Assessment of combined passive cooling strategies for improving outdoor thermal comfort in a school courtyard

Both artificial shading and evaporative cooling have proven to be effective strategies for improve outdoor thermal comfort. However, their combined effect on microclimates or thermal sensations has rarely been investigated, hindering our understanding of the interactions among cooling strategies. In this study, we tested the performance of sun sails with different coverage ratios, mist-spray systems with different nozzle arrangements, and a combination of these two strategies for cooling a kindergarten courtyard using validated ENVI-met models. Among the strategies, we found that the shade + mist strategy is the most effective and can reduce the physiological equivalent temperature (PET) by up to 14.43 °C and heat stress levels by 2–3 categories in originally exposed areas. This was followed by the sun sail shading strategy. The mist-spray system had a relatively weak cooling effect. The cooling effects of sun sails increased with coverage ratios and mounting heights, whereas the spatial cooling distribution of mist spraying was mainly determined by wind rather than by nozzle arrangements. In addition, we found that shading can enhance the cooling effect of mist spraying in terms of air temperature, but reducing its cooling effect in terms of the mean radiant temperature. Our results highlight a great potential of comprehensively using multiple strategies to improve outdoor thermal comfort, and provide a design basis for enhancing thermal comfort in similar school courtyards in Hunan Province in China.