Towards sustainable Net Zero Energy Buildings: life cycle energy performances and environmental impacts of a prefabricated building module

The impact of prefabrication in the building sector is currently undergoing significant growth. Although prefabricated buildings cannot in any situation replace conventional buildings, they have some characteristics, such as reduced construction time, higher safety during construction if compared to traditional buildings and modularity, that make them competitive in specific applications, that are undergoing substantial increase importance and market relevance. However, in a context where the transition towards a low-carbon energy system is quickly becoming an important target of scientific efforts and research, prefabricated buildings, as well as any other type of building, will have a key role in achieving the decarbonisation of the building sector. In this contex, this work of thesis explores the energy and environmental performances of a NZEB modular case study: the IDEA (Integrating Domotics, Energy and Architecture) building. The case study is a prototype of a net zero energy housing module, integrating renewable sources energy generation systems (PV system) and innovative materials (fiber reinforced polymers materials) in Messina (Italy) at the “National Research Council of Italy– Institute for Advanced Energy Technologies”. Through the Life Cycle Assessment (LCA) methodology all life cycle stages were included in the study: materials and component production, construction process, use and end-of-life. Monitoring studies were performed during 2 months. The building use stage was simulated through and energy plus model, validated on monitored data. In addition to investigate the overall energy and environmental performances of the existing prefabricated modular unit, another aim of the research is to analyze several building redesign option through a multidisciplinary approach with a view to the entire building life cycle. In this context, the research proposes a multidisciplinary methodological framework which allows to integrate into the building design and investigate at the same time the use stage energy performances, the load matching and the grid interaction issues, the life cycle overall performances and the economic feasibility. The results show that the materials production stage alone accounted for about 50 - 80% of the total energy and environmental impacts caused by the building. The use stage is the second most impactful stage (about the 31% on average of the total life cycle impacts), while the construction and the end-of-life stages give a marginal contribution to the total impacts. In this context, the findings of the research pointed out the relevance of LCA in the assessment of the building energy and environmental performances. In particular, the study demonstrates that reaching the Net Zero target during the use stage could imply the displacement of the environmental impacts to the other stages, as well with a prevalence towards the production of the building materials. Therefore, a mere focus on the use stage performances cannot give the whole picture that is required in the context of a paradigm shift towards decarbonisation policies. Focusing only on the assessment of the energy consumptions related to the use stage quantifies the reduction of the environmental burdens of this stage but it does not guarantee that the life cycle overall performances will be improved. Thus, the integration of the LCA methodology in the design choices is of paramount importance to support the development of sustainable buildings. Moreover, the research shows that the design of any type of building requires an integrated and multidisciplinary design approach, covering a number of key aspects such as energy saving, life cycle environmental impacts, economic feasibility and many others, to create the conditions for a significant decarbonisation of the building sector. In this context, the multidisciplinary methodological framework can be used to explore and improve the low sustainability performing areas over the life cycle of new modular building designs. Moreover, the methodological approach can also be adopted for sustainability assessment of other type of constructions.