Grundfos E-pumps

Grundfos E-pumps
2
Performance curves of speed-controlled
pumps
Performance curves
The curve chart below shows a CRE 15-3. The top part
of the chart shows the QH performance curves at
different speeds. Curves for speeds between 100 %
and 40 % are included at 10 % intervals. Finally, a
minimum curve at 25 % is shown.
The bottom part of the chart shows P1 (input power
from the power supply). NPSH for the pump at
maximum speed is shown in the same diagram.
eta [%]
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
0
100%
80%
60%
60% 80% 100%
100%
80%
60%
1.0 2.0 3.0 4.0 5.0 6.0 Q [gpm]
0 5 10 15 20 25 30 Q [m3/h]
}
}
}
η MLE
η P
η TOT
TM05 0878 1811
Product overview
Fig. 9
Efficiency curves for MLE, pump and complete
E-pump at 100 %, 80 % and 60 % speed
Fig. 7 Performance curve of a CRE 15-3
Efficiency
The total efficiency of the E-pump η total is calculated by
multiplying the efficiency of the MLE with the pump
efficiency.
Fig. 8
P 1 P 2
MLE
η MLE
P 1 = input power, MLE motor
P 2 = input power, pump
P H = hydraulic power
η pump
Efficiency of an E-pump
The efficiency of the MLE motor depends on the size of
the motor, the speed and the load of the shaft.
Firstly, the efficiency of the pump depends on the flow
Q, and secondly the speed of the pump.
P H
TM03 0433 5104
TM00 8720 4996
Figure 9 shows the efficiency of the MLE and the pump
part and finally the resulting efficiency of a CRE 15-3
with a 4 Hp (3 kW) MLE motor. The curves are drawn
as a function of flow Q and for three different speed
values: 100 %, 80 % and 60 %.
Assuming the situation shown in fig. 9, with a duty
point at 100 % speed equal to Q = 76.6 gpm
(17.4 m 3 /h) and H = 105 ft (32 m), the change in
efficiency at 80 and 60 % speed is shown in the
following table:
Speed
[%]
100
80
60
Q H P 1 P 2 P H η P η MLE η TOT
[gpm
(m 3 /h)]
76.6
(17.4)
61.6
(14)
46.2
(10.5)
[ft
(m)]
105
(32)
69
(21.1)
39
(12)
[kW] [kW] [kW] [%] [%] [%]
3.55
(2.65)
1.97
(1.47)
0.89
(0.66)
2.86
(2.13)
1.53
(1.14)
0.66
(0.49)
2.02
(1.51)
1.07
(0.8)
0.46
(0.34)
71.1 80.4 57.2
70.5 77.6 54.7
70.4 73.8 51.9
The pump efficiency η P is reduced from 71.1 % to
70.4 %, meaning less than one % point drop in
efficiency.
Due to the big drop in speed and shaft load, the
efficiency of the MLE is reduced in the range of 7 %
points resulting in an overall reduction of E-pump
efficiency equal to 5.3 % points.
Efficiency is important, but what counts is the power
consumption as it directly influences the energy costs.
As appears from the table above, the power
consumption P 1 drops from 3.55 Hp to 0.89 Hp
(2.65 kW to 0.66 kW) which is a 75 % reduction.
The conclusion is that the speed reduction is the most
important factor with regard to energy saving, and that
the drop in efficiency will only have minor influence on
the possible savings achieved through speed control.
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