Robust and reliable building renovation strategies for environmental and economic performance

Buildings are one of the largest energy consumers and greenhouse gas emitters in the world. Building renovation is crucial to reduce the environmental footprint of the building stock and meet the greenhouse gas (GHG) neutrality target set by 2050. However, considering the long service life of buildings, renovation solutions might not be reliable due to the many uncertain events that occur during the building’s life cycle. Such uncertainties can be related to the future building operation such as climate change and the time of replacement of components, or can be associated with the input parameters, such as materials properties, costs and environmental impact factors of materials. Not considering these uncertainties in the renovation planning might lead to solutions that are not robust in the uncertain future and to taking wrong decisions when comparing several renovation options.The aim of this doctoral thesis is to identify optimal, robust, cost-effective and climate-friendly renovation solutions for Swiss buildings. Given this objective, the research focuses on creating a novel, integrated framework for environmental and cost assessment for building renovation with an analysis of possible uncertainty sources related to the building life cycle. Multi-objective robust optimization is then carried out to identify the optimal renovation solutions. Life cycle cost analysis (LCCA) and life cycle assessment (LCA) are used for assessing the economic and environmental impacts of buildings. To alleviate the burden of time-consuming conventional uncertainty quantification, surrogate modeling with Polynomial chaos expansions (PCE) is used. To identify the most optimal solution, robust optimization is carried out using non-dominated sorting genetic algorithm II (NSGA-II).Four studies are conducted using the developed methods. The first study provides the insights into the most influential parameters in building renovation. The uncertain parameters within the integrated LCA&LCCA for building renovation are described and global sensitivity analysis using Sobol’ indices is applied. The results of the assessment show that the heating system is the most influential parameter and should be prioritized in building renovation. The second and third studies are performed to identify optimal renovation scenarios with conventional and bio-based renovation solutions. The results show that the currently promoted deep renovation scenario is not optimal when using conventional materials. On the contrary, it leads to higher costs and GHG emissions and can increase risk for overheating during summer months. When considering bio-based materials, the provided solution is leading to the maximum possible insulation thickness. Both studies confirm the importance of the fossil heating system replacement shown in study one.Finally, to evaluate the applicability of the methodology, robust optimization is applied to the building-representatives from all the construction periods in Switzerland that currently require renovation. The results of this fourth study confirm the previously identified results. In the end of the thesis, the conclusions from the four studies are summarized and general recommendations with regards to the optimal and robust renovation solutions are provided for policy-makers.