What Is BACnet? Building Automation Protocol Explained
What Is BACnet?
BACnet is a data communication protocol developed specifically for building automation and control systems. BACnet stands for Building Automation and Control Network and is defined by ANSI/ASHRAE Standard 135.
BACnet provides a common way for building automation equipment from different manufacturers to exchange information. It is used in systems such as HVAC, lighting, energy management, access control, fire monitoring, and other building automation applications.
Why Was BACnet Developed?
Building automation systems historically used many proprietary communication methods. This made it difficult to connect equipment from different manufacturers without custom interfaces or protocol converters.
Work on BACnet began in 1987 when members of the building automation industry met through ASHRAE to develop a standard communication protocol for building automation. The first ANSI/ASHRAE Standard 135 was published in 1995. BACnet later became an international standard as ISO 16484-5 in 2003.
The BACnet standard continues to be maintained and expanded as building automation technology develops.
How BACnet Represents Building Data
BACnet represents information inside a device using objects. An object is a standardized collection of information described by properties.
Objects can represent physical inputs and outputs, software values, schedules, devices, and other functions within a building automation system. The properties of an object describe information about that object and allow other BACnet devices to identify and access its data.
For example, a temperature value can be represented as an Analog Input object. Properties associated with that object can identify the object, describe its units, report its present value, and provide other information about its operation.
Learn more: What is a BACnet Object?
BACnet Objects and Services
BACnet objects describe the information available in a device. BACnet services define how devices communicate and interact with that information.
Services are used for functions such as discovering devices, reading and writing object properties, reporting alarms and events, and performing device-management functions.
A common example is device discovery. A BACnet device can send a Who-Is request, and devices matching that request can respond with an I-Am message. Other BACnet services can then be used to access the objects and properties supported by those devices.
BACnet devices are not permanently limited to acting only as a client or only as a server. Depending on the service being performed, a device can request information, provide information, or perform both roles.
BACnet Network Types
BACnet supports several network technologies for carrying BACnet messages between devices. BACnet/IP and BACnet MS/TP are two of the most commonly used.
- BACnet/IP carries BACnet communication over IP networks.
- BACnet MS/TP uses EIA-485 serial communication and token passing between participating devices.
- BACnet/SC, or BACnet Secure Connect, is a secure BACnet datalink designed for IP networks using authenticated and encrypted communication.
BACnet/SC complements existing BACnet networking options rather than replacing BACnet/IP or BACnet MS/TP.
Learn more: What is BACnet MS/TP?
BACnet Interoperability
One of the main purposes of BACnet is to provide a standardized method for building automation equipment from different manufacturers to exchange information.
BACnet defines objects, properties, services, messages, and communication rules. However, not every BACnet product implements every BACnet capability. The specific capabilities supported by each device are therefore important when designing an interoperable system.
BACnet Interoperability Building Blocks, or BIBBs, provide a standardized way to describe BACnet interoperability capabilities such as reading and writing properties, alarm handling, scheduling, trending, and device management.
Learn more: BACnet Interoperability Building Blocks (BIBBs) Reference Table
BACnet Testing and BTL Certification
BACnet Testing Laboratories (BTL) operates a certification program for BACnet products. Products seeking BTL Certification are independently tested for compliance and interoperability using BACnet testing requirements.
Products that successfully complete the certification process can be identified by the BTL Mark and listed in the BTL product database. Certification helps system designers and integrators identify products whose BACnet capabilities have been independently tested.
Where BACnet Is Used
BACnet was developed for monitoring and controlling building systems. Applications include HVAC equipment, lighting systems, energy management, access control, fire monitoring, and integration between building automation equipment from different manufacturers.
BACnet can also bring information from multiple building systems into a building management system, supervisory controller, workstation, or other BACnet application.
BACnet Gateways and Protocol Conversion
Not every building automation device communicates using BACnet. A protocol gateway can translate data between BACnet and another communication protocol, allowing non-BACnet equipment to exchange information with a BACnet system.
Chipkin provides BACnet protocol gateways and integration solutions for connecting building and industrial equipment to BACnet/IP and BACnet MS/TP networks.
BACnet Testing and Troubleshooting
When commissioning or troubleshooting a BACnet network, technicians often need to discover devices, examine their objects and properties, monitor values, and test BACnet communication.
The CAS BACnet Explorer is a BACnet testing and diagnostic tool for discovering, browsing, monitoring, and testing BACnet devices and networks.