BAS communication standards - Intelligent Buildings and Building Automation - page 73

Interoperation over different subsystems can be achieved. For example, when
a fire alarm occurs, the HVAC system will stop and the relevant image of the
space will be displayed. Lighting is turned on automatically when an author-
ized person intends to enter the laboratory identified by the access control
panel. The digital CCTV camera can be turned to monitor designated loca-
tions and starts to record when a person intends to access the laboratory or
the door is open. The intelligent functions and convenience provided by the
integration of the IB subsystems are amazing.
However, every subsystem has a different protocol in this IB system.
Gateways are needed to realize conversion of protocols to achieve the total
integration of the subsystems. The management software communicates
with subsystems via relevant drivers. If interoperation among subsystems is
needed, the management software plays the role of 'agent'. This interopera-
tion is a vendor's proprietary method only, not a standard method. It is not
flexible and much difficulty will be faced if a new third-party subsystem is
to be added to the system.
Nowadays, the rapid development of information technologies offers
new possible methods and solutions to overcome these difficulties. To have
a clearer understanding of the problem, the hierarchy model of the BAS
network is used as a reference. The BAS network can be divided into three
levels: management level, automation level and field level. Integration and
interoperability can be addressed at different levels. One can achieve integra-
tion and interoperation at all three levels starting from the bottom (field level)
or achieve integration and interoperation at a higher level. This provides two
possible ways to solve the problems of interoperation and integration. One
is to employ the same open communication protocol in all the three levels.
ISO, ASHRAE and several other organizations have been working on this.
For example, ISO adopted a few open protocol standards (e.g. ISO 16484-5
and ISO/IEC 14908-1) from field level to management level to increase the
interoperation of BAS. ISO 16484-5 basically refers to BACnet - A Data
Communication Protocol for Building Automation and Control Networks
presented by ASHRAE. The ISO/IEC 14908-1 refers to the LonWorks com-
munication protocol. However, in light of the fact that different protocols
are currently in use and the need to integrate BAS and other business systems
such as management information systems (MIS), another way is to achieve
integration and interoperation with standard protocols at the upper level
(e.g. management level) to avoid handling the difference of the lower level
protocols directly. For example, OPC (see Section 5.8) and some emerging
IT technologies (e.g. XML, SOAP and Web Services) can be employed to
solve the problem.
5.2 BACnet and its features
There are a few potential candidates likely in the future to dominate open
BAS communication protocols for all the three levels, such as BACnet,