The natural air changes per hour in a building, as calculated by dividing by the LBL ACH50 Factor. The number of cubic feet of air flowing through a house from indoors to outdoors during typical, natural conditions. This figure can be roughly estimated using a blower door, and can also be denoted as (natural air changes/hour or NACH or ACHnat)
abbr. net zero energy house or building. A building that has the capability of producing as much energy as it consumes on an annual basis.