heat_pump_noise

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Calculate the sound pressure level an air source heat pump produces at an assessment position, and whether it meets the 37 dB(A) permitted development noise limit, using the method in MCS 020. The formula is Lp = Lw + 10 log(Q / 4.pi.r^2) - Ab. Lw is the A-weighted sound POWER level of the unit from its product fiche, energy label or the MCS product database. This is not the sound pressure level, which is a smaller number that already has a distance built into it; confusing the two produces an answer that is wrong by about twenty decibels. The figure for low noise mode must not be used. Q is the directivity factor, from the count of reflecting surfaces within one metre of the unit that extend at least a metre past it in two or more directions. The ground counts; vegetation does not. One surface gives Q=2, two gives Q=4, three gives Q=8. More than three cannot meet MCS 020 at all. r is the straight-line distance in metres to the assessment position, which is a window or door of a habitable room in a NEIGHBOURING property, at any floor. Every affected position must be checked separately, and the nearest is not always the worst. Ab is the barrier attenuation. Fences with gaps, and vegetation of any kind, count as no barrier. Where several units serve one position, list them all and they are combined logarithmically. Method from MCS 020. These calculators follow the published MCS methods, for understanding a system and checking a quotation. Anything that gets installed still needs a design and a site survey from a certified installer.