Optimizing albedo for thermal performance of small courtyard spaces in cold semi-arid climates

Thermal comfort and liveability in cities are affected by the Urban Heat Islands (UHI). It is commonly assumed that the impact of the UHI effect is less problematic on thermal comfort in colder climates, at nighttime, and in winter. Among heat mitigation strategies, modifying surface albedo has shown promise in regulating outdoor microclimates (Macintyre et al. 2021). While prior studies have examined albedo or geometry separately, their combined impact in enclosed spaces like courtyards remains underexplored, especially in cold semi-arid climates. This study fills that gap by analyzing how wall and pavement albedo interact with courtyard geometry to affect thermal comfort, offering seasonally responsive insights for climate-sensitive design in underrepresented climatic contexts. On-site measurements validated the ENVI-met model in January and June. Results show that high-albedo surfaces can reduce surface temperatures by up to 25 °C, yet significantly raise PET by up to 5 °C due to intensified radiant reflections, particularly from walls in high aspect-ratio courtyards. A square courtyard layout (1:1 aspect ratio) combined with medium wall albedo (0.3 to 0.4) and high pavement albedo (> 0.7) provides the most balanced thermal performance across both summer and winter. In site-constrained conditions where elongated courtyards are required, aspect ratios between 1:3 and 1:4, especially with NE-SW orientation, offer improved early-hour comfort and benefits when paired with medium-albedo walls (0.3-0.4) and high-albedo pavement surfaces (> 0.7). The findings highlight the importance of balancing reflectivity and enclosure effects in climate-responsive design guidelines.