The use of a
low-conductivity inert gas instead of air in window glazing cavities in
order to reduce heat transmission through the window.
windows have a sealed glazing unit: two or more lites of glass that are
sealed around the perimeter to prevent the transfer of air and moisture
through the window cavity. The gas which fills the inter-glazing cavity
affects the heat transfer through the assembly but has almost no effect on
the solar heat gain or the visible light transmission.
Air, of course, is the most common cavity fill gas, but the use of an
inert gas (typically argon or krypton) can significantly reduce window
heat transfer. Krypton and argon are colourless, odourless and non-toxic.
Argon is the most commonly-used fill gas because it offers good thermal
performance at low cost. Krypton is more effective at reducing heat loss,
but is roughly 200 times more expensive than argon per unit volume.
Because krypton works best at smaller pane spacings (8 mm), it is often
used in triple and quadruple-glazed windows to minimize the overall
thickness of the unit. Other types of gases are used (for example, sulphur
hexafluoride, carbon dioxide) to reduce sound transmission, but these
gases do not offer the improved thermal performance of the inert gases.
Several different techniques are used to fill glazing cavities, but all
techniques result in a mixture of the fill gas and air. A recently
approved Canadian General Standards Board standard requires units to
achieve a 90% fill gas concentration. This concentration will gradually
diffuse over time; this diffusion is estimated at 0.5 to 1% per year.
Thus, after 20 years the fill gas concentration may have dropped to 70 to
80%; this still gives 70 to 80% of the energy benefits of inert gas fills
over conventional windows.
Enermodal Engineering Ltd.
Canada N2K 3S2
tel 1 519 743 8777
1 519 743 8778
||reduces wintertime heat
||can only be used in sealed
The low cost and
good performance of inert gas fills should make their use mandatory
whenever a low-e coating is used in a glazing unit. The low-e coating
reduces radiative heat loss and the inert gas fill reduces convective heat
loss, so that the two technologies used in combination are an effective
barrier to heat loss. The use of inert gas fills without a low-e coating
is only marginally effective in reducing heat
Although inert gas fills are quite
common in residential windows, their use in commercial windows is uncommon
because they are rarely specified by architects. There are, however, many
applications that have demonstrated the long term suitability of this
Green on the Grand
Condominium at 77 Governors Road
The cost of this
technology is about C$3 to $5/m2 of window.
Almost all window and sealed glazing unit
manufacturers offer inert gas fills as an option.
Energy-Efficient Residential and Commercial Window
Reference Guide, Canadian Electrical Association
Canada H3Z 2P9
tel 1 514
fax 1 514 937 6498