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Perimeter slab insulation in OpenStudio

asked 2019-03-13 19:25:45 -0500

duerstad's avatar

An OpenStudio residential model works well otherwise, but all attempts to use an F-Factor construction to add perimeter slab insulation are unsuccessful. In the model's construction set, an internal source construction for radiant heat yields the same plausible results whether it is in the top line (sc., box) for floors, "exterior surface constructions," or the bottom/third line, "ground contact surface constructions." When any F-Factor construction is placed in the top line and the internal source construction in the bottom floor line, the model runs, but the results are the same as if the F-Factor construction wasn't present at all. In this case the spaces tab/surfaces sub tab are the same as when the F-Factor construction simply isn't included. When an F-Factor construction is placed in the bottom line, ground contact, the model warms up, but then fails. In this condition, in the spaces tab/surfaces sub-tab, the F-Factor construction has replaced the internal source construction for all floor surfaces. Everything is green, thus defaults. The outside boundary is ground, as it always is when just using the internal source construction. At this failure, I see: * Severe * ZoneHVAC:LowTemperatureRadiant:SurfaceGroup = ZONE HVAC LOW TEMPERATURE RADIANT VARIABLE FLOW 13FLOORS does not have any surfaces listed. (13 is one of the zones of the model). I have files from both the successful run (internal source construction without F-Factor) and the failure, in case they might be helpful. I have read all the related questions, but still do not understand this.

Regarding the F-Factor construction itself, am I correct that what it calls "area" is the whole area of the slab . . . and is "perimeter exposed" the simple perimeter of the whole slab? I assume the F-Factor is the value of the insulation used.

Thanks for any light you can shed on what I do not understand here.

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answered 2019-03-14 11:55:46 -0500

It seems like you have questions about the inputs for F-Factor constructions. Have you read the EnergyPlus Input/Output Reference and Engineering Reference for this modeling approach? It should address your questions.

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I not only read, but studied all that material. I also read previous questions on the topic, such as Thus, I did not see that others were clear either about how this works in OpenStudio. I was precise, with great effort, in my question here and hope that someone can clarify this. Am I to believe that while BEopt apparently takes into consideration perimeter insulation, horizontal or vertical, OpenStudio ultimately only estimates?! Modeling this residence is very important; I'd really like an answer.

duerstad's avatar duerstad  ( 2019-03-15 08:59:12 -0500 )edit

Sorry, I concluded that you hadn't read that material because you made statements like "I assume the F-Factor is the value of the insulation used". It should be pretty clear from reading the description of the F-Factor input that it is not the same as an insulation R-value (and hence, is given a different name).

shorowit's avatar shorowit  ( 2019-03-15 09:33:52 -0500 )edit

answered 2019-03-17 20:59:45 -0500

Sorry, I concluded that you didn't read the document because you made a statement like "I think F-Factor is the value of insulation used." It will be quite clear when reading the description of the F-Factor input that it is not the same as the insulated R value (and therefore, given a different name).

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Asked: 2019-03-13 19:25:45 -0500

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Last updated: Mar 14 '19