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 covers 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, to a radiative exchange model, determining the net solar and longwave radiation on each urban surface and to a wind driven rain model able to determine the wetting flux on each surface during a rain event. We first evaluate the evaporative cooling potential for different pavement systems during normal summer conditions after a long rain event during night in order to select an optimal pavement system. Then, we design a smart wetting protocol answering the questions ‘when’, ‘how much’ and ‘how long’ a pavement should be artificially wetted for having a maximum cooling effect. We found that a daily amount of 5mm wetting over 10 minutes in the morning, preferentially between 8:00 and 10:00 am, guarantees a maximal evaporative cooling for one day and night during a heat wave.
Highlights
The cooling demand of buildings is expected to increase dramatically in the future mainly due to further urbanization and climate change
In [4], different multilayer pavement solutions are designed optimizing their moisture transport properties and layering structure in order to guarantee the highest evaporative cooling effect. In these previous studies wetting by rain is used, which is an uncertain phenomenon during heat waves, since rain events highly depend on weather conditions and cannot be planned
The microclimate model is composed of a computational fluid dynamics (CFD) model implemented in OpenFOAM solving for turbulent heat, air and moisture transport in the air domain, and coupled to models for heat and moisture transport in urban porous materials, solar shortwave and longwave transport and wind driven rain
Summary
The cooling demand of buildings is expected to increase dramatically in the future mainly due to further urbanization and climate change. The UTCI depends mainly on mean radiant temperature including solar radiation and longwave radiation from surrounding surfaces on a person and local variables such as air temperature, relative humidity (RH) and wind speed In these studies, the authors compared the cooling effect by evaporation occurring in different porous urban materials for different wetting conditions. In [4], different multilayer pavement solutions are designed optimizing their moisture transport properties and layering structure in order to guarantee the highest evaporative cooling effect In these previous studies wetting by rain is used, which is an uncertain phenomenon during heat waves, since rain events highly depend on weather conditions and cannot be planned. A detailed description of this model and its validation can be found in [2, 3 and 4]
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