A Multi-Zone Electrochromic Window System Integrated with Light Shelf

Electrochromic glass (EC), one of the most advanced products in energy efficient window technology, is designed to transform a window from an energy liability to an energy source for the nation's building stock. Electrochromic windows vary their visual and thermal properties by electric field and preserve outside views while controlling transmitted light and solar heat gains. Although EC windows can provide considerable energy savings and relatively stable light levels, they cannot effectively block direct sunlight and tend to have unbalanced light distribution under certain sky and solar conditions. This research focuses on the optimization of EC application in buildings to improve its qualitative and quantitative performances. As one of the proposed optimization options, EC glazing is integrated with light shelf, an interior horizontal light-reflecting device installed approximately 8 feet above the floor adjacent to glazing. The light shelf divides the glazing into two zones, daylight glazing (the zone about the light shelf) and view glazing (the zone below). The light shelf potentially provides protection from direct sunlight and projects daylight into deeper areas of the space. EC glass with different tinting control algorithms based on interior light sensor is installed in the daylight and view glazing areas to dynamically control the visible light transmittance of both zones according to the exterior light intensity and solar angle incident on the window.;Physical experiment is adopted as the primary method for assessing daylighting performance. Two pieces of SAGE electrochromic glass are installed in a full-scale rotatable test-cell at NCSU daylighting lab. The test cell is equipped with 16 photometer sensors for daylight level measurement. The first phase assessment focuses on the initial testing on the electrochromic window configurations and other systems outlined above. The configurations and algorithms are evaluated and optimized based on this preliminary assessment. The second phase assessment focuses on climate-based daylight modeling, which is to monitor the daylighting systems on a long-term basis. The experiments and computer simulation results show that the proposed multiple-zone electrochromic window system integrated with light-shelf system can significantly improve the daylighting performance and visual comfort of the daylit space.