Understanding the impacts of space design on local outdoor thermal comfort: An approach combining DepthmapX and XGBoost

• A new paradigm is introduced to understand design and outdoor thermal comfort. • XGBoost is deployed to accelerate UTCI simulation. • Visibility, connectivity, and building height are the three most important indexes. • The relationship between space design and outdoor thermal value is not linear. • An improved understanding of community-scale cool spots for urban designers. Researchers and designers alike are keen to explore proper space designs to alleviate the heat waves. A niche research area of this type focuses on the smaller scale, local communities to achieve the so-called ‘cool spots’ for residents. However, despite the momentum gained so far, it remains unclear what the key design elements are (e.g., space orientation, aspect ratio, or building density) and how they interact with each other in impacting outdoor thermal comfort (OTC), particularly in some complex, vertical ‘spots’. This research aims to provide an improved understanding of cool spot reasoning by proposing a new paradigm to engage DepthmapX (an analytic tool for urban spatial configuration), XGBoost (a machine learning tool), and on-site verification. By implementing the paradigm on a university campus in Hong Kong for the case study, it was discovered that Percentage of View (PV), Average Height Index (AHI), and Connectivity (CON) are the three most influential factors leading to the formation of a ‘cool spot’. DepthmapX can not only help quantify space designs but also help translate the indexes back to real-life space design options. The XGBoost can help better interpret the pathway from different space design indexes to different OTC but more explainable causal relationships are desired. This research advanced our understanding of the impacts of different space designs on OTC and provided references to designers in achieving OTC in smaller--scale, local communities. It also opens a new avenue to understand the causal relationships in a more detailed and explainable fashion.