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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]

Following development and validation of the SOLENE-microclimat tool, the underlying model was used to compare the impacts of various "greening strategies" on buildings' summer energy consumption and indoor comfort. This study distinguishes between direct and indirect impacts by successively implementing the test strategies on both the studied building and surrounding ones; it also considers insulated vs. non-insulated buildings. Findings indicate that green walls have a direct effect on indoor comfort throughout the entire building, whereas the effect of green roofs is apparently primarily confined to the upper floor. Moreover, the indirect effect of a green wall is greater, mainly due to the drop in infrared emissions resulting from a lower surface temperature. It has also been proven that the indirect effects of green walls and surrounding lawns can help reduce the loads acting on a non-insulated 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]

Abstract: The beneficial influence of trees and water ponds on summer comfort in urban spaces was studied experimentally in situ and in wind tunnels but the modeling needs further development to become effective in practical applications. This paper introduces a numerical approach based on coupling the CFD model of airflow, in which the influence of trees is considered as source terms, and the radiation exchange, completed with thermal conduction. The CFD, radiation and thermal conduction models use the same discretization grid at their common boundaries. The model was used to estimate the influence of trees and water ponds in a real town square. Comparison of results between two situations, with and without vegetation and water pond, indicate that surface temperatures are reduced in presence of trees and the comfort is improved. [Copyright &y& Elsevier]

Highlights • An inverse heat transfer model linked to Bayesian statistics is presented. • This model is used to identify the conductivity and volumetric heat capacity. • In situ measurements are used by the inverse model. • The proposed model can use shorter time series than the standard ISO 9869. • The proposed model produces more accurate and robust results compared to the standard. Abstract Non-destructive thermal diagnosis is necessary for identification and quantification of structural defects and verification of construction performances. In this paper, we test different inverse heat transfer models to identify the thermal conductivity of a building's wall in its environment. The approaches proposed and used in this paper rely only on non-intrusive measurements: inside and outside wall surface temperatures and heat flow through the wall. First, a Bayesian statistical dynamic inference method, which has the advantage to quantify the unknown parameter and its credible interval, is presented. This method considers the uncertainties of the measured temperature and heat flow data and of the unknown thermal properties. Markov chain Monte Carlo (MCMC) algorithm is used to explore the posterior distribution. Then, the average and the dynamic procedures ISO 9869 (I. 9869-1, 2014) are introduced. Finally, the probabilistic distributions of the unknown parameters are presented and compared to the standard results. The impact of experimental conditions (average indoor-to-outdoor temperature) and the measurements length on the accuracy of the results are discussed. The relationship between the number of iterations of the MCMC , time series length, shape of the prior distribution and accuracy are studied as well as the simulation time to run the inverse models. The Bayesian approach gives the most accurate results and has the advantage of considering several unknowns (conductivity and volumetric heat capacity), which is not the case for the studied standard. The Bayesian method needs much shorter time series than the ISO standard and produces robust results at all times of year, including when the average indoor-to-outdoor temperature difference was low. [ABSTRACT FROM AUTHOR]

A building influences its surrounding external environment, and its indoor environment is usually sensitive to its surroundings. In order to obtain a more accurate prediction of the indoor thermal behaviour of a building or a building stock, it is necessary to consider the interactions between the indoor and outdoor thermal environments. The modelling approach presented in this paper is based on a building energy model and the urban modelling tool SOLENE-Microclimat. A sensitivity analysis is undertaken to highlight the parameters which influence the performance of the building model. Then, the thermal indoor behaviour of a building is compared to in situ experimental measurements and the outdoor thermal environment is evaluated in terms of external surface temperatures. The model's accuracy and behaviour is evaluated and a crossover approach with the sensitivity analysis results is proposed. The model obtains a good level of performance for almost all variables, unless some external surface temperatures intervals. [ABSTRACT FROM AUTHOR]

Abstract: To streamline the design of the energy efficient buildings, appropriate tools are needed to assess their energy performance taking into account the microclimatic context. Numerical simulation seems to be the most suitable issue, but none tool is dedicate to the direct evaluation of the microclimate influence on the building energy consumption. A complete solution could be to use both CFD and thermoradiative simulation tools complementary with the coupling technique perspective. This paper presents both a developed CFD–thermoradiative coupled simulation tool and a typical application on an urban fragment. The results lead to two kind of observations: [•] Integration of the thermal model of a building in the microclimatic simulation platform enable a quantitative evaluation of the building energy demand regarding different urban design scenarii (e.g. mineralized vs vegetated). [•] Different physical phenomena do not contribute as much in the energy balance and it is important to compute precisely each one to obtain the small scale microclimatic influence. [Copyright &y& Elsevier]

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]

The Town Energy Balance (TEB) model has been refined and improved in order to explicitly represent street trees and their impacts on radiative transfer: a new vegetated stratum on the vertical plane, which can shade the road, the walls, and the low vegetation has been added. This modification led to more complex radiative calculations, but has been done with a concern to preserve a certain level of simplicity and to limit the number of new input parameters for TEB to the cover fraction of trees, the mean height of trunks and trees, their specific leaf area index, and albedo. Indeed, the model is designed to be run over whole cities, for which it can simulate the local climatic variability related to urban landscape heterogeneity at the neighborhood scale. This means that computing times must be acceptable, and that input urban data must be available or easy to define. This simplified characterization of high vegetation necessarily induces some uncertainties in terms of the solar radiative exchanges, as quantified by comparison of TEB with a high-spatial-resolution solar enlightenment model (SOLENE). On the basis of an idealized geometry of an urban canyon with various vegetation layouts, TEB is evaluated regarding the total shortwave radiation flux absorbed by the elements that compose the canyon. TEB simulations in summer gathered best scores for all configurations and surfaces considered, which is precisely the most relevant season to assess the cooling effect of deciduous trees under temperate climate. Mean absolute differences and biases of 6.03 and +3.50 W m−2 for road, respectively, and of 3.38 and +2.80 W m−2 for walls have been recorded in vegetationless canyons. In view of the important incident radiation flux, exceeding 1000 W m−2 at solar noon, the mean absolute percentage differences of 3 % for both surfaces remain moderate. Concerning the vegetated canyons, we noted a high variability of statistical scores depending on the vegetation layout. The greater uncertainties are found for the solar radiation fluxes received and absorbed by the high vegetation. The mean absolute differences averaged over the vegetation configurations during summertime are 21.12 ± 13.39 W m−2 or 20.92 ± 10.87 % of mean absolute percentage differences for the total shortwave absorption, but these scores are associated with acceptable biases: −15.96 ± 15.93 W m−2. [ABSTRACT FROM AUTHOR]

The TEB model has been refined and improved in order to explicitly represent street trees and their impacts on radiative transfers: a new vegetated stratum on the vertical plane, which can superimpose to road and low vegetation has been added. This modification has obviously complexified the radiative calculations, but has been done with a concern to preserve a certain level of simplicity and to limit the number of new input parameters for TEB to the cover fraction of trees, the mean height of trunks and trees, their specific Leaf Area Index and albedo. Indeed, the model is designed to be run over whole cities, for which it can simulate the local climatic variability related to urban landscape heterogeneity at the neighborhood scale. This means that computing times must be acceptable, and that input urban data must be available or quite easy to define. This simplified characterization of high vegetation necessarily induces some uncertainties on solar radiative exchanges, that were quantified through the comparison of TEB with a high spatial-resolution solar enlightenment model (SOLENE). On the basis of an idealized geometry of urban canyon with various vegetation layouts, TEB is evaluated regarding the direct and diffuse solar radiation received by the elements that compose the canyon, as well as the total shortwave radiation absorbed (after multiple reflections) by these elements. The cases of vegetationless canyons lead to root mean square errors less than 15?W?m-2 and biases less than 5?W?m-2. For the cases with high vegetation, the statistical scores are degraded (with a trend of underestimation of solar absorption by trees) but remain acceptable. It is interesting to emphasize that the summertime TEB simulations gave the best scores (∣bias∣ < 20?W?m-2) for all configurations and surfaces considered, which is precisely the most relevant season to assess the cooling effect of deciduous trees under temperate climate. [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]

Abstract: We present the results of a numerical exercise aimed at comparing the predictions of different conventional turbulent modelling approaches for natural convection at Rayleigh numbers characteristic of applications such as energy savings, fire safety or thermal comfort. A two-dimensional configuration was considered that consists of two adjacent rooms separated by a lintel in which natural convection is induced through heating on their opposite sides and subjected to diffusion of a pollutant from one room to the other. Seven contributions are available. The comparison is carried out, in terms of local or global quantities, for the mean thermal and dynamic fields and for the unsteady diffusion of the pollutant from one room to the other. Characteristic differences between steady RANS and unsteady two-dimensional DNS and LES approaches are observed and discussed. [Copyright &y& Elsevier]

• 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]