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.

Custom Topography for Solving Adjacencies?