HVAC (heating, ventilation, air conditioning) is the technology which helps maintain a consistent indoor temperature. Using HVAC the conditions in a closed area can be maintained using fresh air from outside. It can be kept warm or cool as required. The heating effect is produced by using a boiler and heat is transferred using water and heat transfer takes place by convection through circulation of water. Ventilation includes the exchange of air with the outside and also circulation of air within the building and maintain an acceptable level of air quality in a closed atmosphere. Air conditioning is provided through the removal of heat through a process called the refrigeration cycle. As the liquid refrigerant cycles and evaporates it absorbs energy from air, repeats the cycle. In this process heat is absorbed from indoors which results in cooling of the building. There has been a consistent effort to make HVAC more efficient.