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Futureproofing Comm Protocols Hero
Futureproofing Comm Protocols Hero
Futureproofing Comm Protocols Hero
Futureproofing Comm Protocols Hero
Futureproofing Comm Protocols Hero

BACnet and Modbus are open communication protocols, but can they help future-proof buildings?

June 7, 2022
Buildings IOT master systems integrator Brian Cline provides a primer on widely used communication protocols in building management systems.

Communication protocols often come up in conversations about future-proofing buildings or buildings that are “open.” While the language that a protocol speaks is important, the transmission of the protocol is also critical. A protocol might be in use for the next decade or so, but if the communication media to support that protocol is problematic to install or no longer in use—whether it be through wireless or a physical wire—then nothing is going to help the building owner in the future. This article discusses the importance of both the protocol and the protocol transmission.

BACnet and Modbus are the two open communication protocol standards that building management systems (BMS) often utilize today in applications such as energy monitoring and temperature, lighting, and occupancy controls. Multiple manufacturers and governing authorities developed and implemented these communication protocols, which allowed for the “open standard.” BACnet was developed in 1987 and became an ANSI standard in 1995. Trusty Modbus has been around since 1979.

BACnet: Widely known and used

Created and driven by ASHRAE, BACnet (Building Automation Communication network) is the most widely used communication protocol in the industry. The two main types of BACnet implementations are BACnet MS/TP and BACnet/IP.

BACnet MS/TP (master-slave/token passing) is an older implementation where system integrators run twisted pair wiring (RS-485 standard) through the building as a separate network. BACnet MS/TP communicates at slow baud rates and cannot handle defaults or changes in the physical network configuration. It must be installed with specific end-of-line resistors and biasing resistors. Despite its slow speed, as compared to other communication protocols and implementations, and its limited fault tolerance, BACnet MS/TP is probably the most common installation today.

BACnet/IP is an emerging implementation based on Internet Protocol (IP), meaning it can communicate across an Ethernet cable or IP network. Instead of running a standard MS/TP RS-485 twisted pair of wire, system integrators can plug in a BACnet/IP controller or device as they would a computer. The devices have a network jack that accepts an Ethernet cable. Then a system integrator or IT/OT professional sets up a network and it works.

Generally speaking, building automation engineers or system integrators prefer BACnet, regardless of whether it’s MS/TP or /IP. Integrators can enter a building, plug in a computer, conduct a BACnet scan, see the devices, see what data points (such as ambient temperature or occupancy) are in those devices, and then add these points to the BMS or building automation system (BAS) database.

Of course, integrators must deal with network pieces and parts, such as firewall rules, subnetting, and BBMDs (BACnet/IP broadcast management devices). However, BACnet/IP is a more fault-tolerant installation than if on a serial bus or twisted pair installation due to the nature of IP network designs.

Modbus, the reliable runner-up

Modbus is widely used in industrial environments, such as electrical switchgears. Factories use Modbus for programmable logic controllers (PLCs), and data centers use it for power distribution units (PDUs). Modbus is also prevalent in Europe and the Asia-Pacific region.

Like BACnet, Modbus offers different implementations. Remote terminal unit (RTU) uses a twisted pair of serial bus wires, while transmission control protocol (TCP) uses the Ethernet compatibility implementation.

Unlike BACnet, Modbus does not offer network discoverability. Integrators need a Modbus Register—essentially a blueprint or roadmap of the communication points in a building—along with the data point address numbers. Integrators manually type in those address numbers and then configure each to read the proper value. Though its setup requires more upfront work than BACnet, Modbus works quite nicely once it is up and running.

BACnet and Modbus are long-standing protocols. However, for BAS and, more specifically, the Internet of Things (IoT), one of the latest protocols on the block is Message Queue Telemetry Transport (MQTT). With minimal bandwidth requirements, this lightweight, open messaging protocol provides an efficient way to communicate. As edge devices such as sensors become smarter, MQTT will likely continue to gain market share as the IoT protocol of choice.

On to wireless transmission and IT convergence

For its implementation or delivery, BACnet and Modbus each use a type of media transmission. In addition to physical cabling (twisted pair or CAT), wireless transmission is critical, as are wireless protocols. These protocols enable different types of transmission, such as a mesh-style system, like Zigbee or Z-Wave; or a true Wi-Fi implementation, using the 802.11 standard that our smartphones and tablets use. The mentality for wireless is like that for wired: If the engineer or integrator doesn’t understand the proper installation methods, the implementation will fail.

From an implementation standpoint—and depending on a building’s existing network infrastructure—using Wi-Fi for a BAS might save an owner money because it requires no additional wiring. However, if an installer or integrator surveys a site incorrectly, issues can arise. For example, mounting controllers above a ceiling, inside a mechanical room, or within a metal box will impede the radio frequencies needed by Wi-Fi to connect and communicate. Another mistake is connecting too many Wi-Fi devices in an implementation, thus oversaturating the airways.

As building automation and IT continue to converge, knowledge and training are the keys to reducing the risk of security hacks.

Fortunately, IT and IP are converging. The building automation industry is starting to mesh with the IT/IP folks, as evidenced by the increase in IP networks and the number of controllers and systems connecting to an IT/IP network. More cross-education is also occurring: An everyday control or automation person is learning more about networking and the different aspects of implementing a proper IT network.

As a result, experienced system integrators can mitigate the network security risks of having IP-based building automation systems. System integrators are taking network courses to understand how installing an OT network separate from the IT network can help limit the impact of a network vulnerability.

As building automation and IT continue to converge, knowledge and training are the keys to reducing the risk of security hacks.

Goodbye, proprietary systems

Even after the creation of open communication protocols, the leading control equipment manufacturers maintained proprietary communication protocols distinct from Modbus or BACnet. These proprietary protocols would essentially lock a building owner into that system, requiring the owner to continue installing, repairing, and upgrading the same brand of equipment over time. If a team installed brand X in an office, the team couldn’t also install brand Y because the two brands would be incompatible and unable to communicate with one another.

As a workaround, third-party companies developed communication gateways and protocol changers to allow equipment from different brands, manufacturers, and protocols to communicate. However, those solutions added complexity and, moreover, hardware, which integrators had to program to translate protocols.

Spotting this inefficiency and high cost, ASHRAE had stepped in to create BACnet in 1987. About a decade later, the industry started seeing its widespread adoption, with major BMS manufacturers providing controllers that communicated BACnet. Now, equipment from brand X with a BACnet communication card can transmit data with equipment from brand Y with a BACnet communication card.

To maintain market share and recapture some revenue lost in exclusive contracts with building owners, BAS/BMS manufacturers created software licensing schemes that limit the number of devices or data points that can be integrated into the BAS or BMS. Ideally, building and consulting engineers and system integrators will seek the best solution for their clients and projects—and at a fair price. Open communication protocols have leveled the playing field considerably.

Future of future-proofing

The term “future-proofing” is a misnomer. Technologies will change and new equipment models will continue to roll out. Buying new devices, such as a smartphone or smart TV, can be easier and less expensive than maintaining and repairing existing devices.

The situation is similar regarding building equipment, though owners and engineers generally want to prolong the duration between a complete rip and replace of equipment and systems. As such, system updates are critical to keeping a building secure.

By strengthening and promoting open communication protocols, building owners, engineers, and system integrators will increase their chances for success with smart technologies. Combine that with sharing use cases about what works and what does not, and the end result is a more efficient built environment in which all stakeholders benefit.

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About the Author

Brian Cline

Based in Dayton, Ohio, Brian Cline is a digital service manager, certified BMS trainer, and Master Systems Integrator at Buildings IOT, which helps building owners and managers set and achieve their goals at any phase of a smart building implementation. Brian holds over 20 years of experience in project management, technical solutions implementation, consulting, and training of building management systems.

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