When Motor Efficiency is at a Premium
When forest products giant Weyerhaeuser of Federal Way, Wash., made a corporate decision to pursue "green" policies, a key part of their strategy was resource conservation through greater energy efficiency. And electric motors, which account for the largest single share of Weyerhaeuser's energy bill, are a key element of that policy.
When forest products giant Weyerhaeuser of Federal Way, Wash., made a corporate decision to pursue “green” policies, a key part of their strategy was resource conservation through greater energy efficiency. And electric motors, which account for the largest single share of Weyerhaeuser’s energy bill, are a key element of that policy.
It’s also the law. The Energy Policy Act of 1992 (EPAct) requires that certain types of new motors sold in the United States as of October 24, 1997, must meet or exceed specified efficiency ratings.
It wasn’t EPAct that led to the invention of high-efficiency motors. Motors that met the ratings were commercially available long before the law took effect, and many more have come on the market since. Nor does EPAct require replacement of old motors; a grandfather clause allows users to repair or rewind them if they wish.
Rewinding or rebuilding a motor might improve its efficiency above the value at the time the motor was taken out of service. But because the amount and configuration of the motor steel remains fixed, and no additional copper can be added, the rebuilt motor can at best only attain its original value. Therefore, repair often isn’t the most cost-effective practice.
Owners have three choices when an old motor fails or approaches the end of its expected life: they can repair/rewind the motor, replace it with an EPAct energy-efficient motor, or replace it with a NEMA premium-efficiency model.
Weyerhaeuser chose the final option. However, the company operates or maintains as spares about 87,000 motors, and potentially replacing thousands of them as a matter of company policy involved a lot of analysis.
Setting criteria for choosing the option fell to John Holmquist, P.E., senior scientist with Weyerhaeuser Engineering. “Our goal was to reduce the total cost of ownership for our motors,” he says. “Total cost includes not just the purchase price, but also the cost of electric power consumption and repair costs over the lifetimes of our motors.”
To meet his firm’s goals, Holmquist enlisted the assistance of engineers at the Washington State University Energy Program in Olympia. It was the WSU Energy Program that several years earlier had authored software for the U.S. Dept. of Energy. Holmquist also called in Jim Rooks, P.E., of J&R Consulting, Inc., Tigard, Ore., Rooks used the software to analyze a representative sample—several hundred units—of Weyerhaeuser’s motors.
The software’s inventory program can record each motor’s nameplate data, age, utilization rate (operating hours per year), rated operating efficiency, and loading (as measured by ammeter readings and rewind history), plus any special electrical and mechanical characteristics. It then compares the cost of continuing to operate the motor over its expected life with the total cost of ownership of a premium-efficiency motor of equivalent size.
Jim Rooks crunched some numbers to evaluate Weyerhaeuser’s motor situation. “Some 2,800 new motors, representing about 8% of the company’s NEMA motors, are purchased each year to replace failed motors or as motors for new applications,” he says. “The motors Weyerhaeuser selected under its company-wide energy policy have an efficiency that is one percentage point higher than motors that would just meet EPAct standards. With a 1% improvement in efficiency, those 2,800 new motors, consuming 33.57 kW apiece, yield a savings of 940 kW. For the company’s 7,590-hr. operating year, that represents 7,134,600 kWh in annual energy savings. At $0.04/kWh, the savings is worth $285,384. Add that to the money saved by the retrofit program, and it amounts to almost $400,000 a year—and those savings increase by 100% annually, so long as the policy remains in effect.”
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