Controls: 6 Keys to Wireless Systems
Part 3: Construction Materials Can Interfere With Wireless BAS Signals
Construction Materials Can Interfere With Wireless BAS Signals
By Gislene D. Weig - March 2013 - Building Automation
4. Interference. Whenever dealing with wireless technologies, interference will always be a concern, so prevention is an important detail. Interference is created from other RF (radio frequency) devices that operate within the same ISM band; construction materials can also interfere with wireless signals. Most ZigBee and WiFi devices operate at 2.4GHz, so minimizing that interference becomes a key question during planning.
ZigBee uses 16 channels in the 2.4 GHz ISM band ranging from 2.405 GHz to 2.480 GHz. WiFi has a total of 14 channels, but not all channels are available for use in all countries. In the United States, the Federal Communications Commission (FCC) allows 11 channels to be used for WiFi. These range from 2.412GHz to 2.462GHz. Since ZigBee channels are narrower than WiFi channels, networks can be configured with ZigBee devices communicating between (in the gaps of) WiFi channels. Most ZigBee devices choose these automatically during network start-up; however, they can be manually overridden to allow IT departments to control wireless network channels within a building.
5. Security. Technologies such as ZigBee, BACnet, and TCP/IP have matured and provide provisions for data encryption, mutually authenticated communications, and robust key management. When these technologies are implemented with industry best practices, operators can ensure data security. Also, wireless BAS networks can be separated from an IT network; in other words, it is possible to disable routing between network layers, preventing messages from the wireless BAS network from routing to the IT networks.
6. Power. Most wireless-enabled controllers, repeaters, and sensors still, of course, require some sort of power. The power can be wired or, more common for wireless, through batteries. Most battery-operated wireless sensor devices available today have a battery life of 5 years.
The battery life is affected by three main factors: how far the information needs to be communicated, how much information is being transmitted or received, and how often the communication can be performed or cycled. Engineers should include detailed specification of the application and minimum battery life requirements and should coordinate with building operators to implement preventive maintenance programs to avoid disruption of the system.
EnOcean devices use built-in energy-harvesting technology, rather than batteries, to power wireless sensors. EnOcean technology is capable of using less power than ZigBee and WiFi because the data packets are relatively small (a typical data packet is 4 bytes) and it transmits at much lower frequencies (315 MHz or 868 MHz) than ZigBee and WiFi. At higher data rates, some sort of power, either batteries or wired, will be required.
The bottom line for facility managers is that wireless technology can be as reliable and secure as a wired network, but it requires proper planning and implementation techniques. The advantages of wireless technology outweigh the challenges because, when planned correctly, it provides the building owner flexibility to track building operations from any location, add and remove sensors with minimum disruption to tenants, save wiring costs, and potentially share network costs with other applications in the building by sharing infrastructure.
Gislene D. Weig, electrical engineer, RCDD, is a senior consultant at PlanNet Consulting, where her core business involves U.S. and Latin American markets focused on large scale projects that include voice/data, wired and wireless communication systems, and data network design. She can be reached at firstname.lastname@example.org.