Specification Writing Procedure
More care must be directed to system level functionality since the design and manufacture of components from multiple vendors does not
necessarily address this. These systems should be specified from the top down, starting at the central. Example: "The overall system must be
fully open supporting BACnet communication between operator workstation devices via Ethernet or Arcnet LANs, and supporting LonMark or
BACnet communications standards for control network devices." The specifier then must add functional expectations of the working building
management system (monitor, command, alarm support, change setpoints, etc.), taking care to avoid making the system proprietary.
The controllers and network communications must comply with the control and automation requirements set forth in the detailed sequence of
operation and user workstation display description (points, graphics, etc.). Communication concerns aside, this must always be the overriding
priority. The specifier may allow any combination of the four types of controllers: BACnet/Ethernet, BACnet/MSTP, LonMark or proprietary; or
may place restrictions on any of those controllers.Any restriction will impact the number of acceptable bidders.
No matter what the specified initially, if the user workstation and user workstation LAN are BACnet-compatible, subsequent controller
additions may still be any of the above. Except for the proprietary bus, all other communication links are standard.Any vendor offering an
application-compatible LonMark controller may connect it to the LonMark bus,or if there is none, provide a standard router to connect it to the
BACnet LAN.
If open systems and open bidding is your objective, your are now a step closer to achieving it.
Are You Ready To Specify Your First Open System? Read This First.
As you prepare to stake out your own position on the issues
surrounding openness, proceed deliberately. Continue to read
objective articles on the subject and follow vendor developments. As
you know, some vendors have firmly stated their preference
regarding the protocols while others are still riding the fence. The
decision you make- BA net only, LonMark only, or both - will affect the
decisions of the undecided vendors |
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When you decide there are enough vendors offering open products and systems (BACnet compatible or LonMark compatible) to competitively
bid a project and that meet your client's' functional requirements, try specifying a traditional proprietary DDC system with an open detailed
technical proposal alternate, including delivery and operational experience and availability dates for each component. Then interview the
vendors and make your decision based upon price, experience, risk, differences and the value added by openness. After you have some
practical experience, you may want to consider a more elaborate open solution such as the one presented here.
Open building control systems are here to stay. Many LonMark-equipped controllers are operational in HVAC systems today, all of them
certified by the LonMark Interoperability Association. And products supporting BACnet are now beginning to appear. The role each of thee
standards will play in the future will be terminated by preferences expressed by the specifying community.
Your clients will eventually be the winners, as their systems will be built upon a network of components, communicating via standards, with
fetures ideally suited to meet their needs, at the lowest cost!
The LonMark Interoperability Association is a user-funded organization
consisting of building owners, specifiers, system integrators and product
suppliers. Today there are more than 180 member firms dedicate to
defining open standards for building control applications.
For an up-to-date listing of intelligent HVAC control devices conforming to
Lon Mark standards, visit the LonMark web site at http://www.lonmark.org
Information on BACnet is available from ASHRAE, 1791 Tullie Circle,
N.E., Atlanta, GA 30329. For application or other technical information, call
(404) 636-8400 ext. 515, or visit the ASHRAE website at
http://www.ashrae.org
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Comfort from Experience.
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Home and Building Control
Honeywell Inc.
Honeywell Plaza
P.O. Box 524
Minneapolis, MN 55408-0524 |
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Helping You Control Your World
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http://www.honeywell.com/building
