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BACnet, which stands for Building Automation and Controls network, is a protocol developed by ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers). BACnet was developed as a response to industry concerns about increased networking of BAS components using proprietary communications methods. In the past, these proprietary communications severely limited the building owners' choices for system expansion, upgrade, and replacement. Every major controls vendor in North America, as well as academics, end users, consulting engineers, and government groups participated in its development.

BACnet has been accepted as an open standard by the American National Standards Institute (ANSI) and the European Committee for Standardization (CEN) standards. It is also an International Organization for Standardization (ISO) standard.

BACnet is designed to include all building systems, lighting, security, fire, heating, ventilation, and air conditioning. Its purpose is to promote interoperability - sharing data between systems made by different vendors.

It provides the necessary tools to develop a specification for systems that are interoperable. BACnet provides methods and standards for representing information, for requesting and interpreting information, and for transporting information. - ASHRAE SSPC 135


The BACnet protocol model specifically defines:

Data and control functions structured in anbobject-oriented fashion
Services that describe data requests and responses
Network datalink types
A scalable and flexible internetwork and network architecture


BACnet Network Types:


BACnet over ARCnet or ARC156


ARCnet is an embedded networking technology well suited for real-time control applications in both the industrial and commercial marketplaces. Its robust performance and the availability of low-cost silicon make it the network of choice in BAS's.

ARC156 is a unique implementation of ARCnet. ARC156 is similar to master slave/token passing (MS/TP). The main difference between the two is speed. ARC156 baud rate is 156K baud whereas MS/TP tops out at 76.8K baud.

Also, ARC156 uses a separate communications co-processor to handle the network traffic and a separate processor to handle the program execution. This provides faster processing of applications and handling of communications on the network. ARC156 is the standard communications method used by our translators.


BACnet MS/TP (Master-Slave/Token Passing)


BACnet Master Slave/Token Passing or MS/TP is used for communicating BACnet over a sub-network of BACnet-only translators. Each translator on the network has the ability to hear the broadcast of any other device on the network. The speed of an MS/TP network ranges from 9600 baud to 76.8K baud.


BACnet ISO 8802-3 (Ethernet)


BACnet network type which uses an Ethernet carrier and (Internet Protocol) IP addressing


BACnet Point-to-Point (EIA-232)


PTP is used to connect two distinct BACnet networks so that information can be shared between the networks. PTP uses an EIA-232 connection between two BACnet half-routers. This connection allows for two different BACnet networks to speak to each other, even at different baud rates.




BACnet Web site


BACnet® Certification

The organization that tests and certifies interoperability manufacturers of BACnet devices is called the BACnet Testing Laboratories, or BTL.


BACnet® Device

A BACnet device is a microprocessor-based unit that is designed to understand and use the BACnet protocol.


A BACnet device is typically a controller, gateway, or user interface. A BACnet device contains a collection of information about the device called BACnet Objects and BACnet Properties.


A BACnet device will contain a device object that defines certain device information, including the device object identifier or instance number. A BACnet device object instance number must be unique across the entire BACnet network.


BACnet® Interest group

Associations formed by BACnet users for the benefit of BACnet users. BACnet Interest Groups enable exchange information and experiences about the implementation and application of BACnet. Many BACnet Interest Groups have formed around the world to support BACnet users.

BACnet Interest Groups:
BACnet International -
BIG-EU, Europe -

BIG-PL, Poland -
BIG-RU, Russia -
BIG-SE, Sweden -
BIG-FI, Finland
BIG-CN, China
BIG-ME, Middle East

BIG-AU, Australia

BACnet InternationalBACnet® International

BACnet International is an industry association that facilitates the successful use of the BACnet protocol in building automation and control systems through interoperability testing, educational programs, and promotional activities. The BACnet standard was developed by ASHRAE and has been made publicly available so that manufacturers can create interoperable systems of products.  BACnet International complements the work of the ASHRAE standards committee and BACnet-related interest groups around the world. BACnet International members include building owners, consulting engineers and facility managers, as well as companies involved in the design, manufacturing installation, commissioning, and maintenance of control equipment that uses BACnet for communication.  For more information, please visit


Member of BACnet International logoBACnet International Membership


Members of BACnet International promote the successful use of the BACnet protocol in building automation and control systems.


Current member listing

Get a free individual membership


BACnet® Object

A BACnet object is a collection of information [BACnet Properties] within a device. Objects represent either physical or virtual information, such as analog and digital inputs and outputs, control algorithms, specific applications, and calculated values. Objects also may represent single pieces of information, or a collection of multiple pieces of information such as a logical grouping.


The BACnet standard defines standard objects and allows for the creation of non-standard or proprietary objects for which interoperability with other vendors will typically not be available.

Objects will always be associated with object identifiers. Object identifiers are a binary number containing a code for the object type and the object instance number. Every object, no matter its purpose or function, has a collection of properties that define the object.


BACnet® property

BACnet properties communicate information about a BACnet object. A typical object has an extensive collection of properties, based on the function and purpose of the object. Each property contains two pieces of information: a property name and the property's value.


Properties may be defined as read-only or read/write. A property's purpose is to allow other BACnet devices to read information about the object containing the property, and optionally command [write] a different value to the property. Depending on the type of object that the property resides in, particular object properties may be optional or required for implementation per the BACnet standard.


BACnet® Services

BACnet services are actions that a BACnet device takes to read or write to another BACnet device. Services are grouped into five categories of functionality

object access (read, write, create, delete)

device management (discover, backup, time synchronization, initialize, and restore database)

alarm event (alarms and changes of state)

file transfer (trend data, information and program transfer)

HMI (human machine interface).



Acronym standing for BACnet Broadcast Management Device


The BACnet network discovery utilizes two services that rely on the use of broadcasts:




Routers are used to join IP networks together so messages from one network can be sent to another. Most routers do not forward broadcast messages and this means discovery cannot discover devices on another network.

To solve this problem BACnet provides uses BBMD – BACnet Broadcast Management Device.

BBMDs (either a device or an application) on each BACnet network, are configured by specifying the IP Address and mask of the each BBMD making their respective configurations identical. When the one BBM receives a broadcast, it forwards the messages to the other BBMD which in re-broadcasts on the other network.



Acronym standing for BACnet Interoperability Building Blocks


A term coined by H. Michael Newman of Cornell University. The intent of BIBB is to provide a way for a specifier to write a performance specification without the need to understand all of the technical details of the BACnet Device. All devices expected to be interoperable must support the function required (BIBB) and the "Initiate" or "Execute" side of thefunctionality, depending on the role of the device. BIBBs may also be predicated on the support of certain, otherwise optional, or proprietary BACnet objects or properties.


BIBBs interoperability Functions

Data Sharing

  – Read/write property
– Read/write multiple properties
– Read property conditional
– COV (Change of Value)
– Unsolicited COV


  – Scheduling - internal
– Scheduling - external


  – Viewing and modifying trends - internal
– Viewing and modifying trends - external
– Automated trend retrieval

Network Management

  – Device connection establishment
– Router configuration

Alarm and Event

  – Alarm and event notification - internal
– Alarm and event notification - external
– Alarm acknowledgement
– Alarm summary
– Alarm enrollment summary
– Alarm information
– Life safety alarm

Device Management


– Device binding - discovery and connection
– Object binding - discovery and connection
– Device communication control
– Private transfer of message
– Text message
– Time synchronization
– UTC time synchronization
– Reinitialize device communications
– Backup and restore device database
– List manipulation

– Object creation and deletion
– Virtual terminal


Segmentation support and



A device that connects two networks or two segments of the same network by forwarding messages without analyzing or rerouting them. Unlike routers, bridges are protocol independent.


Example: A bridge might connect an Ethernet and token-ring network.



This is a BTL Listed ProductBTL

What is the BTL?

BACnet Testing Laboratories (BTL) was established by BACnet International to support compliance testing and interoperability testing activities and consists of BTL Manager and the BTL-WG.

General Activities of the BTL
The general activities of the BTL are:
•    Publish the BTL Implementation Guidelines document,
•    Organize the annual BACnet International sponsored Interoperability Workshop,
•    Award worldwide BTL Listings to qualified BACnet devices,
•    Support the activities of the BTL-WG,
•    Provide support to the BACnet community with the help of the BTL-WG when questions arise on the testing package.
•    Publish and Maintain the BTL Test Package with the technical support of the BTL-WG for use by pre-testers and approved BACnet testing laboratories.
•    Approves Testing Laboratories for BTL Testing.

The BTL also provides testing services through its managed BACnet laboratory, SoftDEL.


Current BTL Listings


What is the BTL Working Group?


The working group was formed by BACnet International to oversee the establishment of the BACnet® conformance certification and listing program. The working group is comprised of members of BACnet® International and BIG-EU whose goals are to promote and maintain the BACnet® and BTL® trademark.

The BACnet Testing Laboratories Working Group provides oversight and guidance to the BACnet Testing Laboratories (BTL). The BTL Working Group is responsible for the technical aspects of BACnet International's testing and listing activities, the central goal of which is to improve BACnet interoperability between building automation products.

The BTL Working Group meets by phone usually once a week and has face-to-face meetings quarterly.

Click here to view BTL Working Group Charter.

How do I Join the BTL Working Group?


Contact the Working Group Chairman for more information. 


Building Automation System

A Building Automation System (BAS) is an example of a Distributed control system. Building automation describes the functionality provided by the control system. The control system is a computerized, intelligent network of electronic devices, designed to monitor and control the mechanical and lighting systems in a building.


BAS core functionality keeps the building climate within a specified range, provides lighting based on an occupancy schedule, and monitors system performance and device failures and provides email and/or text notifications to building engineering staff. The BAS functionality reduces building energy and maintenance costs when compared to a non-controlled building. A building controlled by a BAS is often referred to as an intelligent building system.


Building Energy Codes

Click to Launch Building Energy Code Tool [flash]Building codes are a set of rules that specify the minimum acceptable level of safety for constructed objects such as buildings and structures. The main purpose of the building codes is to protect public health, safety and general welfare as they relate to the construction and occupancy of buildings and structures.


Building codes are generally intended to be applied by architects and engineers, but are also used for various purposes by safety inspectors,, commercial developers, contractors and subcontractors, manufacturers of building products and materials, insurance companies, facility managers, tenants, etc...


Launch the Building Energy Code Finder (by state)

Launch the Building Energy Code Finder (by state)


Building Controller (BC)

A fully programmable control module which is capable of storing trends and schedules, serving as a router to devices on a subnet, and initiating read and write requests to other controllers. Typically this controller is located on the Ethernet/IP backbone of the BAS. In many vendors' architectures a Building Controller will serve as a master controller, storing schedules and trends for controllers on a subnet underneath the Building Controller.


Building Intelligence Group LLC

Building Intelligence Group LLC is an independent consulting company dedicated to helping building owners, facility managers, system integrators and suppliers, make the industry transition to Intelligent Building Systems.