Smart wetting of permeable pavements as an evaporative-cooling measure for improving the urban climate during heat waves

Abstract

An urban microclimate model is used to design a smart wetting protocol for multilayer street pavements in order to maximize the evaporative cooling effect as a mitigation measure for thermal discomfort during heat waves. The microclimate model is built upon a computational fluid dynamics (CFD) model for solving the turbulent air, heat and moisture flow in the air domain of a street canyon. The CFD model is coupled to a model for heat and moisture transport in porous urban materials and to a radiative exchange model, determining the net solar and thermal radiation on each urban surface. A two-layer pavement system, previously optimized for maximal evaporative cooling applying the principles of capillary pumping and capillary break, is considered to design a smart wetting protocol answering the questions “when,” “how much,” and “how long” a pavement should be artificially wetted. It was found for the current optimized pavement solutions that a daily amount of 6 mm wetting over 10 min in the morning, preferentially between 8:00 and 10:00, guarantees a maximal evaporative cooling for 24 h during a heat wave.

Urban Heat Island and Its Interaction with Heatwaves: A Review of Studies on Mesoscale

“…In order to mitigate the negative effects of UHI, especially during HWs, numerous strategies have been proposed, such as using permeable pavements [31][32][33] and reflective materials [34,35], increasing vegetation cover [36][37][38][39][40][41][42] and so on. Susca et al [43] evaluated the effectiveness of using vegetation for UHI mitigation in New York City and reported a positive impact since vegetation effectively reduced the building cooling/heating load and the consequent building energy consumption.…”

Evaluating the Combined Effect of Climate Change and Urban Microclimate on Buildings’ Heating and Cooling Energy Demand in a Mediterranean City

“…Particularly the urban areas, which already experience the negative consequences of the heat island effect, are expected to face extreme heat events. In fact, the increase of the air temperature in urban areas is further intensified by the thermal and optical (absorbent, non-reflective) properties of conventional building materials [12,13], the reduced evapotranspiration due to plant deficiency [14], the anthropogenic production of heat, as well as the atmospheric pollution [15].…”

Advancement in Urban Climate Modelling at Local Scale: Urban Heat Island Mitigation and Building Cooling Demand

“…Recent CFD studies of local urban climate assess the impact of different components such as urban morphology [43,44], water bodies [13], vegetation [24] and of urban materials [14][15][16]45]. A majority of CFD studies use Reynolds-averaged Navier-Stokes (RANS) with k-ε turbulence models.…”

“…Typically, moisture transport is either not considered and urban surfaces are considered impermeable to moisture, or moisture transport is taken into account by simplifying it with a uniform latent heat flux, e.g., for uncovered surfaces such as soil. In the research group of the authors, local urban climate models were developed including coupling with heat and moisture transport (HAM) models in porous media [14][15][16]50], allowing to resolve moisture transport in addition to the heat transport within urban materials. Here, moisture flux includes liquid and vapour transport due to the capillary pressure and the vapour pressure gradients respectively and transport due to temperature gradients.…”

“…Factors contributing to the positive thermal balance mainly comprise increasing heat storage due to the adoption of low albedo and high heat capacity construction materials, solar radiation entrapment in street canyons, lessened heat removal by reduced urban ventilation, reduced cooling due to longwave radiation to the sky, less vegetation resulting in lack of evapotranspiration, excessive emission of anthropogenic heat and more. Mitigation strategies are developed, including use of vegetation in the form of grass, green roofs and trees [9,10], adoption of roof materials with high albedo [10,11], temporary shadowing devices [12], presence of water bodies [13], use of permeable pavements introducing evaporative cooling [7,[14][15][16], design of ventilation corridors in building clusters [17], deployment of high efficiency heating and cooling systems to reduce anthropogenic and waste heat [18,19], use of free cooling systems [20,21], etc.…”