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HomeMy WebLinkAboutFile Documents.211 W Hopkins Ave.0078-2021-BRES (45) eimEG Initial Mechanical Noise Review Pan Abode IMEG #21001159.00 RECEIVED 05/21/2021 ASPEN BUILDING DEPARTMENT > IMEG Initial Mechanical Noise Review Pan Abode Aspen, CO IMEG #21001159.00 April 23, 2021 A. This report is a review of the expected noise produced at the Pan Abode property line by three condensing units and a generator located in an alleyway. The expected noise levels have been determined by combined that manufacturer's published noise data for the units as well as calculating the distance between each unit and the property line. 1. Aspen noise ordinances require that in a residential area the maximum noise produced by mechanical equipment, when measured at the property line, cannot exceed 55dBA during the daytime and 50dBA at night. 2. This report assumes that the noise measurements are taken by someone with a microphone at chest height (approximately 4' above the ground). Due to the close proximity of the equipment to the property line, these numbers can change by a noticeable amount as the microphone deviates from the assumed position (such as raising it above a fence or holding it closer to the ground where the units are located). a. The generator has been assumed to be running in the Quiet-Test low-speed mode, as the "normal" load will only be used during an emergency. B. The current plan for the delineating the property line is by adding a slatted fence along the alleyway. A slatted fence provides no acoustical attenuation due to having gaps between the boards. With this current fence the expected noise levels, measured at 4' AFF right on the property line, is 71.6dBA. This is over four times the allowed noise levels during the evening. 1. If the microphone, instead, is recording at the top of the fence (assumed to be 6' tall), the noise level is reduced to 63.4dBA. While this number is still 13dB too high for the noise ordinance, it shows how significant a small change in measuring distance can affect the overall noise levels. This will be the basis of our recommended treatment options, as increasing the path length the noise has to travel will provide the greatest benefit. C. If the fence is adjusted to be a solid fence (no air gaps), then the noise levels when measured at 4' AFF behind the fence is reduced to 47.1dBA. This meets the noise ordinance, even during the night-time quiet hours. However, if someone were to measure the noise above the fence (at our assumed 6' AFF height) the noise level returns again to the 63.4dBA level. RECEIVED 05/21/2021 8900 Keystone Crossing, Suite 210, Indianapolis, IN 46240 >317848.5045 >Fax:317844.2201 >irrK:y•rEtclom BUILDING DEPARTMENT 1. To help prevent this from happening, we would recommend increasing the height of the dividing fence to at least 7' tall, preferably 8'. This will reduce the noise levels measured at 4' even more but will also reduce the likelihood of someone trying to bypass the noise barrier by lifting the microphone above the fence for a "worst-case outcome". D. When we recommend a "solid fence", this does not mean that the fence needs to be solid concrete or a heavy brick construction. The most important point is that the fence has no airgaps in it; the fence could be constructed with 3/4" plywood and it will still be as effective as a CMU wall. E. Finally, it would be beneficial to inquire with the manufacturers of the condensing units and the generator to see if they offer a "quiet package" for their products. Typically, this includes quieter fan blades or wraps on condensing piping which can be noisy. It is always better to reduce the noise at the source than it is to add barriers in the way. Prepared by: Matthew T. Boris MTB/ \\files\Active\Projects\2021\21001159.00\ReportsNarratives\20210423 Initial Mechanical Noise Review.docx Initial Mechanical Noise for eR�Review `v IMEG #21001'fl`—.6eEI ` ED • April Page'��2" 1/2 0 2 1 ASPEN BUILDING DEPARTMENT