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How do you model wood stud walls in EnergyPlus.

asked 2022-08-16 11:41:10 -0500

Crawford's avatar

updated 2022-08-16 17:08:47 -0500

We are new to Energy Plus, so this may seem like a "dumb question" to some of you. It seems there is no basic construction set for this type of wall.

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@Crawford you may find this post useful (or search for "energyplus thermal bridge" on this forum). EnergyPlus only calculates conduction outside-to-inside through a surface, so you can either:

  • Split the wall into a "stud" area vs. "cavity" area, then assign each their own appropriate construction assembly
  • Use a single wall, but define a "representative" material layer that accounts for combining the stud + cavity portions

@mattkoch's answer to use ASHRAE Table A3.4 uses the second approach

Aaron Boranian's avatar Aaron Boranian  ( 2022-08-18 08:19:59 -0500 )edit

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answered 2022-08-17 22:45:42 -0500

mattkoch's avatar

I tend to go by ASHRAE 90.1 For example, ASHRAE-90.1-2016 Appendix A3.4 Wood-Framed Wall. A wood-framed wall is then a layered construction of, for example, 1/2" stucco, 1/2" fiberboard, 3-1/2" wood framed wall with R-13 per A3.4, 1/2" gypsum board. I tend to not add the interior and exterior air film R/U-Values, because these are added by EnergyPlus.

The downside is, A3.4 only gets you the R/U-Value, not the heat capacity or mass density. Those you have to invent (estimate) by considering stud spacing and stud thickness, as well as wood and insulation heat capacity and mass density. Per ASHRAE, this is not a mass wall, though, so in a pinch, you might be able to do without.

EnergyPlus is a powerful simulation engine but a poor user interface, so ready-made anything are hard to come by - though its Examples folder has many an example .idf file. NREL developed OpenStudio as an open-source user interface on top of EnergyPlus. It may not have a wood-frame construction either, but it has a large library of "measures" that can be run from within OpenStudio, and there may be a wood-frame construction among them.

You can either pay "the man" license fees to get a commercial EnergyPlus user interface where all kinds of constructions (and anything else) are drop-down, or you can save a lot of software money in exchange for (much more) labor money and a lot of elbow grease and find/develop these yourself. The advantage of the former is speed to production, the advantage of the latter is you really learn how it all works. Give someone a fish vs. teach someone to fish ...

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Are there examples anywhere that show how you include the thermal mass of the wood framing with insulation included? The "Typical Insulated Wood Framed Exterior Wall" uses a NoMass material which appears to just be the straight R-Value of batt Insulation.

bwatanabe's avatar bwatanabe  ( 2023-12-06 09:36:57 -0500 )edit

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Asked: 2022-08-16 11:41:10 -0500

Seen: 694 times

Last updated: Aug 17 '22