Direct digital control (DDC) systems are used in the commercial building heating, ventilation and air conditioning (HVAC) industry to monitor and maintain environmental conditions.
They consist of local controllers connected to a network with a personal computer (PC) based central station which provides monitoring, reporting, data storage and programming capabilities.
The controllers are optimized for economical HVAC system control, which generally does not require fast execution speeds. Their hardware and control software are proprietary, with either proprietary or open protocols used for network communication.