Tackling the interplay of occupants' heating practices and building physics: Insights from a German mixed methods study

The European Union seeks to reduce CO2 emissions in the residential sector by introducing ever stricter energy efficiency standards for newly constructed projects and energy-oriented modernisations. Despite these regulatory efforts, the actual energy consumption significantly deviates from these ambitious goals. Based on this observation it will be argued that it is possible to explain this deviation by putting the focus on users' practices rather than solely focusing on building physics. In order to determine the impact of building physics and user behaviour on heating energy consumption separately, a mixed methods approach was developed. Actual heat energy consumption data of flats in two German refurbishment areas was collected and semi-standardized interviews with the inhabitants of 80 of these households were conducted. We use qualitative data to identify households' practices related to energy consumption and measure the relative impact of these practices with quantitative data. Aside from the building physics, we can observe that preferences for thermal comfort as well as ventilation practices have the strongest influence on households' heating energy consumption after retrofitting. Based on these findings, it is argued that future policy measures should focus on user-technology interface design rather than solely focusing on ever stricter efficiency standards.