Strawbale and other thick wall assemblies modeling

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I will be modeling a straw-bale house, and was wondering again what is best practice with regards to modeling to the outside or inside of the wall, specially important here given the wall thickness. In the past I have heard practitioners argue for either one: for inside, I was told that it keeps the space volume accurate. For outside of the wall, I was told that solar radiation dominates, and is thus important to model to the outside wall. Anyone care to comment? For inner partitions, I have only heard agreement (i.e. center line of wall).

edwinguerra

asked 2020-08-07 00:42:51 -0500

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__AmirRoth__

updated 2020-08-08 13:14:37 -0500

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You could try it all three ways (outside/middle/inside) and see how much it changes the results. My guess is very little, assuming any inputs based on floor area/volume are also adjusted.

shorowit (2020-08-08 09:55:01 -0500) edit

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The most correct would be to mimic reality. To do this, you might consider the inside dimensions for volume (as your air barrier is on the inside I imagine), then use center line for your exterior wall areas (for thermal transmittance).

The most correct is not always the easiest, so for this reason there's usually some agreed upon convention to make your life easier as an energy modeller.

I have seen technical documents that recommend any one of the three methods (center line, inside, and outside), so I'm sure you could argue any of these to be acceptable practice. Keep in mind that using outside dimensions will be conservative from a total energy use perspective.

Hope this helps.