How do I handle complex systems and retrofit tradeoffs in energy auditing?

You have already learned the ordinary work. Most buildings hold no mystery for you anymore. What is left is the hard part, and it is hard for everyone. The complex systems and the retrofit tradeoffs trip good auditors, not just new ones. Nobody sees the whole picture at once. The people who seem to just slow down, break the building into parts, and reason through one system at a time. A tradeoff is not a test of your worth. It is a set of costs weighed against a set of gains, and you can lay those out on paper like anyone else. Pick one type of complex system that shows up often and study it until it stops scaring you. Then pick the next. You do not have to master everything this year. You only have to be a little less lost than you were last month.