EnergyPlus ground domain - Slab-ON-grade with vertical perimeter insulation

edit

EDITED to remove my confusion between the old slab pre-processor vs the newer ground domain functionality, based on Jamie's helpful feedback.

Hi Community

Sorry for long post but I have been trying to understand this for years. I have Googled and looked at some existing topics on this forum, but can't seem to find anything directly discussing my issue. I will CC this to DesignBuilder support for any comment, but I figure it may be more of an EP question than a DB question.

PROBLEM

Re: EP 9.4.0-217a24fc09 with DesignBuilder v. 7.3.1.003 as front-end on MS Windows 11 platform.

I try to model vertical perimeter insulation board placed around the slab-on-ground (concrete surface bed in my local terminology).

For now I am using the "ground domain" approach. (My next thing to try will be Kiva, which looks amazing, but I went for the GD approach because it seems more mature/tested.)

I set up a ground domain as per attached screen snips in DesignBuilder. When I have no insulation, everything runs fine. But with vertical perimeter insulation, I get the following from eplusout.err (full .err file attached):

   ************* Beginning Simulation
   ** Severe  ** Site:GroundDomain:SlabDoEndOfIterationOperations: Out of range temperatures detected in the ground domain.
   **   ~~~   ** This could be due to the size of the loads on the domain.
   **   ~~~   ** Verify inputs are correct. If problem persists, notify EnergyPlus support.
   **  Fatal  ** Preceding error(s) cause program termination
   ...Summary of Errors that led to program termination:
   ..... Reference severe error count=1
   ..... Last severe error=Site:GroundDomain:SlabDoEndOfIterationOperations: Out of range temperatures detected in the ground domain.
   *************
   ************* ===== Recurring Error Summary =====
   ************* The following recurring error messages occurred.
   *************
   *************  ** Warning ** Temperature out of range [-100. to 200.] (PsyPsatFnTemp)
   *************  **   ~~~   **   This error occurred 30 total times;
   *************  **   ~~~   **   during Warmup 0 times;
   *************  **   ~~~   **   during Sizing 30 times.
   *************  **   ~~~   **   Max=-1058.994812 C  Min=-35351.626953 C

As I understand, a numerical method inside EP is going awry with temperatures shooting off to extreme (cold) values instead of converging nicely.

I have this problem on most occasions that I try to model vertical perimeter insulation. I tried changing aspect ratio, domain size etc thinking I was onto something, but ultimately these were proved to not be the critical parameters. I could never find a pattern to success/failure of the sims.

POSSIBLE SOLUTION

It seems that for my local slab-ON-grade standard building practice (South Africa), with below-grade vertical perimeter insulation against the foundation wall (the below-grade wall above footing) I should rather model as slab-IN-grade with the vertical insulation ticked and just accept some physical inaccuracy due to the slab being modelled in-grade instead of on-grade. I have now done this with three different insulation specs, three sims in a row. All of them ran successfully! For me, this sim reliability was unheard of with [slab-on-grade + vert. perim. insul.]. I'd only get a successful run occasionally, by luck I guess.

QUESTION

Am I correct that for sims using ground domain, slab-on ... (more)