Consulting-Specifying Engineer - May 2008 - (Page 13) M/E Roundtable KOHL: Interoperable standards to enable open wireless technology are not in place today as with conventional wired solutions. There continues to be resistance and conservatism regarding the reliability and security of wireless controls, despite widespread acceptance of the technology in other categories. KUHLMAN: All RF wireless control systems use a very limited commodity, the radio frequency spectrum. There is limited bandwidth, the bandwidth has to be shared with other devices and wireless devices are susceptible to noise and interference. As the use of wireless devices of all types increase the problems of noise and interference also will increase. LANE: Engineers will need to successfully integrate the wireless controls into future designs. The systems will need to prove reliability in actual installations over time. These systems also will need to prove that they will not be susceptible to interference from other wireless systems or cellular technologies in close proximity. Additionally, the wireless controls will have to integrate into existing systems that require new additionally sensors. Standards need to be developed in the industry to ensure interoperability between control devices. CSE: I s lac k of intero perabilit y between wireless control devices an issue? What advances have addressed this issue? LANE: Interoperability between control devices is critical. Two main control technologies have emerged, WiFi (IEEE 802.11) and Bluetooth. WiFi has an effective distance of 500 meters where Bluetooth had an effective distance of approximately 10 meters. Bluetooth and WiFi are the first open source wireless protocols using a star topology. Based on the standard distance between control sensors in the commercial building environment, Bluetooth technology will most likely not play a major role in the future implementation of wireless control systems. Short distance applications, less than 10 meters, required during the commissioning process may be accomplished with shortrange Bluetooth technologies. ZigBee is an open source protocol (IEEE 802.15.4) using Frequency Hopping Spread Spectrum technology. ZigBee is relatively new and can support a range of between 30 to 75 meters. Because of its performance attributes and general implementation in everyday computers, IEEE 802.11b WiFi appears to be the favorite of becoming the established wireless protocol in commercial building equipment control sensors and actuators. KOHL: Interoperable wired solutions like the BACnet, LonTalk, and Modbus protocol standards are available, but no viable wireless solutions are available yet. So this is an issue. TOM: I have not seen any interoperability problems with wireless controls to date, but that is primarily because the systems are new enough that they have been installed and maintained by a single manufacturer. At the top layer of a controls system, interoperability is usually not a problem because at that level most controllers, workstations, and user interfaces use IP networking and WiFi IP networks. Further down the control chain, however, many vendors are using less widely accepted or proprietary wireless network standards, and interoperability could be a problem when it’s time to replace those controllers or expand the network. The recent ASHRAE announcement that a proposed BACnet over ZigBee amendment is out for public review. CSE : Wireless controls typically work best in open environments t h at d o n o t i n t e r f e r e wit h o r absorb RF energy. But what technological advances have been made to wireless controls so they may be installed in other environments? LANE: One of the latest developments in wireless control technology is minimal powered mesh networks. Wireless mesh networks are a multi-hop wireless system where devices help each other to transmit packets through the wireless network. The mesh network is particularly robust in poor conditions. A technician can install the mesh networks in place with negligible preparation. This wireless network is an ad hoc, multi-hop network. Manufacturers recently have incorporated mesh technology networking to reduce the chance of signal interruption. KOHL: Advances, such as the IEEE 802.15.4 standard radios and mesh networking, offer promising solutions for overcoming these issues. They are being designed to coexist with other wireless devices and provide redundant, self-healing network topologies. CSE: Where do you see the future of wireless controls? KOHL: Concerns over reliability and security will fade as technology matures and interoperable solutions become available. TOM: I see wireless controls occupying a significant percentage of the controls market in the future, but I don’t see them completely replacing conventional wired controls. Wireless controls can provide a less expensive alternative to wired controls in many situations, but functionally they serve the same purpose and provide no operational advantage. KUHLMAN: I see the future for wireless in small control systems where it is easier to have an isolated RF network. Control technology allows for building systems to be optimized for efficiency. For commercial systems it allows controls systems to be implemented at a lower construction cost. LANE: Wireless will continue to grow in out industry. For instance, wireless controls transform traditional office Consulting-Specifying Engineer • MAY 2008 13
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