The thing about roomies, renters... hell, just about everybody, is that the second they aren't paying for something directly out of their pocket ALL CONSERVATION FLIES OUT THE WINDOW.
I know for a fact that tenants will open a window in the winter to cool a room down before they'd ever consider turning the thermostat down. And in spite of being shown the math and other data, they'll plug their vehicles in every second they are parked at the house too. They'll run the wash machine and dryer for one article of clothing. They'll let the shower hot water run for 10 minutes before they step in so that everything is nice and toasty; then they'll turn on the vent fan and let that go until the next person comes in to shut it off. They'll forget range burners and ovens on. They'll stand in front of an open fridge forever, and they'll stick hot things in there to cool them down. Basically, people turn into slobs when they don't have to personally fork over for utilities. By that I mean, sure the utilities can be built into the rent, but then the utility costs become "invisible". I'd say, have a base rent charge then clearly present everyone with the utility bills and have everyone pay their share.