When Identical Canopies Fail: Orientation-Dependent Performance of Incremental Architectural Shading at Immersed Tunnel Portals in a Hot-Arid Climate

Nasar, ZA, Alhilo, IA, Farhan, SL, Salman, TT and Kraidi, L ORCID: 0000-0002-2262-2009 (2026) When Identical Canopies Fail: Orientation-Dependent Performance of Incremental Architectural Shading at Immersed Tunnel Portals in a Hot-Arid Climate. Journal of Daylighting, 13 (2). pp. 491-506. ISSN 2383-8701

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Abstract

Global regulations for tunnels, especially concerning tunnel entrance shading and illumination, conceptualize them in terms of universal abstractions of engineering, divorced from geographical and geological features. This research addresses this overgeneralized approach by examining the efficacy of architectures’ structural increments and arrangements for offering shade to these portals in a coastal, hot, arid climate. The research methodology employed Radiance-based daylight and glare simulations via the Honeybee plugin for Grasshopper/Rhinoceros3D, to evaluate four incremental shading arrangements during critical seasonal and temporal conditions. These were applied for two immersed portals of tunnels in Basra (Iraq), specifically at Umm Qasr (W-SW) and Faw (E-NE). Simulation analysis employing the indices of physiological glare (“veiling luminance”, Lveil) and psychological glare (UGR, VCP) evinced that shade efficacy is significantly impacted by orientation. An Lveil-compliant architectural shading achieved a 96% reduction in the east portal’s Lveil, but differed in the west, revealing a hitherto unknown compromise, the “latent Lveil–comfort dissociation.” Overhanging canopies structurally inhibit the veiling luminance, yet legacy bright spots are thrown into higher relief against the darkened background, incurring psychological glare despite enhanced safety. Passive structural solutions thus minimize extreme baseline Lveil, from 445.4 cd/m² to < 80 cd/m² (the PIARC limit) under Option D, while Option C exhibited partial compliance, yet egregious psychological glare continued in both options with intense solar radiation. Outcomes indicate that structural canopies’ efficacy is hampered by low-angle sunlight. In certain microclimates, visual comfort drawbacks may be ignored by architectural shading specifications not calibrated to orientation, thus guidelines should be developed to accommodate structures’ geometric, reflectance, hydrological, and glare performance for particular applications, including coastal, hot, arid portals of tunnels.

Item Type:	Article
Uncontrolled Keywords:	33 Built Environment and Design; 3301 Architecture; 1201 Architecture; 3301 Architecture; 3302 Building
Subjects:	Q Science > QA Mathematics > QA76 Computer software T Technology > TA Engineering (General). Civil engineering (General)
Divisions:	Engineering and Built Environment
Publisher:	SolarLits
Date of acceptance:	3 August 2026
Date of first compliant Open Access:	10 September 2026
Date Deposited:	10 Sep 2026 10:00
Last Modified:	10 Sep 2026 10:00
DOI or ID number:	10.15627/jd.2026.27
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29355

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