BACnet family
BACnet uses objects and services to exchange building system data. Check the network type, supported device functions and security configuration for the installation.
Sources and scopeSource record 25 August 2026
Technical source record: 25 August 2026. Check the linked documentation for current product requirements.
Inherited check dated 13 September 2026. Supporting evidence for this inherited check has not been independently confirmed.
Recorded scope: The BACnet Committee lists ANSI/ASHRAE 135 2024 with protocol revision 31. Certification and device support need the individual listing and product documentation.
Architectural guidance only; normative encoding, service, profile, and conformance requirements are in the licensed standards.
On this page
Overview#
BACnet is a building automation protocol with a standard object model and application services. It can represent devices, analogue and binary values, schedules, trends, alarms/events, access control objects, and other building functions. The current consolidated edition is ANSI/ASHRAE 135-2024; the BACnet Committee reports it as protocol revision 31.1
Transport choices#
| Data link | Typical role | Read next |
|---|---|---|
| BACnet/IP | UDP/IP with BACnet Virtual Link Layer (BVLL), broadcasts and routed subnets | BACnet/IP |
| BACnet MS/TP | Token passing BACnet over an EIA 485 multidrop bus | BACnet MS/TP |
| BACnet Secure Connect | WebSocket/TLS secure data link with hubs and nodes | BACnet/SC |
BACnet routers join data link networks while preserving BACnet network layer addressing. A protocol gateway that maps BACnet to another model has a larger semantic responsibility than a BACnet router.
Object and service contract#
A durable integration identifies an object by device instance, object type and instance, not display name alone. Record property, array index if applicable, units, resolution, writable priority, update mechanism, expected status flags, and ownership.
BACnet commandable properties use a priority array. Writing a present value without an agreed priority and relinquish procedure can mask another controller indefinitely. Store the chosen priority, use NULL/relinquish only as specified by the product and project, and verify the resulting value and status. Never reserve emergency/life safety priorities for ordinary physical security automation.
Change of Value (COV) subscriptions reduce polling but introduce subscription lifetime, renewal, reboot, duplicate notification, and fallback behaviour. Persist neither a subscription nor a cached value as proof of current device state after loss of communication. ReadProperty/ReadPropertyMultiple limits vary by product; bound batches and degrade gracefully.
Discovery and identity#
Who Is/I Am and object discovery reveal protocol addresses and capabilities; they don't authenticate a device. Device instance uniqueness must be engineered across the routed BACnet internetwork. Maintain an approved inventory binding instance, certificate identity where applicable, network/address, vendor/product, firmware, and expected services.
Conformance language#
A Protocol Implementation Conformance Statement (PICS) declares supported BACnet Interoperability Building Blocks, object types, data links, character sets, and options. It is a selection and test input, not proof that two products implement the same project semantics. ANSI/ASHRAE 135.1 defines conformance tests; certification claims should link to the exact listing and version.2
Safety boundary#
BACnet can command HVAC, lifts, door interfaces, and other consequential equipment. Make write paths opt in, authorise by object/property/priority, enforce quality and stale state rules, and keep certified fire/life safety interfaces within their approved design. Discovery and broad ReadPropertyMultiple sweeps can overload small devices; use an isolated lab or an owner approved query budget.