Impact of conduction and convection approaches for urban microclimate assessment: from surface temperatures to outdoor thermal comfort

Source abstract

Urban surface temperature is key to microclimate simulations. It has a significant impact on both outdoor comfort and building energy consumption. However, surface temperatures are particularly complex to simulate, since they require adequate consideration of radiative, conductive, convective and evaporative (in the case of porous surfaces) exchanges between the surface and its environment. Many urban microclimate models exist, based on a wide variety of conduction and convection models. The aim of this study is to assess the influence of these models on the prediction of urban surface temperatures using the SOLENE-Microclimat model. Three conduction models and four convection models are compared across three case studies with different morphologies, each subjected to summer conditions. The study includes several pavements located in France, a street canyon in an industrial district of Singapore and a typical theoretical European neighbourhood under the context of hot clear-sky summer and low wind speeds conditions. The choice of conduction and convection models influences the daily amplitude and the temporal dynamics of the evolution of the surface temperatures. Simulated results are compared with on-site measurements, where available. For the conduction model, the 3R4C model is a good compromise between accuracy of results and complexity, on a neighbourhood scale. It is more complex to conclude which convection model is most suitable, as recommendations vary according to urban surfaces – roof, wall or ground – and the time of day. In addition, a sensitivity analysis carried out on the Mean Radiant Temperature and the Universal Thermal Climate Index highlights the non-negligible influence of the conduction and convection models’ choice while assessing the outdoor thermal comfort of pedestrians.