In this study many researches related to mixing and displacement ventilations in indoor and office rooms were addressed. Good ventilation is one of the most important requirements for space occupants to maintain appropriate environmental conditions, as ventilation increases thermal comfort and improves indoor air quality. However, the studies on mixing ventilation systems based on occupied density have been highlighted in the present work. Improvement of the indoor environment is economically efficient when health and productivity are taken into account. The parts of a room that a person occupies must be characterized by speed and air temperatures suitable for the occupants of the space. In the occupied zone, fresh, clean supply air must reach all its parts, and no stagnation areascan be found there. A group of field studies conducted showed, significant levels ofdissatisfaction with the indoor environment in many buildings despite satisfying the typical ventilation requirements, where there are still many complaints regarding poor indoor air quality and diseases related to poor ventilation of buildings. In enclosed spaces, ventilation is one of the essential methods used to control indoor air quality (IAQ). In buildings, ventilation has an impact on the structure and, as a result, on the people who utilize it. A deteriorated indoor environment increases sick building syndrome (SBS), respiratory illnesses, and reduces comfort and productivity.