The main difference between centralized and decentralized HVAC air systems lies in the location of the central heating and cooling plant equipment. Centralized air systems receive their cooling and heating energy from a remote central plant, whereas decentralized HVAC air systems contain the central heating and cooling plant equipment within the air system itself. This distinction affects the design, installation, and operation of the HVAC system, as well as the distribution of heating and cooling energy throughout the building.