Light-Diffusing Insulation:

Existing Solutions and New Prototypes for Glazing Interlayers

Abstract

Daylighting is an important strategy for low energy buildings today, yet glass compromises the overall thermal resistance of building envelops: even expensive triple-glazed windows conduct heat at over twice the rate of opaque exterior walls, insulated to energy code minimums. Triple glazed windows are also heavy, expensive, and energy intensive in their manufacturing. Today, lighting consumes 1/3 of electricity in commercial buildings, and daylighting may potentially reduce building energy use by 28% or more (Williams 2012). As the energy code continues to constrain the prescriptive window-to-wall ratios of commercial buildings, it is important to develop envelope systems that admit energy-saving daylight while better managing heat gains and losses. A series of graduate courses at Kansas State University examined the performance of several existing glazing-integrated insulation solutions, using this research to propose a variety of innovative alternatives that can increase the thermal performance of transparent assemblies in building facades. With both computer analysis and instrumented testing of small prototypes, the research seeks to better understand the physics of fenestration interlayers, while also identifying new strategies for improving the performance of basic double glazed insulated glass units and double wall construction. Test results in the paper present the thermal performance, light transmission, and light diffusion of existing light-diffusing and translucent products and student-developed prototypes. Following a discussion of the research work, a generalized model attempts to better explain the physics at work in interlayers, and propose how such systems can be optimized to maximize light diffusion while improving the thermal performance of glazing units.