Last month I attended the 2015 AHR Trade Show in Chicago. 62,000 attendees from almost every continent on Earth. Contractors, facility managers, engineers, distributors, manufacturers, integrators, every title, every position imaginable. Anybody and everybody having anything to do with heating and air conditioning was there.

They might speak different languages. They might have different religions, ethnic backgrounds, cuisine, habits and values, but they all know one word; BACnet.

What’s BACnet you might ask? Well, to quote from the ASHRAE (American Society of Heating and Air Conditioning) Website:
“BACnet – A Data Communication Protocol for Building Automation and Control Networks. Developed under the auspices of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), BACnet is an American national standard, a European standard, a national standard in more than 30 countries, and an ISO global standard. The protocol is supported and maintained by ASHRAE Standing Standard Project Committee 135 whose members have created and provided the content for this Website.”
[There’s more of that if you need some help sleeping at: http://www.bacnet.org/]

BACnet was all over the show. There were BACnet meters, BACnet controllers, BACnet enabled gizmos of every shape and size. BACnet devices from big companies, little companies, foreign companies, domestic companies. Boilers with BACnet. Data loggers with BACnet. T-Stats (us cool cats use “T-Stats” as short for thermostats) with BACnet.

And for those people that somehow don’t have BACnet, RTA was there with gateways and modules to BACnet enable your fan, meter or anything else for BACnet operation.

Of course, it’s never as simple as all that. There are various types of BACnet. There are various flavors, different capabilities, and users have to sift and sort through the terminology to figure out what they need and how to use it in an application.

Today nearly all new applications use the BACnet protocol over RS485 or Ethernet. In BACnet’s early days, that wasn’t true. Ethernet wasn’t used in building and industrial application like it is today. At that time there were a number of data link / physical layers used in those applications. To meet the needs of the widest possible set of applications, BACnet was designed to support a whole host of physical and link layers including:

PTP (point-to-point) – PTP provides for inter networked communications over modems and voice grade phone lines. PTP accommodated modem protocols and direct connections using RS232.

MS/TP – A version of BACnet using RS485 signaling. MS/TP uses shielded twisted-pair operating at speeds from 9.6 kbit/s to 76.0 kbit/s. MS/TP is very much in use today.

ARCNET – A token bus standard using single-source chips to handle network communications. ARCNET runs on a variety of media at different speeds – from 150 kbit/s on RS485 up to 7.5 mbit/s over coaxial cable or fiber optics.

LONtalk – A proprietary technology developed by the Echelon Corporation and the only LAN type that requires special development tools and a proprietary chip set to implement.

Luckily, today we’re past much of that nonsense and the majority of new applications go in using BACnet over Ethernet (BACnet/IP) or RS485 (BACnet MS/TP). All those old versions are still out there, but little by little they are getting removed as people demand the increasing bandwidth that only Ethernet can provide.