Retroreflective façades for urban heat island mitigation: Experimental investigation and energy evaluations

• Published in: Applied energy 2015-05, Vol.145, p.8-20
• Main Authors: Rossi, Federico, Castellani, Beatrice, Presciutti, Andrea, Morini, Elena, Filipponi, Mirko, Nicolini, Andrea, Santamouris, Matheos
• Format: Article
• Language: English
• Subjects: Cool façade; Cool materials; Retroreflective materials; Urban canyon; Urban heat island
• ISSN: 0306-2619; 1872-9118
• DOI: 10.1016/j.apenergy.2015.01.129

•Retro-reflective (RR) materials are an effective strategy for mitigating UHI.•Optical properties of RR materials are assessed by a new experimental facility.•Angular distribution of reflected radiation is assessed during daytime.•RR component is treated as a diffusely reflected radiation by a reduction factor.•An algorithm evaluates the cooling potential of RR materials in urban canyons. The optimization of optical properties of buildings’ envelope and urban paving represents an important research field for reducing the urban heat island effect. The overheating of a surface exposed to sunlight can be reduced by improving solar reflectance. In this sense, several studies have demonstrated the positive effect of cool materials on UHI mitigation. In addition to traditional cool materials, retroreflective (RR) materials have been recently proposed for this application. The present paper aims at the assessment of angular reflectance of RR films for several inclination angles of solar radiation. To reproduce variation of solar radiation’s inclination during the daytime, an ad hoc experimental setup was designed and used. Characterization of RR materials when hit by solar radiation with different inclinations allows to assess their behaviour on daytime if used as novel urban coatings for mitigation of the UHI phenomenon. Measurement results are used as input for an original algorithm which allows to quantify cooling potential of RR materials in terms of energy reflected and sent beyond the urban canyon. The experimental characterization and energy evaluations showed that RR materials could be effectively applied as coatings on urban paving and building envelope, in order to reduce the circulating energy into the canyon.