Airflow network modeling in EnergyPlus

The airflow network model in EnergyPlus provides the ability to simulate multizone wind-driven airflows. The model is also able to simulate the impacts of forced air distribution systems, including supply and return air leaks. The air distribution system portion of the model is currently applicable for constant-air-volume systems. Future enhancements will include adding hybrid ventilation control and possible extension to include variableair- volume distribution systems. This paper describes the input objects, calculation procedures, model validation, and example results. The model inputs consist of five main objects: simulation control, multizone data, node data, component data, and linkage data. The model calculates pressure at each node and airflow through each component based on the pressure versus airflow relationship defined for each component. Using these airflow rates and HVAC equipment models, temperature and humidity ratio at each air node are then calculated. All cooling/heating loads resulting from the multizone airflow and air distribution system model are then summed and passed to EnergyPlus’ zone air heat and moisture balance model which calculates zone air temperature and humidity ratio. The loads from multizone air flows are used to predict required system loads, while the loads due to the air distribution system are used to recalculate zone air temperatures and humidity ratios. EnergyPlus’ airflow network model was validated against measured data from both the Oak Ridge National Laboratory (ORNL) and the Florida Solar Energy Center (FSEC). Whole building energy simulations were performed using EnergyPlus in addition to validating specific portions of its airflow network model. There was good agreement between the simulation results and the measured data.