A Multidimensional Optimization Approach to Refurbishment Design on a Multi-Building Scale

European countries face a large challenge in retrofitting their aging building stock, which they need to embark on, in order to reach European Union (EU) energy and emission reduction targets. Despite significant policy interventions, refurbishment rates remain low and the refurbishments that are carried out often do not meet the energy savings targeted by the EU, for example nearly Zero-Energy Building standards (nZEB). One of the key reasons for the lower than expected energy savings is that current refurbishment approaches tend to focus predominantly on energy efficiency improvements for individual buildings. The integrated energy systems perspective that can be leveraged at a multi-building scale – and is related to possible interactions between building sizes, scales, and the different systems – is not taken into consideration in most refurbishment concepts. The result are suboptimal renovation solutions which do not reach the full energy demand reduction potential of the refurbished building(s).This paper introduces a methodology for a tool that aims to develop economically and environmentally optimal nZEB refurbishment concepts for multi-building scale refurbishment actions. Increasing the scale of a refurbishment from a single building to a multiple building, or even a building portfolio, will allow to generate economies of scale (both for solution and workforce cost) and facilitate the integration of renewable energy generation. The tool applies the Lifecycle Assessment (LCA) and Lifecycle Cost Assessment (LCC) methods, which makes it possible to optimize refurbishment concepts, both with respect to economic and environmental criteria. Thanks to a multidimensional optimization approach, based on an evolutionary algorithm that can automatically find the Pareto-boarder for a given design space, Pareto-optimal refurbishment concepts are generated. Refurbishment options presented this way can help housing companies prioritize refurbishment needs and actions in their building portfolios, as well as evaluate and select between different refurbishment approaches in line with overarching targets