Building automation systems - Intelligent Buildings and Building Automation - page 30

Central Computer
Figure 3.2 Computerized control and monitoring system.
devices, automatic reset of analogue outputs, high and low alarm limits,
and reports.
The system of this generation was very expensive and not easy to use. Due
to the high cost of hardware, disc storage was rare. Programs were loaded
manually through a tape reader and it was very hard to change the programs.
The BAS at this stage had low reliability as the entire system was based on a
single central computer, and also involved excessive wiring. This generation
of computerized BAS had few applications and it was quickly upgraded to
a new generation of BAS.
3.2.3 Second generation − BAS based on minicomputer using
data-gathering panel
The use of minicomputers, central processing units and programmable logic
controllers (PLCs) in building automation systems increased dramatically
in the 1970s. New application software packages were incorporated into
their basic automation systems at an extra cost. Application packages for
energy management were introduced, such as duty cycle, demand control,
optimum start/stop, optimum temperature reset, day/night control and
enthalpy control.
During the 1970s, the cost of hardware began to decrease dramatically.
Computers became sufficiently practical to be used for common applications
by non-specialist users. Compared with the computer systems of earlier
stages, systems became user-friendly. It was much easier to program the