Air supply diffusers used in air-conditioning systems can be classified as ceiling diffusers,side-wall diffusers, floor diffusers, jet nozzles and low velocity displacement diffusers. Fixedor adjustable slats are usually used to control airflow directions. Recently, swirling vanes areused in floor diffusers to create a swirling out-flow jet, so that more rapid mixing withambient air can be achieved. In this paper, we use the latest CFD technique to investigate theimpact of these different designs on thermal comfort in the near nozzle region, in view of theincreasing application of floor-level air supply systems. The preliminary simulation resultsindicate that raising air supply temperature from 18 to 22C or reducing the air supplyvelocity from 1.5 to 1.0 m/s can provide better thermal comfort in terms of thermal fielduniformity.The results will be further validated with experiments, and the method is expectedto be used to help optimize diffuser designs.