Embodied impacts of window systems: A comparative assessment of framing and glazing alternatives

Abstract

The embodied impacts of window materials can be considered as hidden impacts. However, as buildings have become more energy efficient, the impacts of the windows are recognized as being increasingly significant and have not been thoroughly analyzed. Thus, comprehensive analysis should be performed to inform the wise selection of energy-efficient windows with lower embodied impacts. This article proposes an approach based on embodied impact assessment and Pareto optimal frontier to support environmentally friendly design of windows. A comprehensive assessment of the embodied environmental impacts of a standard size window was implemented for 32 alternative systems, considering four framing materials (aluminum, fiberglass, polyvinyl chloride, wood) and eight glazing solutions (for single-, double, tripled-glazed). Environmental impacts were calculated for non-renewable primary energy, global warming, acidification, eutrophication, and ozone layer depletion. Pareto optimal frontiers were identified, showing the trade-offs between environmental impacts and thermal transmittance (U-value). The components of the two main parts of a window (frame and glass) have been characterized to identify those that contribute most to the total embodied impacts. The results show that tempered or laminated glass and the glass coating (low-E film) increase the embodied impacts of glazing solutions. Of the framing materials, wood has the lowest embodied impacts in all categories, while aluminum has the highest impacts for the double and triple-glazed solutions. The breakdown of the embodied impacts of aluminum framed window systems shows that the frame has higher impacts than the glazing, as it accounts for 60–80% of total embodied impacts. In the windows with polyvinyl chloride (PVC) and fiberglass frames, the frame is responsible for most of the embodied impacts for single-glazed windows (58–86%) and almost the same proportion for double-glazed windows (46–54%), but lower for triple-glazed (22–40%). The contribution of a wood frame (<30%) is much less significant. Pareto optimal frontiers are identified for the window systems and the non-dominated solutions are discussed for the various environmental impact categories.