Modelling of dew formation on conventional and cool roofs of an industrial district in Singapore: Potential, impact and limitations

Materials with specific radiative properties, known as “cool” materials, have been developed to enhance radiative cooling of buildings and urban microclimate. The choice of roof coating also influences the potential for water condensation. In addition, dew formation is a way to collect water, but it also significantly affect building energy consumption. Other studies have highlighted the impact of condensation on the heat flux exchanged between urban surfaces and the atmosphere, yet none have specifically examined its impact on the urban microclimate. Urban microclimate models often neglect the condensation on roof surfaces, as it is the case with SOLENE-microclimat.

This work therefore aims to integrate dew formation on urban surfaces into the SOLENE-microclimat model. For this purpose, condensation and evaporation processes are added to the roof energy balance. This work focuses on an industrial district in Singapore. The effectiveness of SOLENE-microclimat in representing this district is confirmed by comparing the simulated results with on-site measurements. This comparison validates the simulated surface temperatures for cool and conventional roofs. The results also show a significant dew potential at night in the hot and humid climate of Singapore. The height of condensed water is higher for cool roofs than for conventional roofs. In addition, in the morning, the surface temperatures of cool roofs are lower, which favours a more gradual evaporation of the condensed water film. The impact of dew on urban climate and energy consumption is also investigated.

Furthermore, this work highlights the limitations of urban microclimate models to accurately estimate dew potential. Indeed, the prediction of condensed water height is highly sensitive to uncertainties in input data (air temperature and relative humidity), as well as to model errors.