Abstract: Maintaining optimal temperature and air circulation are the basis of a comfortable indoor environment. This role is played by HVAC(Heating, Ventilation and Air conditioning) systems. All heating, ventilation and air conditioning system account for 60% of the World's total energy consumption this calls for a sustainable solutions for HVAC systems. We discuss many of such techniques used around the globe in this paper. The main objective is to minimise the energy consumption by shifting towards natural renewable sources while maintaining the required comfort level of a building.