04-07-21 Planning Commission - Laserfiche WebLink

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