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The Outlook for BACnet

Nov. 1, 2008
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standing Standard Project Committee (SSPC) 135 met in Atlanta on

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standing Standard Project Committee (SSPC) 135 met in Atlanta on Sept. 22 to review and approve changes to ANSI/ASHRAE/IESNA Standard 135-2004, BACnet — A Data Communication Protocol for Building Automation and Control Networks. Consequently, several exciting developments are coming down the pike.


Addenda a, c, d, e, and f have been published and will be included in Standard 135-2008. Addenda b and m are at the end of the approval process. Once finalized, they also will be included in Standard 135-2008. Addendum b includes the addition of new event-log and trend-log multiple objects and device-restart notification, while Addendum m resolves the foreign-device active-registration grace period and remaining time ambiguities when an Annex J foreign device, such as a roaming laptop workstation, registers with a BACnet broadcast-management device (BBMD) to join a remote BACnet network.

Addenda g, h, j, l, o, r, s, and t could become part of Standard 135-2008 if approved after their public-review periods, which end in November. Of note:

  • More than 100 pages long, Addendum g defines encryption and authentication parameters for network security to secure communications across all BACnet networks. Unlike the network-security method defined in Standard 135-2004, the new approach is secure and computationally efficient enough to be implemented on small controllers.

  • Targeting architectural lighting control, Addendum i adds a new object to present the externally visible characteristics of a lighting output. The working group that revised this addendum also examined theatrical lighting control, which requires control commands that are disseminated much more quickly than those for HVAC systems.

  • Focusing on physical access-control applications, Addendum j adds new object types for access points, zones, users, rights, and credentials. The addendum completes the extensions needed for complete BACnet access controls that began with Addendum f. After ratification, Addendum j will necessitate Addendum g.

  • Addendum l expands operator-workstation categories and explains the requirements for specifying basic-operator-workstation capabilities, specifying new profiles for other types of workstations, and adding BACnet interoperability building blocks to define workstation capabilities.

  • In larger devices, preparations to perform certain backup and restoration operations can take a considerable amount of time. Addendum n helps by backing the configurations of all sorts of BACnet controllers with BACnet workstations.

  • Annex J defines a virtual BACnet/Internet-protocol (IP) network consisting of a group of devices that communicate among themselves. Annex J better accommodates network-address translation and operator access to multiple remote subnets across the Internet, issues that did not exist when Annex J first was developed. Addendum o defines some small but significant networking changes for using the IP network.

  • To give BACnet new capabilities for standardized communications among a wide range of applications, Addendum t defines an extensible-markup-language (XML) syntax that can be used to represent building data in a consistent, flexible, and extensible manner. It is anticipated that this will be the basis for a number of future BACnet capabilities.


Addendum q proposes the use of ZigBee as a BACnet wireless-data-link layer. ZigBee has emerged as SSPC 135's current wireless front-runner. Advantages to wireless include reduced wiring costs and the ability to move units easily as a room's, zone's, or building's configuration changes. It should be noted that these applications will not be battery-powered; they will require wired power.


Various BACnet groups and energy utilities are actively engaged in discussing three main topics: demand-response servers, real-time pricing, and building-price bidding. Communication between buildings and the energy utilities' demand-response automated servers likely will result from these discussions.

For example, buildings or groups of buildings could be contracted to decrease their energy consumption automatically in exchange for lower utility rates. If energy utilities anticipate reaching peak production, they would notify various buildings of the amount of demand reduction needed. One advantage of energy-utility integration is that energy savings are anticipated through the widening of zone-temperature deadbands, or “setbacks,” and lighting control. Another “green” advantage: Integration reduces a utility's need to fire up its inefficient “peaking” energy plants.


BACnet Testing Laboratories (BTL) has published a set of guidelines for the implementation of BACnet devices that play well with others. The guidelines are posted on BACnet International's Website (


“Plugfests” and BTL submissions are recommended for testing new or updated device implementations.

A plugfest is an interoperability workshop during which devices from different manufacturers are paired off and tested on BACnet interactions: configuration, sharing data, scheduling, trending, and alarming. The tests determine if one device can locate another device on the network, read data from another device, process alarms sent by another device, etc.

Because different manufacturers make different assumptions about BACnet implementations, plugfests are opportunities for long-term manufacturers to share their knowledge about BACnet implementation with new manufacturers while verifying correct implementations. When issues do arise, they are likely to become the subject of future implementation guidelines.

North American plugfests take place annually: BACnet International held its ninth-annual BACnet Interoperability Workshop in St. Paul, Minn., Oct. 7-9.

The second method of testing is to submit devices to the BACnet laboratory operated by SoftDel in Mumbai, India, or BACnet Interest Group-Europe's (BIG-EU's) BACnet laboratory operated by WSP Lab in Stuttgart, Germany. If a device passes each test, it receives a BTL Mark, which signifies that the device is interoperable with other devices.

Stateside, BTL is testing BACnet workstations for the first time. The laboratory is expected to complete first-round workstation testing this winter, awarding BTL Marks to passing participants.

Known to many as “BACnet Bill,” William O. Swan leads building-standards initiatives for Alerton in Redmond, Wash. He formerly was the chairman of ASHRAE SSPC 135 and co-chairman of the BACnet Testing Laboratories working group.