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AmerCable Incorporated


energy - conservation - hotels

(intro) (initiative) (lighting)  (HVAC) (boilers) (controls) (laundry) (windows) (water

Window Technology

Windows are one of the most significant elements in the design of a hotel and greatly impact the energy systems of the buildings. Understanding both current advances in window technology and tools for evaluating choices are important aspects of increasing a hotel's energy efficiency.

According to the U.S. Department of Energy, windows account for more than 12 percent of energy use in commercial buildings in the United States. Overall, window-related energy costs account for over 5 percent of the total energy used in the United States.

Whether they are relatively small punched openings in the facade or a completely glazed curtain wall, windows are usually a dominant feature of the hotelís exterior appearance. Windows can appear highly reflective, darkly opaque, or transparent, revealing or hiding activity within the building. Their color, transparency, and reflected patterns can change with the time of day and weather.

External window shading devices such as awnings, roof overhangs, shutters, and solar screens, and internal shading devices such as curtains and blinds, can control the entry of solar heat. However, shutters, solar screens, curtains, and blinds make rooms dark. Curtains and blinds also let in some of the undesirable heat. While exterior shading devices are about 50 percent more effective than internal devices at blocking solar heat, they may create problems with the building's aesthetics and are sometimes expensive.

Solar Heat Gain Control for Windows
The weak thermal properties of clear glass windows made them a prime target for research and development in the attempt to control energy loss in buildings. This led to the development of low-emissivity, or "low-e," coated glass that controls heat gain and loss, reduces glare, and minimizes the fading in carpets and upholstery. New construction and window replacement applications commonly use glazing with these coatings.

Some low-e coatings reduce solar heat gain with little impairment of visible light transmission. Spectrally selective coatings transmit visible parts of the light spectrum while deflecting the heat portions of the spectrum. Similar thermal properties can be obtained with window films although with a noticeable decrease in visible light transmittance.

Laminated glass windows, which provide durability and increased protection from earthquakes, high winds, hurricanes, criminal activities, etc., are frequently used in conjunction with low-e coating. Laminated glass is created by sealing a sturdy plastic interlayer between two panes of glass to create an imperceptible intrusion barrier with visible-light transmittance similar to that of clear glass once the layers are bonded. When laminated glass is coupled with low-e coating, a sturdy, energy-efficient window results.

Other Resources
Several websites provide designers with more complete information on the energy, interior environment, technical, and life-cycle cost impacts of window design decisions in both residential and commercial buildings.

For information on the energy performance of windows in the United States, visit the Efficient Windows Collaborative web site:
www.efficientwindows.org. The site includes information on window technologies such as low-e coatings, emerging technologies, and frame types. It also includes a comprehensive glossary of window terms.

For a comprehensive website that describes both fenestration design options and the performance of such systems in commercial buildings, visit Windows for High Performance Commercial Buildings.

Window Systems for High-Performance Buildings. John Carmody, Stephen Selkowitz, et al. W.W. Norton & Company, New York, NY, 2004.

 

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