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• FND withdrawn by CEN as ENV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.