Submission to Standards New Zealand
with regard to
draft Standard DZ 6808:2009
Acoustics – Wind farm noise
Philip J Dickinson Ph.D., FASA
13 April, 2009
1 The noise immission in any sleeping area, must meet the World Health Organization’s recommendations to protect public health, and minimise sleep disturbance at night – a level of 30 deciBels (LAeq) for steady continuous noise. The draft does not ensure this.
2 Any low frequency noise components in the sound from the windfarm(s) should be limited to ensure room resonances are not set up in any sleeping area to the degree that sleep is disturbed. The draft treats this as of no significance.
3 Windfarm sound has distinct characteristics and is not masked by natural sounds such as that from the wind in trees. The background sound level should not be assumed to mask windfarm sound – as the draft Standard does.
4 The noise limiting criteria should not be based on the background sound level plus 5 dB or 40 dB whichever is greater. This is not sustainable management, as defined in the Resource Management Act. The criteria to meet should be a fixed value to comply with the WHO recommendations, and not related to the background sound at all.
5 There must be a simple method to show compliance (or non-compliance) with any noise rule set. The measurement metric and methodology used in the draft bring in quite unnecessary complications that prohibit any tests by local authorities to relate the noise immission to local noise ordinances. Once the windfarm is in operation there is little one can do to control its noise emissions under the present or draft standard. This is not acceptable.
6 If the WHO recommendations are to be met, the measurement metric should not be based on long term averages or L90, but be the time average level over a short time period (no more than 10 minutes).
7 Any noise prediction for design compliance must include all other wind farms within the locality, say, within 10 km. The draft considers only the noise from one windfarm at a time, excluding all others. The noise predicted at any noise sensitive location will be underestimated and perhaps greatly so.
8 The noise prediction and all working should be written out – as on a spreadsheet – including base data and any assumptions made, so that it may be verified by anyone. With a computer program one can get almost any answer one likes.
9 From experience, at distances over 2 kilometres, the prediction methodology greatly under-predicts the sound immission, often by more than 15 deciBels. Either a new prediction methodology should be produced – one that relates better to reality – or the Standard should use a protocol where prediction does not come into the equation.
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