Energy efficiency by the numbers

Legislative and rare-earth-metal pressures add up to long-term savings for motor users.

By J. Stanton McGroarty, CMfgE, CMRP, senior technical editor

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In brief:

  • With EISA legislation approaching its second year in effect, the impact in the factory still seems limited.
  • Permanent magnet (PM) motors are known to not only provide higher levels of efficiency than can be achieved by induction motors, but do so over a very wide speed and load range, where induction motor efficiency drops off dramatically.
  • Manufacturers have released technologies that are above premium efficiency.

A perfect storm has been brewing around electric motors and drives. On Dec. 19, 2010, the Energy Independence and Security Act of 2007 (EISA) (Public Law 140-110) took effect. The law implemented new energy-efficiency standards for three-phase induction motors from 1 to 200 hp. In addition to the new law, significant increases in the cost of the rare earth elements used in permanent magnets have been anticipated as China’s use of the metals begins to exceed its production. Small-hp motors will be added to EISA in 2015, and the U.S. Department of Energy is looking at new efficiency updates for variable-speed motor-drive systems.

EISA impact

With EISA legislation approaching its second year in effect, the impact in the factory still seems limited. Only about 18% of plants have replaced any motors with EISA qualified units, according to the annual Plant Services survey on the use of motors and drives (Figure 1). However, EISA governs the sale of motors by producers, which could explain why customer involvement remains delayed.

Figure 1. EISA governs the sale of motors by manufacturers, which could explain why customer involvement remains delayed
Figure 1. EISA governs the sale of motors by manufacturers, which could explain why customer involvement remains delayed.

At the motor factories, the picture is somewhat different. As a result of EISA implementation, all integral-horsepower general-purpose electric motors manufactured after Dec. 19, 2010, are required to meet NEMA premium efficiency levels, says Scott Johnson, vice president of NovaTorque (www.novatorque.com). All OEMs are now accountable for the efficiency of motors in their equipment.

“To achieve these higher levels of efficiency, manufacturers of ac induction motors have moved to higher-grade electrical steel, additional copper, and cast aluminum rotors,” says Johnson. ”The improvement has been significant, and the additional cost associated with the manufacturing of these more efficient motors was economically justifiable by the reduced cost of energy.”

Some plants are even specifying premium efficiency motors for other motors not mandated to be premium, adds John Malinowski, senior product manager at Baldor (www.baldor.com).

Rare earth metals

“While further improvements in induction motors are possible, the design has reached the point of diminishing returns,” says Johnson. “The cost of further improvement will not yield sufficient additional energy savings to justify the additional investment. Plus, motor size for the same horsepower would likely have to increase, further complicating the adoption. The next step up on motor efficiency is therefore unlikely to be an induction motor.”

Figure 2. Some plants are even specifying premium efficiency motors for other motors not mandated to be premium, and many applications show acceptable paybacks today when improved system reliability is taken into account.
Figure 2. Some plants are even specifying premium efficiency motors for other motors not mandated to be premium, and many applications show acceptable paybacks today when improved system reliability is taken into account (Source: Baldor)

Permanent magnet (PM) motors are known to not only provide higher levels of efficiency than can be achieved by induction motors, but do so over a very wide speed and load range, where induction motor efficiency drops off dramatically, explains NovaTorque’s Johnson. “As many applications now incorporate speed control for efficiency or process improvement, this provides PM motors with a significant advantage. The issue, however, has been cost. PM motors, due to the use of expensive rare-earth-magnet material, have a first cost than can be double or more than that of an induction motor. Payback on that price premium can be prohibitively long.”

Some of the new technologies, such as permanent magnet rotor motors, are very good efficiency upgrades that will be more adopted as magnet prices fall, says Baldor’s Malinowski. “Even so, many applications show acceptable paybacks today when improved system reliability is taken into account,” he adds (Figure 2). “Many projects cannot be justified on energy savings but on eliminating downtime while also saving electricity. For example, it is difficult to take an operating motor out of service for an efficiency upgrade. Payback may be in the three-to-four-year range, well beyond the two-year payback most companies are seeking. When the motor fails, it will be replaced with an upgraded unit or replaced early before failure if a more robust motor is selected that will prevent downtime, while also saving electricity.”

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