Methodological Perspectives to Evaluate Combined Indoor and Outdoor Thermal Comfort and Improvement Measures in Vienna's Urban Heat Islands

Abstract

The progression of climate change and the resulting amplification of the Urban Heat Island (UHI) effect poses significant challenges on metropolitan areas like Vienna. Past research has often separately examined thermal comfort on indoor and outdoor spaces and the increased energy demand for cooling caused by UHIs. Since cities and their heat and energy dynamics are interconnected entities, where buildings and open spaces are inseparable, the occupant’s wellbeing is not only dependent on indoor spaces but also strongly influenced by outdoor conditions. The objective of this research is to analyze the future thermal comfort in Vienna's heat-vulnerable areas introducing and comparing three holistic thermal comfort indices. The indices innovative aspect lies in its comprehensive integration of existing standards and combination of indoor and outdoor thermal comfort parameters to create a unified framework for assessing urban thermal well-being and its required building cooling demand. We transform general future climate projections for Vienna to site-specific urban microclimate data using a digital urban representation of buildings and their environment as input for an Urban Weather Generator. To assess the indoor thermal comfort and cooling energy demand through the indices, detailed building-level energy simulations are conducted in EnergyPlus through Grasshopper-Honeybee, employing the same urban model as context along with relevant building information on construction and use. The results provide insights into the sensitivity and vulnerability of the case study neighborhood to climate change and Urban Heat Island effects. Additionally, they highlight the varying effectiveness of the proposed indices in capturing the overall heat stress experienced by the local population in their daily lives and the methods ability to illustrate the impact of mitigation strategies.