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Best Practice Guide |
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Food and Beverage Growers and Processors |
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On-the-Farm Energy UseIrrigation pumpingMotors have long served as the "muscle" on modern farms. Motors help clean the barn, milk the cows, pump liquids, grind feeds, and rotate ventilation fans, to name just a few duties. More importantly, motors and pumps transport vital irrigation water to 85 percent of all farmland in California Motors use more energy than any other single category of farm equipment, consuming about 9 trillion British thermal units (Btus) in California each year - this excludes energy used for on-site transportation and district water pumping. According to a study conducted by the American Council for an Energy Efficient Economy (ACEEE), petroleum products power about 55 percent of California farm motors with electricity powering the remaining 45 percent. This varies from national averages, in which petroleum products account for roughly 94 percent of all motor fuel.
In general, savings opportunities fall into three broad categories: motor maintenance and testing, efficient motor and equipment purchases, and overall irrigation-system efficiency. Because of the importance of irrigation, this section focuses on water pumping; for a broader view on motor efficiency, see the Motor Chapter.
Look for programs that assist with irrigation-pump efficiency testing. Contact your utility representative to learn more about programs offered in your area, or contact the Agricultural Pumping Efficiency Program (APEP) managed by the California Center for Irrigation Technology. Tests can generally be completed in less than two hours. Consider replacing pumps that test less than 50 percent efficient. A well-designed and well-maintained motor, by comparison, can achieve efficiencies nearing 90 percent. Pumps that test as 55 to 60 percent efficient might benefit from the repair or replacement of the impeller - the fan-like device found at the core of most irrigation pumps. Adjusting or even replacing impellers can also be a good option for irrigation systems where pump power and pump demand are mismatched. Adding a smaller impeller to a system with an oversized motor, for example, minimizes overpumping - a problem that wastes energy and can lead to motor damage. Or, adjusting the clearance between the impeller and the pump wall can sometimes result in significant improvement in energy efficiency. One final note on pump adjustments: sometimes improving pump efficiency will increase energy consumption because horsepower is also boosted. Remember that with more horsepower, the pump can do the same amount of work in less time.
Irrigation pumps tend to be inefficient whenever overloaded or underloaded. Try to match drive size as closely as possible to expected loads. Dip below 50 percent load for any pump, and efficiency generally plummets. If pump loads fluctuate widely or if pumps are often run at partial loads, adding a variable speed drive may be cost effective since it closely matches output to actual demand. VSD-based pumping systems tend to work best with time-of-use billing schedules and on deep wells with frequent stop-and-start pumping. A quality VSD can help cut down on motor noise, improve production efficiency and eliminate the "voltage sags" (often evident from temporarily dimmed lights) common to motor startup, meaning that the benefits of VSDs extend well beyond just energy savings. See the Motor Chapter for more information on VSDs.
Much like joints and connectors, pipe widths can have a dramatic effect on operating costs. Even slight differences in pipe width can translate to big difference in energy use. A system with 10,000 feet of piping, for example, that pumps 600 gallons per minute using six-inch pipes will cost about four times as much in energy bills as a system with eight-inch pipes. And because pipe width affect pump load, accurately matching pipes to pumping loads can help extend the useful life of an irrigation pump. Similarly, pipe composition can affect operating costs and equipment lifespan. Rigid PVC pipes often improve suction and efficiency, while coated-steal pipes have been shown to reduce friction by more than 40 percent over comparable uncoated pipes. Of course, the power behind the pipes can be just as important as the pipes themselves. Food producers should keep in mind that designing the most efficient irrigation system may require not one but two, three or even more pumps. Multi-pump systems are typically used on farms with fields at different elevation levels; on these farms, small pumps can sometimes efficiently break the irrigation load into segments and achieve a higher level of efficiency than one large pump.
Remember that energy-efficient systems take less time to pump the same volume of water as their less-efficient counterparts. With shorter runtimes, you have more flexibility manipulating schedules to off-peak hours. Another load shifting strategy is to increase reservoir capacity. Large, strategically placed reservoirs can be filled during off-peak hours and can sometimes use gravity to ease daytime pumping needs. Resources See Flex Your Power product guide on motors. The National Electric Manufacturers Association (NEMA) website contains information on the NEMA PremiumĀ® energy efficiency motors program, including product specifications and a list of participating partners. The Consortium for Energy Efficiency (CEE) website on Motors and Motor Systems includes a Motor System Tool Kit, efficiency specifications, resource links and information on the Motor Decisions Matter campaign. Efficient Motors: Selection and Application Considerations. A brochure developed by CEE and the U.S. Department of Energy's Motor Challenge Program. Boston, MA: 1999. U.S. Department of Energy (DOE) free software MotorMaster+ is an energy-efficient motor selection and management tool, including a catalog of over 20,000 AC motors. This tool features motor inventory management tools, maintenance log tracking, efficiency analysis, savings evaluation, energy accounting, and environmental reporting capabilities. U.S. DOE free softwarePumping System Assessment Tool (PSAT) helps industrial users assess the efficiency of pumping system operations. PSAT uses achievable pump performance data from Hydraulic Institute standards and motor performance data from the MotorMaster+ database to calculate potential energy and associated cost savings. Electrical Apparatus Service Association (EASA), Inc. is an international trade organization of over 2,150 electromechanical sales and service firms in 50 countries. The EASA website contains downloadable, in-depth guidelines to improve motor efficiency, repair worn or malfunctioning motors, and to help owners decide whether to replace or repair motor systems. |