Interfacing a Crestron System with a BACnet Based System This
document describes Crestrons recommended method for interfacing a
Crestron control system with a system that uses BACnet for its
communication protocol. Before describing the details of how to set
up this intersystem communication, lets briefly review the
definition of BACnet and who uses it. What is BACnet? BACnet is a
data communication protocol for Building Automation and Control
Networks. The protocol was introduced by the American Society of
Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) in
the late 1980s and has become a communication standard in the HVAC
industry. What makes BACnet special is that it specifically
addresses the needs of building and automation equipment (i.e. how
to ask for the value of a temperature, define a fan operating
schedule, or send a pump status alarm.) Who uses BACnet?
Manufacturers of HVAC, fire and life, lighting control, security
and other building automation systems utilize the BACnet protocol.
The BACnet Manufacturers Association (BMA) is an organization that
encourages the successful use of BACnet in building automation and
control systems. You can find a member listing of manufacturers on
their website, www.bacnetassociation.org. Crestron Interfacing with
a BACnet System Crestron can communicate with a BACnet system by
using the generic communications protocol, Modbus. Modbus allows a
group of addressable points to be accessed by the Crestron system.
For an in depth description of how the Modbus protocol works go to:
crestron.com/tools_and_resources/programming_and_integration_resources/integrated_partner_modules/default.asp?manufacturer_id=120
The communication is achieved using an RS-232 port on the Crestron
processor and the generic Modbus module (see above link) that
Crestron has developed. The Modbus commands that the processor
sends out the serial port will be manufacturer-specific, so there
will have to be a great deal of coordination between a Crestron
programmer and the HVAC/BACnet manufacturer to ensure proper
communication with a specific model/unit. Once the Modbus commands
have been defined, they need to be converted into the BACnet
protocol for communication with the aforementioned BACnet based
system. We recommend Fieldservers FS-8704-02 Modbus to BACnet
converter (www.fieldserver.com) for doing the conversion. Following
is a list of other manufacturers that make Modbus to BACnet
converters: Automated Logic Portal www.automatedlogic.com Alerton
www.alerton.com Tridium www.tridium.com
The most challenging part of setting up this communication will
be coordinating with the HVAC/BACnet manufacturer to develop the
specific Modbus communication strings that will ultimately be
understood by the BACnet system controlled. All other hardware and
software (as described above) is in place to allow the successful
communication of a Crestron System with a BACnet based system. If
you have any further questions regarding how Crestron interfaces
with BACnet, please feel free to call Tech Sales at 1-800-237-2041
or send email to [email protected].
