This clearly indicates that total lifecycle costs are the right way to evaluate the replacement of a motor and its selection. Also, there are several governmental regulations to consider in the selection process, as well as opportunities for tax credits and utility rebates that may affect your decision. With this in mind, let’s take a look at the options you have for replacing a motor, whether it’s serviceable, sick or failed.
Choose the Right Efficiency
If a high-efficiency motor (EPAct) is still in serviceable condition and was installed before December 2010, when the E.I.S.A Federal Legislation came into effect, you might choose to rewind it rather than replace it. In general, rewinding a motor costs about 40% of the purchase price of a new unit — a reasonable savings.
However, the Department of Energy (DOE) indicates that even best-practice rewinding brings a penalty in operating efficiency. The rewinding process raises the amount of energy consumed and, therefore, the motor’s operating cost during its remaining life. The DOE suggests that motors smaller than 70 hp should be replaced, not rewound.
If a motor is beyond repair and rewinding, you have several replacement options to consider. Because E.I.S.A grandfathered in definite-purpose motors (motors that have been built for a specific application such as a pump or a compressor) that were installed before 2010, you might be able to replace your motor with a new custom-built standard efficiency unit. In this case, you’d expect the same ongoing energy cost profile during the next two or more decades. Remember, however, that electricity costs are rising and this trend is expected to continue.
As an alternative, you could consider a NEMA Premium® efficiency motor that meets the current EISA efficiency standards.
Their cost premium of less than 10% compared to high-efficiency motors is offset by their 1% to 4% better operating efficiency within a couple of months (Table 1). In fact, the reduction in energy usage, on average, will pay for the entire motor within a few years or even months and continue to deliver additional savings during the two decades or more of useful life you might expect.
|Size (hp)||EPAct||NEMA Premium|
Table 1. Average efficiency (at 75% load) for various sizes of standard efficiency, EPAct and NEMA Premium® motors
You should always consider the option of replacing a motor rather than rewinding it. In order to make this decision easier, you can use this “Return on Investment” calculator from WEG.
If you are truly concerned about energy savings, and you operate a factory with a good number of electric motors, and if several of your applications are variable torque such as pumps and fans, there are even more options. You might want to consider installing variable frequency drives for those applications that do not need to be running at full speed all the time. Some motor lines use new technologies with permanent magnets that deliver efficiencies close to 100% and are capable of direct-on-line starts without the need of a special starter or drive.
Utilities and state and federal energy regulators have several programs that make these alternatives even more attractive. Rebates, tax incentives and cost-sharing programs vary by state and municipality, but all of them can be substantial, significantly reducing the payback period for energy-efficient motors.
Calculate the Savings
Calculating the potential savings from replacing a standard efficiency motor with a NEMA Premium unit is straightforward:
Savings = 0.746 x hp x hr x rt x (1/Eo – 1/En)
hp = motor size (in horsepower)
hr = operating hours per year
rt = utility rate in $/kilowatt-hour
Eo = efficiency of the existing motor (decimal fraction)
En = efficiency of the replacement motor (decimal fraction)
Replacing a 100 hp standard efficiency motor (Eo = 0.936) that runs 8,000 hours per year with a 100-hp NEMA Premium® motor (En = 0.95) will result in an annual energy savings of more than $750 when a kilowatt-hour costs $0.08.
Savings = 0.746 x 100 x 8,000 x 0.08 (1/0.936 – 1/0.95)
= 47,744 x (1.06838 – 1.05263)
= 47,744 x (0.01575)
= $751.97 per year
Clearly, this would help cover the motor’s cost premium in a few months and the entire cost in a few years, while producing significant savings in lifetime costs beyond that.
Nevertheless, simply replacing a standard efficiency motor with an alternative doesn’t guarantee reduced electricity bills. Factors such as duty cycle, motor oversizing, unbalanced phases and other application variables can reduce the potential savings. Always consult with your motor OEM or distributor to determine the exact savings to expect.
Consider the Future
To help maximize the economic benefit from your motor-replacement choice, the Northwest Energy Efficiency Alliance (NEEA), a nonprofit organization dedicated to making energy efficiency a core business value, suggests establishing a continuous energy improvement program.
Further, DOE estimates indicate that switching from standard efficiency motors to NEMA Premium® Efficiency motors could help save our economy more than $10 billion annually and reduce carbon emissions by nearly 80 million metric tons — the carbon equivalent of taking 16 million vehicles off the road. That’s not only good business — it can make a real environmental difference.
* The remaining 1% is made up of other expenses such as rewinds, re-greasing, etc.
Grainger offers a wide variety of NEMA Premium® motors including those manufactured by WEG Electric Corporation. Several online calculators are available to help determine anticipated cost savings when choosing high efficiency motors.
For more information, visit grainger.com/green