Future climate resilience of energy-efficient retrofit projects in central Europe

This study assesses the performance of buildings affected by climate change under future climate predictions for three time-periods until the end of the 21st century. Objects studied are residential multi-storey buildings, originally built before 1970 and retrofitted during the last decade. A total of four actual retrofit projects, as they were performed, in Denmark and Germany were assessed in their initial and retrofitted stage. The investigation assessed indoor thermal comfort, heating energy demand, heating peak loads by means of building performance simulations. Further, hygrothermal simulations were used to test the performance of constructions in the thermal building envelope. Climate data sets employed composed of a set of nine weather files per location, accounting for non-extreme and extreme cold and warm conditions divided into 30-year periods. The results show for all retrofitting measures a decrease of energy consumed for space heating. Due to the improved building airtightness and thermal conductivity of the building envelope constructions, sizing of heating systems and terminal devices was minimised accordingly. Similar paradigms show for periods closer to the end of the century, as the annual heating energy demand decreases gradually. An increase in summer thermal discomfort towards the end of the century was observed in all study objects, especially during extreme hot summer-periods thermal discomfort is ubiquitous. The German case studies showed that passive measures to decrease local discomfort are insufficient during extreme periods with increasing thermal discomfort towards the end of the century. The realisation of highly insulated thermal envelopes yielded immense overheating issues for the German future climate predictions. The majority of initial thermal envelope constructions showed vulnerabilities for moisture related issues within future climate scenarios. Most retrofitted elements are predicted to withstand climate change without high risk for mould growth. This mainly bases on the material selection which is crucial along with a thorough hygrothermal assessment for ensuring a resilient building design under the uncertainties of future climate.The impacts on building energy use, indoor comfort and hygrothermal performance influenced by climate change, for future climate predictions until the end of the 21st century were assessed for four case studies. The long-term performance of multi-storey dwellings located in Denmark and Germany, originally built before 1970 and retrofitted during the last decade were evaluated. Policy makers around the world, realize the importance of climate change and are taking action. Buildings within the European Union contribute to around 40% of the overall energy use, while 75% of the existing building stock is energy inefficient. Therefore, it is only natural that retrofitting the building stock poses a great potential for energy savings. Nevertheless, future climate holds uncertainties for the development of the heating energy use, indoor thermal comfort as well as moisture safety of the constructions facing the exterior. As extreme events are predicted to become more intense and frequent, building design should be tested for future climate resilience in the early design stages. This study provides a workflow for the assessment of building retrofits under future climate scenarios and conclusions based on the findings of the case study are drawn. The results of the case study showed, that thermal discomfort due to overheating is gradually increasing towards the end of the century, suggesting that active cooling and ventilation systems are gaining importance to guarantee a comfortable indoor environment during warm periods. Additionally, the heating energy demand was effectively lowered in all cases from the initial to the retrofitted building. Over the assessed 30-year periods, a downward trend in heating energy demand was seen, resulting in lower energy use for heating by getting closer to the end of the century. Similar paradigms were explored for the building heating peak loads which decreased and a lower frequency of high heating peaks was obtained for the future periods. The analysis of moisture safety showed that moisture related issues in future climate scenarios are getting more likely, as temperatures becoming more favourable for mould growth due to global warming. In order to design building retrofits resilient to future climate uncertainties, this study showed that a thorough assessment has to be carried out. Moreover, constructions have to be designed with great care to withstand higher temperatures and more frequent weather extremes. The study showed, that passive measures to mitigate overheating and summer discomfort are not sufficient during summer and extreme warm events. System design according to typical weather scenarios showed an underestimation of cold weather extremes. Therefore, accounting for cold and warm extremes should be considered when dimensioning building and zone heating, cooling and ventilation systems. A total of 13 future climate predictions from several institutes with different intensities were used for synthesizing the employed future weather files. Sets of nine weather files per location, representing non-extreme as well as extreme cold and warm conditions divided into three 30-year periods. Building performance simulations with EnergyPlus and hygrothermal simulations with WUFI were carried out in order to assess indoor thermal comfort, energy use and moisture safety. All simulations were executed for the non-retrofitted initial buildings as well as the retrofitted buildings to allow for comparison. Indoor thermal comfort was assessed by analysing if the operative indoor temperature was within a comfort band of 6 °C width, at a minimum of 20 °C (EN 15 251). The building heating energy demand was compared over the different weather scenarios and time periods, further a statistical analysis of the hourly building heating loads was given. To assess the zone heating device design, zone heating peak loads were compared. Moisture safety was evaluated by means of temperature and relative humidity measurements, as well as mould index and mould growth rate according to the Viitanen VTT model