Geoff,
You can always use the "Total" feature for all of the Rooms/Spaces in your model. However, I doubt this is what you are actually looking for to make a design decision.
In Revit MEP 2009 we provide the user an entire building load value, but this is NOT the sum of the peak loads for the individual Spaces in the model. We are simulating the loads for each Space every hour of the day, for every day of the month. We report to you the highest value found for each Space, which is the Peak Load for that particular Space.
The problem is that those Peak Loads rarely occur at the same time of the year, so summing the Peak Loads will result in a higher total building load than is actually every experienced. Think about it, one wall might have southern exposure, and another might have western exposure, they would hit their individual peaks at different times of the year due to the many variables that influence the load.
We calculate the Incident Peak Load, which is really what you need to use to make the design decision. To calculate the Incident Peak Load for the building, we as summing the individual Space Loads for each calculation point (hourly calculation), and then report to the user the Peak Load that is found in that process.
Make sense?
Cheers,
Kyle B
Revit MEP Product Manager
http://inside-the-system.typepad.com
