BACnet 20 Years On

From its roots in North America, the building systems protocol BACnet became an ISO standard in 2003 and is gaining acceptance around the world, used in countries as far afield as Dubai and Korea. In Germany, government buildings are now required to use BACnet, while in Russia, the Moscow State Construction University recently made a BACnet training course a required part of the curriculum. The protocol is even gaining 30% acceptance in Scandinavia where the rival open system LonWorks traditionally held sway.

It is more than 20 years since the American Society of Heating Refrigerating and Air Conditioning Engineers (ASHRAE) began devising the open IT protocol to ease the communications between HVAC equipment and controls in buildings. And it is 14 years since the resulting ANSI/ ASHRAE Standard 135, BACnet, A Data Communication Protocol for Building Automation and Control Networks, was actually produced.

BACnet is defined by ASHRAE as “a set of rules governing the exchange of data over a computer network.” The rules are a written specification that governs “everything from what kind of cable to use, to how to form a particular request or command.” The rules cover things like how to ask for the value of a temperature, define a fan operating schedule, or send a pump status alarm.” While there are other IT communication protocols, BACnet is unique in being designed specifically for building automation and control equipment.

Since BACnet’s inception ASHRAE’s technical committees have worked hard to expand and improve its applications, a task which is often complex and time-consuming.

The latest version of Standard 135 was produced in 2008. It included seven addenda, and 11 more are in the process of being developed. Bill Swan, former chair, (2004- 2008) of ASHRAE’s BACnet Committee and vice-president of the BACnet Interest Group of Europe, says “We are making a lot of changes, or extensions, to the standard. Our pace of activity is such these days that we are putting out large numbers of addenda at the same time.”

Swan, who is also the building standards initiatives leader for Honeywell and lives in Redmond, Washington, explains some key addenda that have been incorporated in the 2008 BACnet standard. He also discusses developments on the horizon that different BACnet SSPC (Standing Standard Project Committee) teams are focusing on.

Load control -talking to utilities

The brainchild of one team –the BACnet Smart Grid working group –is the load control data “object.” It was added to the BACnet protocol as a standard means to configure a building’s automation system to work with a utility. Should the utility be suffering from demand overload, or if the building owner wants to take advantage of off-peak energy rates, the building’s energy consumption can be adjusted.

Swan explains that until now these demand control, or load shedding, exchanges have generally been arranged via a telephone call to the facility manager. “What’s being done now is to automate that whole process.” The building automation system can even send meter information back to the utility to verify that it did comply with the request.

With BACnet, no matter what proprietary system is installed, you can add a BACnet box, “put it in your building and you’ve got the capability for the system to talk to the utility.”

The Smart Grid working group is also developing an addendum for energy trading.

Because much of the communication with the utilities will take place over the internet, security has become increasingly important. In July, the BACnet committee said they will publish an addendum to enable FIPScompliant secure communications to be used with BACnet Web Services.

Wireless Networks

ASHRAE recently published BACnet for ZigBee wireless networks. While wireless networks are still relatively rare, Swan says that they can be useful in older buildings where it’s difficult to run wiring, or in interiors where there could be lots of occupancy changes.

Applications Profiles

The task of the Applications working group is so complex they have been working on it since 1996. They are developing BACnet standard “profiles” or “macro objects” that are tailor- made for particular pieces of equipment, such as chillers and variable frequency drives. Ordinarly BACnet handles data at a more granular level, but the new profiles will represent a larger set of values. “It’s been a difficult job,” says Swan, “but we think that BACnet will be greatly improved by having the larger objects.” The committee has almost completed a profile for variable frequency drives that will be used as a model for developing profiles for other devices.

Testing BACnet devices

Since 2003 there has been a testing standard for BACnet devices, and there are two laboratories that test equipment and authorize the BACnet Testing Laboratory (BTL) mark. Now the Testing and Interoperability working group is finding ways to make the tests much more comprehensive. The group has just achieved a milestone, having completed testing of BACnet building operator workstations. “This means we now have the capability to test all kinds of BACnet devices,” says Swan.

“I always, always, always suggest that