There isn't a single shop or warehouse floor today that isn't being scrutinized for every potential cost saving. And one area that deserves particular attention is the energy consumption of materials handling equipment.

"The cost of electricity is a component of your product cost, just like steel, aluminum, plastic, or any other component used to create your product," states John A. McFarland, president and CEO of Baldor Electric Company, a manufacturer of motors and drives headquartered in Fort Smith, Ark. Most companies work hard to control the cost of components going into their products, yet don't do the same when it comes to electricity. "While we might have trouble controlling electricity costs, we can certainly control its consumption."

In fact, electric motors account for 60 to 64% of an industrial company's electric bill on a yearly basis explains Rick Payton, director of marketing for electric motors at Reliance Electric, Greenville, S.C. These motors, both DC and AC, convert electricity directly into mechanical work as they power conveyors, palletizers, automated storage systems, and other equipment.

"Organizations need to take a long hard look at how energy expenses will effect them in the long run," says John Malinowski, a drive specialist at Baldor. "If they have conveyors, for instance, that are simply running all day at full speed without moving anything, then they have to see this as money being wasted," adds Malinowski.

Maximizing energy efficiency of materials handling equipment can be approached in several ways. These range from selection of an AC or DC motor to the use of sensors and soft start capabilities to further reduce energy use.

To get to where they are today, motor efficiencies have made gains over the years. And as far as AC induction motors are concerned, the hunt for ever greater energy efficiencies has come full circle.

During the energy crunch of the '70s, the AC induction motor came to the forefront with a 75 to 85% efficiency rating. These motors were cost effective and reliable, however, abrupt speed changes caused impact forces that were mechanically detrimental.

Smaller DC motors were introduced with less inertia, touting efficiencies ranging from 82 to 88% during the '80s. These DC shunt-wound motors were more expensive than AC induction motors but provided significantly less impact loading on equipment. In addition to better efficiency, these units, with their smaller size, were able to fit into much tighter spaces than their earlier counterparts. However, motor brush and commutator maintenance issues and the recent lower cost of AC drives forced the exploration of alternatives.

DC servo motors replaced the use of DC shunt-wound motors. This continued the compact, low-inertia high-efficiency direction for materials handling equipment in the late '80s and early '90s. With motor efficiency rates as high as 90%, top of the line enhancements allowed dynamic braking units to recover a significant amount of regenerative power. This results in higher energy efficiency. Unfortunately, these motors too were plagued with maintenance issues including brush wear and commutator service.

The highest efficiency ratings were achieved as DC servo motors were overshadowed by AC servo motors that were called into action during the late '90s. With efficiency ratings approaching 95%, these units are compact and brushless, eliminating the operational issues experienced with prior DC motors.

Employing line regeneration, which returns electrical energy to the power system for maximum efficiency, these models had a smooth acceleration and were extremely equipment friendly. The biggest drawback that existed was cost. AC servo motors were higher cost compared to DC servo systems.

Today in an attempt to lower expenses, there has been a move back to the larger AC induction motors. Design improvements have allowed for energy efficiencies for these units that fall in the 90 to 94% range. Typically 1 to 10 horsepower motors have a 85.5 to 91.7% rating. Forty horsepower motors are considered to be the threshold where 94.1% plus efficiency is achieved.

This is a significant improvement over the meager energy efficiencies of the early '70s models. The biggest advantage for AC induction motors is the significant lifetime cost savings over other AC or DC motor options. In addition, no brushes exist which eliminates the operational issues surrounding other motor options.

Although some organizations have opted to remain with DC motors, many others have implemented AC induction motors due to their superior energy efficient capabilities and superior operation in a wider variety of applications. As a result, AC induction motors have become the industry standard for use in materials handling equipment.

Since the Energy Policy Act (EPAct) took effect in 1997, any general-purpose industrial three-phase motor sold in the U.S. has to meet a minimum efficiency level. To determine this minimum level, motor designs are tested to verify efficiency utilizing the Institute of Electrical and Electronics Engineers, Inc. (IEEE) 112 standards. These standards require the motor to be tested under load at operating temperature via a dynamometer, which most closely matches a field installation.

"Without test standardization, the user has no means to perform a meaningful product comparison and efficiency savings calculation. It limits the purchaser from making an informed purchase decision," says Payton of Reliance Electric. "Every NEMA premium efficient motor is tested to a standard and has a nominal and minimum efficiency listed on the nameplate."

The energy savings of NEMA premium motors can be easily calculated. The factors needed to make the calculation include hours of operation per year, utility rate in dollars per kilowatt/hour, motor horsepower, the efficiency of existing motor (found on the nameplate), and the efficiency of NEMA premium motor. Unless the motor is operated continuously – 24 hours a day – an upgrade to a premium efficient motor may not be warranted. Even many EPAct motors offer efficiency improvements over older motors currently in use.

Software to perform energy-use calculations is readily available from most motor manufacturers, who are also available to help perform energy surveys for customers if needed. In addition, many local utilities provide rebates that help defray the costs of premium efficient motor upgrades. Utilities often offer rebates of 5 to 15% on qualified motors.

Other enhancements to motors deal with the latest energy efficient designs that reduce wasted electricity. This is accomplished mainly with better materials, more types of materials and with less heat to dissipate during normal motor operation (see box below - The anatomy of efficiency ).

Energy conservation does not rely solely on motor design and efficiency. In the case of powered conveyors in particular, other options include sensors and soft-start capabilities as well as adjustable speed drives.

Utilizing sensors, motors in conveying systems can easily be turned off when not in use. As an item on the conveyor system passes an in-line photo eye, the motor controlling the zone is turned on. When the item passes this zone, the motor is turned off. Unfortunately, current surges and delays in conveyance have plagued this approach to energy conservation.

Recent developments in soft-start motors and adjustable speed drives have helped to alleviate some of the problems that existed for cut-off sensor model conveying systems. By eliminating abrupt starts for these motors, energy is conserved while minimizing damage to conveying systems and product.

Adjustable speed drives allow conveyor systems to run at much lower speeds when product is not being transported over a particular section of conveyor. By maintaining a minimal speed, conveyors utilizing these types of motors can easily be brought back up to speed when an item passes into the field of a detector, significantly reducing delays in conveyance and eliminating cold starts.

"Knowing the energy efficiency of motors used by your materials handling equipment is only half of the story as far as consumer goods giant Procter & Gamble is concerned. The other half is to determine exactly what those efficiencies are worth in dollars and cents," says Jim Reizner, a technology leader in corporate engineering at P&G. He was once part of a team that evaluated motor energy efficiency for materials handling equipment. "Our primary objective was to increase P&G shareholder return," explains Reizner. "Energy usage is a large component of our corporate expenditures, so minimizing energy usage is important to us. At the time, only one half of our motors were energy efficient."

In order to reach the best conclusion and to measure their results, P&G formulated a sophisticated return on investment (ROI) spreadsheet. Reizner and his team estimated the approximate quantity of each motor size and speed in use by P&G worldwide. They also determined the average cost of electricity, average motor load, average plant operating hours per year, and tax rates. (Most motor suppliers offer similar tools to help companies determine their own cost versus energy savings ratios.)

Next, P&G obtained the purchase price for all of the sizes of motors in various efficiency ratings and multiplied all of the factors to calculate ROI. "We looked at ROI's on a 7-, 10- and 20-year basis, comparing each motor type to another," Reizner says. "We found that energy efficient motors were the best investment for P&G overall, considering purchase price and energy costs. Due to energy savings alone, we calculated an 80% annual ROI for these types of motors."

At present, P&G utilizes energy efficient motors from the smallest fractional horsepower, all the way up to the 2500 horsepower motor. Ahead of the energy game when compared to many, P&G continues to strive for improvement. "Currently, in the area of electrical energy consumption, we are making larger use of variable speed drives on our fan applications," Reizner comments. "In addition to saving energy costs, we have increased reliability and decreased maintenance."

In other words, a closer look at the energy efficiency of your materials handling equipment can easily lead to other benefits.