Abstract
The focus of this study is on the impact of solar radiation reflected from the building façade to a pedestrian. The possibility of using high-reflectance technology on building façades was evaluated by using a two-dimensional simple building façade model. The effectiveness of applying retroreflective materials to building façades was also evaluated in regards to avoiding adverse effects on pedestrians. The ratio of diffusely-reflected solar radiation to a pedestrian from a given floor is proportional to the ratio of the angle of the reflective arc reaching a pedestrian from that floor to the angle of the reflective arc from the entire building. Specular reflection of solar radiation from the building façade is calculated by ray-tracing method corresponding to solar angle θ. In Japanese cities that are located at mid-latitudes, applying high-reflectance technology to a building façade at the fourth floor and above produces reflection of solar radiation that does not have adverse effects on pedestrians. High-reflectance technology is applicable on building façades above the fourth floor at any latitude, if we ignore a negative effect, since incident direct solar radiation to the building façade around noon is small at low latitude. Retroreflective material was considered for use on building façades below the third floor in order to avoid impacts on pedestrians from the reflection of solar radiation.
Highlights
IntroductionAs a measure to counter the urban heat island phenomenon, high-reflectance technology, such as cool roofs and cool pavement, can be applied to places with large incident solar radiation [1,2,3,4,5,6,7]
As a measure to counter the urban heat island phenomenon, high-reflectance technology, such as cool roofs and cool pavement, can be applied to places with large incident solar radiation [1,2,3,4,5,6,7].Since the solar radiation incident on a building façade is small compared with that on roofs and pavement [8], the priority for cooling measures on building façades is low
High-reflectance technology is applicable on building façades above the fourth floor at any latitude, if we ignore a negative effect, since incident direct solar radiation to the building façade around noon is small at low latitudes (Figure 6)
Summary
As a measure to counter the urban heat island phenomenon, high-reflectance technology, such as cool roofs and cool pavement, can be applied to places with large incident solar radiation [1,2,3,4,5,6,7]. Six thermal parameters (air temperature, humidity, the pedestrian through the longwave radiation heat exchange on a building façade with a low air velocity, mean radiant temperature, col-value, and is metabolic rate)which are required to calculate surface temperature that high-reflectance technology introduced, is calculated in the index same values. Of solar radiation is absorbed by the building façade, and is the specular reflection occurs in the high sun angle condition, the influence by the specular reflection redistributed as sensible or radiative heat flux into the street canyon and to the building interior, should be considered in the high sun angle condition. In the case of a completely diffuse surface, such as concrete, paint, or wood, used as a conventional building façade, 12.5% of the solar radiation is reflected upward and 12.5% is reflected to a pedestrian area. The impact of solar radiation reflected from the building façade to a pedestrian must, be further evaluated
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