How green is your motor?

By John Malinowski, Product Manager AC & DC Motors, Baldor Electric Co., Fort Smith, Ark. December 1, 2008

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With today’s rising gasoline prices, people are looking more closely at fuel efficiency (measured in miles/gallon) than in the past.

Great deals are available for full-size trucks. In Arkansas, for example, Dodge Ram Hemi four-doors are available for $18,995, a price lower than for a much smaller Honda Civic Hybrid ($22,600). The larger pickup has more room for five people, plus it can easily carry a payload or tow a trailer. But most folks just use the truck to commute to work.

Let’s look at the lifecycle of these vehicles, starting with the operating costs for 15,000 miles of highway driving. The U.S. Environmental Protection Agency rates the pickup at 17 mpg, so 15,000 miles requires 882 gallons. At $2.50 per gallon, that’s a total of $2,206 annually and $11,025 for five years. The hybrid’s EPA rating is 45 mpg, using only 333 gallons for 15,000 miles, costing $834 a year and $4,170 for five years.

Comparing these two, the fuel savings for the hybrid car is $6,860 for the five-year period. With city ratings of 13 mpg for the pickup and 40 mpg for the Civic, the savings triple. Plus there is a tax incentive of $525 to $2,100 for the hybrid, so the payback for the Civic’s higher purchase price would happen in the first year. Also, the resale value of the Civic will be much higher than that for the truck at the end of the five years. This simple example of lifecycle cost illustrates why truck and SUV plants are closing.

We can take this example into the commercial and industrial sector. The U.S. Dept. of Energy says that electric motor-driven systems consume two-thirds of all electricity consumed by industry. By practicing better management and using the best practices available today, electric consumption can be reduced by nearly one third.

Premium motors

The Energy Policy Act of 1992 (EPAct) requires that general-purpose motors sold after October 1997 meet certain minimum efficiency requirements defined by National Electrical Manufacturers Assn . (NEMA) MG 1 Table 12-11. Motors with higher efficiencies are called NEMA Premium efficient motors. NEMA defines NEMA Premium motors in its MG 1 standard in tables 12-12 and 12-13. They are available in 1 to 500 hp for voltages of 600 V and less, and 250 to 500 hp for 2,300/4,000 V; speeds are 3,600, 1,800, and 1,200 rpm. There is no industry standard for fractional horsepower NEMA Premium motors with higher than standard efficiencies are available for fractional and two-digit frame sizes.

The purchase price of an electric motor is only about 2% of its cost, so a motor with higher efficiency will pay back its higher first cost. Electric motors have an average life of 28 years. Figure 1 illustrates a typical lifecycle cost for an industrial motor.

When upgrading to NEMA Premium motors, you may take the opportunity to add features to the motor to make it more robust and eliminate downtime. More than 60% of all motor failures are a result of bearing failure. Selecting motors with better enclosures will protect bearings from contamination and prevent failure. Bearing selection for coupled or belted load will do the same.

Many companies use NEMA Premium efficient severe-duty motors meeting IEEE 841-2001 standards that were developed for the petrochemical industry. These cast iron motors have many features to keep contaminants from entering the bearings, offer precision balancing and certified test data, and typically are supplied with a five-year warranty. The food processing industry is switching to all-stainless motors that are designed to be sanitized while keeping water from entering, and are built to NEMA Premium efficiency standards. A wide variety of motors designed for HVAC and pump applications also are available for retrofitting into commercial buildings.

Electric motors

Table 1 illustrates the operating costs for a typical HVAC or pump motor operating continuously with an electricity cost of $0.10 per kWh. It compares the operating costs of the average efficiency for a 20 hp motor from the 1998 DOE Industrial Assessment Survey to EPAct and NEMA Premium efficient motors. At the end of 20 years, the premium motor will save $13,960 in electricity at today’s electric rate. We expect the savings to be much higher as utilities continue to adjust their rates.

Companies establishing green policies should consider electric motors as the keystone of their programs because the motors use so little of the company’s total electricity. Energy Star has a Green Buildings Program that allows buildings to be certified energy-efficient, which usually results in a higher building value.

Only 11% of all companies have written motor specifications, only 12% of facilities have written motor rewind specifications, and 24% of facilities have not yet addressed energy. Yet more than 90% of motor decisions are made at the facility level.

If motors are upgraded to NEMA Premium efficiency only on failure, it may take 18 to 20 years for complete replacement, according to the DOE. Companies should plan motor replacements before motors fail so the correct motor for the application is available. A plant survey should be conducted and each motor marked with instructions on what to do upon failure. Data collected from the survey should include motor voltage, horsepower, speed, efficiency, hours of operation, mounting type, and configuration of the motor. Companies can enter this data into software programs that analyze and calculate the potential savings when upgrading to NEMA Premium motors. These programs also show payback time and can handle offsets from motor repair or rebates.

Another way to maximize energy savings is by using NEMA Premium motors with an adjustable speed control for pumps, fans, and other variable torque loads. Instead of adjusting fan flow with a damper, the motor speed is adjusted by an inverter control, which changes the voltage and frequency input to the motor, changing the motor speed.

These variable torque loads follow the affinity rule that says when the speed is changed, the load changes by the cube of the speed change. So, a fan operated at half speed only requires 12.5% of the energy to operate it, rather than run at full speed with a damper. The return on capital for upgrading to an adjustable speed drive on such an application may be only a few months. These drives easily can be integrated into commercial building control systems.

In many parts of the country, electric utilities offer rebates for premium motor upgrades that usually offset the additional cost of premium motors over EPAct designs. Accelerated depreciation tax incentives are available from the government. Many of these programs also support the adoption of adjustable speed drives. Commercial building owners may benefit from federal tax deductions for certain energy-efficient upgrades.

20 hp 4-pole operating costs DOE average efficiency motor EPAct high-efficiency motor NEMA Premium efficient motor
Efficiency 88.6% 91.7% 93.0%
Electrical cost per year $14,752 $14,253 $14,054

Help with energy conservation and best practices is available from the U.S. Dept. of Energy Industrial Technology Program at its “Save Energy Now” Web site. The EPA’s Energy Star program also is a source for assistance, enabling a company to partner and network with other companies on their successes. Motor Decisions Matter offers assistance in motor management. Motor and drive manufacturers, electric motor service centers, and power transmission distributors all can supply assistance. Companies can also contact local electricity suppliers and state energy offices for details on programs in their area.

Consumption of electricity is a cost that can be controlled and managed.

Author Information
Malinowski has experience in industrial motor applications. He is an IEEE Senior Member and is a member of the IEEE Industry Application Society. He is Baldor’s representative to the NEMA Premium Efficiency Motor Program, the Motor Decisions Matter program, Energy Star Partners, and Standards for Energy Efficiency of Electric Motors in Europe.