Energy Modeling for Complex Facade

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Dear All,

Hope all are well.
Currently I have a ArchiCAD BIM model and need to perform energy modeling to
LEED compliant.
I wonder if anyone has worked on ArchiCAD BIM model before, mind to shed
some thoughts if the Ecodesigner module can perform LEED compliant modeling?
How about alternative softwares?

Since the facade has complex spiral 3D curvy shading system I doubt the
ability of EQuest or Energy Plus to model the geometry.
Appreciate some insightful thoughts from all the members out there.

Many thanks in advance.

Simon C.

Simon C.'s picture
Joined: 2011-10-02
Reputation: 0

Hi Simon,

could you give some more information on the nature of that "complex
spiral 3d shading system"? It would probably be intersting whether this
is a light redirecting system, a solid structure or more like sheet, can
be controlled or is static...

Cheers, Lars.

Lars O. Grobe's picture
Joined: 2011-10-02
Reputation: 0

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.


Marcus Jones, LEED AP, M.Sc.

Marcus's picture
Joined: 2011-10-02
Reputation: 0

12.07.2011 11:04 Marcus wrote:


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.

Lars O. Grobe's picture
Joined: 2011-10-02
Reputation: 0

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 fa?ade. 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

Sami, Vikram's picture
Joined: 2011-09-30
Reputation: -1

Echoing others' advice using Einstein: "A clever person solves a problem. A wise person avoids it."

A thought for "wisdom": if you want to simplify the shading effect of an even helix, one might consider a helix looks identical from any angle along a horizontal plane - you might get a 'good enough' approximation at low sun angles using a simple 2D silhouette of the shape!

If you want to go the "accurate" route (now I'm trying to be clever... oh dear), I was intrigued by the challenge and after playing with the idea a bit in excel I can point you towards the math required to generate vertices for a helical shape... I think it's ultimately possible in eQuest, but it would be very hard. Nothing I'd encourage/advocate in any sense... just sharing what I found for the curious. I would much sooner seek a "reasonable approximation."

x(t) = r*cos (B*t)

y(t) = r*sin (B*t)

z(t) = t


coil height = period = 2pi/B <-- set B = 2pi/(coil height)

r = radius

t = interval for points = angle between points, viewed from above (expressed in fractions of pi)

Those three functions along with the variables as described will return a helix in cartesian (xyz coordinates). You could in theory generate a full set, then "offset" the original along the z-axis by the thickness of your actual "coil" to get the other half of the vertices. Alternating between these sets, you could define a series of 2d planes which together would look pretty much like a coil spiraling as high as you'd want it to... But you would undoubtedly save time by defining polygons for a height equal to a certain even number of periods, then copy/pasting the result as it would repeat for the resulting height. I would definitely advise caution/consideration before setting the 't' variable to anything less than pi/6, lest you end up with magnitudes more polygons beyond reason.

For your sake, I'm starting to hope you don't even read past the first few lines... haha!


PS: Here's a screengrab of what I came up with for illustration:

Nick-Caton's picture
Joined: 2011-09-30
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