HeatResBuild

The heat stress in buildings is continuously increasing due to ongoing climate change and the growing urban sealing. However, the current state of research still contains numerous uncertainties regarding the assessment of overheating in buildings. There is no internationally standardised method for evaluating indoor overheating in residential buildings. Even the applicable German standard, DIN 4108-2, does not consider certain relevant factors in its assessment of summer heat protection through simulation methods. Furthermore, most scientific studies focus on case studies for specific locations without conducting spatial comparisons between urban and rural areas or between different regional climates within a country. The interaction between heat adaptation measures in open spaces and buildings also remains insufficiently researched, as do the reasons for the observed slow implementation of climate change adaptation measures.

The HeatResBuild project addressed these critical research gaps in collaboration with the IÖR research projects HeatResilientCity, Klimakonform, and PoliMod and developed corresponding solutions.

The HeatResBuild project address the following four key research questions related to building overheating:

1. Which indicators are suitable for assessing heat stress in buildings, both scientifically and in practical applications?
2. Is a building that is heat-resilient in Dresden also resilient in other German cities, such as Hamburg or Stuttgart? To what extent does the building’s location—whether in the city centre or the surrounding area—affect indoor overheating?
3. What impact do heat adaptation measures in open spaces have on the intensity of indoor overheating in buildings?
4. How can the implementation dynamics of adaptation measures against summer heat be significantly increased?

In the HeatResBuild project, heat stress in residential buildings was examined from multiple perspectives, focusing on the following key areas:

1. Analysing the cooling effects of heat adaptation measures in open spaces on heat stress in residential buildings
   Using a modelling chain that combined microscale urban climate simulations (conducted by TU Dresden) with building simulations (see figure below), the project assessed the extent to which cooling effects from heat adaptation measures in open spaces influence heat stress inside residential buildings. The key findings have been summarised in easily understandable German-language factsheets:
   • Full report: https://doi.org/10.5281/zenodo.8094182
   • Summary: https://doi.org/10.5281/zenodo.8143329
   • In-depth scientific analyses have been published in an Open Access journal: https://doi.org/10.1016/j.crm.2024.100615
2. Impact of regional climate variations and the urban heat island effect on building overheating
   The influence of different regional climates and urban heat islands on indoor overheating was analysed using meteorological data from the German Weather Service over the past 30 years for four locations across Germany. For each site, an average summer over the last 30 years was determined, along with projections for an average summer 30 years into the future. TU Dresden also simulated the urban heat island effect to assess how indoor heat stress varies between urban and rural areas. Thermal building simulations were then conducted to examine the impact of these meteorological datasets on overheating. The findings indicate significant local variations in urban climates across Germany and highlight that certain building types, which are heat-resilient in suburban areas, may not necessarily be resilient in urban settings or in the future. This research was conducted in collaboration with the HeatResilientCity II project.
   • Key findings in German-language factsheets: https://doi.org/10.5281/zenodo.8143331
   • Scientific publication in an Open Access journal: https://doi.org/10.1016/j.cacint.2024.100163
3. Development of improved indicators for assessing heat stress in buildings
   Existing indicators for evaluating heat stress in buildings have limited reliability. Based on these, the project aimed to improve heat stress assessment by developing more precise scientific and practical indicators. A comprehensive literature review was also conducted to determine whether current scientific and practical knowledge is sufficient to link indoor heat stress to health impacts.
   • Practical indicator: In collaboration with HTW and the HRC II project, a practical indicator was developed to assess indoor heat stress and the effectiveness of heat adaptation measures using a five-level traffic light system. The evaluation was based on previous building simulations and indoor climate monitoring. This indicator provides a general assessment for interested citizens rather than experts and does not replace detailed planning or building simulations. After successful testing by Dresden and Erfurt city authorities, it was integrated into the HRC tool to assess the effectiveness of heat adaptation measures.
   • Scientific indicator set: This was developed based on the over-temperature degree hours method from DIN 4108-2 and expanded to include room usage and human adaptation to changing summer temperatures. This indicator set is freely available in an English-language book: https://doi.org/10.1515/9783111318653-004.

A further literature review examined whether the scientific indicator set could reliably link indoor heat stress to health risks. The main finding was that existing knowledge on how high indoor temperatures affect individuals’ perception of heat stress and related health issues is too fragmented to be incorporated into an indicator at this stage. Research in this area is ongoing. Key insights can be found in Dresden’s Heat Handbook, co-authored by the IÖR: https://doi.org/10.1515/9783111318653-004.

4. Understanding and improving the implementation dynamics of heat adaptation measures
   The implementation of heat adaptation measures in both open spaces and buildings remains slow in practice. To investigate the complex reasons behind this, particularly in the broader context of the Sponge City concept, the project aimed to develop an explanatory system model with input from practitioners.
   • Collaboration with BUND Dresden: Three three-hour modelling workshops were conducted with Dresden's Sponge City working group, which included representatives from various administrative departments and urban drainage services. Together, they developed a qualitative system model (Causal Loop Diagram) that visualises the challenges of implementing sponge city measures in Dresden. The workshops also served as a test to determine whether this method is suitable for public administration stakeholders. The findings are available upon request.
   • Collaboration with PoliMod: A Causal Loop Diagram, System Dynamics Model, and agent-based simulation model were created to analyse the motivation process behind implementing sponge city adaptation measures in residential areas. These models were validated with experts and public authorities and have been published in a high-ranking Open Access journal: https://doi.org/10.1016/j.jclepro.2024.142722.

• Fundamentals of Building Heat Stress Assessment in the Open Access book "Assessing the Overheating Risk of Buildings" (Target audience: engineers).
• Explainer video on the urban climate simulation–building simulation modelling chain: http://heatresilientcity.de/erklaervideo-modellkette/index.htm
• Further insights from the HeatResilientCity projects: http://heatresilientcity.de/ergebnisse/index.htm