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Energy Efficiency Considerations in Pumps and Pump Stations Jeff Foray, P.E. ([email protected]) WSU Extension Energy Program 14 March 2014
Energy Efficiency Considerations in Pumps and Pump Stations
Jeff Foray, P.E. ([email protected]) 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 [email protected]
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
Q x h eff X 3,960
hp = 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
Flow
Head (feet or psi) Dynamic
Losses
Static Pressure
Pump curve
System curve
Operating Point
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 System Curve Normal High Dynamic
Head
Low Dynamic Head
Operation at Low End of Pump Curve System Curve Normal High Dynamic
Head
Low Dynamic Head
Operation at High End of Pump Curve
System Curve Normal High Dynamic
Head
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
Head (feet)
1,800 RPM curve
System curve
Flow (gpm)
1,200 RPM curve
0 500 1,000 1,500 2,000 2,500
250
200
150
100
50
0
90 hp 70 hp
throttling valve
VFD: 36 hp
2,250 gpm 1,125 gpm
System curve: throttled
Pump Selection – Seems Easy H
ead
(feet
)
System curve
Flow (gpm)
70
60
50
40
30
0 0 500 1000 1500 2000 2500 3000 3500
20 40 50 60 74
82 80
81 82
74 60
585 rpm
Looks great for peak design conditions
Not So Fast….. H
ead
(feet
)
System curve
Flow (gpm)
70
60
50
40
30
0 0 500 1000 1500 2000 2500 3000 3500
20 40 50 60 74
82 80
81 82
74 60
585 rpm
Efficiency is just 40% at 500 gpm
500 rpm 460 rpm
Pumps are often unstable and inefficient at average/ minimum conditions
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 drip-
proof, weather protected 1992 Energy Act
► Submersibles use special motors
► Inverter Duty: improved cooling, insulation
Electric Motor Efficiency
► Standard efficiency motors: 90%
► Premium efficiency: 10% more expensive, 5% more efficient
► Efficiency is constant to about 50% load
0102030405060708090
100
0 20 40 60 80 100 120
75 - 100Hp30 - 60Hp15 -25Hp
% full load
% full load efficiency
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
0
200
400
600
800
1000
1200
1400
1600
1800
January February March April May June July August September October November December
Month
Ave
rage
Pow
er (k
W)
-
5
10
15
20
25
30
Average Power ConsumptionCurrent Condition Pumps - 877 kW After PS 1 Upgrade - 780 kW
Ave
rage
Flo
w (m
gd)
After PS 1 Upgrade Current Condition Pumps Projected Average Daily Flow
Energy Before and After Upgrade
Current Condition Pumps
76 kW
614 kW190 kW
Average Hydraulic Power Loss Average Hyd PowerAverage Motor Loss
After PS 1 Upgrade
91 kW
16 kW39 kW
611 kW
123 kW
Average Hydraulic Power Loss Average Hyd Power Average Motor Loss AFD Loss Savings Compared to Current Pumps
