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The urban population rise leads town planners to increase the building density in order to avoid an urban sprawl what can induce higher risks of the heat island occurrence and increases buildings needs for air conditioning. Urban vegetation such as trees, grass areas, green walls and roofs can be a solution to mitigate it. The aim of the study is to evaluate the influence of various greenery types on cooling needs and to classify them according to their ability to mitigate it. Numerical simulations were carried out for canyon street configurations. The 3D numerical tool takes into account the unsteady building thermal behaviour using the SOLENE thermo-radiative model coupled with the outside airflow computed with the CFD tool Code_Saturne. A parametric modelling study considering different kinds of buildings permits to identify the most efficient greenery types and to investigate the interactions between each of them. Green walls and trees appear as the most efficient to reduce cooling needs. The less insulated and the more glassed the buildings are, the more efficient these devices are. The impact of grass areas and green walls applied on neighbouring buildings is only sensible without trees in the street and green cover on the studied building. [ABSTRACT FROM AUTHOR]

Urban shape determines the absorption and emission of radiation. Urban fabrics are characterized by the solar trapping effect due to multiple reflections of radiation within the geometry, in turn generating increased energy absorption that contributes to the urban heat island. Interactions between urban radiative properties and urban shape are studied through an analytical development. A simplified solar balance model is developed based on morphological indicators. A processing chain is performed within OrbisGIS Geographic Information System (GIS) to characterize urban shapes from geographic data supplied by the French IGN. The studied territories are partitioned from the road network into elementary areas of city blocks. The processing chain also includes the production of 3D block models that are used in the SOLENE solar simulation model to perform detailed radiative simulations. The incident and absorbed solar radiations are estimated on 440 actual city blocks from the simplified solar balance model and then compared to the SOLENE computations. The relationships between the simplified solar balance model and the SOLENE simulations are investigated using linear regression analysis. The comparisons show significant correlations and that the simplified solar balance model developed is consistent with the simulations. This contribution produces simple and accurate radiative parametrizations that can be used in urban microclimate models to represent solar trapping and to evaluate radiation availability. [ABSTRACT FROM AUTHOR]

The urban microclimate is due to complex physical interactions with the contribution of water balance, thermo-radiative exchanges and airflows. In this paper, we present and discuss modeling of heat island effects and mitigation techniques in order to give consistent results considering different time and space scales, and different fluxes (heat, water and winds) from ground to urban canopy, including buildings. The models and numerical descriptions are presented in detail and illustrated on typical examples of heat island mitigation techniques. At the neighborhood scale, alternative rainwater management techniques are studied by considering their impact on both seasonal water table depth and surface-atmosphere heat fluxes. Assessing the building thermal performance interactions with the microclimate requires adapted models that have to be refined for a better description of building envelope and systems effects. Two examples at the street and the neighborhood scale, modifying the building radiative properties or using green envelopes, show how simulation brings out the potential benefits of these techniques for the heat island mitigation and building energy performance. [ABSTRACT FROM PUBLISHER]

The urban context is often simplified or neglected in Building Energy Models (BEMs) due to the difficulties of taking accurately into account all the heat fluxes emanating from the environment. Oversimplifying the urban context can impact the accuracy of the BEM predictions. Nevertheless, several approaches can be used to allow for the impact of the urban environment on the dynamic behavior of a building, its heating and cooling demands, and thermal comfort. This state of the art review provides a critical overview of the different methods currently used to take into account the urban microclimate in building design simulations. First, both the microclimate and building models are presented, focusing on their assumptions and capabilities. Second, a few examples of coupling, performed between both modeling scales are analyzed. Last, the discussion highlights the differences obtained between simulations that take the urban context into consideration and those that simplify or neglect urban heat fluxes. The remaining scientific obstacles to a more effective consideration of the urban context impacting the BEMs are indicated. • The local data produced by a selection of urban climate models (UCMs) are presented. • An analysis of how the urban context is taken into account in building energy models (BEMs) is given. • Several chaining or coupling strategies to link UCMs and BEMs are analyzed and compared. • Using local climate data leads to a noticeable impact on the thermal behavior of buildings. • Recommendations for better consideration of the urban context in BEMs are formulated. [ABSTRACT FROM AUTHOR]

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]

• An evaluation toolbox to consider nature-based solutions in urban areas is settled. • Impact of nature-based solutions depends on urban environmental challenges. • A decision-support methodology considering soil-water-climate aspects is developed. • Several indicators were determined and compared to define the toolbox. In the context of climate change, Nature-Based Solutions (NBSs), a recently developed concept, are increasingly considered as part of the adaptation strategies of the cities. Studies using expert models and methods (EMM) receive a great deal of scientific attention. Considering EMM increasing use, this study aims to perform an analysis of the reported evaluation results, reflecting the capability of the EMM to accurately tackle urban challenges identified within the EU Nature4Cities project. Then, we propose a set of indicators and recommendations about sixteen EMM to be used by funders, researchers and practitioners when evaluating the performance of NBSs. The coupling of the different components (climate, water and soil) is not a simple matter. The analysis relies on the definition of the range of the reported metrics and on the investigation of the relationship between the various indices, applied for the EMM evaluation. Secondly, the study assesses the existing EMM, indicating the potential of NBSs: (i) to reduce urban heat island, (ii) to limit surface warming, (iii) to increase the thermal comfort of people, (iv) to limit the overheating and runoff of surfaces due to impervious areas, (v) to increase water retention during stormy episodes, (vi) to improve storm water quality at the outlet of the sustainable urban drainage systems, (vii) to promote the filtration and epuration of storm water runoff in soil and (viii) to be a support for vegetation. The analysis reveals that EMM can be considered as helpful tools for urban microclimate, urban soil and water management analysis, provided their limitations and characteristics are taken into account by the user when choosing tools and interpreting results (e.g. application scale). With regard to the performance of NBSs, the most commonly used indicators clearly depend on the scale of the project. [ABSTRACT FROM AUTHOR]