Enclosing an industrial fan to reduce sound levels is a common measure for preventing or addressing objectionable noise, in accordance with regulations concerning:
- noise at work, e.g. in relation to European Directive 2003/10/EC, which is based on different indicators:
- limit exposure values for workers to noise: exposure level L EX,8h = 87 dB (A) and peak sound pressure pcrête = 200 Pa or 140 dB (C) ref. 20 μPa /li>
- higher exposure values for workers to noise triggering action: exposure level L EX,8h = 85 dB (A) and peak sound pressure pcrête = 140 Pa or 137 dB (C) ref. 20 μPa
- lower exposure values for workers to noise triggering action: exposure level L EX,8h = 80 dB (A) and peak sound pressure pcrête = 112 Pa or 135 dB (C) ref. 20 μPa
- environmental noise e.g. in relation to public helth regulations which distinguish between the daytime period (7 a.m. to 10 p.m. except Sundays and public holidays) and the nighttime period (10 p.m. to 7 a.m. as well as Sundays and public holidays):
- in certain cases, a prefectural decree (when it is not ministerial) sets the noise levels not to be exceeded at the property boundary: this is particularly the case for Facilities Classified for the Protection of the Environment (FCPE) e.g. 70 dB(A) during the day and 60 dB(A) at night
- emergence i.e. the difference between the equivalent continuous A-weighted pressure levels of ambient noise (facility in operation) and residual noise (in the absence of noise generated by the facility, but measured over the period of operation of the facility) is limited in the Regulated Emergence Zones (REZ), which generally include, near the facility: homes, building zones and areas occupied by third parties e.g. Public Access Buildings (PAB), industrial establishments. If the ambient noise level in the REZ (including facility noise) is between 35 dB(A) and 45 dB(A) then the admissible emergence is 6 dB(A) during the day and 4 dB(A) at night. If the ambient noise level in the REZ (including facility noise) is greater than 45 dB(A) then the admissible emergence is 5 dB(A) during the day and 3 dB(A) during the night.
- in the case of a Facility Classified for the Protection of the Environment (FCPE), the marked tone, the presence of which is linked to the difference between the sound pressure level in a given 1/3 octave frequency band and the adjacent frequency bands, is considered undesirable if it exceeds 10 dB in the frequency range 50 Hz-315 Hz or 5 dB in the frequency range 400 Hz-8000 Hz
The frequency of this measure is particularly linked to the widespread use of industrial fans in a variety of contexts:
- for heating and cooling facilities, including cooling towers
- for the evacuation of process gases through chimneys (stacks)
- for ventilation systems in premises and other buildings
- for dust collection systems
- for various processes involving the circulation of a fluid in an air network
ITS participated in enclosing an industrial fan to reduce sound levels, as part of a project related to the compression/transport of carbon dioxide (CO2) in a Northern European kingdom.
The size of this powerful fan was such that it required a floor space of nearly 50 m2 with a height of nearly 5 meters (for the soudproofing enclosure).
Study and manufacture of an enclosure for an industrial fan to reduce noise levels
The study of an enclosure for the industrial fan in question was similar to that of soundproof buildings often marketed elsewhere by ITS for turbomachines of even larger dimensions, e.g. very large capacity compressors, combustion turbines:
- with regard to the study of metal structures: taking into account site conditions (rain, snow, wind, seismic activity), to design structures that are not only strong and durable (with large removable parts - including roofs - for maintenance of the enclosed hardware), but must also comply with local regulations that complicate design tasks
- with regard to calculations for evaluation of acoustical impact and for the design of noise limitation construction elements using SILDIS® software [1] e.g. Module 1 for predicting the acoustic and aeraulic (aerodynamic) performance of silencers; Module 2 for predicting the acoustic performance of flat partitions; Module 10 for predicting the noise emissions of buildings and other constructions
- for the enclosure cooling system; the heat output dissipated by the enclosed fan requires the installation of other fans (smaller, but not silent, and they must also be soundproofed) and noise-limiting devices for the openings
- for the electrical installation: involving fans, sensors
The manufacture of an enclosure for the industrial fan in question is a metal constrction with a (steel) framework and:
- for fixed or easily removable parts, by elements: industrial soundproofing panels with an absorbing face (modular)
- for acces: (rotating) acoustic doorsets with, for translucent parts (with glazing guaranteeing residual safety in the event of accidental breakage): acoustic window sets
In addition, the ventilation air inlets and outlets shall be equipped with ventilation silencers .
The enclosure of an industrial fan for noise reduction must be both robust and airtight, with carefully placed accesses and openings.
If well designed and built with the required care (as when marketed by ITS) such an industrial fan enclosure will limit its acoustic power to a value close to 80 dB(A) - which illustrates a remarkable performance in terms of acoustic insulation for a sound source of such initial acoustic power and size - and it will last a long time, keeping all its functionalities intact - as is desirable.
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[1] cf. https://www.its-acoustique.fr/en/acoustical-insulation-soundproofing/acoustic-simulation-software