Impact of Pump Wear on
Efficiency
Simon Bunn
CTO - Derceto
Copyright © AWWA 2010
Background Information
• “The more than 60,000 water systems and 15,000
wastewater systems in the United States are among
the country’s largest energy consumers, using about
75 billion kWh/yr nationally —3 percent of annual
U.S. electricity consumption.“
Electric Power Research Institute,
Energy Audit Manual for Water/Wastewater Facilities,
(Palo Alto: 1999), Executive Summary
• That’s $10 billion in energy costs per year!
Typical Energy Use in Water Utilities
Pump Life-Cycle Costs
Electricity, 95%
Maintenance, 4%
Purchase Price, 1%
Improving pump efficiency
A major European Union study of pumps1 recommended:
• Select pumps according to duty requirements
• Measure pump performance regularly
• Replace or refurbish poorly performing pumps
• Polish or coat pump surfaces
• Use automatic pump scheduling / pump selection
software targeting efficiency
1. European Commission, “Study on improving the energy efficiency of pumps”, February 2001,
AEAT-6559/ v 5.1
Refurbish or replace?
Pump Installed
Duty
As new Pump efficiency
As new motor efficiency
Present Pump Efficiency
Potential Savings
Present Input Power
Price of Electricity
Present running cost
Potential input power 155.95 kW
Potential running cost $133,610
Saving
$26,435/year
1963
250l/s @ 48 m
82%
92%
70%
14.60%
182.7 kW
10 Cents / kW hr
$160,045/year
New pump efficiency
New motor efficiency
New input power
New running cost
Saving
84%
96%
145.9 kW
$127,801
$32,244
Best Efficiency Point
Effect of Wear on Pump
70
60
50
Head
40
30
20
10
0
0
50
100
150
Flow
• Pump installed 2000
200
250
300
What do the affinity laws predict?
8.33
HPout2
33000
eff 2 

speed 2 3
HPin2
HPin1 * (
)
speed1
speed 2 2
speed 2 2
8.33
Head1 * (
) * Flow1 * (
) *
speed1
speed1
33000

speed 2 3
HPin1 * (
)
speed1
8.33
Head1 * Flow1 *
33000  eff

1
HPin1
Head2 * Flow 2 *
Peak Eff1 = Peak Eff2
But when we measure efficiency...
90%
80%
70%
13%
Efficiency
60%
50%
40%
30%
20%
10%
0%
0
50
100
150
Flow
200
250
300
350
And an older pump...
45
40
35
Head
30
25
20
15
10
5
0
0
100
200
300
Flow
• Pump installed 1988
400
500
..with its peak efficiency
90%
80%
70%
Efficiency
60%
25%
50%
40%
30%
20%
10%
0%
0
50
100
150
200
Flow
250
300
350
400
450
Real Efficiency of a Pump
100%
90%
80%
Efficiency
70%
60%
max eff ratio vs head ratio
50%
40%
30%
20%
10%
0%
0%
20%
40%
60%
80%
100%
120%
140%
head ratio


Results obtained with 95 pumps, still poor correlation
UK based WRC working on similar study with 4000 pumps;
results expected to be published 2010
So water pumps do wear!
• A quick rule of thumb;
1% deterioration on head/flow curve per year
• Though it tends to be faster for the first few years,
e.g. Monroe County found 10% drop in the first 6
years
• ..and slower towards the end as pumps are corroded,
pitted, have tuberculation and reach around 40%
efficiency
• Leads to;
Equivalent % drop in peak efficiency
What does efficiency mean?
• 3 ways of calculating “efficiency”
◦ Power in / Power out (Pump station)
◦ Weighted Average Efficiency (Average value of each
pump’s efficiency weighted by the flow), should be the
same value as Power in / Power out (Pump station)
◦ Volume of water moved per energy unit spent
• The last way allows the comparison of the different
solutions (Pump1, Pump2 or Pump1 // Pump2 ) in
terms of kWh spent
• It also effectively handles distortions created by
velocity head
Best Efficiency Point - reality
BEP
BEP
$
$$
$$
Parallel Pumps’ Efficiency
• 1 pump: 6.3MGD @ 50 ft, efficiency 70%
• 2 pumps: 10.4MGD @ 90 ft, efficiency 85%
So running two pumps makes them run efficiently,
but look at the change in lift.
Calculating actual energy required to deliver the water,
which is really what matters:
1 pump used 223 kWh/MG
2 pumps used 332 kWh/MG, 50% more energy used
Parallel Pumps’ Efficiency
• For example, if running one pump alone in a given
pump station has a ratio of 250 gallons per kWh and
running two pumps in parallel is equivalent to 300
gallons per kWh, running two pumps will be more
efficient.
• This ratio could be calculated by dividing the flow at
operating point by the input power for this flow
(volume/energy  flow/power).
• The solution with the biggest ratio is the one that
carries more water per energy unit spent.
Parallel Pumps’ Efficiency
• Case 1: two identical pumps
Parallel Pumps’ Efficiency
• Here it is more energy efficient to run the two
pumps in parallel, the pumps will also run
closer of their BEP.
Overall pump station
efficiency
80.55%
Pump 2 or Pump 3
efficiency running alone
77.78%
Pump 2 or Pump 3 alone
16.98 G/(HP x min)
Pump 2 and Pump 3 run
together
17.09 G/(HP x min)
Parallel Pumps’ Efficiency
◦ Case 2: Pump 1 and Pump 2 (Two Non-identical Pumps)
Parallel Pumps’ Efficiency
• Here it is more energy efficient to run the Pump 1
only or both pumps in parallel but never use Pump
2 alone.
Overall pump station
efficiency
69.23%
P1’s efficiency while running
alone
68.4%
P2’s efficiency while running
alone
57.6%
P1’s efficiency while p1//p2
73.68%
P2’s efficiency while p1//p2
66.62%
Pump 1 alone
33.9 G/(HP x min)
Pump 2 alone
30.4 G/(HP x min)
Pump 1 // Pump 2
31.9 G/(HP x min)
Case Study 1: Austin TX Power Plant
•
•
•
•
•
•
•
•
•
Reported by Department of Energy1 in 2005
Two 1000-horsepower cooling water pumps
Tested in 1978, at 88% efficiency
Tested in 2005; 50% and 55% efficient
New impellors, diffusers, shrouds and shafts
Retested, now both at 85% efficiency
Increased generation capacity due to more cooling
Saved 43,000 tons CO2 first year
Annual savings of $1.2m per year, 11 month payback
1. US Department of Energy (DOE), 2006. Pumping System Improvements Save Energy at Texas
Power Plant. Energy Matters, Spring, 2006.
Case Study 2: Monroe County (NY)
“We never thought that roughness of internal pump
surfaces could be costing us so much money…”
…“After running tests on pumps in our distribution
system, our engineers were shocked to find that many
were operating 15% to 25% below the manufacturer’s
specifications”
Paul Maier
– Monroe County Water Authority.
Case Study 2: Monroe County (NY)
• Pump efficiency in 2000 was 88%, by 2006 it was 77.8%
• Refurbishment plus coating took it back to 88%
• The more the pump is used the faster the payback
Variable Speed Drives
• Affinity laws say that changing impeller diameter and
rotational speed has the same effect
• According to Schneider Electrics manual, variable
speed drive allows pump to be driven at “high
efficiency no matter what speed is used”
• A presentation from the website
www.energymanagertraining.com says that reducing
the speed of the pump of 50% results in a 1 or 2%
reduction of the peak efficiency
• According to Haestad’s Advanced water distribution
modelling and management the affinity laws are right
Variable Speed Drives
• This is from a major pump test company
Peak Efficiency
Speed
Variable Speed Drive - Fast
Fast Speed (1500 RPM) Efficiency
90
90%
Pump Curve
Efficiency Curve
80%
70
70%
60
60%
50
50%
40
40%
30
30%
20
20%
10
10%
0
0%
0
200
400
600
Flow (l/s)
800
1000
1200
Efficiency (%)
Total Dynamic Head (m)
80
Variable Speed Drive – Mid Speed
Mid Speed (1440 RPM) Efficiency
90
90%
80
80%
70%
Pump Curve
Efficiency Curve
60
60%
50
50%
40
40%
30
30%
20
20%
10
10%
0
0%
0
200
400
600
Flow (l/s)
800
1000
1200
Efficiency (%)
Total Dynamic Head (m)
70
Variable Speed Drive – Slow Speed
Slow Speed (1350 RPM) Efficiency
90
90%
Pump Curve
Efficiency Curve
80%
70
70%
60
60%
50
50%
40
40%
30
30%
20
20%
10
10%
0
0%
0
200
400
600
Flow (l/s)
800
1000
1200
Efficiency (%)
Total Dynamic Head (m)
80
Single Objective : Cost Minimisation
• Five key cost reduction methods are employed
◦ Electrical load movement in time, to maximise
utilisation of low cost tariff blocks
◦ Electricity peak demand reduction.
◦ Utilisation of lowest production and chemical cost
sources of water.
◦ Utilisation of shortest path between source and
destination
◦ Energy efficiency improvements from pumps and
pumping plants.
• Of these, energy efficiency improvements produced
the most unexpected outcome.
Case Study 3: East Bay MUD
EBMUD Aquadapt Pump Efficiency Improvements by Original Efficiency,
2003-2008
25%
Average Efficiency Improvement (%)
20%
15%
10%
5%
0%
45 - 55%
55 - 65%
65 - 75%
Original Average Efficiency Range (%)
75 - 85%
Pump station efficiency improved
universally
EBMUD Aquadapt Pump Efficiency Improvements,
2003-2008
90.0%
Percentage of Pump Stations
80.0%
70.0%
60.0%
50.0%
Pre-Aquadapt
40.0%
Post-Aquadapt
30.0%
20.0%
10.0%
0.0%
45 - 55%
55 - 65%
65 - 75%
Pump Efficiency
75 - 85%
Pumps operate more efficiently
Real-time pump curve data
In this example a pump is running well on its curve and at
peak efficiency
Flat pump curves can be a problem
Derceto AQUADAPT Utility Case Studies – USA
Aquadapt Client
WaterOne KS
Total Utility
Population
Energy
Cost
Savings
Approx
Annual
Savings
Efficiency
Gains
Annual GHG
Reduction
(metric ton)
400 k
14%
$ 745 k
6%
4,800
700 k
10%
$120 k
8%
300
15%
$190 k
8%
240
1.3 M
12%
$360 k
6%
800
1.8 M
11%
$865 k
8%
4,500
1.2 M
10%
C$1.6 M
6%
5,600
800 k
8%
$460k
6%
2,300
Full System – May 2006
Eastern Municipal Water District CA
Stage 1 - August 2006
Eastern Municipal Water District CA
Stage 2 – September 2007
East Bay Municipal Utility District CA
Stage 1 – August 2004
Washington Suburban Sanitary
Commission MD
Full System – May 2006
Regional Municipality of Peel *1 ON
Full System – September 2010
Gwinnett County Dept. of Water
Resources GA
Full System – December 2009
* Factory Tests Complete – Projects being installed now
Conclusions
• You have to be able to measure something before
you can aim to improve it
• Potable water pumps do wear and this wear can
have major implications for efficiency
• More than 90% of all purchased power by Water and
Wastewater Utilities is used by pumps
• With 3% of all generation power going to Water and
Wastewater utilities, getting pumps operating well
should be a key goal
• Payback for these types of projects is exceptionally
good, 3 months to 2 years typically
Thank You
Simon Bunn
sbunn@derceto.com
Wes Wood
wwood@derceto.com