Spray optimization to enhance the cooling performance of transparent roofs in hot-humid areas

Spray cooling was regarded as an effective technique for outdoor cooling but its application to transpar-ent roofs is still limited, owing to the absence of an explicit system design. In this study, the influence of three spray nozzle types with six modes on the spray cooling performance of glass curtain samples that belong to one transparent roof was first determined by a test device. Thereafter, the spray system, designed based on the selected nozzles, was assembled on the transparent roof inside a laboratory build-ing. The thermal property moderation of the roof and indoor environment and the corresponding cost effectiveness generated by this system were further assessed. The results revealed that the spray system could effectively cool glass curtains. Compared to water-spray, mist-spray can achieve a better cooling and shading effect by shaping more dispersed and smaller droplets that effectively enlarge the contact areas with the targeted surface. The exterior glass surface temperature generated by the mist-spray was 8.0 degrees C lower than the surrounding air temperature, and the solar transmittance ratio decreases up to 14% compared to dry conditions. Field experiments further revealed that the mist-spray system could noticeably mitigate indoor overheating and further eliminate thermal stratification among different floors. Air temperature 10 cm below the interior roof surface and black-globe temperature of 1.5 m higher on the third floor demonstrated a decrease of up to 10 degrees C and 8.9 degrees C, respectively. The air temperature gap between these three floors decreased to approximately 4 degrees C. Furthermore, owing to the mist-spray sys-tem, a total of 24.36 kW center dot h of energy saving was realized during the experiment and the general infras-tructure investment could be recovered within 6.26 years. This study is of great significance for promoting the scientific practice of the mist-spray technique to enhance the building thermal performance.(c) 2023 Elsevier B.V. All rights reserved.