Historic buildings to Positive Energy Buildings: a trilemma between energy efficiency, lifecycle carbon and architecture conservation.

Abstract

Heritage buildings define the distinctive character of many urban areas by creating continuity with the past and serving as a visual cultural reference. To ensure their continued use, these buildings must be adapted for better performance that demands energy retrofitting strategies while satisfying indoor environmental quality. Energy retrofit reduces CO2eq emissions in the operation phase but typically entails embodied carbon and is not always applicable to historic buildings that require architectural and cultural conservation. This study phrases it as a trilemma and aims to identify an optimal balance between increased energy efficiency and decreased lifecycle carbon when architecture conservation is acknowledged. The research is applied to a traditional fisherman’s cottage in the village on Howth Head, Ireland with an aim to make it a Positive Energy Building (PEB). First, the construction method and heritage value are investigated followed by an experimental U-value calculation to identify the intervention needs. Then, a range of retrofit strategies to increase the energy efficiency of the building, but sensitive to the architectural conservation agenda, are proposed. Furthermore, using the EnergyPlus simulation engine, the study analyses the implications of different building materials for thermal insulation, building façade and window retrofit, on the building’s operational energy performance. Finally, for each scenario, a lifecycle carbon analysis was applied to identify the optimal strategy when architecture conservation is considered. The best retrofit strategies for reducing operational carbon do not always decrease embodied carbon. Similarly, the optimal materials to be used to achieve the highest level of energy efficiency and reduced life cycle carbon to become a PEB do not adhere to architectural conservation objectives. Further analysis is undertaken to achieve a balanced strategy which can be adopted in similar conservation retrofit projects.