[Bldg-sim] Energy Modeling for Complex Facade

Lars O. Grobe grobe at gmx.net
Tue Jul 12 02:36:24 PDT 2011


12.07.2011 11:04 Marcus wrote:
> I've had a little experience in complex envelope geometry, although I've
> never used ArchiCAD or Ecodesigner. Generally speaking though, energy
> modeling software can't use curved geometry. Any curved surface has to
> be approximated using planar surfaces. Modeling software need this
> planar geometry in it's internal algorithms, especially to calculate the
> radiative heat transfer and shading.
>
> The approach I have used, for Energyplus, is to manually mesh a curved
> surface using many smaller triangular surfaces. There are likely ways to
> automate the process if you have very complex and large geometry.

Hi!

Meshing geometry may be necessary, but will result to a complex model 
with a lot of potential for error. From what I understand, this may 
result in a huge number of polygons, as "spiral 3d shading" sounds a lot 
like smooth shapes possibly highly specular surfaces (which is why I was 
asking for details). Archicad can output meshes (I remember obj), but it 
would be important to check mesh quality.

It would be interesting to assess the need for such a model here, or 
whether the performance could be represented by a simple plane with 
transmissive properties according to the more complex shading. If 
surfaces are diffuse and view is blocked, maybe a flat, 
diffuse-transmissive material could replace the shading's complex 
geometry. If there is direct view through the shading, as long as the 
surfaces are not specular, the actual shape should not matter and a much 
simplified replacement according to thickness and angles related to the 
facade normal would probably be sufficient. If it is a curvy specular 
shading, it is going to be difficult!

Cheers, Lars.



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