Heat Recovery Ventilators/Energy Recovery Ventilators
There are Heat Recovery Ventilators and Energy Recovery Ventilators designed to ventilate just one or two rooms, and ones designed to ventilate the whole house.
Heat Recovery Ventilators (HRVs) have fans that simultaneously bring fresh air from outdoors into a building and exhaust stale air from the building to the outdoors. In the process, HRVs transfer heat from the air in one stream to the air in the other.
In winter the heat is recovered from the warm exhaust air and transferred to the incoming fresh air which is cooler than the indoor air.
In summer, on a hot day where the outdoor air is far hotter than air inside your home, the heat in the incoming fresh air is transferred to the stale but cooler air the HRV is exhausting from the home.