ABSTRACT
Direct Digital Control (DDC), which uses a digital computer with no moving parts, replaces both the conventional pneumatic control panel and the added energy management system. Applying a direct digital control computer to heating, ventilating and air conditioning equipment requires only two considerations. Software, though, is what primarily determines the ultimate capability of a DDC system. The servos are integral to the analog output, therefore, the output value is presented directly to the electric or pneumatic operator. Alarm and reporting programs provide critical and routing alarms, data and trend logging, and energy reports. Adjust commands on older systems were done strictly via operator commands from the central computer. The cost per point for the DDC system is usually higher than that of the other classes, but the following additional benefits are often sufficient to justify the extra cost.
