In the industrial sector of the USA, motor-driven loads account for about 60% of all the electrical energy used. In the commercial sector, motors account for almost half of all electricity used. Therefore, selection of an efficient electric motor, either as a new purchase or as a replacement for a failed unit, is critical to both energy and dollar savings.
With load cycles typical of an industrial or commercial application, the first cost of a motor may represent only one or two percent of the full cost of ownership. The electricity used to run the motor can run 10 to 20 times the purchase price each year.
Defining "Premium" Efficiency
The Consortium for Energy Efficiency (CEE) and the National Electrical Manufacturers Association (NEMA) have agreed on a joint specification defining a "premium" efficiency motor. Motors meeting this minimum specification are eligible to carry the NEMA Premium ®, designation and exceed the EPAct minimum efficiencies in each covered category. The NEMA Premium motors program covers single-speed, polyphase, 1-500 hp, and 2-, 4- or 6-pole squirrel cage induction, NEMA design A or B, continuous rated motors. CDA has publications available that compare NEMA Premium efficiencies to EPAct minimums.
The examples on the reverse side compare standard EPAct minimum-efficiency motors to comparable NEMA Premium models, operating at 75% of nameplate load, along with the annual savings and payback times. The lower operating costs using NEMA Premium motors may result in greater value and save energy expenses. Results that can go right to the bottom line! It pays to do the math, and there are tools available to help you do just that. 1
Having a Plan
There are three occasions for purchasing a new motor: when an existing motor has not failed, but may be inefficient; when an existing motor fails; and when installing a new process or piece of equipment. Each of these calls for an evaluation of the most cost-effective choice for the particular circumstance.
Many large companies, operating hundreds or thousands of motors, have found it prudent to have a motor repair/replacement plan. Using tools such as MotorMaster+, described below, these companies have examined their motor population in advance and have determined which motors may warrant replacement, even if they are still operating. This may be especially true of older motors, whose efficiencies may be so low that energy savings alone can pay for the replacement in a short time.
The second occasion occurs when a motor fails in service. Since production may be down, the need for a replacement is immediate and the result is frequently a fast, but uneconomical, on-the-spot decision. By having a motor plan in place, each motor has been pre-evaluated based on energy use and efficiency, and the proper course of action arranged in advance. One large wood products company has screened all their motors, and determined in advance that all motors 50 hp or less are to be replaced when they fail with NEMA Premium, while failed motors above 50 hp are to be evaluated, based on age, number of times repaired, efficiency, etc. This way, the individual plant operator does not have to make a spot decision in a crisis; the evaluation has already been performed. The motor vendor stocks premium-efficiency inventory for fast replacement.
Remember that when an older motor of poor efficiency fails, it can never be rewound to exceed its original efficiency.
The final case is choosing the proper motor for a new application, including motors that are part of a larger piece of equipment. This circumstance is the ideal time to evaluate the savings and payback times offered by a new motor of NEMA Premium efficiency, or better. Tools such as MotorMaster+ can help in this evaluation. Most motor manufacturers, and better motor shops, can assist with this decision.
And when purchasing new OEM equipment, ask prospective suppliers to submit their bids based on premium-efficiency motors and components. The environment will benefit, along with your bottom line.
Rebates
Some electric utilities or public agencies offer rebates toward the purchase of high-efficiency motors.
Call your local utility to determine if your prospective motor purchase qualifies for a rebate.
Useful Tools for Motor Purchasing Decisions
As an Allied Partner of the Department of Energy's Motor Challenge Program, CDA can provide you with a copy of DOE's MotorMaster+ software 2 as well as other publications on energy efficiency topics. The MotorMaster+ software contains technical and pricing information on thousands of integral-horsepower motors, efficiency data, and can assist with life-cycle cost comparisons, rewind vs. replace decisions, and much more.
CDA can also send you a MotorSlide Calculator™, a slide rule tool to quickly determine the approximate operating cost of a specific motor or the annual savings possible when choosing a more efficient motor over a less efficient model of comparable size. The calculator also has a built-in table of NEMA Premium nominal efficiencies versus EPAct minimums, for quick reference.
Higher-Efficiency Motors Mean Big Savings and Better Reliability
| Example One 50 hp, 1800 rpm, 460 V |
Example Two 25 hp, 1800 rpm, 460 V |
|||
|---|---|---|---|---|
| EPAct Standard | NEMA Premium | EPAct Standard | NEMA Premium | |
| Full Load Efficiency | 93.1* | 94.5 | 92.4 | 93.6 |
| Efficiency (at 75% load) | 93.6 | 95.1 | 93.1 | 94.1 |
| Demand Reduction (at 75% load) | 0.47 kW | 0.16 kW | ||
| Meets EPAct? | yes | yes | yes | yes |
| Incremental Motor Cost | $176 | $96 | ||
| Energy Savings at 75% Load (6000 hrs/year) | 2,829 kWh/y | 958 kWh/y | ||
| *EPAct minimum efficiency for this size motor is 93.0%. The model chosen for comparison has an efficiency of 93.1%. | ||||
| Example Three 10 hp, 1800 rpm, 460 V |
Example Four 5 hp, 1800 rpm, 460 V |
|||
|---|---|---|---|---|
| EPAct Standard | NEMA Premium | EPAct Standard | NEMA Premium | |
| Full Load Efficiency | 89.5 | 91.7 | 87.5 | 89.5 |
| Efficiency (at 75% load) | 90.8 | 92.6 | 88.2 | 90.3 |
| Demand Reduction (at 75% load) | 0.12 kW | 0.07kW | ||
| Meets EPAct? | yes | yes | yes | yes |
| Incremental Motor Cost | $60 | $27 | ||
| Energy Savings at 75% Load (6000 hrs/year) | 719k Wh/y |
443 kWh/y | ||
Benefits of using the higher-efficiency motor:
| Duty Cycle | Energy Cost, $/kWh | Annual Savings | Payback, in Months |
|---|---|---|---|
| 4,000 hrs/Year | $0.075 | $141 | 15 |
| 6,000 hrs/Year | $0.075 | $212 | 10 |
| 8,000 hrs/Year | $0.075 | $283 | 7 |
| 4,000 hrs/Year | $0.09 | $170 | 12 |
| 6,000 hrs/Year | $0.09 | $255 | 8 |
| 8,000 hrs/Year | $0.09 | $339 | 6 |
| Duty Cycle | Energy Cost, $/kWh | Annual Savings | Payback, in Months |
|---|---|---|---|
| 4,000 hrs/Year | $0.075 | $48 | 24 |
| 6,000 hrs/Year | $0.075 | $72 | 16 |
| 8,000 hrs/Year | $0.075 | $96 | 12 |
| 4,000 hrs/Year | $0.09 | $57 | 20 |
| 6,000 hrs/Year | $0.09 | $86 | 13 |
| 8,000 hrs/Year | $0.09 | $115 | 10 |
| Duty Cycle | Energy Cost, $/kWh | Annual Savings | Payback, in Months |
|---|---|---|---|
| 4,000 hrs/Year | $0.075 | $36 | 20 |
| 6,000 hrs/Year | $0.075 | $54 | 13 |
| 8,000 hrs/Year | $0.075 | $72 | 10 |
| 4,000 hrs/Year | $0.09 | $43 | 17 |
| 6,000 hrs/Year | $0.09 | $65 | 11 |
| 8,000 hrs/Year | $0.09 | $86 | 8 |
| Duty Cycle | Energy Cost, $/kWh | Annual Savings | Payback, in Months |
|---|---|---|---|
| 4,000 hrs/Year | $0.075 | $22 | 15 |
| 6,000 hrs/Year | $0.075 | $33 | 10 |
| 8,000 hrs/Year | $0.075 | $44 | 7 |
| 4,000 hrs/Year | $0.09 | $27 | 12 |
| 6,000 hrs/Year | $0.09 | $40 | 8 |
| 8,000 hrs/Year | $0.09 | $53 | 6 |
Many manufacturers have product lines that exceed NEMA Premium ® efficiency levels, so look for the most economical choice that will suit your task. Rewinding a failed pre-EPAct motor will miss an important savings opportunity. In addition, potential savings may greatly exceed those shown here.
The motors above all meet the Energy Policy Act (EPAct) and Energy Independence and Security Act (EISA) minimums. Savings do not include possible reductions in demand charges or utility rebates. All examples are derived from MotorMaster+ software that is available by request at AMO Tools Help Desk.
Premium-Efficiency motors are those as defined in the NEMA Premium ® Efficiency Motor Program. Please call your electricity supplier to learn about any available efficiency rebate programs.
References
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Different motors of the same nominal horsepower can have varying starting current, torque curves, speeds, and other variables. Selection of a particular motor for an intended task must take all engineering parameters into account. - MotorMaster+ is a publication of the US Department of Energy, and includes data on integral horsepower motors. Typical residential size motors are not included, and this offer is intended for industrial and commercial purchasers, engineers, and electrical contractors.