Preliminary study of the impact of urban greenery types on energy consumption of building at a district scale: Academic study on a canyon street in Nantes (France) weather conditions

International audienc

SOLENE-microclimate: A Tool to Evaluate Envelopes Efficiency on Energy Consumption at District Scale.

International audienc

CFD prediction of the daytime climate evolution inside a greenhouse taking account of the crop interaction, sun path and ground conduction

International audienceThe management of the local climate inside a greenhouse is essential to control the plant growth and reach the expected quality level for commercialization. In recent years, Computational Fluid Dynamics (CFD) proved to be an efficient tool to predict the greenhouse climate and therefore could serve as decision-making tool in the next future. Nevertheless, up until now, very few studies included together the sun path, plant interaction with local environment, and ground inertia effects. In addition, validation was generally based on only one or two parameters. The present study aims at analysing the evolution of the climate inside a greenhouse using CFD and taking account of the main heat and mass transfer processes at a daily time scale. A particular attention was paid to the validation of the model, considering air temperature and humidity inside and above the crop, as well as leaf temperature, crop transpiration and ground temperature. The CFD model solved the Reynolds Averaged Navier-Stokes equations, using a k-ε closure for turbulence. Specific submodels were established to include the sun path as well as the crop interaction with the local climate. The ground was also meshed to assess its inertia effects. 2D unsteady simulations were launched, considering only cases for which the wind blew perpendicular to the ridge. The validation of the model was undertaken on the basis of experiments conducted for a 100 m2 Venlo-greenhouse with Impatiens pot plants grown on shelves. A typical sunny day of spring in Angers, France, was retained. The model showed its ability to correctly predict the temperature and humidity dynamics inside the greenhouse as well as the leaf temperature and crop transpiration evolutions. Although slight discrepancies were observed for the air temperature and humidity inside the crop, the main trends were correctly predicted

The use of SOLENE-microclimat model to assess adaptation strategies at the district scale

International audienc

How to Design a Park and Its Surrounding Urban Morphology to Optimize the Spreading of Cool Air?

Green areas induce smaller increases in the air temperature than built-up areas. They can offer a solution to mitigating the urban heat island impacts during heat waves, since the cool air generated by a park is diffused into its immediate surroundings through forced or natural convection. The purpose of this study is to characterize the effect of several variables (park size, morphology of surrounding urban area, and wind speed) on the spreading of cool air. A parametric study is performed to run computational fluid dynamics simulations. The air temperature entering the computational domain was set at 35 °C, and the 2-m high surface included within the 34 °C isotherm was defined as an indicator of cool air spreading. The effects of park shape and orientation were negligible in comparison with size effects. The number of buildings was better correlated with the cooled surface area than the typical urban parameters identified in the literature (i.e., building density, aspect ratio, or mean building height). Since the number of buildings is obviously related to the number of streets, this result suggests that the greater the number of streets around a park, the wider the area that cool air spreads

What is the required level of details to represent the impact of the built environment on energy demand?

International audienceA full coupling between a CFD code, a thermo-radiative model and a building energy simulation model enables Solene-microclimat software to calculate both building thermal behavior and urban microclimate with the retroaction of buildings on microclimate. However, this full coupling is time consuming and it is legitimate to wonder if it is always necessary to perform such detailed simulations. In the framework of the MERUBBI project, simulations were carried out to answer this question. A set of simulations was designed to explore different kinds of configurations: three cities in France (Nantes, Paris and Strasbourg), three levels of density (from an isolated building to an implementation in the dense city center) and three kinds of buildings (an individual house in Paris, a residential building in Nantes and an office building in Strasbourg). To study the sensitivity of energy demand to the coupling detail, for each thermal flux at the external surfaces of the building, several levels of details were taken into account. For the impact of wind on convection, three modalities were considered: a constant convective heat transfer coefficient, calculated from the wind velocity at 10m; a convective heat transfer coefficient calculated from a vertical wind profile; a convective heat transfer coefficient calculated from the local wind velocity simulated with a CFD code. For the impact of air temperature on convection, two modalities are considered the use of the temperature measured at the nearest meteorological station; a local temperature calculated with the CFD simulation. For the impact of long-wave radiative exchanges, three modalities: the building exchanges with the sky without taking into account the masks of the environment and the long-wave radiative exchanges with the other surfaces; the building exchanges with the sky, taking into account the mask effects but not the exchanges with the surrounding surfaces; long-wave exchanges are taken into account with all kinds of surfaces in function of view factors. For the impact of shortwave radiations, two modalities: only direct and diffuse solar fluxes are taken into account; inter-reflections are considered. The results indicate that if the calculation of air temperature and convective heat transfer coefficient have few impacts in all the cases, the way of calculating long-wave and short wave radioactive fluxes has to be carefully considered, in winter as in summer. More detailed recommendations are given according to the density of the site in which the building will be implemented

Outil d'alerte pour identifier les périodes propices au rafraîchissement des parcs

International audienceAlert tool for identifying good periods to refresh parks. In the coolparks framework, mobile measurement campaigns will be performed to quantify the cooling induced by urban parks and the cool air diffusion within their surrounding urban areas. In order to identify the optimal conditions to implement these campaigns, fixed air temperature measurements performed during several years within parks (in Nantes, France) and their surrounding urban environment are utilized. Five interesting periods per season are identified for future campaigns : 3 are diurnal and 2 are nocturnal. For each of the {period, season} combinations, the meteorological conditions that allow to maximize the park cooling or the cool air diffusion within their close environment are investigated. Decision trees are constructed to facilitate the weather alert implementation allowing to identify the favorable days for future measurement campaigns taking place.Dans le cadre du projet CoolParks, des campagnes de mesures mobiles vont être menées pour mesurer le rafraîchissement occasionné par des parcs et la diffusion de cette fraîcheur dans leurs quartiers environnants. Afin d'identifier les conditions propices pour la mise en oeuvre de ces campagnes, des mesures fixes de température de l'air réalisées pendant plusieurs années dans des parcs nantais et leur environnement urbain sont utilisées. Cinq périodes intéressantes par saison sont identifiées pour les futures campagnes : 3 périodes diurnes et 2 périodes nocturnes. Pour chacune de ces combinaisons {période, saison}, les conditions météorologiques permettant de maximiser le rafraîchissement des parcs ou la diffusion de fraîcheur dans leur environnement proche sont étudiées. Des arbres de décision sont construits pour faciliter la mise en oeuvre d'alertes permettant d'identifier les journées propices à la tenue des futures campagnes de mesure

Implementation of street trees within the solar radiative exchange parameterization of TEB in SURFEX v8.0

International audienceThe 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

A pavement-watering thermal model for SOLENE-microclimat: development and evaluation

International audienceIn a dense urban area, pavement watering could be a solution to mitigate the Urban Heat Island. For now, mainly experimental studies have been used to evaluate watering techniques. In this study, a soil model dedicated to pavement watering has been developed within the urban climate model SOLENE-Microclimat. This watering model is presented and evaluated via a measurement campaign performed on an asphalt car park during hot days. The measurements campaign reveals that the surface cooling is mainly due to evaporation (80%). However, under warm conditions, the heat flux exchanged between the runoff water and the surface should also be modelled. Indeed, watering events are modelled through a runoff convective heat flux and a latent heat flux. The mean daily RMSE between estimated and observed surface temperature is 1.04 °C, 0.86 °C, 0.66 °C, 0.35 °C and 0.21 °C

PÉREZ, MARÍA E HIJAS [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201