Urban Heat Islands in High-Rise Residential Quarters

Abstract

Study intent: This case study investigates the effect of urban design factors on summertime urban heat island (UHI) intensity in ten high-rise residential quarters in the inner city of Shanghai during summer months. On-site design variables were developed to quantify the thermal impacts from density, building layout, and greenery. The design variables that were measured on site were correlated with the variation in UHI intensity during the day and night. Based on the resultant empirical models, design strategies can be formulated for summertime UHI mitigation so as to improve outdoor human thermal comfort and lower housing air-conditioning energy consumption. Result and discussion: Variations in UHI are in part due to site planning, building design, and greenery. Site characteristics in plot layout, density, and greenery have different impacts on UHI-day and UHI-night patterns. The overall daytime and nighttime UHI models explain up to 77 and 90% of UHI variation, respectively. On the site level, shading from either buildings or vegetation canopy is the most important factor influencing daytime UHI. The shading factor can distort and dilute behavior of other variables, e.g., green ratio and surface albedo. Nighttime UHI is more complicated due to the influence from anthropogenic heat and is significantly related to vegetation density and coverage. Considered diurnally, the semi-enclosed plot layout with a fairly high density and tree cover has the best outdoor thermal condition. To mitigate summertime UHI, it is recommended to manipulate site layout and building mass, to improve shading during the day while facilitating site ventilation at night, and to increase site vegetation cover through strategic tree planting. Beyond the site and up to the local/urban scales, urban ventilation has significant impact and therefore urban wind corridor would benefit UHI mitigation on the urban scale.