PDD Practice exam - mechanical duct layout

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    Michael Ermann

    That question is a bad one…I’m trying to get NCARB to change it…it’s based on an error in MEEB (that I’m also trying to get fixed in the next edition)
    Duct elbows do not help attenuate fan noise. This has been a myth, believed by many architects that architectural acousticians have been fighting against for years and NCARB suggesting that duct elbows mitigate fan noise on these exams that every architect sees has set that effort back decades. Argh,

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    Rachel Baker

    So in these situations, NCARB is looking for THEIR answer? It feels so backwards!

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    Michael Ermann

    UPDATE: I received assurances from MEEB’s authors that the next edition of the book will fix that passage…and from NCARB that they will very soon replace that bad question with a better one one.

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    Zhongyuan Luo

    I don't think this is a bad question. It's a typical "Cross Talk" situation where unwanted sound could be transmitted from one room to another through short, common air ducts. The owner wants more privacy, meaning less sound transmitted from one room to another. The best way to solve it is to provide long enough common ducts or dog-legged paths. So you should be looking for layout that has more bends. In option B, sound needs to travel through 7 bends to reach another diffuser. Other options has less bends. More bends doesn't mean more noise. Imagine a duct that has 1000 bends. More bends do mean more friction loss though. 

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    Michael Wentland

    This is a fine question.  Both B & C are answers with B being the best answer.  The question mentions nothing of "fan" noise and "privacy" is the key word.  

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