Field-Ready · Lesson 6.1
BACnet
The protocol written for buildings. What it is, how it works, and what to do when it does not.
What BACnet Actually Is
BACnet stands for Building Automation and Control Networks. It is an ASHRAE standard (ASHRAE 135), developed specifically for building automation, not adapted from an industrial protocol or borrowed from IT networking. This matters because it was designed with HVAC data models in mind from the beginning.
Before BACnet, every controls manufacturer used a proprietary protocol. A Johnson Controls controller could not talk to a Siemens controller without an expensive custom gateway. The owner was locked into one vendor for the life of the building. BACnet's promise was interoperability: buy controllers from different manufacturers and have them communicate on a common network.
The honest caveat
BACnet interoperability in the real world is not seamless. Each manufacturer implements the standard differently, uses different sets of optional features, and sometimes extends it with proprietary objects. Two devices can both claim to be "BACnet compliant" and still not communicate well with each other without careful configuration. Reading the PICS (Protocol Implementation Conformance Statement) of both devices before an integration project tells you what each device actually supports.
Despite this, BACnet is the closest thing the building automation industry has to a universal language. If a modern controller speaks any protocol natively, it almost certainly speaks BACnet.