FANS
Retrofit and bio- mimicry inspired fan evolution
Fans should become ever more effi cient and quieter. Initially, the manufacturers only had the effi ciency of the motors in mind and optimised consumption with EC motors. Recently, developers have been using discoveries from nature to make the overall system quieter and more effi cient. Old ventilation systems in particular can be rebuilt quickly and cost-eff ectively to signifi cantly reduce energy consumption and noise. Les Fish of Zhiel-Abegg explains.
T
he vast majority of fans are driven by electrical motors and these have gone through
an evolutionary process where AC motors were initially used almost exclusively, with EC (electronically commutated) motors used more and more of late as a result of their increased effi ciency. In the case of directly-driven fans it is the combination of the effi ciency of the motor and the impeller driven by the motor which determines the effi ciency of the fan assembly. This is represented by the formula:
Direct-Drive Fan Effi ciency = motor effi ciency x impeller effi ciency.
The achievement of maximum fan effi ciency then, relies upon combining the motor having the highest effi ciency with the impeller having the highest effi ciency. Electric motor effi ciencies have increased over recent years through the result of various innovations whereby effi ciency classes for low voltage AC motors were created, these initially being EFF3, EFF2 and EFF1, EFF3 being the lower of the three effi ciencies, EFF1 being the higher. These low voltage motor effi ciency classifi cations were superseded when motor effi ciencies higher than EFF1 were achieved, such that motor effi ciency grades referred to as IE1, IE2, IE3, IE4 and IE5 were introduced, IE1 being the lower effi ciency in the scale, IE5 being the higher effi ciency in the scale. EC motors use permanent magnet technology,
enabling effi ciencies to be achieved which place such motors in the so-called ‘Ultra-Premium Effi ciency Class’ IE5, so the combination of these
motors with the highest effi ciency impellers will result in the highest effi ciency fans. The design of impellers of multiple types has evolved over the years, in pursuit of higher effi ciencies and reduced noise emissions. Biomimicry, from aerodynamics (ornithology), hydrodynamics (marine biology) and biomechanics (trees), in the design of fan impellers has led to surprising advances in their performance, both in terms of effi ciency gains and reduced noise emissions. Examples of such natural world features which have provided inspiration in fan impeller development include: Owls’ Wings: – Owls are renowned for their near silent fl ight, enabling them to fl y very close to their prey without being detected. Owls’ wings have been studied in great detail by scientists, biologists and engineers, the fi ndings being that the owl’s wings feature a number of characteristics which contribute to minimising the noise generated by the wings during fl ight. Their wings have serrations on their leading edge in the form of many small
22 January 2020
www.acr-news.com
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