Modelling moisture sources due to air leakage with the HAMT extension for EnergyPlus

The moisture performance of building envelope components is one of the main challenges of energy efficient buildings. The combined Heat and Moisture Transfer (HAMT) model in EnergyPlus can provide moisture profiles through multiple material layers of an envelope assembly using a coupled, onedimensional, finite volume model simulating the movement and storage of heat and moisture. Currently only a limited assessment of the effects of moisture sources inside an assembly to determine impacts on durability, indoor air quality, and energy performance is possible. This paper discusses different strategies to model moisture sources in building components due to air leakage. Models that enable air leakage to result in a moisture sink or source at an arbitrary location extend the existing mass transfer equation with a source term that includes water vapor deposit from air flow through an assembly. New sub-models with different levels of complexity to calculate the airflow through the assembly are developed. The airflow can be user defined, it can be computed as a result of the stack height and a user defined ventilation overpressure or completely derived from an airflow network. We explain the model enhancements, discuss the required inputs for every option together with related limitations, showcase the model application and make the source code publicly available for external use.