Abstract: The study simulated the airflow pattern, thermal comfort and occupational exposure to CO_2 under two ventilation modes using computational fluid dynamics (CFD). A wall supply diffuser was located at the floor level for the displacement ventilation case while the supply air diffuser was placed at the ceiling level for the mixing ventilation mode. The manikin served as a jet, exhaled air through the nostrils downward at an angle of 45 degrees below the horizontal line. The CO_2 species was modeled as a passive scalar transport convection-diffusion equation. From the result obtained, the mixing ventilation case showed a low level of CO_2 concentration than in the displacement ventilation case. Also, higher vertical temperature gradient was noticed in the displacement ventilation case as opposed to the mixing ventilation scenario. Lastly, the mixing ventilation case showed higher tendencies of local draft than displacement ventilation case.