Health care facilities, offices, as well as workshops and other commercial occupancies, require ventilation and air conditioning for thermal comfort and removal of contaminants and other pollutions. A good design of ventilation and air conditioning provides a healthy and comfortable environment for patients, workers, and visitors. The increasing developments of computational fluid dynamics (CFD) in the recent years have opened the possibilities of low-cost yet effective method for improving HVAC systems in design phase, with less experiment required. This work presents numerical simulations of thermal comfort and contaminant removal for two typical working spaces where these factors are critical: a hospital operating room with various configurations of inlet and outlet arrangements, and an office with two cases of air distribution systems: underfloor and overhead, also with alternative cases. The 2-D simulation approach was employed. Temperature, relative humidity, contaminant concentration, thermal sensation, predicted mean vote (PMV), and contaminant removal factor were computed and used for assessing thermal comfort and contaminant removal characteristics of the office room and operating room. The result shows good agreements with experimental data taken from related literature.