HO-2683 -- Heat Transfer in Metal Window Frames and Glass Support Structures

The thermal performance of window systems has long been of great concern in energy efficient building design. A summary of the many criteria by which this performance may be evaluated has been presented by Wilson and Sasaki.' Among these are : (1) resistance to heat losses to the exterior under winter conditions and heat gains under summer conditions ; (2) provision for interior surface temperatures that are above the dew-point temperature of the interior air space to avoid excessive condensation on these surfaces; (3) maintenance of interior surface temperatures which are within limits that provide acceptable mean radiant temperature conditions from the standpoint of human comfort recpUrements. All three of these criteria are related directly to heat transfer through the window system by surface convection, conduction., and possible convection across enclosed air spaces.

The manner in which thermal performance is affected by metal (usually aluminum) window support structures is the concern of the present paper.