Wednesday, May 6, 2009

GBXML 2010

To save time and energy I'm attaching a link to the Bimology post on the same topic. Without re-hashing any details I plan to dwell on only a couple of things: shading devices and curtain walls.
When exporting to gbxml you now have 5 settings for how Revit will translate the model. You can either export as "simple" or "complex" which determines whether or not glazing will be broken up by mullions. If you choose "complex" Revit translates the window openings very accurately while still rationalizing curves. If you choose "simple" the panes all cluster together into one large window with an equivalent area. Both settings give you the choice to export with or without shading elements(4), and with "complex" you can also choose to export the mullions as shading elements(5)

Troll House shown in Revit

Detail level:"simple with shading surfaces."

Detail level:"complex with shading surfaces and mullions."

When importing the gbxml into Ecotect you can clearly see the differences in the curtain walls between "simple" and "complex." The 5th options which now allows us to export mullions as shading elements gives us some new options when designing exterior shading devices. But if you'll notice one of the overhangs was ignored.

If we are using Ecotect we can still import this as geometry and incorporate it either in our Ecotect analysis or in an export to another program like Green Building Studio.

If you are using Ecotect there is one glitch however: an entire curtain wall is read as a window with windows inside of it. When you look at what's supposed to happen in the Revit export you see that the perimeter, the mullion gaps between panes, and any solid curtain panels should translate as a single, solid wall.

But in Ecotect it all comes in as glass so you need to take a minute to reassign the parent wall as a material other than glass.

Now that was all fairly simple but let's look at a more complicated building. Below we have on the right side a glass curtain wall with horizontal shading elements made out of "mullion" objects. On the left we have a solid wall with the circular curtain wall elements cut out, or "embedded."

Revit actually does a fairly good job of rationalizing these shapes for the energy model.

When we view by "zone color" we can see that we have a problem with one floor. Ideally we would solve this issue by diagnosing or Revit model so we would never see it again. However if our diagnosis did not fix the problem, or if we were working in a non-integrated team structure where we didn't have access to the source file, we could always clean this up quickly in Ecotect

For buildings with repetitive floor plates you can always take one clean floor and copy it up. Or if you are doing design energy modeling and are only worried about relative values you can delete all but a typical level, make the floor and ceiling adiabatic, then study different form and facade options in your energy model.


KyleB said...

With that Shading Surface thaat didn't translate to gbXML, what Category of Element was it? Was it set to be Room Bounding?


Jon Gardzelewski said...

I'm using an in-place family. I've tried it as a floor and as a roof. When I define it as a roof I have the option to make it room bounding, but it's still not recognized as an analytical surface. A shape this basic could easily be made with a system family "floor" or "roof" and Revit would pick up the analytical surface. But when we get into more complicated shapes like any type of brie soleil, we have to make a custom family. Am I missing a way to define shading surfaces in families?

KyleB said...

You are indeed correct, In-Place Familes are not supported in the gbXML Analytical Model. I didn't realize that was an in-place Family from the image.

I spoke with our developer behind our gbXML functionality, and he informed me that the primary limitation is that we don't know what surfaces to generate to represent the In-Place Family. With System Familes we know to generate based upon the Centerline. We would need to allow the user to add additional information to the In-Place Family during creation so that we would know where to generate the Analytical Surface(s).

Something for us to investigate for a future release.