gbXML from Revit to HAP

[adammeil]

I work for an engineering firm who is currently designing a 300,000 sq. ft. hospital. The architects are building this hospital in Revit, but our firm is not yet designing the MEP in Revit. We have, though, purchased a few licenses of Revit in order to extract architectural information for a gbXML file to use for Carrier's Hourly Analysis Program. The problem is that whenever we export to gbXML from the architectural files, far too many exterior walls (exposures) are listed in the HAP program. We called the carrier tech representative and he basically said that too many exterior wall surfaces were showing up and that the walls were broken up too much in the Revit model. Upon inspection of the Revit model, however, all of the walls appear to be properly inserted and are properly identified as interior or exterior walls. We have tried on two different Revit models from two different architects on two completely different buildings and the results are the same - too many exterior walls. Has anyone else had this problem? Is there anyone out there who has been successful in creating a gbXML file from Revit to import into HAP? Any information would be of great help.

Adam Meil
PWI Engineering
215-241-9100 ext. 252

[KyleB_Autodesk]

Hey Adam,
The Analytical Model that is produced for gbXML differs from the Physical Model that you see in Revit Views. The best way to visualize the Analytical Model before it is exported is to open the Heating and Cooling Loads dialog.

I highly recommend that you read the White Paper, http://images.autodesk.com/adsk/files/building_performance_analysis_using_revit.pdf ,on this subject, as it will provide some good information for you. I suspect that we are breaking up the wall into individual Surfaces due to the way we produce the Analytical Model.

Carrier HAP has within it limitations on surfaces that do not exist in our other analysis partners like Green Building Studio and the IES Virtual Environment. In order for us to accurately produce Analytical Models that properly represent our Revit Physical Models, we need to handle things the way that we do, and that is not a problem for those other folks.

Cheers,
Kyle B
Revit MEP Product Manager
http://inside-the-system.typepad.com/

[tomislav_zigo]

You also might take another look at your model and verify the presence of structural elements. RAC 2009 treats them in a slightly different fashion than 2008. This recent article might be useful in figuring out what is going on with your model.

http://bimology.blogspot.com/2008/04/revit-architecture-2009-to-gbxml.html

Tomislav Zigo
ARBA Studios
http://bimology.blogspot.com

[KyleB_Autodesk]

Thanks Tomislav, good information.

Cheers,
Kyle B
Revit MEP Product Manager

[tomislav_zigo]

No problem Kyle.

Cheers to you as well!

TZ

[adammeil]

Thank You for the info Kyle-

I can open the Heating and Cooling Loads dialog and see each room individually and everything looks to be okay. I have read the white paper you suggested and it does not cover the problem that I'm having. Having the incorrect offset may be a problem, but that should only show (2) extra exposures. Even in the most simple rooms with 4 basic walls, there are many exterior surfaces showing up.

Would you suggest another Autodesk analysis partner like Green Building Studio? Also, have you seen success with large multi-story Revit files generating usable gbxml files?

[KyleB_Autodesk]

Adam,
I'm not sure what would be causing your described issue. I am not aware of any such obvious issues with our gbXML production. Would you be able to ZIP and attach your gbXML output from Revit? I could look at that for you and see if I could find anything. It would also be very helpful to see some screen captures of your "simple" 4-wall buildings.

The primary cause that I assumed was happening was segmenting of walls due to adjacency. Most people don't initially expect us to handle it that way.

The best way to visualize the analytical model in these cases is to use the Shading Graphics Style, as you can usually see the boundaries if the Analytical Wall Surfaces.

As for suggested analysis partners, much of that recommendation depends on a number of variables regarding output needs, project workflows, experience, etc, so I wouldn't recommend one solution over an other without more information.

As for large multi-story files and gbXML, yes I have seen a great deal of success with this approach, it just requires that Architects be mindful of the way that they are constructing their buildings.

Hope that Helps,
Kyle B
Revit MEP Product Manager. Message was edited by: Kyle B [Autodesk]

[adammeil]

Thanks for your patience and all your help. We are getting much closer and have pretty much figured out how the gbXML is created from the Revit model. There is just one more thing that seems to be getting in the way which I can't figure out. How do you deal with spaces, such as mechanical shafts, which are undefined by architect? The gbXML looks at these walls as being exterior because they don't have "rooms" on both sides. Is there a way to remedy this problem?

Thank You
Adam Meil

[KyleB_Autodesk]

In 2008, I can provide only a vicodin to that problem. There is no concept for a building void in gbXML beyond the Space (that's what gbXML calls 2008 Revit Rooms). Because of that, there's not much we can do to help the analysis engine.

You can always open up the linked architectural model and add a room to occupy the mechanical shaft volumes. You will need to repeat this with every new version of the architectural model you receive. Like I said, a vicodin.

In 2009, we have a vitamin for you in the form of a Space, as it is something the engineer owns and can define based upon linked architectural elements.

Cheers,
Kyle B
Revit MEP Product Manager