Optical analysis of glass bead retro-reflective materials for urban heat island mitigation

Yuan, Jihui; Emura, Kazuo; Sakai, Hideki; Farnham, Craig; Lu, Sifen

doi:10.1016/j.solener.2016.03.011

Cited by 42 publications

(18 citation statements)

References 23 publications

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“…Retroreflectance can be assessed by (A) measuring retroreflection with coincident light source and light detector, such as those in a fiber spectrophotometer [20][21][22]; (B) measuring bi-directional reflectivity, or at least the angular distribution of reflected light, with a goniometer [23][24][25][26][27][28][29][30][31]; or (C) using calorimetry to gauge directional-hemispherical solar reflectance from temperature rise in the sun, then subtracting from this value directional-hemispherical solar reflectance measured in a spectrophotometer with fitted with an integrating sphere [32][33][34][35]. Method C works because perfectly retroreflected light escapes through the inlet port of the integrating sphere.…”

Section: Measurement Of Retroreflectancementioning

confidence: 99%

Design, characterization, and fabrication of solar-retroreflective cool-wall materials

Levinson

Chen

Slack

et al. 2020

Solar Energy Materials and Solar Cells

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Raising urban albedo increases the fraction of incident sunlight returned to outer space, cooling cities and their buildings. We evaluated the angular distribution of solar radiation incident on exterior walls in 17 U.S. climates to develop performance parameters for solar-retroreflective walls, then applied firstprinciple physics and ray-tracing simulations to explore designs. Our analysis indicates that retroreflective walls must function at large incidence angles to reflect a substantial portion of summer sunlight, and that this will be difficult to attain with materials that rely on total internal reflection. Gonio-spectrophotometer measurements of the solar spectral bi-directional reflectivity of a bicycle reflector showed little to no retroreflection at large incidence angles. Visual comparison of retroreflection to specular first-surface reflection for four different retroreflective safety films using violet and green lasers suggest their retroreflection to be no greater than 0.09 at incidence angles up to 45°, and no greater than 0.30 at incidence angles of up to 70°. Attempts to produce a two-surface retroreflector with orthogonal mirror grooves by cutting and polishing an aluminum block indicate that residual surface roughness impedes retroreflection. Ongoing efforts focus on forming orthogonal surfaces with aluminized Mylar film, a material with very high specular reflectance across the solar spectrum. We investigated (1) folding or stamping a free film; (2) adhering the film to a pre-shaped substrate; and (3) attaching the film to a flat ductile substrate, then shaping. The latter two methods were more successful but produced imperfect right angles.

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Section: Measurement Of Retroreflectancementioning

confidence: 99%

Design, characterization, and fabrication of solar-retroreflective cool-wall materials

Levinson

Chen

Slack

et al. 2020

Solar Energy Materials and Solar Cells

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“…It was concluded that the glass bead-type RR materials are more effective when the incidence angle of sunlight is low. Several RR materials using glass beads with refractive indices of 1.5 and 1.9 have been developed by a research [16]. The reflective directional characteristics of these developed glass bead RR materials were investigated using optical apparatus in the laboratory.…”

Section: Introductionmentioning

confidence: 99%

Performance of Retro-Reflective Building Envelope Materials with Fixed Glass Beads

2019

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Urban heat islands (UHI) are growing in size and intensity, which is partly attributable to the large amount of anthropogenic waste heat. Moreover, heat emitted from building exterior walls accounts for a large portion of the total anthropogenic waste heat. Thus, strategies and technologies for preventing the emission of heat from building exterior walls are being pursued by researchers worldwide. Amongst these technologies, the potential of use of retro-reflective (RR) materials instead of diffuse highly reflective (HR) materials applied to building envelopes for UHI mitigation is being studied widely. However, RR materials haven’t been applied to building envelopes in practice due to their unproven weather resistance. In order to develop RR materials with high weather resistance for application to building envelopes, two types of micro glass beads with different refractive indices (1.5, 1.9) and five different colors of base layers were evaluated in this study. Their RR performance was measured by optical experiment and compared to two types of RR sheets commercially available in Japan. The results showed that the glass bead RR samples with a refractive index of 1.9 had much higher retro-reflectivity (better RR capacity) compared to those with a refractive index of 1.5.

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“…Strong efforts have been made to investigate innovative cool materials such as retroreflective materials (RR) [32][33][34], thermo chromic pigments [35], and directional reflective materials [36].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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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.

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Optical analysis of glass bead retro-reflective materials for urban heat island mitigation

Cited by 42 publications

References 23 publications

Design, characterization, and fabrication of solar-retroreflective cool-wall materials

Design, characterization, and fabrication of solar-retroreflective cool-wall materials

Performance of Retro-Reflective Building Envelope Materials with Fixed Glass Beads

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

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