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HVAC 101 <br />Pneumatic Controls - A mechanical device designed to measure temperature or <br />pressure and transmit a corrective air signal to the final control element. <br /> <br />DDC - Direct digital control (DDC) is the automated control of a condition or process <br />by a digital device. <br /> <br />VAV Boxes - Variable Air Volume (VAV) is a type of heating, ventilating, and/or air- <br />conditioning (HVAC) system. Unlike constant air volume systems, which supply a <br />constant airflow at a variable temperature, VAV systems vary the airflow at a <br />constant temperature. <br /> <br />Ton - A ton is the cooling capacity of an air conditioning system and is equal to <br />approximately 12,000 BTU/h.