Understanding the CreateGroundZone component

Hello all,

I am, like many before, trying to simulate the effect of a shade canopy on outdoor thermal comfort. I’m also a designer trying to understand physics so please forgive any mistakes!

For now, I am just trying to understand the ground surface temperatures without any shading context. I have been following Chris Mackey’s Trees in Outdoor Thermal Comfort example on Hydra (Hydra Viewer)
and am using the ‘CreateGroundZone’ component to apply ‘outdoor’ conditions to my HB zone.

I would like to understand the theory behind creating the ground zone properly. I believe even with the GroundZone component, the geometry is still modelled as an EnergyPlus ‘room’ with a volume of air inside? I understood this from the existence of a “zone air temperature” result.

Wouldn’t this give inaccurate results for the ‘roof’ outdoor surface temperatures?
If so, is there a method to make that air volume negligible? Or is there a different component I should use?
Because even if the air volume was negligible, Energy Plus would consider a convective resistance between the ground zone air temperature and the zone surfaces, as well as a radiative heat exchange between the bottom of the “roof” and the back of the “walls”."

Many thanks in advance!

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