Abstract
In hot, arid regions on university campuses, students are more vulnerable to heat stresses than in street canyons in terms of function; however, the knowledge of the impact of built environments on thermal performance is still lacking. In two summer and winter days, the shading effect of the existing urban trees pattern in a university campus in Egypt was examined to correlate their Sky View Factor (SVF) with the thermal environment, meteorology, Physiological Equivalent Temperature (PET), and Universal Thermal Comfort Index (UTCI). The ENVI-met model was used in order to assess meteorological parameters, followed by SVF calculation in the Rayman program. Meteorological field measurements validated the simulation model and measured the Leaf Area Index (LAI) of two native urban trees to model the in-situ canopies foliage. In summer, the results showed a significant direct impact of the SVF on mean radiant temperature (Tmrt), PET, and UTCI; however, the excessive shading by trees on materials with a low albedo and low wind speed could lead to a slight increase in air temperature. Meanwhile, in the winter, SVF did not affect the microclimatic variables, PET, or UTCI. The resulting insight into the correlation between SVF and Tmrt emphasizes the importance of urban trees in modifying the microclimates of already-existing university plazas.
Highlights
In the hot arid climate that prevails in countries like Egypt, due to the long exposure of urban structures to excessive solar radiation and the Urban Heat Island (UHI) phenomenon, uncomfortable outdoor spots appear on a microclimatic scale [1,2]
The minimum value of air temperature was at point 17 at 09:00 Local Solar Time (LST) in the hot season, and the mean radiant temperature was at its minimum at point 4 at 17:00 LST
The air temperature was at its maximum at point 11 at 13:00 LST, and the mean radiant temperature was at its maximum at point 8 at 14:00 LST
Summary
In the hot arid climate that prevails in countries like Egypt, due to the long exposure of urban structures to excessive solar radiation and the Urban Heat Island (UHI) phenomenon, uncomfortable outdoor spots appear on a microclimatic scale [1,2]. To alleviate the impact of the UHI phenomenon on the health and well-being of the occupants of these outdoor spaces, investigating and manipulating the impact of urban built environment elements such as the arrangement of buildings, the orientation of open spaces, the aspect ratio, and shaded areas on the thermal comfort performance of these spots become crucial in the early stages of the design process either on the urban or architecture scale [4]. Urban open spaces’ geometry, which is formed by building density, height, and orientation, differentiates one urban canyon from another, causing a different impact on microclimate, mostly through trapping heat.
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