What does recuperation mean?

Recuperation is a process of recovering heat from the discharged, used air and handing it over to the supplied air, without mixing these two streams. This process consists of two stages: At the first stage, the heat of the exhausted air is transferred to the heat exchanger surface; at the second stage, heat from the pre-heated area, is transferred to the fresh air supplied to the building interior. An appliance which carries out such a process is called a recuperator.