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Energy Saving Tips for Irrigators


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Energy Saving Tips for Irrigators

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Energy Saving Tips for Irrigators

  1. 1. ATTRA Energy Saving Tips for Irrigators A Publication of ATTRA - National Sustainable Agriculture Information Service • 1-800-346-9140 • www.attra.ncat.orgBy Mike Morris and This publication describes ways that irrigators can save energy to reduce irrigation costs. It describesVicki Lynne recommended irrigation system installations, explains how utilities charge their irrigation customersNCAT 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.ContentsIntroduction ..................... 1RecommendedInstallations ...................... 2Centrifugal Pumps ......... 2Turbine Pumps ................ 4Electrical Use andCharges .............................. 5Causes of WastedEnergy ................................ 6HardwareImprovements ................. 7Estimating SprinklerPlant Efficiency ............. 11References ...................... 13Further 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 energyATTRA—National SustainableAgriculture 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 theseter for Appropriate Technology(NCAT) and is funded under a irrigation equipment. (U.S. Department of cases, our technicians identified at leastgrant from the United States Agriculture, 2003) one equipment change or repair that wouldDepartment of Agriculture’sRural Business-Cooperative Ser- Most irrigation systems are not as effi - quickly pay for itself in energy savingsvice. Visit the NCAT Web site( cient as they should be. A Kansas study alone. Very often, the irrigators who ownedhtml) for more informa-tion on our sustainable found that, on average, irrigation systems these inefficient systems were unaware ofagriculture projects. use about 40 percent more fuel than they any problems.
  2. 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 continuesNCAT 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 allPublications a wind turbine to generate electric- used in making commercial fertilizers andBiodiesel – a Primer ity or by making your own biodiesel pesticides. In 2002, commercial fertilizers fuel, for example. (nitrogen, phosphate, and potash) accountedDrought Resistant Soil This publication focuses on mechanical for 29 percent of all energy consumed inDrought 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 farmerstor’s Pocket Guide strategy is to eliminate unnecessary watering, can do to reduce energy consumption andSoil Moisture meeting only the water needs of your crops. energy-related costs is to reduce their use ofMonitoring: Low-Cost But you might also consider less obvious commercial fertilizers and pesticides. ManyTools and Methods options such as changing to less water-inten- ATTRA publications are available on thisWind-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 SoilRanches: 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, andMeasuring andConserving 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 motorPage 2 ATTRA Energy Saving Tips for Irrigators
  3. 3. considered together.) It’s a false economy to • An eccentric reducer to keep airsave money by installing undersized valves from becoming trapped in theand fittings. You’ll only achieve greater fric- reducer fitting.tion loss and higher pumping costs. The • A vacuum gauge to indicate whethernext time you rebuild your pump, replace the primer is pulling a vacuumthe fittings so that your pumping plant looks or just moving air through the Ideal in Figure 1. On the Discharge Side of PumpFigure 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 ViewsAn 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 maximumFigure 2 shows what a plant should look like Straight run of at least Supports as requiredwhen pumping from a surface source such as 10 pipe diameters “D” or straightening vanes Top Viewa river or canal. The pumping plant should for testing flowalso have the following features: Check valve Shut-offOn 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.) ATTRA Page 3
  4. 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. 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 horsepowerElectrical Use and Power during each billing period. ThisBill 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 energyequivalent to using one kilowatt (kW) over a b. The demand charge may be basedone-hour period. To visualize one kilowatt- on maximum wattage during thehour, it may be helpful to imagine ten 100- billing period. In this method, awatt light bulbs burning for one hour. special demand meter measures wattage for each 15-minute intervalAlthough billing procedures vary among (or some other interval) during theelectric providers and in different regions of billing period. The demand chargethe country, irrigation bills typically include would be based on the 15-minutethree basic charges for electricity. interval with highest wattage during1. 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 ATTRA Page 5
  6. 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. 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 Pcharacteristics 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 areCavitation damages impellers, reduc- cally involves replacing the bear- two to four percenting efficiency. If your pump is cavitating, ings, rewinding, and “dipping and more efficient thandetermine whether you have sufficient net baking,” and is done by qualified standard-efficiencypositive suction head (NPSH). You should motor repair shops. motors.also have a valve on the discharge side of • Consider a premium-eff iciencythe 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 whenamount of sediment, re-engineer the intake the cost of rewinding exceeds 65structure 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 than4. Improperly sized or designed standard-efficiency motors. Besides fittings saving energy, premium-efficiencyEvery minute that irrigation water passes motors usually have higher servicethrough undersized valves or other fit- factors, longer insulation and bear-tings at a high velocity, profits drain away. ing life, and less vibration thanReplace undersized fittings with ones of standard-efficiency motors.the correct size. Caution: Some premium-efficiency motors draw a higher startup5. Water source changes current. Make sure your system can handle it.If you’re using a well for irrigation and thewater table has dropped, you may have to • If you put in a new system, bereset the pump to a lower level. To com- aware that an 1,800 rpm motorpensate for the increased head, you may is more efficient than a 3,600have to add more stages to turbine or sub- rpm motor. For example, an openmersible 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, ATTRA Page 7
  8. 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 photoPage 8 ATTRA Energy Saving Tips for Irrigators
  9. 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 waterTurbine 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 poundSprinkler 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 ATTRA Page 9
  10. 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. 11. A Simple Method to Esti- Step 1. Find total dynamic headmate the Pumping Plant (TDH) in feet.Efficiency of an Electri- Reading pressure from gauge psi × 2.31 (a conversion factor) = feetcally Powered SprinklerIrrigation System Add height* if pump is above water surface + feetPumping plant efficiency, sometimes called OR“wire to water” efficiency, is the overall Subtract height* if pump is below water surface – feetenergy efficiency of the pump and motorconsidered together, and is defi ned as the To get total dynamic head (feet). TDHratio of water horsepower (“power out”) toelectric horsepower (“power in”). Energy * Height is defined as distance from the water surface to the centerline of the discharge lost by every pump and motor, and effi-ciencies in the mid-70 percent range are Step 2. Find flow rate in gallons perabout the best any pumping plant canachieve. A 70-percent pumping plant effi- minute.ciency would mean that 70 percent of the 2a. For hand move, side roll, orhorsepower 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 inated every several years or whenever there cubic feet per second (cfs), multiply cfs times 448.8 to get cause for concern (such as a noticeabledecrease in performance or an increase gpmin 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 docan save energy and money by adjusting, a bucket test:rebuilding, or replacing the existing pump Measure the flow of one sprinkler per lateralor 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 = gpmthese six ATTRA Page 11
  12. 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 tableTable 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 followingPage 12 ATTRA Energy Saving Tips for Irrigators
  13. 13. method may work. Cut the end of a finger off an old rub- management, equipment maintenance, and handyber glove, insert a short piece of metal pipe, and attach a conversions and formulas. Get a free printed copy byhose 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 overa pivot nozzle of almost any type and the flow rate can bemeasured with a bucket test. Other Publications Comparing Irrigation Energy Costs. 1999. By Danny H. Rogers and Mahbub Alam. MF-2360, Kansas StateReferences 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, naturalFuel Bills. Kansas State University Cooperative Exten- gas, diesel, and propane as irrigation energy options.sion Service, Manhattan, Kansas. 4 p. Can be downloaded from:, Blaine. 2002. PUMP UP: Improving plantefficiency 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. PNWDavis, CA. 6 p. 291. Oregon State University, Corvallis, OR. 2 p.Idaho Power. 2005. Irrigation Energy Saving Ideas. 12 p. Lists strategies for keeping the electrical charges on an irrigation system as low as possible. AlsoJenkins, 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 StateNational Renewable Energy Laboratory. 2 p. University Extension, P.O. Box 645912, Pullman, WA, 99164-5912 or by calling 509-335-2857 or 800-723-1763.Loftis, J.C., and D.L. Miles. 2004. Irrigation PumpingPlant Efficiency. Colorado State University Cooperative Irrigation Energy Saving Ideas. 2000. By RichardExtension Service, Fort Collins, CO. 4 p. F. Beard and Robert W. Hill. Utah State Extension Service, Logan, UT. 5 p.Miranowski, John. 2004. Energy Consumption in U.S. Describes factors that affect electric motor performanceAgriculture. In: Proceedings of the conference Agri- and service life and describes procedures for controllingculture 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 Policy and New Uses. 43 p. fi les/engrpubs/ Maintaining Electric Motors Used for Irrigation. 2000.U.S. Department of Agriculture, National Agricultural By Richard F. Beard and Robert W. Hill. Utah StateStatistics Service (NASS). Farm and Ranch Irrigation University Extension Service, Logan, UT. 5 p.Survey (2003), Vol. 3, Special Studies, Part 1, 2002Census of Agriculture. Washington, DC, November Describes factors that affect electric motor performance2004. 216 p. and service life and describes procedures for controlling internal motor heat.Further Resources Can be downloaded from fi les/engrpubs/biewm06.pdfNCAT PublicationsThe Montana Irrigator’s Pocket Guide. 2003. By Web SitesMike Morris, Vicki Lynne, Nancy Matheson, and Al Agricultural Energy PublicationsKurki. National Center for Appropriate Technology, University of Wisconsin Cooperative ExtensionButte, MT. 161 p. 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 ATTRA Page 13
  14. 14. Energy in Agriculture Program WaterightCalifornia Energy Commission Center for Irrigation Technology at California University, Fresno Offers publications, links, and other resources on irrigation and many other topics. A “multi-function, educational resource for irrigation water management.” Includes an energy use/costIrrigation 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. Dozens of publications on irrigation management and hardware.NotesPage 14 ATTRA Energy Saving Tips for Irrigators
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  16. 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: or IP278 Slot 278 Version 071806Page 16 ATTRA