Degradation of Insulating Glass Units: Thermal Performance, Measurements and Energy Impacts

Abstract

Insulating glass unit (IGU) degradation has been studied extensively. However, there is limited understanding of how present durability evaluation standards relate to product lifetime. Furthermore, there is debate on how to quantify performance of installed windows over time to better understand degradation processes. More knowledge on these topics is required to link durability evaluation to product lifetime projections based on energy performance. Energy models provide helpful estimations of total annual building energy consumption. However, most models are based on “as installed” performance of envelope components and fail to account for performance degradation. This can lead to an underestimation of building lifetime energy consumption. A better understanding of the relationship between durability and energy performance can inform integration of degradation dynamics into energy modeling software. This will improve lifetime building energy consumption estimations as well as inform appropriate retrofit strategies and timing. This paper reviews current durability literature, various standards for window performance ratings and weathering methods, existing in situ IGU energy performance measurement techniques, and whole-building energy effects. The challenges and disparities among various studies are analyzed and discussed. The authors hope that further work in this area will lead to the development of improved in situ test methods to assess IGU degradation in the field and link this knowledge to improved energy performance modeling approaches.

Long-Term Viscoelastic Behavior of Polyisobutylene Sealants before and after Thermal Stabilization

“…A group of extremely important window materials are sealants, which are highly affected by the temperature, UV light, and other factors, which induce the formation of internal stresses and deformations, such as the displacement of thermoplastic sealants resulting in various defects, such as twisting, bulging, cracking, out-of-straightness, and out-of-squareness of the edge seal [ 11 ]. The resulting changes in cavity pressure exert lateral load on the glass panes and deflect them, which induces deformations in sealants and leads to a reduction in the lifetime and energy performance (or energy estimation of buildings) [ 12 ]. Moreover, the above-mentioned factors can lead also to chemical structural changes, affecting the fragility of PIB, which decreases with increasing molecular weight [ 11 ].…”