The aim of this study is to make available new data concerning the validation of CFD (Computational Fluid Dynamics) results through experimental measurements campaigns on full scale mechanically ventilated test rooms. The experimental set-up is based on a new configuration of the test cell “Minibat” (CETHIL – INSA Lyon, France), equipped with a realistic mixing ventilation system. In this paper, experimental – numerical comparisons are presented in terms of mean air velocity for an isothermal situation. The investigations have been focused in the region near the supply air diffuser as the overall air flow in ventilated enclosures is mainly due to the inlet air jet. The results show a decent agreement between measurements and numerical values in terms of velocity profile at the inlet. In addition, the overall flow development in the air jet is well represented numerically. However, there are some discrepancies concerning the point of maximum velocity in the air jet which must be addressed by further investigations, both experimentally and numerically.