A client has a project with the glazing units butt jointed at the
vertical joints between sections. He thinks that this may have less
thermal bridging then for a vertical joint with typical framing
details. Does any one have any experience with this type of
joint? The glazing units are double pane sealed units with warm edge
spacers.
Chris Jones, P.Eng.
Hello Chris,
Seems like you would need to (appropriately) average out "edge of
glass"
and "center of glass" u-values. This may be a function of the size of
the glass plane, i.e. a large glass plane will have predominantly
"center of glass" u-value characteristics rather than "edge of glass".
My question back to the bldg-sim(ers) will be -- are there any studies
/
empirical data drawing relationship between edge effects and center of
glass conductance values with respect to different types of glazings
and
their sizes.
Neeraj Kapoor
Neeraj is correct regarding the size (and aspect ratio) of the pane making a difference. Essentially - the ratio of perimeter to area s a bid riving factor. I think you could arrive at the overall U-value using Window 5.2 by LBNL - it allows for different window sizes, and you can customize your frame conductance.
With regards to frame conductance, most manufacturers will give you those numbers if you ask them - they should have it for butt glazed systems too (I assume you mean structural silicone glazing where the frame is behind the glass).
Vikram Sami, LEED AP