As building envelope performance and HVAC equipment efficiencies continue to be improved to reduce building energy use, a greater percentage of the total energy loss of a building can occur through envelope leakage. Although the energy impacts of unintended infiltration on a commercial buildings energy use can be significant, current energy simulations and building designs generally do not accurately account for envelope infiltration and the impacts of improved airtightness. New strategies to incorporate airflow calculations into building energy calculations have been developed, which are more accurate than current approaches in energy simulation software and easier to apply than multizone airflow modeling (Ng et al. 2014). These new strategies are based on relationships between infiltration rates calculated using multizone airflow models, weather conditions, and building characteristics, including envelope airtightness and HVAC system operation.