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BACnet is a communications protocol for building automation and control networks. It is an ASHRAE, ANSI, and ISO standard[1] protocol.

BACnet was designed to allow communication of building automation and control systems for applications such as heating, ventilating, and air-conditioning control, lighting control, access control, and fire detection systems and their associated equipment. The BACnet protocol provides mechanisms for computerized building automation devices to exchange information, regardless of the particular building service they perform. Proper communication between building automation devices is critical for maximizing building energy efficiency, indoor air quality, and other aspects of "green" buildings.[2][3]


The development of the BACnet protocol began in June, 1987, in Nashville, Tennessee,[4] at the inaugural meeting of the Standard Project Committee (SPC). The committee worked at reaching consensus using working groups to divide up the task of creating a standard. The working groups focused on specific areas and provided information and recommendations to the main committee. The first three working groups were the Data Type and Attribute Working Group, Primitive Data Format Working Group, and the Application Services Working Group.

BACnet became ASHRAE/ANSI Standard 135 in 1995, and ISO 16484-5 in 2003. The Method of Test for Conformance to BACnet was published in 2003 as BSR/ASHRAE Standard 135.1. BACnet is under continuous maintenance by the ASHRAE Standing Standard Project Committee 135.

BACnet had an almost immediate impact on the HVAC controls industry. In 1996 Alerton announced a complete BACnet product line for HVAC controls, from the operator's workstation down to small VAV controllers. Automated Logic Corporation and Delta Controls soon followed suit. As of January 26, 2014, 721 Vendor IDs have been issued and are distributed internationally. Those vendor identifiers can be viewed at the BACnet website.

H. Michael (Mike) Newman, Manager of the Computer Section of the Utilities and Energy Management Department at Cornell University, served as the BACnet committee chairman until June, 2000, when he was succeeded by his vice-chair of 13 years, Steven (Steve) Bushby from NIST. During Steve Bushby's four-year term as committee chair the BACnet standard was republished twice, in 2001 and 2004, each time with new capabilities added to the standard. The 2001 version featured, among other things, extensions to support fire / life-safety systems. In June, 2004, 17 years after the first BACnet meeting and back in Nashville, William (Bill) Swan (a.k.a. "BACnet Bill") from Alerton began his four-year stint as committee chair. During his term the number of committee working groups grew to 11, pursuing areas such as support for lighting, access control, energy utility/building integration and wireless communications. In June 2008, in Salt Lake City, Dave Robin from Automated Logic Corporation took over the reins as the new committee chair after serving 4 years as vice chair. During Dave's term, 22 addenda were published for the 135-2008 standard and republished as 135-2010. Several addenda were published for 135-2010 and will be republished as 135-2012. In June 2012, in San Antonio, Carl Neilson from Delta Controls took over the reins as the new committee chair after serving 4 years as vice chair.

In January 2006 the BACnet Manufacturers Association and the BACnet Interest Group of North America combined their operation in a new organization called BACnet International.

Protocol overview[edit]

The BACnet protocol defines a number of services that are used to communicate between building devices. The protocol services include Who-Is, I-Am, Who-Has, I-Have, which are used for Device and Object discovery. Services such as Read-Property and Write-Property are used for data sharing. The BACnet protocol defines a number of Objects that are acted upon by the services. The objects include Analog Input, Analog Output, Analog Value, Binary Input, Binary Output, Binary Value, Multi-State Input, Multi-State Output, Calendar, Event-Enrollment, File, Notification-Class, Group, Loop, Program, Schedule, Command, and Device.

The BACnet protocol defines a number of data link / physical layers, including ARCNET, Ethernet, BACnet/IP, Point-To-Point over RS-232, Master-Slave/Token-Passing over RS-485, and LonTalk.

BACnet objects[edit]

The standard specifies 54 types of objects

Access Credential
Access Door
Access Point
Access Rights
Access User
Access Zone
Alert Enrollment
Analog InputSensor input
Analog OutputControl output
Analog ValueSetpoint or other analog control system parameter
Binary InputSwitch input
Binary OutputRelay output
Binary ValueControl system parameter
Bit String Value
CalendarA list of dates, such as holidays or special events, for scheduling
Channel Object
Character String Value
CommandWrites multiple values to multiple objects in multiple devices to accomplish a specific purpose, such as day-mode to night-mode, or emergency mode
Credential Data Input
Date Pattern Value
Date Value
Date Time Pattern Value
Date Time Value
DeviceProperties tell what objects and services the device supports, and other device-specific information such as vendor, firmware revision, etc.
Event EnrollmentDescribes an event that might be an error condition (e.g., "Input out of range") or an alarm that other devices to know about. It can directly tell one device or use a Notification Class object to tell multiple devices
Event Log
FileAllows read and write access to data files supported by the device
Global Group
GroupProvides access to multiple properties of multiple objects in a read single operation
Integer Value
Large Analog Value
Life Safety Point
Life Safety Zone
Lighting Output
Load Control
LoopProvides standardized access to a "PID control loop"
Multi-state InputRepresents the status of a multiple-state process, such as a refrigerator's On, Off, and Defrost cycles
Multi-state OutputRepresents the desired state of a multiple-state process (such as It's Time to Cool, It's Cold Enough and it's Time to Defrost)
Multi-state Value
Network Security
Notification ClassContains a list of devices to be informed if an Event Enrollment object determines that a warning or alarm message needs to be sent
Notification Forwarder
Octet String Value
Positive Integer Value
ProgramAllows a program running in the device to be started, stopped, loaded and unloaded, and reports the present status of the program
Pulse Converter
ScheduleDefines a weekly schedule of operations (performed by writing to specified list of objects with exceptions such as holidays. Can use a Calendar object for the exceptions
Time Pattern Value
Time Value
Trend Log
Trend Log Multiple

BACnet testing[edit]

BACnet Testing Laboratories was established by BACnet International to test products as per BACnet standard and support compliance testing and interoperability testing activities and consists of BTL Manager and the BTL-WG. The general activities of the BTL are:

The BTL also provides testing services through its managed BACnet laboratory. BACnet International and BTL have reached an agreement with SoftDEL Systems to establish and maintain a test lab for BACnet products.[5] SoftDEL is headquartered in Pune, India where the test facility operates BTL. The BTL Manager and BTL working group of BACnet International will administer the test lab. This BACnet lab is ISO 17025 accredited [6]

See also[edit]


  1. ^ Standard 135-2012-- BACnet--A Data Communication Protocol for Building Automation and Control Networks (ANSI Approved). 2012. 
  2. ^ Rajecki, Ron. "BACnet Technology Key to ‘World’s Greenest Office Building’". HPAC Engineering. Retrieved 11 September 2013. 
  3. ^ "BACnet: The Backbone of Intelligent Buildings". Building Operating Management. Retrieved 16 September 2013. 
  4. ^ BACnet protocol June, 1987, in Nashville, Tennessee
  5. ^ "BACnet test lab at SoftDEL" 4 April 2006
  6. ^ "SoftDEL BACnet Testing Laboratory achieves ISO accreditation." 6 Apr 2010

External links[edit]