Danfoss FC 102 Design Manual page 24

Introduction to VLT® HVAC D...
2.7.5 Example with Varying Flow over 1
Year
2 2
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 =P
shaft shaft output
[h] t
2000
1500
1000
500
100 200
Table 2.6 Energy Savings
H
(mwg)
60
50
40
30
20
10
0
P
(kW)
shaft
60
50
40
30
20
10
0
Illustration 2.13 Example with Varying Flow
22
Q
300 400
[m 3 /h]
s
B
A
1650rpm
1350rpm
C
1050rpm
750rpm
100 200 300
A 1
1650rpm
1350rpm
B 1
1050rpm
C 1
750rpm
100 200 300
Danfoss A/S © Rev. 06/2014 All rights reserved.
Design Guide
m 3 /
h
% Hours Power Consumption
350 5
300 15
250 20
200 20
150 20
100 20
Σ 100 8760
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
and provides power factor correction for the cos φ of the
( )
m 3 /h
400
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
( )
400 m 3 /h
if a frequency converter is used.
As illustrated in Illustration 2.14, a frequency converter does
not consume more than rated current.
Distri- Valve regulation
bution
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
® HVAC Drive has a cos φ of 1
Frequency converter
control
Power Consumptio
n
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
MG11BC02