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Countdown for inefficient fan systems in the EU

14 August, 2013

New technologies

Permanent magnet motors are synchronous motors where the rotor windings and brushes normally used for excitation have been replaced by permanent magnets, creating a constant flux in the air gap. The motor is energised directly on the stator using a variable-speed drive (VSD).

The synchronous reluctance motor has a rotor without windings. As a result, there are no rotor losses and the rotor temperature remains low. As well as higher energy efficiency, this also gives higher power density that could double the output from a given frame size, potentially increasing the flow without needing to modify the system mechanically for a larger motor. This motor type is also energised by a VSD.

Both of these technologies achieve superior efficiencies by no longer producing the rotor loss, which is inherent with an induction motor.

VSDs are also very useful in combination with traditional motor technologies. A VSD can, for instance, be used to cover the speed range between the fixed speeds of motors with two, four and six poles and to enable a fan to operate at its best efficiency point. For many fans, the best efficiency does not occur at motor synchronous speed – for example, 1,000 or 1,500 rpm – and using a VSD can achieve this optimum with directly-coupled fans, especially when the manufacturer is selling in both 50Hz and 60Hz markets. The use of variable-speed is also a bonus under the legislation and can help to get a system qualified. 

Installing it right

However, just because a system complies with the ERP directive doesn’t mean it will always be energy-efficient under all circumstances. The end-user is still responsible for ensuring that the system is specified, selected and installed correctly. Frequently, an oversized system is chosen because the extra cost for a slightly larger system seems small in the context. But an improperly sized system will bring additional costs for energy use and maintenance, because an oversized fan may be subject to mechanical stress when working away from its best efficiency point. The user is also responsible for providing ductwork that is sufficiently large and straight to eliminate friction losses and to optimise the complete system. When selecting a fan system, it may be a good idea to take advice from an engineering contractor.

So, while fan manufacturers do their best to provide more efficient designs and motor manufacturers develop new technologies to augment these designs, a huge deal of responsibility still remains with the end-user to ensure that the technology is used to its best effect. The person who is paying the energy bill needs to make an informed choice. 

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