The efficiency of any fan varies significantly over the range of its performance curve. Even our high efficiency fans which at their peak achieve total efficiencies of over 90% and static efficiencies of over 86%, if selected on different part of the curve may achieve considerably less.
For a given duty (volume and pressure) it is not uncommon for us to be able to select from over a 100 fans or more. From that selection, the operating total efficiency of the selected fans may range from just over 90% down to 40%, with the static efficiency ranging from about 86% down to 30%
Although any of these fans will meet the required duty, the power required can vary by a factor of 3. As a general rule for a given duty, the smaller fans listed in the selection will result in higher speeds, lower efficiency and therefore higher absorbed power
Smaller fans generally result in lower cost, but that cost may be offset by an increase in a higher motor cost and possibly drive cost if the impellor is not driven by a vee belt.
Direct drive fans (see arrangements No4 / No7 ) result in the lowest final absorbed power since there are no losses encountered in driving the impellor.
As a general rule Belt Driven Fans (see arrangements No1 / No9 / No2) incur an increase in absorbed power of between 7% and 9%.
Using an inverter on any fan also comes with an increase in power of about 5%.
As stated previously, neglecting the whole of life cost may result in a signifcant increase in the energy consumption of the fan.