Light temporary textile structures for the mitigation of thermal comfort. Dynamic Modelling of microclimate and thermal comfort in the urban environment

In built environments a plurality of microclimates is generated by the different way the atmosphere interacts with man-made and natural surfaces and objects (i.e. buildings and infrastructure, vehicles, people, etc.). As widely reported in the literature, in summer conditions, especially in case of weak circulation (i.e. lack of wind) urban areas are often affected by heat islands effects, resulting in higher air temperatures compared to those in an adjacent non-urban area, especially during the night. Cities themselves generate weak ventilation conditions, since the high momentum roughness. Moreover, people when outdoors in urban areas, in summer days, are surrounded by hot surfaces, thus emitting a large amount of long-wave radiation. High albedo materials and green roofing are commonly referred as effective techniques for mitigating heat islands, but few options are available for mitigation interventions below the rooftop level. To assess the mitigation potential of light and temporary structures we modified an urban canyon model, in the context of Milano, including a tent over the street with different optical properties, and computing the surface temperatures by means of a heat and moisture transport dynamic finite difference model. This coupled model computes short-wave and long-wave incident radiation on each surface after multiple reflections, fluxes of turbulent sensible and latent heat, wind velocity and relative humidity, and the air temperature within the urban canyon, below the tent. In addition, we also assess the thermal comfort by means of the evaluation of UTCI Universal Thermal Comfort Index.