Daylighting Systems : Development of Techniques for Optical Characterization and Performance Evaluation

• Main Author: Nilsson, Annica M.
• Format: Doctoral Thesis
• Language: English
• Published: Uppsala universitet, Fasta tillståndets fysik 2012
• Subjects: Optical spectroscopy; integrating sphere; ray tracing; light scattering; window physics; Venetian blinds; core daylighting; optical characterization
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-183307; http://nbn-resolving.de/urn:isbn:978-91-554-8512-2

Successful integration of daylighting systems requires the ability to predict their performance for given climates. In this dissertation, a bottom-up approach is applied to evaluate the optical performance of a selection of daylighting systems. The evaluations are based on the optical properties of the included materials, and part of the dissertation focuses on developing new optical characterization methods. The work on characterization techniques uses an integrating sphere method to characterize the transmittance of light scattering samples more accurately. The method's principle is to reduce the discrepancy in light distribution between the reference and the sample scans by using an entry port beam diffuser. For samples exhibiting distinct light scattering patterns, the benefits of improved uniformity outweigh the errors introduced by the diffusing material. The method is applicable to any integrating sphere instrument, and its simplicity makes it suitable for standard measurements. In addition to normal-hemispherical properties, many daylighting applications require knowledge of the system's spatial light distribution. This dissertation presents a method combining experimental techniques and ray tracing simulations to assess the light distribution from a Venetian blind system. The method indicates that ray tracing based on simplified optical data is inadequate to predict the light distribution for slat materials exhibiting both specular and diffuse properties. Ray tracing is a promising complement to experimental methods used to characterize light guiding or light redirecting systems. Here, spectrophotometric measurements of a scaled mirror light pipe validate a ray tracing model. The model shows excellent agreement with experimental results for both direct and diffuse incident light. The spectral evaluation shows no dramatic color changes for the transmitted light. The ray tracing model is used to evaluate four daylighting systems for a selection of Swedish locations. The percentage of occupied time when the studied systems achieve full design illuminance is relatively low, but the systems provide a valuable contribution to the required illuminance. Additionally, this dissertation provides an overview of available energy efficient windows and illustrates the importance of including the solar energy transmittance when evaluating window energy performance. Overall, this dissertation presents optical characterization techniques for improved performance evaluations of daylighting systems.