How to reduce the noise of a fan?

This question is frequently asked in relation to the limitation of noise exposure of employees in factories, and in some cases also, in relation to the protection of residents, against noise pollution due to equipment or facilities.

This is why, depending on the context, the architect, the designer, the engineer working for a Technical Studies Office (TOS) or the builder of a construction, but also the installer of an equipment, the Hygiene Safety Environment (HSE) manager of an industrial site is at the origin of the questioning, when it is not the trustee of a condominium.

Indeed, the noise emissions of a fan (aka extractor, blower), noisy equipment by nature, are often able to create disorders when it is installed in an aeraulic network (e.g. ventilation system, various processes) or when it is integrated into an equipment used to transport air (pure, or mixed with other gases, or even containing particles) or for a cooling process (e.g. air condenser, cooling tower).

How to reduce fan noise depends on the location of the noise source in question.

Because when the noise emissions of a fan are problematic, it is generally illustrated by exceeding noise limits (sometimes: not only because of high values of the sound pressure level at a specified location, but also because of a marked tone, the consequence of which is the perception of an undesirable whistling sound):

  • near the casing (i.e. the enveloppe) of the fan: it is then necessary to consider, depending on the context, the lagging of the fan wheel (if it is centrifugal) or else (in particular: if it is an axial fan) an enclosure (which must then itself be equipped with a ventilation system to avoid overheating) by means of industrial soundproofing panels whose constitution and thickness must be selected according to the targeted acoustic objective (in general, steel panels, 60 to 120 mm thick, with rock wool or sufficiently dense polyester wool insulation are appropriate); sealing around the suction and discharge ducts (to limit the propagation of sound) requires special constructive arrangements, just like the other openings (cable and duct penetrations), and also around the easily removable panels or else doors that maintenance constraints may make necessary
  • suction or discharge: it is then useful to consider silencers whose noise attenuation principle (by dissipation, by reaction, by resonance), dimensions, internal parts (e.g. airways, lining sound absorbing system) must be defined not only according to the targeted acoustic objective, but also according to other technical imperatives: frequency distribution of the acoustic pressure level of the fan, total admissible pressure loss, sensitivity to physico-chemical aggressions for the different possible materials, constraints linked to the size (it is not uncommon for a silencer to be installed in an existing chimney, the casing of which then serves as an envelope for the internal parts of the silencers e.g. the absorbing splitters), the weight, the wind resistance (it is common for silencers to be installed on building roofs with limited support possibilities (sometimes with glass or fiber cement roof)

On-site measurements, acoustic and aeraulic performance simulations, impact calculations, definition and marketing, with or without on-site installation: ITS knows how to reduce fan noise, whatever the context.

The applications are varied, and depending on the case, the diameters of the fans are counted in decimeters or meters: ventilation and air conditioning systems, but also: paint booths, suction networks, draft fans, air condensers and air coolers, not forgetting the fans coupled to the engines of the generator sets, and the larger fans: those of the wind tunnels (aeroacoustic or not) and of cooling towers.

How to reduce fan noise, by endeavoring to offer technically efficient, guaranteed and affordable solutions: this is the problem that ITS human resources succesfully faces since decades, in all activity sectors with Orginal Equipment Manufacturers (OEM), integrators (and installers), and also with final users.