Lets first lay out the goals, and then look at potential ways of doing it.

Goal 1 saving money
Goal 2 automating the heating/cooling
Goal 3 occupancy detection/self resetting overrides.
Goal 3 scheduling/remote control of the automation (over the internet)

Goal 1 is pretty simple, reduce our cost by not heating/cooling when its not needed,

Goal 2 Some method for safely controlling both 220v and 110v large load circuits, preferably without running a huge amount of under floor wiring, or modifying the existing heaters/structure too much.

Goal 3 Occupancy detection, our current lighting systems are good, but either more sensors, or better system for people sitting working for long periods to keep it from shutting down. But idiot proofed to keep it simple.

Goal 4, both heating and cooling take time to do their magic, so scheduling is important, start warming up/cooling off an hour or two before Hacknights/Co-working/events. But sometimes people may want to work outside the schedule, so a internet based override would be good, allowing people to start it up from home/smartphones.

Added bonus would be to get a few locations temperature data too, so one can tell if an over-ride was somehow left on/failure/or if /heating/cooling is needed at all.