Sound Planning has completed a project for EMI Records in London, where external chiller units on the roof of the property at Wrights Lane, Kensington were a potential noise nuisance.
Consisting of 16 air source chiller units that could potentially be operating 24 hours a day, seven days a week, the mechanical plant is under the jurisdiction of the Royal Borough of Kensington and Chelsea, where specific requirements are in place for applications of this type – requests for residential and commercial developments must undergo a noise survey. A report should be carried out by an acoustician who is a member of the Institute of Acoustics, after a noise assessment has been completed to determine whether the noise falls within acceptable levels.
Noise from industrial sources in residential areas is normally assessed against British Standard BS 4142, using a method to determine whether specific noise from an industrial source will lead to complaints from nearby residential dwellings. If the difference between the Rating Level of the specific noise and the background noise is +5dB, this is considered to be of “marginal significance” and therefore acceptable – balancing the requirements of commerce with residents’ quality of life. However, a difference of +10dB or more indicates complaints are likely and this is the threshold at which most local authorities will take action against the organisation producing the noise.
A noise assessment carried out between 3am and 3.50am revealed a noise level of 54.5dB when eight chillers were in use and 57.5dB when all 16 chillers were utilised. The background noise was 45dB, so the excess noise was measured at 12.5dB. The local authority required a reduction of 22.5dB, so the noise from the mechanical plant would fall within their guidelines.
Sound Planning recommended achieving a 23dB reduction through the installation of circular attenuators, connected directly to the chiller exhaust fans. The attenuated noise level would be 32dB(A) at the nearest noise sensitive receivers – 13dB below the lowest measured background level. The addition of 90° cowls at the end of the circular attenuators would provide further noise reduction if required.
The addition of this noise mitigation solution meant the mechanical plant conformed to the local authority’s noise criteria and therefore, noise should not be a factor that could prohibit the granting of planning permission.
If you require further information regarding our bespoke solutions, please don’t hesitate to contact the experts at Sound Planning. We can devise an acoustic solution to even the most complex noise related challenges.