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Community and Q&A

How best to model and heat/cool a 2-floor space?

bennettg | Posted in General Questions on

What is the best way to model the heating & cooling loads of a 2-floor space with a  mezzanine?  I have an “A-frame” 1.5 story with a 2-story cathedral ceiling over the living area and a smaller second floor area open to the floor below.

Is the best approach to consider it one, two story space, or two separate spaces when modeling the thermal loads and when designing the supply and return ducting for a forced air system?

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  1. Expert Member
    Peter Yost | | #1

    Hi Bennett -

    For the loads, it's all about the geometry of the enclosure, it's u-values, and it's airtightness (ACCA Manual J).

    In terms of supplies and returns, that also tied to the above but worked out with ACCA Manual D.

    Beyond that, my response will kick this up to the home page so that others with more HVAC background can help.


  2. bennettg | | #2

    Thanks, Peter! I think I understand the basic principles for getting the load for the entire space. I'm looking for some encouragement that there is a well thought out process for conditioning a space like this - two stories of open space with two living areas on two floors within it. There are many anecdotes of it not being done well across the web and some here on GBA. OTOH, there are commercial buildings with a two story mezzanine open to an entire glass wall that seem ok.

    My own experience is that the space is more comfortable when the air handler runs a fair percentage of the time, conditioning and mixing the entire volume of air in my house at least once an hour.

    Surely someone here has "been there, done that" and can point out that Manual J&D get directly at this problem, or there is an approach to using them that does.

    I'll see what I can find on manual D in the meanwhile.
    ETA: I found the NREL Building America program document "Air Distribution Basics and Duct Design" a good introduction. The Orlando house example makes a lot of sense, but is 1-story. I'm looking for similar treatment of of the two-story-with-open-area-between problem.

    Thanks again.

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