More energy-efficiency awareness needed
Frank J. Bartos, P.E., Control Engineering -- Control Engineering, 8/1/2007
Engineers have an implicit goal to design and build efficient equipment, but cost tradeoffs affect the process of how efficient to make products or systems. While not a new consideration, cost of energy to run equipment has grown to be a major issue for users and producers of automation systems.
Optimizing energy efficiency requires a “system view,” including the drive and gear reducer. However, electric motors are a prime target for efficiency improvement due to their huge installed numbers, heavy energy consumption, and long operating life.
The U.S. Energy Policy and Conservation Act (EPAct) of 1992—effective Oct. 1997—was a global first that set into law minimum nominal efficiencies for general-purpose 3-phase motors of 1-200 hp size sold or imported into the U.S. EPAct applies to open (ODP) and enclosed (TEFC) foot-mounted 2, 4, and 6-pole motors running on 230/460 V supply. Canada, Australia, and New Zealand have adopted similar mandatory rules, but numerous other nations have yet to move such initiatives beyond voluntary status. Following EPAct, Europe adopted a classification and labeling agreement (not law) for nominal efficiency of 2 and 4-pole motors in the 1.1-90 kW (1.5-120 hp) range, operating at 400 V and 50 Hz. This agreement defines three efficiency zones, of which Eff1 (high efficiency) and Eff2 (improved efficiency) are noteworthy. Eff1 ranges upward from EPAct values; Eff2 ranges from below EPAct values to about EPAct equivalents.
In mid-2001, the energy-efficient (EE) motor regulation bar was raised by harmonizing standards of the National Electrical Manufacturing Association (NEMA) and the Consortium for Energy Efficiency into a trademarked specification known as “NEMA Premium.” It expanded coverage of ODP and TEFC motors in the 1-500 hp range (2, 4, and 6-pole) at inputs up to 600 V. NEMA Premium also expanded its scope to medium-voltage 250-500 hp, special-purpose motors with inputs up to 5 kV and mountings not covered in EPAct. These efficiencies are substantially higher than EPAct—topping out at 96.2% for the 500 hp low-voltage model.
Market appeal of NEMA Premium (NP) motors has widened by inclusion of 50-Hz motors in NEMA MG 1 standard as of April 2007, complementing 60-Hz NP motors. Meanwhile, the new energy bill working its way through the U.S. Congress is expected to include these higher efficiency motor specs and other NEMA recommendations, to take effect 36 months from the date of enactment, says NEMA.
Motors meeting existing standards are available worldwide. This includes efficiencies higher than NEMA Premium made possible by developments like die-cast copper rotor bars. SEW-Eurodrive and Siemens offer copper rotor motors. Baldor Electric believes its innovations enable building “above NEMA efficiency” motors with aluminum rotors, while eliminating the higher cost of copper and required tooling.
Lifecycle cost is key
As previously noted in Control Engineering, there appears to be less than full awareness of savings offered by EE motors in appropriate applications. An unusual source of agreement comes from former U.N. Secretary-General Kofi Annan, who said at a 2006 climate-change conference, “… it’s baffling that readily available, energy-efficient technologies and know-how are not used more often—an approach that produces [among others] more electricity and more output.”
EE motors contain more “active” electric materials, thus command a 10-30% initial cost premium, which in many applications can be rapidly amortized by energy cost savings. In fact up to 97% of motor lifetime operating cost is attributed to electric energy charges. However, higher initial cost is too often a turn-off for the potential buyer. Added awareness is needed to pinpoint the hidden cost of inefficiency.
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