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[EnergyPlus_Support] Ground Temperature

In E+, there's a field for specifying ground temp.
For a very big slab on grade 1 floor building, 100,000+ sqft.
The core ground temp will be different from perimeter ground temp.
  Perimeter ground temp will be close to "undisturbed" ground temp.
  Core ground temp will be close to indoor air temp.
So, is the Average ground temp calculated by "slab.exe" the solution
which should be filled in the ground temp field in E+ idf file ?
Is there any suggestions how accurate slab.exe is ?

For the very big slab on grade 1 floor building, 100,000+ sqft.
  interior zone floor will not have ground temp = avg. ground temp.
  exterior zone floor will not have ground temp = avg. ground temp.
So then the load calc and system sizing for zones in E+, which uses 
average ground temp, will be off some error.
The error in the 100,000+ sqft case is "big".

Is there any way to deal with it ?

>Msg#1005<mjwitte@g...> wrote:
>The ground underneath a building tends to be much closer to 
>the indoor temperature of the building than the undisturbed 

>There is a utility included with EnergyPlus called "slab.exe" in the 
>EnergyPlus\PreProcess\GrndTempCalc\ folder. This utility calculates 
>monthly core, perimeter, and average ground temperatures...  

>Msq#250<mjwitte@g...> wrote:
>If you have no other data, a reasonable assumption is to use 18C for
> all 12 months for the ground temperature and to describe the slab 
>floor construction with concrete as the outside layer (no soil layer 
> as some of the examples show).  This is reasonable, because the 
> ground temperature under the main portion of the floor of a 
> conditioned space tends to stabilize to a temperature driven by the 
> indoor conditioned space temperature.

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