A transdisciplinary approach to understand, compute and visualize the city interface

In order to face the climate change and to improve the sustainability of our cities, architects and urban planners focus on an efficient urban design, improving the energy fluxes within the built environment. But frequently, due to the complexity of the urban metabolism, the impact of the buildings on the urban climatic conditions, as well as on the outdoor thermal and visual conditions is left behind. Indeed, several famous buildings, due to their form and reflectivity, are examples for the uncomfortable conditions created by their facades [1]. The main problem during the design phase, is that, up to now it is quite difficult to compute all the energy fluxes animating the city, and no tool is available to completely support architects and urban planners. In order to overcome this problem, we propose the development of a digital framework [2] to compute and digitalize the urban environmental conditions, and their variation as function of the city interface. In the present work, the city interface is defined as the space in-between the indoor and the outdoor environment, i.e. the building envelopes. The present study focuses on the impact of the city interface on the urban microclimate and the outdoor thermal comfort of pedestrians. An interdisciplinary approach (architecture, bioclimatology, engineering and physics) trying to fill a gap of knowledge within the urban simulations and design will be applied. Firstly, we modelled three urban canyons (East-West and North-South oriented) with a height-width ratio included between 0.5 to 3. Then, with the urban energy tool CitySim, we computed the outdoor thermal comfort perceived by the pedestrians, by the means of the comfort energy model COMFA* budget. In order to understand the impact of the buildings envelope with an advanced glazing system [3], the glazing percentage and glazing interface properties (e.g. the specular and diffuse reflectivity from glazing to the outdoor environment) are varied. The effect of the city interface on the urban microclimatic conditions (outdoor air temperature and wind speed) is investigated by the simulation. The results underline the importance of the city interface on the thermal comfort of pedestrians, being highly responsible, as function of the canyon geometry, the glazing properties and the climatic conditions, for the discomfortable hours during the daytime. Finally, thanks to the proposed methodology, all the energy fluxes affecting the pedestrian’s thermal sensation are quantified (short and longwave radiation, evaporation, convection and metabolic activity) and visualized. A future development of this study is presented, focusing on the computation of the city interface on the energy demands of buildings and on the energy systems optimization.