Direct digital control systems
The Illustrated Guide to Mechanical Building Services, Third Edition (BG 31/2017), by David Bleicher, published by BSRIA in 2017, defines direct digital control systems (DDC) as: ‘…microprocessor-based with analogue inputs from sensors that are digitised. Some manufacturers make a distinction between DDC intended for primary plant control, such as for boilers, and those intended for secondary or terminal unit control such as fan coil units. Primary DDC units are freely programmable with control software configured for a particular method of plant control. DDC units intended specifically for terminal units usually have specific application software built in and only relatively minor configuration settings may need to be adjusted.’
Networked DDC systems: '...consist of two or more DDC controllers that are connected together enabling the exchange of information. Each controller usually controls one particular plant group and can operate autonomously in the event of communications loss. Typical examples of information exchanged between controllers are shared sensor readings, common plant start signals, and interlock signals between different plant groups. If a networked DDC system includes one or more permanent operator terminals it is classified as a building management system (BMS).'
--BSRIA
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