Journal of Architectural Engineering

In semiarid climates, buildings with extensive glazing often become overheated by direct solar radiation in the summer. Careful selection of shading devices (SDs) is crucial to mitigate this issue. This study is a comprehensive evaluation of the indoor thermal performance of various internal and external SDs in a semiarid Indian city. A total of 150 simulations using EnergyPlus were conducted for windows with no shading (NS), fixed shading elements [egg-crates (ECs) and overhangs (OVs)], and movable SDs [louvers (LVs) and internal blinds (BLs)]. Such parameters as the window/wall ratio (WWR), the window facade direction, the slat angle of LVs and BLs, and the OV depth were varied. Indoor thermal performance was assessed for windows facing south and west before the monsoon (May) and in winter (December). Results indicated that LVs and BLs with a 45° slat angle offered superior thermal conditions, reducing mean radiant temperature (MRT) and indoor air temperature by up to 3.0°C and 1.5°C, respectively, for west-facing windows with larger WWRs in summer. Moreover, LVs at 45° showed better reduction in cooling energy consumption than NS conditions (from 7.5% to 16.8% for west-facing windows) at varied WWRs compared with other SDs. Increasing the OV depth to 1 m reduced window heat gain rates but had minimal impact on indoor air temperature and MRT. This study has implications for buildings in similar climates, where summers are hot and winters are mild.

The Leadership in Energy and Environmental Design (LEED) v4 daylight credit criteria were adjusted, and the Annual Sunlight Exposure (ASE) threshold was increased from 10% to 20%. The ASE < 20% threshold was also implemented by the Illuminating Engineering Society in the recent lighting measurements standard in 2023. However, the implications of this change across diverse sky conditions remain unclear. Simulations for a typical office space across 32 cities (15°N to 65°N) considered various sky conditions, encompassing 360° orientations and 5%–100% window-to-wall ratios (WWRs). Implementing the ASE < 20% threshold increased accepted daylighting cases from 21% to 52%. Spaces with WWRs between 85% and 100% and oriented between 140°S and 230°S now consistently achieve acceptable daylighting performance in all tested cities, compared to those oriented between 150°S and 210°S, when ASE is ≤10%. The new threshold resulted in greater sensitivity to the sky conditions, aligning more closely with the city’s latitude. Applying both the old and new thresholds shows that spaces with WWRs less than 20% do not achieve acceptable daylighting, regardless of orientation or location. The ASE < 20% appears to favor cities at lower latitudes, with a 168%–260% increase in accepted cases for cities closer to the equator (latitude 15°N to 35°N), compared to a 125%–150% increase for cities further north (latitude 45°N to 65°N). This is related to the spatial Daylight Autonomy limitations imposed by the sky conditions of the northern locations. This disparity suggests that the LEED daylight credit criteria may be more difficult to achieve in higher latitude locations. It is suggested that the LEED credit criteria could be reconsidered in the future for those locations so that they become more sensitive to the differentiated sky conditions in various latitudes.