[Bldg-sim] Energy Modeling for Complex Facade

[Sami, Vikram]

I agree with Lars here. Energy efficiency applies to the modeling process too.

You might want to start out with a sensitivity study just to establish what percentage of the total project energy, cooling & heating loads are coming from the façade. If its relatively small, then it doesn't make sense to use a ton of resources modeling it exactly, and you might want to create an approximate equivalent - either by simplifying the geometry or by scheduling transmittance.

If it is actually a large percentage of your building load, then I would look a little bit more in depth as to how it might be modeled.




Vikram Sami, LEED AP BD+C
Sustainable Design Analyst
1315 Peachtree St. NE, Atlanta, GA 30309
t: 404-443-7462    f: 404.892.5823       e: vikram.sami at perkinswill.com   www.perkinswill.com
Perkins+Will.  Ideas + buildings that honor the broader goals of society


-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Lars O. Grobe
Sent: Tuesday, July 12, 2011 5:36 AM
To: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Energy Modeling for Complex Facade

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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