A Building Automation Controller (BAC) is a type of control system used to monitor and control the various systems and subsystems in a building. It is designed to be a single, centralized point of control for all of the building’s systems, such as HVAC, lighting, security, and energy management. The BAC is connected to the various systems in the building and can be programmed to control them in a variety of ways. For example, it can be programmed to turn off the lights in a room when no one is present, or to turn down the thermostat when the temperature outside is cool. The BAC can also be used to monitor the building’s energy usage and to provide feedback to the building’s occupants on how to save energy. The BAC is an important part of any building’s automation system, as it allows for the efficient and effective control of the building’s systems.