Urban thermal environment and surface energy balance in 3D high-rise compact urban models: Scaled outdoor experiments

Abstract

This study investigates the diurnal characteristics of air-surface temperatures and surface energy balance (SEB) of outdoor scaled arrays under different sky conditions from October to December 2017 in Guangzhou. Key geometrical parameters of the arrays include aspect ratio H/W = 2.4 (building height H = 1.2 m, street width W = 0.5 m), building area density λp = 0.25, and frontal area density λf = 0.6. Two types of buildings are investigated: “hollow” model means hollow concrete buildings and “water” model filled with water.Direct solar radiation, wall height, and wall orientation are significant factors that affect the diurnal variations of air-wall surface temperatures. The wall temperature shows a common declining trend from the upper heights to the lower heights. The water model experiences a smaller mean daily temperature range (DTR) of about 10 °C than the hollow model (mean DTR = 15.5 °C) due to heat storage. Moreover, 50%~60% net radiation (Q*) are partitioned into heat storage (estimated by the element surface temperature method) for the water model, which is about two times for the hollow model between 10:00 to 16:00. For the hollow model, the sum of sensible and latent heat fluxes contributes to the majority fraction of Q*. On clear sky days, the diurnal variation of short-wave radiation shows a single peak, while more complicated variations in occasionally cloudy days. The mean albedo is mainly affected by solar altitude angle, sky conditions which ranged from 0.21 to 0.23 with H/W = 2.4 in current study. The present study may provide experimental data to validate numerical and theoretical models for urban climate studies.