In each apartment there is a small air handling unit, providing controlled equal pressure heat recovery ventilation. It is usually located under the ceiling of the toilet, from where the incoming fresh air is usually ducted under the ceiling to the living rooms via long-range nozzles. Exhaust air is extracted from the bathrooms, toilets and kitchen. The supply and extract of outdoor air is solved according to the situation - whether it is a single apartment or a group of apartments and taking fire requirements into account, for example. If it is solved by a common internal supply shaft, thermal insulation of both ducts is necessary.
From the operation point of view, the air handling unit is entirely up to the user - setting the ventilation output, changing of filters and paying for the operation of the unit.
Installation is also possible within just one apartment in the whole building, taking into account all technical constraints.