Experimental investigation of the impact of urban fabric on canyon albedo using a 1:10 scaled physical model

Kotopouleas, Alkis; Giridharan, Renganathan; Nikolopoulou, Marialena; Watkins, Richard; Yeninarcilar, Muhammed

doi:10.1016/j.solener.2021.09.074

Cited by 13 publications

(6 citation statements)

References 33 publications

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“…The ambient temperature increase caused by specular reflective (glazed) facades is to be determined, but the canyon albedo with specular reflectors and glazed facades is known [63]. If the façade is fully glazed, with a high window to wall ratio, the canyon albedo is lower than 0.05 with high solar elevations [63], while it is more than 0.15 with wall albedos of 0.50 (as also documented experimentally [64]). Additionally, values lower than 0.10 for the canyon albedo are computed when walls are covered by purely specular reflectors [65].…”

Section: Discussionmentioning

confidence: 89%

Experimental Assessment of the Reflection of Solar Radiation from Façades of Tall Buildings to the Pedestrian Level

et al. 2022

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Urban climates are highly influenced by the ability of built surfaces to reflect solar radiation, and the use of high-albedo materials has been widely investigated as an effective option to mitigate urban overheating. While diffusely solar reflective walls have attracted concerns in the architectural and thermal comfort community, the potential of concave and polished surfaces, such as glass and metal panels, to cause extreme glare and localized thermal stress has been underinvestigated. Furthermore, there is the need for a systematic comparison of the solar concentration at the pedestrian level in front of tall buildings. Herein, we show the findings of an experimental campaign measuring the magnitude of the sunlight reflected by scale models reproducing archetypical tall buildings. Three 1:100 scaled prototypes with different shapes (classic vertical façade, 10% tilted façade, curved concave façade) and different finishing materials (representative of extremes in reflectance properties of building materials) were assessed. A specular surface was assumed as representative of a glazed façade under high-incidence solar angles, while selected light-diffusing materials were considered sufficient proxies for plaster finishing. With a diffusely reflective façade, the incident radiation at the pedestrian level in front of the building did not increase by more than 30% for any geometry. However, with a specular reflective (i.e., mirror-like) flat façade, the incident radiation at the pedestrian level increased by more than 100% and even by more than 300% with curved solar-concentrating geometries. In addition, a tool for the preliminary evaluation of the solar reflectance risk potential of a generic complex building shape is developed and presented. Our findings demonstrate that the solar concentration risk due to mirror-like surfaces in the built environment should be a primary concern in design and urban microclimatology.

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Section: Discussionmentioning

confidence: 89%

Experimental Assessment of the Reflection of Solar Radiation from Façades of Tall Buildings to the Pedestrian Level

et al. 2022

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“…However, they do not impact the air temperature in street canyons, due to the high solar angle. Consequently, a cool façade receives less solar radiation, leading to a lower impact on the air temperature (Kotopouleas et al 2021).…”

Section: Discussionmentioning

confidence: 99%

“…This, in turn, reduces heat absorption (Rahman et al 2021;Fang et al 2023) and makes the outdoor environment much more comfortable. Previous studies (Srivanit & Jareemit 2020;Kotopouleas et al 2021;Tochaiwat et al, 2023) have explored the benefits of shading in hot-humid climates through increasing the ratio of building height to street width (H/W), planting trees along streets, and using varying building orientations. It has been found that the impact of cool pavements in terms of a reduction in air temperature in shaded areas is not significant due to the shade protect surface pavement directly exposed to the solar heat resulting in less heat absorption (Schrijvers et al 2016;Nasrollahi et al 2020;Zhang et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Cool Facades and Pavements: Mitigating Heat Stress and Improving Urban Thermal Conditions in Affordable Housing Project – a Case Study in Thailand

Maneechote,

Liu,

Jareemit

2024

Future Cities and Environment

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An increase in urban air temperature raises heat stress and mortality risk for city dwellers. This study assessed the potential reductions in air temperature and heat stress through the combined effect of cool façades and floor pavements, in two street canyons in an affordable housing project in Thailand. The air temperature and mean radiant temperatures were simulated for 81 design scenarios where materials with low, medium, and high albedos were used for the walls of buildings, parking areas, and road using ENVI-met v5.0. The risk of exposure to heat stress under extreme conditions was estimated using a heat index equation. The results showed that the avenue canyon (height-to-width ratio, H/W = 0.6) with a low-albedo road surface was hotter than the regular one (H/W = 1.2), due to the larger areas of road pavement and smaller shaded areas. A medium to high albedo for the pavements could reduce the street-level air temperature by up to 2.3°C, but the average mean radiant temperature was raised by 9.3°C. The regular canyon (H/W = 1.2) provided better thermal conditions, and had fewer 'hot spot' areas exposed to heat stress than the avenue canyon. This study explored the benefits of using cool pavements to improve the thermal conditions in areas with limited shade. In addition, this study identified safe outdoor areas not being directly exposed to solar radiation during the hot summer months. These findings could be important for planning safe outdoor activity spaces under extreme heat conditions.

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“…Secondly, the analytical results and model outputs under two extreme cases (extreme case 1: very shallow canyon, extreme case 2: bottomless canyon) were compared to verify the robustness of the model. Finally, the model was validated with Aida's experimental test results [51] for an ideal urban canyon and Kotopouleas et al [50] for an actual urban canyon.…”

Section: Model Validationmentioning

confidence: 99%

A mathematical model for a rapid calculation of the urban canyon albedo and its applications

et al. 2022

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Experimental investigation of the impact of urban fabric on canyon albedo using a 1:10 scaled physical model

Cited by 13 publications

References 33 publications

Experimental Assessment of the Reflection of Solar Radiation from Façades of Tall Buildings to the Pedestrian Level

Experimental Assessment of the Reflection of Solar Radiation from Façades of Tall Buildings to the Pedestrian Level

Cool Facades and Pavements: Mitigating Heat Stress and Improving Urban Thermal Conditions in Affordable Housing Project – a Case Study in Thailand

A mathematical model for a rapid calculation of the urban canyon albedo and its applications

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