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Since some years, dense cities and compact buildings are promoted as sustainable and energy efficient designs. Nevertheless, urban planning strategies should take into account the interactions between buildings and the microclimate because the Urban Heat Island (UHI) phenomenon can increase the cooling load of buildings and is strongly influenced by urban morphology, urban landscaping and the thermal properties of buildings and soil. The modification of these parameters, such as building density, can mitigate UHI, with direct and indirect improvement of building energy performances. The case study presented in this paper concerns a new district in La Rochelle (France) named Atlantech. Currently at the design stage, the goal is to transform this old military camp into a zero carbon district. This study was performed in parallel with urban planning using EnviBatE and SOLENE-Microclimate simulation. Two building densities are compared through the impacts on solar irradiance, wind airflows, building indoor temperatures and energy demand. Analysis of reference and densified district highlights various impacts such as the wind velocity decrease, up to 80%, and the effect on an existing nearby building solar irradiation, reduced by 7%. These results underline the potential usefulness of these simulation tools for urban planners at the design stage. [ABSTRACT FROM AUTHOR]

Abstract: Energy performance of air conditioned buildings and summer comfort can be improved with high solar reflectance and high emittance of building envelopes. Widely used for roofs, this technique known as cool roof, has a direct impact on the external surface temperatures peaks which reduces both heat transfer to the building and to the environment. In this paper, this technique used with façades is experimented in a confined environment similar to a typical urban scene. This reduced-scale of 4 street canyon rows is designed in order to give realistic measurements of thermal confinement. Then, the temperatures of a street canyon with brown cool selective paint façades are compared with a standard brown coating on another street façades, and with an asymmetrical configuration. The analysis of thermal effects on both buildings and outdoor environments gives interesting prospects for urban heat island mitigation. [Copyright &y& Elsevier]

In this paper, we propose a practical approach for decision-making regarding passive cooling design for buildings in dense urban contexts. For non-cooled buildings under temperate climates, assessment of summer thermal discomfort determines the usual passive cooling design together with fossil energy and GHG savings at earth scale. However, passive cooling techniques for indoor climate can be also valuable for local environment impacts, especially urban heat islands’ mitigation. Lack of simple representative criteria and complexity of simulation outputs constitute a barrier for the development of passive cooling. Based on a study of a generic commercial building, we analyzed several designs with Sankey diagram and we developed two performance indexes. This chart synthesis of complex output data allows a direct comparison of design solutions. This analysis gives hints for better designer understanding of urban climate and building interactions for the studied passive cooling solutions: cool roofing, nocturnal natural ventilation and rooftop PV system as shading device. Our results show that nocturnal natural ventilation is efficient to moderate indoor overheating compared to the "cool roof". In addition, cool roofs reduce anthropogenic heat transferred to urban environment. PV panels as shading device mitigate summer discomfort and produce energy that increase building energy efficiency through the year. We defined two Key Performance Indexes (KPIs) to define cooling potential of both indoor and urban environment. These KPIs obtained for different temperate climates highlight new prospects for the design of efficient urban designs with controlled environmental impacts and decision process of stakeholders. [ABSTRACT FROM AUTHOR]