Direct Digital Control (DDC)
CSI Division 25, Integrated Automation
The individual electronic controllers, sensors, and actuators installed at each piece of mechanical equipment, an air handler, a VAV box, a boiler, that read real-time conditions and adjust equipment output automatically according to a programmed sequence of operation, the field-level hardware a [[concept-building-automation-system|building automation system]] sits on top of and coordinates.
Why it matters
A DDC controller can fail or be miswired at an individual piece of equipment even when the building-wide BAS dashboard looks completely normal, a problem the software layer can't fix if the field hardware underneath it isn't actually working correctly.
On a real project
A controls contractor installs a DDC controller at a VAV box that reads the space's actual temperature and modulates the box's damper to hold the programmed setpoint, reporting its status up to the building automation system.
Who this matters most to
An Electrician or specialty controls technician installs and wires the individual DDC controllers. A MEP Engineer writes the sequence of operation each controller executes.
Where this goes wrong
A controls technician wires a VAV box's DDC controller to the wrong terminal. The box reports normal status on the BAS dashboard while actually stuck fully open, and the mistake isn't caught until an occupant complains the space is too cold and a technician traces the fault back to the field wiring.