HVAC here stands for Heating, Ventilation and Air Conditioning. Thus, a HVAC control system applies regulation to e.g. a heating. Usually, a sensing device is used to compare the actual state (e.g. temperature) with a target state. Then, the control system draws a conclusion what action has to be taken
Central controllers and most terminal unit controllers are programmable, meaning the direct digital control program code may be customized for the intended use. The program features include time schedules, setpoints, controllers, logic, timers, trend logs, and alarms.
More complex HVAC systems can interface to Building Automation System (BAS) to allow the building owners to have more control over the heating or cooling units. The building owner can monitor the system and respond to alarms generated by the system from local or remote locations. The system can be scheduled for occupancy or the configuration can be changed from the BAS. Sometimes the BAS is directly controlling the HVAC components. Depending on the BAS different interfaces can be used.