Saving with more efficient motors

THE Australian introduction of Minimum Energy Performance Standards (MEPS) for electric squirrel-cage induction motors is, in some respects, old news.

THE Australian introduction of Minimum Energy Performance Standards (MEPS) for electric squirrel-cage induction motors is, in some respects, old news.

This Australian Greenhouse Office (AGO) initiative, which was first legislated in October 2001, represented an important first step for Australia. Since this inauguration, both the Australian and international MEPS scene have been anything but stagnant.

In April 2006, the two Australian efficiency levels were ratcheted up a notch. A revised edition of the standard (AS/NZS1359.5:2004) saw the previous ‘high efficiency’ (HE) levels specified in AS/NZS 1359.5:2000 effectively become the new MEPS levels (often referred to as ‘MEPS2′), coupled with an entirely new, and more-stringent HE level.

This new HE level targeted a further 15% reduction in losses on the 2001 MEPS ‘high efficiency’ levels. In the long-term, these new standards should reduce total Australian energy consumption by 8900GWH, and cut the country’s greenhouse emissions by 7.7MT [1].

Internationally, there are moves to harmonise the disparate electric motor efficiency standards, such as those of the US and Europe, into common International Electrotechnical Commission (IEC) standards over the coming years. Yet research and development work is already being undertaken by global industry bodies that go beyond the bounds of the electric motor itself. This work is exploring the domain of what is often described as ‘total drive efficiency’.

Beyond MEPS

While current MEPS-compliant electric motors realise a 2-3% efficiency improvement over old ‘standard’ efficiency motors, it is valuable to see how such figures sit within the context of a total drive train efficiency upgrade. While MEPS compliance is vital, it is equally vital to look beyond the motor itself and consider the drive train as a whole.

Originally, the drive train comprised a MEPS-compliant motor, coupled to the head-drive via a vee-belt, worm-gear unit and chain/sprocket drive. The inherent efficiencies across the three-stage drive train resulted in an overall drive efficiency of 60.8%.

A high efficiency helical-bevel gear unit, close coupled to the MEPS-compliant motor, replaced this inefficient drive train. The resultant efficiency of this replacement assembly was 88%.

Most important are the energy savings achieved as a result of this almost 30% efficiency improvement. Based on an energy cost of $0.10/kWh, the new installation saves almost A$2500 per annum in reduced energy costs. The estimated return on investment (ROI) in this particular scenario is around two to three years. There would also be a significant reduction in greenhouse gas emissions.

It should be noted that the average life expectancy of a typical induction motor can be around 20 years [2]. As a result, the energy savings determined here offer commercial benefits well beyond the ROI period.

A further consideration is the application of frequency inverter technology, used in conjunction with high efficiency electro-mechanical systems.

Studies have shown that pumped flow regulation systems can achieve significant efficiency improvements by replacing traditional ‘single-speed pump plus throttle valve’ technology with a pump driven by a variable speed inverter [3]. This efficiency improvement can reduce energy consumption to a fraction of what would be required if the pump speed regulation is coupled with high efficiency motors, pumps, couplings and piping systems.

References:

[1] Regulatory impact Statement for Minimum Energy Performance Standards for Electric Motors, Syneca Consulting, December 2003.

[2] EUP Lot 11 Motors, Report No. 3, Analysis of existing technical and market information, ISR- University of Coimbra, Aníbal T. de Almeida et al, April 2007.

[3] Motor Challenge – Energy Efficient Motor Driven Systems, European Copper Institute, April 2004

*Frank Cerra is SEW-Eurodrive’s Engineering Manager.