The brief

Coupland Bell noise and vibration consultants were asked to provide technical support for a tender for a power station project.  Far field noise at the nearest house was a key concern. For our client’s bid to be successful, it would be necessary to show a thorough understanding of the noise sources on the proposed development and how they could be adequately treated.

The brief was to develop a numerical model leading to predictions of the far field noise.  The predictions would be used as part of the Planning application and sufficient background evidence would have to be supplied for the Planning authority to complete its Due Diligence process.

The model would need regular updates, to keep pace with the site design and would be used to select acoustic treatment.

Spreadsheet model

Our noise and vibration consultants have developed a library of noise source data for power stations over the years.  This was used to build a simple spreadsheet model of the entire power station.  It included the interior of the power halls, transmission through doors and breakout from ducts.  Various receptor positions that were of interest to the Planning authorities were included. Initial predictions were straightforward and showed how the limits imposed by the Planners could be achieved.  The model was constantly updated as the layout of the proposed site was changed, for engineering reasons.

The predictions were then used to influence the site layout and optimise the screening of plant.

An embankment around the project was planned and its screening effect was included in the model.  The construction of the buildings was optimised, based on the acoustic transmission loss necessary to meet the far field requirements.  This allowed accurate cost estimates to feed into the bid.

CadnaA model

The bid was successful and our client was awarded the construction contract.  The Planning authorities asked to see predicted noise contours for the whole area surrounding the development.

Our noise and vibration consultants built a propagation model using CadnaA software.  This confirmed the validity of the spreadsheet model, to within 1 dB(A).

Noise contours were predicted, within the site boundary and out to the nearest residential properties.  The contours within the boundary were useful for confirming that the contract maximum of 80 dB(A) would not be exceeded, where items of plant were closely spaced.

The CadnaA model also confirmed that although the earth bank would provide local screening, it would not justify lower specification noise treatment to the buildings, because of the need to maintain limits at the first floor windows of distant houses.