Displacement ventilation has been known to lower energy consumption and improve air quality, but it has major thermal comfort limitations. The aim of this paper is to optimize, by computational fluid dynamics modelling, the DV supply conditions to achieve acceptable CO2 concentration in the breathing layer at minimum energy cost while preventing local discomfort due to draft and air temperature difference between ankles and head. Results revealed that up to 44% energy savings can be achieved if the selection of supply conditions are optimized. The model can be put into practice to give recommendations on displacement ventilation preliminary design.