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BACnet Basics

BACnet Basics. Ben H. Dorsey III VP, Marketing & Communications KMC Controls, Inc. Preview. BACnet—the standard BACnet—the community BACnet—and you. Caution. BACnet is BIG. Part 1. BACnet—the standard. What is BACnet?. A book An open standard A data communications protocol

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BACnet Basics

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  1. BACnet Basics Ben H. Dorsey III VP, Marketing & Communications KMC Controls, Inc.

  2. Preview • BACnet—the standard • BACnet—the community • BACnet—and you

  3. Caution • BACnet is BIG

  4. Part 1 BACnet—the standard

  5. What is BACnet? • A book • An open standard • A data communications protocol • An acronym: Building Automation and Control Networks • A means of integrating building systems • A way of life!

  6. So . . . • BACnet is a data communications protocol and an agreed-upon set of rules for creating interoperable networks of building systems.

  7. Encompassing . . . • Building Automation Systems (BAS) • HVAC Central Plant (Chillers, Boilers, Large Air Handlers) • Lighting • Perimeter and Object Security • Fire and LifeSafety • Elevators • The integration of all of the above.

  8. Who did it? • A working group (standard project committee) of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). • Began work in 1987 under tremendous opposition (some said it would NEVER be done). • Published as a standard in 1995. • Supported and maintained by ASHRAE Standing Standard Project Committee 135.

  9. It’s Alive!!! • By design, the standard is under continual revision. • First published in 1995. • In recent times, most manufacturers’ products have been designed to the 2004 and 2008 versions of standard.

  10. Not a Reactive Process • Addenda are issued as the committee works. • Public review and comments are mandatory and common. • So, for example, when 2008 was issued, it consisted of 2004 + previously issued addenda. (No surprises.)

  11. What the Standard Defines • In essence, the standard defines the messages that devices exchange and how they are delivered. message transport

  12. Further . . . • The rules of the protocol apply to • Electrical signaling • Addressing • Network access (master/slave, peer-to-peer) • Error checking • Flow control • Message sequencing, segmentation, checkpointing • Presentation format (compression, encryption) • Message format Source: Mike Newman, BACnet pioneer

  13. The protocol can be viewed as a matrix of layers. Another Pyramid?

  14. The nucleus to the BACnet atom—the smallest piece of BACnet information Properties can be read and written. Properties can provide command control. They consist of names and values. Properties

  15. Properties • Example: high_limit = 78.0 • The standard requires some properties; other properties are optional; still others can be proprietary. • Required properties must be implemented for each object type. • Optional properties do not have to be implemented, but if they are, they must conform to the specification.

  16. Property Identifiers • Property types 0 – 511 are reserved as standard. • 166 of these are currently defined in the BACnet specification. • Property types above 511 are proprietary and unique to the vendor. • The Vendor ID property is used to identify the manufacturer.

  17. Objects are the fundamental building blocks (atoms) of the standard. Objects represent data that originates in physical inputs, physical outputs, or software processes. Each BACnet Object possesses a number of properties. Objects

  18. The standard specifies 25 types of objects: Object Types

  19. Objects • Vendors can implement proprietary object types. • When they do so, they use standard data types to promote interoperability.

  20. Object IDs • Numerical identifier that combines object type and instance number. • Object types 0 – 127 are reserved to identify standard BACnet objects. • Object types 128 – 1023 are used to identify proprietary objects.

  21. Object IDs • BACnet devices will support any mixture of object types up to a limit of 4,194,303 instances. • Object IDs are typically referred to in this manner: Analog Input, 5

  22. Objects—Summary • Objects standardize the organization of data to facilitate the exchange of data between different vendors’ products.

  23. There are six device types or profiles specified by the standard: Operator Workstation (B-OWS) Building Controller (B-BC) Advanced Application Controller (B-AAC) Application Specific Controller (B-ASC) Smart Actuator (B-SA) Smart Sensor (B-SS) Devices

  24. Think of BACnet services as the messages that BACnet devices send to each other. Some services read and write properties of one or more objects. Other services send notification of alarms or special events. Still other services read and write files. Services

  25. Services • BACnet services follow a Client-Server model. • A BACnet client is a device that requests a service • A BACnet server is a device that performs a service

  26. Categories of Services • Alarm and Event • Routing & event notification • File Access • Accessing & manipulating files contained in devices • Object Access • Read and write properties • Create and delete objects • Manipulate lists of data • Remote Device Management • Remote monitoring and control of devices • Virtual Terminal • Used by a client user to establish a connection to an application program server in another BACnet device.

  27. Services—ReadProperty We wish to read the present value for an analog input called “SPACE_TEMP” Service= ReadProperty ‘ObjectIdentifier’ = (Analog Input, Instance 5) ‘PropertyIdentifier’ = Present_Value Operator Workstation (client) MS/TP AAC (server) Assuming the target machine can locate the object with this ID and the requested properties, the result would be: Service= ReadProperty ‘ObjectIdentifier’ = (Analog Input, Instance 5) ‘PropertyIdentifier’ = Present_Value ‘Value’ = 72.3 The result indicates that the present value of “SPACE_TEMP” is 72.3 Source: ANSI/ASHRAE Standard 135-2004, page 494

  28. BACnet Interoperability Building Blocks BIBBS are collections of services BIBBS define 5 areas of interoperability: Data Sharing Alarm and Event Management Scheduling Trending Device and Network Management BIBBS BIBBS

  29. Data Sharing BIBBS

  30. Alarm & Event Management BIBBS

  31. Scheduling & Trending BIBBS

  32. Device & Network Management BIBBS(1 of 2)

  33. Device & Network Management BIBBS(2 of 2)

  34. BIBBs Summary Example: B-BC • Data Sharing • Ability to provide the values of any of its BACnet objects • Ability to retrieve the values of BACnet objects from other devices • Ability to allow modification of some or all of its BACnet objects by another device • Ability to modify some BACnet objects in other devices • Alarm & Event Management • Generation of alarm/event notifications and the ability to direct them to recipients • Maintain a list of unacknowledged alarms/events • Notifying other recipients that the acknowledgement has been received • Adjustment of alarm/event parameters • Scheduling • Ability to schedule output actions, both in the local device and in other devices, both binary and analog, based on date and time • Trending • Collection and delivery of (time, value) pairs • Device & Network Management • Ability to respond to queries about its status • Ability to respond to requests for information about any of its objects • Ability to respond to communication control messages • Ability to synchronize its internal clock upon request • Ability to perform re-initialization upon request • Ability to upload its configuration and allow it to be subsequently restored • Ability to command half-routers to establish and terminate connections

  35. Transport Options • BACnet IP • BACnet Ethernet (8802-3) • Master Slave/Token Passing (MSTP) • ARCnet • LonTalk • Point-To-Point (PTP)

  36. Transport Comparison

  37. BACnet Layers vs OSI Layers Standard OSI Reference Model Application BACnet Layers Equivalent OSI Layer Presentation BACnet Application Layer Application Session BACnet Network Layer Network Transport ISO8802-2 (IEE 8802.3) Type 1 Data Link MS/TP PTP Network LonTalk ISO8802-3 (IEE 802.3) ARCNET Physical EIA-485 EIA-232 Data Link Physical Source: ANSI/ASHRAE Standard 135-2004, page 9

  38. Router  Auxiliary Devices • Routers • Useful when networks using different BACnet transport options need to exchange data.* Operator Workstation on BACnet IP network BACnet MSTP Controller Network *This concept is referred to as “Internetworking.”

  39. Gateway  Auxiliary Devices • Gateways • Useful when devices on a BACnet network must exchange data with devices on a non-BACnet network.* *This is also Internetworking. Proprietary Network BACnet network

  40. So, what’s the difference? • A router is really a pass-through device. It doesn’t change the form or content of the message but just the packaging—much like repackaging a standard USPS letter for sending via Fedex. • A gateway has to translate and is inherently more complex. It opens the letter, translates it into a second language, and puts it back into some sort of envelope and sends it on. Source: Mike Newman, BACnet pioneer

  41. How Does BACnet Work? Representing Information • Objects Application Language Making Requests and Interoperating • Services • LANs • Internetworking Transport System Source: David Fisher, PolarSoft

  42. Typical System View Operator Workstation Management Level Ethernet or IP LAN Router Gateway Integration Level MSTP LAN Proprietary LAN Field Controller Level ASCs & AACs Proprietary Controllers Application Level BACnet-enabled Applications & other apps

  43. Part 2 BACnet—the community

  44. Engineers & Educators • Members of ASHRAE • 12 standard regions with 7-16 chapters in each • Beyond America, ASHRAE reaches into Canada and South America. • Beyond the Americas, ASHRAE reaches into • Hong Kong Middle East Scotland • Malaysia India Wales • Philippines Africa Ireland • Singapore Europe • Taiwan Scandinavia • Thailand England

  45. SSPC 135 • Consists of 7 working groups: • Applications • Lighting Applications • Life Safety & Security • Network Security • Objects & Services • Utility Integration • XML & Web Services

  46. Manufacturers, Integrators, Owners • BACnet International • Formed in January 2000 to "encourage the successful use of the data communication protocol, "BACnet", in building automation and control systems, through interoperability and compliance testing, educational programs, and promotional activities."

  47. Corporate BI Members

  48. Plugfests • Among the many initiatives undertaken by BACnet International are interoperability workshops or “plugfests.” • Dozens of member compnaies routinely take part in these 3-day events for validating product interoperability.

  49. Interests Groups • BIGs consist of users, integrators, manufacturers, contractors, and other interested parties. BIG-SU BIG-FI

  50. BTL • BACnet Testing Laboratories • Established under direction and continued supervision of BACnet International in Feb 2000 • “Our goal is to improve interoperability between BACnet products through a combination of BTL lab testing, multi-vendor interoperability testing, and adherence to the BTL's device implementation guidelines.” (Jim Butler, BTL Manager) • Lists products by issuing mark

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