In venti­la­tion, air condi­tioning and refrig­er­a­tion appli­ca­tions, designers and oper­a­tors often discover that the fans installed in their equip­ment are noisier or less energy-effi­cient than expected. The condi­tions of instal­la­tion are often to blame, as they can have a nega­tive effect on power consump­tion, air perfor­mance and noise emis­sions. The fan’s impeller, motor, control elec­tronics and housing are opti­mized for energy effi­ciency and noise emis­sion, and the actual condi­tions of instal­la­tion in AHUs should not be neglected.»