In WI we now have this requirement on multifamily
Habitable rooms. Habitable rooms without openable windows shall be provided with a balanced mechanical ventilation system producing one air change per hour of fresh outside air while the room is occupied.

Well there is no way to determine when the room is occ, because they may not have the lights on or be moving around. So how do I go about achieving this without running a fresh air into the return 24/7? I'm thinking percentage timer?