An integrated energy simulation and life cycle assessment to measure the operational and embodied energy of a Mediterranean net zero energy building

Abstract

Net Zero Energy Buildings can play a key role in reducing the energy use, greenhouse gas emissions and the use of natural resources associated to the built environment. It is widely recognized that in low energy building a shift in relevance may occur from the operational to the embodied impacts. However, building performance assessment focus mostly on the operational phase and on primary energy consumption. This study aims to assess the energy and environmental impacts of a residential net zero energy building expanding the analysis to the full life cycle and to a wide range of environmental impact categories. The methodological approach integrates a non-steady state building energy simulation and the life cycle assessment methodology. The analysis is performed by considering four different design scenarios using alternatively two thermal insulation materials (extruded expanded polystyrene (XPS) and cellulose fibres (CF)) combined with two configurations for a building integrated photovoltaic system (with and without a battery storage system). The main results highlight that the CF/battery storage system scenario has the lowest impact in almost all the energy and environmental categories investigated, while the configuration with XPS and without battery storage system has the worst performances. In detail, the indicators “global energy requirement” and “climate change” are 18% and 34% lower than the XPS/no battery scenario. However, the impact increases in terms of resource depletion (4%). This outcome confirms the importance of a life cycle perspective to orient the low energy buildings design process towards more sustainable solutions. Moreover, very different results can be achieved if the credits beyond the building system boundaries are included or not in the balance. In detail, if system boundaries are expanded to include the net environmental credits, the configuration with CF and without battery storage system is the best, while the XPS/battery storage system one is the worst. “Global energy requirement” and “climate change” decrease, respectively, by 37% and 29% from XPS/battery configuration to CF/no battery storage configuration. Therefore, the management of the credits beyond the building system boundaries is an aspect not to be overlooked in similar approaches while defining a clear and unambiguous procedure to manage it in the perspective of a wide diffusion of low energy buildings.