Product Review

Quadruple-Glazed Window Includes Phase-Change Materials

GlassX Crystal uses four panes of tempered safety glass that form three separate insulating glazing units (IGUs); these combine to form a single glazing assembly approximately three inches thick (79 mm) and weighing 19.5 lb/ft2 (95 kg/m2). The outermost IGU is filled with low-conductivity argon or krypton gas and contains a suspended prismatic filter that rejects higher-angle sunlight (greater than 40°) but allows low-angle sunlight (less than 35°) to pass through (see diagram). This filter works like a passive solar control system for south-facing windows, keeping out high summer sun to minimize cooling but allowing in low-angle winter sun to aid in heating. The two panes of the middle IGU have low-emissivity (low-e) coatings and are also filled with argon or krypton gas (this middle “IGU” could be thought of as a space between the inner and outer IGUs).

The final, most unusual IGU contains sealed polycarbonate channels encapsulating a salt hydrate phase-change material that stores heat and releases it slowly back into the room. When any material is heated to change its “phase” from solid to liquid, its actual temperature doesn’t change, even though a great deal of “latent heat” is absorbed by the material. Think of melting ice as warmth from the air is added to it, for example; the material can absorb a lot of heat while the temperature stays at about 32°F (0°C).

Published July 30, 2010

Ehrlich, B., & Alex, W. (2010, July 30). Quadruple-Glazed Window Includes Phase-Change Materials. Retrieved from