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What's the best way to add thermal bridges in OpenStudio?

asked 2018-03-16 19:12:16 -0500

Jono's avatar

updated 2018-03-19 10:11:33 -0500

Hi Everyone,

I'm wondering what techniques modelers have for adding thermal bridges in OpenStudio. To be clear, I'm curious on how modelers put the values into OpenStudio once the bridges are already calculated.

I'm still learning this software and as far as I can tell, I have 3 options:

1) Use a multiplier on wall surfaces of a certain construction. Is this possible in OpenStudio? I can't seem to find it anywhere.

2) Make new surfaces that represent the thermal bridge areas and make a custom material with conductivities and widths that give me the U-value I want to represent the bridge. I liked this approach because although it's more work, it is a good visual representation. However, it requires much more drawing in Sketchup and leads to the infinite amounts of drawing errors that come with using the Sketchup Plugin.

3) Calculate an effective u-value for a surface with bridges, then apply that to the construction used in the surface. I was thinking of making a custom material with a negative conductivity that would represent all the losses from bridges, but it seems negative conductivities are not allowed in OpenStudio. The only way I can think of is to make new assemblies with a single material that gives the U-value I want. That would be a drag, because I like having the assembly made up of BCL materials so the model is transparent and easy to follow.

Look forward to hearing any tips the community is willing to share.

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answered 2018-03-19 17:24:45 -0500

I suggest option 2 - make a custom material.

You'll have your wall construction as you normally would, but take your studs + cavity insulation and make it one material that matches the thickness and de-rated U-value. This is what California Title 24 does for compliance models.

There is an excellent discussion here on de-rating wall insulation. I recommend referencing Title 24 stated values, which are from THERM models that account for thermal bridging.

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Thanks for the info. For reference, I would also like to add BC Hydro has a well-organized excel sheet to apply TBs for the de-rated U-value (see link):

Jono's avatar Jono  ( 2019-09-13 11:59:57 -0500 )edit

Just to add to the BC Hydro Excel sheet suggestion above, there's a neat online BETBG calculator. It does require a fair amount of manual "take-off" input (e.g., areas and thermal bridge lengths). We released the TBD measure in late 2020 (+subsequent releases) to automate this process entirely within OpenStudio.

Denis Bourgeois's avatar Denis Bourgeois  ( 2021-04-23 04:47:47 -0500 )edit

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Asked: 2018-03-16 19:12:16 -0500

Seen: 1,130 times

Last updated: Mar 19 '18