Development and evaluation of a simulation-based adaptive shading control for complex fenestration systems (2019)

The necessity of solar control for the fenestration systems of commercial buildings has been extensively discussed over the past decades bringing forward issues such as energy efficiency, visual and thermal comfort, privacy, visual contact to the outside and aesthetics. However, a number of problems arising from manual control has been identified pointing towards the direction of automatized systems. Such systems continuously readjust the shading configuration in order to enhance comfort and energy efficiency during the day. To effectively address visual comfort, a balance between the two opposing aspects of daylight maximization and glare protection must be found; a task requiring a number of costly and sophisticated measurement devices. Therefore, driven by considerations of visual comfort, the implementation of automatic shading control systems presents difficulties which tend to increase with the sophistication of the system. The cost and the complexity of the commissioning process due to the extensive use of sensors inhibits the commercialization of multi-variate controllers. Additionally, the installation of multiple measurement devices in the office space leads to disturbance and low acceptance of the users. A new control system for venetian blinds and electric lights focusing on office spaces, which substitutes the illuminance sensors and luminance cameras with real-time daylight simulations, was developed to explicitly address both daylight and glare aspects. By using the Radiance-based Three-phase-method the required computational time was substantially reduced. Additionally, an optimization engine based on the principles of Fuzzy Logic was developed to evaluate the visual conditions in the room and decide on the trade-off between the horizontal and vertical illuminance before applying a shading configuration. Considerations of view contact to the outside, thermal comfort in the sense of overheating prevention, and adaptation of the system to the user wishes were taken into account to improve the overall user acceptance. For periods of low occupation, the solar heat gains, selectively accepted according to time and season, contributed to the heating and cooling energy demand reduction. Two controller prototypes were built and tested; one in a rotatable test facility at Fraunhofer ISE in Freiburg, Germany, and a second one in a real-life office in the same area. The purpose of the first prototype was to evaluate the accuracy with which the simulations predicted the horizontal and vertical illuminances in the room and to test and tune the overall operation of the controller. The second prototype was created to test the compatibility of the system with already existing components and to evaluate the user acceptance and the adaptation process under real-life operation conditions. An additional motivation was to identify weaknesses of the system perceived by a user unfamiliar to the control algorithm. To further investigate the potential of the controller a case study was conducted. Its purpose was to show the benefits of the new simulation-based controller over other shading control strategies and theoretically evaluate the reliability of the developed algorithm. The prototype testing revealed a well operating open-loop system and a good agreement between the simulated and the measured illuminance values. Although during normal operation the positioning accuracy of the system was reduced, the overall visual comfort in the room, defined by glare control and daylight provision, remained within the acceptable limits. During the real life testing the performance of the controller was considered an improvement over the previously installed system and despite the shortcomings due to the age and restrictions of the existing components the defined conditions were fulfilled. The theoretical comparison of the system showed the potential of important energy reductions in relation to other shading control strategies in combination with an improved glare control mechanism. However, the benefits of the glare control were found to depend greatly on the shading device used since perforated or specular reflecting systems were incompatible with the developed algorithm. By including any obstacles in the surroundings of the installation site in the controller simulation the controller adjusted its operation in order to avoid any unnecessary window coverage and to improve the daylight admission in the room.