Sustainable Technology: Glass/Glazing

Sept. 1, 2008

Glass and Glazing Advancements Increase Efficiency

By William D. Smith and Chris Matthews

Exterior glazing is growing in popularity as advancements transform the industry. Whereas low-e glazing was state-of-the-art just a decade ago, there are now "self cleaning" photocatalytic coatings, "smart glass" that controls light and heat with the press of a button, and transparent conductive oxide-coated glass for solar panels. Recent developments in framing systems offer enhanced energy efficiency along with improved convenience and comfort for occupants.

Progressive Glass Products
Photocatalytic coatings are generally titanium dioxide that uses ultraviolet light to
react with a photocatalyst that breaks down dirt on the glass surface. The loosened dirt is then washed away by rainwater that, instead of forming as droplets on the glass surface, spreads to form a sheet of water that washes the dirt from the glass.

Smart glass technology is based on electrochromic, suspended particle, or liquid crystal devices. Electrochromic devices modify light transmission by response to a short burst of electricity. Suspended particle devices use a laminate of randomly oriented particles suspended in fluid between two glass plies or attached to one layer that absorb light, making the glass appear dark; when electricity is applied, the particles are aligned and allow light to pass through. Unlike electrochromic devices, suspended particle devices require a small continuous electrical current to maintain transparency. In polymer-dispersed liquid crystal devices, randomly oriented liquid crystal droplets are arranged in a sheet between two layers of glass. When switched on, the droplets align according to the electric field. Liquid crystals scatter light without blocking it, so the glass looks white even in its transparent state.

As the search for alternatives to fossil fuels continues, the use of solar cells continues to expand. Procurement of crystal silicon solar cells is expected to become more difficult, and development of thin film silicon solar cells has provided a good alternative. Glass coated with transparent conducting oxides, a product that uses about 100th the amount of silicon, is the latest breakthrough in solar panels. By using a coating that is fired into the glass during manufacturing, this product provides high light transmission, conductivity, and durability.

Advanced Framing Systems
Advanced framing systems, such as curtain walls, storefronts, skylights, and operable windows and doors, when used in conjunction with modern glass products, can add energy efficiency to a building. Designs now include photovoltaic panels and next-generation thermal barrier materials and can be produced using computer simulation and building information modeling (BIM) programs.

Photovoltaic panels can now be mounted in the spandrel areas of curtain wall and skylight systems, where they collect and convert solar energy to electricity, which is routed through the framing to a building's power system. Advanced thermal barrier materials within aluminum framing systems are now chemically structured nylon/glass fiber composites, providing improved resistance to exterior/interior thermal transfer and increased glazing system longevity. Responding to growing interest in computer simulations to predict long-term building performance, manufacturers now offer modeling programs that simulate a project's structural and energy performance over time. This computer technology will improve in step with the industry-wide movement toward comprehensive modeling programs.

Even low-tech approaches are now improving energy performance. Renewed interest in passive control of solar light and heat is addressed with thermally isolated exterior aluminum sunshades and screens installed on curtain walls. Manually operated "trickle" ventilation ports in fixed glazing systems allow limited air flow, naturally helping control indoor temperature and condensation. Interior reflecting light shelves increase natural lighting with minimal thermal impact, decreasing artificial lighting requirements.

The glass and glazing industry continues to work with architects and building professionals in developing new ways to improve energy use and efficiency. Implementing these materials can result in an improved interior environment for occupants while maximizing energy savings.

William D. Smith ([email protected]) is president and Chris Matthews ([email protected]) is vice president of Glazing Consultants International LLC, a West Palm Beach, FL-based building envelope consulting firm.

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