Understanding BACnet - A Comprehensive Overview

An overview on BACnet Data Communication Standard


 Building Automation and Control Network (BACnet) is a data communication standard for building automation and control systems (BACS) developed by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). It is an open protocol that facilitates the exchange of information between different building automation devices and systems. In this article, we will provide a detailed overview of BACnet, its features, benefits, testing laboratories, layers, objects, devices, services, client-server relationship, BIBBS, transport formats, MS/TP, routers, and gateways.

What is BACnet?

BACnet is a communications protocol designed specifically for HVAC controls and building automation systems. It was published in 1995 by ASHRAE, a professional organization that focuses on HVAC&R engineering. The BACnet standard was developed to help integrate various building automation systems and devices, making it easier for them to communicate with each other.

BACnet Testing Laboratories: 

BACnet Testing Laboratories (BTL) is an independent organization that tests and certifies BACnet products for compliance with the standard. It ensures that BACnet products are interoperable and compatible with each other. BTL certification provides assurance to end-users that the product they are purchasing conforms to the BACnet standard.

Features of BACnet:

  • Open Protocol: BACnet is an open protocol that allows different manufacturers' devices to communicate with each other seamlessly.
  • Scalability: BACnet supports systems ranging from small to large buildings and can be easily expanded as the building's needs change.
  • Interoperability: BACnet enables devices from different vendors to work together effectively.
  • Flexibility: BACnet supports various communication technologies such as Ethernet, IP, and MS/TP.
  • Fault Tolerance: BACnet has built-in mechanisms to ensure that systems continue to operate even in the event of equipment failures.

Benefits of BACnet:

  • Reduced Costs: BACnet's open protocol allows building managers to choose from a wide range of compatible products, reducing the cost of installation and maintenance.
  • Single Seat Workstation: With BACnet, a single-seat workstation can be used to monitor and control all building automation systems, simplifying system management.
  • Improved Energy Efficiency: BACnet enables building automation systems to be optimized for maximum energy efficiency, reducing operating costs.
  • Better Comfort: BACnet allows the integration of various building automation systems, leading to better comfort for occupants.

BACnet Layers: 

BACnet has four layers - application, network, data link, and physical. The application layer handles communication between devices, the network layer defines how devices communicate across networks, the data link layer provides error checking, and the physical layer specifies the hardware requirements for devices.

BACnet Objects: 

BACnet objects are the building blocks of BACnet systems. They represent various components such as HVAC equipment, lighting, and security systems. There are required objects that every BACnet device must have, and optional objects that manufacturers can include based on the specific functionality of their device.

BACnet Devices: 

BACnet devices can be classified according to the services they offer. These include advanced application controllers (AAC), building controllers (BC), operator workstations (OWS), and field-level devices (FLD).

BACnet Services: 

BACnet services enable communication between devices. They include read/write property, subscribe COV, and alarm & event services.

Relationship of Client and Server: 

In BACnet, devices can either act as clients or servers. A client sends a request to a server to perform an action, while a server responds to the client's request with the appropriate action.


BACnet Interoperability Building Blocks (BIBBs) define the functional requirements for BACnet devices to ensure interoperability. There are five areas of interoperability defined by BIBBS - Data Sharing, Device Management, Alarm and Event Management, Scheduling, and Trend Log Management.

BACnet Transport Formats: 

BACnet supports various transport formats such as Ethernet, IP, and MS/TP. Each format has its own advantages and disadvantages.

BACnet MS/TP: 

BACnet Master-Slave/Token-Passing (MS/TP) is a communication protocol that uses a token-passing mechanism to control access to the network. It is commonly used in small to medium-sized buildings.

BACnet Routers and Gateways: 

BACnet routers and gateways enable communication between BACnet systems across different networks. A router connects two or more BACnet networks, while a gateway enables communication between BACnet and non-BACnet systems.


BACnet has become a widely accepted standard for building automation and control systems due to its open nature, scalability, interoperability, flexibility, and fault tolerance.

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Understanding BACnet - A Comprehensive Overview
Administrator December 22, 2023
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