Did you know that the UBC only requires openable windows in assisted living homes? That means your mother/grandmother living in one, with dementia, probably in a wheelchair or using a walker, has to get up every hour or so and open/close their window so that they can get breathable outside air. In a nursing home or hospital you get 10 air changes/hr with mechanical ventilation, in assisted living you get NONE.
As to caulked-tight/no infiltration living units, a heat exchanger is as simple as a small fan and double pipe duct : outgoing exhaust air heats incoming fresh air. Yes, you lose about half the heat but it isn’t that big a deal energy-wise. The code requires 2 air changes/hr, look at the numbers, not that much vs OXYGEN to stay alive.
Everytime you walk in or out the front door you get air exchange and heat loss. There’s no such thing as “NONE”. Not to mention exhaust fans in bathrooms and range hoods.
As for your theoretical example, the best way to conserve heating costs is to make people live in huge apartment buildings. These building typically are running the A/C until christmas. The larger the building, the lower the surface area to volume ratio. And if they are covered in glass, the solar gain is considerable.