The urban heat island effect is strongly linked to the use of dense mineral pavements with high thermal inertia and lacking passive heat dissipation mechanisms. This article evaluates the potential of evaporatively cooled concrete pavers, based on capillary action and evaporation by incorporating recycled, bio-based, and lightweight materials to develop functional porosity. Ten paver formulations were developed using natural or recycled sand, hemp fibers and shives, and lightweight aggregates. Compressive strength, density, capillary absorption, and thermal behavior were characterized. Tests were conducted outdoors in full sunlight over 48 h in comparison with reference urban materials. The results show that capillary action alone is insufficient to induce effective cooling. The raw recycled sand formulation exhibits high capillary absorption but reaches maximum temperatures of 43-44 °C, which may be due to its low interconnected porosity that limits evaporation. Conversely, formulations incorporating bio-based materials or lightweight aggregates showed a more favorable balance between water availability, reduced density, and surface cooling performance. Hemp-based pavers reach maximum temperatures of 38-40 °C, while those incorporating expanded clay range between 37 and 39 °C, representing a reduction of 7 to 13 °C compared to bitumen and maintaining mechanical strengths suitable for pedestrian use. The results suggest that effective evaporative cooling is associated with sufficient capillary absorption, efficient water transfer toward the surface, and moderate density limiting heat storage. This study demonstrates that high capillary absorption alone does not ensure effective evaporative cooling. By systematically comparing recycled, bio-based and lightweight aggregates, the results reveal that evaporative cooling efficiency probably depends on the functional connectivity of the pore network and on a moderate material density limiting heat storage.

In Building Energy Simulations (BES), thermal interactions between buildings and their surroundings are frequently represented using simplified Convective Heat Transfer Coefficient (CHTC) models based on idealized urban environments. Climatic conditions such as heatwaves can intensify natural convection, thereby modifying airflow and surface heat exchanges. However, the majority of CHTC models employed in BES do not explicitly account for natural convection. Among those that do, the formulations vary significantly, which can lead to further discrepancies in BES outcomes. The present study investigates the impact of different convective regimes within the street canyon (inertially driven, thermally driven and transitional flows) on CHTC calculation through the dimensionless Richardson number (Ri). A CFD URANS model of a 2D street canyon was developed, calibrated, and validated against experimental data from the literature. By enabling or disabling the buoyancy hypothesis within the numerical model, the ratio of the overall CHTC (hc,ext) to the forced convection component (hc,for) was computed over a range of Ri = [2.6 10-3 ; 1.2 102]. The findings of this study indicate that natural convection becomes non-negligible on CHTC calculation above a critical Richardson number (Ric) ranging from 0.140 to 0.689, depending on the street walls and diurnal or nocturnal conditions. When the flow is fully dominated by thermal effects, this ratio displays a power-law dependence on the Richardson number, scaling as Ri0.4 during daytime and Ri0.5 during nighttime. A comparative analysis was conducted to evaluate the numerical results against CHTC models of BES tools and previous studies incorporating natural convection.

Lightweight, bio-based walls often suffer from low thermal inertia, leading to sensitivity to external temperature fluctuations. This study explores how clay-based plaster can enhance this behaviour through analytical and experimental investigations. The analytical approach highlights the role of internal areal heat capacity and show that increasing the effusivity and thickness of the inner plaster layer improves the wall's dynamic thermal response. Experimental results demonstrate that applying the studied clay plaster increases the internal surface heat capacity of wood walls from 16.8 kJ & sdot;m-2 & sdot;K-1 to 60.8 kJ & sdot;m-2 & sdot;K-1, which represents about 90% of the value observed in heavier structures. These findings provide practical insights into the use of earthen coatings to enhance thermal inertia and energy performance in lightweight construction systems.

The Urban Heat Island (UHI) effect describes the phenomenon whereby, during the nighttime, cities experience higher temperatures than the rural surroundings. This phenomenon amplifies indoor and outdoor heat stress for city residents during heat waves, which are becoming more frequent and intense as a result of climate change. Several factors determine the indoor temperature experienced by the occupants of buildings, including the building’s solar exposure, the materials used in its construction, and the storey on which it is located. For instance, during heat waves, people living on the upper storeys of buildings suffer greater thermal discomfort, which can lead to an increase in morbidity. To evaluate indoor comfort, the urban processes at the city scale (e.g. UHI) and the building‑level processes must be simulated simultaneously. This is achieved by coupling an Urban Canopy Model (UCM) with a Building Energy Model (BEM). Consequently, this work focuses on improving the BEM included into the Town Energy Balance (TEB) urban climate model, with the goal of better assessing indoor heat stress and city‑wide heating and cooling energy consumption. A significant improvement is the implementation of a multi‑storey energy balance model that represents indoor air temperature, specific humidity, and mean radiant temperature across the building storeys. All processes that were once modeled as averages over the entire building are now modeled storey‑by‑storey. For instance, shutter operation and window opening are simulated separately for each storey.The improved TEB‑BEM is validated by comparing its results with newly conducted measurements from the VERTIC (Vertical Evaluation of Residential Indoor Comfort) campaign. The measurement campaign is conducted in a single, unoccupied building (a former student residence) that features two sets, West and East-facing, of four vertically stacked bedrooms. Continuous recordings of air temperature, relative humidity, mean radiant temperature, and conductive heat fluxes through the envelope are taken for each room throughout a full year in Toulouse. The meteorological forcing data required for TEB simulations is also collected. The results from the VERTIC campaign, launched in October 2025 and still in progress, will be presented with a particular emphasis on the differences between temperature and thermal comfort on different storeys (e.g. ground storey compared to top storey). The evaluation results for the improved TEB-BEM will also be presented.Ultimately, this research will increase our understanding of how urban climate affects occupants’ thermal comfort and building energy demand while delivering decision‑support tools that enable cities to design effective adaptation strategies for climate change challenges.

Indoor swimming pools (ISPs) consume significant amounts of electrical and thermal energy to ensure the heating of water and air, ventilation, and maintaining adequate humidity levels. This is measured in GWh per year for large installations, such as Olympic swimming pools (SPs). In this paper, the problem is initially addressed using a phenomenological approach at steady state of the air-water coupling, based on a real case study. The aim is to identify the key phenomena and the constraints that are the most sensitive, including those related to water and air quality management. A key action lever is found in evaporation, and more specifically, water temperature and the indoor dewpoint temperature, which act as its precursors. In a second step, two different strategies were tested to reduce energy consumption for water heating. It was determined that a strategy which incorporates night setback in conjunction with a precise restart time yields a maximum gain of 4%. The second strategy aims to enhance the energy recovery of thermal solar panels by enabling slight overheating of the pool. Its large volume provides effective energy storage, with estimated energy savings of up to 17% for a 1 degrees C overheating. This strategy appears to be a viable option, as it is straightforward to implement. However, the impact of water overheating on the energy consumption of AHU still needs to be analyzed and managed.

Improving our understanding of thermal interactions between urban buildings is a major challenge regarding future climate projections. In this paper, we quantify the influence of radiative trapping on indoor thermal comfort into dwellings located in an urban canyon during a summer heatwave. A numerical urban model based on the finite element method (FEM) coupled to a radiosity method is used to simulate a Mediterranean city building. The complete thermal problem, including conduction, convection, and radiation, is solved in a transient regime using meteorological data representative of heatwave conditions. Physiological Equivalent Temperature (PET) indicator is used to assess indoor comfort, accounting for radiation exposure. The results show that longwave radiative trapping leads to a sustained increase in indoor PET of approximately 4K, whereas the influence of shortwave varies by +/- 1K.

Thermochemical energy storage (TCES) is a method of storing energy by using reversible chemical reactions to absorb and release heat. TCES materials generally possess the highest volumetric energy density and negligible heat losses during cyclic charging/discharging when compared with sensible and latent heat storage materials. The controllable charging/discharging processes in the TCES materials make them suitable for long-term or seasonal thermal energy storage, which can help improve the resilience of the existing energy system and built environment. In recent years, there has been a growing number of studies on the use of cementitious materials as low-cost and low-carbon thermochemical energy storage materials, including ettringite, calcium aluminate cements, and geopolymers. In this study, the state-of-the-art development using cementitious materials for thermo-chemical energy/heat storage applications is reviewed and systematically compared in terms of their compositions, energy storage operating conditions, and energy storage performance. Technical recommendations are proposed for standardised characterisation and testing protocols of these cementitious (composite) materials used for thermochemical heat storage. The current research challenges and future research needs in this field are also discussed.

Moisture transfer is a key phenomenon for simulating the energy balance of the walls of historical buildings as it has an impact on indoor and outdoor comfort, energy consumption and the durability of the walls. It is therefore essential to consider moisture transfer through walls when simulating old city centres, in order to properly assess the impact of different retrofit solutions on building and city energy balances. However, urban climate models neglect this phenomenon. The objective of this paper is to integrate the coupled mass and heat transfers into the urban climate model Town Energy Balance (TEB). A specially designed numerical method for solving hygrothermal transfers at the urban scale is updated and the hygrothermal transfer through walls is integrated using an IMplicit/EXplicit (IMEX) discretization scheme with large spatiotemporal scales. The reliability of this modified version of TEB for representing a historical district is verified by comparing the simulated results with in-situ measurements in a building of the medieval city centre of Cahors (France). The comparison is carried out for several points in the wall and for indoor conditions, running from June to December 2021. The integration of the moisture transfers through the walls greatly improves the moisture estimation inside the building. This new version of the model gives a good representation of the hygrothermal behaviour of a historical building and could therefore be used to compare several renovation scenarios for the medieval centre of Cahors, with regard to durability, energy and microclimatic issues.

Cementitious material with a high ettringite content can be considered effective in a long-term (seasonal) thermochemical energy storage (TCES) system, resolving the issue of intermittency between production and availability of renewable energy. However, to evaluate the behavior of the storage material, an experimental study of energy storage in a thermochemical reactor containing the proposed material was required. A new and innovative large-scale energy storage prototype based on ettringite material has been developed and tested. This prototype regulates the temperature, humidity, flow rate, and pressure of the flow circulating through a 50 L CSA (calcium sulfoaluminate) sample monolith. This CSA cement formed an ettringitic phase (3CaOA & sdot;Al(2)O(3)A & sdot;3CaSO(4) A & sdot;32H(2)O) to store thermochemical energy at about 60 C-degrees. After the storage cycle (high temperature, low relative humidity), the material was cooled down to room temperature and kept there until energy was needed. The stored energy was released on demand by the hydration of cement from a cold, humid nitrogen flow. About 50 MJ/m(3) was discharged from the 50 L monolith during the hydration cycle. The prototype showed the monolith's ability to store and release energy: the first discharge phase experimental test showed an energy release of about 10 % of the theoretical value (43 MJ/m(3)) for a temperature increase of 6 K. Complementary investigations have to be performed to understand the impact of the monolith cracks on the energy performances.

Cool pavements represent an innovative and promising technique to mitigate the urban heat islands phenomenon. The cool pavements studied in this work, allow limiting the increase in the surface temperature, thanks to the evaporation of the water conducted through capillary pores. The cooling effect of the pavement is reflected by its surface temperature value. When pavements having the same initial conditions are exposed to the same weather conditions, their thermophysical properties control their surface temperatures. Therefore, this study focuses on an exhaustive thermophysical characterisation of a large number of concrete pavements by measuring their properties related to the cooling effect according to literature.In this context, this work covers an experimental study consisting of three stages and involving 21 concrete pavements of different formulations divided into two series. Firstly, the different studied pavements are identified. The second stage details the thermophysical characterisation of these pavements. In the third stage, they are simultaneously exposed to the solar radiation for three sunny summer days and their surface temperatures are monitored. The results obtained from this study show a wide range in the properties of the pavements, with an order of magnitude that can reach 2.107 for hydraulic conductivity and 3.7 for thermal effusivity. Furthermore, they reveal that the pavements can be divided into two types according to their ability to drain water, draining or non-draining pavements. The wide range in the results is mainly due to the different formulations that constitute the pavements, which provides importance and novelty to this study. Finally, this latter will constitute an appropriate database for two upcoming works. The first one will investigate the coupling of cool pavement's properties that controls its cooling effect under outdoor summer conditions. The second work will develop a numerical model of coupled heat and mass transfers that occur in this pavement.

Historical city centres face two major challenges in the 21st century: heritage conservation and energy retrofitting. Wall insulation in traditional buildings is at the crossroads of these two issues. When studying the retrofit of the walls, other factors also need to be considered, such as the durability of the walls, the life cycle of the materials used for insulation, the indoor and outdoor comfort in summer. The aim is to propose a method for taking all these objectives into account when choosing the insulation technique for historical walls. To do this, the TEB (Town Energy Balance) urban climate model is used, because it considers the urban microclimate, the energy behaviour of buildings and moisture transfer through walls. A VTT model is integrated into TEB, to include the risk of mold growth. The medieval city centre of Cahors (France) was used as a case study. The retrofit of two types of wall was assessed: “massive” brick walls, and “light” walls with a timber-framed structure, filled with bricks. Six renovation scenarios were studied, including four insulation materials and both internal and external insulation positions. The results obtained underline the need to study the retrofit of the two types of building separately, because the recommendations made for insulation vary depending on the type of wall studied.

Impermeable paving surfaces constitute one of the main causes of the aggravation of the urban heat island phenomenon. The replacement of such surfaces with cool pavements represents an innovative and promising approach to mitigate this phenomenon. In this study, the investigated cool pavements allow to restrict the rise in the surface temperature by facilitating the evaporation of water through capillary pores. This process occurs from the water-supplied base to the surface exposed to solar radiation. The pavement's cooling potential is quantified by its surface temperature, influenced by various factors, including prevailing weather conditions, thermophysical properties of the pavement, and its initial temperature and saturation state. Within the scope of this research, the pavement’s qualification for its cooling potential is carried out based on the results of an experimental thermophysical characterization. The main objective is to identify the thermophysical properties governing the surface temperature of the pavement under external climatic conditions.To achieve this objective, 21 cement concrete pavements with different formulations are initially identified. These pavements are categorized into two series: the first (denoted as BS) comprises 8 pavements made from recycled sand and containing hydrophilic materials, while the second (denoted as BI) includes 13 pavements made from structural insulating concrete. The methods employed for pavement characterization are outlined, and the corresponding results, encompassing thermophysical properties measurements and surface temperature values, are presented. Analysis of these results reveals new correlations between thermophysical properties and surface temperature. These correlations highlight the coupling between pavement properties, that dictate surface temperature under real summer conditions, contingent on whether the pavement is draining or non-draining. Furthermore, a robust negative linear correlation (R2= 0.92) is identified between surface temperature and evaporation rate under controlled conditions. This underscores the pivotal role of evaporation in substantially regulating the surface temperature of both types of pavements.

Calcium sulfoaluminate (CSA) cement-based materials have high ettringite content enables heat storage, enhancing the thermal inertia of buildings. This study aims to optimize the porous network of foamed CSA material in terms of porosity, permeability and mechanical strength so that they can be effective in building applications as supporting structures with heat storage capacity. To achieve these goals, a foaming process method using hydrogen peroxide (H2O2) and surfactant was used to control the porous network. The H2O2 and surfactant contents varied from 0.5 % to 1.2 % and 0.01 %-0.05 %, respectively, and generated a wide range of material densities from 589 to 1184 kg/m3- and hence a wide range of properties in terms of porosity (43-70 %), permeability (2.6 10- 13 -7.1 10-12 m2) and compressive strength (0.8-9.4 MPa). Then, an abacus correlating material properties, found by surface fitting, linking porosity, gas permeability and compressive strength, allowed the material to be optimized in accordance with the needs of each building application. The CSA paste consisting of 1 % H2O2 and 0.03 % surfactant, with 66 % porosity, 4.1 10-12 m2 permeability, and 1.8 MPa compressive strength, was the optimal mix- design for solar storage box applications (for short-term storage). The CSA paste consisting of 0.5 % H2O2 and 0.01 % surfactant, with 43 % porosity, 5.6 10-13 m2 permeability, 9.4 MPa compressive strength, appeared to be optimal for self-supporting wall storing solar heat (longterm storage).

A perforated heat flux plate for building use is presented and compared with traditional full surface plates. Laboratory calibration tests using a guarded hot plate apparatus showed that the performance of the new perforated CAPTEC® plate is comparable to a solid, standard plate. However, in-situ tests with surface-mounted sensors in a building wall indicated that the CAPTEC® plates were reliable but their poor thermal contact and the edge effects in the perforations lead to an offset factor for the output voltage. The presence of perforations did not lead to any significantly improved measure due to evaporation or condensation on the wall. A basic simulation was performed to show the edge effects caused by the perforations and an experimental correction factor for the field measurements is proposed.

Greenery strategies and shaded pedestrian passages have become requirements for designing smart cities in developed countries. One of the most difficult challenges for designers is designing cities in hot and arid climates while maintaining a proper level of outdoor thermal comfort. The designers focus on creating a comfortable climate for people throughout the afternoon under the hot sun, particularly in countries where summer temperatures rise excessively for more than seven months per year, as in Iraq. This study compares two Baghdad cities: Haifa Street, which was built in 1984 on a Western design pattern, and the second city, which the researchers designed according to the requirements of construction in an arid climate, such as street and building orientation, aspect ratio, sky view factor, the influence of courtyards, and the role of albedo. The second city is planned to cover the same total area as the first. The results of the two cities were compared and analyzed using ENVI-met software. To conduct a comparison between the two cities on a typical summer day, two indices, PMV and Tmrt, were used. The results showed that the proposed new city design reduced Tmrt and PMV, contributing to improved thermal comfort. The proposed design reduced the Tmrt value in the model by 10.5°C in proportions of 90% of the total urban area. Furthermore, the suggested design offers superior thermal values on a typical summer day than Haifa Street.

To properly evaluate retrofit solutions for historical city centres on an urban scale, it is necessary to consider moisture exchange through walls.However, urban climate models usually neglect moisture transfer through walls.This work proposes a new numerical method for solving coupled mass and heat transfer, especially adapted to urban scale simulation.This method has been numerically validated by comparison with a reference tool DELPHIN, on several study cases.Moreover, its reliability for representing old walls is verified by comparing the results of the simulations with data measured in historic buildings in Cahors (France).The integration of a coupled transfer model solved with this resolution method into an urban climate model allow the simulation of the hygrothermal behaviour of old walls and the evaluation of their energy and microclimatic impact at the urban scale.Peer-review under the responsibility of the organizing committee of the ICMB23.