The influence of surface type on the absorbed radiation by a human under hot, dry conditions

Abstract

Given the predominant use of heat-retaining materials in urban areas, numerous studies have addressed the urban heat island mitigation potential of various "cool" options, such as vegetation and high-albedo surfaces. The influence of altered radiational properties of such surfaces affects not only the air temperature within a microclimate, but more importantly the interactions of long-and shortwave radiation fluxes with the human body. Minimal studies have assessed how cool surfaces affect thermal comfort via changes in absorbed radiation by a human (R abs ) using real-world, rather than modeled, urban field data. The purpose of the current study is to assess the changes in the absorbed radiation by a human-a critical component of human energy budget models-based on surface type on hot summer days (air temperatures >38.5 • C). Field tests were conducted using a high-end microclimate station under predominantly clear sky conditions over ten surfaces with higher sky view factors in Lubbock, Texas. Three methods were used to measure and estimate R abs : a cylindrical radiation thermometer (CRT), a net radiometer, and a theoretical estimation model. Results over dry surfaces suggest that the use of high-albedo surfaces to reduce overall urban heat gain may not improve acute human thermal comfort in clear conditions due to increased reflected radiation. Further, the use of low-cost instrumentation, such as the CRT, shows potential in quantifying radiative heat loads within urban areas at temporal scales of 5-10 min or greater, yet further research is needed. Fine-scale radiative information in urban areas can aid in the decision-making process for urban heat mitigation using non-vegetated urban surfaces, with surface type choice is dependent on the need for short-term thermal comfort, or reducing cumulative heat gain to the urban fabric.

Microclimate Variation and Estimated Heat Stress of Runners in the 2020 Tokyo Olympic Marathon

“…The full detailed methods are found in Hardin and Vanos (2017) and Kenny (2008) [33,34]. Below, we outline any changes made from studies [21,28,32] for the given study.…”

The Effect of Building Facades on Outdoor Microclimate—Reflectance Recovery from Terrestrial Multispectral Images Using a Robust Empirical Line Method

“…However, higher solar reflectance within cities may also increase reflected solar radiation to near-surface facets and people [37,[51][52][53][54][55][56][57][58][59] although the magnitude of reflected solar radiation and its…”

“…Additionally, via long-wave radiative transfer, hotter surfaces emit infrared radiation to cooler objects within view [51]. In summary, increasing surface reflectance-which in the solar spectrum is referred to as the surface's albedo-potentially reduces the surface's surface temperature, the convective transfer intensity to the air and the emitted infrared radiation to surfaces in view.However, higher solar reflectance within cities may also increase reflected solar radiation to near-surface facets and people [37,[51][52][53][54][55][56][57][58][59] although the magnitude of reflected solar radiation and its…”

Seasonal and Diurnal Surface Temperatures of Urban Landscape Elements

“…There have been significantly fewer surface temperature studies on other hard surfaces such as stone, ceramic and gravel [25][26][27][28], and on softer or pervious LEs such as mulch, sand, soils, turf grass or artificial turf grass, which are common features of domestic gardens [29][30][31][32]. Results for hard LEs, which demonstrated that smooth light-coloured materials were cooler whilst rougher, darker materials were warmer [27], were also applicable to soft LEs.…”