Consulting-Specifying Engineer - June 2008 - (Page 69)

Equipment Lifecycles Feed your Page Power packs Power packs are a key component of low-voltage sensor-based lighting control systems. They provide low-voltage power to occupancy sensors, including the ceiling sensors discussed above, and switches provided for manual control. Power packs respond to signals from the sensors and switches to switch a relay controlling the lighting. Low-voltage sensor systems are inexpensive to install and easy to relocate should the space be reconfigured. Power packs also can provide advanced features such as switched inputs and inputs for scheduling, daylight sensors, and dimming control. These features, and many others, provide a finer degree of control over the different loads in a building and allow control strategies to be combined to achieve USGBC LEED credits or other goals. All the control needs should be considered before choosing the best power pack for the project. Electrical considerations The wall switch sensor or power pack must have a sufficient load rating for the combined current consumption of the fixtures that will be controlled, and also must work with the building’s input voltage. Power devices also must be rated for the type of load that will be connected, and power packs that will be mounted on boxes in the plenum must be plenum rated. If the design calls for bi-level control, or control of two independent loads, solutions include a dual-relay wall switch sensor. Alternately, one ceiling sensor and two low-voltage wall switches may be used to control individual power packs capable of manualon operation. Devices that use zero crossing technology provide reliability and long relay life by protecting the relay each time it is turned on. Zero crossing is important when switching electronic ballasts, which can strain relays due to high inrush current. Commissioning and training Some occupancy sensors are preset for typical applications and do not require commissioning. However, it is beneficial to have features such as an adjustable time delay, sensitivity setting, and controls for enabling advanced features in order to optimize sensor performance. If needed, settings for sensitivity and time delay should be made according to the anticipated activity level. Lengthen time delay setting for spaces with lower activity levels; shorten time delay setting for highactivity areas and maximum energy savings. Finally, recommend that occupants be educated about the lighting controls. Once the sensors are operational, no maintenance is required, and typically no readjustment is needed. Manufacturers are careful to make the controls for sensor settings inaccessible to the end-user in order to prevent unauthorized changes. Should the space be reconfigured, or the use changed, the sensor system may have to be adapted for the new application. Maintenance personnel or a contractor can move or reconfigure sensors as needed. Proper sensor selection will prevent the nuisance problems such as false triggering (on or off) that distract occupants and can prevent energy saving goals from being achieved. When occupancy sensors are properly specified and installed, they will operate reliably for years to come. Fournier is product manager of commercial occupancy sensors and controls at Watt Stopper/Legrand. Stimulate your Brain deliver the latest headlines from Consulting-Specifying Engineer directly to your feed page or inbox everyday. Go to csemag.com to choose from our custom RSS Feeds. Receive vital engineering and new product information how you want it, when you want it. RSS Feeds The first destination for consulting engineers Consulting-Specifying Engineer • JUNE 2008 69 www.csemag.com http://www.csemag.com http://www.csemag.com

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Consulting-Specifying Engineer - June 2008 Contents Viewpoint Letters News M/E Roundtable No Gambling Allowed on Smoke Control in Las Vegas Be Prepared: Hospital Protections for Catastrophic Events Ready for Retail Commissioning Documents: Necessary Evil Codes & Standards Codes & Standards Case Study Equipment Lifecycles New Products Advertiser Index Green Space

Consulting-Specifying Engineer - June 2008

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