The BACnet Protocol

BACnet is described by experts in the field as a data communication protocol for Building Automation and Control networks. Previous products were not able operate within another developer’s system or device. This aspect is referred to as interoperability. During the late 1980s, members of the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) and others began to draft a standard building automation protocol in a committee setting. This first meeting developed the foundations of BACnet. In 1995, ASHRAE presented Standard 135; this details the BACnet protocol. The standard is a set of regulations that specifies the exchange of information over a computer network. The regulations consist of a written specification that states the requirements a developer of building automation devices must adhere to in the protocol. All aspects are included in the standard from hardware issues to the command requests of the protocol. The BACnet Protocol was specifically developed for the building automation industry for many applications from environmental to security of a building.

BACnet is based on the client-server system where a client device sends a request to the server for a specific task. The task is performed and a result report of that task is sent back to the client device. BACnet functions are referred to as “objects”. These objects are a collection of related information, and each object has its own properties that further describe it. An important property of an object is called the “identifier”. The identifier is a numerical designation that allows BACnet to access in a clear, precise manner. The current BACnet contains over 30 message types within 5 categories. BACnet messages perform a variety of functions from event alarms, temperature control, remote device management, and many other functions related to building automation.

The BACnet Protocol offers a variety of advantages and disadvantages. Among the advantages is the protocol’s specific design for the building automation industry. Another advantage of BACnet is its “open” nature because of its development through the ASHRAE committee meetings. A disadvantage of BACnet was a compliant issue. Due to this disadvantage the BACnet Testing Laboratories (BTL) were introduced in 2000. BTL is an independent testing and compliance organization. Their goal is to test BACnet products to determine compliance to the standard, if approved; the product receives the BTL logo.

The BACnet Protocol has been included in numerous products and major building projects such as the federal building in San Francisco, California. The Phillip Burton Federal Building is often referred to as “450 Golden Gate”. BACnet products are very available within the building automation industry. Some of these product examples include the Alerton BCM-ETH, a BACnet router and controller through a BACnet Ethernet and a BACnet MS/TP network connection. The CAS BACnet Explorer for testing, debugging and exploring BACnet networks. Another interesting product is the Network Automation Engine (NAE) produced by Johnson Controls, Incorporated. This BACnet-compliant device can function as an operator workstation and building controller. In the first function, the NAE can maintain a network of BACnet devices. As a controller, the NAE has the ability to “read and write” to other BACnet products within any of the four NAE models developed by Johnson Controls, Incorporated.

Written by: Scott Cosby

© Chipkin Automation Systems 2007