Glazing Façade Design for Energy-Efficient Buildings, Improved Thermal Comfort and UHI Mitigation in Dense Urban Center

With continued urbanization and the increasing occurrence of extreme weather events, urban areas have become more vulnerable to environmental and infrastructural challenges than in the past. A key concern in this context is the Urban Heat Island (UHI) effect. It is primarily driven by two factors: solar irradiation— which includes both direct sunlight and indirect reflections or re-radiation from building facades and urban surfaces—and anthropogenic heat, such as emissions from vehicles and waste heat from HVAC systems. Among these, glazing façade play a pivotal role by interacting with solar radiation, emitting surface heat, and contributing anthropogenic heat through HVAC systems, collectively influencing the surrounding outdoor microclimate. The situation is further intensified by certain material choices and designs—such as low-emissivity (Low-E) windows—that are intended to enhance building energy efficiency and indoor thermal comfort but can inadvertently increase solar reflection and create "heat traps" in the surrounding area. To address the challenges posed by current glazing façade designs and to enhance energy efficiency, thermal comfort, and UHI mitigation in a coherent manner, we propose several innovative alternatives, including Low-E/ATO co-coated double-pane windows, retro-reflective coated windows, translucent windows, and window-integrated greenery or gardens. These glazing façade designs are then tested both experimentally and numerically and benchmarked against other commonly used glazing systems. By examining key performance indicators from multiple perspectives—such as Energy Use Intensity (EUI), Total Solar Irradiance (TSI), and the Universal Thermal Comfort Index (UTCI)—we identify the most suitable design and further derive the optimal design strategy. The results show that with newly proposed Low-E/ATO co-coated double-pane window, modelled urban area could achieve the similar energy performance as the highly reflective Low-E window, but drastically reduce the adjacent ground's TSI (up to 25%) and therefore improve the outdoor thermal comfort (some locations up to 3.2°C UTCI decrease).