Air curtains have been widely used as a barrier against infiltrations and associated energy losses through building entrances while still permitting an unobstructed pedestrian entryway. However, the evaluation of the energy performance of an air curtain often needs to quantify the infiltration rates under variable ambient conditions and door usage patterns. This study develops an approach to determine the infiltration and the exfiltration characteristics of building entrance equipped with an air curtain. A detailed parametric study for different ambient temperatures, pressure differences across the air curtain and different door usage frequencies was conducted by using computational fluid dynamics simulations. The calculated air infiltration rates were then correlated to the pressure differences across the air curtain. The numerical approach was first verified by comparing the obtained correlations for the building entrance without the air curtain to the published data in the literature. New infiltration/exfiltration correlations of the modeled air curtain were then developed as the functions of pressure difference, flow coefficient, and flow modifier. Compared to the single door without air curtain and the door with vestibule, the air curtain was found to reduce the infiltration significantly, especially for the mild ranges of pressure differences. (C) 2014 Elsevier B.V. All rights reserved.