Communication Protocols in Building Automation

An infographic overview of the key protocols shaping modern intelligent buildings, based on "A Comprehensive Overview of Communication Protocols in Building Automation" by Giuliano Molon.

Modbus

The "lingua franca" of industrial devices. Simple, robust, and ideal for legacy system integration.

Architecture: Client/Server (Master/Slave)

Data Model: Simple Registers & Coils

Media: RS-485 (RTU), TCP/IP

Best For:

  • Integrating industrial or HVAC equipment (meters, chillers).
  • Simple data acquisition.
  • Low-cost implementations.

KNX

The global standard for home and building control, known for its decentralization and interoperability.

Architecture: Decentralized (Peer-to-Peer)

Data Model: Standardized Datapoints (DPTs)

Media: Twisted Pair (TP), IP, RF, Power Line

Best For:

  • Comprehensive control (Lighting, HVAC, Blinds, Security).
  • Multi-vendor projects requiring high interoperability.
  • Residential and commercial buildings of all sizes.

BACnet

The protocol designed for building automation, with a rich, object-oriented model for complex systems.

Architecture: Client/Server (Object-Oriented)

Data Model: Standardized Objects & Properties

Media: MS/TP (RS-485), BACnet/IP

Best For:

  • Large, complex commercial buildings (hospitals, airports).
  • HVAC system integration and management.
  • Projects requiring BTL-certified interoperability.

DALI

The specialized standard for digital lighting control, offering precise, addressable control of every fixture.

Architecture: Master/Slave

Data Model: Commands, Groups, Scenes

Media: 2-wire bus, IP (DALI+)

Best For:

  • Dedicated, granular lighting control.
  • Daylight harvesting, scene setting, energy monitoring.
  • Integration into larger BACnet or KNX systems.

MQTT

A lightweight messaging protocol for the Internet of Things (IoT), perfect for connecting sensors and bridging data to the cloud.

Architecture: Publish/Subscribe (Broker-based)

Data Model: Topic-based, Flexible Payload (JSON)

Media: TCP/IP, WebSockets

Best For:

  • IoT sensor networks and device integration.
  • Real-time data feeds to cloud platforms.
  • Low-bandwidth or unreliable networks.

When to Choose Which Protocol?

Use Modbus...

for integrating specific, industrial-grade equipment without complex data needs.

Use KNX...

for a unified, multi-vendor solution in residential or commercial projects.

Use BACnet...

for large-scale commercial buildings, especially with complex HVAC systems.

Use DALI & MQTT...

as specialized sub-systems integrated into a main KNX/BACnet backbone for lighting and IoT.