C102 - Rev. 2013-08-20 21
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