Field Commissioning of a Daylight-Dimming Lighting System

Citation: 

D. Floyd and D. Parker. Presented at the Right Light Tree, 3rd European Conference on Energy Efficient Lighting, Newcastle upon Tyne, England, June 18-21, 1995

Review by Scott Schuetter, Energy Center of Wisconsin: 

The authors performed a lighting retrofit on an elementary school cafeteria in Florida. The cafeteria had 70% glazing on its east and west facing facades, as well as vertical blinds. The retrofit replaced the magnetically-ballasted, 40W T12 lamps with an electronic dimming ballast and two 32W T8 lamps. Additionally, the lights were controlled via photosensors to a minimum of 20%. The building's lighting and HVAC energy usage, desktop illuminance, and exterior solar insolation were all monitored both before and after the retrofit. The retrofit showed a 66% decrease in the cafeteria's energy usage. Approximately 76% of this decrease was attributable to the lower power required by the new luminaires. The remainder was attributable to the photosensor dimming of the lights. The daylight controls were calibrated in order to enhance their energy savings potential. Multiple issues arose during this commissioning. Those issues included the necessity of utilizing the manufacturer supplied shields to the photosensors. Further, it was necessary to obtain knowledge of the photosensor sensitivity range, which was not readily available. Also, the photosensors controlled the lights to different levels between day and night, requiring a trial and error approach to properly calibrate them. Finally, it was important to verify the illuminance in the room against measured data. The usage of the blinds also affected the dimming of the system. It was found that when the blinds were left open, the dimming saved 36% of energy usage, while this number decreased to 27% when the occupants were allowed to adjust the blinds.