ESB TONAL NOISE ASSESSMENT. 30 May West Offaly Power Station. Report Author: Stephen Kearney

Transcription

1 Allegro Acoustics Limited, Unit 2A Riverside, Tallaght Business Park, Tallaght, Dublin 24 Tel/Fax: +353 (0) ESB West Offaly Power Station TONAL NOISE ASSESSMENT 30 May 2016 Report Author: Stephen Kearney Report: DC

2 REPORT CONTROL Document Title: Tonal Noise Assessment Project: West Offaly Power Station Tonal Noise Assessment Client: Electricity Supply Board West Offaly Power Station Job Number: DC File Origin: Report Author: Signed: Date: 30 May 2016 Z:\Allegro Acoustics\Projects\DC1521\Reports Stephen Kearney BEng MIEI Issue Date Status Checked By Signed 1 27/05/2016 DRAFT 2 30/05/2016 FINAL David Cawley BE MSc CEng MIEI MIOA David Cawley BE MSc CEng MIEI MIOA Page 2

3 TABLE OF CONTENTS 1 INTRODUCTION Description of Terminology METHODOLOGY Noise Monitoring Meteorological and Local Environmental Conditions RESULTS Frequency of Tonal Component Noise Measurements Noise Mapping DISCUSSION CONCLUSION REFERENCES APPENDICES Appendix A - Noise Measurement Data Appendix B - Calibration Certification Page 3

4 1 INTRODUCTION Allegro Acoustics was retained by ESB West Offaly Power Station to undertake a noise assessment at the West Offaly Power Station in Shannonbridge, Co. Offaly. The purpose of this assessment is to locate the source of a tonal component in the 160Hz 1/3 rd Octave band identified during annual environmental monitoring at NSL3 on the 12 th and 13 th of May This noise assessment was undertaken on the 26 th of May This report presents the results of this noise assessment and discusses the findings. 1.1 Description of Terminology Noise indicators referenced throughout this report are defined below. LAeq: Equivalent Continuous A-weighted Sound Level. The continuous steady noise level, which would have the same total A-weighted acoustic energy as the real fluctuating noise measured over the same period of time. Leq: Equivalent Continuous Unweighted Sound Level. The continuous steady noise level, which would have the same total unweighted acoustic energy as the real fluctuating noise measured over the same period of time. NSL: Noise Sensitive Location; in the case of this assessment, the Noise Sensitive Location is representative of the nearest residential receptors to the Power Station. 1/3 rd Octave Band Analysis: Frequency analysis of sound such that the frequency spectrum is sub divided into bands of one third of an octave each. An octave is taken to be the frequency interval, the upper limit of which is twice the lower limit (in Hertz). This analysis can be used to identify a tonal component to audible sound (note such as a hum, whine or whistle). 1/12 th Octave Band Analysis: More in depth frequency analysis of sound such that the frequency spectrum is sub divided into bands of one twelfth of an octave each. An octave is taken to be the frequency interval, the upper limit of which is twice the lower limit (in Hertz). This analysis can be used to identify a tonal component to audible sound (such as a hum, whine or whistle). 2 METHODOLOGY 2.1 Noise Monitoring A number of short (1 minute) measurements were taken at numerous locations in the vicinity of NSL3 (the Old Fort Restaurant) and at numerous locations throughout the Power Station site. All measurements were taken using an NTi Audio XL2 sound level analyzer. The sound level analyser was set up to simultaneously measures sound pressure levels in each 1/12 th Octave Band between 7Hz and 215Hz. A 1/12 th octave sound level analyser was used for this assessment as it provides a narrow filtering and hence a more detailed assessment. The sound level analyser was calibrated before, throughout and after the survey and up to date calibration certification for the sound level meter and calibrator is available to view in Appendix B of this report. Page 4

5 2.2 Meteorological and Local Environmental Conditions There was no precipitation during noise measurements on the 26 th of May The ground was dry throughout all measurements. The wind speed and temperature was measured during each noise measurement using a Skywatch Explorer 2 hand held anemometer. During all measurements, the average wind speed and occasional gusts were observed to remain below 5m/s. Air temperatures were observed to range from 7 C to 12 C during all measurements. There was no mist or fog observed during noise measurements with conditions being described as clear. 3 RESULTS 3.1 Frequency of Tonal Component Noise monitoring was carried out at NSL3 during an annual environmental noise survey on the 12 th and 13 th of May Noise measurements taken at NSL3 during day, evening and night time measurements showed the presence of elevated sound energy in the 100Hz and 160Hz 1/3 rd octave frequency bands. Only the elevated sound energy in the 160Hz 1/3 rd octave frequency band was sufficiently above both its adjacent 1/3 rd octave bands to be deemed tonal according to the methodology outlined in Guidance Note for the Noise, NG4 [1]. As such only the 160Hz 1/3 rd octave frequency band will be discussed in detail in this report. Figure 1: Extract from a report previously issued to WOP on the 18th of May 2016 detailing the results of an annual environmental noise survey. This graph shows the tonal component in the 160Hz 1/3 rd octave band. 1/12 th octave measurements were taken at NSL3 using a sound level analyser to determine the exact frequency of the offending noise source. Figure 2 below shows that tonal components were measured at 100Hz and 150Hz. As both of these tones are exact multiples of 50Hz i.e. the frequency of electricity in Ireland, it is highly likely that the source of the tone is electrical noise. As only the 150Hz tone falls with the 160Hz 1/3 rd octave frequency band, only noise at 150Hz is assessed in this report. Page 5

6 Figure 2: Graphed results of a 1/12 th octave measurement taken at NSL3 between 7Hz and 215Hz showing elevated sound energy at 100Hz and 150Hz. 3.2 Noise Measurements The results of measurements taken at every 1/12 th octave between 7Hz and 215Hz are presented in Appendix A of this report. Table 1 below shows the measured Sound Pressure Level, L eq at 150Hz at each measurement location. The location of each measurement is shown in the noise maps below. Measurement Table 1: Summary of measured L eq at 150Hz. db Leq 150Hz Page 6

7 3.3 Noise Mapping Figures 1 and 2 below show a contoured noise map of measured 1/12 th octave noise levels at 150Hz at the Power Station and at NSL3. Figure 1: 2D noise map of measured 1/12 th octave noise levels at 150Hz throughout the Power Station. Figure 2: 2D noise map of measured 1/12 th octave noise levels at 150Hz at NSL3. Page 7

8 4 DISCUSSION Figure 2 above shows that there is elevated sound energy at 150Hz emanating from behind a palisade fence at measurement locations 5 and 6 near NSL3. Allegro Acoustics personnel observed the source of this tone to be an electrical valve or similar (view was partially obstructed by general clutter behind the fence). Measurements 2 and 3 were taken on the other side of a 2m wall obstructing the view of the noise source behind the palisade fence. These measurements have the exact same line of sight to the Power Station as measurements 5 and 6 and are a similar distance to the Power Station. Measurements 2 and 3 show no evidence of elevated sound energy at 150Hz. The tone at 150Hz is not detectable on the other side of the large wall (measurements 2 and 3) which completely blocks the line of sight to the palisade fence and still maintains clear and direct line of sight to the Power Station. This indicates that the problematic noise source at NSL3 is coming from behind the palisade fence and not from the Power Station. Figure 3: Picture showing noise source behind palisade fence and the 2m wall blocking the noise source from measurement locations 2 and 3. This noise source was not immediately obvious during the initial environmental noise survey as the tone blends in with the generic hum from the Power Station during night time measurements and is drowned out by traffic noise during the day and evening time measurements. In order to firmly rule out the Power Station as a potential source, 1/12 th octave noise measurements were taken throughout the Power Station at 150Hz. A noise map showing the contoured distribution of sound energy levels at 150Hz throughout the Power Station is displayed in Figure 1 above. Figure 4 below shows the contoured noise map of the Power Station superimposed onto a satellite image of the area. There is some elevated sound energy at 150Hz at the Power Station, this sound energy is however largely shielded from NSL3 and partially shielded from NSL1 and NSL2 by the Power Station and Bord Na Móna pant and buildings. Measured noise levels at NSL1 and NSL2 during the environmental noise survey were not found to be tonal using the assessment methodology outlined in Guidance Note for Noise, NG4 [1]. These locations were found to be in compliance with the limits set out by the EPA in IEL licence P for the Power Station. There was no elevated sound energy measured at the Power Station at 150Hz on the north or west façades of the Power Station so it is deemed very unlikely that elevated sound energy at NSL3 at 150Hz could be attributable to the Power Station. Page 8

9 Figure 4: 2D noise map of measured 1/12 th octave noise levels at 150Hz at the Power Station superimposed on top of a satellite image showing the Power Station and NSL1, NSL2 and NSL3. 5 CONCLUSION Noise levels were measured at NSL3 in every 1/12 th octave band between 7Hz and 215Hz. It was found that the cause of the tonal component in the 160Hz 1/3 rd octave band measured during the environmental noise survey is attributable to a tone at 150Hz. 1/12 th octave noise measurements were taken at numerous locations near NSL3 and at numerous locations throughout the Power Station. These measurements were mapped onto contoured noise maps to identify areas of elevated sound energy at 150Hz at both NSL3 and at the Power Station. These maps show that there is elevated sound energy at NSL3 emanating from an electric valve or similar on an oil tank located behind a palisade fence at NSL3. There was no elevated sound energy measured at the Power Station at 150Hz on the north or west façades of the Power Station so it is not considered possible that elevated sound energy at NSL3 at 150Hz could be attributable to the Power Station. Figure 2 above shows elevated sound energy at 150Hz measured beside the palisade fence. Figure 2 also shows that there are no elevated noise levels at 150Hz at NSL3 once the line of sight to the palisade fence is obstructed but there is still a clear line of sight to the Power Station (measurements 2 and 3). This indicates that the source of the tone at 150Hz is coming from behind the palisade fence and not from the Power Station. Following the assessment of elevated noise levels in the 160Hz 1/3 rd octave frequency band it has been concluded by Allegro Acoustics that the source of elevated sound energy at NSL3 is from an electric valve or similar behind a palisade fence at NSL3 and is not attributable to the Power Station. Page 9

10 It is otherwise concluded that there is a low level of sound energy in the 160Hz 1/3 rd octave frequency band emanating from the Power Station. However Allegro Acoustics has concluded that this is not significant enough to be defined as tonal in nature according to the methodology outlined in Guidance Note for Noise, NG4 [1], or to cause annoyance due to perceived tonal characteristics. 6 REFERENCES [1] Guidance Note for Noise: License Applications, Surveys and Assessments in Relation to Scheduled Activities (NG4) ENVIRONMENTAL PROTECTION AGENCY: 2016 [2] ISO 1996 Acoustics Description and Measurement of Environmental Noise INTERNATIONAL STANDARDS ORGANISATION: 2003 [3] Guidelines for Community Noise WORLD HEALTH ORGANISATION: 2000 [4] BS4142 Methods for rating and assessing industrial and commercial sound BRITISH STANDARDS: 2014 Page 10

11 Appendix A Noise Measurement Data

12 Frequency Testing Agency: Testing Operator: SLM: SLM Serial Number: SLM Factory Calibration Date: Sound Field Correction: Bandwidth: Time Weighting: Allegro Acoustics Stephen Kearney BEng MIEI NTI Audio - XL2 A2A E0 18/06/2015 Free Field 1/3 rd Octave - Fully Integrating Fast Measurement Number Hz

13

14 Appendix B Calibration Certification

15