Irrigation Pumping Plants
ByBlaine HansonUniversity of California, Davis
Questions
How do pumps perform? How can I select an efficient pump? What causes a pump to become
inefficient? How can I determine my pump’s
performance? How can I improve my pump’s
performance? Will improving my pump’s
performance reduce my energy bill?
Basic Concepts
DefinitionEnergy = kilowatt-hours
oOne kilowatt is 1.34 horsepower oHours = operating time
Energy cost is based on kwhr consumed and unit energy cost ($/kwhr)
Reducing energy costsReduce Input HorsepowerReduce Operating HoursReduce Unit Energy Cost
Improving Pumping Plant Efficiency
Adjust pump impellerRepair worn pumpReplace mismatched pumpConvert to an energy-efficient
electric motor
Shaft Frame Impeller Discharge Inlet
StuffingBox
BalanceLine
Volute WearingRings
Centrifugal or Booster Pump
Deep Well Turbine
Deep Well Turbine
SubmersiblePump
Terms
Total head or liftCapacityBrake horsepowerInput horsepowerOverall efficiency
Pumping Water Level
Pump
MotorDischarge Pressure Gauge
Discharge Pipe
Static or Standing Water Level
Pump Head
Ground Water
Ground Surface
Pumping Lift
Discharge Pressure Head
Height of a column of water that produces the desired pressure at its base
Discharge pressure head (feet) = discharge pressure (psi) x 2.31 Note: a change in elevation of 2.31
feet causes a pressure change of 1 psi
Total Head or Total Lift = Pumping Lift (feet) + Discharge Pressure Head (feet)
Example
Pumping Lift = 100 feetDischarge Pressure = 10 psiDischarge Pressure Head = 10 psi x 2.31 = 23.1 feetTotal Head = 100 +23.1 = 123.1 feet
Intake Pressure
Discharge Pressure
Pump Discharge Pipe
Pump Intake
Total Head or Lift of Booster Pumps
Difference between pump intake pressure and pump discharge pressure
Multiply difference (psi) x 2.31 Example
o Intake pressure = 20 psio Discharge pressure = 60 psio Difference = 40 psio Total Head = 40 x 2.31 = 92.4 feet
Brake Horsepower = Shaft Horsepower of Motor or Engine
Input Horsepower = Power Demand of Motor or Engine
Overall Pumping Plant Efficiency =
Gallons per minute x Feet of Total Head
3960 x Input Horsepower
Pump Performance Curves
o Total Head or Lift - Capacityo Pump Efficiency - Capacityo Brakehorsepower - Capacityo Net Positive Suction Head -
Capacity (centrifugal pumps)
200 250 300 350 400
PUMP CAPACITY (gallons per minute)
0
50
100
150
200
250T
OTA
L H
EA
D (
feet
)
Worn Pump
New Pump
Total Head - Capacity
200 250 300 350 400
PUMP CAPACITY (gallons per minute)
0
10
20
30
40
50
60P
UM
PIN
G P
LA
NT
EF
FIC
IEN
CY
(%
)
Worn Pump New Pump
Efficiency - Capacity
0 100 200 300 400 500 600 700
CAPACITY (gpm)
0
2
4
6
8
10
BR
AK
E h
OR
SE
PO
WE
R
New Worn
Horsepower - Capacity
0 200 400 600 800 1000 1200 1400
PUMP CAPACITY (gpm)
0
20
40
60
80
100T
OTA
L H
EA
D (
fee
t)
0
20
40
60
80
100B
RA
KE
HO
RS
EP
OW
ER
Brake Horsepower
Total Head9
8.5
8
70
8082
8383
8280
83.5
How Do You Use Performance Curves?
o Selecting a new pumpo Evaluating an existing pump
Selecting an Efficient Pump
• Information needed– Flow rate (gallons per minute)– Total Head (feet)
• Consult pump catalogs provided by pump manufacturers to find a pump that will provide the desired flow rate and total head near the point of maximum efficiency
A B C
Capacity (gpm) 940 940 940 Total Head per Stage (feet) 57 73 37 No. Stages 4 3 6 Actual Total Head (feet) 228 219 223 Pump Effi ciency (%) 84 69 76 Pump or Brake Horsepower 64 73 69 Annual Energy Cost ($) 7162 8225 7721
Selecting a New PumpDesign: Total Head = 228 feet, Capacity = 940 gpm
Common Causes of Poor Pumping Plant Performance
Wear (sand)Improperly matched pumpChanged pumping
conditionso Irrigation system changeso Ground water levels
Clogged impellerPoor suction conditionsThrottling the pump
Improving Pumping Plant Performance
Impeller Adjustment
Effect of Impeller Adjustment
Capacity (gpm)
Total Head (feet)
Overall Efficiency
(%)
Input Horsepower
Pump 1 Before 605 148 54 42 After 910 152 71 49 Pump 2 Before 708 181 59 55 After 789 206 63 65 Pump 3 Before 432 302 54 61 After 539 323 65 67 Pump 4 Before 616 488 57 133 After 796 489 68 144
Same Operating Time
Same Volume of Water
Pump 1 +16.7% - 22.8% Pump 2 +18.2% +5.0% Pump 3 +9.8% - 12.3% Pump 4 +8.3% - 16.8%
Effect of Impeller Adjustment on Energy Use
Repair Worn Pump
Effect of Pump Repair
Before Pumping lift =
95 feet Capacity = 1552
gpm IHP = 83 Efficiency = 45%
After Pumping lift =
118 feet Capacity = 2008
gpm IHP = 89 Efficiency = 67%
Summary of the Effect of Repairing Pumps
63 pump tests comparing pump performance before-and-after repair
Average percent increase in pump capacity – 41%
Average percent increase in total head – 0.5% (pumping lift only)
Average percent increase in pumping plant efficiency – 33%
IHP increased for 58% of the pumping plants. Average percent increase in input horsepower – 17%
Adjusting/Repairing Pumps
Adjustment/repair will increase pump capacity and total head
Adjustment/repair will increase input horsepower
Reduction in operating time is needed to realize any energy savings More acres irrigated per set Less time per set
Energy costs will increase if operating time is not reduced
Replace Mismatched Pump
A mismatched pump is one that is operating properly, but is not operating near its point of maximum efficiency
Capacity (gpm)
Effi
cie
ncy
(%)
00
Improperly Matched Pump
Matched Pump
Mismatched Pump
Pumping Plant Test Data Pumping Lift (feet) 113 Discharge Pressure (psi) 50 Total Head (feet) 228 Capacity (gpm) 940 I nput Horsepower 112 Overall Effi ciency (%) 48
Test 1 (Normal)
Test 2 Test 3
Capacity (gpm) 940 870 1060 Pressure (psi) 50 79 15 Pumping Lift (feet) 113 112 112 Total Head (feet) 228 295 147 IHP 112 112 104 Overall Efficiency (%) 48 57 38
Multiple Pump Tests
Replacing this pump with one operating at an overall efficiency of 60% would: Reduce the input horsepower by 19% Reduce the annual energy consumption by 34,000 Kwhr Reduce the annual energy costs by $3,400 (annual operating time of 2000 hours and an energy cost of $0.10/kwhr)
Replacing a Mismatched Pump
Pumping plant efficiency will increase
Input horsepower demand will decrease
Energy savings will occur because of the reduced horsepower demand
How do I determine the condition of my pump?
Answer: Conduct a pumping plant test and evaluate the results using the manufacturer’s pump performance data
Pumping Lift
Pump Capacity
DischargePressure
FLOW METER
8 PIPE DIAMETERS DIAMETERS2 PIPE
FLOW
InputHorsepower
Is a pump worn or mismatched?
Multiple pump testsCompare pump test
data with manufacturer’s pump performance curves
0 100 200 300 400 500 600 700 800 900 1000 1100
PUMP CAPACITY (gpm)
0
50
100
150
200TOTAL HEAD (feet)
REPAIRED PUMPPumping Lift = 102 ftCapacity = 537 gpm
Input Horsepower = 28Overall Efficiency = 50%
Kwhr/af = 211
WORN PUMPPumping Lift = 45 ftCapacity = 624 gpm
Input Horsepower = 19Overall Efficiency = 39%
Kwhr/af = 123
LargeDifference
SmallDifference
2000 2400 2800 3200 3600
PUMP CAPACITY (gpm)
0
20
40
60
80
100TOTAL HEAD (feet)
1983 (64%)1984(54%)
1985 (62%)
2000 2400 2800 3200 3600
PUMP CAPACITY (gpm)
0
20
40
60
80
100TOTAL HEAD (feet)
1983 (64%)
1984 (66%)
1985 (55%)
Recommended Corrective Action
Eo greater than 60% - no corrective action
55% to 60% - consider adjusting impeller
50% to 55% - consider adjusting impeller; consider repairing or replacing pump if adjustment has no effect
Less than 50% - consider repairing or replacing pump
Energy-efficient Electric Motors
Horsepower Standard Energy Efficient
10 86.5 91.7 20 86.5 93.0 50 90.2 94.5 75 90.2 95.0 100 91.7 95.8 125 91.7 96.2
Efficiencies of Standard and Energy-efficient Electric Motors
Variable Frequency Drives
What is a Variable Frequency Drive?
Electronic device that changes the frequency of the power to an electric motor
Reducing the power frequency reduces the motor rpm
Reducing the motor rpm, and thus the pump rpm, decreases the pump horsepower demando A small reduction in pump rpm results in
a large reduction in the horsepower demand
When are Variable Frequency Drives Appropriate?
One pump is used to irrigate differently-sized fields. Pump capacity must be reduced for the smaller fields
Number of laterals changes during the field irrigation (odd shaped fields)
Fluctuating ground water levels Fluctuating canal or ditch water levels
Unthrottled Throttled VFD
Acres 80 50 50 Pressure (psi) 80 64 60 Capacity (gpm) 1,100 600 700 Input Horsepower 128 90 55 RPM 1770 1770 1345 Overall Efficiency (%) 40 24 44
Centrifugal pump used to irrigate Both 80-and 50-acre fields
Note: Pumping plants should be operated at the reduced frequency for at least 1,000 hours per year to be economical
Convert To Diesel Engines
Options for Converting From Electric Motors to Engines
Direct drive (gear head) Engine shaft to pump shaft
efficiency = 98%
Diesel-generator Engine shaft to pump shaft
efficiency less than about 80%
Considerations
Brake Horsepower = Shaft HorsepowerEngines and motors are rated based on
brake horsepower ( 100 HP electric motor provides the same horsepower as a 100 HP engine
Input horsepower of an engine is greater than that of an electric motor for the same brake horsepower
Engine Horsepower
Maximum horsepower Continuous horsepower
About ¾’s of the maximum horsepower
Derated for altitude, temperature, accessories, etc.
110
128
144
157167
173
1200 1400 1600 1800 2000 2200
ENGINE RPM
0
50
100
150
200B
RA
KE
HO
RS
EP
OW
ER
0.39
0.38
0.37 0.370.37
0.38
1200 1400 1600 1800 2000 2200
ENGINE RPM
0.30
0.32
0.34
0.36
0.38
0.40F
UE
L C
ON
SU
MP
TIO
N (
lb/b
hp
-hr)
33.2
34.2
35.1 35.134.7
33.9
1200 1400 1600 1800 2000 2200
ENGINE RPM
30
32
34
36
38
40
EN
GIN
E E
FF
ICIE
NC
Y (
%)
1400 1500 1600 1700 1800 1900 2000 2100 2200
RPM
0
20
40
60
80
100
120
140
160H
OR
SE
PO
WE
RPUMP HP CONTINUOUS ENGINE HP
Fuel Use Versus RPM RPM Pump Flow
Rate (gpm) Gallons of Diesel
per Hour Gallons of Water
per Gallon of Diesel
1500 1228 9 8187 1600 1731 11 9617 1700 2161 15 8644 1800 2486 19 8019
Electric Motors vs Diesel Engines: Which is the Best?
Unit energy cost Capital costs, maintenance costs,
etc Hours of operation Horsepower Cost of pollution control devices
for engines
Electric Motor
Diesel Engine
Capital Cost $5,500 $11,500 $16,500 $16,500 Unit Energy Cost $0.14/kwhr $0.95/gal $0.95/gal $1.25/gal Total Cost ($/af) 60.5 37.8 39.9 48.5
Comparison of electric motor and diesel engine100 HP1,100 gpm2,000 hours per year
That’s All, Folks
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