Experimental Analysis of the Effect of Geometry and Façade Materials on Urban District’s Equivalent Albedo

Elena Morini,Andrea Nicolini,Federico Rossi,Andrea Presciutti,Mirko Filipponi,Beatrice Castellani,Elisabetta Anderini

doi:10.3390/su9071245

Abstract

Urban Heat Island (UHI) is influenced by urban form, geometry, and the properties of surfaces. Retroreflective (RR) materials have been proposed as a countermeasure to UHI, thanks to their optical property of reflecting most of the incident solar energy back towards the same direction. In this paper, the effect of RR materials on urban districts was investigated. They were applied on building façades of urban districts with different urban forms and orientations. To this aim, an experimental model resembling urban districts with different geometries was built and RR materials on vertical surfaces were tested and compared to conventional construction materials with similar global reflectance. The trend of the instantaneous albedo was monitored during the day and a new parameter called “equivalent albedo” was used to demonstrate the effectiveness of the RR materials. The comparative analysis shows that the RR façades lead to an increase of the equivalent albedo for all of the investigated urban patterns. For a block pattern, the equivalent albedo increase is equal to 3%, while for canyon patterns it is equal to 7%. Results of energy evaluations show that the energy savings obtainable with the use of RR materials is comparable to the values of anthropogenic heat emissions in residential areas.

Highlights

The Urban Heat Island (UHI) effect is a phenomenon that occurs in urban areas
The comparative analysis shows that the retroreflective materials (RR) façades lead to an increase of the equivalent albedo for all of the investigated urban patterns
The equivalent albedo increase is equal to 3%, while for canyon patterns it is equal to 7%

Summary

Introduction

The Urban Heat Island (UHI) effect is a phenomenon that occurs in urban areas. It is due to build environment and human activities that make cities several degrees warmer than rural and suburban areas [1]. Studies have analysed different strategies to introduce in urban planning tools in order to address climate change and subsequent risk disaster [42] Such instruments are based on three pillars: energy efficiency (EE), renewable energy sources (RES), and greenhouse gas emission reduction. Solar energy technologies have already been presented as a good opportunity Due to their demonstrated ability to reduce urban albedo and their cooling potential in terms of energy reflected and sent beyond the urban canyon [38], RR materials could be considered a mitigation and adaptation strategy of climate change to add to the kit of urban planning tools. The results show that RR materials increase the equivalent albedo for all of the investigated urban patterns with a major effect on canyon schemes

The Test Field

Findings

Conclusions