This article describes CFD simulation results and measurements using a swirl diffuser. Thediffuser is able to provide relatively low velocities within the occupied zone while supplying high airflow rates. The flow pattern produced by the air diffuser was validated by measurements with a flow rate of 133 l/s and 4 C lower temperature than ambient air. Turbulence was modelled using the RNG k- e model with additional swirl modification. Measurements were conducted by using 340 measurement points in the near zone of the diffuser at distances of 0.5 m and 1.0 m respectively from the diffusers edge. The study confirms that the simplified boundary conditions provided by the manufacturer could model diffuser performance accurately enough not only very close to the diffuser, but also in other parts of the room.