| Aluminum with Thermal
Break
Aluminum window frames are light, strong,
durable, and easily extruded into the complex shapes required
for window parts. Aluminum frames are available in anodized
and factory-baked enamel finishes that are extremely durable
and low-maintenance.
The biggest disadvantage of aluminum as a window frame
material is its high thermal conductance. It readily conducts
heat, greatly raising the overall U-factor of a window unit.
In cold climates, a simple aluminum frame can easily become
cold enough to condense moisture or frost on the inside
surfaces of window frames. Even more than the problem of
heat loss, the condensation problem has spurred development
of better insulating aluminum frames.
The most common solution to the heat conduction problem
of aluminum frames is to provide a "thermal break"
by splitting the frame components into interior and exterior
pieces and use a less conductive material to join them.
Current technology with standard thermal breaks has decreased
aluminum frame U-factors (heat loss rate) from roughly 2.0
to about 1.0 Btu/hr-sq. ft-°F. In hot climates, where
solar gain is often more important than conductive heat
transfer, improving the insulating value of the frame can
be much less important than using a higher-performance glazing
system. |
