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SYSTEM FUNCTIONS
GENERAL
Each BMCS level provides some degree of stand-alone
capability and collects and preprocesses data for other
processing levels. The following discussion starts with the
functions provided by the lowest level of processing in the
configuration, or hierarchy, and progresses to the highest level.
ZONE-LEVEL CONTROLLER FUNCTIONS
The primary function of the zone-level controller is to
provide direct digital control of unitary equipment. To support
the resident DDC programs, the zone-level controller interfaces
with sensors and actuators and performs the functions of point
processing as well as execution of the DDC programs.
SYSTEM-LEVEL CONTROLLER
FUNCTIONS
System-level controllers provide increased processing
capability, higher I/O capacity, and more universal application
flexibility than zone-level controllers and have greater stand-
alone capability. System-level controllers handle multiple
DDC loops and the complex control sequences associated with
built-up air handling units and other HVAC equipment. Other
types of system-level controllers monitor multiple zones of
fire alarm, security points, and/or lighting control. They can
also provide emergency evacuation control through speakers
and control personnel movement with access control and card
readers. For a detailed description of system-level controllers,
refer to Microprocessor-Based/DDC Fundamentals section.
Processed point data at the system controller level is used
directly by the resident DDC, EMS, and time/event programs.
The data is also available for readout at local control panels,
portable terminals, and can be communicated up to the
operations-level processor and to other system-level
controllers. In addition, all parameters and output values
associated with DDC and other resident programs are
accessible for local and operations-level readout and
adjustment. Data point values may be shared between zone-
level controllers, between system-level controllers, and
between zone- and system-level controllers.
OPERATIONS-LEVEL FUNCTIONS
GENERAL
The operations level is the third tier of the BMCS
configuration. Building or facility operations and
management personnel interact on a day-to-day basis through
this level. The hardware and software for this tier is dedicated
ENGINEERING MANUAL OF AUTOMATIC CONTROL
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS
to interfacing with operating personnel rather that with
mechanical systems, as the controllers do in the lower tiers
of the BMCS configuration.
HARDWARE
The operations-level processor supplies the processing
capacity and memory required for all communications and
operator interface software as well as the peripheral capacity
for dedicated alarm and report printers and work stations It is
usually a PC consisting of:
— Full keyboard, with mouse or other entry device.
— High resolution color monitor.
— RAM or working memory.
— Hard disk memory.
— Diskette drive.
— Multiple peripheral ports.
— Communications interface boards.
— At least one printer.
SOFTWARE
While hardware enables operator interaction and the
display and printout of data, the software determines how
the interaction takes place, the data is displayed, and the printer
output is formatted.
Standard Software
Most BMSs run under Microsoft Windows™ and use
standard mouse conventions, such as drop-down menus, dialog
boxes, radio buttons, and up-down arrows. Many systems allow
the use of other standard Windows compatible programs such
as word processors, spread sheets, and data bases to operate
concurrently with the BMS. In such cases, a BMS alarm
overwrites the monitor screen until acknowledged and canceled.
Other standard programs are often embedded in BMS
software. A spread sheet may be an integral part of the trend
report utility. This allows the operator not only to view the output
of the requested report, but to review and edit it in the
spreadsheet format. The spread sheet also can be called up as a
stand-alone utility. System graphics are usually based upon
standard graphics software.
Communications Software
Software at the operations level communicates with all
system- and zone-level processors in a peer-to-peer fashion.
Communications functions include:
— Receiving alarm and return-to-normal reports (including
remote device communications failures).
— Receiving trend status' and values.
— Passing global data and alarm reports to other devices
on the ETHERNET LAN.
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