Optical Properties of Glazing and Shading Systems

 

Simple glazing and the IGDB: Specular glazing, often called "simple glazing",  consists only of plane parallel layers with or without thin-film coatings, all having specular optical properties.  A practical definition for simple glazing arises from the condition that their relevant optical properties can be easily measured in commercial spectrometers. Characterization and collection of data for specular glazing is far advanced compared to more complex glazing and shading systems. An extensive database of simple glazing products is available in the International Glazing Database (IGDB). The integrity of the database is maintained by various methods including a technical review by LBNL staff of all submitted data and a peer review by all manufacturers in the IGDB group. Perhaps the most important safeguard is the periodic Interlaboratory Comparison (ILC) conducted by LBNL. Properties of combinations of simple glazing materials (e.g., double and triple glazing units)  can be modeled using freely available computer programs such as WINDOW 5.1 developed by LBNL. It is even possible to design new glazing materials such as laminates and applied films by combining components in the IGDB using the Optics 5.1 software. Diffuse and patterned glazing: Although it is apparently possible to measure nonspecular materials using conventional spectrometers equipped with integrating spheres, the results are often inaccurate or insufficient for further modeling of more complex systems. Using goniometric instruments to obtained detailed bidirectional properties of diffusing materials and correlating to measurements made in the more common unidirectional spectrometers we hope to develop simplified methods for obtaining accurate properties. We are working with the International Commission on Glass TC10 understand this important class of materials. Once properly characterized the algorithms in the new Window 6 program can be used to combine either specular or diffusing layers into multiple glazing systems. Complex glazing and shading systems: The next generation of energy-saving and energy-producing window technologies will be designed and characterized with powerful new methods.  Direct experimental characterization of geometrically complex systems from slat shading to prismatic panels can be performed  in a slow and laborious way using either our 2-meter integrating sphere or large-scale bidirectional scanning radiometer.  Whenever possible we will combine measurements on component materials, either diffuse or specular, to calculate the properties of systems with raytracing. Some recent  papers give examples of this approach: M. Rubin, J. Jonsson, C. Kohler, J. Klems, D. Curcija and N. Stojanovic, Bidirectional optical properties of Slat Shading: Comparison Between Raytracing and Radiosity Methods, submitted to Solar Energy (2007). download pdf. M. Andersen, M. Rubin, R. Powles, J.-L. Scartezzini,  Bi-directional transmission properties of Venetian blinds: experimental assessment compared to ray-tracing calculations Solar Energy 78 (2005) pp 187-198: download pdf M. Andersen, M. Rubin, and J.L. Scartezzini, LBNL-51169, Comparison between ray-tracing simulations and bi-directional transmission measurements on prismatic glazing, Solar Energy 74 (2003) 157-173. LBNL-51169. download pdf