An active sunlight redirection system for daylight enhancement beyond the perimeter zone

Abstract

Over the past years, extensive research has been carried out in the creation of working environments that utilize natural light as their primary source of illumination. Transferring glare-free daylight into the core of the building can significantly increase lighting energy savings but it can increase cooling needs as well. Traditional daylighting systems mainly focus on controlling the incoming solar beam radiation, thus regulating the illuminance levels, usually near the perimeter zones. This paper proposes a sunlight redirection system that uses a number of movable mirrors, installed on a light shelf and capable of tracking the sun. Reflected sunlight is projected towards a specified, fixed target area on the ceiling. The theoretical framework for the operation of the proposed system is presented in detail, together with a daylight and energy analysis for the summer and winter solstices, representing the two extreme trajectories of the sun. Five cases were examined, representing various shading system configurations. The results indicate an increase of 99%, in the daylighting levels in the secondary (non-daylit) area during the summer solstice and a reduction of 21%, during the winter solstice, when compared to an unshaded, unobstructed reference case. If a case with a shading system (i.e. external static blinds) is used as a reference case, the proposed system increases the daily illuminance values during both solstices by 152% (summer) and 12.5% (winter). Unfortunately, there is a slight increase (<5%) in daily primary energy consumption. Simulations were performed using Radiance and EnergyPlus while the data needed as input, was created with a new algorithm capable of producing 3D models of the proposed system together with the reflected sunpatch geometry on the ceiling.