In this study, the effect of inlet supply temperature on energy consumption optimization, thermal comfort and mean local air age has been investigated for a displacement ventilation inside a typical room. Based on the results obtained from this study, an increase in the inlet supply temperature for a displacement ventilation from 17.8 to 25.8 in summer leads to a 50% reduction of consumed energy. Owing to the fact that optimization of consumed energy is an action bound to maintain thermal comfort of occupants, PMV(predicted mean vote) and PPD(predicted percentage of dissatisfied) parameters as two general thermal comfort indices have been investigated. In addition temperature gradient in vertical direction as local thermal discomfort index and mean local air age as air quality index have been probed. All the aforementioned indices except that of mean local air age, lie within the sightly range of ISO7730 standard with an increase in temperature, but air quality index experiences some quality drop in inhalation region, This slight drop is negligible and displacement ventilation system can be used as a suitable ventilation system for summer applications.