BacNet In HVAC

What is BacNet? In the early days of building automation control, many companies and provider of control systems of big commercial buildings come up with their own set of proprietary control protocols in controlling their equipment.

This makes life difficult for customers as they will have to have many workstations to control different aspect of the building such as one for HVAC, one for security control, another one for fire and alarm system, yet another one for lighting and the list goes on.

At times, they may have to employ consultants to provide gateways that enable inter-operability between each system. This is not only costly but a lot of time is wasted trying to understand and integrate these different protocols.

As heating, ventilation and air conditioning system plays an important role in the design of modern buildings, the need to have a standardized communications protocol that is open to anyone to integrate became critical then.

Hence, ASHRAE or American Society of Heating, Refrigerating and Air Conditioning Engineers decided to develop a standard communication protocol known as BACnet in the year 1987. These standards were developed by representatives from government agencies, educational institution, manufacturers and consultants.

BacNet Logo

Since then, it has undergone various revisions and was finally published as an ASHRAE standard in 1995. At the end of the same year, it was approved by American National Standards Institute (ANSI) as a national standard. Updated standard was published in 2001. It became a ISO 16484-5 Standard in 2003.

BACNET is an acronym for Building Automation and Control Networks and is a standard communications protocol where different vendors of equipments for building automation system can integrate their devices as long as they are produced with this protocol built-in during design stage.

It is basically a set of software and hardware rules. With this protocol, customers can now use one workstation to monitor and control the heating and ventilation system in the building, fire alarm system, security control system, lighting system and other related services.

The customers now have the option to choose products from different vendors that are 100% compatible. This means that they are not tied down to a dedicated supplier of the equipment. They can now choose to replace the equipments with another brand if necessary. It is also possible to expand other applications that have yet to be developed in the future.

Alerton, Automated Logic Corporation and Delta Controls started the ball rolling in developing HVAC related products.Other big companies such as Honeywell, Johnson Controls and Siemens have also developed products that are compatible with these standards.


The data communincation protocol rules that have been developed specifically for building automation and control is as listed below:

  • Addressing
  • Electrical Signalling
  • Master/Slave and Peer/Peer Network Access
  • Flow Control
  • Error Checking
  • Message Format, Message Sequencing, Segmentation
  • Compression and Encryption Presentation Format

Physical and Data Link Layers

The physical and data link layers that have been defined using this protocol include:

  • RS 485(Master/Slave and Token Passing)
  • RS 232(Point to Point)
  • Ethernet
  • LonTalk

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