Cost Effective Simplified Controls for Daylight Harvesting

Most commercial spaces have enough daylight next to windows to eliminate the need for electric lighting. Daylight harvesting systems automatically dim or switch electric lights depending on daylight availability, offering significant energy savings. Most important they offer significant peak demand reduction, since peak demand usually occurs during the highest levels of daylight availability. Dimming electric lights based on available daylight is expensive with significant equipment (dimming ballasts) and commissioning costs. To date, only a small fraction of side-lit dimming applications operate satisfactorily. While useful in low daylight areas, dimming is not really necessary in areas with high levels of daylight where dimming is only useful during the early morning and late afternoon. This paper focuses on the development and laboratory testing of a new Simplified Daylight Harvesting (SDH) approach designed to operate as a bi-level lighting system and applicable to existing bi-level systems, which have been required in California by Title 24 since 1983. The SDH system works “out of the box,” i.e., without need for either calibration or commissioning. SDH system automatically operates the bi-level lighting system through its high, low and off states based on available daylight levels. The SDH operation is based on a simplified control algorithm that avoids cycling and supports simple and easy occupant adjustment of the ON and OFF set points. This paper includes descriptions of the overall SDH strategy and system, as well as initial results from laboratory testing of a working prototype showing potential energy savings and effects on the luminous environment. Initial results show that the SDH system can significantly reduce energy and peak demand, offering 100% savings for most of the daylight hours in work spaces adjacent to windows. The cost of the SDH system is very low, offering the potential for cost-effective commercial products that will help reduce energy and peak demand requirements in new and existing commercial buildings.