Neal Andersen - Wind Turbine Noise Study Update

Neal Andersen - Wind Turbine Noise Study -Falmouth Massachusetts USA
TECHNICAL MEMO 2015-004Infrasound Measurements of Falmouth Wind TurbinesWind #1 and Wind #2Michael Bahtiarian, INCE Bd. Cert.Allan BeaudryFebruary 27, 2015NCE JOB No. J14-100Prepared for:CHRISTOPHER SENIE & ASSOCIATES5 East Main Street, 2nd FloorWestborough, MA 01581Attention: Mr. Christopher Senie, Esq.Prepared by:NOISE CONTROL ENGINEERING, LLC799 Middlesex TurnpikeBillerica, MA 01821978-670-5339978-667-7047 (fax)www.noise-control.comTM 2015-004 Infrasound Measurements of Wind TurbinesNoise Control Engineering, LLC- ii -TABLE OF CONTENTS0.0 EXECUTIVE SUMMARY .......................................................................................................11.0 INTRODUCTION .....................................................................................................................22.0 BACKGROUND .......................................................................................................................23.0 TEST OVERVIEW ....................................................................................................................34.0 INSTRUMENTATION .............................................................................................................35.0 RESULTS .................................................................................................................................46.0 CONCLUSION ..........................................................................................................................6REFERENCES ...............................................................................................................................7APPENDIX A: Vestas Model V82 Wind Turbine Data SheetTM 2015-004 Infrasound Measurements of Wind TurbinesNoise Control Engineering, LLC- 1 -0.0 EXECUTIVE SUMMARYNoise Control Engineering, LLC (NCE) was retained by Senie & Associates P.C. to evaluate theacoustic impact at the home of Neil and Betsy Andersen at 211 Blacksmith Shop Road, EastFalmouth, Massachusetts. The goal of the evaluation was to determine if the three nearby windturbines were detectable within the interior of the home. These wind turbines are all Vestas,model V82 at 1.65 megawatts. Two wind turbines are owned by the Town of Falmouth; knownas âWind #1â and âWind #2â. The third turbine is privately owned by Notus Clean Energy andreferred to as the âNotusâ turbine. Wind #1 is the closest to the Andersen home at a nominaldistance of 1,385 feet. The other two wind turbines are more than double that distance.Soon after the first wind turbine was operational, complaints were filed by the Andersens andother neighbors. In the following years, evaluations of audible sound were performed by variousorganizations including NCE, consultants for the Town, consultants for Notus, and even theMassachusetts Department of Environmental Protection (MADEP). Various results werereported with some evaluations showing compliance and some showing non-compliance.The study reported herein differed in a number of ways from previous evaluations performed byNCE and others. The major difference is that the primary measurements reported here isinfrasound. Briefly, infrasound is sound pressure levels with frequency below 20 hertz which isgenerally considered an inaudible frequency range. Another difference is that measurementswere taken both inside and outside the home. All previous tests were performed at exteriorlocations due to the fact that State regulations and local ordinance were only applicable atoutdoor locations.The methods used herein allowed for the collection of infrasonic sound pressure levels within theinside of the Andersen residence. Inspection of this data shows that there is a readily identifiableacoustic signature that is attributable to the Wind #1 Turbine, and to slightly lessor extent theWind #2 turbine both inside and outside the Andersen home. These results are similar to resultsfrom other international researchers with references given in the report.Based on our experience, NCE can unequivocally state that the infrasonic signature capturedinside the Andersen residence with the wind turbines operational is 100% attributable to one orboth of the Townâs Wind Turbines. To put the conclusions more commonly, this study finds thatthe wind turbine(s) produce acoustic emissions which are âacoustically trespassingâ into theAndersen home.TM 2015-004 Infrasound Measurements of Wind TurbinesNoise Control Engineering, LLC- 2 -1.0 INTRODUCTIONNoise Control Engineering, LLC (NCE) was retained by Senie & Associates P.C. ofWestborough, Massachusetts to evaluate the acoustic impact at the home of Neil and BetsyAndersen at 211 Blacksmith Shop Road, Falmouth, Massachusetts. The goal of the evaluationwas to determine if the sound from the nearby wind turbines is detectable within the interior ofthe home. This evaluation was conducted by measuring infrasound.2.0 BACKGROUNDIn 2010 the Town of Falmouth erected the first of two Vestas V82, 1.65 megawatt wind turbines,known as âWind #1â and in 2012 the second turbine known as âWind #2â was installed. Also in2010, Notus Clean Energy erected the same Vestas V82 wind turbine known as the âNotusâwind turbine. Appendix A provides a copy of the equipment data sheet for information only.Figure 1 shows the locations of the three wind turbines in relation to the Andersen Home at 211Blacksmith Shop Road. As shown in Figure 1, Wind #1 is the closest to the residence with adistance of 1,385 feet. Wind #2 is 2,600 feet and Notus is 3,900 feet from the residence1.Soon after the first wind turbine was operational, complaints were filed by the Andersens andother neighbors. In the following three years, evaluations of audible sound (20 to 20,000 hertz)were performed by many different organizations. NCE conducted some of the first soundmeasurements and reported these results to the Town of Falmouth during a meeting with theBoard of Selectman (reference 1). NCE identified a characteristic time domain pattern known asâAmplitude Modulationâ which demonstrated excess to the Town of Falmouth 40 dB(A) windturbine sound ordinance (reference 2).Following this work a series of evaluations were performed by another consultant, Harris MillerMiller & Hanson (HMMH) under contract to the Townâs engineering firm that supervised theinstallation of the wind turbines. The purpose of this evaluation was to compare acousticperformance to the Massachusetts Department of Environmental Protection (MADEP) noiseregulation2 (reference 3). The wind turbines were found to be somewhat in compliance in bothassessment reports which evaluated the data using two different approaches, (references 4, 5).However, the results showed that 4 dB to 15 dB increases in broadband sound over thebackground sound occurred depending on the measurement location (reference 4, 5).Another consulting firm, Epsilon Associates, Inc. evaluated the Notus wind turbine and reportedresults in reference 6. This study evaluated the wind turbine sound with respect to the FalmouthSpecial Permit conditions, reference 7. The special permit conditions required no more than a 6dB increase in A-weighted sound pressure level, no pure tones and no more than 6 dB increase ininfrasound. The Town of Falmouth Zoning Board of Appeals applied a 6 dB allowance overbackground noise for Notus and in connection with one other privately owned turbine. In 2013the Falmouth Town Meeting adopted the 6 dB limitation as a Town-wide zoning provisionapplicable to all wind turbines. The Epsilon report found that the wind turbine was compliant for1 All distances are nominal and determined using Google Earth.2 Compliance with the State regulations requires two conditions: (1) the source of sound cannot produce an Aweightedsound pressure (SPL) level that is greater than 10 decibels above the background A-weighted SPL and (2)the source of sound cannot produce a âpure toneâTM 2015-004 Infrasound Measurements of Wind TurbinesNoise Control Engineering, LLC- 3 -all three conditions. However, the infrasound condition was found to have an increase of asmuch as 5.7 dB.Lastly, in 2012, the MADEP conducted their own set of measurements using only MADEP stafffrom the Lakeville office. Attended measurements were performed on multiple days during boththe nighttime (reference 8) and daytime (reference 9). The nighttime report found that Wind #1exceeded the 10 dB regulation while the daytime report found no excess to the 10 dB regulation.In summation, the purpose of this section is to indicate the variety of acoustical evaluations thatwere performed of the Falmouth turbines (Wind #1, Wind #2 and Notus). Three differentacoustical consulting groups conducted surveys for three different clients (Town of Falmouth,Notus Clean Energy, and residence groups) and compared results to three different sets ofrequirements (Falmouth Wind Turbine ordinance, Notus, special permit, and MADEPregulations). Within all these evaluations, various degrees of compliance and non-compliancewere declared.3.0 TEST OVERVIEWThis evaluation differs in a number of ways from previous tests performed by NCE and others asnoted in Section 2. The major difference is that the primary measurements performed herein areâinfrasoundâ. Briefly, infrasound is sound pressure levels with frequency below 20 hertz whichis generally considered an inaudible frequency range. Another difference to previous studies isthat measurements were taken both inside and outside the home. All previous tests described inSection 2 were performed at exterior locations due to the fact that State regulations and the localordinance were only applicable at outdoor locations.As noted in Section 2, the Falmouth Wind Turbines were found to be out of compliance withMADEP regulations. To be out of compliance with MADEP noise regulations requires that thesource of noise (the Wind Turbines) have an A-weighted sound pressure (SPL) level that is 10decibels above the background A-weighted SPL. This condition was usually found to occur inthe late evening and overnight, not because the wind turbine sound increased, but mostly becausethe background sound decreased during the night. Because of this situation, the court ordered(reference 10) that both Wind #1 and Wind #2 be shut down during the hours of 7pm to 7am. Assuch, the infrasound measurements were performed from the hours of 5pm to 8pm to allow foreasy comparison of the measured infrasound with and without the Wind #1 and Wind #2operating.4.0 INSTRUMENTATIONInfrasonic SPL was measured using a Bruel & Kjaer infrasonic microphone, model 4964. Thefrequency response is useable within ±1 dB accuracy from 0.04 to 8,000 Hz3. The system wasfield calibrated by a Larson Davis model CAL200 calibrator at 94 dB (relative to 20 micro-Pa) at1,000 Hz. The microphone was covered with a standard wind screen and mounted on a tripod ata nominal height of 5 feet above the ground for all measurements.3 ±2 dB from 0.03 to 20,000 Hz and ±3dB is from 0.02 to 20,000 Hz

Data acquisition was performed using a National Instruments, model 9234 4-channel dataacquisition module. The software used is based on the National Instruments Sound & VibrationToolkit. The system is configured to collect narrowband sound spectrum measurements usingthe Fast Fourier Transform (FFT) signal processing algorithm. The FFT settings were slightlydifferently for each of the four visits as the test methods were refined. The typical settings were20,480 lines, 0.05 hertz resolution, 10 averages (200 seconds of sampling, 3.3 minutes), and aHanning window.All acoustic instrumentation was laboratory calibrated to NIST standards by an accreditedlaboratory within the past 12 months. Calibration certificates will be provided upon request.5.0 RESULTSInfrasonic measurements were performed during 4 visits to the Andersen residence between July2014 and February 2015. Table 1 provides a summary for each visit including date, time of day,and wind conditions.Table 1: Site Visit Date, Time, and Wind ConditionsMeasurement Approximate WindDate Start Time Direction SpeedJuly 5, 2014 1:30 pm Northwest 17 mphNovember 21, 2014 6:30 pm Southwest 26 mphDecember 13, 2014 6:30 pm Northwest 8 mph*February 5, 2015 6:30 pm Northwest 18 mph*Notus Turbine was not operating on this dayWith the exception of the initial visit in July 2014, each visit occurred during the nightlyshutdown of the Wind #1 and Wind #2 at 7:00pm. This allowed for a direct comparison ofturbine operation and ambient conditions within a 1 hour period. In general, for data presentedherein, operational measurements were taken between 6:30pm and 7:00pm while ambientmeasurements were taken from 7:00pm to 7:30pm, immediately following the shutdown of theturbines. As the July 2014 site visit occurred earlier in the afternoon, ambient measurementswere not taken. For the November, December, and February visits, asynchronous infrasonicmeasurements were taken both within the interior of the Andersen residence and right outside thehome. Indoor measurements were taken within the living room while outdoor measurementswere taken on the front lawn.Figures 2-5 present the indoor infrasonic sound pressure levels measured from 0 to 10 Hz foreach visit. The graphs for the latter three visits also include the measured outdoor operationaland indoor ambient infrasonic sound pressure levels. In each figure, regular discernable tones44 The sharp amplitude peaks shown do not strictly meet the requirements for most standardized definitions of a tone,however, for the purposes of this report, they will be referred to as such for brevity.TM 2015-004 Infrasound Measurements of Wind TurbinesNoise Control Engineering, LLC- 5 -can be identified to varying degrees between 0.7 and 5 Hz. It was determined that the lowest ofthese tones, occurring at 0.72 Hz, coincides with the blade pass frequency (BPF) of the VestasV82 turbine at full rotation speed (as given in the Vestas data sheet, Appendix A). The bladepass frequency is seen in all rotating machinery with blades including fans and propellers and isa function of the machinery rotation speed in revolutions per minute (rpm) and the number ofblades. The BPF in hertz is calculated using the following formula:ðµðð¹ (ð»ð§) =ððð¡ðð¡ððð ððð¡ð60â [ðð. ðð ðððððð ]For the 3-bladed Vestas V82 turbine rotating at 14.4 rpm, the BPF is:ðµðð¹ (ð»ð§) =14.4 ððð60â 3 ðððððð = 0.72 ð»ð§In addition to the blade pass frequency, rotating bladed machinery produces harmonics of theBPF which occur at integer multiples of the BPF. Table 2 shows the turbine blade passfrequency (1x BPF) and the first seven harmonics (2x â 8x BPF). Each of the frequencies shownin Table 2 was identified during at least one visit and many were found during all operationalmeasurements.Table 2: Calculated Blade Pass Frequency Harmonics1x BPF 2x BPF 3x BPF 4x BPF 5x BPF 6x BPF 7x BPF 8x BPFFreq. (Hz) 0.72 1.44 2.16 2.88 3.60 4.32 5.04 5.76Of note in Figures 3-5, while these tones are clearly identified in the operational indoormeasurements, they are completely absent from the ambient indoor measurements following theshutdown of the turbines. Clear identification of these tones is less consistent in the outdoormeasurements due to higher overall broadband infrasonic noise, likely due to wind which is notfound for measurements taken indoors.Examination of the data with the two Town wind turbines shut down shows no indication of anyresidual infrasound inside the home. This would be the case if the Notus Wind turbine had anyimpact at the Andersen residence. It should be noted, that the differences between the infrasonicmeasurements with the wind turbines secured and with the Wind #1 and Wind #2 operating aremuch greater than 6 dB.Figure 6 is a compilation of the measured indoor infrasound from the four visits. This graphshows that the tones associated with the BPF and its harmonics occur at consistent frequenciesover the span of the four visits. Further, with this figure, the substantial variations in amplitudebetween the visits can be more easily seen and explanations for this variation can be theorized.Note that the highest measured levels for these tones were taken during the July visit during amoderate (17 mph) downwind condition while the lowest levels were taken during the Decembermeasurements during a low (8 mph) downwind condition. While substantially lower in absoluteamplitude, the December measurements have a similar peak-to-trough difference (10+ dB) fromthe tones to the frequencies between the tones suggesting, even within the house, the windTM 2015-004 Infrasound Measurements of Wind TurbinesNoise Control Engineering, LLC- 6 -controls the ambient broadband infrasonic sound level. Finally, measurements performed inNovember show both high broadband levels and lower peak-to-trough differences suggestinghigh wind speed and/or an upwind wind direction partially obscure the clearly identifiable windturbine infrasonic signature.Historically, when the wind turbine sound is particularly bothersome, Mrs. Andersen hasreportedly sought refuse in the dining room which is located in the back of the home. NCEunderstands that at times she has used this room as a second âbedroomâ. NCE tested this roomand found a lower level of infrasound in the 4 to 7 Hertz range as shown in Figure 7. NCE doesnot have any explanation why this room has lower infrasound only at these frequencies, but heractions are consistent with these test results.
6.0 CONCLUSIONSThe methods used herein allowed for the collection of infrasonic sound pressure levels within theinside of the Andersen residence. As shown in Figure 6, there is a readily identifiable acousticsignature that can be definitively attributable to Wind #1 and possibly Wind #2 located outsidethe Andersen home. To NCEâs knowledge, this is the first time such measurements have beenperformed and reported with respect to the Falmouth wind turbines. However, this is not the firsttime such measurements have been performed, and other researchers have collected lowfrequency infrasonic acoustic signatures at other wind turbine sites in Wisconsin and Australia(references 11, 12). As reported in these other studies, the same blade passage rate infrasoundand harmonic shown inside the Andersen home have been identified.Given NCEâs signature analysis and the dramatic change in this acoustic signature when thewind turbine(s) are shut down, NCE can unequivocally state that the infrasonic signaturecaptured inside the Andersen residence is 100% attributable to either one or both of the Town ofFalmouth Wind Turbines. To put the conclusions more commonly, this study finds that the windturbine(s) produce acoustic emissions which are âacoustically trespassingâ into the Andersenhome.