Computational Fluid Dynamics (CFD) is a powerful and expensive technique to simulate natural ventilation. CONTAM, as an alternative computer program, is based on the bulk airflow network model therefore it is less computationally expensive. However, some key inputs, such as discharge coefficients, require user specifications. This study develop empirical equations for calculating window discharge coefficients of two common types of opening configurations: awning windows and blinds. An automated process combining CFD, Rhino scripts and the Grasshopper plug-in is introduced for data generation for the regression study. Derived from the regression analysis, the empirical equations can help designers to simplify natural ventilation study with acceptable quality.