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Ground coupling - small building floor slab

asked 2022-01-10 00:50:29 -0600

Bill gravatar image

updated 2022-01-10 10:22:17 -0600

I am using latest OpenStudio Application 1.3.0 running OpenStudio SDK 3.3.0 to model small residential buildings.

The models run fine with Outside Boundary Condition = "Ground" but I understand this is not likely to be accurate with small footprint buildings and constant ground temps of 18C. When I try to use any of the other Outside Boundary Condition options the run fails, including Ground Preprocesser for which I get the error "The ExpandObjects program has not been run" (even though it is in the correct folder). I have reviewed the many posts here but they seem to be quite old and haven't helped. I can't find a measure in the BCL. The BCL says the "AEDG small to medium office slab and basement" measure requires a newer version of OpenStudio? There is nothing in the BCL under "Kiva".

Can someone please advise the simplest way to accurately model a floor slab for small buildings using the latest OpenStudio Application.

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If you want Kiva inputs added to the OpenStudio Application, you can create a new issue here and request it.

shorowit gravatar image shorowit  ( 2022-01-10 15:30:59 -0600 )edit

The enhancement request was posted by Bill here - great idea. I added a few notes.

Denis Bourgeois gravatar image Denis Bourgeois  ( 2022-01-11 09:25:50 -0600 )edit

@shorowit, does the NREL residential team not have any Kiva generation measures? Is that something that would be useful for your team?

macumber gravatar image macumber  ( 2022-01-11 21:47:06 -0600 )edit

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answered 2022-01-10 07:11:21 -0600

updated 2022-01-10 07:23:14 -0600

You can generate a complete set of KIVA inputs (foundations, settings, exposed perimeters) for your model using the Thermal Bridging and Derating (or TBD) Measure. The autogenerated exposed perimeters (if applicable) should reflect your model's exact configuration (e.g. geometry, boundary conditions) - nothing more needed. The generated settings are simply KIVA defaults, while the generated insulation configurations reflect a basic/generic circa 1980-1990s setup. Best to first rely on Apply Measures Now (to permanently generate all required KIVA inputs), which one can then adjust with a text editor (or preferably an SDK-based script). You can safely re-open your modified .osm in the App - it will preserve the generated KIVA inputs, despite not offering opportunities to further edit. (You may want to first try this out on a test copy of your model :).

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Many thanks Denis. When I run TBD with the setting "non thermal bridging" the measure fails: Error: undefined method `getThermalResistance' for # OpenStudio::Model::AirGap:0x000001a093d46608>

When I run with one of the default TB settings the measure runs, and correctly derates wall / roof surfaces but I get an EnergyPlus warning "Didn't find data for Surface Average Face Conduction Heat Transfer Energy" for the floor surfaces and there are no heat gains or losses through those surfaces.

Are you able to identify what I am doing wrong? Also not clear where I can modify the Kiva settings?

Bill gravatar image Bill  ( 2022-01-10 23:47:41 -0600 )edit

Bill, you found a bug! Sorry - we simply didn't have a single air gap material in our test cases, and therefore never triggered the same error you came across. It's fixed, tested, and re-released. Not sure about the 2nd E+ warning you mention - I can't reproduce it. Finally, as I first mentioned the only way to modify the TBD-generated KIVA inputs (like settings, or insulation configurations) is via a text editor (e.g. - or via an SDK-based script for the more experienced user.

Denis Bourgeois gravatar image Denis Bourgeois  ( 2022-01-11 06:38:46 -0600 )edit

Thanks again Denis. TBD measure now runs successfully but again EPlus run fails. I thought it might be something in my model or the weather file so tried it with the OSApplication Example file with Denver weather and still no luck - whether or not the TB options selected. A problem with how OSApplication itself is treating the measure output?

Bill gravatar image Bill  ( 2022-01-12 00:08:57 -0600 )edit

By example file, do you mean the seb.osm that comes with OpenStudio? And you have trouble running this model, without/with KIVA, and without/with TBD? That model has been part of the TBD test suite for a long time. I just ran a bunch of OpenStudio App v1.3 tests on it (Quebec City EPW & DDY files):

  • 256.76 GJ (original model)
  • 250.06 GJ (+KIVA inputs from TBD)
  • 250.06 GJ ("non thermal bridging" option in TBD, i.e. does not derate)
  • 254.35 GJ ("uncompliant" option in TBD)
Denis Bourgeois gravatar image Denis Bourgeois  ( 2022-01-12 03:23:26 -0600 )edit

No errors or relevant warnings in the ESO files. I do notice that the OpenStudio Results Measure is having difficulty creating an Envelope Summary for the original "seb.osm", but this has nothing to do with KIVA or TBD.

... by any chance, do you have any AirGap or Massless materials in your surface constructions facing ground conditions? These are not compatible with many ground conduction models in E+, including KIVA. Any chance you can share your OpenStudio model (e.g. Google Drive)?

Denis Bourgeois gravatar image Denis Bourgeois  ( 2022-01-12 03:39:28 -0600 )edit

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Asked: 2022-01-10 00:50:29 -0600

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Last updated: Jan 10