Air wall, Open air connection between zones[LINK]

Modeling the interactions between thermal zones which are connected by a large opening requires special consideration. EnergyPlus models only what is explicitly described in the input file, so simply leaving a void (no surfaces) between two zones will accomplish nothing - the two zones will not be connected. A building surface or fenestration surface with Construction:AirBoundary may be used connect the zones. Construction:AirBoundary has options for modeling the interactions which occur across the dividing line between two zones which are fully open to each other:

Convection or airflow

transfers both sensible heat and moisture. Some modelers use ZoneMixing (one-way flow) or ZoneCrossMixing (two-way flow) to move air between the zones, but the user must specify airflow rates and schedules for this flow. Other modelers use AirFlowNetwork with large openings between the zones as well as other openings and cracks in the exterior envelope to provide the driving forces. ZoneMixing flows can be linked to HVAC system operation using ZoneAirMassFlowConservation or AirflowNetwork:Distribution:*. Construction:AirBoundary has an option to automatically add a pair of ZoneMixing objects.

Solar gains and daylighting

gains in perimeter zones often project into a core zone across an open air boundary. Normally, the only way to pass solar and daylight from one zone to the next is through a window or glass door described as a subsurface on an interzone wall surface. Note that all solar is diffuse after passing through an interior window. Construction:AirBoundary groups adjacent zones into a common enclosure for solar and daylighting distribution allowing both direct and diffuse solar (and daylighting) to pass between the adjacent zones.

Radiant (long-wave thermal) transfer

can be signifcant between exterior surfaces of a perimeter zone and interior surfaces of a core zone with an open boundary between them. Normally, there is no direct radiant exchange between surfaces in different thermal zones. Construction:AirBoundary groups adjacent zones into a common enclosure for radiant exchange, allowing surfaces in different zones to “see” each other.

Visible and thermal radiant output

from internal gains will not normally cross zone boundaries. Construction:AirBoundary will distribute these gains across all surfaces in the grouped enclosure.