[Bldg-sim] Energy Modeling for Complex Facade

[Nick Caton]

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

 

where:

  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!

 

~Nick

 

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

  

 

 

NICK CATON, P.E.

SENIOR ENGINEER

 

Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com 

 

 

-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Sami, Vikram
Sent: Tuesday, July 12, 2011 10:11 AM
To: Lars O. Grobe; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Energy Modeling for Complex Facade

 

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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