Life cycle assessment (LCA) studies the environmental impact of energy systems in complex buildings. It looks at how energy and materials used in building construction and operation affect the environment and human health. The process involves defining goals, analyzing inventory, assessing impacts, and interpreting results. For complex buildings, an input-output analysis is used to track energy and material flows. The study identifies environmental burdens like acidification, eutrophication, greenhouse effect, and ozone depletion caused by building activities.