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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]

• The interconnections distribution in fibers determines the heat transfer model. • The development of a thermal conductivity equation considers the radiative heat transfer. • The bale's thermal conductivity varies according to the fiber orientation. • Thermal conductivity depends on the chemical composition of the straw. Straw fibers are natural fibers that have a strong insulating property and a minimal environmental effect, making them suitable construction materials. In the construction sector, to predict the building energy consumption, the thermal conductivity of the materials composing the envelopes must be precisely known, which is not the case for the straw material. The properties of a straw bale are variable and mainly depend on its density, fibers orientation, chemical composition, temperature and relative humidity. Consequently, this study consists of determining a mathematical equation to predict the effective thermal conductivity of straw bales that can be applied to all straw types, in different circumstances. For this purpose, the size, distribution, and morphology of straw fibers are first determined from microscopic images. Second, a mathematical model for estimating the thermal conductivity is suggested using the heat transfer models of porous and fibrous materials. The numerical model is validated by an experimental study that measures the thermal conductivity of straw bales by altering their density between 80 and 120 kg/m3, their relative humidity between 15 % and 95 %, and their temperature between 15 ˚C and 55 ˚C. The experimental results show that the thermal conductivity increases from a minimum of 0.047 W/(m∙K) to a maximum of 0.09 W/(m∙K) when increasing the three altered factors. For a straw fiber having 40% cellulose content, the thermal conductivity increased from a minimum of 0.05 W/(m∙K) to a maximum of 0.0832 W/(m∙K). This behavior is found the same for the numerical findings. The comparison of numerical and experimental values shows a good agreement, with a root mean square error of 0.005 W/(m∙K) and a scatter index of 5.5 %. [ABSTRACT FROM AUTHOR]

• A mathematical model to predict the aerogel blanket's effective thermal conductivity at the material scale is developed considering the gaseous, radiative, and solid heat transfer. • The in-situ thermal performance of the aerogel-based blankets is estimated via a real-scale experimental test facility using the average method as well as using two dynamic statistical methods. • The annual energy performance and economic analysis of a single-family detached house with and without the aerogel-based blanket is examined for different climate. Composite materials made of silica aerogel in a fibrous inorganic mat, hereafter called "aerogel blankets", represent promising insulating materials that can overcome the low mechanical resistance of monolithic aerogels, while preserving their very low thermal conductivity. Firstly, this paper details an experimentally validated mathematical model to predict the aerogel blankets' effective thermal conductivity, as a function of the blankets' density, fiber volume fraction, and temperature. Secondly, an experimental test building retrofitted internally with a layer of needle glass fiber (NGF) aerogel blanket is monitored, and its thermal behavior is compared to the baseline case before the retrofit. The retrofitted wall U-value is derived from experimental data series using stationary and transient parametric methods. Then, a validated whole building Energy Plus numerical model is used to predict the annual energy consumption of a detached single-family house retrofitted with an NGF aerogel blanket, in the climates of Brussels (Belgium), Nice (France), and Stockholm (Sweden). Lastly, a 1-D COMSOL multiphysics model evaluates the economic profitability of installing the blanket as an interior thermal insulation system. Results show that the aerogel blankets have an effective thermal conductivity of about 0.0165 W.m−1.K−1. The designed mathematical model can reliably predict the gaseous conduction in the blanket, but deviations from the experimental measurements appear when considering the radiative and solid conduction components. The blanket's effective thermal conductivity increases with fiber volume fraction and temperature while its dependency curve to density is concave, with a minimum for densities of around 140 kg.m−3. Retrofitting a wall with 2.5 cm of NGF aerogel blanket as an internal insulation system almost doubles the thermal resistance of the experimental wall and decreases the heating load by more than 40 % in all tested climates. Internal thermal insulation with aerogel blankets is more profitable than conventional insulation materials, in places of high floor area price, because it can preserve the indoor living space. [ABSTRACT FROM AUTHOR]

The thermal conductivity of commonly used phase change materials (PCM) for thermal energy storage (TES), such as, fatty acids, paraffin etc., is relatively poor, which is one of the main drawbacks for limiting their utility. In the recent past, few attempts have been made to enhance the thermal conductivity of PCM by mixing different additives in the appropriate amount. Graphene nanoparticles, having higher thermal conductivity may be a potential candidate for the same, when mixed appropriately with different PCM. In present study authors have carried out the numerical investigation for the melting of graphene nano-particles dispersed PCM filled in an aluminum square cavity heated from one side. In this work, the graphene nanoparticles are mixed in three different volumetric ratios (1%, 3%, and 5%), with three different commonly used categories of organic, inorganic and paraffin PCM (namely, Capric Acid, CaCl 2 ·6H 2 O, and n -octadecane) to see the effect on melting of composite PCM developed. The resulting transient isotherms, velocity fields, and melting front and melt fractions thus have been deliberated in detail. These results clearly indicate that the addition of graphene nanoparticles increases melting rate but can also hamper the convection heat transfer within large cavities. The study also shows that such enhanced PCM can be effectively used for different TES applications in different fields. The prediction of temperature variation and rate of melting or solidification may be found useful especially for designing such TES devices. [ABSTRACT FROM AUTHOR]