As an acoustic consultancy, we are often tasked with ensuring that noise produced by mechanical equipment does not adversely affect its surrounding environment and the people within it.
British Standard 4142 (BS4142: 2014, Methods for rating and assessing industrial and commercial sound) provides a method for assessing the potential impact of commercial or industrial noise sources affecting residential properties.
This case study considers noise associated with new mechanical ventilation plant serving five schools in the Hounslow area that are affected by aircraft noise.
Mechanical ventilation systems negate the need to open windows in warmer weather, which in turn minimises noise ingress that can otherwise negatively impact teaching and learning in classrooms. As an example, Springwell Infant School had ventilation plant mounted on the roof in nine locations, serving existing classrooms, the hall, an IT suite and group rooms.
Our role was to make sure that noise radiating from the new ventilation plant caused no adverse impacts to local properties surrounding the schools, in accordance with local authority requirements and BS4142.
Working for Kier Construction, Anderson Acoustics was a natural choice to undertake this project given our experience with BS4142 assessments and our knowledge of schools in the Hounslow area gained through supporting Heathrow with their Community Buildings Noise Insulation Scheme.
At each school, the first task was to establish the existing underlying noise environment outside the surrounding residential properties prior to any new mechanical plant being introduced, typically known as the background noise level. This was obtained by measuring continuous noise levels over a period of several days at a position representative of nearby homes.
Using the noise data gathered, a design limit was then established which must not be exceeded by noise from the new plant. This limit is typically set to ensure the existing background noise level does not increase which minimises the likelihood of any adverse impact.
With the design limit established, the next task was to predict noise emissions from the proposed mechanical plant without any noise mitigation measures in place. This was done using noise modelling techniques and is based on performance data for the proposed new ventilation plant (supplied by Ridge mechanical consultants).
Where noise from the plant was predicted to exceed the established design limit, mitigation advice was provided to reduce the noise accordingly. The mitigation recommended at Springwell involved the introduction of silencers to air handling units and acoustic screens to condenser units.
Work on a further four schools in the area is continuing.
Joe Baggaley, Anderson Acoustics’ Principal Consultant for Buildings and Schools Acoustics, commented, “The main challenge with this project was obtaining the ‘true’ background noise level around the various schools, given the acoustic environment can change significantly from one day to the next with runway operations out of Heathrow Airport. Given our experience with Heathrow we were able to plan our surveys efficiently with no set-backs, ensuring we delivered the required assessment on time and within budget.”