Chapter hvac engineering Fundamentals: Part 1 Introduction

8.7.1
Energy management
and control system
As noted above, EMCS is also known by other names, including BAS
and SCADA. The concept applies to a great many existing systems but
in new HVAC work has been largely superseded by the DDC system
(see Sec. 8.7.2).
Design Procedures: Part 6
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280
Chapter Eight
Figure 8.61
EMCS schematic arrangement.
Figure 8.62
Digital message.
Figure 8.61 is a generalized schematic of an EMCS. The central
console includes a computer, software (programs), display monitor,
printer, and the keyboard through which the operator communicates
with the system. The group consisting of the monitor, printer, and
keyboard is sometimes called the
operator-machine interface
(OMI) or
workstation. The communication link is usually a coaxial cable or a
‘‘twisted pair’’ of wires. Information is transmitted on the link by
means of digital ‘‘words’’ (Fig. 8.62), which include the address of the
destination, the message, and a method of checking for accuracy. The
field interface device
(FID) serves as an interface between the com-
munication link and the local loop devices. In many systems, the FID
Design Procedures: Part 6
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