Danfoss VLT AQUA Drive FC 202 Design Manual page 19

Product Overview
100% speed
1
3
Flow
Operating
Pump curve
point
1
3
Flow
1 Operating point using a throttle valve
2 Natural operating point
3 Operating point using speed control
Figure 2.3 Flow Reduction by Valve Control (Throttling)
Speed control
The same flow can be adjusted by reducing the speed of
the pump, as shown in Figure 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.
MG20N622
Design Guide
2
Natural
operating point
2
H
p
H
s
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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
Figure 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(%)
Figure 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 Figure 2.7.
The result obtained shows energy savings in excess of 50%
at the given flow distribution over a year,
see Figure 2.6. The payback period depends on the price of
electricity and the price of the adjustable frequency drive.
In this example, payback is less than a year, when
compared with valves and constant speed.
Natural
Operating point
2
H
p
H
s
VSD
control
Ideal pump
control
50 60 70 80 90 100
17
2 2