Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
The zonemixing object is used for one-directional air transport between two zones, the direction of airflow is defined in this object and the airflow rate is fixed throughout the simulation. Users are required to balance the zones air flow; otherwise, users have to take its impact in the analysis of their simulation results accordingly. Common use of this object that I have seen is in RestaurantFastfood and RestaurantSitdown buildings as described by others. In these two buildings the mixing object represents airflow from the dinning area to the kitchen. It implies that the airflow between these two adjacent zones is triggered by an exhaust fans installed in the kitchen. So, the EnergyPlus, allows users to specify a zonemixing object to represent air drawn from the dinning area to the kitchen and then eventually to the outside via the exhaust fan. If the dinning zone is served with a constant volume system, then one can create a balanced zone air flow using the zonemixing object and the kitchen exhaust fan by specifying a balanced flow rates. It is difficult to balance the zone air mass flow when you have a VAV system serving a building. It is partly for this reason than we added the object "ZoneAirMassFlowConservation" to ensure zone air mass flow balance.
when this object (ZoneAirMassFlowConservation) is specified, EnergyPlus triggers zone air flow balance calculation. In this situation, the zonemixing objects airflow rates are ADJUSTED in order to balance to zone air mass flow. The zone air mass flow balance calculation includes: supply air flow, return air flow, exhaust air flow, zone mixing and infiltration airflow for each time step. There are two methods allowed how the air infiltration flow is treated (adjusted or added) to enforce the zone air mass flow balance (see the IDD for further explanation). A thermal zone can be connected as many zones as (as many zonemixing objects as) the number of adjacent zones. Zone air mass flow conservation is enforced to all zones that used as either a source zone or a receiving zone in the mixing objects. And the air infiltration flow rate adjustment or addition is applied to those thermal zones defined as a source zones in the zonemixing object. The basis of this object need is allowing inter-zone air flow and ensure zone air mass flow balance where air-flow-network is not worth the effort.
