Experimental Determination of Pedestrian Thermal Comfort on Water-Retaining Pavement for UHI Adaptation Strategy

Abstract

Artificial impervious surfaces are one of the most significant factors contributing to urban heat islands (UHIs). Adapting to UHIs is a challenge in achieving thermal comfort. We conducted a quantitative and subjective evaluation of a closely paved novel water-retaining pavement (WR) and a conventional dense-asphalt pavement (AS). We investigated the thermal states of humans based on the human energy balance known as “human thermal load” as an indicator for the assessment, and the original human thermal load method was improved for assessing nonuniform environments such as pavements. We looked for individual thermal perceptions simultaneously. The experiment was conducted in typical summer weather. The surface temperature of the WR was found to be significantly lower, by 9.5 °C, while the air temperature and humidity above both pavements were not significantly different. Thus, air conditions did not directly affect the sensible and latent heat loss. The reflected solar radiation was significantly larger, and the infrared radiation was significantly smaller on the WR than on the AS due to the lower surface temperature from the water evaporation and higher reflectance. Further, the human thermal load at a pedestrian level of 1.5 m was found to be significantly different: 237 W/m2 for AS and 215 W/m2 for WR. In a subjective evaluation, the perceptions of WR tend to be distributed in smaller human thermal load, thereby resulting in a cooler and comfortable sensation. Therefore, we demonstrated that when compared to AS, WR significantly improves thermal comfort.

The Future of Climate-Resilient and Climate-Neutral City in the Temperate Climate Zone

“…Covering with elements of the urbanized environment is one of the indicators of the intensity of development, showing a close relationship with the surface temperatures [ 289 , 290 ]. Impermeable surfaces in the neighborhood unit represented by buildings and roads have constant high LST and UHI [ 161 , 172 ], and modulation of the coverage parameter strongly influences their variability [ 291 , 292 , 293 , 294 ]. The increase of paved surface coverage leads to LST and UHI increases [ 295 ].…”

“…Increasing the built-up area coverage by 1% may cause a rise of the UHI effect intensity up to 1.7% [ 170 ]. On the other hand, a 1% reduction may cause a decrease in the night-time near-surface air temperature by 0.1 °C [ 292 ]. Urbanization degree is proportional to the distance from the city center [ 187 ] and size-dependent urban area [ 172 ].…”

The Use of Cool Pavements for the Regeneration of Industrial Districts

“…These characteristics help to decrease the surface temperature, reducing the convection of heat from the pavement to the atmosphere and thereby decreasing the air temperature. Previous studies have demonstrated that an increased albedo by 0.1 is estimated to reduce the maximum pavement surface temperature by more than 3.0 • C [20,21]. Lower air temperatures contribute in mitigating the UHI effect [22], while also decreasing the energy demand for cooling, and slowing the formation of urban pollution [23].…”

Review of regulation techniques of asphalt pavement high temperature for climate change adaptation

“…However, the porous structure will also reduce the pavement reflectivity and weaken the cooling effect [73,92]. Water retaining pavement can absorb water during raining or watering, and prolong the time with water [93][94][95]. In addition, water-retaining materials are generally in light color, which can improve the reflectivity of the pavement to a certain extent, thereby improving the cooling effect [92].…”