Wind Turbine Noise Conditions.pdf

Measurements must be taken simultaneously inside and outside the residential dwelling, with the measurement taken no further away than 3.5m from the residence. Attenuation of the sound through the walls of the residence is predicted for audible frequencies but is significantly different for ILFN.

Measurements must sample all the significant wind directions and wind speeds of the annual wind rose of the area. Winds measured over one period, of even several weeks, will often not include winds from all directions and wind speeds seen throughout the year.

Continuous sound recording must be made over the entire span of the measurement interval. Intervals should be at least one week in length. All the sound recordings must be made available to all interested parties through secured cloud storage.

The sound must be recorded in uncompressed, 10–20-minute, WAVE files with at least 16-bit resolution and at least 44.1 kHz sampling frequency. All frequencies of interest must be accurately recorded, from the lowest blade-pass frequency of any industrial wind turbines within 20 km of the recording site.

Calibration tones must be recorded on the recordings at least once per week. A GPS location and GPS-based timestamp must automatically be included in the metadata of each WAVE file at the time of recording. A digital signature must be provided that can provide chain-of-evidence for the original recording and its metadata.

Analysis of the measurements should not be limited to audible or weighted acoustic parameters such as A-weighted measures. The following requirements should be included in addition to those already proposed by acoustical standards.

Sonograms of unweighted sound from the blade-pass frequency, or below, to at least 1 kHz, with at least 1-second temporal and 1/36-octave frequency resolution for each sound file. Harmonic analysis of each sound file to identify harmonic series from the blade-pass frequency to at least 0.3 times the highest frequency in the sonogram.

Calculation of the blade-pass harmonic prominence for each sound file. Blade-pass harmonic prominence should be presented in time-of-day plots covering each measurement interval. Wind roses of harmonic prominence over all the measurement interval.

The target noise limits from ETSU-R-97 are too high for an occupier of a tent or caravan to achieve undisturbed sleep. The target noise limit for a camp site is 30 dB, LAeq (as per World Health Organisation recommendations). Any such site must be evaluated accordingly in each assessment for the three wind farms.

Dwellings are generally considered to be Noise Sensitive Receivers (NSR) and the ETSUR97 night time noise limit of 43 dBA outside a dwelling assumes significant attenuation from outside a dwelling to inside a bedroom where it is assumed that a target noise limit of 30 dBA, Leq will be achieved to protect sleep (WHO Guidelines).

In the case of a camping ground it is impossible to achieve any significant attenuation of sound from outside a tent to inside where people sleep. The target night time noise limit for camping areas should be set at 30 dBA, Leq, or 28 dBA, L90.

Target noise limits outside any camp site area at night are determined as the base noise limit of 28 dBA, L90 or Background plus 5 dB, whichever is the greater, over the operating wind speeds of the wind turbines.