Energy Saving Tips for Irrigators

1. ATTRA Energy Saving Tips for Irrigators
A Publication of ATTRA - National Sustainable Agriculture Information Service • 1-800-346-9140 • www.attra.ncat.org
By Mike Morris and This publication describes ways that irrigators can save energy to reduce irrigation costs. It describes
Vicki Lynne recommended irrigation system installations, explains how utilities charge their irrigation customers
NCAT Energy for electricity and describes common causes of wasted energy, as well as common energy-saving hard-
Specialists ware improvements. It also includes a do-it-yourself method to estimate the efficiency of electrically
© 2006 NCAT powered irrigation systems. A listing of references and resources follows the narrative.
Contents
Introduction ..................... 1
Recommended
Installations ...................... 2
Centrifugal Pumps ......... 2
Turbine Pumps ................ 4
Electrical Use and
Charges .............................. 5
Causes of Wasted
Energy ................................ 6
Hardware
Improvements ................. 7
Estimating Sprinkler
Plant Efficiency ............. 11
References ...................... 13
Further Resources ........ 13
NCAT photo
Introduction would when properly sized, adjusted, and
maintained. (Black and Rogers, 1993) A
Especially in times of high energy costs, study in Colorado, Wyoming, Nebraska,
efficient irrigation equipment is essential to and other states found that, on average,
the viability of farms and ranches. Accord-
about 25 percent of the electrical energy
ing to USDA’s 2003 Farm and Ranch Irriga-
used for irrigation pumping was wasted
tion Survey, there were 43 million pump-
due to poor pump and motor efficiency.
irrigated acres in the United States, with
energy costs for these systems averaging (Loftis and Miles, 2004)
$1.5 billion per year, or $36 per irrigated Since 1988, NCAT has conducted energy
ATTRA—National Sustainable
Agriculture Information Service
acre. Farms spent an additional $12 per efficiency audits on more than 400 irriga-
is managed by the National Cen- acre, on average, to maintain and repair tion systems. In the vast majority of these
ter for Appropriate Technology
(NCAT) and is funded under a irrigation equipment. (U.S. Department of cases, our technicians identified at least
grant from the United States Agriculture, 2003) one equipment change or repair that would
Department of Agriculture’s
Rural Business-Cooperative Ser-
Most irrigation systems are not as effi - quickly pay for itself in energy savings
vice. Visit the NCAT Web site
(www.ncat.org/agri. cient as they should be. A Kansas study alone. Very often, the irrigators who owned
html) for more informa-
tion on our sustainable
found that, on average, irrigation systems these inefficient systems were unaware of
agriculture projects. use about 40 percent more fuel than they any problems.

2. This publication On the other hand, mechanical improve-
describes ways to ments do not necessarily result in energy sav-
save energy and ings, unless the irrigator makes management
reduce irrigation changes that reduce hours of operation. (See
energy costs. There Hanson, 2002) This is a key point that
are basically four is frequently misunderstood. Mechani-
ways to do this: cal improvements like the ones described in
• Ma ke mechani- this article generally improve irrigation sys-
cal improvements, tem performance, resulting in higher pressure
so the irrigation and increased volumes of applied water. These
system uses less improvements in turn should make it possible
energy during each to meet crop water needs with fewer hours
hour it runs. of irrigation. But if the irrigator continues
NCAT photo to run the system for the same number of
• M a k e m an a ge - hours, energy consumption often stays the
ment changes, so the system runs same or even increases.
fewer hours.
This publication focuses on direct energy
• Reduce cost per unit of energy by, for
consumption—using electricity and fuel to
example, negotiating a better rate
run irrigation pumps and motors. Indirect
with the utility, switching fuels, or
energy costs are at least as important for
finding a lower price for diesel fuel.
Related ATTRA
many farm operations. Natural gas, elec-
• Make your own energy by installing tricity, fuel oil, and other fossil fuels are all
Publications
a wind turbine to generate electric- used in making commercial fertilizers and
Biodiesel – a Primer ity or by making your own biodiesel pesticides. In 2002, commercial fertilizers
fuel, for example. (nitrogen, phosphate, and potash) accounted
Drought Resistant Soil
This publication focuses on mechanical for 29 percent of all energy consumed in
Drought Resource improvements. Of course, good management U.S. farm production. (Miranowski, 2004)
Guide The cost of these inputs has skyrocketed in
is also critically important for saving energy.
The Montana Irriga- The most obvious energy-saving management recent years. One of the best things farmers
tor’s Pocket Guide strategy is to eliminate unnecessary watering, can do to reduce energy consumption and
Soil Moisture meeting only the water needs of your crops. energy-related costs is to reduce their use of
Monitoring: Low-Cost But you might also consider less obvious commercial fertilizers and pesticides. Many
Tools and Methods options such as changing to less water-inten- ATTRA publications are available on this
Wind-powered
sive crops, timing plantings to take better topic. See, for example, the ATTRA publica-
Electric Systems for advantage of natural precipitation, reducing tions Cover Crops and Green Manures, Alter-
Homes, Farms, and irrigated acreage, using mulches and cover native Soil Amendments, Sustainable Soil
Ranches: Resources cropping to increase soil organic matter and Management, Pursuing Conservation Tillage
build the water-holding capacity of your soils, Systems for Organic Crop Production, and
Measuring and
Conserving or taking steps (such as planting wind breaks) Farm-Scale Composting.
Irrigation Water to reduce evaporation in your fields.
Equipment problems and management prob- Recommended
lems tend to go hand in hand. Equipment Installations
that is badly designed, inefficient, or poorly
maintained reduces the irrigator’s degree Centrifugal Pumping
of control over the way water is applied.
Problems like patchy water distribution
Plant Installation with
and inadequate pressure make it impossi- Electric Motor
ble to maintain correct soil moisture levels, Especially if you have an older system, your
leading to crop stress, reduced yields, pumping plant might look like Poor in Fig-
wasted water, runoff, soil erosion, and many ure 1, on the discharge side. (The term
other problems. pumping plant means the pump and motor
Page 2 ATTRA Energy Saving Tips for Irrigators

3. considered together.) It’s a false economy to • An eccentric reducer to keep air
save money by installing undersized valves from becoming trapped in the
and fittings. You’ll only achieve greater fric- reducer fitting.
tion loss and higher pumping costs. The • A vacuum gauge to indicate whether
next time you rebuild your pump, replace the primer is pulling a vacuum
the fittings so that your pumping plant looks or just moving air through the pump.
like Ideal in Figure 1.
On the Discharge Side of Pump
Figure 1. Ideal and Poor Installations • A valve that is the same
diameter as the mainline.
IDEAL Discharge pressure
Concentric
gauge with ball valve
• A non-slam check valve to pre-
expansion Shut-off valve Discharge pipe
larger than pump
discharge size
vent back spin of the pump
when shutting it off.
• An air relief device when a
Flexible joint permits some
Pipe
support
buried mainline is used.
• A discharge line water veloc-
Check misalignment and axial
valve movement; resolves most
thermal expansion problems
Valve too ity of less than seven fps.
POOR small
Five fps is best.
• An energy efficient 1,800
rpm motor with a 15 percent
Sudden
expansion safety factor.
(Adapted from Saving Energy on Montana Farms • A simple shade over the motor.
and Ranches, Montana Department of
Environmental Quality.)
Figure 2. Recommended Pump Installations, Top and Side Views
An ideal installation should also have:
• A discharge concentric expansion, Solid
foundation
Gradually increasing
tapered section
instead of an abrupt change in pipe Sump volume (in gallons)
at least twice maximum gpm
diameter, to minimize head loss, tur-
Inlet
bulence, and air pockets. All joints
Uniformly distributed flow
• A discharge valve the same diameter Cone increaser
water tight
Pressure
placed at pump
as the mainline. outlet if required gauge o
45 maximum
Figure 2 shows what a plant should look like Straight run of at least
Supports as
required
when pumping from a surface source such as 10 pipe diameters “D”
or straightening vanes Top View
a river or canal. The pumping plant should for testing flow
also have the following features: Check
valve
Shut-off
On the Suction Side of Pump valve
• A well-designed and screened sump
that keeps trash out. Primer Straightening vanes or
straight run as short as Side View
possible but not less than
• Suction line joints that are airtight Globe
isolation
Vacuum
6 pipe diameters “D”
1/4” per foot
under a vacuum. valve
gauge
minimum upward
slope to pump Grating, bar racks
and screens at
beginning of
• No high spots where air can collect. Smooth maximum width
section
long-radius
• A suction line water velocity of five elbows
feet per second (fps) or less. Two to
three fps is best. Anchor Pipe supports “D”
Minimum water
level
(as required)
• A suction entrance at least two pipe- Drainage
bolts Eccentric 4 “D” Minimum
inlet
Inlet
away from reducer minimum
turbulence
bell diameters from sump inlet. motor
Suction bell
Inlet below
• A suction lift (vertical distance from As close as
possible
“D” minimum
minimum
water level
“D” = pipe
diameter
water surface to pump impeller) less
than 15 to 20 feet. (Adapted from Energy Efficient Pumping Standards, Utah Power & Light Company.)
www.attra.ncat.org ATTRA Page 3

4. Figure 3. Deep Well Turbine Pump
Pump motor
RECOMMENDED
Sounding tube Discharge pipe
access
Grout seal
Casing centered in hole
with 3 spacers @ 40’
intervals
Pumping
water
level
Static water
level
NCAT photo Drawdown less
than 60% of water
depth
Pump housing
About Pressure Gauges
Air line
A good quality oil- or glycerin-filled pressure gauge on the discharge
side of the pump tells a lot about a system’s condition. If operational
pressure remains close to the original design pressure, the pump is
probably in good working order. Pressure changes can indicate clogged
suction screens, leaks, pump wear, worn nozzles, and other problems.
Excess pumping rate;
Use the gauge when filling the mainline to reduce electrical demand drawdown more than
60% of water depth
and water hammer. Extend the life of the gauge by installing a ball NOT RECOMMENDED
valve on the riser. Keep the valve closed except when referring to the
gauge. With a ball valve in place, the operator can remove the gauge
(Adapted from Energy Efficient Pumping Standards, Utah
during the winter. Power & Light Company.)
Turbine Pump Installation Control Panel for Electric Motors
Refer to the left half of Figure 3 for proper The importance of a properly installed
installation of a turbine pump in a well. control panel cannot be overemphasized,
Many of these same principles apply to tur- both for personal safety and to protect your
bine pumps in sumps. The properly con- investment in the pump and motor.
structed well should also:
Your control panel should:
• Be at least six inches in diameter
larger than the outside diameter of • Have a shade over it to cool
the well casing when a gravel pack thermal breakers.
is required. • Be mounted on secure poles
• Have horizontal well screen slots or foundation.
that continue below the pumping
• Have any missing knockout plugs
water level. The openings should
hold back at least 85 percent of the and other holes in the starting
surrounding material. switch box replaced and screened
or puttied against rodents, insects,
The poorly constructed well in the lower and dirt.
right half of Figure 3 shows a well casing
not centered in the well. Vertical slotted • Have a small hole (about 3/16-inch
pipe perforations are above the minimum diameter) in the bottom of the panel
water level, creating cascading water. to allow moisture to drain.
Page 4 ATTRA Energy Saving Tips for Irrigators

5. electric consumption or
energy rate. This may
remind you of the ante in
a poker game—a fee to
get into the energy con-
suming game.
2. Electric Consumption
or Energy Charge. This
cha rge is based on
the amount of electric-
ity used over time as
recorded on a kilowatt-
hour meter, with a rate
charged for each kWh
NCAT photo consumed.
Your control panel should include the 3. Electric Demand Charge. Many utili-
following controls, at a minimum: ties charge larger customers an amount
over and above the electric consump-
• Circuit breakers for overload tion charge. The basic rationale for
currents these demand charges is that the util-
• Lightning arrester ity incurs costs to maintain enough
• Surge protector capacity to serve the needs of its large
customers. Electric providers gener-
• Phase failure relay, to protect the ally calculate the demand charge in
motor from phase reversal or failure one of two ways. Each method gives an
and from low voltage approximation of the customer’s size or
• A pressure switch to shut off the power requirements.
motor if pumping pressure drops to
undesirable levels. a. The demand charge may be based on
connected load or horsepower, with
a fi xed rate charged per horsepower
Electrical Use and Power during each billing period. This
Bill Charges charge is usually based on “name-
Electricity is measured in watts or kilowatts plate” horsepower. For example, if
(equal to 1,000 watts). The number of watts the demand charge is $10 per horse-
is the product of operating voltage times the power, the demand charge for a 40-
current (or amps) flowing to the load. A horsepower system would be $400.
kilowatt-hour (kWh) is an amount of energy
equivalent to using one kilowatt (kW) over a b. The demand charge may be based
one-hour period. To visualize one kilowatt- on maximum wattage during the
hour, it may be helpful to imagine ten 100- billing period. In this method, a
watt light bulbs burning for one hour. special demand meter measures
wattage for each 15-minute interval
Although billing procedures vary among (or some other interval) during the
electric providers and in different regions of billing period. The demand charge
the country, irrigation bills typically include would be based on the 15-minute
three basic charges for electricity. interval with highest wattage during
1. The Base Rate or Meter Charge. This is the billing period.
either a monthly or seasonal charge. For example, suppose the demand charge is
Some utilities roll this charge into the $10 per kilowatt, and your demand meter
www.attra.ncat.org ATTRA Page 5

6. records use of 29 kilowatts for some 15- 2. The wrong pump for the system
minute intervals in the billing period, 30
A pump that is oversized, undersized, or just
kilowatts for other 15-minute intervals,
not right for your system, will never operate
and 31 kilowatts for other intervals. You
efficiently. While it may be possible to trim
would be billed $310. A key point is that
the pump impeller, re-nozzle the sprinklers,
demand charges are based on the size of
or redesign the layout of the mainline
your system—not on how many hours you
operate the system. A demand charge is
incurred even if you operate your irrigation Net Positive Suction Head (NPSH)
system for just one 15-minute interval and Cavitation
during the entire monthly billing period.
Many people are surprised to learn
Customers with small motors may not have that centrifugal pumps don’t pull water
a demand charge. through a suction pipe; they can only
pump water that is delivered to them.
Common Causes of When air is removed from the suction
pipe by a primer pump, the weight
Wasted Energy of the earth’s atmosphere forces water
to rise into the pipe, delivering water
1. Lack of system maintenance to the pump.
Impellers that are out of adjustment,
plugged screens, worn nozzles, engine Even in the best of circumstances (includ-
drive units that need a tune-up, worn shaft ing a near-perfect vacuum) the maximum
water column that can be forced by atmo-
sleeves, leaking gaskets and drains, and
spheric pressure never exceeds about 33
dried-out bearings and pump packing are feet in height. As elevation, water tem-
only a few of the problems that are avoided perature, and pipe friction increase, the
with regular maintenance. height of the water column that can be
forced drops. The maximum column of
water that can be created in a pipe under
a given set of conditions is known as Net
Every kWh Counts Positive Suction Head or NPSH.
Some irrigators mistakenly assume that since they are charged for Insufficient NPSH often occurs at startup.
demand, they won’t save money by turning off their pumps and reduc- Since the pump is working against low
ing hours of operation. It’s true that the demand charge is often a sub- pressure, it pumps a larger volume than
stantial percentage (as much as half or more) of a total electric bill. But in normal operation. This larger volume
all electric providers bill for every single kWh consumed. You will always
creates friction losses in the suction line,
save energy and money by reducing your hours of operation.
reducing NPSH. Too little available NPSH
Talk to a customer service representative at your utility for an explana- can result in vaporization of water in the
tion of the rate structure. Know when your meter reading date is each eye of the impeller, causing cavitation, a
month, since this can influence management decisions. If your power noisy condition where vapor bubbles col-
bill includes a demand charge, remember that this charge will be about lapse violently in the pump.
the same whether you operate your system for one day or 31 days dur-
To stop cavitation while occurring,
ing a billing period.
close the discharge valve. If cavitation
is allowed to continue, the impeller and
pump casing can become pitted and
damaged, reducing pump capacity. To
Time-of-Use Rate Schedules
eliminate cavitation as well as water ham-
In some parts of the country, irrigators can sign up for a time-of-use bill- mer, and to prevent high amperage draw
ing schedule. Under time-of-use billing, rates are higher at peak times on demand meters, each time you start
(when demand is greatest) and lower at “off peak” times. Time-of-use up the pump open the discharge valve
billing allows some irrigators to adjust work schedules so they can irri- slowly to fill the mainline.
gate when rates are low. Call your utility to find out if time-of-use billing
is available in your area, and to see whether a time-of-use rate schedule Caution: Don’t let the pump run more
may work for you. than two minutes with the discharge
valve closed.
Page 6 ATTRA Energy Saving Tips for Irrigators

7. to the water source in order to create
sufficient NPSH.
If turbine or submersible pump capacities
do not fit the well characteristics, you may
need to replace the bowls with new ones
suited to the well capacity.
Hardware Improvements
Some common energy efficiency improve-
ments are listed below. No matter what
kind of system you are operating, you’ll
probably fi nd at least one cost-effective
idea below to improve the effi ciency of
NCAT photo
your irrigation system.
and laterals, a new pump with different
P
characteristics is most likely necessary. Electric Motors remium-
• Rebuild older motors and gain sev-
3. Pump wear from cavitation efficiency
eral percentage points in motor
or abrasion efficiency. This procedure typi- motors are
Cavitation damages impellers, reduc- cally involves replacing the bear- two to four percent
ing efficiency. If your pump is cavitating, ings, rewinding, and “dipping and more efficient than
determine whether you have sufficient net baking,” and is done by qualified standard-efficiency
positive suction head (NPSH). You should motor repair shops. motors.
also have a valve on the discharge side of • Consider a premium-eff iciency
the pump, allowing you to fi ll the mainline motor instead of a standard-
slowly and avoid cavitation. efficiency motor when installing a
new system, when replacing over-
If your water source contains a high
or undersized motors, and when
amount of sediment, re-engineer the intake
the cost of rewinding exceeds 65
structure to allow sediment to settle out of
percent of the price of a new motor.
the water before entering the suction line.
Premium-efficiency motors are two
to four percent more efficient than
4. Improperly sized or designed standard-efficiency motors. Besides
fittings saving energy, premium-efficiency
Every minute that irrigation water passes motors usually have higher service
through undersized valves or other fit- factors, longer insulation and bear-
tings at a high velocity, profits drain away. ing life, and less vibration than
Replace undersized fittings with ones of standard-efficiency motors.
the correct size. Caution: Some premium-efficiency
motors draw a higher startup
5. Water source changes current. Make sure your system
can handle it.
If you’re using a well for irrigation and the
water table has dropped, you may have to • If you put in a new system, be
reset the pump to a lower level. To com- aware that an 1,800 rpm motor
pensate for the increased head, you may is more efficient than a 3,600
have to add more stages to turbine or sub- rpm motor. For example, an open
mersible pumps. If you’re using surface drip-proof 3,600 rpm, 40-horse-
water and the level has dropped, centrifu- power motor is 91.7 percent effi-
gal pumps may need to be relocated closer cient whereas an 1,800 rpm, 40-
www.attra.ncat.org ATTRA Page 7

8. horsepower motor is 93 percent fan. Check with an engine equip-
efficient. Since 1,800 rpm motors ment dealer for more information.
make half the revolutions of 3,600 • Think about using the variable
rpm motors, maintenance needs are speed ability of engines to your
lower and motor life is longer. advantage. By varying the rpm of
• Consider a variable speed drive the engine you can vary the flow
(also sometimes called a variable rate, total dynamic head, and brake
frequency drive) if you need to pro- horsepower requirements of the
duce a wide range of flows and pump to save fuel and meet vary-
pressures to meet varying system ing system needs. Consult an engine
needs. For example, a pump serv- equipment or irrigation equipment
ing three pivots and equipped with dealer for advice.
a variable speed drive could run at
slow speed with one pivot turned Centrifugal Pumps
on, at a higher speed with two piv- • Rebuilding an older pump to
ots turned on, and at full speed with increase its efficiency can be a
all three pivots turned on. Steep ter- cost-effective alternative to pur-
rain and the use of corner “swing chasing a new pump. Rebuilding
arms” on pivots also cause chang- usually involves replacing shaft
ing flow and pressure requirements sleeves, packing, and wear rings,
and sometimes justify the cost of a and re-machining or replacing
variable speed drive. In 2005, the the impeller.
typical cost of variable speed drives
was between $90 and $200 per • For optimum efficiency, the pump
horsepower. (Idaho Power, 2005) must match the requirements of the
Whether this investment is cost- water source, water delivery system,
effective for your situation depends and irrigation equipment. If your
on operating hours, pump size, and pump is under- or oversized and
crop value, among other factors. does not match the system needs,
pump replacement is the best
• Constant-pressure
valves or fl ow-control
nozzles may be a lower-
cost a lter nat ive to
a variable speed drive,
a lt hough t hey a re
less energy effi cient.
Contact your equip-
ment suppl ier for
more information.
Engines
• If your radiator-cooled
engine uses a cooling
fan, five to eight per-
cent of the fuel going
into the engine is used
to run the fan. You can
install equipment that
uses irrigation water to
cool the engine, elimi-
nating the need for a NCAT photo
Page 8 ATTRA Energy Saving Tips for Irrigators

9. option. Running an oversized pump inch or psi) or very low pressure
with a mainline valve half-closed is (10 psi) and installing drop tubes.
like driving a car with your foot on Reduce your pump size or have the
the brake and the accelerator at the impellers trimmed to reduce horse-
same time. power. In addition to saving energy
and money, you’ll increase water
Turbine Pumps application uniformity because wind
• Vertical shaft turbine pumps lose drift will be reduced and the water
efficiency when not regularly discharge point will be closer to the
adjusted. Only qualified pump ser- ground. Be aware that a low-pres-
vice personnel should adjust deep sure pivot could exceed your soil’s
well turbine pumps. infi ltration rate, causing runoff.
• Rebuilding an older turbine pump • Sprinkler options have come a long
to increase its efficiency is usually a way in the past decade, and this is
cost-effective alternative to purchas- especially true for pivot and linear
ing a new pump. Rebuilding usu- move systems. Spinners produce
T
ally involves replacing shaft sleeves, large droplets that are more rain- ake
packing bearings, and re-machining like and reduce wind drift. Dual advantage
or replacing the bowls. spray heads allow for different spray of gravity
options for crop germination or irri-
Mainlines gating later in the season. Spray
if you have suffi-
• Mainlines too small for the volume cient elevation drop.
plates can also be replaced to allow
of water pumped through them con- for different spray patterns. Check Many irrigators
tribute to high head requirements out sprinkler packages at your local underestimate the
and lowered system efficiency. irrigation equipment dealer to fi nd energy savings and
Water velocity through a mainline one suitable for your operation. pressure available
should never exceed seven feet
per second (fps). Velocities below • Eliminate your pump completely or to them.
five fps are best, and are achiev- reduce your horsepower require-
able through good design. Your ments and pump size by taking
local irrigation equipment dealer or advantage of gravity, if you have
Natural Resources Conservation sufficient elevation drop. Many irri-
Service (NRCS) office can help gators underestimate the energy
determine whether a system’s main- savings and pressure available
line is the right size. to them. An elevation drop of just
2.3 feet is equivalent to one pound
Sprinkler Systems per square inch of pressure. Your
• If you have a high-pressure pivot local irrigation equipment dealer
with impact sprinklers, you can real- or NRCS office may be able to help
ize significant energy and demand determine whether your system can
savings by converting to low pres- be converted to a full or partial
sure (20 to 35 pounds per square gravity system.
Table 1. Recommended Maximum Flow Rate of Different Pipe Sizes
Pipe Diameter
(inches) 2 3 4 5 6 8 10 12 16
Flow rate
(gpm) 50 110 200 310 440 780 1225 1760 3140
Note: For maximum efficiency, water velocity in the suction line should not exceed 5 fps; 2 to 3 fps is best. Water velocity in the
mainline should not exceed 7 fps; less than 5 fps is best. Increasing the pipe size, reducing the flow rate, and changing the pipe type
can save energy by lowering the water velocity.
www.attra.ncat.org ATTRA Page 9

10. • You can also convert a pivot or lin- Sprinkler Nozzle Wear
ear move system to Low Energy
To check nozzle wear, remove the nozzle
Precision Application (called LEPA)
and clean out the interior. Then get either
by installing hoses or drag socks on
a numbered drill index, with bits measured
the drop tubes. The water is applied
in thousandths, or a new high-speed drill
directly at the soil surface, virtu-
bit of the size printed on the nozzle. If a
ally eliminating wind drift. These
drill bit is used, get a new nozzle to com-
systems also eliminate deep wheel
pare alongside the worn nozzle. Insert the
tracks because the ground is wet
index into the nozzle opening and compare
behind the wheels instead of in front
the size to that printed on the nozzle. Or
of them. A Colorado study calcu-
insert the shank (smooth end) of the drill
lated average LEPA conversion cost
bit into the nozzle opening. The fit should
for pivots at around $15,000, with
be snug. If you can wobble the bit sideways
energy savings of up to 40 per-
even slightly, the nozzle is worn.
cent and paybacks of only
three to four years. (Jenkins,
How Leaks Cost You Money Surface Irrigation
2001) LEPA systems do not
Many producers aren’t very con-
cerned about leaks because
work for all crops (for exam- Many surface irrigators can save water and
the water “ends up on the field ple, tall ones like field corn) energy by replacing open ditches with gated
anyway.” What they don’t realize is or situations. pipe. Gated pipe allows water to flow out
that leaks reduce system pressure, • Producers raising orchard through evenly-spaced “gates” or openings
causing a poor sprinkler distribu- and vegetable crops can along the length of the pipe, giving irriga-
tion pattern. Reduced pressure also
somet imes dramat ica l ly tors increased control over the way water
moves the pump operating point
reduce energy costs by con- is applied.
out of the range where the pump is
most efficient, increasing demand verting from hand-move
costs. An NCAT study found that laterals or other high pres-
Figure 4. Gated Pipe
each worn sprinkler nozzle costs its sure sprinklers to drip or
owner up to $4.00 per year in unnec- micro sprinklers. Micro-irri-
essary energy costs, depending on gation systems operate at very
the degree of wear and the prevail- low pressure and allow pre-
ing cost of electricity. Significant
leaks can also cause motor overload-
cise application of water to a
ing and shorten motor life. limited area of soil adjacent
to the plant.
If you’re already using gated pipe, you
may be able to save additional energy by
installing a surge valve. Surge valves auto-
matically alternate the water from one set
of furrows or border strips to another. This
method causes the water stream to advance
much faster. Deep percolation at the upper
end of the field is reduced and water pen-
etration at the lower end is increased,
NCAT photo
resulting in more even water distribution.
Page 10 ATTRA Energy Saving Tips for Irrigators

11. A Simple Method to Esti- Step 1. Find total dynamic head
mate the Pumping Plant (TDH) in feet.
Efficiency of an Electri-
Reading pressure from gauge psi × 2.31 (a conversion factor) = feet
cally Powered Sprinkler
Irrigation System Add height* if pump is above water surface + feet
Pumping plant efficiency, sometimes called OR
“wire to water” efficiency, is the overall Subtract height* if pump is below water surface – feet
energy efficiency of the pump and motor
considered together, and is defi ned as the To get total dynamic head (feet). TDH
ratio of water horsepower (“power out”) to
electric horsepower (“power in”). Energy * Height is defined as distance from the water surface to the centerline of the discharge pipe.
is lost by every pump and motor, and effi-
ciencies in the mid-70 percent range are Step 2. Find flow rate in gallons per
about the best any pumping plant can
achieve. A 70-percent pumping plant effi- minute.
ciency would mean that 70 percent of the 2a. For hand move, side roll, or
horsepower delivered to the motor is trans- linear move systems:
mitted to the water leaving the pump.
Pumping plant efficiency should be evalu-
If your system has a flow meter, read the gallons per minute (gpm). If the meter reads in
ated every several years or whenever there cubic feet per second (cfs), multiply cfs times 448.8 to get gpm.
is cause for concern (such as a noticeable
decrease in performance or an increase gpm
in demand charges on your power bill).
The do-it-yourself pumping plant evalua-
tion described below reveals whether you If you don’t have a flow meter you can do
can save energy and money by adjusting, a bucket test:
rebuilding, or replacing the existing pump Measure the flow of one sprinkler per lateral
or power unit. that is situated on relatively level ground.
To conduct th i s test, you’ l l need The selected sprinkler should be about one-
the following: third down the length of the lateral from the
mainline. Use the hose to direct the flow
• A good quality pressure gauge into the five-gallon bucket. Using the stop-
(preferably oil-fi lled) mounted on watch, estimate the time in seconds to fi ll
the discharge side of the pump. the bucket. For greater accuracy, take more
• A five-gallon bucket and a length than one reading per sprinkler and average
of garden hose that will fit over a the times. Repeat for the other sprinklers
sprinkler head OR a working flow on other laterals.
meter mounted at least fi ve pipe
diameters downstream of the pump
or other bends, valves, or changes Number of seconds to fill bucket = seconds
in pipe. Mark with a permanent
marker the five-gallon line on the
Average gpm/sprinkler = 300 divided by the number of seconds
inside of the bucket.
300 ÷ seconds = gpm
• A stopwatch (or a watch with a
second hand) and a calculator.
When the system is operating under Total flow per hand line or wheel line =
nor ma l, st a ble cond it ion s, fol low Average gpm per sprinkler × number of sprinklers = gpm
these six steps:
www.attra.ncat.org ATTRA Page 11

12. 2b. For pivots:
3.6 × (revs) × (Kh) ÷ (secs) = Input kW
If you are using a pivot irrigation sys-
tem and don’t have a flow meter, use the (KW) × 1.34 = EHP
following method.
First, measure the flow of one sprinkler in Step 4. Find water horsepower
each set of nozzle diameters along the pivot (WHP), using results from steps
using the method described in 2a.
1 and 2.
Seconds to Average gpm Number sprinklers Total gpm in
fill bucket per sprinkler in each set each set
(TDH) × (gpm) ÷ 3,960 = WHP
300 ÷ sec = gpm × = gpm
300 ÷ sec = gpm × = gpm Step 5. Determine pumping
300 ÷ sec = gpm × = gpm
plant efficiency, using results from
Total Flow = gpm
steps 3 and 4.
Next, estimate flow from end gun using (WHP) × 100 ÷ (EHP) = % Efficiency
end gun pressure and nozzle diameter from
table below.
Step 6. Compare your efficiency
= gpm to expected values in the table
Table 2. Estimated End Gun Flow in GPM below.
Diameter of end gun nozzle (inches) Table 3. Expected Pumping Plant Efficiency
PSI ½ ¾ 1 1½ 2 Rated Motor Expected
10 23.6 53.2 94.4 212 378 Size (HP) Efficiency (%)
20 33.4 75.3 134 300 534 3 to 5 66%
30 40.9 92.2 164 368 654 7.5 to 10 68%
40 47.2 106 189 425 755 15 to 30 69%
40 to 60 72%
50 52.8 119 211 485 845
75+ 75%
Note: These efficiencies are for older pumps in excellent con-
Finally, add the results from Step 1 dition. New pumps and used pumps under mild conditions or
and Step 2 above to calculate total flow improved design will have higher efficiencies.
for pivot.
= gpm Any system whose pumping plant efficiency
is less than 65 percent has some room for
improvement. A result in the 50 percent
Step 3. Find Input kW and range or lower indicates a significant prob-
electric horsepower (EHP). lem requiring attention. Contact your irriga-
For pivots, turn off the pivot drive and end tion equipment dealer or your local NRCS
gun booster pump if possible while measur- office to discuss your options.
ing energy use. You want to measure just
the electricity that the pump motor is using Other flow measuring
to pump the water. methods for pivots
Locate the meter constant on the meter: The flow from impact sprinklers mounted
marked Kh and followed by a number such on the top of the pipe can be measured with
as 57.6 or 43.2. Using a stopwatch, time the a bucket test, using a longer garden hose
number of seconds it takes for the disk in the that fits over the nozzle.
meter to make 10 revolutions (or for the little In the case of pivots equipped with “wobbler”
bar to move across the screen 10 times). or “spinner” sprinkler heads, the following
Page 12 ATTRA Energy Saving Tips for Irrigators

13. method may work. Cut the end of a finger off an old rub- management, equipment maintenance, and handy
ber glove, insert a short piece of metal pipe, and attach a conversions and formulas. Get a free printed copy by
hose clamp. Attach a length of garden hose to the other end calling 800-346-9140.
of the metal pipe with a hose clamp. Place the glove over
a pivot nozzle of almost any type and the flow rate can be
measured with a bucket test. Other Publications
Comparing Irrigation Energy Costs. 1999. By Danny
H. Rogers and Mahbub Alam. MF-2360, Kansas State
References University Cooperative Extension Service, Manhattan,
Black, Richard D., and Danny H. Rogers. 1993. KS. 4 p.
Evaluating Pumping Plant Efficiency Using On-Farm Explains how to compare the cost of electricity, natural
Fuel Bills. Kansas State University Cooperative Exten- gas, diesel, and propane as irrigation energy options.
sion Service, Manhattan, Kansas. 4 p. Can be downloaded from:
www.oznet.ksu.edu/library/ageng2/mf2360.pdf
Hanson, Blaine. 2002. PUMP UP: Improving plant
efficiency does not always save energy. California Electrical Demand Charges: How to Keep Them Low.
Agriculture Vol. 56, No, 4. University of California, 1986. By Hugh J. Hansen and Walt L. Trimmer. PNW
Davis, CA. 6 p. www.irrigation.org/ibt/0212/p22.htm 291. Oregon State University, Corvallis, OR. 2 p.
Idaho Power. 2005. Irrigation Energy Saving Ideas. 12 p. Lists strategies for keeping the electrical demand
www.idahopower.com/pdfs/energycenter/irrigation.pdf charges on an irrigation system as low as possible. Also
Jenkins, Jack. 2001. Low Energy Precision Applica- has tips for using a watthour meter to measure power.
tion Irrigation Assistance Program. Report from the Can be purchased for $0.25 from Washington State
National Renewable Energy Laboratory. 2 p. University Extension, P.O. Box 645912, Pullman, WA,
www.westgov.org/wieb/irrigate.htm 99164-5912 or by calling 509-335-2857 or
800-723-1763.
Loftis, J.C., and D.L. Miles. 2004. Irrigation Pumping
Plant Efficiency. Colorado State University Cooperative Irrigation Energy Saving Ideas. 2000. By Richard
Extension Service, Fort Collins, CO. 4 p. F. Beard and Robert W. Hill. Utah State University
www.ext.colostate.edu/pubs/crops/04712.html Extension Service, Logan, UT. 5 p.
Miranowski, John. 2004. Energy Consumption in U.S. Describes factors that affect electric motor performance
Agriculture. In: Proceedings of the conference Agri- and service life and describes procedures for controlling
culture as a Producer and Consumer of Energy, spon- internal motor heat.
sored by the Farm Foundation and USDA’s Office of Can be downloaded from http://extension.usu.edu/
Energy Policy and New Uses. 43 p. fi les/engrpubs/biewm06.pdf
www.farmfoundation.org
Maintaining Electric Motors Used for Irrigation. 2000.
U.S. Department of Agriculture, National Agricultural By Richard F. Beard and Robert W. Hill. Utah State
Statistics Service (NASS). Farm and Ranch Irrigation
University Extension Service, Logan, UT. 5 p.
Survey (2003), Vol. 3, Special Studies, Part 1, 2002
Census of Agriculture. Washington, DC, November Describes factors that affect electric motor performance
2004. 216 p. and service life and describes procedures for controlling
internal motor heat.
Further Resources Can be downloaded from http://extension.usu.edu/
fi les/engrpubs/biewm06.pdf
NCAT Publications
The Montana Irrigator’s Pocket Guide. 2003. By Web Sites
Mike Morris, Vicki Lynne, Nancy Matheson, and Al Agricultural Energy Publications
Kurki. National Center for Appropriate Technology, University of Wisconsin Cooperative Extension
Butte, MT. 161 p. http://cecommerce.uwex.edu/showcat.asp?id=7
A take-to-the-field reference to help irrigators save Dowloadable publications on many farm energy
energy, water, and money; includes guidelines for water topics, including irrigation.
www.attra.ncat.org ATTRA Page 13

14. Energy in Agriculture Program Wateright
California Energy Commission Center for Irrigation Technology at California State
www.energy.ca.gov/process/agriculture/index.html University, Fresno
Offers publications, links, and other resources on www.wateright.org/energy.asp
irrigation and many other topics. A “multi-function, educational resource for irrigation
water management.” Includes an energy use/cost
Irrigation Engineering Publications calculator, guidelines for estimating fuel requirements,
University of Nebraska Institute of Agriculture and options for reducing energy use and costs, and discus-
Natural Resources sions of various other energy-related topics.
http://ianrpubs.unl.edu/irrigation
Dozens of publications on irrigation management
and hardware.
Notes
Page 14 ATTRA Energy Saving Tips for Irrigators

15. Notes
www.attra.ncat.org ATTRA Page 15

16. Energy Saving Tips for Irrigators
By Mike Morris and Vicki Lynne
NCAT Energy Specialists
© 2006 NCAT
Paul Driscoll, Editor
Amy Smith, Production
This publication is available on the Web at:
www.attra.ncat.org/attra-pub/energytips_irrig.html
or
www.attra.ncat.org/attra-pub/PDF/energytips_irrig.pdf
IP278
Slot 278
Version 071806
Page 16 ATTRA