gbXML (Green Building XML) is a very useful format for transferring building models across a number of platforms. Bentley Hevacomp's Design Database contains a gbXML import that allows you to take advantage of this functionality. There are some pitfalls you should try and avoid.
The import feature can be found in the Utilities program
The program offers a number of options to help with the import function; Default surface types can be specified and invalid polylines can be discarded, for example. The import function will attempt to error correct the drawing as it is loaded and a comprehensive import document will be created detailing any problems with the gbXML file.
Any serious errors reported by this document should be fixed in the original model and the gbXML created again, for another attempt at importing.
Once you have successfully imported the gbXML file go into the CAD Input program to examine your model. Use the 3D view to check that everything is as it should be. If your model appears extant then you should go into Roof/floors and set up Intermediate floors, Ground floors and Roofs to ensure the rooms are correctly connected vertically.
Design Database required the gbXML file to be correctly formatted and complete. Walls should be defined as walls, internals as internals, etc. From this information Design Database is able to build up the rooms that will be used for calculations. If information is missing - a common example being internals defined as 'space' objects - then Design Database cannot create functioning rooms, and the room will be discarded.
If you end up with an incomplete model it may be prudent to examine the gbXML file for errors before asking for the original architect model to be modified.
The Import Document created by Design Database may help with this, and we have found a very useful debugging tool in the FZK Viewer from the Karlsruhe Institute of Technology. As this program does not attempt to create a working model it allows you to view the gbXML model as simple polylines. You can quickly identify where problems are in the model and use this information to correct your original model.
The Karlsruhe Institute of Technology FZK viewer can be downloaded from here.
A guide on producing correctly formatted gbXML from the AutoDESK® Revit program can be found here. For further assistance with AutoDESK® Revit program, please consult the AutoDESK® forums.