All instrumentation is gathered by various analog and digital converters which use the network to transport these signals to the central controller.
The centralized computer then follows all of its production rules (which may incorporate sense points anywhere in the structure) and causes actions to be sent via the same network to valves, actuators, and other heating, ventilating, and air conditioning components that can be adjusted.
The program features include time schedules, setpoints, controllers, logic, timers, trend logs, and alarms.
Examples of open protocol language are Building Automation Control Network (BACnet), LonWorks (Echelon), Modbus TCP and KNX.
In many cases, the HMI (human machine interface) or SCADA (Supervisory Control And Data Acquisition) are part of it.
[1] These systems may be mated with a software package that graphically allows operators to monitor, control, alarm and diagnose building equipment remotely.