13
p
n
n
H
Q
P
981
.
0
In the calculation sheets, calculations are at single points for Q = 20% to 100%
of nominal pump flow Qn. Q is the actual flow. H is the total dynamic head at
flow Q. The efficiency figures are multiplied with k-factors witch take into
account operating conditions with some accuracy. These correcting factors are
defined based on experience.
Graph 2. Typical efficiencies.
This gives the following formulas for power calculations:
Frequency converter control
vsd
kvsdi
kmi
m
p
Hsi
Qi
Pvsdi
*
81
.
9
, where
Hn
Hst
Qn
Qi
kmi
2
.
0
2
.
0
table
kvsdi
Throttling control, assuming constant motor efficiency
m
kpi
p
Hpi
Qi
Pthi
81
.
9
, where
Qn
Qn
Qi
Qi
kpi
44
.
1
4
.
2
ON/OFF control, assuming constant motor and pump efficiency
m
p
Hn
Qi
P
avg
OFF
ON
81
.
9
_
Efficiency
Flow
PUMP
DRIVE
MOTOR
100 %
95 %
80 %
vsd
m
p
