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04-07-21 Planning Commission
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04-07-21 Planning Commission
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4/2/2021 2:30:25 PM
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Mr. Jeff Hejl February 5, 2021 <br />Boston Scientific Corporation Page 3 <br /> <br /> <br />Chiller noise at a radius of 300’ from chillers, which is within the BSC property line <br />boundaries. The 300’ radius is shown in Figure 1. There will be three chillers on the roof of <br />the addition, although only two will operate simultaneously. Further, we have been told that <br />the two chillers will only operate at 75% of full load capacity simultaneously. The <br />manufacturer’s sound data at 75% of full load was used in the calculations. <br />We propose to use a barrier wall to mitigate the chiller noise. Figure 2 shows an elevation <br />sketch of the building addition and site that was used for calculations to determine the barrier <br />wall design and predict chiller noise. Sample calculations are in Attachment B. <br /> <br />Figure 2 – Sketch showing the chillers and barrier wall arrangement used to evaluate noise <br />for the Building 14 addition. <br />For a 13’ high barrier, the noise level at 300’ from the building was calculated to be 41.6 dBA. <br />The total noise was 49.7 dBA when combined with the ambient noise level of 48.9 dBA. <br />Raising the wall an additional 6’ to match the penthouse roof elevation reduce chiller noise to <br />36.8 dBA, however when combined with the ambient noise of 48.9 dBA, the total noise was <br />only reduced 0.5 dB to 49.2 dBA. It may not be good value to raise the barrier wall above 13’. <br />The objective of our engineering work was to determine mitigation necessary to control chiller <br />noise at the residential property lines. We determined a barrier wall height that will attenuate <br />chiller noise to a level that meets the MPCA requirements when combined with the other BSC <br />noise in the environment. The calculation results show that the wall should be at least13’ <br />high. We will work with RSP to evaluate the final wall details. <br /> <br /> <br />
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