Techno-economic and environmental performance assessment of radiative sky cooling-based super-cool roof applications in China

Highlights: • Radiative sky cooling-based super-cool roof model was experimentally validated. • Super-cool coating enables to reduce roof surface temperature by over 43%. • Cooling electricity savings range from 42.9 to 97.8 kWh/(m²·yr). • Acceptable incremental cost is within 34.6–64.7 $/m² for 5-yr payback period. • Carbon emissions can be reduced by 24.6–56.1 kg/(m²·yr). Integrating radiative sky cooling materials into buildings as a super-cool roof strategy can be one of the most direct pathways to implement this passive cooling technology. Accordingly, this study conducts comprehensive assessments on techno-economic and environmental performance of super-cool roof applications in China by combining model development, experimental validation, and numerical modeling. A novel radiative sky cooling-based super-cool roof model was developed in which the full spectral selectivity of radiative cooling materials can be incorporated and the model was experimentally validated with root mean square errors below 4.69%, verifying its good accuracy. Field experiments with reduced-size modeling buildings in a hot and humid region revealed that radiative cooling roofs can effectively reduce rooftop and indoor air temperatures for heat removal. The validated model was used for evaluating super-cool roof applications in ten typical cities of China. The results show that the super-cool roof can achieve the sub-ambient temperature of 2.6 °C under the solar radiation of 950 W/m² in a hot and humid climate. Compared to the baseline of traditional roofs, the super-cool roof can reduce the maximum and average daytime roof temperatures by 24.8 °C (43.4%) and 10 °C (29%), respectively. Cumulative roof thermal transfer values can be decreased by 63.0–195.8 kWh/m² (78.5–148.2%) in cooling seasons. The annual electricity saving in hot cities ranges from 42.9 to 97.8 kWh/m² on average, in response to varying coefficients of performance. Super-cool roof induced maximum acceptable incremental cost falls within 34.6–64.7 $/m² and 55.36–103.52 $/m² for 5-yr and 8-yr simple payback periods, respectively. Besides, carbon emissions can be averagely reduced by 24.6–56.1 kg/(m²·yr). This study deeply elucidates the energy efficiency, economic feasibility and carbon neutrality potential of radiative sky cooling-based super-cool roof applications in China.