Field-Measured Performance Evaluation of a Digital Daylighting System

In 2005, the largest field study to-date concluded that automated dimming controls in side-lighted spaces consistently underperformed relative to expectation, and were still to be considered an 'emerging' technology. Motivated by a desire to accelerate the adoption and acceptance of such controls in, this paper details a field-measured assessment of a digital daylighting system recently introduced to the US market. Two intentionally challenging offices were retrofit with controls, and automated data acquisition hardware, and system performance was evaluated across several parameters throughout a twelve-month period. The field data and user interviews indicate that the system was relatively straightforward to commission compared to other dimming controls, and overall was well received by the occupants. Energy savings in the private and open-plan installations were between 17 percent and 20 percent. In the private office, the pre-existence of occupancy sensing, and automatic-ON in the retrofit system precluded even deeper energy savings, whereas false triggering of the occupancy sensor limited the achieved savings in the open plan space. The controller was largely able to maintain target illuminance on the worksurface, although increased daylight availability led to increased variability and a 100-lx increase between noon and 2PM. Key recommendations to increase the acceptance of similar systems include the provision of shielding options for occupancy sensors, manual-ON options for private offices, remote-access commissioning tools, and improved clarity of written materials describing system function, operation, and installation.