Numerical modelling is performed for three-dimensional turbulent buoyant flows emerging from an air diffuser in an air-conditioned, ventilated room. The velocity and temperature distributions of air in the room are calculated, and the calculated results are found to be in reasonable agreement with published experimental observations. Calculations of Air Diffusion Performance Index (ADPI) for a sidewall grille are carried out for different flow rates of air supply. The predicted ADPI values are found generally to be consistent with the corresponding experimental values.