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International audience; This paper presents a simulation tool chain for the prediction of thermal comfort in passive urban buildings during summer and under heat wave conditions. The tool chain encompasses EnergyPlus building energy model and the Urban Weather Generator and UrbaWind tools to consider the impacts of the urban environment on building loads. This chain of tools is computationally efficient and does not require notable expertise for the simulations. To assess its accuracy, this simulation results are compared to in situ measurements. This paper describes the measurement setup, analyzes the measurement results and reveals a satisfactory model accuracy through a comparison

One significant effect of urbanization is the modification of environmental conditions, with potential effects on the functioning of urban ecosystems and on their ability to perform functions and to provide service. This is due to both the multiple changes of surfaces and soils, and to an increased human pressure. These changes have indeed major negative impacts on natural resources such as air, water, soil, and biodiversity they host, and may affect locally the human thermal comfort, in addition to the climate change. A better understanding of the physical and biogeochemical processes leading to these changes is then crucial in order to propose and to optimize the mitigation and adaptation strategies. Following the recent efforts in the development of Critical Zones Observatories (CZOs), a new research initiative will regroup well-monitored and well-characterized urban field sites all over the French national territory within a National Observation Service called Observil. This observatory aims to address a multidisciplinary approach of urban environments, through a smart definition of appropriate variables and indicators required to better describe the physical and geochemical processes involved in the quality and the dynamic of the soil-surface-atmosphere compartments in cities. To do that, a common Spatial Information System dedicated to the creation of a structured observation database is under construction, in order to regroup the data from a large network bringing together 9 French cities under very contrasted environmental conditions (urban morphology, geology, climate). The main scientific questions addressed by this observation network project will be presented, along with a description of the the selected variables measured on the different sites.

International audience; The current challenge is to reduce the building energy consumption, in hot and humid climates, for which air conditioning is widespread. Up to now, the lack of criteria that identify the available cooling resources and the level of performance of technical solution has represented the major obstacle. To address these issues, the authors propose a new set of indicators to fully inform the decision-making process of the bioclimatic design of fully space-conditioned buildings in a hot and humid climate. This set of indicators provides an overview of the exploitable environmental resource (external air through external convection, natural ventilation and sky radiation cooling) referred as the Environmental Resource Indicators and of the capacity of the building to exploit those resources referred as the Building Performance Indicators. The indicators are implemented for a very basic two-story residential building in the hot, humid climate of Djibouti. The case study shows not only the ability of the indicators to reflect the bioclimatic performances of the buildings but also their ability to give an overview of the building heat exchanges, from which the implication of improper bioclimatic solutions on building cooling consumptions can easily be identified. These indicators are a means to help choose which technical solutions are most suited to the local climate, which is very useful for designers and architects in the early stages of building design.

International audience; In the Sub-Saharan African countries like Djibouti, the energy situation, the high rate of urban areas growth and the inadequate techniques of construction offer an exciting potential for the bioclimatic approach and sustainable construction. However, this poorly explored potential requires an investigation of different construction types in Djibouti and a good knowledge of the behavior of buildings components. Further a low energy building can be obtained because of the good realization of all its components. In fact, roofs call for attention as they represent a large part of a building's total surface area and amount of absorbed solar radiation. The goal of this paper is to investigate the benefit of using double skin-ventilated roofs for reducing cooling load under the Djiboutian climate. It is a first step towards ideas that will transform local construction practices to make them effective in energy, economic and functional dimensions. During investigation, we compared a ventilated roof assembly with traditional configuration after that the consistency of our model was validated with experiment of the literature findings. The computational fluid dynamics (CFD) model has been used for the characterization of the airflow and heat transfer phenomena in the ventilation cavity and provide fundamental information about the thermal performance of the roof. The results show the amount of the energy saving obtainable by the double-skin ventilated roof.

International audience; The aim of this study is to make available new data concerning the validation of CFD (Computational Fluid Dynamics) results through experimental measurements campaigns on full scale mechanically ventilated test rooms. The experimental set-up is based on a new configuration of the test cell “Minibat” (CETHIL – INSA Lyon, France), equipped with a realistic mixing ventilation system. In this paper, experimental – numerical comparisons are presented in terms of mean air velocity for an isothermal situation. The investigations have been focused in the region near the supply air diffuser as the overall air flow in ventilated enclosures is mainly due to the inlet air jet. The results show a decent agreement between measurements and numerical values in terms of velocity profile at the inlet. In addition, the overall flow development in the air jet is well represented numerically. However, there are some discrepancies concerning the point of maximum velocity in the air jet which must be addressed by further investigations, both experimentally and numerically.

Superficial condensation phenomena often occur on the glazed elements of buildings. As a result, the aim of this study is to put forward an experimental approach to assess the condensation rate on building glazing surface for full-scale room tests under realistic conditions. The proposed method for condensation quantification is applied in this work for surface condensation on a cold glazing (2.90 m × 2.30 m) within a ventilated test room (6.20 m × 3.10 m x 2.50 m). We first describe the full-scale test cell, focusing then on the experimental apparatus employed for the condensation study. This is followed by the description of the methodology for the condensation rate quantification. The approach is based on image processing techniques, using condensation pictures. This allows also to reveal the mechanisms behind the condensation appearance and growth. On the other hand, the experimental data achieved by this method are compared with theoretical results based on condensation rate and heat transfer coefficient correlations available in the literature. An overall difference of up to 18% between the measured results and the theoretical results was found for the condensation rate. Consequently, the method proposed in this work leads to promising results concerning the condensation rate quantification on cold glazing within full-scale enclosures.

On one hand, physical adsorption, also named physisorption, is a process that can be used to storage thermal energy with an energy density higher than sensible or latent storages. On the other hand, in Europe, 26% of the final energy consumption is related to the energy systems of households [1] and 80% of this energy is needed for heating purposes [2] . The consequence is the development of thermal energy storage systems, based on physisoprtion, for building application. The objective of this paper is first to present the basics concerning physisorption heat storage. Then, experimental developments from the literature are reviewed, based on three scales: the material scale, the reactor scale and the system scale. From the review, development of commercial systems faces with scientific and technological issues that must be addressed to reach a higher technology readiness level with an acceptable system cost.

International audience; The paper investigates the effect of natural convection during differential scanning calorimetry measurements of phase change materials. We performed series of numerical simulations to characterize and quantify the perturbation on the measured thermogram. This perturbation becomes significant at the end of the fusion process. It manifests itself as an increase of the heat flux amplitude which accelerates the fusion process. Three correlations are built from the simulation results. The two first correlations quantify the amplitude of the heat flux deviation. The third correlation locates the time at which the perturbation occurs. The correlations are valid for large DSC capsules (around 1ml), and high Prandtl materials (paraffins, salt hydrates, fatty acids). They enable to define the experimental conditions for which natural convection becomes negligible.

International audience; This paper presents a heat exchanger prototype containing PCM material designed to provide a 1kW heating power during 2 hours (i.e. energy storage of 2kWh). The exchanger is tested in a closed-loop wind tunnel, used to provide constant airflow rates with temperature changes selected so that the PCM is allowed to melt, then to solidify. Temperature and air velocity measurements are achieved for eight airflow rates and the heating power is estimated. The second objective of this work is to provide detailed results suitable with the validation of numerical models. Therefore, the geometry of the exchanger is detailed and the uncertainty associated with the heating power measurement is given. Results show that enough energy is stored in the exchanger, yet the heating power is lower than 1kW before 2 hours because of the use of a of constant airflow rate during the tests. On the other hand, the global behaviour of the heat exchanger is rather simple, which gives confidence in using a simplified approach in further work and help with optimising the current prototype.

Excessive indoor moisture promotes the growth of mold and condensation on building envelope, which lead to severe IAQ problems. Given the transient, unsteady heat and mass transfer problem, studies dealing with the condensation phenomenon are generally lacking in the literature, especially studies on the condensation rate prediction. Consequently, this paper presents a method to quantify experimentally the condensation rate of droplets formed on a cold glazing surface in a full-scale entirely controlled test room (6.2 x 3.1 x 2.5 m). The condensation qualitative characterization, i.e. the moment of its appearance and its growth mechanism, is achievable using a macro-photography technique. From the time-series of droplet images captured, an image post-processing method is used to detect the droplet contours and to estimate the condensation mass flow rate. Comparisons between experimental and theoretical results show some agreement, which could validate the feasibility of imaging techniques in full-scale condensation studies. Those first results are encouraging and valuable since there were no similar studies in the literature at such the scale. Further investigations are needed in order to clarify all these aspects related to the accuracy of the condensation rate quantification methodology developed in this work.

Recent studies concerning phase change material (PCM) characterization show that important errors occur if differential scanning calorimetry (DSC) experiments are misinterpreted. Therefore, it is important to know the influence of such misinterpretation on system modeling. The present work deals with phase change materials integrated in building structure to reduce overheating. The objective is to evaluate the discrepancies consequences (temperatures, heat fluxes), due to the use of the misinterpreted DSC experiments at different heating rates to determine the enthalpy, in comparison with those determined with the actual value of the enthalpy of the PCM determined by a proven inverse method. A numerical model of a single-family house with a phase change material mortar is developed to evaluate the thermal comfort in the building. The results show that for free-running temperature, none of the enthalpy curve deduced directly from DSC can predict correctly the thermal behavior of the house and the thermal comfort. Moreover, the more the DSC heating rate and the more the discrepancy with the results from the reference inverse method.

Computational Fluid Dynamics (CFD) is a promising way, nowadays, to predict the air Flow in enclosures. As a result, the objective of this study is to assess the potential of CFD technique to predict the air Flows driven by buoyancy in heated real-scale rooms. The numerical model is validated using experimental data for fullscale test rooms; therefore, the experimental set-up is rst presented. This is followed by the numerical model description, focusing on its principal elements: computational domain geometry, discretization, turbulence model, radiation model, and thermal boundary conditions. In addition, a simpli ed approach is proposed to integrate a heat source in CFD models: Term source homogeneously spread all over the volume of the heat source. Comprehensive experimental-numerical comparisons are presented in terms of heat transfer to the walls of the test room, heat source behavior, and plume development. The results show that the model developed in this study leads to realistic predictions. Finally, the simpli ed CFD description of heat sources developed here can be extrapolated for other con gurations - di erent power, heat emission (convection/radiation), dimensions, and shape. Consequently, this method can be applied in detailed studies dealing with thermal comfort, indoor air quality, and energy consumption for heated rooms.

International audience; An experimental investigation is conducted to characterize the natural convection heat transfer along panels which contain phase change materials (PCM). A dedicated configuration has been defined for this study. In this configuration, the natural convection heat transfer is triggered by a temperature scan in the ambient air. The temperature scan is responsible for the energy storage and release in the PCM panels. The corresponding experimental setup was built and several melting and solidification tests were performed, with different values of the ambient temperature scan speed. The tested PCM panel is the Energain®wallboard by DuPont—. The system first reaches a stationary regime when the PCM is fully solid or liquid. During the stationary regime, the wall to air temperature difference and the convection heat flux are constant. The phase change causes an increase of these quantities. It is characterized by a first dynamic stage, a wall temperature slowdown / retrogression process, and a second dynamic stage. The two dynamic stages are well correlated to the PCM thermal characteristics. However, the temperature slowdown / retrogression phenomenon is unexpected. It consists in an extreme slowdown of the wall surface temperature evolution, which turns into a retrogression during the solidification experiments. The temperature slowdown / retrogression has never been observed before with PCM wallboards.

International audience; In construction, the use of Phase Change Materials (PCM) allows the storage/release of energy from solar radiation and internal loads. The application of such materials for lightweight construction (e.g., a wood house) makes it possible to improve thermal comfort and reduce energy consumption. The heat transfer process between the wall and the indoor air is convection. In this paper, we have developed a numerical model to evaluate several convective heat transfer correlations from the literature for natural, mixed and forced convection flows. The results show that the convective heat transfer highly influences the storage/release process in case of PCM walls. For the natural convection, the numerical results are highly dependent on the correlation used and the results may vary up to 200%. In the case of mixed and forced convection flows, the higher is the velocity, the more important is the storage capacity.

International audience; This paper is the continuity of Guo's work [Phys.Rev., 2009, 046708] about a lattice Boltzmann model for axis-symmetric flows. This is a radius weighted LBM model: all the moments are proportional to the radial coordinate r. A Taylor series analysis is performed on the discrete Boltzmann Model in order to assess the consistency. The truncation error terms do not indicate any error increase along the radial direction, but they contain a spurious term u r /r which considerably reduces the model accuracy when radial velocity is non-null: simulation results highlight a reductions of the order of accuracy (from second to first). A new axis boundary condition was created to improve the model accuracy and to cope with the spurious error term. It was assessed though several test cases.

International audience; The objective of this study is to evaluate three different phase change models used to predict the energy behaviour of a PCM cement mortar sample. Reference data are measured on large samples of composite material using a special experimental set-up. The phase change models tested are: the apparent specific capacity method, the enthalpy method assuming a pure body and the enthalpy method assuming a binary mixture. Numerical results are compared to the reference data of heat flux and energy stored/released. The main conclusions of the study are: (1) the thermodynamically inconsistent apparent specific capacity method is not suitable, (2) the enthalpy method gives better results than the specific capacity method and (3) the enthalpy method gives better results with an appropriate guess of the enthalpy curve.

This chapter deals with the use of phase change materials integrated in building opaque walls. Many considerations are discussed in this chapter including physical considerations about building envelope heuristic arguments, phase change material integration, experiments and numerical modelling. Even if the integrated phase change material has a good potential for reducing energy demand, further investigations are needed to really assess their use.

International audience; The present paper is the first comprehensive review of the integration of phase change materials in building walls. Many considerations are discussed in this paper including physical considerations about building envelope and phase change material, phase change material integration and thermophysical property measurements and various experimental and numerical studies concerning the integration. Even if the integrated phase change material have a good potential for reducing energy demand, further investigations are needed to really assess their use.

International audience

International audience; The aim of this article is to analyse CO2 emissions caused by passenger transport in France: which socio-demographic groups travel, for what kinds of journey (local or long distance), how and why? Research focusing on the analysis of individual travel can improve the understanding of CO2 emissions by identifying upstream socio-economic factors, and also enable a better assessment of the potential social impact of measures introduced to limit greenhouse gases due to transport.Calculations are based on the latest French national transport survey (1994). Distances covered and CO2 emissions were estimated for each journey and for each surveyed individual. A socio-demographic characteristic typology was built and results were obtained through this analysis.If equity and accessibility issues are to be taken into account, planned policies cannot be of the same type if linked to mobility segments. An environmental tax system to limit CO2 emission increases appears appropriate for long-distance trips. Results are more varied for local journeys, which are often more of a necessity. Nevertheless, income brackets, and measures concerning urban planning or the growth of new car fleets, seem more pertinent.

This paper provides a new correlation to determine the heat transfer coefficient between an air flow and a plate made of phase change material (PCM). This correlation was built for the simulation of heat storage units containing PCM plates subjected to an inlet temperature step. The presented correlation has the following form: NuPCM x;t ¼ NuPSM$f PCM. The first term NuPSM is for a plate made of traditional material. The term fPCM is a perturbation due to the phase change in the plate. Each term depends on 5 non-dimensional parameters. One of them represents the advance in the total heating or cooling process, in order to take into account the transient evolution of the convective coefficient. The correlations are built using the Least Squares Method, from series of CDF simulation data. The shape of the perturbation fPCM reveals a complex evolution of the temperature repartition in the PCM plate. Finally, a nodal model of the plate has been developed in order to test the provided new correlation and other correlations available in the literature. The results obtained with the present correlation show better agreements with the CFD results, which make this correlation suitable for the simulation of PCM heat storage systems. This work was supported by the “Corporación Tecnológica de Andalucía” by means of the project “MECLIDE-Soluciones estructurales con materiales especiales para la climatización diferida de edificios” with the collaboration of DETEA. The work was partially funded by the Spanish Government (ENE2011-22722 and ULLE10-4E-1305) and the European Union (COST Action COST TU0802). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2009 SGR 534).

Radiative cooling is a renewable technology that can complement or partially replace current cooling technologies. Coupling radiative cooling with another technology, such as solar collection could foster its development and implementation in the market. Therefore, a numerical model capable to simulate the behavior of a coupled radiative cooling and solar collection system is developed and presented in this paper. The model is validated with experimental data for both solar collection and radiative cooling operation, and a sensitivity analysis is performed in order to determine the most influencing parameters. Results show the potential of the device to perform the double functionality: solar thermal collector and radiative cooler. As expected the heating power ( 17.11 k W h / m 2 ) is one order of magnitude higher than the cooling one ( 2.82 k W h / m 2 ). The sensitivity analysis determined the existence of an important role played by 5 parameters (air gap thermal conductivity, absorptivity/emissivity of the radiator at 7–14 μm wavelength range, transmissivity of the cover material 2 at 7–14 μm wavelength range, water inlet temperature, and water inlet flow) and 4 combinations of these parameters in the radiative cooling mode.