Real time flow simulation is crucial in emergency management in buildings, such as fire or accidental release of chemical/biological agents. Proper measures can be taken to minimize casualties with correct and timely prediction of the spread of the fire or contaminants. Although the traditional CFD simulation in buildings is accurate, it is too time consuming. Multizone flow modeling is fast, but its accuracy is poor. Therefore, it is very necessary to develop a new method that is faster than the traditional CFD, but more accurate than the muitizone modeling. Recently, the modified semi-Lagrangian method based on Navier-Stokes equation has been used for flow simulation. This method is unconditionally stable and can use a larger time step than traditional CFD. The method has been successfully used in computer game industry and in computer graphic science. However, the results are only virtually real and are not rigorously validated. This investigation used the method to systematically study three basic flows in buildings and compared the numerical results with the corresponding experimental data or direct numerical simulation data from the literature. The results conclude that it is possible to conduct flow simulations faster than real time by using the method, although some discrepancies exist between the numerical results and the data.