Impacts of Vertical Greening System (VGS) on daylight quantity and quality in buildings
ABSTRACT: With the efforts to reduce building energy consumptions and to improve occupant comfort, use of natural light in buildings has become inevitable. Buildings of today have large glazing on their facades to allow sunlight into building interiors. When adequately introduced, natural light provides numerous benefits ranging from energy saving to occupant comfort. However, natural light can also cause thermal and visual discomfort to occupants by uneven distributions of illuminations or extremely high luminance in occupant's field of view. Vertical greening system (VGS) on exterior building facades can be utilized to control the amount of sunlight in building interiors. Multi-angled reflective and translucent surfaces of plants reflect and diffuse direct sunlight so that appropriate amount of daylight can be introduced in buildings. In order to verify potential daylighting benefits of VGS, physical experimentation was performed. Three different vines that are widely used in VGS were chosen and their influences on the quality and quantity of natural light were investigated. A wooden cube box was built to simulate building interior space and fitted with an acrylic panel to simulate a south-facing window. The vines are mounted on a metal trellis with a square grid of 6-inches to mimic the natural growth of the vine and installed 6inches away from the window. The model was then mounted on a Heliodon and tested for different times in the year using the Sun as a light source. Lighting characteristics such as illuminance, luminance, discomfort glare and light color temperature were measured and analyzed. The findings show that discomfort glare levels were greatly decreased with the help of the vines as vertical illuminance levels were lowered and luminance distributions became more even by reflecting and diffusing direct sun penetrations. It was also observed that illuminance level and discomfort glare reduction are not only affected by the physical characteristics of plants. They are also affected by sun positions such as altitude and azimuth angles in different times and dates of the year.
KEYWORDS: Vertical greening system, Daylighting, Vines, Discomfort glare, HDR Photography.