Optimizing retrofit strategies for terraced dwellings: ConstrucThor case study

Since 85% of European buildings were built before 2000 and amongst those 75% have a poor energy performance, increasing their energy efficiency is a crucial part of legislative strategies enforced by European policymakers. This research aims to address the challenge of enhancing efficiency in existing buildings and quantifying the actual improvement, specifically focusing on 1920s terraced houses typically found in Belgium and Western European countries.

These dwellings often have heritage-protected facades, limiting the possibilities of refurbishment. Therefore, the presented study uses a parametric approach to optimize retrofitting strategies for building fabrics comparing two opposing occupancy profiles. These renovation strategies considered partial refurbishment scenarios (e.g. replacement of windows or insulation of different elements), which both lower the energy demand and improve the thermal comfort of inhabitants. For this purpose, building energy simulations are employed and carried out using the IDEAS library in Modelica.

Simulation results show the impact of renovation scenarios on the heating demand and a decreasing trend in requirements. However, despite these perceived benefits, energy savings were not always substantial, and occupant behaviour remained a key factor in the actual energy performance. Thus, the results highlight the necessity of integrating both renovation strategies and occupant engagement measures to achieve optimal energy-efficient outcomes.

On top of the opposing occupant behaviours affecting the energy savings in different scenarios, they also affected the interpretation of energy performance KPIs. Evaluating energy performance through the heat transfer coefficient based on measured data revealed a more comparable assessment of energy efficiency across both occupancy profiles than relying solely on energy use. However, for practical implementation in energy labelling, key challenges remain.

Considering the trade-off between implementing different, or even partial, refurbishment scenarios this work is particularly relevant in the context of European climate policy, as it addresses the urgent need for effective strategies to renovate the existing building stock.

The selected case study is part of the ConstrucThor testing facility and unlike original dwellings from that era, offers a well-documented database and the opportunity for step-wise practical implementation. Moreover, it allows for future on-site measurements and comparisons with the outputs generated by the digital twin developed in this work. The ongoing collaboration in the construction process also provided valuable data for comprehensive modelling, reinforcing the faithful representation of the as-built building and the digital twin.