This study deals with the possibility of the under floor air distribution system usage in a dense occupied space (80 occupants) regarding to the general thermal comfort conditions of occupants, local thermal discomfort, and indoor air quality. Computational fluid dynamics methods are used to predict general thermal comfort conditions of occupants, local thermal discomfort, and indoor air quality in this space. Different locations for the diffusers and velocities of the supply air are varied to determine what produces a better performance for the under floor air distribution system. It is found that when the diffusers are installed under seats, higher temperatures are measured at relatively lower heights due to the impedance in the injection of the fresh air supply. Moreover, the mean local age of air, as indoor air quality index, is increased by reducing the supply air velocity, which means that there is a less fresh air in the breathing zone of occupants. However, general thermal comfort conditions and local thermal discomfort should be considered as determining factors in each study. Based on the overall results of the study, under floor air distribution system is capable of creating a comfortable indoor environment in a dense occupied space. (C) 2016 Elsevier B.V. All rights reserved.