According to the National Electrical Manufacturers Association (NEMA), electric motors account for nearly 40% of total electricity consumption in the US, especially in the industrial and commercial sectors. Improving motor efficiency across the country represents a significant opportunity to save energy, which is why NEMA released the first version of its Premium Efficiency standard for motors in 2001.
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The US Department of Energy estimated that the program could produce the following economic and environmental benefits during the decade after its launch:
- Saving 5,800 gigawatt-hours of electricity for U.S. homes and businesses.
- Avoid the emission of 80 million tons of carbon, which is equivalent to removing 16 million cars from circulation.
NEMA Premium Efficiency motors exceed the minimum efficiency legally required by the Energy Independence and Security Act of 2007 (EISA), and the program covers motors with the following characteristics:
- Nominal capacity from 1 HP to 500 HP
- Low Voltage Three-Phase Power Supply
- NEMA Project A and B
- General, special and specific use engines
Although engines below 1 HP are not covered by the standard, similar efficiency levels can be achieved with electronically commutated engines (ECM), which are better suited to fractional horsepower applications. ECMs also have built-in speed control, meaning they do not require a variable frequency drive (VFD) to operate below rated speed.
How efficient are NEMA Premium motors?
It is important to note that motor efficiency typically varies depending on wattage and percentage of load, so there is no single efficiency value that applies to all NEMA Premium Efficiency motors. However, NEMA Premium is the highest motor efficiency level in US standards, surpassing NEMA Energy Efficient motors (intermediate level) and NEMA Standard Efficiency motors (low level). In general, efficiency levels increase as engine power increases, as shown in the following NEMA table:
|
HP Engine |
Standard Efficiency (%) |
Energy efficient (%) |
Premium Efficiency (%) |
|
7.5 15 25 50 75 100 |
85.5 86.6 89.3 91.3 91.7 92.3 |
89.5 91.1 92.4 93.2 94.1 94.5 |
91.7 92.4 93.6 94.7 95.4 95.4 |
This table is for engines operating at full load. However, NEMA Premium Efficiency motors can typically operate at high efficiency for all load values above 50%, reaching their peak efficiency at around 80% load.
While the efficiency gains may seem small when upgrading to a higher engine class, consider that the reduction in power loss is significant. To illustrate this, suppose a standard 100 HP motor will be upgraded to a NEMA Premium version.
- The standard motor consumes 80.8 kW, while the NEMA Premium version consumes 78.2 kW.
- A reduction of 2.6 kW may seem small compared to the rated engine power, but it provides a saving of 20,800 kWh, assuming 8,000 hours of use per year.
- With an electricity cost of $0.10/kWh, this translates into annual savings of $2,080.
Motor efficiency gains between classes appear small when viewed as percentages, but the benefits are clear when the percentage gains are translated into kilowatts and energy bill savings.
Recommendations for NEMA Premium Motors
As with any energy efficiency upgrade, it is important to perform a detailed technical and financial assessment before purchasing NEMA Premium Efficiency motors. Consider the following recommendations before proceeding with the purchase:
- NEMA Premium Efficiency motors are an excellent option in new construction where there is already a base cost dedicated to purchasing motors. In these cases, the efficiency gains of a NEMA Premium motor are weighted against its incremental price, not its total price. There are also many cases where replacing an existing engine is financially attractive, but the greatest return on investment is achieved in new installations.
- Upgrading to a NEMA Premium motor yields a greater return on investment when the operating schedule is long. Keep in mind that energy savings are the product of energy savings and hours of operation. Upgrading a 15 HP engine that operates 8,000 hours/year will generate twice as much energy savings as replacing one of the same capacity that only operates 4,000 hours/year.
- Consider that percentage efficiency gains are greater for smaller motors. For example, NEMA estimates an annual savings of $126 when upgrading a 10 HP motor from Energy Efficient to Premium Efficiency, and $278 when upgrading a 100 HP motor, assuming both operate 8,000 hours/year. If a company has to choose between several small engines or a few larger engines due to budget constraints, the return per dollar invested is typically higher for smaller engines. However, an energy audit is recommended, as there are always exceptions.
- Before purchasing NEMA Premium motors, it is recommended that your company review local incentive programs. For example, Con Edison customers who upgrade to NEMA Premium motors in New York City can claim an incentive of $0.16 per kWh saved, which can cover up to 50% of project costs or $1,000,000 , whichever is smaller.
- Extra savings can be achieved by upgrading electric motors located in climate-controlled spaces, which is common in commercial environments. NEMA Premium motors dissipate less heat than motors of the same power and lower efficiency, and this heat is subtracted from the AC equipment load.
Electric motors built to International Electrotechnical Commission (IEC) standards also have efficiency classes comparable to those of NEMA motors. IE1 is equivalent to Standard Efficiency, IE2 is equivalent to NEMA Energy Efficient, and IE3 is equivalent to NEMA Premium Efficiency. The IEC also introduces class IE4, which is typically marketed as “Enhanced NEMA Premium” or “Above NEMA Premium” in the US.
Note that efficiency values are comparable between NEMA and IEC motor classes, but not identical. IEC efficiency classes cover motors from 0.75 kW (slightly above 1 HP) to 375 kW (503 HP), with a nominal voltage of 1,000 V or less. Motors can have 2, 4 or 6 poles and can be designed to operate at 50 Hz or 60 Hz.
Conclusion
NEMA Premium Efficiency motors can yield thousands of dollars in annual savings when deployed in commercial and industrial installations, and even greater savings are available if supplemented with a variable frequency drive (VFD). However, remember that engines must also be suitable for their application to ensure efficient operation and long service life, so professional guidance is highly recommended before any engine upgrades.
