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In the context of the energy transition, new construction materials are emerging, notably bio-based materials such as wood concrete. This paper investigates the hygrothermal performance of walls constructed with wood–cement concrete. First, the thermal properties of wooden concrete, namely thermal conductivity, effusivity, and diffusivity, are experimentally characterized in both dry and wet conditions. Second, in situ measurements are carried out on a house in Lyon, a city in France, constructed with mono-layered wood–cement walls. This involves monitoring the temperature and relative humidity levels both inside and outside the building, as well as at three distinct positions within the wood walls over a 6-month period (from 20 April 2023 to 20 October 2023). The hygrothermal analysis at the center of the wall reveals that the wood wall effectively moderates fluctuations in the external temperature and relative humidity. Following this, a numerical study is performed to check the reliability of the adopted Reduced Heat, Air, and Mass (HAM) model to reproduce the hygrothermal performance of the wood–cement wall. The results show a strong agreement between the simulated and measured data, confirming the applicability of the 'Reduced HAM' model for the prediction of the hygrothermal behavior of wood–cement walls. [ABSTRACT FROM AUTHOR]

Straw bale building construction is attracting a revived public interest because of its potential for reduced carbon footprint, hygrothermal comfort, and energy savings at an affordable price. The present paper aims to summarize the current knowledge on straw bale construction, using available data from academic, industry, and public agencies sources. The main findings on straw fibers, bales, walls, and buildings are presented. The literature shows a wide variability of results, which reflects the diversity of straw material and of straw construction techniques. It is found that the effective thermal conductivity, density, specific heat, and elastic modulus of straw bales used in construction are in the range 0.033–0.19 W/(m·K), 80–150 kg/m3, 1075–2000 J/(kg·K), and 150–350 kPa respectively. Most straw-based multilayered walls comply with fire resistance regulations, and their U-value and sound reduction index range from 0.11 to 0.28 W/m2 K and 42 to 53 dB respectively, depending on the wall layout. When compared to standard buildings, straw bale buildings do provide yearly reductions in carbon emissions and energy consumption. The reductions often match those obtained after applying energy-saving technologies in standard buildings. The paper ends by discussing the future research needed to foster the dissemination of straw bale construction. [ABSTRACT FROM AUTHOR]

Highlights: [•] Evaporation and transpiration were evaluated separately. [•] The thermal resistance of green roofs was evaluated using a low-speed wind tunnel. [•] The impact of grey water on evapotranspiration and green roof thermal resistance was studied. [ABSTRACT FROM AUTHOR]

Abstract: Green roofs have several environmental benefits, such as improving building energy efficiency. The present paper provides a comprehensive study of the impact of a green roof on building energy performance. A model of green roof thermal behavior was coupled with a building code to allow the evaluation of green roof foliage and soil surface temperatures. Simulations were conducted for a single-family house with conventional and green roofs in a temperate French climate. In the summer, the fluctuation amplitude of the roof slab temperature was found to be reduced by 30°C due to the green roof. The heat flux through the roof was also evaluated. In the summer, the roof passive cooling effect was three times more efficient with the green roof. In the winter, the green roof reduced roof heat losses during cold days; however, it increased these losses during sunny days. The impact of the green roof on indoor air temperature and cooling and heating demand was analyzed. With a green roof, the summer indoor air temperature was decreased by 2°C, and the annual energy demand was reduced by 6%. The present study shows that the thermal impact of green roofs is not functionally proportional to the leaf area index parameter. It also shows the high dependency of this impact on the roof insulation. Finally, the simulations suggest that green roofs are thermally beneficial for hot, temperate, and cold European climates. [Copyright &y& Elsevier]

Abstract: Green roofs have a positive effect on the energy performance of buildings, providing a cooling effect in summer, along with a more efficient harnessing of the solar radiation due to the reflective properties found inside the foliage. For assessing these effects, the thermodynamic model was developed as well as the thermo-physical properties of the green roof components were characterized. Its typologies and vegetation styles should also be studied. The proposed model is based on energy balance equations expressed for foliage and soil media. In this study, the influence of the mass transfer in the thermal properties and evapotranspiration were taken into account. We then added the water balance equation into our model and performed a numerical simulation. By assuming the outdoor conditions, the roof support temperature and the drainage water as inputs, the model evaluates the temperatures evolution at foliage and soil ground levels. A parametric study was performed using the proposed model to classify green roofs depending on the considered climate condition. Comparisons were undertaken with a roof slab concrete model; a significant difference (of up to 30 °C) in temperature between the outer surfaces of the two roofs was noticed in summer. The model was experimentally validated according to green roof platform, which was elaborated. The mass transfer effect in the subtract was very effective in reducing the model errors. Simulation results show that the use of vegetation in the roof building improves not only thermal comfort conditions, but the energy performance of a building. [Copyright &y& Elsevier]

Plant-based concrete is a construction material which, in addition to having a very low environmental impact, exhibits excellent hygrothermal comfort properties. It is a material which is, as yet, relatively unknown to engineers in the field. Therefore, an important step is to implement reliable mass-transfer simulation methods. This will make the material easy to model, and facilitate project design to deliver suitable climatic conditions. In recent decades, numerous studies have been carried out to develop models of the coupled transfers of heat, air and moisture in porous building envelopes. Most previous models are based on Luikov's theory, considering mass accumulation, air and total pressure gradient. This theory considers the porous medium to be homogeneous, and therefore allows for hygrothermal transfer equations on the basis of the fundamental principles of thermodynamics. This study presents a methodology for solving the classical 1D (one-dimensional) HAM (heat, air, and moisture) hygrothermal transfer model with an implementation in MATLAB. The resolution uses a discretization of the problem according to the finite-element method. The detailed solution has been tested on a plant-based concrete. The energy and mass balances are expressed using measurable transfer quantities (temperature, water content, vapor pressure, etc.) and coefficients expressly related to the macroscopic properties of the plant-based concrete (thermal conductivity, specific heat, water vapor permeability, etc.), determined experimentally. To ensure this approach is effective, the methodology is validated on a test case. The results show that the methodology is robust in handling a rationalization of the model whose parameters are not ranked and not studied by their degree of importance.