The BACnet historyHe has a real problem ...
The BACnet historyHe has got a solution ...
BACnet history ...• 1987
• 1991
• 1995
• 1998
• 2001
• 2002
• 2003
• 2004
• Foundation of the ASHRAE (American Society of Heating Refrigeration and Air-Conditioning Engineering) committee SPC135. Team charter: Development of a communication protocol which would be neutral and allow monitoring, control and energy management within buildings.
• First draft version of the new protocol available
• BACnet was published as ASHRAE 135-1995 standard. BACnet also becomes ANSI standard
• BACnet becomes EN 1805-1 and ENV13321 by CEN TC247
• FND withdrawn by CEN as ENV
• ANSI/ASHRAE 135-2001 published
• BACnet becomes worldwide ISO norm as the only BMS-protocol
• The first BACnet devices are conformance tested in Europe
What is BACnet?• BACnet (Building Automation and Control Network)
is a true, non-proprietary open protocol communication standard.
• BACnet makes ist possible for products, created by various manufacturers to fully interoperate in a building automated control system
• The BACnet protocol defines a model for BAS to communicate between devices and systems. The protocol model specifically defines:
• Data and control functions structured in an object oriented manner
• Services that describe data requests and responses
• Network data link types
• A scalable and flexible internetwork and network architecture
• Device Integration
– Physical interconnection
– Network routing
– Data representation
– Data exchange
– Action-Requests/Response
– Capability
Boiler – Chiller – Air Handler
• Functional Integration
– Data representation options
– Data exchange options
– Action-Requests/Response options
– Capability options
HVAC – Access Control
• Application Integration
– Data representation options
– Data exchange options
BAS – Asset Management
• Application Integration
– Data representation options
– Data exchange options
BAS – Remote Monitoring
What networks does BACnet specify?
• BACnet specifies six network types to accomodate different project and system requirement.
- Ethernet - 10Mbs to 10Gbs, CSMA/CD, allows devices to transmit when the medium is clear.
- Arcnet - 150kbs to 7.5Mbs, token bus standard, rarely used.
- MS/TP (a twisted pair RS-485 network created by BACnet) -9.6kbs to 76.8kbs, low cost
- Point-to-Point (also created by BACnet) - 9.6kbs to 56.0kbs, internet-worked communications over modem, direct cable communication
- LonTalk
- BACnet/IP (also called BACnet over IP, this was added later to accomodate BACnet messages to be transported across the Internet) - devices only speak BACnet, communicate diretly from device to device.
Tip!
Think of network
types as different
transportation
methods for the
same message,
like delivering a
letter via plane,
train, or
automobile.
Network Layers
BACnet Client/Server architecture
• A BACnet device may trigger a service or can react on a service request:
- Client: Requests services (Service user)
- Server: Offers services (Service provider)
• A DDC-system for example may act as a
- client for various field devices in an automation system,
- server for other DDC-systems or for a BMS (Building Management System) that requests specific data or alarms
SC
Initiate
Service
Execute
Service
BACnet Protocol• The BACnet Protocol is based on devices, objects,
properties, and services
- Devices – microprocessor-based unit designed to understand the BACnet protocol, typically a controller, gateway, or user interface that contains a collection of information about the device called objects and properties. (Includes device identifier and instance number)
- There are six device types specified by the standard, also known as PICS (Protocol Implementation and Conformance Statement.
- PICS disclose the following areas of information about a BACnet device:
B-OWS (BACnet Operator Workstation)
B-BC (BACnet Building Controller)
B-AAC (BACnet Advanced Application Controller)
B-ASC (BACnet Application Specific Controller)
B-SS (BACnet Smart Sensor)
B-SA (BACnet Smart Actuator)
Tip!
Objects and
Properties are
similar in
concept to
folders and
documents in a
PC. Think of an
object as a folder
containing
documents
describing the
information in
the folder.
The folder is the
object, and
the documents
describing
the folder are the
properties.
- Objects – a collection of information within a device, represents physical and virtual information such as AI/AO, DI/DO, algorithms, specifand calculations. ic applications, Standard defines 25 standard object types for which a vendor may be able to provide interoperateability, non standard objects may also be created. Objects will always be identified with object identifiers that are 32-bit binary number containing object type and instance number. Every object has a collection of properties that define the object.
- Properties – property conveys information about a object, typical object has an extensive collection of properties based on function and purpose of the object. Each propertie contains two pieces of information – a name/identifier and values.
Its purpose is to allow other BACnet devices to read information about the object and possibly command it to a different value. Properties may be required or optional. The BACnet standard identifies 192 property identifiers.
- Services – are actions that a BACnet device takes to read or write to another BACnet device.Currently there are 38 services on the application layer which are subdivided into the following catagories:
- Object Access – read/write data, create/delete
- Device Management – discover, time, snchronize, backup, and restore
- Alarm and Event – alarms and changes of state
- File Transfer – trend data, program transfer
- Virtual Terminal – HMI via prompts and menus
- Security
- Summary
Tip!
Services act like
the action verb
in the BACnet
protocol.
Services
ask for an action
to take place,
like a read
temperature
request
or a write to
setpoint request.