| dc.description.abstract | A percentage of insulating glass (IG) units break each year due to thermally induced perimeter
stresses. The glass industry has known about this problem for many years and
an ASTM standard has recently been developed for the design of monolithic glass plates
for thermal stresses induced by solar irradiance. It is believed that a similar standard can
be developed for IG units if a proper understanding of IG thermal stresses can be developed.
The objective of this research is to improve understandings of IG thermal stresses
and compare the IG thermal stresses with those that develop in monolithic glass plates
given similar environmental conditions.
The major difference between the analysis of a monolithic glass plate and an IG unit is
energy exchange due to conduction, natural convection, and long wave radiation through
the gas space cavity. In IG units, conduction, natural convection, and long wave radiation
combine in a nonlinear fashion that frequently requires iterative numerical analyses
for determining thermal stresses in certain situations. To simplify the gas space energy
exchange, a numerical propagation procedure was developed. The numerical propagation
procedure combines the nonlinear effects of conduction, natural convection, and
long wave radiation into a single value. Use of this single value closely approximates the
nonlinear nature of the gas space energy exchange and simplifies the numerical analysis.
The numerical propagation procedure was then coupled with finite element analysis to
estimate thermal stresses for both monolithic glass plates and IG units. It is shown that the maximum thermal stresses that develop in IG units increase linearly with input solar
irradiance during the transient phase. It is shown that an initial preload stress develops
under equilibrium conditions due to the thermal bridge effects of the spacer. It is shown
that IG units develop larger thermal stresses than monolithic glass plates under similar
environmental conditions. Finally, it is shown that the use of low-e coatings increase IG
thermal stresses and that the location of low-e coating as well as environmental conditions
affect which glass plate develops larger thermal stresses. | en |
