This brief report describes a simplified method for estimation of

levels of structure-borne sound in buildings to which a micro-wind

turbine (MWT) is attached. The method is applicable to two specific

designs of MWT, each for three lengths of mounting pole and for

masonry buildings. The output gives expected noise level for

given rotational speed of the MWT. Applicability and limitations

of the method are described. 

A more general methodology is provided in companion 

reports but requires specialist knowledge to implement. 

Structure-borne sound is notoriously difficult to predict

and several assumptions have been necessary in order to

produce a sufficiently simple estimation method. 

Therefore, caution is required in relying on the 

predictions until sufficient confidence has been built

up through experience of real installations

Eastwick, G

Elliott, AS

Evans, TA

Le Bescond, V

Moorhouse, AT

Ryan, A

von Hünerbein, S

Waddington, DC

English

This brief report describes a simplified method for estimation oflevels of structure-borne sound in buildings to which a micro-windturbine (MWT) is attached. The method is applicable to two specificdesigns of MWT, each for three lengths of mounting pole and formasonry buildings. The output gives expected noise level forgiven rotational speed of the MWT. Applicability and limitationsof the method are described. A more general methodology is provided in companion reports but requires specialist knowledge to implement. Structure-borne sound is notoriously difficult to predictand several assumptions have been necessary in order toproduce a sufficiently simple estimation method. Therefore, caution is required in relying on the predictions until sufficient confidence has been builtup through experience of real installations

University of Salford Institutional Repository

Defra NANR244Part 3: Prediction methodologyJanuary 2011Prepared byAndy Moorhouse1, Andy Elliott1, Graham Eastwick2, Tomos Evans1, Andy Ryan1, Sabine von Hunerbein1, Valentin le Bescond1, David Waddington11: Acoustics Research Centre, University of Salford, M5 4WT, www.acoustics.salford.ac.uk2: Encraft Ltd, Perseus House, 3 Chapel Court, Holly Walk, Leamington Spa, CV32 4YSThis research was commissioned by the previous government. The views and analysisexpressed in this report are those of the authors and do not necessarily reflect those ofthe Department for Communities and Local Government, the Department of Energy andClimate Change or the Department for Environment Food and Rural Affairs.The work was funded by the Department forCommunities and Local Government, the Department of Energy and Climate Changeand the Department for Environment Foodand Rural Affairs.Executive SummaryThis brief report describes a simplified method for estimation of levels of structure-borne sound in buildings to which a micro-windturbine (MWT) is attached. The method is applicable to two specificdesigns of MWT, each for three lengths of mounting pole and formasonry buildings. The output gives expected noise level forgiven rotational speed of the MWT. Applicability and limitationsof the method are described. A more general methodology is provided in companion reports but requires specialist knowledge to implement. Structure-borne sound is notoriously difficult to predictand several assumptions have been necessary in order toproduce a sufficiently simple estimation method. Therefore, caution is required in relying on the predictions until sufficient confidence has been builtup through experience of real installations. 01 NANR244, Part 3: Prediction methodologyContents1. Introduction 32. Applicability and limitations 43. Prediction method 54. Concluding remarks 95. References 902NANR244, Part 3: Prediction methodology1  Introduction This report defines a simple methodology for prediction of structure-borne sound from building-mounted micro wind turbines (MWTs). It isone of the outputs of the project reference NANR244funded jointly by Defra, DECC and CLG from October2009 to September 2010. The purpose of the project was to “research the quantification of vibration from a micro turbine, andto develop a method of prediction of vibration andstructure borne noise in a wide variety of installationsin the UK”. The project was motivated by a desire tostimulate use of renewable energy generation by removal of planning restrictions. Permitted development rights are currently granted for some renewable energy generating technologies but building-mounted MWTs are excluded due to concernsabout the potential impact of structure-borne noiseand vibration on attached neighbouring dwellings. The outcomes of the project are described in three reports:Part 1: Review and proposed methodology1;Part 2: Development of prediction method2;Part 3: Prediction method.This report is Part 3, the aim of which is to present asimple form of the prediction methodology suitable foruse by non-specialists. Parts 1 and 2 include detailedsupporting information, together with a more generalprediction methodology suitable for use by specialistsin situations not covered by the simple method.  Whenever operating machinery is connected to abuilding there is potential for structure-borne sound;the simple method presented here predicts the level ofstructure-borne sound inside a room in a building towhich an MWT is attached. However, it is not intendedto provide guidance on the acceptability or otherwiseof the resulting noise levels. The prediction method employs the concept of a ‘reference installation’, defined as a solid brick buildingwith a micro-wind turbine (MWT) attached to thefaçade directly backing onto the ‘most exposed room’.The most exposed room is defined as having a volumeof 50 m3 and a reverberation time of 0.5 secondswhich is typical for many living rooms and bedrooms.The expected levels of structure-borne sound in suchan installation are presented in graphs. Adjustmentscan then be made for cavity or solid brick walls, forroom volume and for building layout, in particularwhere the room of interest is not immediately adjacentto the MWT.Prediction of tactile (feelable) vibration was includedin the original aims of the project. However, no incidences of perceptible vibration were encounteredin field trials2 and therefore, in the interests of simplicity, no method for prediction of vibration is provided in this report. Guidance is given in Part 22 soas to enable suitably qualified specialists to carry outsuch predictions should the need arise in the future.Rattling of fixtures and fittings and building damagedue to vibration was also considered in parts 1 and 2but, again, since no cases were encountered in fieldtrials these potential sources of disturbance are notdealt with here.  It is important to take account of the limitations of themethod as described in the following section. 03 NANR244, Part 3: Prediction methodology2  Applicability and limitations The prediction method applies to structure-bornesound, i.e. sound transmitted through the buildingstructure from the points of attachment of the MWT.Airborne sound, which is transmitted through the air,through windows etc., is not included but could besignificant in various common scenarios. Therefore, aseparate assessment of airborne sound is recommended.  The simplified method presented in this report appliesto two specific models of MWT, masonry buildings andwall mountings of three different lengths (where mastlength is defined as the free pole length, i.e. from thetop bracket). The majority of current domestic installations are of these types. The more generalmethodology, presented in the companion reports(particularly Part 2) is applicable to other MWT models,different mounting systems including roof mountingsand building types other than masonry. However, themethod is more complicated and will require an assessment of the properties of the relevant MWT,mast or building by a specialist and will possibly alsorequire measurements to be made of the componentto be changed.  For the two models of MWT studied here the dominant frequency range for structure-borne soundwas in the range 160-300 Hz. The corrections given inFigure 3, Table 1 and Table 2 are optimised for this frequency range. If, for other models of MWT ormounting system, there is significant structure-bornesound outside this frequency range then this will needto be taken into account and potentially a new set ofcorrections will need to be derived. Corrections given for cavity walls are derived from asmall number of measurements and should be treatedwith some caution since the acoustic performance ofcavity walls is known to vary significantly with detailssuch as the type of wall ties and junctions. Based on the field trials reported in Part 2 the predicted noise levels are expected to lie within aboutplus or minus 5dB of the measured values. Consideringthe complexity of the phenomena involved in generation and transmission of sound this is considered to be a reasonable accuracy. However, italso indicates that variations are likely from site to sitedepending on wind conditions and direction andbuilding construction details. The noise levels are given as a function of rotationalspeed of the MWT. Ideally, noise levels would be givenin terms of wind speed but there is insufficient knowledge of how rotor speed varies with wind speedto be able to provide the results in this form. In part 2,sound levels are given in terms of wind speed for somespecific wind conditions which can be related toNOABL databases. However, the results cannot easilybe generalised to other wind conditions. 04NANR244, Part 3: Prediction methodology3  Prediction method A flow chart for the prediction is given in Figure 1. Thestarting point is the noise levels in the reference installation obtained from Figure 2 or Table 1. Havingselected a type of MWT and mast length the noiselevel in the reference installation is read from the appropriate curve of Figure 2 or column of Table 1 fora given rotational speed. A correction can also be made for room volume according to Table 3. The correction is zero for 50 m3volume since this is the assumed size of most exposedroom of the reference installation. For larger rooms,slightly lower sound levels are expected and for smallerrooms slightly higher values. 05 NANR244, Part 3: Prediction methodologyFigure 1: Flow chart for prediction of noise levels as a function of rotor speed.06NANR244, Part 3: Prediction methodologyFigure 2: Sound pressure level in the reference installation for three different mast lengths. Upper: MWT1. Lower: MWT2.07 NANR244, Part 3: Prediction methodologyTable 1: Tabulated sound pressure level  in the reference installation for three different mast lengths for MWT1 and MWT2Correction for solid brick constructions 0 dBCorrection for cavity brick construction -10 dB08NANR244, Part 3: Prediction methodologyTable 2: correction for wall constructionTable 3: correction for room sizeFigure 3: Corrections for remote rooms (the corrections for vertical transmission are the same as those for horizontal transmission)Volume (m3) 25 30 40 50 60 80 100 120 150Correction (dB) 3 2 1 0 -1 -2 -3 -4 -5Finally, in many situations the room of interest will notbe the most exposed room. An adjustment may bemade for more remote rooms by using the correctionsgiven in Figure 3.09NANR244, Part 3: Prediction methodology4  Concluding remarksUsing the above procedure it is possible to estimatethe noise level in a masonry building caused by an attached MWT. The noise levels are given as a function of the rotorspeed. Ideally, noise levels would be given as functionof wind speed but there is insufficient knowledge ofhow rotor speed varies with wind speed to be able toprovide the results in this form. In part 2, sound levelsare given in terms of wind speed for some specificwind conditions but these cannot easily be generalisedto other wind conditions. Due to guidelines for government reports the makesand model of MWT has been anonymised in this seriesof reports. Due to the large number of assumptions made inorder to create a method of sufficient simplicity it isadvisable to exercise caution in relying on the predictions until there is a sufficient body of data fromfield trials. 5  References1. Andy Moorhouse, Andy Elliott, Tomos Evans, AndyRyan, Sabine von Hunerbein, Graham Eastwick,Valentin le Bescond, David Waddington (2010).Noise and vibration from building-mounted microwind turbines: Part 2 Results of measurements andanalysis. University of Salford report ref NANR244. 2. Andy Moorhouse, Andy Elliott, Sabine von Hunerbein, Graham Eastwick, David Waddington(2010). Noise and vibration from building-mountedmicro wind turbines: Part 1 Review and proposedmethodology. University of Salford report refNANR244. University of SalfordSalford Greater ManchesterM6 6PUUnited Kingdom T +44 (0)161 295 5000F +44 (0)161 295 5999www.salford.ac.uk

Noise and vibration from building-mounted micro wind turbinespart 3 : prediction methodology

Noise and vibration from building-mounted micro wind turbines: Part 1 Review and proposed methodology.

Tomos Evans, Andy Ryan, Sabine von Hunerbein, Graham Eastwick, Valentin le Bescond,

https://salford-repository.worktribe.com/file/1454793/1/Defra_NANR244_Final_Report_Pt3_Prediction_methodology.pdf

Noise and vibration from building-mounted micro wind turbines part 3 : prediction methodology

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