Life cycle assessment of a plus-energy house

Abstract: Purpose: This study analyses the environmental impacts of a plus-energy house. Such buildings produce more energy in their use-phase than they consume, by generating energy with photovoltaic cells and saving energy via extensive insulation. The entire life cycle of the building is investigated form cradle to grave. The research focuses on the identification of environmental hotspots and the break-even time, after which the avoided burdens from the energy surplus even out the environmental impacts. Method: To answer the research questions, an ISO 14040 compliant environmental impact assessment (LCA) was conducted. It covers the raw material extraction, production and manufacturing of the building, the energy consumption by the inhabitants, the demolition and subsequent waste processing as well as the energy generation from the photovoltaic cells during 50 years lifetime. The life cycle impact assessment method was based on EN 15804 with seven impact categories: global warming potential, depletion potential of the stratospheric ozone, acidification potential of soil and water, eutrophication potential, formation potential of tropospheric ozone, abiotic depletion potential for non-fossil resources, and abiotic depletion potential for fossil resources. Results: The use-phase with energy generation and consumption dominates in all the impact categories except for the stratospheric ozone depletion potential. Photovoltaic cell production has the largest impact in terms of resource and ozone depletion. The building does not set off its impacts with its avoided burdens during its lifetime. The break-even time is calculated for each impact category and starts at 654 years for global warming potential. The geometric standard deviation is calculated for every process, so that a Monte-Carlo simulation can be run. This makes it possible to calculate the standard deviation of the results. Discussion: It is possible to enhance the environmental performance of the building by focusing on the hotspots. A sensitivity analysis shows that enhancing the energy surplus during the use-phase would be the most effective measure. This could be achieved by increasing the photovoltaic cell area or decreasing the energy consumption.