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BACnet System Specifying is on the Rise

David Fisher
PolarSoft® Inc.

August 2001

Building owners, consultants, and specifying engineers have been hearing about BACnet for a long time. This six-year-old American National Standard (published as BACnet—A Data Communication Protocol for Building Automation and Control Networks) by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and The American National Standards Institute (ANSI) in 1995 has permanently changed the rules for building automation. With tens of thousands of installations, and a worldwide presence, BACnet is fast becoming the only serious choice for full-scale building automation where interoperability is an issue. While there are many factors that contribute to BACnet’s success, the following are often cited:

  • BACnet is an ANSI standard
  • BACnet provides a wide range of compatibility with existing LAN standards, integrated within the same internetwork
  • BACnet provides robust internetworking of small, low-cost LANs like MS/TP, ARCNET, and LonTalk with high performance BACnet over Ethernet and BACnet over TCP/IP over Ethernet
  • BACnet has the most advanced and flexible model for data representation and standardized object framework that is safely extensible without requiring "permission"
  • BACnet was developed with the cooperation of nearly every major vendor of building automation, controls, and mechanical equipment.
Over the past several years there have been significant efforts focused on simplifying the specification of common BACnet interoperability needs. The breakthrough was the idea of defining BACnet Interoperability Building Blocks (BIBBs), a term coined by H. Michael Newman of Cornell University. The intent of BIBB is to provide a way for a specifier to write a performance specification without the need to understand all of the technical details of how it would be implemented. In essence, a BIBB is a simple definition of an interoperability function or capability that refers to a specific set of BACnet features that must be implemented by a device to support that BIBB. Under the continuous maintenance procedures for the BACnet standard, a complete set of BIBB definitions have been proposed in Addendum D, which is now in the final stages of its second public review.

A companion Addendum E further defines standard device profiles that make use of these BIBBs to recommend prototypical kinds of BACnet devices. Although facilities may have a large number of building automation and controls functions and types of controller devices, there are relatively few unique kinds of interoperability relationships. Often, it is straightforward to define several generic "interoperable controller types" that have the same kinds of requirements for interoperability. This greatly simplifies the problem of specifying interoperability using BACnet. A profile defines a collection of interoperability characteristics in a concise and easy-to-understand way.

As these addenda become incorporated into BACnet in the coming months, the job of interoperability specifying with BACnet will become significantly easier than ever before. ASHRAE offers Understanding and Specifying BACnet, a one-day professional development seminar that covers this topic in some detail.

The fundamental robustness of the standard, coupled with these advances in specifying technique and a rapidly expanding product base, has spawned a growing trend toward BACnet-based interoperability specifications in North America, Europe, and the Pacific Rim. Besides the English language version, the standard has been reproduced in Japanese, Chinese, and Korean versions. From the beginning, BACnet has been created using internationally accepted standards for communications and standards development. It comes as no surprise that BACnet is the only serious contender under consideration as an international standard.

Practical applications

There are three areas of significant opportunity for applying BACnet: interoperability, integration, and migration.

Municipal and institutional owners have long been saddled with the potential of having to support multiple vendors’ systems in the same facility, due to requirements for lowest bidder procurement. In the past, this meant that systems were difficult or impossible to integrate into a common operating framework, leading to training and maintenance and cost-of-ownership issues. BACnet provides real multi-vendor interoperability for a wide range of vendors and types of equipment, and those capabilities are proven in practice.

The same mechanisms that make BACnet suitable for interoperability across vendors turn out to also be well suited to the integration of historically separate types of systems, such as HVAC, lighting, vertical transport, and fire/life safety systems. An intense effort over the past several years, in concert with manufacturers from the fire and life safety field and the NIST Building/Fire Research Laboratory, has led to a consensus and addenda to BACnet that provide significant enhancements for fire/life safety applications that will greatly simplify the integration of systems with other BACnet-based components. Similar initiatives in lighting control and other areas are also beginning to bear fruit.

Increasingly, manufacturers are providing BACnet-capable gateway devices as a bridge to allow the integration of proprietary or older systems with the new BACnet-centric trends. This provides owners with migration strategies for older equipment and systems. Although the availability of these kinds of gateways had been initially limited, many manufacturers are being forced to provide a migration path, or face losing customers who are finally starting to get some real choices.

David Fisher, is president of PolarSoft Inc., Pittsburgh, Pennsylvania. He was a charter voting member of ASHRAE’s Standards Project Committee 135P and has helped develop the BACnet standard (ANSI/ASHRAE 135-1995) since its inception. He has taught many courses including ASHRAE’s professional development seminar "Understanding and Specifying Basic BACnet Systems."

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