Mechanical Ventilation with Heat Recovery (MVHR) provides fresh filtered air into a building whilst retaining most of the energy that has already been used in heating the building.
https://www.greenbuildingstore.co.uk/information-hub/heat-recovery-ventilation-mvhr
If anyone needs in depth information about the specification, installation and operation of MVHR Systems, one if the best independent sources of information and support is the Buildhub, a self build forum, run by people self building homes.
https://forum.buildhub.org.uk/search/?q=Mvhr