Let the Plant Breathe

Generators, chillers and air handling plant all need air, and air needs an opening. Every opening in a plant room wall is also a path for noise to leave the building. An acoustic louvre exists to resolve that conflict — letting the plant breathe while reducing what escapes — and choosing one well means understanding the limits on both sides of that trade.

Noise at the boundary is now regulated

In Saudi Arabia, the Ministry of Environment, Water and Agriculture began implementing its noise regulation across the Kingdom in June 2021. As reported by the Saudi Gazette, it covers residential, commercial, industrial and environmentally sensitive areas as well as roadsides and construction sites, while excluding indoor noise. Its listed violations include failing to comply with approved noise times and permissible levels, failing to prepare a noise reduction plan after notice, and failing to provide required monitoring data to the National Center for Environmental Compliance. For plant that sits on a facade or roof near a site boundary, the louvre is often where that compliance is won or lost.

Effective industrial noise control can reduce unwanted noise and improve workplace comfort.

Limited at both ends of the spectrum

Research presented at the Acoustics 2018 conference of the Australian Acoustical Society by Hayne, Tan, Devereux and Mee examined how acoustic louvres are tested and how their performance should be reported. The authors explain that a louvre's performance is limited at low frequencies by mass and at high frequencies by the gaps between the blades, and recommend reporting performance in octave bands from 125 Hz to 8 kHz rather than as a single figure. The most common test is the reverberant-to-reverberant method in AS 1191 and ISO 10140-2.

The trade-off with airflow

The same paper identifies the central design constraint. Closer blade spacing improves attenuation in principle, but the air pressure drop rises rapidly to a level too high for the fans on the plant being served. A louvre that attenuates brilliantly but starves a generator or chiller of air is not a solution, so acoustic performance and air performance have to be selected together.

Why published figures do not always compare

Hayne and co-authors also found that published data formats varied between manufacturers — insertion loss, transmission loss, sound reduction index and noise reduction were all in use — which makes like-for-like comparison difficult. They further note that transmission loss measured between reverberant chambers is higher than a louvre's field performance because of coupling between the rooms, with potential errors of up to 5 dB when results fall below 15 dB. The practical lesson: confirm which metric a figure represents and how it was measured before comparing two products.

Learn more about common sources of industrial noise to understand its role in acoustic design.

The air side has its own standard

Air, water and sand performance are tested separately. ANSI/AMCA Standard 500-L, published by the Air Movement and Control Association International, covers five laboratory tests for louvres: pressure drop, airflow leakage, water penetration, wind-driven rain and wind-driven sand. In the water penetration test, the rating point is the intake velocity at which the water collected does not exceed 3 g/m² (0.01 oz/ft²) of free area. For exposed plant in a desert climate, the wind-driven sand test is worth asking about alongside the acoustic data.

The acouStick approach

acouStick supplies weather-rated acoustic louvres in depths from 150 to 300 mm for generator rooms, plant rooms and facades. Selection balances the attenuation needed at the boundary against the airflow and pressure drop the plant can tolerate, using octave-band data and a clearly stated test method.

Learning what is soundproofing is a useful first step toward reducing unwanted noise.

If your generator room, chiller yard or plant room faces a site boundary or a neighbour, acouStick can help you select a louvre that meets the noise target without choking the plant.

Email: info@acoustick.co | Call: +966 51 130 809 | Web: www.acoustick.co

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REFERENCES

• Saudi Gazette. "Environment ministry begins implementation of noise regulation across Saudi Arabia." 2 June 2021 — Ministry of Environment, Water and Agriculture noise regulation: saudigazette.com.sa/article/607325

• Hayne, M., Tan, D., Devereux, R., & Mee, D. "Testing and Performance Quantification of Acoustic Louvres." Proceedings of Acoustics 2018, Australian Acoustical Society, Adelaide, 7–9 November 2018: acoustics.asn.au/conference_proceedings/AAS2018/papers/p54.pdf

• International Organization for Standardization. ISO 10140-2:2021, "Acoustics — Laboratory measurement of sound insulation of building elements — Part 2: Measurement of airborne sound insulation."

• Air Movement and Control Association International (AMCA). "Understanding the ANSI/AMCA Standard 500-L Tests": amca.org/assets/resources/public/documents/Understanding_the_ANSI-AMCA_Standard_500-L_Tests.pdf