Experimental investigation of ceiling circular grille air jets was conducted in a full-scale entirely controlled test room (6.2 x 3.1 x 2.5 m). Our case study is based on a realistic ventilation system configuration: it introduces a plenum box, two air exhausts, as well as a vertical wall near the air inlet. Analyses were initially concentrated at the air inlet region since it is the zone having strong gradients. Deviations concerning the trajectory of the actual jet were observed with respect to the theoretical jet. These results are particularly interesting because, based on the academic configuration of the circular turbulent air jet, which is very well documented in the literature; our configuration introduces architecture elements which will necessarily have an impact on the jet. Therefore, it is this deviation from the theoretical model which will become discriminating as to the capacity of a CFD numerical model to simulate airflows in buildings. These results obtained allow for further cases studies under non-isothermal and moisture conditions and also in the presence of condensation in order to provide new useful data concerning airflow and hygrothermal fields in mechanically ventilated rooms.