Design and Access Statement Site: Lyng Farm, NR20 4JE

Design and Access Statement
Site: Lyng Farm, NR20 4JE
Appendix B - Noise Report: Evance R9000
Acoustic Impact Assessment of Small Wind System Installation
In considering the noise generation of small wind systems and the impact of this noise level on
neighbouring properties, Windcrop has been working with local Environmental Health Officers
to develop a practicable and clear method of presenting the expected impact. This makes use
of the ETSU-R-97 assessment approach which takes into account not only the noise levels at
noise sensitive locations but also sets these against the expected background noise levels for
the normally experience range of site wind speeds.
Under the ETSU-R-97 methodology, the site background noise is measured against wind speed
and this is then compared against the expected noise immission from the wind system(s). To
undertake this type of testing for a small system is completely uneconomic and as such the
approach being developed is that tests are being carried out on a range of typical site types to
generate a reliable empirical generic forecast of background noise for a range of site types.
Whilst this work is in progress, and to enable safe assessment to be made of the impact of
small wind systems on noise today, a low level assumed background noise curve has been
agreed as shown on the attached graph. This is based on data taken on open, treeless sites and
so represents a lowest expected background noise. It is also based on a base level of
background noise with no wind of only 28dB. It is therefore expected that any typical rural site
will have actual background above this level.
The noise immission from the wind system(s) is then overlaid onto this background noise curve
to enable an assessment to be made of the wind system noise compared with the background
noise across the wind speed range. This shows that a worst case at a wind speed of around
7.5m/s wind speed. A decision is then needed on the relative level of the wind system to
background. To date the approach has focussed on the nigh time levels at the façade of a
neighbouring property and set the limit as 3dB above background. A secondary level has also
been reviewed based on amenity use of a garden taking 5dB above background at the
boundary of a neighbouring garden. At present only the façade level is being assessed on the
basis that the typical boundary immission at the worst case of 7.5m/s wind speed is under
40dB and is considered well inside acceptable daytime amenity levels.
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