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Countdown for inefficient fan systems in the EU

14 August, 2013

Induction motors have losses in the region of 5–15%, depending on size, and belt drives about 5–10%. The fan itself has losses that can be as small as 10%, but may be higher than 50%, depending on the type of fan. So, on the face of it, it would seem that the fan has the greatest potential for improvement.

Choosing the most efficient fan option may not be feasible for several external reasons – space, price and so on – so, although a high-efficiency design is available, it may not be chosen. The system is thus not optimised for best efficiency. In the end, it is the balance of cost versus specification that decides the day.

The issue is similar when it comes to transmissions. A direct-drive fan will always be more efficient than one with belt drive. But sometimes direct drive is not possible – for instance, for reasons of space or if the fan needs to rotate at a different speed from the motor.

This leaves the motor. Over recent decades, the efficiency of electric motors has improved significantly and can help to improve the efficiency of the complete system. For instance, a modern 110kW four-pole motor has 30% lower losses than an equivalent motor from 1980, even though the two motors look similar.

Improving motor efficiency

Motors used in the EU come in three efficiency bands: IE1 for standard efficiency; IE2 for high efficiency; or IE3 for premium efficiency. Since June 2011, only motors in classes IE2 and higher can be sold. From January 2015, only IE3 motors or IE2 motors equipped with variable-speed drives can be sold.

A new class for super-efficient motors, called IE4, has also been introduced. However, the efficiency levels required for this class are not expected to be achievable for smaller fan motors using traditional induction motors, so this class is likely to be exclusive to new motor technologies such as synchronous reluctance and permanent magnet motors.

Higher-efficiency motors cost more to buy because they use more costly materials and production techniques, but the saving in operating costs can offset the initial outlay relatively quickly. At 8,000 operating hours per year, the additional cost of an IE3 motor is paid back in less than two years. Even at a modest 2,000 operating hours per year, the energy saving results in a payback in less than half a typical 15-year lifespan.

At the moment, many fan manufacturers still use IE2 motors, but they are increasingly asking for IE3, and even IE4. IE3 motors are often adequate for systems with large and medium-sized motors, where the efficiency targets can be met with traditional induction motors. In smaller systems, efficiency improvements are more difficult to achieve, so it may be necessary to look at other technologies, such as permanent magnet or switched reluctance motors.

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