Green Technology: More-Efficient Motors

Despite media hoopla about energy- efficient lighting, the real opportunity to save energy for many businesses and even for homes is in motors. Motorized equipment accounts for 64% of the electricity U.S. manufacturers consume.

The Federal government began mandating energy efficiency for motors in 1992. Motor-efficiency standards (MEPS) went into effect five years later. However, MEPS only covered general-purpose ac motors. Specifically, the Energy Policy Act, or Epact, which took effect in 1997, listed minimum efficiency levels for polyphase acinduction motors between 1 and 200 hp having rigid mounting bases.

The regulations stuck to basemount motors because “regulators felt this was the most common configuration and they didn’t want to get into specialty motors,” says Baldor Electric Co. Motor Product Manager John Malinowski. “It was a starting point. Industry anticipated follow-up specs but they never happened.”

That situation changed last year with the enactment of the Energy Independence and Security Act of 2007. The Act applies to motors made after Dec. 19, 2010. It boosts mandated efficiency levels for motors covered under the old Act and applies standards to seven motor types formerly excluded. Motor makers say this fills a gap in the original legislation.

“The 1992 standards missed a lot of common motors throughout industry,” says Baldor’s Malinowski. “One example is round-body Cface motors which are the most common type for conveyor systems. (In motor-mount parlance, a C-face attachment lets a gearbox or pump connect to a motor.) Pump motors are another example. For some industries they are the main source of electricity use. These represent literally millions of dollars of annual motor sales that the old Act missed.”

With the new Act taking effect in less than three years, OEMs should start designing for new efficiency levels today, even for equipment destined to be sold overseas. “The overseas markets are rapidly catching up to the motor regulatory environment in the U.S.,” says Emerson Motor Co. Director of Marketing Robert Boteler. “If you are exporting, it would be a wise decision to get your products aligned with U.S. energy-efficiency regulations.”

In one regard, some of the distinctions spelled out in the Epact legislation have become less important. The Act sets efficiency requirements for general-purpose motors of both A and B designs. The difference is that design-A motors can handle higher locked-rotor or inrush current. In practice, however, the two types of motors perform much the same.

“For the most part, everyone has gone to IEC starters. These starters can handle the higher inrush of premium motors,” says Malinowski. “There is even less consequence when the motor is used with a drive because the drive functions as a soft starter.”

The legislation enacted last year basically moves integral-horsepower motors having up to 200 hp from efficiencies specified in Epact to efficiencies dubbed NEMA Premium level. These levels are spelled out in table 12-12 of a NEMA standard called MG-1. The efficiencies are more stringent than those Epact dictated. Meanwhile, generalpurpose motors in the 1 to 200-hp range that Epact didn’t cover must now comply with the efficiencies spelled out in the old Epact legislation. Similarly, those in the range of 201 to 500 hp must comply with table 12-11 of the same NEMA MG-1 standard.

Motor s abl e to me e t the NEMA Premium levels have been around for some time. But they are more expensive than conventional motors because they use pricey materials.

“Premium motors are trying to eliminate losses. So they use a better grade of steel to minimize magnetic and load losses. They also use more copper in the windings to keep down resistance,” says Malinowski.

“In the lower horsepower ranges the cost differential is likely to be between 15 and 20%. In the 150 to 200-hp range it might be 12 to 15%,” says Emerson’s Boteler. “In lower horsepower motors, material costs can exceed 50% of the total cost,” he says.

Motor manufacturers emphasize that motor economics should not be judged just on the initial cost, but rather on the total cost over a typical 20-year life span. The purchase price of an industrial motor is only about 2% of what users ultimately spend. Energy accounts for 97% of total expenses.

Despite the higher cost, about 25% of the general-purpose motors now sold in North America carry Premium efficiency ratings. And industry analysts say their use is growing at a high rate.

Motor manufacturers feel future legislation will eventually boost the efficiency ratings of motors now covered by the old Epact tables to NEMA Premium levels. That shouldn’t be a problem, however, because NEMA Premium motors can already be had for these categories. That includes C-face and vertical pump mount, explosionproof, wash-down duty, and so forth. In general, manufacturers say, NEMA Premium models can handle almost any application that can use a design B motor.

But there will be adjustments on the part of some motor manufacturers. “A certain percentage of NEMA Premium motors today are hand wound where similar Epact motors are machine wound. Going forward, motor manufacturers will have to switch from having NEMA Premium product being perhaps 25% of their volume to roughly 90%,” says Boteler.

There are other reasons to go NEMA Premium besides energy conservation. The motors run cooler so bearings and grease last longer. Most Premium motors use finned cast-iron frames which help minimize noise and vibration. And some states offer end users incentives to install equipment that is more energy efficient.

Bigger role for three phase
The majority of capital equipment runs from three-phase motors. But motor manufacturers say ancillary apparatus is often driven by single-phase motors, and there may be an opportunity to cut energy use by swapping them out for three-phase units. Conventional single-phase motors typically exhibit about 80% efficiency. In contrast, Premium three-phase units can hit 90.2%, and even ordinary three-phase motors come in at 87.5%.

The same argument may be made for replacing large, brush-dc motors with efficient ac versions. The best large dc motors, as used for powering equipment such as plastic extruders, have efficiencies of about 92%. That’s not bad, but the equivalent NEMA Premium three-phase ac units can hit 96%, say motor manufacturers. Elimination of brush maintenance is another plus, they point out. And ac drives are somewhat less expensive than the SCR drives necessary for big dc-brush units.

Another avenue for energy savings is in running motors at variable speeds. The ability to work efficiently at less than rated speed brings obvious benefits. Permanentmagnet- rotor motors can have efficiencies exceeding those of NEMA Premium units by a few percentage points, even at sizes of 500 hp and larger. And industrial firms seem to be installing these units despite their higher purchase price.

One approach where caution is in order concerns use of older ac motors with modern variable-speed drives. This is particularly true for motors built over 20 years ago.

“The Premium motors have been designed with enough room in their thermal rise to accommodate pulsewidth- modulated power supplies,” says Malinowski. “And they have insulation that will withstand the PWM waveform spikes. But older motors have insulation that may not hold up. You will see energy savings but they will run hotter and may fail prematurely.”

Will there ever be an Energy Act that applies to variable-speed motors? Probably not. “It’s unlikely you’ll ever see regulations in this area,” says Boteler. “The range of variable-speed applications is pretty much infinite. So it is tough to regulate that and not run the risk of damaging someone’s application.” Variable-speed motors are also looked on as a means for realizing energy efficiency in residential settings. One example of the trend is the recently developed imPulse motor from Marathon Electric Commercial Motors. This is a brushless- dc unit designed to power the water pump on a hot tub.

The 1.8-hp, 230-V motor runs a 2-hp pump at speeds down to 400 rpm as well as in jet mode for to 64% fewer watts than the standard permanent split-capacitor induction motor it replaces, The savings can be about 100 W/hr, says Marathon, because a typical hot tub runs nearly 22 hr daily in lowspeed circulation mode.

Similarly, variable-speed motors are viewed as one means of meeting mandated efficiency levels for HVAC systems and refrigeration units. “The compressor and circulating motors are the two items that are most key to SEER (seasonal energy-efficiency ratio) ratings. Variable-speed motors are one of the levers designers can pull to lower their watts and improve their efficiency,” says Paul Selking, Regal-Beloit Corp. industry leader for residential ECM products.

Nevertheless, the majority of HVAC units still employ ordinary split-capacitor induction motors rather than variable-speed units. Selking estimates that less than 30% of all residential HVAC systems make use of variable-speed technology. The majority of units hit SEER targets by simply increasing the size of condenser coil real estate and of other heat-transfer components.

That design strategy may change, however, as the effects of last year’s energy act start to kick in. The Act forces HVAC manufacturers to establish guidelines for maximum electrical energy consumption. The thought is that actual limits won’t become law for perhaps 10 years, but manufacturers predict this schedule could get accelerated.

The U.S. isn’t the only country scrutinizing the energy that HVAC systems consume. “Canada is looking at similar legislation by the end of next year that would require HVAC manufacturers to record power consumption as a step toward limiting it later on,” says Regal-Beloit’s Selking.

Other applications where variable- speed motors are showing up include blower motors in refrigeration units. Some manufacturers are also looking at the idea of variablespeed motors for a/c compressors. Variable-speed a/c compressors have been a power-saving necessity in China because residences there have much less electrical capacity than in the U.S. One advantage of variable-speed compressors is that they may potentially eliminate the need for a second compressor in central ac units. (See Motors Move Toward More Efficiency, Machine Design, Apr. 8, 2008)

Finally, updates of power-transmission components can enhance efficiency regardless of motor technology. For example, speed reducers with helical gears can be significantly more efficient than those with worm gears. Potentially this could let a motor with less horsepower produce the same output torque as a larger model.

“Something as simple as going from a solid V belt to notched V belt is good for 2% more efficiency,” points out Baldor’s Malinowski. “The more you can back away and look at how you are driving the load from a systems viewpoint, the more you will save when you select components for the best efficiency.”

Make Contact Baldor Electric Co., Ft. Smith, Ark., baldor.com
Emerson Motor Co., St. Louis, Mo., emerson.com
Marathon Electric Commercial Motors, Wausau, Wis., marathonelectric.com
Regal-Beloit Corp., Beloit, Wis., regalbeloit.com

Sidebar: The loss budget of an electric motor

Six factors account for most of the energy lost in an ordinary induction motor: iron-core losses, stator resistance, rotor resistance, windage and friction, and stray load losses. NEMA Premium motors minimize these factors in a variety of ways, usually through use of high-grade steel and increased use of active materials. For example, high-grade steel in the rotor lets manufacturers use thicker laminations that take less time to manufacture, but which still reduce ironcore losses caused by circulating currents. Similarly, manufacturers reduce stator resistance by boosting the amount of copper in the stator windings.