Is there a default ground plane at z=0 for energy and daylight simulations?

Hi there, simple question I can’t seem to find on the forum.

When I make a model without defining a ground plane as context surface. Does honeybeen automatically assume there is one at origin height? Is the case the same for energy and daylight simulations?

If I make a one story height space with the floor at height z=0 and run it, would it simualte as it is floating in space or sitting on a ground?

Thank you!

No default geometry is created. You need to take care of it.

There is no geometry but Z = 0 is considered ground level in EnergyPlus simulation. This means if you have a horizontal surface on Z = 0 the boundary condition will be set to Ground instead of Outdoor. If you have a zone which is below Z = 0 it will be considered underground and Honeybee splits the surfaces if part of them are located at Z < 0 to be able to assign correct boundary conditions.

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if there is custom topography on the project and Z<0 does not always represent below ground nor Z>0 does not always represent above ground for this particular project masses, is there a methodology to have Honeybee use a topography polysurface to determine what is above vs below ground for different parts of the massing model in lieu of the Z<0 assumption?

@josh.greenfield ,

The answer is unfortunately no and the main reason is that such a topography surface would have to split the zone surfaces in two (one that goes above ground and the other below). These intersections get to be very tricky for a Nurbs topography surface and the type of intersection you would get with with a Nurbs surface would be curved (resulting in meshing and subsequently a much longer E+ calculation). I can imagine adding a workflow in the future that let’s you change the plane that defines the ground but, if your ground is not define-able by a plane, then this won’t help much. In this case the best I can offer is to split your zone surfaces with the ground manually and use surface-by-surface workflows to build your zones assigning different BC’s depending on whether the surface is above or below ground.


Hi @chris

We don’t have still the option to define our custom ground topography that is not horizontal?
and your solution is to just define a new CPlane or divide the surface then define it with our BC?

Hey @Nariman.Rafati . Yes, nothing has changed in legacy Honeybee since that last post so my recommendations are still the same.

We have the ability to change the ground plane within the SDK of the new Ladybug Tools plugin that is under development but I’m not sure how we’ll expose it yet. We’ll come back to this after that plugin is officially released.