The internal variables called “Zone Air Volume" and “Zone Floor Area" provide basic geometric information about each zone. EnergyPlus calculates these from the geometry in the IDF, or you may input the zone air volume in the zone input object. These internal variables in Erl programming should be useful during a parametric study where the shape of the building is being varied, as for a massing study. For example, you could use the zone floor area to normalize Erl calculations with a per-unit area. Or you could use the zone air volume to convert between air flows in m/s to air changes per hour (ACH).