ASHRAE Standard 135 Resource Files

ASHRAE 135 A Data Communication Protocol for Building Automation and Control Networks (BACnet)


This standard defines data communication services and protocols for computer equipment used for monitoring and control of HVAC&R and other building systems and to define, in addition, an abstract, object-oriented representation of information communicated between such equipment, thereby facilitating the application and use of digital control technology in buildings.


This protocol provides a comprehensive set of messages for conveying encoded binary, analog, and alphanumeric data between devices.

This protocol models each building automation and control computer as a collection of data structures called "objects," the properties of which represent various aspects of the hardware, software, and operation of the device. These objects provide a means of identifying and accessing information without requiring knowledge of the details of the device's internal design or configuration.

About the BACnet Standard

BACnet is the global data communications protocol standard for building automation and control networks. BACnet was developed and is continuously maintained and enhanced by the BACnet Committee, a standing technical committee (SSPC 135) of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). BACnet is an ISO standard (EN ISO 16484-5), a European standard and a national standard in many countries.

BACnet provides a vendor-independent networking solution to enable Interoperability among equipment and control devices for a wide range of building automation applications. It was designed specifically to meet the communication needs of building automation and control systems. It includes specific support for building automation applications such as heating, ventilating, air-conditioning, lighting, access control, elevators, security and fire detection systems. BACnet enables interoperability among these systems by defining communications messages, formats and rules for exchanging data, commands, and status information. BACnet provides the data communications infrastructure for intelligent buildings and is a key component of smart cities.

This web site hosts supporting material for Standard 135 and Standard 223p, including:

  • XD Files are the supporting electronic files to be used with Standard 135.

  • ESI Datatype Definitions provide the datatype definitions for BACnet Energy Services Interfaces ("ESI").

  • ASHRAE 223p Turtle File provides the RDF data model for Standard 223p.

  • Open 223 provides a set of third party open source software tools and reference documentation for Standard 223p. Note that these tools are neither endorsed nor developed by ASHRAE.