Investigating the effect of emissivity of fully glazed façade on outdoor thermal comfort in low to high urban canyon ratios

• Emissivity of glazed facades significantly influences the outdoor thermal comfort. • Emissivity of 0.84 increases MRT by up to 6°C and PET by up to 2°C on summer days. • Emissivity of 0.07 improves summer microclimates but slightly worsens winter ones. • Low-emissivity façades with higher H/W ratios improve summer outdoor comfort. Growing concerns about urban heat stress highlight the need to enhance outdoor thermal comfort (OTC) in both existing and future urban environments. Fully glazed façades are increasingly common in Australian architecture, yet their impact on outdoor microclimates remains underexplored. This study investigates the influence of glass emissivity (0.84, 0.5, 0.3 and 0.07), canyon orientation (every 30°), and aspect ratio (1:4 to 12:1) on Mean Radiant Temperature (MRT) and Physiological Equivalent Temperature (PET) in the urban context of Adelaide, South Australia. Using a validated model in ENVI-met (v5.6.1), 168 simulations were conducted for the city’s hottest and coldest days in 2024. The results are as follows. (1) Higher-emissivity façades increase MRT and PET, particularly during summer. MRT was the most sensitive parameter to emissivity changes, with seasonal variation influencing comfort levels (18 °C < PET < 23 °C). In winter, high-emissivity façades improved OTC, while in summer, low-emissivity materials enhanced outdoor comfort. (2) Canyon orientations of E-W and ESE-WNW resulted in the highest MRT and PET values. (3) In summer, the H/W ratio of 12:1 consistently resulted in the coolest thermal conditions compared to other canyon ratios in every canyon orientation, indicating greater potential for heat mitigation. Conversely, lower H/W ratios produced higher PET values in winter, increasing OTC. These findings demonstrate that selecting appropriate façade emissivity is complex, but applying low-emissivity materials can improve OTC in summer in all H/W ratios and canyon orientations scenarios. The results underscore the importance of façade materials, particularly emissivity, together with canyon orientation across low to high urban canyon ratios, in shaping outdoor microclimates, and offer valuable insights for climate-sensitive urban design.