An inverse approach to identify selective angular properties of retro-reflective materials for urban heat island mitigation

Abstract

This work presents the preliminary stages of a wider study aiming at assessing the potentials of retro-reflective (RR) materials to mitigate urban heat island effects. Th study herewith reported is based on an inverse approach, which originates from the evaluation of the solar irradiation incident on urban surfaces (i.e. façade, roof, and paving) and leads to the identification of the optimal angular properties required to activate such a material. The solar radiation geometry and the solar irradiation collected by the south-exposed vertical and the horizontal surfaces, were assessed by solar dynamic simulation tools. Furthermore, the angular distribution of the solar direct irradiation component and the direct to global solar irradiation ratio were estimated. The analyses were carried out for nine locations between Oulu (Finland) and Doha (Qatar), with an increment of 5° latitude between two locations.The results demonstrate that the application of RR materials to horizontal surfaces can always be effective, whereas when applied on the vertical surface, the solar geometry influences to a much greater extent the performance of these materials. The main findings of this study show that the selective angular properties of an ideal RR material should be in the angular interval between 25° and 55° and between 30° and 90°, in case of vertical surfaces and horizontal surfaces, respectively. Best practices related to the application of RR materials and the activation of their selective angular properties in different climate zones are also reported.

Effects of Orientations, Aspect Ratios, Pavement Materials and Vegetation Elements on Thermal Stress inside Typical Urban Canyons

“…Future development of the study could include an economic evaluation to estimate the financial impact of each specific intervention and its relation with indoor energy consumption. Furthermore, analyses on the use of novel cooling materials for pavement such as retro-reflective could be undertaken [112,113,114]. Finally, another potential intervention in terms of cooling effect can be the application of vegetation elements on the building envelope such as green façades on existing and new buildings [115,116].…”

Optimized Cool Coatings as a Strategy to Improve Urban Equivalent Albedo at Various Latitudes

“…The virtual clones implemented by Manni et al [40] were utilized in this study. The RR materials were characterized and modelled; then, the angular ranges of activation identified by Manni et al [38] for each climate zone were applied to these. In this manuscript, data used for modelling the virtual clone of RR materials are reported, while a more complete description of the protocols applied for the characterization, and the characterization results themselves can be found in the study by Castellani et al [47].…”

“…RR surfaces may contribute to increased glare-related issues and light pollution, while reducing solar loads in winter. Hence, Sakai et al [37] and Manni et al [38] implemented an angular-selective behavior on RR materials to enhance their effectiveness. The concept behind the angular-selective retro-reflective (AS-RR) materials is to have surface treatments that are responsive to the solar radiation stimulus and are capable of modifying their optical properties depending the angle of incidence of the sunrays (Figure 1).…”

“…The concept behind the angular-selective retro-reflective (AS-RR) materials is to have surface treatments that are responsive to the solar radiation stimulus and are capable of modifying their optical properties depending the angle of incidence of the sunrays (Figure 1). Methodologies to define their angular range of activation were investigated by Manni et al [38]. Numerical analyses estimated a reduction of solar irradiation absorbed by the façade of up to 8% due to the application of AS-RR instead of conventional coatings [39,40].…”

High-reflective Mulching Membrane for a Sustainable Development: Monitoring Campaign

“…Also, they can contribute to lowering buildings' energy consumption throughout the year [15]. However, there are also some issues related to the exploitation of high-reflective coatings in densely built environments such as the increasing of inter-building reflections [16][17][18]. It generally led to the increment of solar irradiation amounts trapped in the urban corridors, thus nulling the cooling effects from high-reflective materials.…”