BACnet Communication: Protocol Overview

What is BACnet Communication?  

BACnet is a data communication protocol that makes building automation easier by standardizing communications between building automation devices from different manufacturers. BACnet, an acronym for Building Automation and Control networks, is an international standard (ISO 16484-5), a European standard, and an ANSI standard.

How Does BACnet Communication Work?

BACnet is an open communication protocol that promotes interoperability between smart building devices. It supports interoperability through its BACnet standardized method and is implemented in three ways.

1. Representation of Information as An Object

Information is represented in the form of an object that is accessible over the network. The object can be physical information, such as devices like a thermostat, or nonphysical, such as calculations or software.

Each object has a set of behaviors used to get or give information from other objects. You can picture each object as a two-column table. In the left column is the object's name, and in the right column is its value or properties. For example, a thermostat might have properties such as analog, 72, a high limit, and a low limit. These properties would appear on the right-hand side.

2. Communication Between BACnet Devices

A BACnet device is a collection of objects performing a specific function. BACnet uses a Client-Server model to communicate, sending messages between the controller and devices.

3. Selection of Network Technologies

BACnet operates on various network technologies, including Ethernet, MS/TP twisted pairs, IP, Lontalk, ARCnet, Point-to-Point, and ZigBee. Most enterprises use either BACnet over IP or BACnet over MS/TP. BACnet MS/TP is more prominent in BMS sensors, whereas BACnet IP is used more for controllers to communicate with each other and the cloud.

Why Is BACnet Used?

Companies use BACnet communication for their building systems for four primary reasons:

1. Its wide use and acceptance internationally and in the United States.
2. It has an open protocol, which means no licensing fees.
3. The system is user-friendly. For example, one can plug in a computer, do a BACnet scan, see devices and their data points, and then add the points to the building management system or building automation system.
4. The system is built for a future where buildings rely increasingly on an IT infrastructure.

How is BACnet Used in Buildings?

BACnet has many uses in buildings and across multicampus control systems. One way would be to adjust the HVAC, so it only operates in occupied parts rather than paying to heat or cool the entire building. Another way is to cut off lights in parts of the building that are not in use or to dim lights in the conference room at the hour the meeting is supposed to end.

BACnet vs. Modbus: What's the Difference?

BACnet and Modbus are both open-source protocols. Modbus preceded BACnet and has changed very little since its launch. BACnet is more advanced and complex and has kept up with technological advances. The two protocols are very different, even at their core. BACnet was initially created for HVAC and mechanical systems and has recently been used for lighting and security. Modbus, on the other hand, has been traditionally used in industrial applications.

Devices discover BACnet very easily, and discovered devices respond quickly to a simple "Who is" message sent on the network. Communication flows through multiple data points. Alternatively, Modbus operates only with a single data point. BACnet provides lots of data, and Modbus will only answer one question. Responses are, however, quite fast.

BACnet is compatible with more devices than Modbus. For example, it automatically retrieves information from one subnet to another on BBMD routers. IT staff must manually set up routers with Modbus. BACnet also supports all types of systems, including fire, HVAC, security, and access. BACnet also uses BACnet Test Laboratories to certify its protocol. Modbus is self-certified.

Modbus to BACnet Converter

Enterprises with a native Modbus system who want to convert to a BACnet system can do so with a Modbus to BACnet converter such as this one. The converter also allows for integrating various Veris meters (which run on Modbus) with Building Automation Systems via the BACnet protocol.

More than 64 percent of users have adopted BACnet. If you have a Modbus system and want to convert to BACnet, choose one of these Veris converters.