I am Charles Ebbing, President of Ebbing Acoustics, and am actively involved as an Acoustical Consultant on Noise and Vibration Issues associated with Industrial Wind Turbines and from the HVAC (Heating, Ventilation, and Air-Conditioning) Industry.
I worked from 1967 to 1999 for Carrier Corp, in the Research Division as Technical Leader in Acoustics, as Product Manager, and as the Carrier Corporate Noise Control Consultant.
After retiring from Carrier, as an Adjunct Professor, I taught Graduate Noise Control Courses at RPI and at Syracuse University associated with Building Mechanical Noise, Noise Control in Buildings, and the Use of Noise Criteria in the design of occupied spaces.
Overview
The Industrial Wind Industry continues to assert that Low Frequency Noise need not be evaluated for Industrial Wind Turbines and that dBA provides the information needed to access the noise impact on the adjacent community.
They also contend that Low Frequency Noise from Industrial Turbines is not a major problem, and thus dBC noise measurements it should not be required in the final Article X Guidelines.
They also assert that collecting dBC Noise data imposes an unrealistic burden on the Industrial Wind Industry.
I challenge the technical basis for these positions based on my personal Research and Experience as Acoustical Engineer specializing in these areas.
should not be required in the final Article X the technical basis for these positions based on my personal Research and as Acoustical Engineer specializing in these areas.
I am the lead author of the Book, “Application of Manufacturers’ Sound Data” that resulted from ASHRAE Research Project RP-786, Oct 1, 1998 (WWW.ASHRAE.ORG). The book has an extensive discussion of the use of RC Criterion to evaluate the expected low frequency noise level in occupied spaces and determine the required noise reductions to meet the Noise Goals established for Occupied Spaces in Buildings.
It is important to realize that industrial wind turbines are basically electrical generators turned by very, very large turbine blades. Noise is produced by the air flow and air turbulence over the turbine blade.
The noise producing mechanisms for HVAC fans are quite similar except that the fans are much smaller in Building Air Conditioning Systems and are driven by electrical motors and produce much less Low Frequency Noise.
Fan Noise is produced by the air flow and air turbulence over the fan blade that is induced by the fan blade rotation.
The Spectrum of the noise produced by Turbines and that produced by HVAC Fans both produce more Low Frequency Noise than Mid or High Frequency Noise.
In operation, the fan blades and the turbine blades both generate broad band and tonal noise which increases at low frequencies and decreases at the higher frequencies.
Wind Turbines produce increased Low Frequency Noise when the air flow entering the Turbine Blades deviates from Laminar Flow. The Wind Industry rates the noise from their units striving for the most laminar flow entering the turbine blades.
Similarly fans produce increased noise with highly turbulent inlet conditions or poorly designed ductwork in the fans discharge.
My field experience with HVAC Units that produced unacceptable time varying low frequency Rumble was because of the excessive time modulation of the noise in the 63, 31.5, and 16 Hz bands.
The characteristics of the wind turbine sound emissions are similar to those of problematic HVAC systems
My field experience is that tenants of new office buildings with Rumble from HVAC systems were unable to “tune out” the amplitude modulated low frequencies and wanted to return to their old offices to get away from the noise.
It was only when we able to reduce the Low Frequency Noise Radiation in the first three Octave Bands, to that indicated by the ASHRAE RC curves, that the occupants were satisfied.
The Low Frequency noise source ratings of the Turbines are needed to estimate the low frequency impact in the Homes of Occupants of interest. This impact cannot be determined from just considering the dBA noise levels of the Turbines. The literature shows that the dBA high frequency noise reduction of homes is significant, whereas low frequency noise reduction coupled with amplification from resonance of homes vary but on average the expected dBC reduction is close to zero.
Based on my experience the is no way to evaluate or anticipate Low Frequency Noise LFN Problems from Wind Turbines unless a proper study is conducted and that cannot be done if the focus is only on dBA.
Further, the types of symptoms that are being reported from people with long term exposure to Low Frequency Noise in their homes from Industrial Wind Turbines are similar to the reactions, I witnessed from many LFN exposed knowledge workers inside of occupied spaces which were generated by Buildings HVAC fans.
The Wind Turbine Applicants should provide the information needed to evaluate the noise impact on the adjacent community. The largest impact, in my opinion is inside the Occupants Homes. They cannot estimate this without knowing a rational estimate of the expected dBC outside their homes.
The Industrial Wind Industry should disclose both source dBA and dBC Sound Power Ratings of their turbines and document estimates of the expected noise levels at the Property Lines of the Residents both in dBA and dBC so that it is possible to evaluate both the expected dBA and dBC inside the residences’ home. Low frequency noise problems cannot be anticipated or prevented from dBA data.
Data collection of both dBC and dBA as well as octave or 1/3 Octave band is not considered difficult and burdensome by the HVAC industry. Why should the Wind Industry claim that that it is too difficult and burdensome for them, when they use the same high quality acoustical instrumentation that the HVAC Industry uses to collect the noise rating of their machinery?
The HVAC Industry has acknowledged that Low Frequency Noise Rating data from Rooftop Units and Central Station Fan Units are important to achieve acceptable Room Noise Levels. To do this the HVAC Industry looked to its Technical Society ASHRAE to set these recommendations.
It is apparent that the Wind Industry has not chosen to recognize that the HVAC Industry has effectively dealt with the low frequency noise problems of its industry since the mid 80’s.
Below is an ASHRAE listing of the research projects
The Wind Turbine Applicants should provide the information needed to evaluate the noise impact on the adjacent community.The largest impact, in my opinion is inside the Occupants Homes. This cannot be estimated without knowing a rational estimate of the expected dBC outside their homes.
The Industrial Wind Industry should disclose as a minimum , both source dBA and dBC Sound Power Ratings of their turbines and document estimates of the expected noise levels at the Property Lines of the Residents both in dBA and dBC so that it is possible to evaluate both the expected dBA and dBC inside the residences’ home.
Low frequency noise problems cannot be evaluated or anticipated from dBA data.
The HVAC Industry has acknowledged that Low Frequency Noise Rating data from Rooftop Units and Central Station Fan Units are important to achieve acceptable Room Noise Levels. To do this the HVAC Industry looked to its Technical Society ASHRAE to set these recommendations.
The ASHRAE Research that follows should not be ignored in setting Article X noise standards for evaluation of the expected noise from Wind Farms.
[Note: I am having difficulty with the way these charts display on my blog~ I am working on it!]
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SHRAE Research
Charles Ebbing
President Ebbing Acoustics
LaFargeville, NY
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