S
peed reg
ulation
TPE E-circulators
4
8
4. Speed regulation
Affinity equations
Normally, TPE pumps are used in applications
characterized by a
variable
flow. Consequently, it is
not possible to select a pump that is constantly operat-
ing at optimum efficiency.
In order to achieve optimum operating economy, select
the pump on the basis of the following criteria:
• The max. required duty point should be as close as
possible to the QH curve of the pump.
• The flow rate at the duty point required should be
close to the optimum efficiency (eta) for most
operating hours.
Between the min. and max. performance curve TPE
pumps have an infinite number of performance curves
each representing a specific speed. Therefore it may
not be possible to select a duty point close to the max.
curve.
Fig. 1
Min. and max. performance curves
In situations where it is not possible to select a duty
point close to the max. curve, affinity equations can be
used. The head (H), the flow (Q) and the input power
(P) are the appropriate variables you need to be able
to calculate the motor speed (n).
Note:
The approximated formulas apply on condition that the
system characteristic remains unchanged for n
n
and n
x
and that it is based on the formula H = k x Q
2
, where k
is a constant.
The power equation implies that the pump efficiency is
unchanged at the two speeds. In practice this is
not
quite correct.
Finally, it is worth noting that the efficiencies of the
variable frequency drive and the motor
must
be taken
into account if a precise calculation of the power sav-
ing resulting from a reduction of the pump speed is
wanted.
WinCAPS and WebCAPS
WinCAPS and WebCAPS are both selection programs
offered by Grundfos.
The two programs make it possible to calculate a TPE
pump’s specific duty point and energy consumption.
By entering the dimensional data of the pump,
WinCAPS and WebCAPS can calculate the exact duty
point and energy consumption. For further information,
please contact Grundfos or see Grundfos’ homepage
www.grundfos.com.
TM
01
49
16
48
03
Max. curve
Min. curve
E-circulator.book Page 8 Friday, October 7, 2011 4:01 PM
