We are all familiar with the benefits and drawbacks of using large amounts of glass in home or office construction. The natural light and warmth of the sun makes any space more useable and pleasant. Numerous studies suggest that adding natural light to a workspace can improve workers’ productivity and reduce absenteeism. Unfortunately, windows can dramatically increase energy consumption by letting in too much heat during the day, and letting it leak out again at night. In an era of increasing environmental awareness corporations and individuals are seeking ways to make their homes and offices more energy efficient. Windows are a great place to start.

Solar control glass is any type of glass that seeks to reduce the increased energy costs associated with glass by changing the way light passes through it. There are a few different types of solar control glass, each with its own approach to saving energy. The oldest and most familiar type is reflective glass, which is common in commercial buildings. Reflective glass has a metallic coating, which reflects light and heat away from the building, reducing cooling costs during hot summer months. Unfortunately, this approach also blocks desirable solar energy during cool winter months, increasing heating costs. 

Low-E glass is another type of solar control glass which evolved from reflective glass. It uses the same type of metallic coating, but in extremely thin layers. Low-E glass appears to be transparent.  In fact it reflects or absorbs many types of light, including short-wave heat energy and damaging ultraviolet (UV) light. This keeps solar heat out on hot days, and can significantly reduce cooling costs. However, Low-E glass has some limitations. It blocks some desirable solar heat on cold days, and traps heat created by electric lights, even when it is hot. 

Smart glass is the next evolution in solar control glass. The term applies to any type of glass that can manually or automatically increase and decrease the amount of light that passes through it.   This type of solar control glass helps maximize energy savings in all seasons by reflecting the sun’s energy outside on hot days, and allowing it into the building when temperatures are cool. Existing types of smart glass need electricity to transition from their transparent to darkened or reflective states. Unfortunately, this requirement offsets some of the energy savings created by these windows, and makes them costly and difficult to install. 

RavenBrick’s filter technology represents a leap ahead of existing smart window systems. RavenWindow is an active-passive, thermoreflective filter; it darkens in response to an increase in the temperature of the window without an electric current or human intervention. This eliminates the need for additional wiring and control systems, and simplifies installation and maintenance. Unlike other smart glass technologies, RavenWindow can be retro-fitted to improve existing windows, including low-e windows. Best of all, RavenWindow costs dramatically less than other smart window systems currently on the market. 

In 2003, a study of smart windows was performed by The U.S. Department of Energy’s Lawrence Berkeley National Laboratory (LBNL) on behalf of the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE). The study focused on smart-glass window systems capable of darkening or shading automatically, such that the Solar Heat Gain Coefficient (SHGC) varied between 0.26 and 0.40. Analyses were performed for eight U.S. cities: Boston, Seattle, Denver, Washington D.C.; Kansas City, Sacramento, Jacksonville, and Phoenix.^[5]

The ASHRAE study found that across all eight climate zones, buildings with low-E glass saved an average of 8-15% on their total annual energy (heating, cooling, and ventilation) costs, whereas the addition of smart window systems saved an additional 6-19%.^[5] In other words, the savings associated with a smart window are approximately as large as the savings associated with low-E. Furthermore, because smart windows and low-E save energy by completely different mechanisms, their effects are complementary and thus their savings can be added together.  In addition, while low-E glass reduced peak cooling loads by 2-14%, the smart windows provided an additional 5-38% reduction in peak cooling load,^[5] allowing significant downsizing of the building’s air conditioning system.

The report concluded that smart windows “offer the potential for significantly greater HVAC savings than can be achieved with currently available high-performance windows,” that they have “much lower energy costs than static windows,” and that they “provide the best of all worlds”.

RavenWindow film is transparent when cold and partially reflective when hot, allowing an SHGC range between 0.12 and 0.43 -- more than twice the range studied by LBNL. Studies performed by RavenBrick using LBNL tools show energy savings up to three times those of low-E glass alone.

Assuming a retail cost of $25 per square foot, RavenBrick has determined that for large buildings across multiple climate zones, the pay-back period is about 5-8 years. The pay-back period does not include capital cost reduction on HVAC systems, reduction in the cost of window coverings, and the tax and building permit savings associated with LEED certification.