False ceiling: plenum or a layer of air in construction? (in EnergyPlus) [closed]

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Thank you for your reply. In the discussion that you mentioned, there are advantages and disadvantages listed for each strategy. Why do you recommend the 2nd one?

2 (on your list) is the most accurate because it correctly accounts for separate air volumes and external conduction. With your #1 the air volumes might be OK as long as the ceiling void isn't a return air plenum, however you would need to be sure that your external wall areas are correct, because the area adjacent to the ceiling void should not directly conduct to the occupied space. If you were careful about this and there are no return air plenums, then #1 could be an acceptable simplification, but it is less correct.

I don't recommend the 2nd one necessarily, I just wasn't very clear in my answer. I've amended the answer.