energy contained in normally exhausted air of a building or conditioned space, using it to treat (precondition) the incoming outdoor ventilation air. The specific equipment involved may be called an Energy Recovery Ventilator, also abbreviated ERV.
Ductless ERVs provides fresh air, recovers the heat to save energy, and doesn't need ducts running to each and every room in the house.
Commercial Energy Recovery Ventilators (ERVs) are the best choice for ventilating your home or workplace. These units are designed to provide fresh air into the building while exhausting an equal amount of stale air to the outside.
http://www.adencn.com/erv/
