Best Practice Guide for Warehouses 2008 - (Page 7) WAREHOUSE BUILDINGS Lamps and Ballasts Fluorescent Lamps • Fluorescent lamps can be switched on and off, and do not require a warm up period to reach full light output upon initial start, or upon restarting when the cathode is still hot. Therefore, occupancy sensors, time clocks, and on/off daylighting control strategies can be effectively implemented with fluorescent lamps. • Use programmed rapid-start (PRS), or program start (PS), electronic ballasts when linear fluorescent lamps are frequently switched using occupancy sensors. These ballasts maintain lamp life even when lamps are operated less than 3 hours per start. • When using occupancy sensors with PS ballasts, be sure to specify ballasts with short cathode preheat and lamp starting times. This will speed the actual activation of the lighting after an occupancy sensor signals the ballast to turn on. Metal Halide Lamps • Metal halide lamps require a warm-up period to reach full light output upon initial start, and when restarting while the cathode is still hot. Because of this warm-up time, the use of occupancy sensors is not typically recommended for turning lights on when a space becomes occupied. • The best control strategy for metal halide lamps is to use scheduling strategies for turning lights on and off, and using occupancy sensors to operate lamps at a lower power level when the space is vacant, returning them immediately to full light output upon occupancy. • Constant wattage autotransformer (CWA) ballasts are required when hi/lo strategies are used. As a general rule of thumb, CWA ballasts, controlled using a hi/lo strategy typically operate at a 40% reduced power when operating at the ‘lo’ level • HID electronic ballasts are now available that incorporate design features improving system performance, such as end-of-life detection. Lamps operating on these ballasts typically have improved lumen maintenance and reach full light output after only two minutes. Some manufacturers include an integral lamp timer into the ballast circuitry, which allows the metal halide lamp to warm up for 15 minutes at full power upon initial startup before dimming or switching the lamp to a lower power level. Daylighting • Toplighting, or using an array of skylights, is the most common method for daylighting warehouses. This technique provides a relatively inexpensive way for providing daylight in the large cavernous warehouse space. • The percentage of roof area devoted to skylights determines how well the floor space is daylit. Buildings with a small percentage of roof area devoted to skylights will have high daylighting levels beneath the skylight, but will have lower, and sometimes insufficient daylight levels in between skylights. Buildings with a high percentage of roof area devoted to skylights will typically have high and uniform daylight levels beneath and in between skylights. • Daylight uniformity is often interrupted when racks are introduced into the space. This frequently occurs when racks are tall and the distance between the top of the rack and the skylight is small. • Aisleways require specific considerations; in these areas, the vertical daylight illuminance on the rack is critical to design, rather than horizontal illuminance. Personnel in rack aisles perform vertically-oriented visual tasks (reading labels on boxes, taking inventory, etc.). Therefore, daylighting control solutions need to provide the minimum target illuminance for the vertical surfaces in these areas. Warehouse Areas Bulk Storage Areas • Use passive infrared occupancy sensors in bulk storage areas because line-of-sight detection is required for these areas. • Mount occupancy sensors to the luminaires to facilitate installation and maintenance. This also keeps sensors above the main level of activity and provides optimal coverage. • Use multiple occupancy sensors with overlapping coverage patterns to overcome obstacles such as stacked palettes. Published coverage patterns will need to be derated for these applications to accommodate obstructions; therefore, additional occupancy sensors are typically recommended. www.wattstopper.com • 800.879.8585 7 http://www.wattstopper.com http://www.wattstopper.com
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