Emmanuel Bozonnet

Modelling the radiative exchanges in urban areas: A review

In the consideration of building energy performance and urban climate models, irradiation is a key parameter. From the city scale to the detailed building interchange, different approaches and models with various levels of details are explained in this review, and their scope and usefulness considered. The first part of the study deals with solar and longwave sky irradiance models. Six models of sky diffuse irradiance are presented, together with details of the models of longwave sky irradiance. At city scale, the influence of an urban area on the atmospheric radiative budget requires knowledge of the radiative flux leaving the urban area. Albedo and longwave reflectivity models are detailed in the second part to determine shortwave and longwave fluxes from urban areas. Solar access quantifies the shortwave radiative energy received by an urban surface for a specified period, determined by the buildings scale and type of facade. Depending on the urban morphology, tridimensional city models are presented in this section to compute the solar access. In order to calculate the energy budget of building walls, the radiation interchanges in the district have to be coupled with other physical phenomenon. Thus, some simplifications and various models to reduce computation time are discussed.

Technical advances in the EU-Cool Roof project

Cool materials keep the roof cool under the sun by reflecting the solar radiation away from the building and radiating the stored heat away during night time. The potential of the technology is very promising at EU level and, in particular, in the Mediterranean area. EU supports the Cool Roofs Project, where important technical actions are developed. The technical and scientific activities include: development of the first EU cool materials database; implementation of five case studies with different building typologies equipped with different cool materials; development and validation of a dedicated toolkit; production of the cool materials handbook. The paper summarises the most significant results achieved in the project.