Computational Fluid Dynamics (CFD) simulation technique was used to study the effect of air distribution and supply parameters on ventilation performance and comfort of occupants in a government office building in Ottawa, Canada. The floor studied had two separate ceiling-based air supply systems, a slot system and a nozzle system with personal environmental control capability. In situ measurements were used to validate the results of the CFD simulation. Good agreements between the measured and predicted data were observed. The range of system configuration and parameters investigated include: (1) seasonal operating conditions (spring vs. summer); (2) supply airflow rate; (3) supply room temperature; (4) air throw orientation; and (5) diffuser location. Indoor air temperature, air velocity, mean age of air, Predicted Mean Vote (PMV), and Air Change Effectiveness (ACE) were estimated to investigate the performance of the ventilation system during occupancy.