[EnergyPlus_Support] Ground temp problems

["taharvey2001" <taharvey@xxxxxxxxxxxxxxxx>]

We keep finding the ground loss methods in E+ nearly unusable. The fact that the Slab 
preprocessor generates a fixed floor temperature at the outside surface of the slab, 
instead of the outside surface of the insulation causes all sorts of havoc with the rest of 
the dynamic simulation. We always end up with bogus building results from using 
slab.exe. With well insulated slabs we'll  see nonsense like the slab heating the space with 
a large positive energy balance during night setbacks because the static temperature it on 
the wrong side of the insulation.

It would be much more useful (and accurate) if the slab & basement preprocessors would 
generate ground temperatures on the *outside* surface of the *whole* floor assembly (or 
basement wall), then you would model the wall or floor construction assembly as normal 
in E+. That would allow the slab or wall surface temperature to float, and react realistically 
to internal conditions and solar radiation. Also with the current preprocessor configuration 
the preprocessor doesn't handle multi-layer basement wall assemblies (ICFs, etc).

I'd like to hear any workarounds til this gets fixed.

Currently we have been adding 6' of soil in a few layers below the slab, and running a 
undisturbed soil temperature program, to generate monthly soil temps for a depth equal 
to the average vert. depth + horz. length. Of course this doesn't consider the building 
influence on ground temperatures. At high levels of ground insulation it appears to get 
reasonable results, though at low or no insulation I have my concerns. 



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