ASHRAE Journal - August 2008 - (Page 76)

Wireless for Controls: An Update By Kurt Roth, Ph.D., Associate Member ASHRAE; Louis Quartararo, P and James Brodrick, Ph.D., Member ASHRAE .E.; W ireless systems in commercial buildings offer the potential to reduce the installed cost of communicating sensed data by supplanting or augmenting wired infrastructure with digital radio-based communications. A generic wireless data transmission system includes transmitters and receivers, and a translator to allow the wireless receiver to communicate with a control network. It may also use repeaters to increase the range of wireless signals. Basic wireless systems include wire replacement systems, where the sensor, transmitter and receiver use line power but communicate wirelessly, and fully wireless schemes (i.e., having all battery-powered components). More sophisticated wireless systems use mesh networks, where some or all nodes can serve as transmitters and receivers and as routers that can relay messages from their neighbors. An effective mesh network provides multiple communication pathways and dynamically identifies the optimum transmission path for each node in response to network traffic and interference.1,2 Consequently, the network tends to become stronger as the number of devices connected to the network increases (more potential paths from one node to another).3 This redundancy increases reliability in real-world building applications, where objects are moved and floorplans altered after network deployment.4 Wireless systems with extended antennae installed as part of a building’s infrastructure may provide pervasive indoor radio, cell phone, pager, Wi-Fi, communications, as well as low-power systems used for building control applications.5 In 2006, a consortium of interested parties founded the In-Building Wireless Alliance to realize this vision. A variety of wireless-enabled sensor products have come to market, both within and outside of the HVAC industry. Wireless temperature sensors are most common, and wireless thermostats, relative humidity sensors, electric meters, gas meters, and outlet power draw meters also exist. Recently, standardization in wireless systems for building control applications has increased. The ZigBee® Alliance, with more than 200 member companies,3 has produced a standard for wireless transmission of digital data that addresses many key needs of wireless building control networks. ZigBee-compliant devices operate at low data rates to reduce energy consumption and prolong wireless sensor battery life, incorporate data security options, leverage communication technologies to reduce interference, and have a low cost.1,2 The networks are self-configuring, which facilitates deployment and addition of devices to the network.3 Plans are underway to tunnel BACnet® communications over ZigBee networks.6 76 ASHRAE Journal Although devices that conform to ZigBee are not necessarily interoperable because ZigBee does not specify a data format (e.g., what values the data represent or measurement units),1 ZigBee has developed public application profiles to help address this issue. Available public profiles include ZigBee Commercial Building Automation, which offers “standard interfaces for the control of lighting, HVAC, power outlets, access control, security” and other devices.7 Other wireless communication protocols used in commercial buildings include Wireless HART (primarily an industrial protocol)4,8 and Z-Wave (more commonly used in residential applications).9 Energy Savings Potential Wireless sensors and wireless communications are enabling technologies that decrease the cost to implement energy-saving building controls and diagnostic measures in cases that require additional sensors, notably in retrofit applications. In particular, wireless can be used to augment the supervisory control capabilities of older building automation systems, such as pneumatic systems and older digital systems with very limited programming capabilities and data bandwidth.4,10 Energy-saving approaches that often require additional sensors include: • Ongoing commissioning;11 • Airside fault detection and diagnostics;12 • Conversion of constant-air volume systems to variable air volume using additional temperature sensors, new software, and a variable-frequency drive;4,10 • Enhanced data center cooling control;10 and • Occupancy-sensor-based lighting control. In addition, wireless communications and controls can enable demand response (DR), i.e., reduction of electric demand during peak demand periods.13 Market Factors Ultimately, the success of wireless communication systems in commercial building HVAC systems depends on their ability to decrease the installed cost of sensors and to operate reliably. Thus, wireless solutions must compete effectively with conventional wired solutions. Perhaps the greatest barrier to greater use of wireless is the low cost of pulling wires during new construction.4 Cost-Effectiveness The cost-effectiveness of a wireless system depends on several application- and implementation-specific factors. In genashrae.org August 2008 http://ashrae.org

Table of Contents Feed for the Digital Edition of ASHRAE Journal - August 2008

ASHRAE Journal - August 2008 Contents Commentary Industry News Letters Meetings and Shows Maintain to Sustain—Delivering ASHRAE’s Sustainability Promise Ultraviolet Germicidal Irradiation: Current Best Practices Improving Humidity Control With Energy Recovery Ventilation Single- or Two-Stage Compression Data Center Cooling: Using Wet-Bulb Economizers Building Sciences InfoCenter Practical Pointers Products Emerging Technologies Washington Report People Special Products Classified Advertising Advertising Index

ASHRAE Journal - August 2008

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