by Phillip G. Deighton
Ever since human beings began building structures, we have faced the problem of effectively managing the choices between light, comfort, security, appearance and cost. When the Egyptians built the great pyramids thousands of years ago, they found that 40,000 tons of stone make an impressive statement, yet also yield high costs and greatly limit the opportunity for natural daylight and ventilation.
Todays architects and builders are confronted with many of the same fundamental problems that the Egyptians faced. However, the advances in materials, comfort engineering and illumination options have increased the opportunities to manage efficiently living and working environments tremendously. Glass manufacturers have developed numerous products to aid the design professionals and builders in making those all-important choices between natural light, building comfort, solar heat gain, energy cost management and construction costs. So far, no one has found a universal solution that will work in all situations, so its the choices and combinations of possibilities that continue to keep the game interesting.
Three basic properties of glass affect energy performance in a glazing system. The first of these is the amount of solar energy that passes through the material. By controlling the levels of trace elements in the batch material, glass manufacturers can produce products ranging from extremely transparent clear product with high visible light transmission value to a dark glass product with low light transmission.
Second, the type of batch material used determines the spectral absorption of the glass. This is important because some of the solar energy that passes through the glass is converted to heat energy, causing the glass temperature to increase. The absorption and reflection characteristics also determine the color and appearance of the glass itself.
A third property of glass is its ability to conduct heat. The thickness of the glass, the fabrication of the glass and the type of coating applied to its surface can make the glass either a fairly good conductor of heat or a reasonably good insulator. Glass is an excellent substrate material for the application of thin metal coatings that can be used either to reflect energy or to allow certain wavelengths to pass through it selectively while blocking others.
For many projects, the most important consideration of the builder is managing the amount of solar heat load entering into a building. Electrical equipment, including artificial lighting and computers, and even the occupants add to this challenge. Cooling costs are often a greater expense, both in terms of equipment and on-going cost of operation, than either lighting or heating. A glass system that provides low solar energy transmission can be very helpful in managing heat load, while allowing for natural light and vision to the exterior. In instances such as sunrooms or Northern climates, solar heat gain may be desirable; therefore, a glass that maximizes transmission and provides high insulation value may be the best choice.
Each situation is different, but good planning and design result in highly effective energy management for the structure. The essence of elegant design is to maximize the use of "free" energy, minimize overall energy costs, determine an affordable price, while taking into consideration the packages aesthetics. Few choices will make as much difference as the selection of the right glass and glazing system.
In the past few years, the two most important advances in glass include the introduction of multi-layer metallic/ metallic-oxide coatings applied to the glass surface and improved melting technology. Multi-layer coatings, particularly with regard to low-emissivity (low-E) coatings, enhance the insulating property of glass. Additionally, improved melting technologies allow for a whole new class of super-tinted glass. Both of these developments are moving glass into the high-tech arena of energy management.
Extremely thin multi-layer coatings applied to the glass surface allow for sophisticated management of specific wavelengths of energy, while retaining the traditional appearance of the glass. Three types of supertint glasses have been introduced recently, and are available from several manufacturers in shades of blue, green and gray. These products exceed traditional tinted glasss ability to block heat and provide an economically-attractive alternative to additional air conditioning tonnage.
With energy costs at a 25-year low, some might ask, "Whats the big deal?" Even though most buildings are not designed to last as long as the pyramids, many things can change during the useful life of a building.
There are several trends that are likely to have significant impact on energy costs in the future. Even though the availability of fossil fuels is not a problem now, most of the easy sources have already been discovered. It stands to reason that development around the world will increase demand and supply will continue to deplete, resulting in higher fuel costs in the future. Alternate energy sources, such as nuclear power, have significant drawbacks and little new capacity has been added in the past few years. When existing generating stations reach the end of their useful lives, its reasonable to expect some cost increases for electricity.
Nobody can predict the future with certainty, but its a pretty safe bet that energy-efficient glass will continue to be an important factor in influencing the comfort and operational costs for buildings in the 21st century.
Phillip G. Deighton is the manager of marketing and sales support in the Commercial Glass Strategic Business unit of Visteon Glass Systems Division. Visteon is an enterprise of Ford Motor Company.
Visteon Automotive Systems of Dearborn, MI, is offering Visteon Versalux, a new brand of architectural glass that includes the Versalux Blue 2000 and Blue 2000 reflective glass, as well as Green 2000 and Green 2000 reflective glass. The glasses are available coated and uncoated, in a variety of performance levels and in gray and bronze. The glass also contains upgraded thermal characteristics that include what the company says is a 17-percent improvement in "shading coefficient."
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