R. Neal Elliott, Ph.D., P.E.
February 2001
Report Number IE013

EXECUTIVE SUMMARY

Background

Over the last decade and a half, energy efficiency advocates have achieved significant success working with regulators and equipment manufacturers to transform the market for integral-horsepower (hp), polyphase motors—the workhorses of industry. Research has indicated that these motors account for a significant share of motor electricity consumption. We have a good understanding of the efficiency of these motors and how they are used in commercial and industrial applications. However, fractional motors (those with output requirements of less than one horsepower) substantially outnumber these integral-horsepower motor. These motors are produced in both single and polyphase configurations, and are ubiquitous in commercial and industrial applications, from small pumps and fans to compressors and conveyors. Our knowledge of the efficiency of these motors and their applications is much more limited than for their larger siblings. Studies have hinted that the energy consumption in this sector is huge, and that the opportunities for efficiency improvements are much larger than with larger motors. For example, a survey of reported efficiency levels in manufacturers' catalogs indicated that efficiencies range from less than 50% to over 80% for 0.5 and 0.75 hp polyphase motors. No testing data was available to corroborate these reported numbers, so Southern California Edison commissioned testing of the most efficient fractional polyphase motors. This data will be used to support the setting of incentive levels for these motors for the SCE Next Step premium efficiency motor program.

Testing

Advanced Energy's Industrial Energy Laboratory's (IEL) motor testing laboratory conducted the testing. This facility, located in Raleigh, North Carolina, is the preeminent independent motor test facility in the United States. Eight of the most efficient 0.5 hp models and 11 of the most efficient 0.75 hp models available from major manufacturers were selected for testing. ACEEE and IEL developed a testing methodology derived from the Institute of Electrical and Electronics Engineers (IEEE) Standard 112 Test Method (b). The full-load efficiency for each motor model was determined following a heat run. All but five motors exceeded the guaranteed minimum efficiency level corresponding to the nameplate efficiency. In addition, a sample of five models for five of the 0.75 hp motors were tested without heat run to assess variation in efficiency within a model. The motors from all five manufacturers had a reasonable tight variation in efficiency within the sample.

Discussion

This testing and the Southern California Edison efficiency program that it supports represent the first venture into fractional motors by the energy community since the Canadian work in the early 1990s (McKay 1992). Results indicate that efficiency opportunities in the program are being realized in the field. The manufacturing processes for these motors appear to be sufficiently uniform resulting in limited variation in efficiency between samples. The reliability of the nameplate information varies by manufacturer, possibly due to the use of different automated efficiency testing methods by different manufacturers. All the measured efficiency values fall below the nominal values. If this trend extends to all of this class of product, as anticipated, then the "actual" efficiency will be offset from the nameplate values by a given amount for each manufacturer's product.

As noted earlier, it is difficult to accurately measure the efficiency of small motors, and the procedure used by Advanced Energy extended the IEEE 112 Method (b) beyond its proven range, so the efficiency levels should be taken with some degree of uncertainty. With experience and appropriate equipment, the 112 (b) test should work. The efficiency values of all motors fell at or below the mean for the nameplates, which might indicate that the test procedure produces values with a slight negative bias. However, consistent patterns did emerge from the testing.

While 0.5 and 0.75 hp three-phase motors are not covered under Section 12 of NEMA MG-1, the test results for most manufacturers indicated that the measured efficiency falls within allowable variation. Several manufacturers test values fell very close to the nameplate mean. However, two manufacturers' motors showed a pattern of test efficiency values substantially below their nameplate. One, the manufacturer with the highest nameplate efficiency, sent a mixed message to the SCE program. Their 0.75 hp motors have by far the highest nameplate efficiencies. While the nameplate efficiency levels appear optimistic, they were the most efficient motors tested during this analysis.

From this analysis we can conclude that significant differences exists in the efficiency level for fractional polyphase motors, and that the savings from the more efficient products would result in significant energy savings in applications with high operating hours. For most motors tested, the nameplate or catalog efficiency represents a good indicator for the actual motor efficiency. However, it does appear that these numbers may be optimistic compared to those using the 112 (b) test method.

Fractional motors are an important sector of the motor market that has received limited attention. This work only represents a first step into this area and needs to be followed up with further testing, complimented by market research to understand how these motors reach the end-user and how they are used in the field. Motor manufacturers mirror the lack of attention to this sector by the energy efficiency community. Manufacturers have not expended much effort on improving the efficiency of this class of product until now because there has been no market demand for energy-efficient products. If the energy efficiency community focuses attention on this area, manufacturer response is likely to as positive as the response to the integral motor efficiency programs.