Abstract
We undertake Life Cycle Assessment (LCA) of the cumulative energy demand (CED) and global warming potential (GWP) for a portfolio of 10 multi-family residences in the U.S. We argue that prior LCA studies of buildings use an inconsistent boundary for processes to be included in the supply chain: The operational phase includes all energy use in a building, but supply chains for the production of appliances, equipment and consumables associated with activities done in the building are neglected. We correct this by starting the analysis with an explicit definition of a functional unit, providing climate controlled space, and including processes associated with this functional unit. Using a hybrid LCA approach, the CED for low, mid and high-rise multi-family residences is found to increase from 30, 34, to 39 GJ/m2, respectively. This increase is due to the need for energy-intensive structural materials such as concrete and steel in taller buildings. With our approach, the share of materials and construction of total life cycle energy doubles to 26%, compared with a 13% share that would be obtained with inconsistent system boundaries used in prior studies. We thus argue that explicit definition of functional unit leads to an increase in the contribution of supply chains to building energy life cycles.
Highlights
The environmental impacts of urban structure have been a focus of research for many years
Wood has a comparatively lower overall cumulative energy demand (CED)/global warming potential (GWP), when considering total mass and energy intensity, than steel or concrete which are alternative framing materials required for higher-rise multi-family dwellings
The second reason that the study suggests a direct correlation between increases in CED/GWP and building rise is due to the increasing operation energy
Summary
The environmental impacts of urban structure have been a focus of research for many years. In. 2007, the United Nations reported that cities were responsible for 75% of global energy consumption and 80% of all greenhouse gases (GHG). Program reported that buildings alone were responsible for about 40% of global energy and resource consumption, and approximately 33% of global GHG emissions [1,2]. Life cycle assessment (LCA) has become a common tool to examine the environmental impacts of industrial systems, including buildings. LCA is a “cradle to grave” approach that assesses the environmental impacts, such as the total energy consumed or GHG emissions produced, through its entire life cycle, or, as a result of raw material extraction, through the end-of-life of an industrial product or system. Life cycle assessment provides a picture of the environmental trade-offs often made in product or process selection and can help avoid shifting problems from one life cycle phase to another [3]
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