What is BACnet Protocol?
BACnet stands for Building Automation and Control Network which leverage ASHRAE standards. ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) is an American professional association seeking to advance heating, ventilation, air conditioning and refrigeration (HVAC&R) systems design and construction.
BACnet Serves data on Serial interfaces like RS232(DB-9) and RS485 and on ethernet interface. On RS485 Serial interface it known as BACnet MSTP (Master Slave Token Passing). On RS232 Serial interface it known as BACnet PTP (Point to Point). On Ethernet it known as BACnet IP(Internet Protocol).
On RS485 Serial interface you can make a daisy chain between all MSTP devices as per below diagram. Maximum 31 devices recommend to connect in single daisy chain. You can connect more devices in single chain but that may affect on communication performance. Maximum loop length recommended is 1200-1500 feet with standard quality serial cable. You can increase its device capacity in a single loop and cable length by using high quality cable and decreasing EMF in cable with isolated cable protections.
On RS232 Serial interface you can connect two devices point to point as per below diagram. Recommended RS232 cable length is 1 – 1.5meter. two devices only can connect, point to point.
On Ethernet interface there are not physical limitations. You can connect N number of devices so they can communicate with each other. Please note that number of BACnet devices in network will create traffic in network and raise WHO-IS and I-AM type of service request.
BACnet IP is non-routable protocol. So, we cannot route it on internet. BACnet IP protocol communicate on virtual port number 47808 over UDP.
BACnet protocol uses Client – Server base communication model. There is not limitation of Client and server in network. You can configure multiple clients and multiple servers in single network. As per standard, I can recommend to use 50 devices for single device communication.
BACnet protocol uses different services like Who-Is, I-Am, etc. for device discovery. There are services which uses such properties like read and write to share the data from source to destination. BACnet support more than 60 standard Objects services which are approved by ASHRAE. Standard BACnet protocol has to pass the BTL certification. We will share more information on BACnet in upcoming Blog. Please write your queries and feedback in comment section.