Quick Answer: BACnet is a communication protocol for building automation and control networks. It is defined by ANSI/ASHRAE 135 and ISO 16484-5. BACnet was designed to allow communication of building automation and control systems for applications such as heating, ventilating, and air-conditioning control, lighting control, access control, and fire detection systems and their associated equipment. The BACnet protocol provides mechanisms for computerized building automation devices to exchange information, regardless of the particular building service they perform.