Life-cycle assessment; sustainable buildings; environmental impact
Buildings account for 39% of the CO2 emissions in the U.S. Although emerging building energy-efficient technologies lead to improved energy efficiency and lower environmental impact in the operational phase, not much attention has been paid to the environmental impact associated with the materials and manufacturing of the building mechanical systems. This paper presents an integrated life-cycle assessment method for buildings that accounts for the embodied and use phase carbon impacts of the building and its mechanical systems. The proposed methodology relies on EnergyPlus to generate the use-phase energy consumption for any given building. A material 'grabber' routine was developed to automatically extract building envelope material information from EnergyPlus models, which is then used for envelope embodied carbon analysis. For the mechanical equipment, embodied carbon accounting was performed for two representative air-conditioning and heat pump units: a 4-ton packaged unit and a 4-ton split heat pump. The different elements were incorporated in the overall life-cycle assessment tool along with lighting embodied data to allow generation of a whole building environmental performance report. Five Department of Energy commercial building prototypes were used as case studies and analysis results for seven U.S. climate locations are presented in this paper. The results show that for the investigated prototypical buildings, the use phase energy consumption has a dominant impact on the overall building environmental performance: the embodied carbon contribution is less than 9% for all considered cases. However, the tradeoffs could change dramatically as the U.S. moves towards net-zero buildings and the tool presented in this paper could be used to consider these tradeoffs.