Energy Efficiency Considerations
in Pumps and Pump Stations
Jeff Foray, P.E. (JeffForay@KennedyJenks.com)
WSU Extension Energy Program
14 March 2014
How Do You Save Energy?
► Don’t
design it wrong
► Operate smart
► Fix stuff
Thanks for your time, any questions e-mail me at
JeffForay@KennedyJenks.com
Energy in a Pumping System
Pumps and Other Fluid Movers
►
Centrifugal pumps are
the most common




►
►
End suction
Split case
Turbines
Submersibles
Positive displacement
pumps
Other devices
 Fans
 Compressors
Some Basic Stuff
►
►
►
►
►
Flow: 1 mgd = 694 gpm
Head: 1 psi = 2.31 feet
Head Loss: liquid friction,
velocity2
Power: 1 hp = .75 kW
Money ($.07/kwhr)
 1 mgd at 100 feet (22 hp) for a
year is about $10,000
 2 mgd in same pipe is about
$18,000 a year
 1 hp for a year about $500
What is Efficiency?
►
►
Good divided by
the total
Energy Losses in
Pumps:
 Mechanical
(friction in
bearings, etc.)
 Volumetric
(recirculation)
 Hydraulic (liquid
friction)
Calculating Pump Horsepower
hp =
Qxh
eff X 3,960
Q = flow in gpm
h = head (pressure) in
feet (1 psi = 2.31 feet of
head)
eff = efficiency
• Water horsepower: ignore efficiency
• Brake horsepower: pump efficiency only (size the
motor)
• Wire-to-water horsepower: pump x motor
efficiency (size the electrical service)
Typical Pump Efficiencies
►
Pump only (brake, no motor)




►
►
Non-clog centrifugal, 25 hp: 65%
Submersible wastewater, 34 hp: 75%
Vertical turbine, water, 30 hp: 81%
End Suction, water, 30 hp: 75%
Bigger is better: add about 5 points at
200 hp
Slower is better: add a couple points
below 1200 rpm
Pump Curve: Superbasics
Operating Point
Pump curve
Head
(feet or psi) System curve
Dynamic
Losses
Static
Pressure
Flow
Pump Curve: Less Basic
►
►
►
►
Nerdy but crucial
Best Efficiency
Point (BEP)
Typically drops
off about 20%
from BEP
How pump is
applied
determines how
efficient it will be
Minimum/Maximum/Normal
Pump and System Curves
System Curve
Normal
High Static
Head
Low Static
Head
Dynamic Losses May Vary
High Dynamic
Head
System Curve
Normal
Low Dynamic
Head
Operation at Low End of Pump Curve
High Dynamic
Head
System Curve
Normal
Low Dynamic
Head
Operation at High End of Pump
Curve
High Dynamic
Head
System Curve
Normal
Low Dynamic
Head
Variable Speed Pumping
►
Variable Speed
Drives (VFD’s)
 Vary motor
speed from
about 50% to
100%
 Drive is about
98% efficient
 2 to 4 times cost
of starter
►
Why? Moving water
slower reduces
friction
Why VFD’s? Throttling Stinks
250
1,800 RPM curve
1,125 gpm
2,250 gpm
throttling valve
70 hp
200
Head
(feet)
90 hp
1,200 RPM curve
VFD:
36 hp
150
100
System curve:
throttled
50
0
System
curve
0
500
1,000
1,500
Flow (gpm)
2,000
2,500
Pump Selection – Seems Easy
70
20
Head (feet)
60
40
Looks great for peak
design conditions
50 60
74
82
50
80
System curve
81
82
40
74
60
30
585 rpm
0
0
500
1000
1500
Flow (gpm)
2000
2500
3000
3500
Not So Fast…..
Pumps are often unstable and inefficient
at average/ minimum conditions
70
20
60
40
74
Head (feet)
Efficiency is just 40%
at 500 gpm
50 60
82
50
80
System curve
81
82
40
74
60
30
585 rpm
460 rpm
0
0
500
1000
1500
Flow (gpm)
500 rpm
2000
2500
3000
3500
Follow Standards
►
Hydraulic Institute
 Pump Intake
Design (9.8)
 Allowable
Operating Region
(9.6.3)
►
Read “Pumping
Station Design”
(Sanks)
Electric Motors
►
Most applications: NEMA
standard
 Enclosure type: TEFC, open dripproof, weather protected
 1992 Energy Act
►
►
Submersibles use special
motors
Inverter Duty: improved
cooling, insulation
Electric Motor Efficiency
►
►
►
Standard
% full load
efficiency
efficiency
motors: 90%
Premium
efficiency: 10%
more expensive,
5% more
efficient
Efficiency is
constant to
about 50% load
100
90
80
70
60
50
40
30
20
10
0
75 - 100
Hp
30 - 60
Hp
15 -25
Hp
0
20 40 60 80 100 120
% full load
Improving Pump Efficiency
►
Don’t Design it Wrong
 Invest in a good predesign
 Decide how it will operate before messing around with
layouts and equipment selection
 Pick pumps to operate efficiently operate at conditions
where the pump will actually operate most of the time
 Consider variable speed drives or smaller pumps to
improve efficiency at low flows
Improving Pumping Efficiency
►
Operate Smart
 Pump as slowly as possible
 Utilize storage to level out pumping rate
 Eliminate throttling
►
Fix Stuff




Test pumps regularly (inc electrical measurements)
Visual inspection of interior
Modify or replace impeller to match conditions
Replace old motors (pre Energy Act, 1992 to 1997)
Example: Big Water Pump Station
Figure 3 - Projected Average Day Power Usage, 2011 Projected Average Day Flow
1800
30
25
1400
1200
20
1000
15
800
600
10
400
5
200
0
January
February
March
April
May
June
July
August
September
October
November
Average PowerMonth
Consumption
Current Condition Pumps - 877 kW
After PS 1 Upgrade - 780 kW
After PS 1 Upgrade
Current Condition Pumps
Projected Average Daily Flow
December
Average Flow (mgd)
Average Power (kW)
1600
Energy Before and After Upgrade
Current Condition Pumps
After PS 1 Upgrade
76 kW
39 kW
16 kW
91 kW
614 kW
190 kW
611 kW
123 kW
Average Hydraulic Power Loss
Average Hyd Power
Average Motor Loss
Average Hydraulic Power Loss
Average Hyd Power
Average Motor Loss
AFD Loss
Savings Compared to Current Pumps