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Basement walls exposed to outdoors

I want to model a building with a basement floor. There is a sunken plaza, and part of the basement floor is exposed to outdoors.

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I'm considering two options for how to set Z coordinate.

Option A: Z=0 at 1F level.
Option B: Z=0 at B1F level.

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Which Option should be used? Or either is fine? I'm not sure what kind of problems arise in EnergyPlus.

I thought Option A (i.e., Outside Boundary Condition of a wall whose Z coordinate is less than 0 is Outdoors.) might not work, but when I tried, the simulation ran successfully. I got the following warning message, but it doesn't seem to be much of a problem.

   ** Warning ** CalcSurfaceCentroid: 1 Surface has the Z coordinate < 0.
   **   ~~~   ** ...in any calculations, Wind Speed will be 0.0 for these surfaces.
   **   ~~~   ** ...in any calculations, Outside temperatures will be the outside temperature + 9.750E-003 for these surfaces.
   **   ~~~   ** ...that is, these surfaces will have conditions as though at ground level.