Window Technologies: Argon or Krypton Gas Fills
An improvement that can be made to the thermal performance of insulating
glazing units is to reduce the conductance of the air space between the layers.
Originally, the space was filled with air or flushed with dry nitrogen just prior
to sealing. In a sealed glass insulating unit, air currents between the two panes
of glazing carry heat to the top of the unit and settle into cold pools at the
bottom. Filling the space with a less conductive, more viscous, or slow-moving
gas minimizes the convection currents within the space, conduction through the
gas is reduced, and the overall transfer of heat between the inside and outside
is reduced.
Manufacturers have introduced the use of argon
and krypton gas fills, with measurable
improvement in thermal performance. Argon is inexpensive, nontoxic, nonreactive,
clear, and odorless. The optimal spacing for an argon-filled unit is the same as
for air, about 1/2 inch (11-13 mm). Krypton is nontoxic, nonreactive,
clear, and odorless and has better thermal performance, but is
more expensive to produce. Krypton is particularly useful when the space between
glazings must be thinner than normally desired, for example, 1/4 inch (6 mm). The
optimum gap width for krypton is 3/8" (9mm). A mixture of krypton and argon gases
is also used as a compromise between thermal performance and cost.
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