Wind Turbine Noise Assessment in Ontario Jim Salmon York University ESS 5210 2013-11-26 (Tuesday) Toronto, Ontario, Canada
Noise Assessment
Sound Hz: measurement of frequency (tone) db: measurement of volume or sound pressure level dba: db adjusted for human hearing Wind Turbine Sound and Health Effects: An Expert Panel Review: CanWEA/AWEA
Wind Turbine Sound and Health Effects: An Expert Panel Review: CanWEA/AWEA
Wind Turbine Noise Considerations Generation Transmission Reception
Turbine Noise Generation Two primary types: Aerodynamic white noise (all audible frequencies) from blade tips (mainly) passing through air at high speed (70 to 100 ms-1 tip speed) Amplitude modulation can occur when blade is moving downwards (about 1 Hz) Tonal noise from turbine hardware (not common in modern turbines) Ranges Audible sound (20 to 20,000 Hz) Infrasound (< about 20 Hz; very low energy content)
Turbine Noise Measurement
Turbine Noise Measurement
Turbine Noise Measurement
Turbine Noise Measurement
Turbine Noise Measurement
Turbine Noise Measurement
Turbine Noise Measurement
Turbine Noise Propagation Geometrical spreading. (Adiv = 20log[r] 11 db, at a distance r) Molecular absorption. This is conversion of acoustic energy to heat and is frequency dependent Turbulent scattering from local variations in wind velocity and air temperature and is moderately frequency dependent Ground effects reflection, topography and absorption are frequency dependent; their effects increasing as the frequency increases Near surface effects temperature and wind gradients.
Turbine Noise Propagation The sound pressure at a point, distant from source, is given by LfT = LW + Dc A (db) In which: LfT is the sound pressure level at the receiving point LW is the sound power level of the turbine in decibels re 10-12 watts Dc is a directivity index, which takes non-uniform spreading into account A is attenuation All of the above are frequency dependent. Near surface meteorological effects are complex, as wind and temperature gradients affect propagation through the air. Turbine noise sources are unique due to their height.
Turbine Noise Propagation Best known sound propagation standard Basis of Ontario MoE Noise Guidelines Relatively conservative Not perfect: generally designed for ground-based noise sources does not specifically handle temperature inversions, for example
Reception Summation from all turbines for all octave bands (8) {[ n L AT DW =10log10 8 10 0.1 [ L ft ij A f j ] i=1 j=1 ]} LAT(DW) is the equivalent continuous A-weighted downwind sound pressure level at a receptor location, n is the number of turbines Af(j) is the standard A-weighting for octave band j j is an index indicating the eight standard octave-band midband frequencies from 63 Hz to 8 khz
Reception LfT(ij) LfT(DW) is the equivalent continuous downwind octave-band sound pressure level at a receptor location for turbine i and octave band j, and is given by L ft DW =LW DC A LW is the octave-band sound power level, in decibels, produced by the point sound source relative to a reference sound power of one picowatt DC is directivity correction in decibels
Reception A is the octave-band attenuation, in decibels, that occurs during propagation from the turbine to receptor, and is given by A=Adiv Aatm Agr A bar Amisc Adiv is the attenuation due to geometrical divergence Aatm is attenuation due to atmospheric absorption Agr is the attenuation due to the ground effect Abar is attenuation due to a barrier Amisc is the attenuation due to miscellaneous other effects
Reception AATM is given by αd A= 1000 α is the atmospheric attenuation coefficient, in decibels per kilometre, for each octave band at the mid-band frequency d is the distance from the turbine to the receptor Highly frequency dependent
Reception Agr = As + Am + Ar Result of interference of direct and reflected sound Strictly applies only to ground which is (nearly) flat Three regions: source, middle, receiver; 30h Regions acoustical properties accounted for by ground factors: Gs, Gm, Gr Hard ground: G=0.0 pavement, tamped ground, ice Porous (soft) ground: G=1.0 grass, trees, vegetation, crops Mixed ground: 0.0 < G < 1.0 Frequency dependent
Reception Combining sound pressures at a receptor: 1x turbine contributing 40 dba, results in 40.0 dba 2x turbines contributing 40 dba each, result in 43.0 dba 3x turbines contributing 40 dba each, result in 44.8 dba 4x turbines contributing 40 dba each, result in 46.0 dba
Reception Example calculation for receptor and turbine 632 m apart Octave band 1 2 3 4 5 6 7 8 Mid-band frequency (Hz) 63 125 250 500 1000 2000 4000 8000 LW (dba) Adiv (db) Aatm (db) Agr (db) 82.4 93.0 96.0 99.8 100.1 96.5 89.6 85.7 67.0 67.0 67.0 67.0 67.0 67.0 67.0 67.0 0.1 0.3 0.7 1.2 2.3 6.1 20.9 74.8-3.0 1.0-0.1-0.7-0.7-0.8-0.8-0.8 LfT(DW) (dba) 18.3 24.7 28.4 32.3 31.5 24.1 2.4-55.4 Resultant receptor sound pressure level is 36.5 dba
Ontario MoE Noise Guidelines Interpretation document of Ontario MoE NPC-205, NPC-232 (note update to NPC-300) Likely due for an update Conservative Sets noise level limits at receptors Theoretically: dependent on ambient 10 m wind speed In practice: 40 dba at receptors 45 dba at participants (notional)
MoE Noise Guidelines
MoE Noise Guidelines Definitions Point of Reception (Receptor): means any point on the premises of a person within 30 m of a dwelling or a camping area, where sound or vibration originating from other than those premises is received. Participating Receptor (Participant): means a property that is associated with the Wind Farm by means of a legal agreement with the property owner for the installation and operation of wind turbines or related equipment located on that property.
MoE Noise Guidelines Definitions For the purpose of approval of new sources... the Point of Reception (Receptor) may be located on any of the following existing or zoned for future use premises: permanent or seasonal residences, hotels/motels, nursing/retirement homes, rental residences, hospitals, camp grounds, and noise sensitive buildings such as schools and places of worship. For equipment/facilities proposed on premises such as nursing/retirement homes, rental residences, hospitals, and schools, the Point of Reception may be located on the same premises.
MoE Noise Guidelines Definitions Vacant Lots: must be considered as potential host for receptor (1 ha) where zoning permits Vacant Lot Surrogate Receptors (VLSRs) Therefore: three types of points of reception: Receptors, VLSRs, Participants with different rules.
MoE Noise Guidelines Transformer sub-stations: Must be considered in the noise assessment Must include 5 db tonal penalty Presence of a sub-station triggers different rules for determining the exact Point of Reception for noise calculations
MoE Noise Guidelines Location: Point of Reception
MoE Noise Guidelines Distance Requirement: Assessment required if one or more receptors or participants are located within 1,500 m of a turbine. (Requirement is slightly modified if project includes sub-station.) Adjacent Wind Farms: must be included in assessment. (Note: only type of noise assessment where other noise sources must be considered!) Tonality: 5 db penalty assessed if there is tonality in the turbine noise. Distant Turbines: Turbines further than 5,000 m from a Point of Reception do not need to be included in the noise assessment.
MoE Noise Guidelines Specification of Parameters: Noise assessment must use atmospheric attenuation coefficients for 10C and 70% relative humidity. Maximum allowable source, middle, and receiver ground factors (G) of 1.0, 0.8, 0.5 respectively; 1.0 soft; 0.0 hard Vertical wind shear power law profile must be derived for summer night-time wind shear conditions. 550 m Distance Setback: The well-known 550 m distance setback from receptors is not included in the MoE Noise Guidelines. It is included in Ontario Regulation O. Reg 359/09 under the Environmental Protection Act (Renewable Energy Approvals, REA)
O. Reg. 359/09
Noise Assessment
Noise Assessment with additional setbacks