BACnet and Modbus are two of the most common building communication protocols. What’s more, both have open communication protocol standards, setting them apart from other protocols. This is one of the shining gems that draws many to these protocols. .

However, since both systems are so great, it makes picking one or the other more difficult. Luckily, this guide is here for you. It will walk you through what you need to know about BACnet, and Modbus, and choose one or the other.

Table of Contents

What Is a Building Automation System?

Both BACnet and Modbus are BAS (Building Automation System) technologies. These are technologies that allow a building’s many different systems to be controlled from a single point of contact.

These are critical features in many different buildings, especially in smart buildings or manufacturing facilities. They improve the functionality of the building as a whole. Plus, they are an integral part of managing and reducing the building’s energy consumption.

What Is BACnet?

BACnet is short for Building Automation and Control Network. It is a communication system designed to automate and control the systems within a building. These systems could include access control, lighting, safety features, security features, and a number of different HVAC systems.

BACnet uses a communication structure based on a client-server model. A server is set up to communicate with other devices in the system, which are clients. Communication between these two goes back and forth since clients and servers can request or send information as needed. Communication can even occur between clients.

BACnet supports a wide range of communication methods. This includes Ethernet, IP, MS/TP, ARCNET, Point-to-Point, LonTalk, and ZigBee.

What Is Modbus?

Modbus is another open protocol communication system designed to automate and control systems within a building. However, Modbus started with a different purpose. It was originally designed for buildings involved in heavy industry. This has led to it being more commonly used with more industrial systems rather than commercial ones.

In a Modbus system, an entirely different communication setup is used. Modbus uses a master-slave setup. One device is designated as the master device, while others are designated as slave devices. The master device is responsible for giving commands and communicating. The slave devices are only able to respond to these commands but cannot communicate with each other.

Modbus can also communicate over many different formats. This includes Ethernet, USB, RS-232, and RS-485.

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BACnet vs. Modbus

The fight between BACnet and Modbus is like a clash of the Titans where neither truly wins out. Each system is an open protocol system. These are easier to work with and offer cost savings. However, the systems have plenty of differences between them too.

Alt text: A woman looks into the wires running through a building

Accessibility

BACnet is well-known for being very easy to access. You essentially just need to plug into the system and then gain full access to that system. This makes it easy to access and work with.

Meanwhile, Modbus is a little more difficult to work with. Using it requires a Modbus Register, which contains exact details regarding the building setup. This makes the initial process of accessing a Modbus system more difficult. However, once this initial process is taken care of, working with it from that point onward is just as easy as it is for BACnet. This means that BACnet only has a very slight advantage in this category compared to Modbus.

Complexity

BACnet is known for being more complex and advanced than Modbus. The branching nature of the communication structure allows for more to take place within a BACnet system. For example, in a BACnet system, devices can speak to each other directly, while in a Modbus system, communication exclusively comes from the master device.

Scalability

Scalability is another area where BACnet comes out ahead of Modbus. The very nature and overall structure of the client-server setup is highly scalable. This allows the BACnet system to accommodate more devices overall.

In addition, BACnet supports a wider range of communication systems. This allows it to integrate and work alongside a wider range of systems and devices.

Ease of Use

While BACnet is more complex and advanced than Modbus, complexity isn’t always a good thing. No one wants to actually use the most complicated system in the world because it is, by its very nature, too complicated. Following this line of thinking, BACnet systems are usually more difficult to use than Modbus systems.

The master-slave setup is a big part of this. This model allows for less to take place within it than the client-server model. However, this makes it more streamlined and creates fewer opportunities for the system to get confused or for things to go wrong. Meanwhile, the client-server setup is more difficult to work with and has more opportunities for error.

The complexity of a BACnet system can lead to additional resources being necessary for running it, especially when compared to a Modbus system. This may make it impossible or at least very impractical to run a BACnet system over a Modbus system. In some cases, this limits the choice so much that Modbus is the only logical option.

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Choosing Between BACnet and Modbus

Choosing between BACnet and Modbus is like choosing between apples and oranges. However, there is general advice to follow when picking between the two.

Generally, BACnet systems are better when the system is larger and more complex. BACnet has more capabilities and can do more in this regard. However, the budget and resources of the project need to be able to handle the increased needs of a BACnet system.

Meanwhile, Modbus systems are better when something straightforward and simple is necessary. They are also a great choice when the requirements of a BACnet system are simply too much.

All of these factors need to be considered whether you’re looking at a smart office or a manufacturing facility. Making the wrong choice can create problems down the road and lead to inefficiencies in the management of the building.