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Historically, proprietary systems from different manufacturers have been difficult or impossible to integrate together. Through accident or intent, many owners have discovered that by buying in to a particular vendor, their choices for system expansion, upgrade and replacement have been severely limited.

There are ways to interconnect products made by different manufacturers without a standard protocol but they are difficult. A single front end system can be made which "knows" the proprietary communications technique of each system, effectively bridging their differences together completely in software. This approach requires the cooperation of multiple manufacturers, or reverse engineering. In practice these systems have been very costly to implement and support, as the various systems they interface with evolve and change independently.

Another approach has been for one or more vendors to publish their protocols, or even place them in the public domain for other vendors to develop interfaces to. Without assurances that protocols will not change arbitrarily going forward, most vendors had been reluctant to adopt any of several proposals like this which had been tried.

Another method which had been tried involved defining a common protocol between a centralized front end and individual "gateways" to proprietary systems. This approach also proved costly, and was not really supported by vendors, many of whom were threatened by "open systems" thinking.

The end result is that building owners feel trapped, locked-in to products made by a single manufacturer.

Around 1984 various people in the industry began voicing their concerns about the burgeoning use of networking of building automation system components using proprietary (non-standardized and often secret) communications methods. The resulting controversy prompted ASHRAE to form SPC-135P, a committee with the express charter to investigate and develop a new standard to address these issues. Through a consensus process involving nearly every major vendor of controls in North America, as well as academics, end users, consulting engineers and government interests, the BACnet standard was born after nearly nine years of effort.

An often misunderstood aspect of BACnet is that the standard, from its initial charter, was targeted to address the needs of all building systems, and not just HVAC. The whole concept of BACnet is the enabling of interoperability between different building systems types as well as different manufacturers.

Largely because of fear and entrenched interests, and the ponderous consensus building process, it took a long time for the standard to emerge. Under ASHRAE standards procedures, which are very rigorous, public review is required for all draft standards. BACnet received three public reviews, each lasting for 3-6 months. These reviews generated over 790 public review comments, over and above those generated by committee members. An interesting historical aside is that nearly 300 comments came from a single individual, coincidentally an employee of a major vendor.

These public review comments represented views from a large cross section of manufacturers, end users, consulting engineers and others. A strong international interest was also clear, and the incorporation of those concerns into the final standard has put BACnet in the leading position as a potential world-wide standard going forward. No other standard even comes close to BACnet in this regard.

Every major vendor had the opportunity to be involved in BACnet over a long period of time, so no aspect of BACnet should be a surprise.

Finally, in September of 1995, ASHRAE's board of directors voted to ratify the standard and publish ASHRAE 135-1995. Since ASHRAE is an approved ANSI standards body, the standard was also submitted to ANSI and in December of 1995 became an American National Standard, ANSI/ASHRAE 135-1995.

The SPC was disbanded and immediately reformed into a "standing standards project committee" or SSPC. Two key efforts began at that time. One was to begin work on a new testing standard for BACnet which later became known as 135.1P (for provisional). The other was to begin work on addenda to 135-1995.

Over the course of six years from 1995 to 2001, various addenda to the standard were released under the ASHRAE Continuous Maintenance rules. In 2001, ASHRAE released a revision to the standard that incorporated all of the known errata and addenda. This new standard is called ANSI/ASHRAE 135-2001.

The 135-2001 standard was also submitted to the International Organization for Standards (ISO). In January of 2003 the ISO published the result of its ballot among participating member nations. BACnet became an international standard ISO 16484-5. This BACnet milestone was the result of work with ISO's Technical Committee 205, Building Environment Design, which launched the enquiry following a letter ballot in the spring of 2002. The countries that voted to approve BACnet were: Australia, Belgium, Canada, China, Denmark, Egypt, Finland, France, Germany, Greece, Italy, Japan, Korea, Norway, Russia, South Africa, Spain, Sweden, the United Kingdom, and the United States. There were no negative votes. Under ISO procedures this means that the Draft International Standard could go immediately to publication, skipping the "Final Draft International Standard" stage. In October 2003, ISO 16484-5 passed the final hurdle and was officially and finally sanctioned.

At the same time, in June 2003 ASHRAE, having completed two rounds of public review and revision to 135.1P, finally published the ASHRAE 135.1 test standard which should become an ANSI standard sometime late in 2003 or early 2004.

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