Investigation and Evaluation of Insolation and Ventilation Conditions of Streetscapes of Traditional Settlements in Subtropical China

Abstract

Global warming, the urban heat island effect (UHI), and the risks of fossil fuel depletion necessitate a re-evaluation of traditional settlements that have been adapted to local climatic conditions, topography, and available resources, including materials and construction methods, through passive strategies to achieve thermal comfort. Although vernacular settlements have received considerable attention, few have examined and evaluated their streetscapes. This study investigates the impact of topographical features and architectural forms on insolation and ventilation conditions in traditional settlements in China’s southern subtropical climate. The aim is to explore traditional planning configurations of streetscapes at different altitudes to identify architectural forms and planning strategies that effectively improve outdoor users’ thermal comfort conditions. For this purpose, case studies are conducted on three traditional settlements in Lingnan; the Lingnan region has a typical subtropical climate in southern China. The chosen cases represent the main features of different topographical conditions, architectural forms, and climate zones in the Lingnan. We systematically simulated the insolation and ventilation in these settlements’ streetscapes on a monthly and quarterly basis and analyzed their sunlight hours, incident solar radiation, shading percentages, sky view factors (SVF), and wind speed. The findings show the following: (1) Specific terrains can affect streetscapes’ shading percentages and wind speed. The mountain settlement (With an average elevation of 600 m) is located on a southeast-facing slope (10° < slope < 20°). It receives an additional 10% of incident solar radiation compared to gentle terrain. (2) Compared to settlements located in coastal hills and mountainous, plain settlements have better shading and ventilation conditions in streetscapes. In terms of insolation, plain settlements have denser building configurations and narrower, elongated street corridors with a height-to-width ratio (H/W) = 1.9~5.5 (the height–width ratio value as street’s H/W (H = height, W = width); note that it is unitless), which can generate greater lower SVF (44.5%), and shading percentages (63.6%). Regarding ventilation, it is easier to create a “cool lane” (i) when the main street, oriented towards the dominant wind direction in summer, forms an angle <30° with it, (ii) when the primary street follows a NE–SW longitudinal orientation, while SE–NW horizontal streets intersect and weave through it, and (iii) with a H/W = 3~4 resulting in wind speeds of 2.9~4.0 m/s. (3) All the streetscapes have overshadowing occurring in winter; similarly, varying sizes of calm wind zones are created in summer. To alleviate these issues, widening the streetscapes along the buildings can permit solar penetration and natural ventilation. (4) In summer, installing shading devices along the horizontal plane of covered street corridors with a H/W = 1~4 and N–S longitudinal orientation can provide an additional shading of 3.6–22%.