April 2011

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BACnet's Continuing Growth
The original authors of the BACnet standard developed a method of organizing application data using objects, and the standard was structured in such a way that new object types and application services could be added to the BACnet standard in the future. 
Jim Butler

Jim Butler,
Cimetrics, Inc.

This article attempts to briefly answer the questions “Why isn’t BACnet done yet?” and “What has changed in BACnet since 1995?”

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What is BACnet?

BACnet is the ASHRAE, ANSI, and ISO standard network protocol for building automation systems.  Since its initial publication as an ASHRAE standard in 1995, BACnet has grown substantially from a standard that was initially focused on enabling interoperation within multi-vendor HVAC control systems.  Today, BACnet is also used for lighting control, physical access control, life safety, and more.

What accounts for BACnet’s ability to address the communication needs of a variety of building systems?  The original authors of the BACnet standard developed a method of organizing application data using objects, and the standard was structured in such a way that new object types and application services could be added to the BACnet standard in the future.  Companies were allowed to extend the standard object types and to develop proprietary object types for their products.  As well, BACnet supports several different networking technologies.

BACnet’s History as a Standard

ASHRAE formed a standard project committee to develop BACnet in 1987.  BACnet was approved an official ASHARE and ANSI standard in 1995 as ANSI/ASHRAE Standard 135-1995.  Major updates were published by ASHRAE in 2001, 2004, and 2008, with another major update scheduled to be published in 2011.

BACnet is also an international standard.  In 2003, BACnet was approved for publication as an ISO standard (currently ISO 16484-5:2010).  BACnet has been approved as a European Standard (currently EN ISO 16484-5:2010), and several other countries have adopted BACnet as a national standard.

There is a companion standard that describes tests for conformance to the BACnet standard.  Originally published as ANSI/ASHRAE Standard 135.1-2003, major updates were published in 2007 and 2009.  This standard is the basis for BACnet product testing programs developed by BACnet International and the BACnet Interest Group Europe.

BACnet for HVAC Control

BACnet includes robust support for HVAC control applications.  From the original version of the standard, BACnet has supported data exchange, alarming, and scheduling.  Distributed trend data collection and retrieval functionality was added in 2000.  Device management and file transfer services facilitate the configuration, operation, and maintenance of BACnet-based systems.

BACnet for Lighting Control

BACnet has been used for lighting control for many years.  However, the BACnet object types defined in the current version of the standard are not ideal for all lighting control applications.  The BACnet committee’s Lighting Applications Working Group has been developing extensions to the BACnet standard in order to address the needs of some of the more sophisticated applications.  The ASHRAE Journal article “Seeing the Light with BACnet” (2008) contains a summary of the working group’s technical direction.

BACnet for Life Safety

The BACnet committee’s Life Safety and Security Working Group developed two new standard object types in order to better model the behavior of life safety systems such as fire alarm systems.  The specification of these new object types was originally published as an addendum to the 1995 version of the BACnet standard, and minor revisions were made in an addendum published in 2005.

BACnet for Physical Access Control

A relatively new application of BACnet is physical access control, which includes card access systems for doors.  The specifications of several BACnet object types designed specifically for physical access control systems were published as addenda to the 2004 and 2008 versions of the BACnet standard. The white paper “Physical Access Control with BACnet” (2008) describes how BACnet can be used in physical access control systems.

BACnet for Elevators

The BACnet committee’s Elevators Working Group is developing extensions to BACnet to better enable BACnet systems to monitor elevators and other vertical transport systems. 

BACnet and the Smart Grid

Most building control systems and energy management systems are designed to manage the energy consumed by HVAC and lighting systems.  The growth of Smart Grid applications such as demand response will increase the potential benefits of energy management within facilities.  BACnet’s Load Control object type (defined in an addendum to the 2004 version of the BACnet standard) is specifically designed to facilitate active management of electrical demand.  The ASHRAE Journal article “BACnet and the Smart Grid” (2009) has much more information about this subject.

The BACnet committee’s Smart Grid Working Group is one of several industry groups that are developing communication standards for Smart Grid applications.

[an error occurred while processing this directive] The Impact of New Networking Technologies on BACnet

Networking technology has changed greatly since BACnet was designed in the late 1980’s and early 1990’s.  BACnet was initially designed for several different types of networks that were in use at that time, ranging from Ethernet to serial multi-drop (RS-485), and it was anticipated that BACnet would need to support new types of networks in the future.

It quickly became apparent that there would be benefits to using TCP/IP protocols within building control systems.  The first addendum to the BACnet standard, published in 1999, defined a mechanism for directly connecting BACnet devices to IP networks.

As the Internet blossomed, many organizations began to develop web services to allow programmatic access to data using the HTTP protocol.  In 2006, the BACnet committee developed a specification that was designed to allow business applications to easily access data within building control systems using SOAP-based web services.  The BACnet committee’s XML Working Group is currently developing major enhancements to that specification.

Wireless networking technologies are now being used in some building systems.  An addendum to the 2008 version of the BACnet standard specifies how ZigBee networks can be used to transport BACnet messages.  The BACnet committee’s Wireless Networking Working Group WN-WG is developing potential enhancements for BACnet’s support for wireless communication technologies.

Network security is a continuing concern in IT systems, and control systems are not immune to network-based attacks.  An addendum to the 2008 version of the BACnet standard specifies a new method for securing BACnet messages that uses the AES, HMAC and SHA-256 algorithms.  This is a replacement for the method included in the original version of the BACnet standard that was rarely if ever used.

IPv6 is a networking frontier for BACnet.  Designed as successor to IPv4, IPv6 has seen limited deployment so far, but it is expected to be a key protocol for enabling the “Internet of things”.  In March 2011, ASHRAE concluded the first public review of proposed extensions to BACnet to support IPv6.  The IP Working Group is leading the BACnet committee’s IPv6 efforts.

BACnet’s Future Growth

If the past 15+ years are any indication, BACnet will continue to grow in order to support new applications and networking technologies.

The BACnet committee (ASHRAE SSPC 135) welcomes participation by anyone who wants to contribute to the continuing development of the BACnet standard.  There are also opportunities for people who are interested in marketing, education, and product testing to participate in projects within BACnet International and other BACnet interest groups.

About the Author
Jim Butler, CTO of Cimetrics, has participated in the development of the BACnet standard since 1994.  He served as the first manager of the BACnet Testing Laboratories (BTL).  Jim is currently the convener of the BACnet committee’s IT Working Group.

About Cimetrics
Cimetrics provides BACnet communication products, continuous building commissioning services, and energy information systems.  The Cimetrics BACstac, a BACnet protocol stack (SDK), has been licensed by many manufacturers of HVAC controls, lighting controls, physical access control systems, and industrial control systems world wide.


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