Measurement and Critical Investigation of the Actual Annual Daylighting Performance of a Middle School in North Carolina


This research investigates and documents the performance of the daylighting design at Northern Guilford Middle School over an entire year. Photometric sensors and dataloggers were used to collect illumination data from the school from March 2007 to February 2008. A few experiments were performed as well during this period to determine the effect of certain design elements on the daylighting. The daylighting design uses a unique curved translucent interior light-shelf that is intended to distribute light deep into the classroom. Illumination values at fixed locations within a classroom are presented on a monthly basis as a direct measure of the daylighting performance. The research indicates that this daylighting design is highly dependent on direct beam sunlight falling on the translucent light-shelf with the annual daylighting performance varying depending upon the position of the sun in the sky. The daylighting performance can be identified as being distinctly different for the winter, equinox and summer periods. On an average, the illumination levels in the winter are well above 300 fc, near the equinox at 300 fc while in the summer they fall below the 50 footcandle target required in a school classroom. Tests performed on the three classrooms wings oriented 10° different from each other revealed uneven performance and that the large white reflective roof contributes about 50% to the daylighting in classrooms on the north side of each of the wing hallways. The high light levels during winter months cause problems with projectors and other visual aids that are used more frequently now than before for teaching in schools. Also, like with many side-lit daylighting systems, there is a significant drop in light levels from the front to the back of the classroom. The relatively low position of the interior light-shelf in the south-side classroom introduces discomfort glare during the winter months when direct light falls on the light-shelf. The research emphasizes the changing light levels over the seasons, the high front to back gradient and the inconsistent performance of different wings as the major issues with this daylighting design. Despite some of these issues, this design need not be discarded, especially since it is the most cost effective amongst other daylighting strategies implemented across schools in North Carolina. An accurate physical model would allow real world testing of methods to alleviate some of the problems in this design. Of importance too, is the effect of daylighting on the energy performance of the school, which needs to be investigated as well. Perhaps the most novel component of this design, the curved light-shelf, needs to be worked upon before its performance can be predicted and optimized under various solar conditions.



North Carolina, annual, light-shelf, side-lighting, school, Daylighting





Mechanical Engineering