This is a comprehensive list of HVAC Acronyms and HVAC Terms. High Performance HVAC is certain there are more terms and acronyms. If you know of something we missed please email us. Thanks! AC – Air Conditioning or Alternating Current ACCA – Air Conditioning Contractors Associations AFUE – Annual Fuel Utilization Efficiency AHU – Air Handling Unit AI – Analog Input AMCA – Air Movement and Control Association AO – Analog Output AQS – Air Quality Systems ASHRAE – American Society of Heating, Refrigerating, and Air Conditioning Engineers AV – Automatic Air Vent AWG – American Wire Gage B – Boiler BACnet – Computer communication protocol for building automation systems and control networks BAS – Building Automation System BI – Binary Input BMS – Building Management System BO – Binary Output BP – Backflow Preventer BTU – British Thermal Unit BTUh – Brtish Thermal Units per Hour