Understanding pavement-surface energy balance and its implications on cool pavement development

The idea of using cool pavements to mitigate the urban heat island has gained momentum recently. Many studies have focused on the temperature of a cool pavement, whereas limited studies have reported on the pavement's sensible heat to the surrounding air. This paper demonstrates the energy partition at the ground surface, with focuses on the sensible heat releasing from the pavement surface. The energy partition of a typical dry pavement is simulated and compared to that at an irrigated grass surface. Pavements with different surface albedos and different thermal inertia are simulated to demonstrate influences of surface modification and heat-storage modification on the releasing sensible heat. Instantaneous solar absorption by the pavement is prone to be partitioned into heat conduction. Most of the absorption is discharged as sensible heat and long-wave emission, whereas the daily cumulative heat conduction is roughly 5% of the absorption. Both increasing the surface albedo and enhancing the evaporative flux are effective to suppress the sensible heat and to promote cool pavements. Raising the thermal inertia of the pavement decreases the sensible heat during the daytime but increases this factor at nighttime. Therefore, it should be cautious to design cool pavements by varying their thermal inertia.