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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.

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.

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.

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If surfaces are ~insensitive to convective heat transfer (e.g. mild climate, sheltered), either option should do. For colder wind swept locations, not prudent IMHO to ignore such a warning. Where Z=0 is set determines how climate data is transposed to your model (see Site:WeatherStation, Site:HeightVariation): surface-specific wind speed, air temperature & pressure - not so critical for a 3-story building. If Option A (while harnessing KIVA as per Scott's recommendation), you could raise sunken surface material emissivity to compensate a 0 m/s wind speed.

( 2022-05-05 10:29:19 -0500 )edit

you could raise sunken surface material emissivity to compensate a 0 m/s wind speed.

( 2022-05-11 03:48:37 -0500 )edit

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If you use the Kiva foundation model, there is documentation (with images) describing how to construct a walkout basement. There were a couple important bugfixes to Kiva in the most recent E+ release, so you would want to use E+ version 22.1.

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Thank you for your answer. I haven't used Foundation:Kiva model, but looks interesting. I'll learn how it works. I'm going to use GroundFCfactorMethod for this building as it is for LEED certification based on ASHRAE90.1.

( 2022-05-11 03:42:02 -0500 )edit

Hi, Keigo! In these cases I usually set z = 0 at 1F level and then change the boundary conditions of the walls that are in touch with the ground to 'Ground' (as well as making sure they are set as NoSun, NoWind), you can do this manually or with some sort of coding.

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Thank you for your opinion. I'm going to follow the same z cordinate setting.

( 2022-05-11 03:12:14 -0500 )edit

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