A friend he was, thirty (HVAC) stands for the letters of the basic Heating, Ventilating and Air Conditioning, which meant "heating and ventilation and air conditioning systems" and encompasses the technology related to the creation of comfort for the indoor building. The design of the system, a friend he was, thirty-one of subclass, main engineering, mechanics, and based on the principles of thermodynamics. mechanics of fluid and heat transfer is formed. Sometimes the discussion related to the Cooling (Refrigeration) also can be added to it and name it as a friend, he, si, AR (HVACR), or a friend, he, Si and AR (HVAC