Thermal and daylighting analysis of building perimeter zones equipped with combined dynamic shading systems

Advanced façades include a combination of active and passive solar shading and daylight harvesting systems to reduce energy demand while maintaining occupant comfort. A comprehensive simulation study was carried out to evaluate the impact of an advanced dynamic shading configuration on the thermal and daylighting performance of building perimeter zones. The studied system consists of a fixed exterior reflective overhang and a movable internal light-shelf in the upper window section as well as controlled bottom-up roller shades in the view aperture. The overhang provides partial exterior shading, blocking solar gains in the summer, and reflects natural light into the room through the upper portion of the façade. The movable internal light-shelf not only blocks sunlight from entering the room through the top window, but also enhances daylight distribution in the room as a result of deeper natural light penetration. However, if no additional shading is provided for the view aperture, glare and overheating are bound to happen, offsetting the energy benefits, and resulting in occupant discomfort. Controlled bottomup roller shades were therefore employed in the view aperture so as to eliminate direct glare and allow partial view to the outside. The bottom-up controlled shades and the light-shelf are appropriately controlled so as to always block direct sunlight. The study was conducted for a classroom located in Chicago, IL, and the impact of the following parameters on energy demand was investigated: exterior overhang characteristics; interior light shelf position, size, surface reflectance and tilt angle control; roller shade control modes and fabric material properties. In order to accurately model solar gains and exterior luminous sources for the entire year, the façade was split in three variable parts depending on the position of the shades and the relative position of the overhang. In this time-varying 9-surface enclosure, dynamic view factors were calculated between all surfaces throughout the year. For the thermal analysis, a comprehensive thermal network (heat balance) model was developed, and solved explicitly using the finite difference method to quantify the impact of the above parameters on the building’s thermal loads. A parametric analysis of the studied variables allows for selection of overhang and light shelf characteristics and suitable shade fabric to reduce building energy demand. It was observed that the implementation of the system can result in up to 43% and 16% reduction in annual cooling and heating demand respectively. Moreover, peak heating and cooling demands were cut down by 50% and 32% in that order. In the daylighting analysis, a multiple bounce radiosity method was used to determine hourly horizontal work plane illuminance and daylight autonomy. Energy savings resulting from the implementation two lighting control strategies (on/off control and continuous dimming) were also evaluated. Compared with standard automated interior roller shades, the studied system provides better natural light distribution, lower contrast ratios and longer periods of view to the outside. Lighting energy savings reached 45% with on/off electric lighting control, and up to 70% with continuous dimming control