Triple bottom line sustainability assessment of window-to-wall ratio in US office buildings

The window-to-wall ratio (WWR), or the proportion of glazing in a building's envelope, influences many design and performance aspects of a building across its life cycle, including aesthetics, material use, daylighting, HVAC size and operating energy consumption, view, and human satisfaction. Prior work argued for reducing WWR to reduce operating energy consumption. The objective of this study is to comprehensively assess the environmental, economic, and social effects of various WWR levels using a triple-bottom line approach. A building information model of the US DOE's large office (12 story) prototype building was developed using Autodesk Revit (R). The Tally (R) Revit application and DOE's EnergyPlus (TM) were used to perform life cycle assessment (LCA) and assess implications on HVAC equipment sizing, embodied energy of materials, and distribution of operational energy. Designs altering WWR from a baseline of 40% were compared in three different climate zones of the United States. Results showed that increasing the WWR in large office buildings leads to increases in environmental impacts, occupant dissatisfaction, and the life cycle cost for the three different climate zones studied. Most reductions in energy use and environmental impacts were approximately 1% from the baseline scenario for the office building under study. The results imply that while reductions in the WWR do result in improvements across the suite of metrics assessed, other design strategies need to be employed either in conjunction with, or separate from, in order to meet target energy consumption and environmental impact reduction goals within this building program, such as Architecture 2030 Challenges.