The role of materials selection in the urban heat island effect in dry mid-latitude climates

Abstract

© 2015 Springer Science+Business Media Dordrecht This work investigates the role of materials selected for different urban surfaces (e.g. on building walls, roofs and pavements) in the intensity of the urban heat island (UHI) phenomenon. Three archetypal street-canyon geometries are considered, reflecting two-dimensional canyon arrays with frontal packing densities (λ<inf>f</inf>) of 0.5, 0.25 and 0.125 under direct solar radiation and ground heating. The impact of radiative heat transfer in the urban environment is examined for each of the different built packing densities. A number of extreme heat scenarios were modelled in order to mimic conditions often found at low- to mid-latitudes dry climates. The investigation involved a suite of different computational fluid dynamics (CFD) simulations using the Reynolds-Averaged Navier–Stokes equations for mass and momentum coupled with the energy equation as well as using the standard k-ε turbulence model. Results indicate that a higher rate of ventilation within the street canyon is observed in areas with sparser built packing density. However, such higher ventilation rates were not necessarily found to be linked with lower temperatures within the canyon; this is because such sparser geometries are associated with higher heat transfer from the wider surfaces of road material under the condition of direct solar radiation and ground heating. Sparser canyon arrays corresponding to wider asphalt street roads in particular, have been found to yield substantially higher air temperatures. Additional simulations indicated that replacing asphalt road surfaces in streets with concrete roads (of different albedo or emissivity characteristics) can lead up to a ~5 °C reduction in the canyon air temperature in dry climates. It is finally concluded that an optimized selection of materials in the urban infrastructure design can lead to a more effective mitigation of the UHI phenomenon than the optimisation of the built packing density

Relating microclimate, human thermal comfort and health during heat waves: An analysis of heat island mitigation strategies through a case study in an urban outdoor environment

“…Li et al (Li, Pan, Zheng, & Shao, 2016) examined the microclimate in Xianghe Segment of China's Grand Canal (XSCGC) suggesting the realization of different functional areas to improve its livability. Kakoniti et al (Kakoniti, Georgiou, Marakkos, Kumar, & Neophytou, 2016) analyzed the influence of the materials on the microclimate coming to the conclusion that if chosen meticulously they can affect more the micrometeorological variables than an optimization of the built packing density. Then Liu and Niu (Liu & Niu, 2016) investigated different turbulence models and compared the performances of the Steady Reynolds Averaged Navier-Stokes (SRANS) RNG k-, Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) examining the wind flow around an isolated building.…”

Effect of pore modulating additives-sepiolite and colloidal nano silica-on physical, mechanical and durability properties of lime-based renders

“…Another aspect to consider for the selection of appropriate finishing materials in high urban temperatures is that the mitigation of overheating requires the use of low thermal-conductivity building materials [45,46] since they may heat up at the surface but will not transfer the heat throughout the layers behind the surface as quickly as those with higher conductivity. Both the renders with sepiolite additions (SEP and SEP_SC) show the lowest thermal conductivity values (Fig.…”

Temperature characteristics and heat load in the City of Dubrovnik

“…During the nighttime, results are the opposite, according to the results of WE and TR, it is visible that heat load is reduced with the decrease of built-up density. Some studies (Kakoniti et al, 2016) show that in dry climates, which could be linked with the climate in the city of Dubrovnik, sparser geometry of urban canyons, like here class 3, does not guarantee lower surface temperatures. In sparser parts of the city, during the day, surface temperatures are higher, while there are more surfaces under direct solar radiation and there are no shading effects like in denser urbanised parts.…”