I've ALWAYS avoided predictive modeling (telling a client your energy usage
will be below X) as I've been scared. Now I'm pretty deep into a project
performing Green Star energy modeling and my client has popped the question.

We've discussed "why it is hard" and the big three un-knowns: Infiltration,
Occupant behavior!!, and Actual Weather. They still want me to go forward
and are willing to put a bunch of caviates and an agreed margin on the
results.

This is an old 1930's building 200,000 sq ft with original metal window
frames (single pane) that will not be replaced (heritage). We're insulating
the roof and basement ceiling and a completely new HVAC system. Is there a
standard process I can follow or specific suggestions the community could
offer?

So far my idea is to try and guesstimate infiltration, box in comfort
behavior with lease agreements and a survey, and put some margin on weather.

--
Jason