Wireless Options For Building Automation
August 7, 2014
Today's briefing comes from Josh Thompson, principal consultant with Point Source, LLC. All building management systems (BMS) communicate by using a language that is understood by every device connected to the system. Unfortunately, these languages, or "protocols" vary from system to system, and not all languages conform to a uniform standard of communications. Some systems have specifications that are accepted by standards organizations, such as the ISO/ESA; others do not. Each system has its own set of advantages and disadvantages, but it is important to note that not every BMS protocol will communicate over every wireless technology. Thankfully, there have been significant advances in translation, and for a relatively small investment, most BMS languages can be converted into a standard that can be communicated wirelessly, one way or another.
With that in mind, there are a wide variety of ways to transmit data between devices without wires. The simplest and most common is infrared. From motion and occupancy detectors that use our body's temperature to trigger an event, or the TV remotes we use to change channels, IR is an important wireless control tool. IR is secure — it can't penetrate walls; it can be passive (like a motion detector) or active (as a remote control), but its communications are typically "simplex," which means it can either send or receive information in one direction. Clearly, in a BMS system, it is as important to know the status of a device as it is to control the device, so "duplex," or bi-directional wireless communication systems have come into favor.
One recent solutions is EnOcean. Focusing on energy harvesting, EnOcean devices use the energy in the environment to operate. A light sensor uses light energy, flow and movement sensors use kinetic energy, etc. They transmit at a reasonable data rate of 120Kbps in a mesh/grid network. More importantly, they communicate in a relatively low frequency range, which allows for transmission distances of up to 300 meters and separates them from other nearby devices.
Another wireless control protocol is Zigbee. It has vast market acceptance in the commercial building control systems community, which keeps development costs lower and, thus, offers a lower cost of deployment. Zigbee is a standards-based protocol (IEEE 802.15.4), with reasonably fast data rates of 250Kbps across a self-forming meshed network. Manufacturer and user support resources for Zigbee systems are readily available. When professionally integrated, most BMS, administrative reporting and even audiovisual controls can be managed with little or no translation.
Finally, the wireless technology that is by far the most widely deployed is WiFi (802.11 a/b/g/n). Used extensively in information technology (IT) systems to network computers and other smart devices, WiFi operates in the ISM frequency bands and is capable of data rates of 20Mbps (rev. a), 54Mbps (revs. b/g) and 300Mbps (rev. n). This is more than enough bandwidth to support hundreds of BMS devices, including networked video, audio and other AV sources across the network, and is very easily managed and maintained by most IT personnel. Such performance comes at a cost, however; although very capable, WiFi devices have relatively high power consumption when compared with other systems.