Having a specification that allows for any system option and protocol leads
to a more complex system, one that is more cumbersome to install, commission,
and maintain. It can be compared to allowing all employees in a company to use
PCs, Macs, UNIX, and Linux computers, while also allowing Ethernet, ARCNET, and
Token Ring as network communications media, and insisting that the IT department
maintain and service all of these. The workload becomes unbearable, which is
typically why IT departments pick one platform and stick with it.
Likewise, it is typically recommended to pick one common protocol for the
entire building control system infrastructure and stick with it. The costs go
down and the maintainability goes up. If there is a specific application or
subsystem component that is not available on this standard protocol or if there
is a specific need for using an alternate, this should be justified and a
gateway (protocol translator) identified and specified. However, this should be
the exception, not the norm.
Defining a common system architecture using standard, open methods is
important and more appropriate than specifying the “buffet” style that allows
anything to be used. An open building automation system provides
interoperability where software and hardware from multiple vendors can
communicate and coexist without the use of protocol converters and gateways.
There is a variety of open protocols on the market including an interoperable
protocol from LonMark International. LonMark is a non-profit association made up of member companies who
are manufacturers, designers, and system integrators, as well as end users committed
to the development, manufacture, and use of open, interoperable products and
networks.
A good open building automation system specification will define the
requirements for each aspect of the system. When defining an open spec,
try to remember it is more than just the protocol that needs to be specified.
There are five elements that need to be defined:
1. The Infrastructure- Including the
protocol, routers, media type, IT connectivity, etc. All these should be
specified based upon open standards, not on one vendor’s specific product. A
single system infrastructure provides the benefits of a reduction in
construction costs, lower life cycle and maintenance costs, as well as
providing an improvement in performance for the whole building.
2. The Devices- These are the
controllers in the network that produce, consume, or manipulate data and
control/monitor the system. In an open system, it is possible to use devices
from different vendors, because they all conform to a uniform industry
standard, such as LON. This means that the system is not locked into a single
supplier, allowing the best and most cost-effective equipment to be used. In
this way, suppliers are able to concentrate on developing products, which focus
on their core competency and not have to develop a complete system. Conversely,
an integrator who is capable of working with the open protocol will be able to
install a complete system selecting the most suitable products from different
suppliers. This way, only one integrator is required for the entire system
instead of multiple integrators, which can be expensive and cause isolation of
the subsystems. An open system also makes upgrading easier and more flexible.
3. The Tools- These are the
software or network management tools that configure, commission, and maintain
the system. The tools on the system need to be able to co-exist. Device
configuration plug-ins (modules) have been developed to allow use of any
standard network management tool. This allows vendors to configure their
devices with an open tool, meaning users are free to use tools from any vendor
they choose.
4. Graphical User Interfaces- These are
typically the visualization tools that the user or controls manager uses to
obtain a view into the system. User interfaces allow control, monitoring,
reporting, alarming, scheduling, and diagnostics. An operator workstation (user
interface) affords the means to efficiently and effectively manage operations
as well as display and print a graphical representation of the control network.
A user interface provides the same look and feel for monitoring and control
regardless of which vendor’s system or subsystem an operator is
viewing. As a result, system operators need only become proficient with
one user interface.
5. Enterprise Connectivity- The method for
connecting the building control network into the data network - also known as
the LON-LAN-WAN architecture. This ensures that the control system becomes an
element of all the data sources available to the enterprise. Open interfaces
have been developed to ensure data communication between the LON (the building
control network) and LAN (Local Area Network) is accessible by a vendor. To
provide this connectivity, enterprise level infrastructure devices are needed,
and they must be specified as open. Standard routers are used which means no
gateways are required.
Given this summary, it is strongly suggested to limit the main system
specification to just one methodology for communication. To ensure a truly open
system, all five systems elements must be open. This means each element must be
interoperable and all training and servicing must be specified as open, in
other words not locked into one system service provider. This, of course, is
assuming there is a desire to reduce costs, improve flexibility and choice of
products, provide the option for choosing the best system integrator, and allow
for open bidding on both the initial installation and the long-term service
contract.
For more information on open system architecture and on LonMark interoperable
open systems, visit www.lonmark.org.
Publication date:09/08/2008
