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Countdown for inefficient fan systems in the EU

14 August, 2013

With the introduction of the EU's ERP directive, fan manufacturers face the challenge of either improving the efficiency of their systems that don’t comply, or seeing them withdrawn from the market. As Frank Griffith, a consultant drives engineer with ABB in the UK, explains, there are technical difficulties in improving the efficiency of impellers and transmissions, so many are looking to use more efficient motors.

The clock is ticking for inefficient fan systems in the European Union. Since January 2013, any new fan systems sold in the EU have had to comply with the Energy Related Product (ERP) directive, a set of mandatory efficiency levels that apply to the whole fan system, from the input of electricity to the output of air flow. The mandatory efficiency values vary with the type and size of the fans. From January 2015, the regulations will be tightened further.

The directive will force providers to improve the efficiency of non-compliant systems, or take them off the market. For fan manufacturers, this means going through their product ranges to see what can be done. It’s simply a question of measuring, make modifications, measure and try again.

Not so long ago, users of fan systems would look to the efficiency of the individual components in the fan system to get the best value. Today, they are more inclined to look at the total system efficiency, an approach that is encouraged by the new legislation. 

This is not to say that the efficiency of individual components is irrelevant. The efficiency of the motor, the impeller and the drive system are essentially the variables that the fan manufacturer has to work with. But to optimise the system’s performance for energy efficiency, it is important that these components are correctly dimensioned in relation to each other. It is also essential that the fan system itself is selected and installed correctly. In this respect, a great deal of responsibility still rests with the end-user to provide correct and relevant information.

In some categories of fan systems, meeting the efficiency target is fairly straightforward for the fan manufacturers, while for others, it is more of a challenge. In particular, small fan systems have turned out to be problematic and for some fan types, with poor aerodynamic properties, it may be necessary to re-design the system using a larger fan or a higher speed. This could mean that the system might generate more noise, or need more installation space. These are trade-offs that should come down on the side of energy efficiency.

Counting the losses

When optimising a fan system, there are only a few components to work with – the motor, the transmission and the fan itself. In case of direct-drive fans, the transmission is eliminated, which leaves only two components to work with.

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.

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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