On Wind Turbine Noise and Air Pressure Pulses
- May 7, 2012
- 821 views
The von Trapp family came to Vermont, because it reminded them of Austria, where “the hills are alive with the sounds of music”. Those sounds will soon be replaced by the health-damaging infrasound and low frequency noise from the Green Mountain Power 63 MW Lowell Mountain wind turbine facility with (21) 3 MW Danish, Vestas V-112 wind turbines, 367.5-ft (112 m) rotor diameter, 275.6-ft (84 m) hub height, total height (275.6 + 367.5/2) = 459 ft, stretched along about 3.5 miles on 2,600 ft high ridge lines. The housings, 13 ft x 13 ft x 47 ft (3.9 m x 3.9 m x 14 m), on top of the 280-ft towers, are much larger than a Greyhound bus, owned by GMP/Gaz-Metro-Canada. Total site area, including conservation and buffer zones, about 2,700 acres.
Assuming a buffer zone of about 1 mile for noise attenuation to rural nighttime ambient noise levels of 20-40 dBA, the area of the Lowell Mountain wind turbine facility would need to be about (3.5 + 2) x 2 = 11 sq mi = 7,040 acres to minimize audible adverse impacts on restful sleep. Beyond 1 mile, the unattenuated noise would be mostly low frequency noise, LFN, (audible as a beating, rumbling, droning sound) and infrasound (air pressure pulses that are not audible, but felt).
The 21 wind turbines will emit various noises, such as:
– machinery noise in the nacelle
– rhythmic/pulsating, trailing-edge noise from the blades (“blade swish”) as they slice through the air at up to 200 mph
– irregular, low frequency noise (LFN) and infrasound from the blades due to in-flow air turbulence
– LFN and infrasound at the blade-tower-passage frequency and its harmonics.
US Government 1987 Wind Turbine Noise Study: The US government has known about the adverse health effects of infrasound and low frequency noise from wind turbines since 1987. It was concerned enough to commission a study. The below study was a research project funded by the U.S. Department of Energy, Contract No. DE-AC02-83CH10093.
Dr. N.D. Kelley, Solar Energy Research Institute, Golden, Colorado, performed the study titled: “A Proposed Metric for Assessing the Potential of Community Annoyance from Wind Turbine Low-Frequency Noise Emissions.
Note: “Community Annoyance,” is now called Wind Turbine Syndrome; “Low Frequency” includes infrasound; “Emissions” includes noise and vibrations.
Infrasound: Consists of air pressure pulsations, less than 20 Hz; not audible, but felt. Usually, it is not measured by acoustics engineers, because standard dB meters cannot measure it. It is largely ignored by state regulators and state noise codes.
Wind energy promoters (vendors, project developers, financial types with tax-shelter schemes for the top 1% of households, legislators getting “campaign” contributions, etc.) want to maintain the status quo. Their mantra is: wind energy is “clean and green” and LFN and infrasound are non-issues.
As the 3-bladed rotor turns at 15 to 20 rpm at greater wind speeds, a blade passes the mast 45 to 60 times per minute, or 0.75 to 1.0 Hz. At lesser wind speeds the frequencies are less.
The infrasound has audible components (20 to 500 Hz, with peak amplitudes at about 200 to 500 Hz) and inaudible components (0 to 20 Hz, with peak amplitudes at about 0.75 to 1.0 Hz). The infrasound travels great distances, a mile of more, for large, utility-size wind turbines.
Note: Infrasound contains air pressure pulses of many frequencies less than 20 Hz. The wavelength of a 1.0 Hz infrasound air pressure pulse (about the beat frequency of the human heart) = velocity of sound/1.0 Hz = 1,115 fps/1.0 Hz = 1,115 ft.
A continuous pulsing at this frequency will disturb the sleep of people even at 6,600 ft = 1.25 miles = 2 km. Continuous sleep disturbance is a major cause of bad health. See the 3rd URL with a 14-minute video.
Here is a list of minimum distances from various places in the world.
Audible Noise: Audible noise has LFN components (20 Hz – 200 Hz), similar to the very low sounds of a big church organ. The other audible components (200 Hz – 20,000 Hz) are the common everyday noises that are covered by noise codes that, unfortunately (deliberately?), do not take into account the unique noise spectra of utility-scale wind turbines.
At 350 m (1,148 ft) from a 1 MW wind turbine, the audible sound emitted by:
– a well-behaving IWT with no in-flow turbulence and low wind shear is about 35 dBA; often during daytime when the sun is warming the ground and air.
– a badly-behaving IWT with in-flow turbulence and/or high wind shear is up to 55 dBA; often during nighttime when a stable atmosphere forms.
This compares with rural nighttime ambient noise of 20-40 dBA, and urban residential nighttime noise of 58-62 dBA.
As almost all utility-scale IWTs with greater capacities, say 2 – 3 MW, make more noise, and as almost all such IWTs are in rural settings, government noise codes should use the rural nighttime ambient noise level as THE basis for limiting wind turbine noise levels. Exceeding these levels may adversely impact restful sleep of people. Restful sleep is a basic requirement for good mental and physical health, as are food, water, air, etc.
45 dBA outside a house, averaged over an hour
30 dBA inside a house with windows closed, averaged over one hour.
Requiring rural people to close their windows to have restful sleep is an imposition.
Recently, Maine reduced the not-to-exceed noise level from 45 dBA to 42 dBA outside a house for ridge line IWTs, but is still experiencing significant public opposition to IWTs, including from Governor Paul LePage. Clearly, 42 dBA is still not low enough.
The difference with above rural nighttime ambient noise levels is not trivial. The sound pressure level, SPL, is doubled as the dB instrument reading increases by 6 dB.
Note: If at 800 uPa (micropascal) the SPL = 20 log (800/20) = 32 dB, at 1600 uPa it is 38 dB, and at 3200 uPa it is 44 dB, where 20 micropascal is the lowest SPL the human ear can sense, it is used as the reference pressure.
SELECTED ACOUSTICS TERMS
Here are some common terms often used in acoustics reports:
LApeak is the maximum A-weighted SPL occurring within a specified time period.
Lpeak is the maximum deviation of a signal from its mean value within a specified time period.
LA1 is the A-weighted SPL that is exceeded 1% of the time.
LA10 is the A-weighted SPL that is exceeded 10% of the time.
LA10 (1 hr) is the A-weighted SPL that is exceeded 10% of the time within a 1-hour period.
LA90 is the A-weighted SPL that is exceeded 90% of the time; usually the background SPL
LAeq is the A-weighted SPL which over a period of time has the same sound energy as the time-varying noise.
LA10 – LA90 is a measure of the “choppiness” of the noise.
Ld = LAeq (15 hrs) is the A-weighted SPL of daytime noise 7 AM – 10 PM
Ln = LAeq (9 hrs) +10 dbA is the A-weighted SPL of max. allowed nighttime noise 10 PM – 7 AM
C-weighted SPLs are required for LFN; A-weighing would render meaningless the SPLs of LFN.
LCpeak is the maximum C-weighted SPL occurring within a specified time period.
Note: Wind energy proponents, project developers and wind turbine vendors usually have “behind-the-scenes” inputs to state and local wind turbine noise codes, as they did in Vermont and Maine. They prefer to comply with a weak standard, such as 45 dB LAeq (1 hr).
– Wind turbine noises will vary greatly during any given hour, and
– Are usually loudest at night when fathers, mothers, and children are trying to get a good night’s sleep to be ready for the next day, and
– People react to loud noises, not averages,
the AVERAGE sound energy level may still be below 45 dBA during any given hour, which will enable wind project owners, such as GMP, to claim “see we are in compliance”, implying it is you (the complainer) who has a problem.
TERRAIN AND WEATHER CONDITIONS INFLUENCE NOISE
The wind speeds and directions upstream of a wind turbine vary due to:
– Terrain effects, such as hilliness and ridge lines
– Objects on the surface of the terrain, such as buildings and trees
– Daytime thermal effects
– Upwind wind turbines.
During daytime, as the 3-bladed rotor turns, it encounters air at various speeds and directions which produces a combination of sound effects, i.e., rhythmic/pulsating blade swish about 3 dBA above the steady aerodynamic noise, and a steady rhythm of LFN and infrasound.
During nighttime, air speeds and directions, not influenced by daytime thermal effects, become more varied, the atmosphere becomes more stratified and background noise is less causing the various sound effects (aerodynamic noise, rhythmic/pulsating noises, rhythmic LFN and infrasound) to be noticeably more intense than during the daytime. The daytime blade swish noise often becomes a nighttime clapping, beating, or thumping noise.
The wind speeds and directions downstream of a wind turbine are similar to the vortices leaving the ends of airplane wings, except they all rotate in the same direction.
When the wind direction aligns with the ridge direction of the wind turbines, the downwind turbines will have a degraded performance of up to 20 to 30 percent, i.e., a reduced CF, due to wake turbulence, and they will be noisier, and they will have increased wear and tear.
EMERGING NOISE GUIDELINES
Professional acoustics and medical consultants have the knowledge base to develop guidelines for wind turbine noise. Here are some of their findings and recommendations:
– Hayes-McKenzie Partnership recommendations made in 2006 limited maximum wind turbine sound levels at residences to 38 dBA and no more than 33 dBA if “beating noises” are audible.
Note: Wind turbine capacities have increased since 2006; increased capacity, increased noise, especially LFN and infrasound.
– Dan Driscoll presented his analysis in 2009 (Environmental Stakeholder Roundtable on Wind Power, June 16, 2009) with a Composite Noise Rating analysis of 33 dBA to reduce rural community response to the level of “sporadic complaints”.
– Michael Nissenbaum issued his findings in 2010 from his medical study at Mars Hill, recommending a 7,000-foot setback for public health. The World Health Organization published sound level thresholds of sleep disturbance and adverse health effects from peer-reviewed medical studies (Night Noise Guidelines for Europe, October 2009).
– Stephen Ambrose and Robert Rand, professional acoustical consultants, advise the noise level not exceed 32 dBA AT THE PROPERTY LINE of any abutter of a wind turbine facility to ensure minimal LFN and infrasound content; the 32 dBA measurement would be a proxy for LFN and infrasound. Wind turbine facility designers and their acoustical consultants would need to have a design target of 30 dBA to ensure 32 dBA is realized. If utility-scale (1.5 MW to 3 MW) wind turbines are sited at least 1 mile from the property line of any abutter, it is likely any audible noise wiil be attennuated below 32 dBA. To avoid devaluating any abutter’s property, etc., the abutter property line is used, because, for example, an abutter may want to use his land for one or more residences near the property line in the future.
– Rick James and George Kamperman, professional acoustical consultants, have extensively studied wind turbine noise. They recommend a noise limit AT THE PROPERTY LINE for:
Audible noise: 35 dBA or no more than 5 dBA above the pre-construction ambient dBA level, whichever is lower
LFN: 50 dBC or no more than 20 dBC above the pre-construction ambient dBC level, whichever is lower
“Wind Turbine Health Impact Study: Report of Independent Expert Panel,” January 2012, prepared for the Massachusetts Department of Environmental Protection and the Massachusetts Department of Public Health cites five peer-reviewed studies, upon which it relies. Those studies are the following:
– Pedersen and Waye, “Perception and Annoyance Due to Wind Turbine Noise: A Dose—Response Relationship,” Journal of the Acoustical Society of America, December 2004
– Pedersen and Waye, “Wind turbine noise, annoyance and self-reported health and well-being in different living environments,” Occupational and Environmental Medicine, March 2007
– Pedersen and Larsman, “The impact of visual factors on noise annoyance among people living in the vicinity of wind turbines,” Journal of Environmental Psychology, 2008
– Pedersen, van den Berg, Bakker & Bouma, “Response to noise from modern wind farms in The Netherlands”, Journal of the Acoustical Society of America, 2009
– Shepherd, D., McBride, D., Welch, D., Dirks, K. N., & Hill, E. M., “Evaluating the impact of wind turbine noise on health-related quality of life”, Noise Health, 2011.
These studies all found that IWT noise contributes to sleep disorders and diseases associated with the serious adverse responses to the infrasound generated by the IWTs.
There are other nations and some U.S. states that have found the noise from IWTs is sufficiently harmful to health that a setback of more than 4,500 feet to any residence is required. Examples:
– Rural Oregon has set the minimum setback at 2 miles.
– Victoria and New South Wales, NZ have set the minimum setback at 2 km (1.25 miles).
– In a settlement reached in a wind turbine dispute in Fayette County, Pennsylvania, the setback was set at 6,000-foot (1.1 mile).
– An investigation into wind farms and noise by the UK Noise Association (UKNA)” finds an appropriate setback to be 1 to 1.5 mile setback (7,900 ft).
– “Recommendations on the Siting of Wind Farms in the Vicinity of Eskdalemuir, Scotland (2005)” finds an appropriate setback to be 10 km (6.2 mile or 32,730 ft).
– Beech Ridge Wind Farm (West Virginia) has a setback of 1 to 4 miles.
MISCARRIAGES AND BIRTH DEFECTS DUE TO WIND TURBINES IN DENMARK
Below is an article, which details the impact on newborns when wind turbines are placed too close to people and animals. The article is food for thought/introspection for Shumlin, Klein and other wind turbine aficionados.
Wind turbines adversely impact the fetuses of pregnant women and other fauna species susceptible to low frequency vibrations from wind turbines, a.k.a. infrasound with frequencies less than 20 Hz. Infrasound cannot be heard, but is felt. Infrasound travels much longer distances than audible sounds that have higher frequencies.
The PSB, so-called “Protector of the Public Interest”, refuses to:
– Admit adverse health effects exist, despite numerous reports to the contrary
– Measure and regulate infrasound, despite numerous complaints from nearby people
– Regulate and enforce minimal setback requirements of about 2 km from a residence.
Excerpt from the article:
“Politicians, and wind industry shills who … deny the risks to health, are now liable to be successfully sued by wind farm victims. And so are governments, as they still refuse to measure infrasound emitted by modern wind turbines.”
In Denmark last month, 1,600 animals were born prematurely at a mink farm. Many had deformities, and most were dead on arrival. The lack of eyeballs was the most common malformation. Veterinarians ruled out food and viruses as possible causes. The only thing different at the farm since last year has been the installation of four large wind turbines at a distance of 328 meters, or about 1,000 ft. The wind farm consists of four 3 MW turbines, VESTAS model V112, reaching out to 140 meters in height at the tip of the blades. When they became operational last fall, a first mishap was reported by the mink farmer at a parliamentary committee on wind farms in January this year.
NOTE: The 3 MW turbines are exactly the same as at LOWELL MOUNTAIN!!!
The Green Mountain Power, 63 MW Lowell Mountain wind turbine facility with (21) 3 MW Danish, Vestas V-112 wind turbines, 367.5-ft (112 m) rotor diameter, 275.6-ft (84 m) hub height, total height (275.6 + 367.5/2) = 459.3 ft, stretched along about 3.5 miles on 2,600 ft high ridge lines, has nothing to do with community-scale wind, everything with industrial, utility-scale wind. The housings, 13 ft x 13 ft x 47 ft (3.9 m x 3.9 m x 14 m), on top of the 280-ft towers, are much larger than a Greyhound bus.
GOVERNMENT NOISE CODES
Traditionally, state and local government codes dealt mostly with measured sound values that are weighed (adjusted) using the A scale which covers most of the audible frequencies. The A scale corrects dB measurements according to the sensitivity of human hearing. It should not be used for frequencies less than 200 HZ, as the low frequency noise (LFN) and infrasound would be “weighed” out.
The following scales should be used to properly weigh all frequencies, especially those less than 20 Hz that are emitted by wind turbines:
Most audible noises in the range of 200 – 20,000 Hz; dB weighed with the A scale, dBA.
LFN, in the range of 20 – 200 Hz; dB weighed with the C scale, dBC.
Infrasound less than 20 Hz; dB weighed with the G scale, dBG.
Note: The instrumentation to quantify infrasound frequencies and amplitudes is expensive and the values obtained vary with the method and instruments used. Applying the G scale to such values may not be meaningful.
The human ear can hear LFN at 95 dBG levels, the inner ear is sensitive to LFN at 65 dBG levels. Audible thresholds for perception of 95 dBG represent the median response to a steady pure tone in a laboratory environment.
If a person is more sensitive to LFN and infrasound, say at the 10% boundary, the treshold for perception may be as low as 85 dBG for a steady pure tone. The treshold for perception will also be lower with multiple tones between 0 and 100 Hz that rapidly modulate in amplitude and frequency, as with wind turbine noise.
Professional acoustical engineers know the government codes, the outcome government regulators are expected to hear and conduct their tests according to standard procedures using mostly the A scale. Wind turbine vendors report sound levels adjusted to the A scale and almost everyone is satisfied. The LFN and infrasound are usually not covered by government codes. Here are some examples of government noise codes:
The new LFN noise code, adopted January 2012 after about 6 years of complaints, requires a 20 dBA INDOOR limit for wind turbines at wind speeds of 6 m/s and 8 m/s (wind turbines run around the clock). The code does not mention open/closed windows. The LFN is not measured, but calculated from measurements close to the turbine nacelle.
Vestas, concerned its 3 MW wind turbine sales would be adversely affected, lobbied the Danish government to not be too strict with noise codes, as they would become a model for other nations. Accordingly, the codes were watered down to the consternation of Danish academic acoustical experts.
Professor Moller, an internationally known acoustical scientist who disagrees with the methods of testing and measurement, wrote: “All these errors sum up to probably not far from 10 dB, which means that the limit is suddenly not 20 but rather 30 dB. But the rules are claimed to give the same protection as for industrial sources, which is simply not true. At low frequencies the perceived intensity, the loudness, increases more steeply above threshold than at higher frequencies. This means when the level is a few decibels above the 20 dB limit, the consequences are more severe, than if a limit for higher frequencies is exceeded by the same amount. A few people would probably accept 25 dBA in their home at night, but hardly anyone would accept 30 dBA.”
In Massachusetts, noise is considered pollution if it exceeds the ambient noise level by 10 dBA. The Department of Environmental Protection, MassDEP, measures noise levels at the complainant’s location and at other nearby locations that may be affected, such as residences and/or buildings with other sensitive receptors. If the noise level at a sensitive receptor’s location is more than 10 dBA above ambient, MassDEP requires the noise source to mitigate its impact. The LFN and infrasound are not covered.
The Massachusetts code is grossly inadequate. Noises from wind turbines are 24/7/365 and are as random as the wind which greatly adds to annoyance and sleeplessness. The 10 dBA value would be reduced to zero, if the wind turbines were sited at least a mile from where people reside, recreate and work.
In Michigan, the Centerville Township, after 4 years of study, developed and approved a 19-page zoning ordinance for commercial wind energy systems. It is strict and comprehensive and should serve as a model for other government entities.
Audible Noise Standard:
From 6:00 A.M. until 10:00 P.M., for wind speeds from cut-in to rated-output of the wind turbine facility, the noise level due to the wind turbine facility at the property line closest and at locations within 1 mile of the wind turbine facility shall not exceed the greater of 35 dBA, or the established outdoor background sound level by more than 5 dBA.
From 10:00 P.M. until 6:00 A.M., the noise level due to the wind turbine facility at the property line closest and at locations within 1 mile of the wind turbine facility shall not exceed the established outdoor background sound level by more than 3 dBA. Background sound level shall be established separately for daytime (6:00 A.M.-10:00 P.M.) and for nighttime (10:00 P.M.-6:00 A.M.) values.
LFN or Infrasound:
No LFN or infrasound from wind turbine facility operations shall be created which causes the noise level both within the project boundary and a 1 mile radius beyond the project boundary to exceed the following limits:
Octave Band Center Frequency, Hz SPL, dB
Tonality and/or Repetitive, Impulsive Tone Penalty:
In the event the audible noise due to wind turbine facility operations exhibits tonality, contains a pure tone and/or repetitive, impulsive noise, the Audible Noise Standard shall be reduced by a total of 5 dBA.
In Maine, codes require noise levels not to exceed:
– the one-hour average daytime limit (between 7 a.m. and 7 p.m.) of 55 dBA, as measured within 500 feet from a residence, seasonal camp, or business, at “protected locations”
– the one-hour average nighttime limit (between 7 p.m. and 7 a.m.) of 42 dBA, as measured within 500 feet from a residence, seasonal camp or business, at “protected locations”
– 55 dBA, 24 hours of the day, at greater than 500 feet from a residence, seasonal camp or business, at “protected locations”
– 75 dBA at the wind turbine project boundary.
Maine Department of Environmental Protection 06-096 CMR c. 375.10.
The Maine code is inadequate, because it uses one-hr and 24-hr AVERAGES of noise. Noises during an hour, or a day, could be greater (as with sleep-depriving, pulsating noises) or less than the above dBA limits, but the average dBA would still meet the code. The noises should be averaged over about 5 minutes to better record the noise spikes.
The Maine code allows 75 dBA at the wind turbine project boundary, which means IWTs would be allowed on very small land parcels. People whose lands border such parcels would not have full, undisturbed use of their land, i.e., some of their land become useless, has less value, for future development, such as building a house
Till now, 32 Maine towns have passed their own wind facility ordinances that are stricter than the state ordinance, because they do not trust the state to protect the environment and the quality of life, public safety, health, property values and welfare of the people.
This site provides the URLs of the text of the wind ordinances of 12 Maine towns. Vermont towns should get copies of them and use them as a guide to write their own ordinances before it is too late.
The PSB set the maximum noise level as 45 dBA (exterior), and 30 dBA (interior, with windows closed), averaged over an hour.
Dr. Lovko testimony before the VT-PSB: “The problem with the limit of 45 dBA(exterior)(Leq)(1hr) is that it is simply too high to protect people from the adverse effects of noise from wind turbines. Averaging the levels over time further compounds this fact by allowing even higher sound levels to occur for periods of time during any hour.”
One wonders why the VT-PSB is wasting time and taxpayer money holding hearings, etc., instead of quickly implementing the above Maine noise standard for ridge line IWTs. After all, Maine has so much more experience with IWTs on ridgelines than Vermont.
GMP’s PR people keep saying the Vermont code is strict, whereas, infact, it is not strict at all, thanks to the PSB not implementing some of Dr. Lovko’s recommendations.
The PSB is bending over backwards to enable Governor Shumlin to proceed as quickly as possible, to build as many ridge line IWTs as possible, to destroy as many ridge lines as possible, to grab as much state and federal subsidies as possible for Vermont’s wind energy oligarchy, which consists mostly of multi-millionaires in the top 1%.
WIND TURBINE NOISE ANNOYANCE
On an annoyance scale that is based on interviews of people who live near wind turbines, airports, railroads and highways, wind turbine noise is much more annoying at less than 40 dBA, than the noise from aircraft, highway and rail traffic at less than 70 dBA.
This additional annoyance is due to the LFN and infrasound emitted by wind turbines. The measured wind turbine noise appears to be benign and within code, but the annoying/unhealthy LFN and infrasound were filtered out by the A scale weighing.
People: At less than 20 Hz (infrasound) and above 20,000 Hz (ultrasound) most people do not “hear” noise, but a person’s ears and body are sensitive to infrasound which cause nausea, headaches, insomnia, elevated blood pressure, palpitations, tinnitus, imbalance, dizziness, lack of concentration, moodiness, irritability, anxiety, etc., in SOME people who live about 1/2 mile or less from large, say 1.0 MW, utility-size wind turbines.
The infrasound and low frequency noise, LFN, is harmful to humans. Humans should reside, work, study, play, etc., at least 1.5 mile from 3 MW wind turbines (based on Lowell Mountain experience), especially households with:
– pregnant mothers, babies, infants, school-age children, autistic children, ADD children, etc., to avoid genetic damage and developmental impacts
– people with heart disease, to avoid aggravating their condition
– elderly people, who generally are less able to bear the disturbances from IWT noises
Wildlife and Livestock: Infrasound and LFN also is harmful to wildlife and livestock. Domestic and wildlife animals are reported to be skittish near wind turbines. Animals with genetic defects have been found near wind turbines. Little data has been systematically gathered about the issue, but there is anecdotal evidence indicating problems. These symptoms are collectively known as “Wind Turbine Syndrome”.
These symptoms occur because the natural frequencies of the internal human and animal organs are in the same frequency range, i.e., 1 to 8 Hz, as those of house walls and floors. Floor resonance can cause the internal organs of the occupants to resonate resulting in an uneasy, irritating feeling. The infrasound is often amplified indoors due to resonating of house walls and floors.
Most peoples’ heart beat is less than 1.25 Hz, or a 75 pulse rate. People who live close to large wind turbines in Falmouth, MA, Ontario, Australia, etc., have complained about feeling internal pressures and having heart troubles and other symptoms which they did not have before the wind turbines were installed.
The symptoms mostly disappear after people move away and reappear after they move back. After many complaints over a long period of time, the Falmouth ruling council finally slowed down the wind turbines at greater wind speeds by partially feathering the blades.
Infrasound: Adding insulation to a house and double-pane or triple-pane windows will attenuate higher frequency noise, but not the infrasound and the lower frequencies (less than about 40 Hz) of the LFN.
As higher-frequency air pressure pulses (which have low energy) impact a wall, most of their energy is absobed by the wall materials, the indoor surface of the wall vibrates very little, i.e., the energy level of the noise is attenuated.
As lower-frequency air pressure pulses (which have high energy) impact a wall, only a small fraction of their energy is absorbed by the wall, the indoor surface of the wall vibrates much more, i.e., the energy level of the noise is very little attenuated. The resulting indoor air pressure pulses cause the other walls to vibrate/resonate as well, setting up standing waves of air pressure that create “noise spots” in the room; people often report their feeling of discomfort as being “worse indoors than outdoors”.
The indoor noise spectrum will contain mostly lower frequencies having greater impacts on people, as any masking from higher frequencies is reduced.
LARGER WIND TURBINES, STRONGER VIBRATIONS
The symptoms studied up till now typically are from exposure to the LFN and infrasound from smaller wind turbines, say up to 2 MW, with 290 ft diameter rotors, as on Lempster Mountain, NH.
The 3 MW Lowell Mountain wind turbines, with 367.5 ft diameter rotors, on 275.6 ft masts, on 2,600 ft high ridge lines, will have greater impacts over larger areas. See website.
The relative amount of LFN is greater for large turbines (2.3–3.6 MW) than for small turbines (less than 2 MW), i.e., the noise from larger wind turbines affects a larger area than from smaller wind turbines. The difference is statistically significant for one-third-octave bands in the frequency range 63–250 Hz.
During the day, ambient audible noise (background noise) in rural areas is much greater than at night, whereas, because of greater nighttime wind speeds, the wind turbine noise is greater at night than during the day. The result is rural people notice audible wind turbine noise much more at night than during the day. Wind turbine promoters arrange field trips for legislators and the public during the day from May-September when wind speeds and noise are minimal.
DEALING WITH COMPLAINTS
Many people living near wind turbines complain about sleep-disturbing nighttime noises that upset their lives to such an extent that their houses are bought by wind turbine owners after they sign gag orders.
As more and larger wind turbines are built near where people work, study, play, etc., the complaints will just multiply, until political pressures restrict the siting of wind turbine projects without suitable buffer zones, or require siting them offshore.
Dismissing the effects as mostly psychological and saying the physical effects are due to something else is not an option; there are just too many people, in too many geographical areas, living too near large wind turbines, with too many complaints. It is better to deal with the problem.
One way to deal with it is to have sufficient distance between people’s houses and utility-scale wind turbines to ensure people are not disturbed by noise and infrasound. Various studies show people living in flat terrain with wind turbines should be at least 1.25 miles (2 km) from such wind turbines. People living in mountainous terrain with wind turbines on ridge lines should be at least 2 miles (3.2 km) from such wind turbines. Such distance standards are becoming more prevalent in Europe, Australia, etc.
Vestas is concerned its 3 MW turbine will not meet stricter noise codes and has actively opposed noise code changes in Denmark, because it fears such changes will set a precedent for changing noise codes throughout the world, thereby adversely affecting 3 MW turbine sales. Other wind energy promoters are also actively opposing noise code changes.
After numerous complaints from people near wind turbine facilities, the Maine Board of Environmental Protection has finally adopted by a 5-4 vote new rules that lower the maximum allowable sound levels emitted by wind farms from 45 dBA to 42 dBA, between 7 p.m. and 7 a.m., as measured from houses and other “protected locations” within one mile of the turbines; a good step in the right direction, but inadequate for rural settings.
Vermont state officials are imprudently rushing to have as many ridge line wind facilities built as possible before various federal subsidies expire.
Because of this rushing, they have not heeded, or played down, or dismissed, the environmental concerns of professional testifiers and the complaints from people who live near the Lowell Mountain wind turbine facility. They likely will also not heed the complaints from the fauna and flora currently inhabiting this pristine ridge line.
Because of them, Vermonters are in danger of losing an international reputation of being preservers of their environment and in danger of losing a part of their soul.
By means of various rigged polls to provide CYA for legislators and by means of PR campaigns by wind energy promoters, including foreign companies selling wind turbines, Vermonters were swayed/bamboozled to be in favor of “clean and green” wind energy on ridge lines. However, after they saw the environmental destruction on the 2,600 ft-high Lowell Mountain ridge line, they quickly sobered up.