BACnet, which stands for Building Automation and Control Networks, is a data communication protocol designed specifically for building automation and control systems. Developed under the auspices of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), BACnet has become an international standard (ISO 16484-5) since its introduction in 1995. It provides a comprehensive set of standardized object types and services that allow for seamless integration of various building systems, including HVAC, lighting, access control, and fire detection.

Compared with the simplicity of the Modbus protocol, BACnet is considerably more complex, offering high‑level functionality such as device auto‑discovery. Its discovery tool can greatly reduce the time required to configure and commission large systems.

Physical layer

A major strength of BACnet is its flexible network architecture. It supports several network types, including BACnet/IP (for Ethernet and Wi‑Fi), BACnet MS/TP (Master‑Slave/Token‑Passing over RS‑485), BACnet ARCNET, and BACnet LonTalk. This versatility enables deployment in buildings of any size—from small commercial facilities to large industrial complexes. The protocol also incorporates security features to address cybersecurity concerns in modern building‑management systems. Historically, MS/TP and BACnet/IP have been the most common, with BACnet/IP gaining market share as LAN infrastructure becomes ubiquitous.

Discovery

Because BACnet includes auto‑discovery, configuring system software is generally straightforward. The main challenge with BACnet installations is ensuring device compatibility. In addition to using the same physical layer (e.g., RS‑485, RS‑232, BACnet/IP), users must verify that the BACnet object types are compatible. The most common object types are described below:

Object types

BACnet uses an object‑oriented approach to represent the functions of building automation devices. These objects include both standardized types (such as Analog Input, Binary Output, and Schedule) and vendor‑specific types, allowing for both interoperability and innovation. Each object has a set of properties that define its characteristics and behavior. BACnet devices communicate using a client‑server model, where devices can request or provide information as needed. This model supports both polling (where a client regularly requests data) and Change of Value (COV) reporting (where a server sends updates only when significant changes occur), allowing for efficient network utilization.

Analog Input

Sensor values are read via the Analog Input object. BACnet analog input objects include the engineering unit and support floating‑point values, so configuration is typically unnecessary. They are widely supported and can be used even when no higher‑level objects are available on a device.

Trend Log

The Trend Log object was introduced to the BACnet standard later, so it is less widely supported. It provides a way to retrieve historical sensor data, rather than only the most recent sample available via the Analog Input object.

Analog output

Control values are set using the Analog Output object. Like the Analog Input, it offers a low‑level interface for direct manipulation of device outputs.

Hardware and software

Paragon’s N‑Series controllers and BACnetDiscover software enable integration with any existing BACnet infrastructure at a site. Two common applications that require BACnet hardware integration are:

• Connecting to legacy BACnet hardware – An N‑Series controller can be installed to communicate with older BACnet devices and provide gateway translation to numerous other output types. Wireless BACnet can also be supplied easily with this setup.
• Converting non‑BACnet sensors and controls to a BAS – Large commercial buildings often have an existing BACnet‑based building automation system (BAS). When non‑BACnet sensors and controls are added, an N‑Series controller can bridge the two systems.