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HomeMy WebLinkAboutPoint Lay Wind Turbine Project Noise Analysis Memorandum - Mar 2012 - REF Grant 704002799/214 This memorandum summarizes the existing and future noise levels near the city of Point Lay, Alaska. Summary This project will install a wind turbine generator farm outside of Point Lay Alaska. The project proposed to use one Vestas V47, three Vestas V27’s, or one Fuhrländer 600 wind generator(s). The wind turbine nearest to the southern edge of town will be located approximately 3800 feet to the south. Noise due to the operation of the wind turbines is expected to be audible in the town, although the overall noise levels are low, and are not projected to exceed 29 to 34 dBA. In addition, the noise from the wind turbines should not exceed the ambient by more than 1 to 5 dBA except in extreme cases accompanied by high winds, low ambient noise levels and frozen ground. Introduction The project site is 3800 feet west of the City of Point Lay, near the Point Lay Airport. The topog- raphy in the area is mostly flat, with no features that are expected to affect the transmission of noise from the site. The site has convenient access to existing roads and power lines and is in an area with steady wind flow. The project is to install on of three options: 1. One Vestas V47 600 KW generator 2. Three Vestas V27 225 KW generators 3. One Fuhrländer 600 - 600 KW generator Under option two with three Vestas V27’s, the turbines will be spaced at approximately 200 foot increments, which is typical for this type of turbine generator. The configuration considered for this analysis assumes that the turbines will placed in a line heading south. Figure 1 is an over- view of the project area and shows the proposed location of the wind turbines. Prepared for: Erin McLarnon \ Powercorp Alaska, LLC Prepared by: Michael A. Minor, Michael Minor & Associates, Portland, OR Date: Tuesday, March 06, 2012 Subject: Noise Analysis Memorandum Project: Point Lay Wind Farm 100/214 101/214 Methods This section provides an introduction to acoustics and general information on noise analysis methods. Acoustic Terminology Human response to sound is subjective and can vary greatly from person to person. Factors that can influence individual response include the loudness, frequency, the amount of back- ground noise present, and the nature of the work or activity (e.g., sleeping) that the sound af- fects. When sounds become unpleasant, or are unwanted, we tend to classify them as noise. Traffic noise is measured in terms of sound pressure level. It is expressed in decibels (dB), which are defined as 10 log P2/P2ref, where P is the root-mean-square (rms) sound pressure and Pref is the reference rms sound pressure of 2 x 10-5 Newtons per square meter. In general, the dB scale is a logarithmic conversion of absolute air pressure to units that are more convenient and easier to understand. To better approximate the sensitivity of the human ear to sounds of different frequencies, the A- weighted decibel scale was developed. Because the human ear is less sensitive to higher and lower frequencies, the A-weighted scale reduces the sound level contributions of these frequen- cies. When the A-weighted scale is used, the decibel levels are denoted as dBA. A 10-dBA increase in noise levels is judged by most people as a doubling of sound level. The smallest change in noise level that a human ear can perceive is about 3 dBA, and increases of 5 dBA or more are clearly noticeable. Normal conversation ranges between 44 and 65 dBA when speakers are 3 to 6 feet apart. Noise levels in a quiet rural area at night are typically be- tween 32 and 35 dBA. Quiet urban nighttime noise levels range from 40 to 50 dBA. Noise lev- els during the day in a noisy urban area are frequently as high as 70 to 80 dBA. Noise levels above 110 dBA become intolerable and then painful, while levels higher than 80 dBA over con- tinuous periods can result in hearing loss. Table 3 provides a scale of several different noise sources and typical public response. All noise levels referred to in this report are stated as sound pressure levels in terms of decibels on the A-scale (dBA). The A-scale is used in most ordinances and standards, including the ap- plicable standards for this project. To account for the time-varying nature of noise, several noise metrics are useful. The equivalent sound pressure level (Leq) is defined as the average noise level, on an energy basis, for a stated time period (for example, hourly). 102/214 Table 3: Sound Levels and Relative Loudness of Typical Noise Sources Noise Source or Activity Sound Level (dBA) Subjective Impres- sion Relative Loudness (human judgment of different sound levels) Jet aircraft takeoff from carrier (50 ft) 140 Threshold of pain 64 times as loud 50-hp siren (100 ft) 130 32 times as loud Loud rock concert near stage, Jet takeoff (200 ft) 120 Uncomfortably loud 16 times as loud Float plane takeoff (100 ft) 110 8 times as loud Jet takeoff (2,000 ft) 100 Very loud 4 times as loud Heavy truck or motorcycle (25 ft)90 2 times as loud Garbage disposal, food blender (2 ft), Pneumatic drill (50 ft) 80 Moderately loud Reference loudness Vacuum cleaner (10 ft), Passenger car at 65 mph (25 ft) 70 1/2 as loud Large store air-conditioning unit (20 ft) 60 1/4 as loud Light auto traffic (100 ft) 50 Quiet 1/8 as loud Bedroom or quiet living room, Bird calls 40 1/16 as loud Quiet library, soft whisper (15 ft) 30 Very quiet High quality recording studio 20 Acoustic Test Chamber 10 Just audible 0 Threshold of hearing Sources: Beranek (1988) and EPA (1971) Land Use Land use near the site is entirely undeveloped with no noise sensitive land use. The only struc- ture in the immediate area is the tank storage facility. In the city of Point Lay, land use includes residential and commercial uses. As stated, the nearest noise sensitive land use is approxi- mately 3400 feet from the wind farm. Existing Noise Levels No actual noise measurements for Point Lay are available. However, measured noise levels taken in Alaska at other small Alaskan villages, such as Pedro Bay, Nondalton and others was available from other projects in rural Alaska. Measurements at these small villages were taken over the last 3 to 4 years as part of other environmental documentation. Measured noise levels in small communities typically ranged from below 20 to 40 dBA Leq during normal daytime hours. Maximum noise levels ranged from 55 to 70 dBA during pass-bys of ve- hicles, ATV’s and snow machines. Minimum noise levels typically ranged between 20 and 30 dBA. Background noise sources typically include personal generators residential and commer- cial activities, wind and birds. Minimum noise levels during winter months are often governed by local generators. Table 2 provides a summary of noise levels during different time of the year and at different times of the day for a small Alaskan village. 103/214 Table 2: Typical Noise Levels in a Quiet Alaskan Village Daytime Levels1 Evening Levels2 Nighttime Levels3 Leq L10 Lmax Lmin Leq L10 Lmax Lmin Leq L10 Lmax Lmin Summer 40 55 65 30 40 50 65 28 35 45 50 26 Winter 42 60 65 30 40 50 65 28 40 40 50 28 Notes: 8. Daytime is 7:00am to 7:00pm 9. Evening is 7:00pm to 10:00pm 10. Nighttime noise levels derived from daytime/evening levels and noise levels from similar are- as between 10:00pm & 7:00am 11. Minimum short-term noise level of 30 dBA or less Project Noise Control The City of Point Lay does not have a noise control ordinance. For reference, the City of Port- land Noise Control Ordinance was used as a guideline for the project. This ordinance defines three classes of property usage and the maximum noise levels allowable for each. For exam- ple, the noise caused by a commercial property must be less than 60 dBA at the closest resi- dential property line. A summary of the City of Portland Noise Control Ordinance is given in Ta- ble 4. Between the hours of 10:00 p.m. and 7:00 a.m., the maximum allowable levels shown in Table 1 are reduced by 5 dBA. In addition, for steady state sources, such as the turbines, the noise lev- els in Table 4 are reduced by 5 dBA between 7:00 am the 10:00 pm, and by 10 dBA between 10:00 pm and 7:00 am. For this analysis, the wind turbine facility is considered a commercial land use, therefore, the daytime limits at residential land use is 50 dBA, and the residential nighttime criteria is 45 dBA. Table 4: City of Portland Noise Control Ordinance Property Usage Maximum Allowable Sound Level, dBA Residential Commercial Industrial Residential 55 60 65 Commercial 60 70 70 Industrial 65 70 75 Future Noise Levels This section provides the projected noise levels from operation of the three Vestas V27 wind turbines or one Vestas V47/ Fuhrländer 600. The Vestas V47 and Fuhrländer 600 are both 600 KW generators and are expected to produce approximately the same sound power level versus wind speed curves. Reference Noise Levels No direct measured noise levels were available for Vestas V27 or Vestas V47/ Fuhrländer 600 wind turbine. There are, however, several reports and available data on similar systems. A technical paper "Acoustic Tests of Small Wind Turbines", authored by Paul Migliore, Jeroen van 104/214 Dam, and Arlinda Husky, was presented January 5-8 2004 in Reno, Nevada. This report con- tinued the measured sound power levels for several different small wind turbines. Table The data shows that the turbine noise levels are directly related to the wind speed and turbine load. Information from the Small Turbine Report and information on larger wind turbines are used to predict worst case noise levels for operation of the Vestas V27 and Vestas V47/ Fuhr- länder 600 wind turbines. Sound Power noise levels are predicted for the V27 and Vestas V47/ Fuhrländer 600 wind turbines for winds speeds of 10 mph, 20 mph and greater that 30 mph. For each of the wind speeds, future noise levels were predicted for three locations in the town of Point Lay. Noise levels were compared to a typical noise ordinance and the projected existing noise levels to determine if noise impacts are likely. Operational Noise Levels Noise level for the wind turbines were projected for three different speeds at three representa- tive receiver locations in Point Lay. Receiver R-1 is the southernmost residential land use and is approximately 3800 feet from the wind turbine site. Site R-2 is near the center of town by a tank facility, approximately 4800 feet from the wind turbine site, and site R-3 is in the northern end of town, 6500 feet from wind turbine site. The receivers and locations of the turbines are shown on Figure 2. The Wind Turbine Noise Model (WTN) used for this analysis is derived from the method docu- mented by the International Energy Agency: Expert Group Study on Recommended Practices for Wind Turbine Testing and Evaluation, Acoustics Measurements of Noise Emission from Wind Turbines, National Physical Laboratory, 1994. The WTN is a simple noise model that as- sumes spherical spreading from a point source either in free space (spherical) or over a reflec- tive plane (hemi-spherical). It can also take into account atmospheric attenuation, using an at- tenuation rate entered by the user. The source sound power and the absorption coefficient are both assumed to be broad band. Source to receiver distances are calculated by simple geomet- ric means and the total received noise from each turbine logarithmically added. The model does not take account of topography conditions; however there are no topographical features that are expected to affect the transmission of noise. Because of the potential for in- creased sound transmission during winter months, the calculations were performed for free- space and reflective plane which provides a range of noise levels that may be experienced with the variations in weather. The reflective plane levels simulate noise when the ground is frozen and noise attenuation is reduced. 105/214 106/214 Noise Projections for Three Vestas V27 Wind Turbines Table 5 provides the results of the noise calculations for a set of three Vestas V27 wind turbines for three wind speeds at the three representative receiver locations. Table 5: Wind Farm Noise Level Projections (dBA) Receiver Locations Sound Pressure Level w/10 mph Sound Pressure Levels w/20 mph Sound Pressure Levels with/>30 mph Free Space Reflective Plane Free Space Reflective Plane Free Space Reflective Plane R-1 22 24 26 29 31 34 R-2 18 21 23 26 28 31 R-3 12 15 17 20 22 25 Note: Sound levels projections for four V25 – 225KW wind turbine generators running simul- taneously Assuming maximum Sound Power level of 103 dBA Under the three V27 alternative noise levels in the Point Lay community from the operation of the turbines are projected to range from 22 to 34 dBA in the southern end of town, reducing to 12 to 25 dBA at the northern edge of town. Noise levels at the closest resident to the farm range from a low of 24 dBA to 34 dBA during periods of efficient noise propagation. In general, noise from the wind turbines may be audible at times in most parts of the town. The noise will be most notable in the northern edge of town during quiet periods, however, with typical noise levels ranging from 22 to 31 dBA at the nearest noise sensitive properties, no noise impact are projected. Noise Projections for One Vestas V47 or One Fuhrlander 600 Wind Turbine Table 5 provides the results of the noise calculations for a single of Vestas V47 or Fuhrlander 600 wind turbine for three wind speeds at the three representative receiver locations. Table 5: Wind Farm Noise Level Projections (dBA) Receiver Locations Sound Pressure Level w/10 mph Sound Pressure Levels w/20 mph Sound Pressure Levels with/>30 mph Free Space Reflective Plane Free Space Reflective Plane Free Space Reflective Plane R-1 20 23 25 28 30 33 R-2 17 20 21 24 26 29 R-3 12 15 16 19 21 24 Note: Sound levels projections for Vestas V47 or Fuhrlander 600 – 600KW wind turbine gen- erators running simultaneously Assuming maximum Sound Power level of 108 dBA 107/214 With a single 600 KW wind turbine noise levels in the Point Lay community from the operation of the turbines are projected to range from 20 to 33 dBA in the southern end of town, reducing to 12 to 24 dBA at the northern edge of town. In general, the overall difference between using three Vestas V27 and one Vestas V47/ Fuhrlander 600 wind turbines is not likely to be measur- able. However, the two alternatives may sound different with the three Vestas V27’s likely hav- ing a slightly higher overall frequency content. The noise will be most notable in the northern edge of town during quiet periods, however, with typical noise levels ranging from 23 to 30 dBA at the nearest noise sensitive properties, no noise impact are projected. Due to the relatively large distance from the farm, the turbines are not predicted to cause and noise impacts. Although it is possible that noise from the turbines will be audible in the town, it will only be noticeable during periods of low ambient noise levels and efficient noise propaga- tion. It should also be noted that noise from the wind farm will likely have a low frequency rum- bling sound, as opposed to a “swishing” sound heard a closer distances.