Heating Ventilating and Air conditioning (HVAC) System is capable of providing heating humidification during the winter, cooling and dehumidification during summer, the supply of fresh air through - out the year and capability to furnish each of these services in a controlled manner and when sought by building occupants.A fully developed HVAC system will generally consist of a heating source, a refrigeration (chilling) source, Distribution devices for transporting the ventilation air, heat and cool air to individual spaces in the building, a medium for transporting, sensors for detecting the natures of the thermal environment and the air quality and controls for regulating the operations both of the overall system and individual elements within the system.Based on the fluid media used in the thermal distribution system, HVAC systems can be classified as:All air systems, All water systems, Air- water systems, Unitary refrigerant based systems. The basic steps in the development and use of a large air conditioning system are the design, construction, commissioning, operation, energy efficiency upgrading, and maintenance.