This occurs without the opening of windows or doors, through forced ventilation ducts, connected, indoors, to aspirations (for the removal of stale or polluted air) and the diffusers (for the introduction of new air).
The ventilation systems also allow to recover the cooling or heating energy that would be lost with a simple exchange of air.
This occurs thanks to the use of heat exchangers.
In these exchangers the outgoing and incoming air flows are crossed, so that one flow heats the other while it cools down.
In this way, in winter the air that comes out heats the one that enters, while in summer the reverse occurs.