Simulation runs without ground temperatures set?

asked 2021-09-23 09:30:09 -0500

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updated 2021-09-23 09:36:17 -0500

My model runs fine. Yay! However, I want to scrutinize what's happening with the ground slab heat transfer: is the heat transfer reasonable? how is the heat transfer being calculated and what are the ground temperatures in the model? There's a good number of posts that mention ground temperatures (i.e. adding to a model), but I have not found any that describe how to either look at model results since my model runs, or to look at the osm/idf/other file to inspect how ground temperature is being addressed. Could someone help me with that?

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answered 2021-09-23 10:37:28 -0500

Petros Dalavouras

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In openstudio you cannot set directly the ground temperature however, you can use a measure if you want to change it. By default your simulation runs with a constant ground temperature of 18oC throughtout the year, which you can also see at the .err file when the simulation completes. You will get a message like the one below:

* Warning * GetHTSurfaceData: Surfaces with interface to Ground found but no "Ground Temperatures" were input. * ~~~ * Found first in surface=SURFACE 1 * ~~~ * Defaults, constant throughout the year of (18.0) will be used.

As far as the heat transfer is concerned it depends from the outside boundary condition of your floor surface and the heat balance algorithm you chose. For more information you can see the documentation here and here. The most precise way, to my knowledge, would be to use KIVA with a measure. I hope this helped

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To add to what's above, it's a good idea to familiarize yourself with the different boundary conditions you can set in OpenStudio: - The "ground" condition is the default and is set at 18C constant if unmodified - F-Factor method you may be familiar with from ASHRAE 90.1: https://unmethours.com/question/11062... - The "foundation" condition uses 3-d heat transfer to find the heat loss of your foundation objects. https://unmethours.com/question/44879...

Jono ( 2021-09-23 15:04:47 -0500 )edit

Thank you both very much for the responses. Very helpful and great reference point. Is KIVA accessible in an existing measure? Or are you referring to writing a new measure? I haven't written one measure yet. There's a first time for everything but I'm looking for a way to do it with brute-force editing of osm/idf file if it's not too programmy. 65F is not a bad start.

keb ( 2021-09-23 15:17:35 -0500 )edit

See the 2nd hyperlink in my previous comment. In short, there is an OS measure that will create everything you need. You can then open a text editor to make any adjustments if required. It's really not that complicated once you get used to it. Best of luck :)

Jono ( 2021-09-23 15:19:44 -0500 )edit

Thanks I'll look into it. That doesn't sound like much of a learning curve in so far as getting perhaps monthly ground temps into the model.

keb ( 2021-09-23 15:54:10 -0500 )edit

I'm not sure how I get this measure from OS SDK into OS. Is this actually the one I want?

keb ( 2021-09-23 16:16:54 -0500 )edit

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