Open, Interoperable Systems For Energy Control

Abstract

In the early days of energy control systems, before the advent of
control networks, control systems consisted of masses of wires con-
nected to relays, switches, potentiometers, and actuators. Cabling was
installed in a point-to-point fashion between electrical panels, effectively
wire-routing stations filled with terminal blocks, and the sensor inputs
and actuator outputs. The functionality of these control systems was
relatively rudimentary and inflexible, and adds, moves, and changes
required extensive rerouting of wiring and connections.
The advent of solid state technology offered a means of using logic
circuits to replace wire and relays . Electrical panels gave way to pro-
grammable logic controllers (PLC), which were programmed not with a
screw driver but a data terminal. These PLC, first developed for the
industrial process control industry, gradually migrated to the environ-
mental control industry in the form of Direct Digital Control (DOC).
In fact, DOC rapidly evolved to the reference term that identified
any piece of distributed direct digital control equipment. Distributed,
meaning that the devices had an integral microprocessor; and direct
digital control meaning that this intelligent device was mounted as
close as possible to the point of control. Though DOC are used in some
applications for environmental control, the predominant technology in
the buildings industry is DOC. As increasingly powerful algorithms
were developed, tighter control over processes could be achieved.