Effects of retro-reflective and angular-selective retro-reflective materials on solar energy in urban canyons

Mattia Manni,Marta Cardinali,Gabriele Lobaccaro,Francesco Goia,Andrea Nicolini,Federico Rossi

doi:10.1016/j.solener.2020.08.085

Mattia Manni, Marta Cardinali + Show 4 more

Open Access

https://doi.org/10.1016/j.solener.2020.08.085

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Abstract

The study deals with the application of retro-reflective (RR) and angular-selective retro-reflective (AS-RR) coatings on surfaces (i.e. the street ground and the south-exposed façade) within the urban canyon. Solar analyses were conducted at different latitudes (Oslo, Milan, and Cairo) by varying the urban canyon height-to-width ratio (H/W) to determine the variation in solar irradiation absorbed by north and south façades. Both summer and winter conditions were considered, and up to five material patterns (one reference case and four enhanced scenarios) were investigated for each combination of latitude and height-to-width ratio values. A validated Monte Carlo-based numerical model was used to conduct full-ray tracing analyses and to simulate the behavior of these coatings. The outcomes allowed the development of guidelines for the adoptions of RR and AS-RR materials in different scenarios. It was demonstrated that RR and AS-RR materials applied to the street performed better in low-density urban environment (H/W ≤ 0.5) with a consequent increase of the solar energy gains on the north façade by up to 15%. Employing RR and AS-RR materials on the south-exposed façade showed greater effectiveness on high-density urban canyon (H/W ≥ 2.0) and reduced by up to −8% the solar irradiation absorbed by the façade.

Highlights

Urban morphology and materials properties play a relevant role in assuring a healthy and comfortable living environment (Santamouris et al, 2015; Zhou et al, 2016), especially because the recent growth of the population living in cities has caused an increase in the densification of the urban pattern (United Nations, 2014)
The same was observed for the north-exposed façade. This behavior is due to the var iations in the geometry of the sun: in summer, the sunrays were almost parallel to the façade in the Southern zone, while in winter were lower above the horizon
The greatest irradiation absorbed (Irrabs) values for each latitude were observed on the façades overlooking wider urban canyons (UC) (H/W = 0.5)

Summary

Introduction

Urban morphology and materials properties play a relevant role in assuring a healthy and comfortable living environment (Santamouris et al, 2015; Zhou et al, 2016), especially because the recent growth of the population living in cities has caused an increase in the densification of the urban pattern (United Nations, 2014). Such a growth can lead to several climate-related issues amongst which the most documented is the so-called Urban Heat Island (UHI) effect (Rahman et al, 2017; Xu et al, 2018). Surface treatments and building coatings are demonstrated to impact on the urban microclimate, exploiting materials with a high solar reflectance in the visible range and high infra-red (IR) emissivity allows one reducing surface and air tempera tures, lowering both energy use for cooling and electricity energy peaks,

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