Remember if you are using RAC 2008 or 2009 you can take advantage of their free VE-Ware plug-in. Here is a screen capture of their web site page dedicated to Revit.
This is text from their VE-Ware download section:
VE-Ware - Free software for yearly energy, carbon and Architecture 2030 Challenge assessment. You can also try a licence for the easy-to-use VE Toolkits, but not the whole
Recommended for: New Users and Architects etc. who want straightforward performance calculations.
Install process: You’ll need to register and Download VE-Ware (54Mb) here
(For ease of deployment, a single file installs VE-Ware with both the SketchUp and Revit Plug-ins)