The Basics – What is BACnet?

An ASHRAE Protocol

BACnet is a popular building automation protocol used worldwide to enable communication between devices in commercial automation systems. Industrial automation systems have historically used other protocols such as OPC, Modbus, and proprietary protocols. BACnet standardizes communication across vendors and simplifies the integration process.

The name BACnet stands for building automation and control network. It was created by the American Society of Heating, Refrigerating and Air-Conditioning Engineers to modernize communication for automation systems using an open protocol.

The Object-oriented Model

The BACnet standard defines an object-oriented framework for describing heating and cooling systems. Every sensor value and every physical output is an object. A modulating valve actuator is an “analog output” because it can have a range of positions. A fan starter is a boolean output because it can either be on or off.

These objects may also come with meta-data that describes what they represent physically. A description field can describe in text what the point represents (ex: “Fifth floor VAV actuator under tile 6”). Units can be specified for sensor values. Alarm limits are also embedded in that meta-data, presenting the user of the system a rational and consistent model.

Open & Closed Standards

BACnet is an open standard. Anyone can get a full copy of it from ASHRAE if they are willing to pay for it. Closed standards are proprietary communication systems created by vendors for their own devices. Open systems allow multiple vendors to utilize a common communication backbone and automation front end. Open systems have become standard because customers do not want to be locked in to a single vendor and prefer the lower cost of installation.

BACnet is Open – To Interpretation

BACnet is a very easy standard to comply with, as it requires very little of you as a device manufacturer. This can be a challenge for system integrators. A device does not need to support much of the standard to be a compliant. So long as it knows how to say hello to other devices, it’s a BACnet device.

Vendors can implement as much or at little of the standard as they like. Sometimes a vendor won’t bother to put any useful metadata in the standard fields for points. You’ll see analogObject_1 through 500 with no way of determining what these represent. This kind of lazy implementation might as well be Modbus. The vendor will market it as an open system, but these are often considerably more difficult to integrate.

Bottom Line -What is BACnet?

When implemented well by the vendor, BACnet is damn near pleasurable to work with. It makes many hard things easy since it is designed for our industry. The old school controls guys are often not fans of BACnet because larger systems get into the realm of computer networking, which requires a different skill set. It can be complicated, and it can be simple. That’s BACnet in a nutshell.