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Part 2: WiFi Is Still Leading Option for Wireless BMS
By Josh Thompson
March 2012 -
Building Automation Article Use Policy
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 enough bandwidth to support hundreds of BMS devices, including networked video, audio and other AV sources across the network, and is 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.
In addition to the power consumption and BMS system compatibility concerns, another significant factor for consideration is that of wireless radio frequency (RF) interference between nearby systems. Most of the technologies in use today operate in the Industrial, Scientific and Medical (ISM) frequencies. This spectrum, which spans from roughly 900MHz through 2.5GHz, falls within what is known as the "wireless sweet spot," which is so called because these frequencies offer the best compromise between the signal's capacity to transmit data (bandwidth) and the distance over which these signals can be transmitted.
Because of this balance, however, literally millions of devices operate within this spectrum. This may cause problems, which are further complicated by the fact that the ISM frequencies are unregulated, meaning that there is no guarantee that the device deployed as part of a BMS will not be interfered with by another device, such as a door opener, a neighbor's WiFi system or even a nearby microwave oven. This brings the decision to deploy any wireless technology into a facility into question, and all but excludes its use in a life-safety system.
Clearly, there is no right or wrong answer when considering the deployment of a wireless technology as part of a building management system. The decision should be based on a careful weighing of the risks versus the rewards of such an integration. If a facility stands to save a significant amount of money in energy costs, with nothing to lose by an occasional loss of communications with a device, then the answer is clear. If, however, a flow meter or sensor is to be monitored, the loss of which would compromise a critical building system, perhaps a wired solution is the best option at any cost.
Josh Thompson is principal consultant with Point Source, LLC. He can be reached at firstname.lastname@example.org.
Part 1: Wireless Building Automation: EnOcean and Zigbee
Part 3: Wireless BAS: Factors Facility Managers Should Consider