Automatic Lighting Controls Demonstration: Long-term Results
An advanced electronically ballasted lighting control system was installed in a portion of an office building to measure the energy and demand savings.
The lighting control system used an integrated lighting control scenario that included daylight following, lumen depreciation correction, and scheduling. The system reduced lighting energy on weekdays by 62% and 51% in the north and south daylit zones, respectively, compared to a reference zone that did not have controls. During the summer, over 75% energy savings were achieved on weekdays in the north daylit zone. Even in the south interior zone, which benefited little from daylight, correction strategies (scheduling and lumen depreciation) and adjustment of the aisleway lights to a low level resulted in energy use of only half that of the reference zone. Although, in general, the savings varied over the year due to changing daylight conditions, the energy reduction achieved with controls could be fit using a simple analytical model (Figure ES-1).
Significant savings also occurred during core operating hours (6 A.M. to 6 P.M.) when it is more expensive to supply and use energy. Compared to the usage in the reference zone, energy reductions of 49%, 44%, and 62% were measured in the south daylit, south interior, and north daylit zones, respectively, during core operating hours throughout the year.
Lighting energy usage on weekends decreased dramatically in the zones with controls, with the usage in the north daylit zone only 10% that of the reference zone.
A simple survey developed to assess occupant response to the lighting control system showed that the occupants were satisfied with the light levels provided.
During the load-shedding test, the lighting control system was used to lower light levels by about 15% for short intervals in the afternoons in simulated response to a peak demand situation. The dimming controls were effective in implementing load-shedding control; occupant response to the strategy was neutral.
A novel two-part control photosensor was effective in providing appropriate control; it allowed daylighting and lumen maintenance strategies to be implemented simultaneously with the same hardware. With this photocontrol system, design light levels were maintained at the workplane regardless of the daylight contribution or the age of the lighting system.