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Keep it in perspective

Despite the impending changes to Energy Related Products (ErP) Directive in January 2015, AC motors are still an efficient option for future projects, says Ian Morehouse

In recent months there has been a great deal of discussion, not least in RAC, surrounding electrically commutated (EC) motors and how they compare with their asynchronous (AC) relatives in fan applications.

Some manufacturers have been quick to dismiss AC as a past product that is no longer relevant in today’s tough energy efficiency targets and EU legislation.

AC motors have a clearly defined future in the fan market. They will not be replaced by EC any time soon and, in many instances, will be the only viable option, especially for high-temperature applications.

The source of this debate is a result of the next stages to the Energy Related Products (ErP) Directive, due in January 2015. For readers who are unaware of the updates, they derive from ErP Regulation EU 640/2009, which came into force in January 2011 and requires IEC-rated motors to have efficiencies higher than IE2 level.

However, from January 2015, motors with a rated output of 7.5kW to 375kW cannot be less efficient than the IE3 level, or, when used in conjunction with a variable speed drive (VSD), must meet an IE2 level.

Also established in 2011 was Regulation (EU) No. 327/2011, which applies to all fans driven, or designed to be driven, by electric motors with an input power of between 0.125kW and 500kW.

This specified minimum combined fan/motor efficiencies for all fan types, regardless of whether they operate as an individual unit or as a component within a device. Again, these levels are set to increase substantially from January 2015.

Not the only option

Why is it that some manufacturers consider EC versions to be the zenith of fan design? Yes, EC motors have the potential for higher efficiencies than AC motors, particularly in the low power range. But intimating they are the only option ignores and neglects other vital aspects of fan design.

Surely computational fluid dynamics (CFD), optimisation of impeller design and careful analysis of every fan component are the first factors to consider when improving fan efficiency?

If the motor is installed in the airstream, its presence will affect airflow and can impact on aerodynamic performance and efficiency.

Simply fitting an EC motor to an existing fan design is not the most effective, long-term approach – especially as the industry will be asked to further improve product efficiencies.

Certainly at Fläkt Woods, we have considered all available avenues in order to improve energy efficiency. One area that has provided huge gains is a holistic design approach, taking into account the interaction between all components in the airstream.

This has delivered fans with very high aerodynamic efficiencies, enabling target combined efficiencies to be easily achieved, even when AOM-rated IE1 or IE2 motors are fitted.

Using IE3 or IE4 motors will give even better results, ensuring there is a wider range of options for specifiers, contractors or suppliers to consider, instead of resorting to more expensive EC alternatives.

The energy-saving potential generated by ErP-compliant AC motors, coupled with efficient fan designs will offer substantial cost savings, as well as attractive payback periods.

This highlights another misunderstanding in the efficiency debate, where in the midst of an EC vs AC discussion, the overall objectives of the ErP legislation are sometimes lost.

There is no doubt that using the latest technology is an important and key aspect of the legislation, but it often masks the overarching objective; using energy efficiently at all stages of the energy chain, in order to reduce final consumption and running costs.

Having already limited the number of compliant fans on the market, the legislative changes in 2015 are likely to remove an additional 20 per cent of products.

Responsibility for improving the efficiency of fan units lies solely with the manufacturer.

Despite some claims by other manufacturers, 2015 will not usher in an EC-dominated fan market. Instead, there will be greater focus on specifying the best product for the application, taking into account the initial capital outlay and the relative payback periods.

Using AC motors, combined with aerodynamically optimised fan design is sure to use less electricity, significantly reduce energy bills and cut carbon emissions for years to come.

So rather than viewing AC technology as a thing of the past, think of it as the ultimate adapter; still relevant in today’s tough energy-driven industry. 

Ian Morehouse is vice-president for Fläkt Woods’ UK fan business

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