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BACnet

Scope / Goals

Specify a gateway interface between the BACNET object model and OPC UA -> integration of building and industry automation.
The main purpose of this mapping document is to describe an interface to specify observation, operation and engineering.

TYPICAL USE-CASES INCLUDE

Observation: Providing energy information like consumption, operating-hours or maintenance intervals to enterprise systems.
Operating: Commanding building automation systems by writing data like temperature setpoints, operatingmodes or acknowledge alarms.
Engineering: Specifying operating modes or schedule programs, configuration of alarm-detection.
Advantages: Using this mapping profile vendors in building automation find ready-to-use methods to provide building or energy data while manufacturers of SCADA-systems or enterprise connectivity directly access the required data without the need for interpretations or conversions.

The current mapping specifies the data flow from BACnet to OPCUA. In a future revision of this mapping document OPC-UA data may be connected to BACnet as well.

Technical content

Both OPC UA and BACnet specify objects to model application data. Unlike in other standards or more simple communication protocols not only the values are provided. Extra information like the name of an object, a description text, the engineering-unit, alarm-limits, operating-hours or change-of-state count, etc. is provided. The mapping document describes a gateway interface between the two object models. The methods how to retrieve the data (polling, Change-of-Value) and the network media to be used is a local matter and not part of the mapping profile. The following picture shows an example of a BACnet Analog-Input object (left hand box) represented as OPC UA Analog Input Object (middle and right boxes).

MAPPING BACNET ➞ OPC UA

BACnet Objects / Properties ➞ OPC UA Object Types
BACnet Events ➞ OPC UA Alarms & Conditions
BACnet Logging ➞ OPC UA Historical Access
BACnet Data Structures ➞ OPC UA Structure Data Types
BACnet Units ➞ OPC UA Engineering Units

While BACnet uses a flat model (structured objects providing their properties) OPC UA allows for inheritance. Wherever possible the mapping combines functional items in re-usable groups. E.g. alarm parameters are collected as a group of properties and can be used for different object types.

➞ Supporting organizations:
The BACnet standard was developed and is still maintained by the ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers in the SSPC-135 (Standing Standard Project Committee aka the BACnetCommittee). ASHRAE granted use of the BACnet standard and greatly supported the process of developing this mapping document. BACnet International (BI) and the BACnet Interest Group Europe (BIG-EU) are the two largest organizations promoting BACnet world-wide. Members of both organizations volunteered in this working group. In many face-to-face meetings and teleconferences finally the first version got approved and was presented to the public. The working group awaits feedback by early adopters or companies prototyping the mapping in their products.