Danfoss VLT AQUA Drive FC 202 Design Manual page 19

Product Overview
Speed control
The same flow can be adjusted by reducing the speed of
the pump, as shown in Illustration 2.4. Reducing the speed
moves the pump curve down. The point of operation is
the new intersection point of the pump curve and the
system curve (3). The energy savings can be calculated by
applying the affinity laws as described in
chapter 2.1.3 Example of Energy Savings.
Operating
Pump curve
point
1
Speed
reduction
3
Flow
1 Operating point using a throttle valve
2 Natural operating point
3 Operating point using speed control
Illustration 2.4 Flow Reduction by Speed Control
140
130
120
110
Recirculation
100
90
80
Throttle
70
control
P(%)
60
50
Cycle
control
40
30
20
10
0 10 20 30 40
Q(%)
Illustration 2.5 Comparative Flow Control Curves
2.1.5 Example with Varying Flow over 1
Year
This example is calculated based on pump characteristics
obtained from a pump datasheet, shown in Illustration 2.7.
MG20N602
Design Guide
Natural
Operating point
2
H
p
H
s
VSD
control
Ideal pump
control
50 60 70 80 90 100
Danfoss A/S © 09/2014 All rights reserved.
The result obtained shows energy savings in excess of 50%
at the given flow distribution over a year,
see Illustration 2.6. The payback period depends on the
price of electricity and the price of the frequency
converter. In this example, payback is less than a year,
when compared with valves and constant speed.
[h] t
2000
1500
1000
500
100 200
t [h] Duration of flow. See also Table 2.2.
Flowrate
Q [m 3 /h]
Illustration 2.6 Flow Distribution over 1 Year (Duration versus
Flowrate )
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
Illustration 2.7 Energy Consumption at Different Speeds
Q
300 400
[m 3 /h]
A
1650rpm
1350rpm
1050rpm
( 3 )
m /h
300 400
A 1
1650rpm
1350rpm
( )
3
300 400 m /h
17
2 2