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 hotel’s 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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