The objective of this webinar is to give an introduction to energy saving in pumping systems, with an emphasis on the control strategies available for optimising the different types of systems commonly found in industry and commercial buildings. It will also give an overview of the cost effective selection of energy efficient pumps and motors. Pumping systems use more energy than any other type of motor driven system, and so should always be a primary candidate when looking to make energy savings at a site.

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2. • How pumps work
• How to interpret pump curves
• The different types of system curves
• Different methods of pump control
• Control of Multiple pump configurations
• Pump deterioration
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3. • Having a good understanding of the system characteristics is
important for selecting the best method of control, and hence
saving energy.
• VSDs can save lots of energy in Circulation systems – but not so
much if the system has a high static head.
• VSDs enable precise control of pressure.
• Pump duty can be cheaply reduced by using a smaller impeller.
• In parallel multiple pump systems, take care to switch off any
pumps not required.
• Select high efficiency motors, but beware of the reduced slip.
• Pumps wear out, and should be repaired or replaced as required.
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4.  Not included today are Positive displacement or Wastewater pumps
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Ilustrations (left
to right):
Archimedes
screw pump,
hydraulic pump,
wastewater
pump

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6. 6
Image: Wikipedia
Diagram is of a typical small
end suction single stage pump
for clean water duty with own
bearings.

7. 𝐐𝐐 ∝ 𝐍𝐍
𝐇𝐇 ∝ 𝐍𝐍𝟐𝟐
𝐏𝐏 ∝ 𝐍𝐍𝟑𝟑
Where,
N = rotational shaft speed
Q = Flow
H = Head
P = Power
The Power
Cubed Rule
P ∝ 𝐐𝐐. 𝐇𝐇

8. • The manufacturer should supply the
following pump system curves:
 Total head vs. flow
 Efficiency vs. flow
 Power vs. flow
 NPSHR (net Positive Suction Head Required)
• Additional curves might show the variation
with different impeller diameters.
• Power consumption will need adjusting for
specific gravity of fluid being pumped.
• Some pumps will be characterised for use
with two motor speeds.
• Data is for the pump only, and does not
include motor performance data
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Diagram: Waterworld magazine

10. Mostly
static
head
All
frictional
head
Figure Courtesy of Oak Ridge National Laboratory

11. • Total system resistance from
frictional losses (vary as
function of the cube of speed)
plus static head losses to
provide lift.
• Head falls with the Square of
the speed, so falls off very
quickly as the speed is
reduced.

12. Bringing together the pump
and system characteristics,
and ways to alter it to save
energy
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13. The System operating point
is where the pump and
system curves intersect
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Grundfoss

14. Diagram: Sergio Bastos, Linked In
Where
Power α Flow x Head

15. The energy saved by
replacing a throttle
control with a VFD is
given by the area
bounded by the two
power curves.

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• An increase in internal
recirculation means that
efficiency will decrease a
little.
• But the system energy savings
from speed reduction will in
good VSD applications be
much larger.

17. • All system losses must
be friction losses for
the affinity laws to
apply.
• Therefore, systems with
low static head tend to
be better candidates for
VSDs.

18. 18
• Pump impeller will be most efficient
close to maximum diameter.
• A smaller impeller will be less efficient,
but the system energy savings will be
large.

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• Large water cooling
systems are used to
cool the plant and
product.
• Multiple parallel
pumps are switched on
and off to meet the
varying demand.

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• The combined pump curve of
parallel pumps is found by
adding the flows. The maximum
head stays the same. (For non-
identical pumps, the process is
similar).
• Parallel systems are optimised
for a specific number of pumps.
• Operating away from this can
have severe power
consequences.
• Additional pumps often left on
for safety.

22. • Essential to stop backflow
through unused pump.
• Valve that doesn’t open
properly will act as a
throttle.
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24. Diagrams: Wilo
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• End suction own bearings pump (Top
left)
• End suction close coupled pump
(Bottom left)
• End suction in-line pump with
integrated controller (Right)

25. Motor Sizing
• Acceleration time determined by the difference
between the motor and system torque, and the
system inertia. So a larger motor will accelerate
the pump faster.
• Smaller pumps will be supplied with a motor
designed for maximum pump power
consumption, and so the user does not need to
worry.
Higher Efficiency Motors
• High Efficiency Motors should be recommended
for their lower energy consumption, but:
 More efficient motors will have lower slip and
hence higher speed. If the increase in work done
exceeds the motor efficiency gain, then the
overall energy consumption will increase.
 This is most significant in systems with a high
friction load.
 This is not a problem where the system is
properly controlled, or for new plant that takes
account of the actual running speed.
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Diagram from myelectrical.com
New Operating point with
increased speed and torque

26. Building cooling/heating systems
follow a standard demand: time
profile. The total running hours
vary with location.
A sealed circulation system, and
so variable speed is an ideal
solution.
Similarly with secondary cooling
system loops
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H
Q
Hmax
Q25% Q50% Q75% Q100%
H
Q
Hmax
Q25% Q50% Q75% Q100%
Flow
(%)
Time
(%)
100 6
75 15
50 35
25 44

27. • Batch process with cyclical
demand.
• Large pumps make it
impractical to turn on and
off very frequently
• Variable Speed drives allow
smooth speed increase and
decrease.
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Corus, Llanwern, Wales

28. • Varying pump speed can
give much tighter control
than on/off switching.
• This also illustrates how
in many systems, the
pump will work at
differing operating
points. This should be
taken into account when
selecting a pumps.

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• Pumps lose efficiency over
time, but this will usually go
un-noticed
• Pump efficiency monitoring
useful on larger pumps for
determining when to
refurbish

31. Pump Operation
Figure Courtesy of P. Barringer.
Operating away from
the Best Efficiency
Point will also
decrease the pump life

32. • Having a good understanding of the system characteristics is
important for selecting the best method of control, and hence
saving energy.
• VSDs can save lots of energy in Circulation systems – but not
so much if the system has a high static head.
• VSDs enable precise control of pressure.
• Pump duty can be cheaply reduced by using a smaller impeller.
• In parallel multiple pump systems, take care to switch off any
pumps not required.
• Select high efficiency motors, but beware of the reduced slip.
• Pumps wear out, and should be repaired or replaced as
required.
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33. • System efficiency:
Europump series of
publications
• Pump Efficiency: Pump
efficiency for single stage
centrifugal pumps
• Centrifugal Pumps:
Centrifugal Pumps:
Karassik and McGuire,
Chapman & Hall
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34. Thank you for listening
Any Questions?
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