Energy Efficiency MeasuresINDUSTRIAL: MOTORS AND MOTOR SYSTEMSEfficient motors run cooler and generally have longer lifetimes than do less efficient motors. Motor efficiencies vary with horsepower and number of poles. In order to be counted as "premium efficiency," according to the National Electrical Manufacturers Association (NEMA), a motor's efficiency must meet or exceed the values listed in the table below. Nominal Full Load Efficiencies for EPAct -covered equipment: 1-200 horsepower NEMA design A and B, three phase, integral horsepower, general purpose motors (1200, 1800, 3600 RPM).
New motors manufactured and imported for the U.S. market must meet or exceed these full load nominal efficiencies. Table courtesy of Consortium for Energy Efficiency, and can be found on-line at www.cee1.org/ind/motrs/Cee-nema.pdf. In most cases, motors that are more efficient than those listed are available and should be chosen whenever feasible. When purchasing new motors, it is best to look for NEMA Premium brand products. Paybacks over their lifetimes are routinely quite large. Motor maintenance programs are essential both to long-term reliable performance and to energy savings. Elements of the program should include cleaning; inspection and lubrication of bearings (using a stethoscope, infrared scanner, or digital thermometer as appropriate); motor mount inspection, belt inspection, and alignment; and inspection of overload protection circuitry. In the case of critical motors, additional measures such as vibration analysis, oil sampling, and even partial disassembly may be necessary. Infrared scanners that produce two-dimensional images of thermal information are particularly useful, and spot radiometers that remotely read temperatures with good precision have become quite inexpensive. Both are helpful in identifying overheating bearings and belts, as well as hot spots in circuit breaker and electrical junction boxes. Motor System OptimizationWhen efficient motors use variable speed drives and are matched well with their loads, excellent savings are routine. In a 2003 study of 41 industrial motor system optimization projects representing an aggregate investment of $16.7 million, average annual rates of return of over 40% from energy savings alone were achieved.1 In addition to energy savings, over one-third of the projects also experienced an increase in productivity (in production or product quality), and a number of companies saved in maintenance costs and avoided equipment purchases. Authors of the study maintain that if manufacturing plants in the U.S. that account for 50% of industrial energy consumption would implement similar projects, annual savings of as much as 83 billion kWh and $4 billion would be achieved. In general, any task whose requirements change with time provides opportunities for increasing efficiency. A woodworking facility with gates at 90 work stations for removing sawdust installed variable frequency drives on a pair of 100 + hp fan motors. The motors are throttled back when some gates are closed, while ensuring that adequate static pressure is maintained to thoroughly remove sawdust from operating work stations. The result of matching fan power to instantaneous load yields both energy savings and better productivity since each work station now enjoys virtually constant sawdust-removing power regardless of the configuration of the others. Using variable speed devices on motors used to drive evaporator fans on large cold storage units housing many tons of fruit can save over half of the electrical energy used in these facilities while maintaining consistent and uniform temperatures throughout cooled areas2. A single electronic package can control devices on all of the fans on a given evaporator coil, so retrofits are relatively inexpensive and payback periods are short. Better matching of cooling power to load saves electricity because under many circumstances air movement can be cut back to 50% of full flow, which reduces electric energy requirements for evaporator fan motors to only 15% of peak. Waste heat from the motors themselves is also diminished, thereby further lowering the overall cooling load in the cold storage units. Analogous circumstances apply in a range of other air moving tasks (including compressed air, see below) as well as to liquid moving tasks. Generally, the slower one can move a fluid through a duct or a pipe, the less motive power is required for the task since motor energy varies as the cube of the fluid velocity. Of course, designs with smaller cross sectional area ducts or pipes and those with many elbows that require abrupt changes in direction are least efficient. Instead of variable speed drives on a single motor, it is frequently more effective to use several motors, bringing them on incrementally to meet load demand. This can simplify systems and avoid the costs associated with variable speed drives. For example, over a hundred schools in Indiana have two-pipe HVAC systems which use a 7-horsepower motor for circulating warm water to unit ventilators in classrooms and a 15-horsepower motors for circulating cool water (since they are operated at temperatures closer to ambient and require higher flow rates). MotorMaster+MotorMaster+ is comprehensive computer software that facilitates motor management functions at medium- and large-sized industrial facilities. It was designed for utility auditors, industrial energy coordinators, and plant and consulting engineers, although its reports are also useful for senior management. MotorMaster+ aids motor and motor systems improvement planning through identifying the most efficient action for a given repair or motor purchase decision. MotorMaster+ can be used to identify inefficient or oversized motors and it computes the energy and demand savings associated with the selection of an energy-efficient replacement model. It contains a motor manufacturers' motor price and performance database that is updated periodically via email. MotorMaster+ performs energy conservation analyses and life cycle costing, and has energy accounting and savings tracking functions. The software also contains a motor inventory module that includes maintenance logging and tracking functions. Washington State University's Cooperative Extension Energy Program has been involved in the development of MotorMaster for eight years and it has become a "BestPractice" tool supported by U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy. Version 4.0 was released on March 6, 2003. The software and a comprehensive User's Manual may be downloaded for free at http://mm3.energy.wsu.edu/mmplus/mmdownload/mmdnld_nmc2.cfm. The Motor Decisions Matter national education campaign has developed a Motor Planning Kit consisting of tools, internet links, and procedures for organizing a comprehensive motor management plan. For example, the Kit contains observations and graphics like the following:
The Motor Planning Kit may be downloaded for free at www.motorsmatter.org. For additional information, access the Motor Systems Toolkit on the website of the Consortium for Energy Efficiency, at www.cee1.org/ind/mot-sys/mot-sys-tools.php3. Replace drive belts on large motors with energy-efficient cog belts. Standard V-belts have an efficiency of about 92%. Cog belts, which have notches, flex more easily and have been shown to increase the efficiency of drive systems by 2-8%. Limiting waste in air compressor systems begins with a thorough inspection to locate and repair leaks (and potential leaks) in couplings, hosing, actuators, and other elements. At a more subtle level, an inspection of the system may reveal opportunities to reroute piping, form a closed loop so flow from compressors to users of compressed air can be split thereby lowering frictional losses, and diminishing the need for high system pressures. Since every drop of 2 pounds per square inch (psi) of pressure saves 1% of electric energy use, maintaining the system at as low a pressure as practical is desirable. Variable speed drives used on high-efficiency motors along with adequately-sized storage tanks can meet periods of high demand while reaping the energy saving advantages of good efficiency during periods of part load. If there are only several work stations that require high pressure compressed air, it is sometimes cost-effective to meet those requirements with a small, dedicated high-pressure system, thereby allowing the main system to be run at substantially lower pressures. This also allows for the compressor and storage tank that feed the high-pressure system to be located close to the point of use, thereby decreasing frictional losses. In multi-compressor operations, metering and monitoring of flows, pressures, and energy use is both useful and becoming less expensive with modern electronic equipment. The resulting information can be used to both enhance maintenance quality while lowering costs and ensure that production needs are optimized. In addition, both demand and energy costs can be lowered by cycling compressors and turning off units during periods of low demand. Older style compressor controls result in wide swings of pressure, which means that higher average pressures need to be maintained in order to ensure a given minimum pressure is always available. Since each psi of higher pressure results in about a half a percent of energy waste, it is valuable to employ modern microprocessor-based controls which can maintain a much narrower range of pressure swings. Controls which minimize pressure fluctuations can save about 8 percent of compressor energy. Lower overall system pressure also lowers leakage. Use synthetic lubricants in compressors and motor systems. Industrial data demonstrates that synthetic lubricants have improved characteristics resulting in lowered equipment frictional energy losses. Replacing the lubricant in the air compressors with a synthetic-type lubricant saves energy. To learn more, visit www.compressedairchallenge.org. 1 "Industrial Motor System Optimization Projects in
the US: An Impact Study," by Robert Bruce Lung, Resource Dynamics Corporation;
Aimee McKane, Lawrence Berkeley National Laboratory; and Mitch Olszewski, Oak
Ridge National Laboratory, 2003 Proceedings of the ACEEE Summer Study on Energy
Efficiency in Industry. |
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Introduction | Recommendations by Sector | Energy Efficiency Measures Performance Contracting & Energy Service Companies | Program Profiles Case Studies | Glossary of Energy Terms | Home © 2003- Southwest Energy Efficiency Project |
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