A practical method for in-situ thermal characterization of walls

AbstractA practical and fast method for thermal characterization of walls based on complex Fourier analysis is proposed to determine the thermal capacitance (defined as the product of density and specific capacity) and the thermal conductivity for a building wall using the monitored inner/outer surface temperatures and outer heat flux. This method is useful for in-situ determination of walls’ thermal properties in stochastic regimes and therefore does not require any particular constraints in boundary condition.The minimum measurement duration was analyzed by determining the relative deviation between consecutive optimal values for R and C in order to reduce as much as possible the monitoring duration for energy auditors without losing accuracy

Thermal Analysis of Concrete Mixtures with Recycled EPS Aggregates

Reusing recycled waste materials in buildings is gaining more and moreattention for what it offers economic, environmental, and energy benefits;and many researchers are nowadays working on producing new sustainableconstruction materials incorporating recycled wastes. In this scope, thiswork uses an experimental approach aiming at understanding the effect ofincorporating Expanded Polystyrene (EPS) beads in concrete and proposingthermally improved concrete mixtures for the production of hollow blocksin Lebanese constructions by substituting fine aggregates with recycledproducts such as EPS in order to promote their insulating properties. Threedifferent diameters of EPS beads (2 mm ~ 3 mm, 3 mm ~ 4 mm and 4 mm ~5 mm) are studied with different volumetric ratios (20%, 40%, 60% and80%) in order to investigate the effect of EPS on the thermal properties ofconcrete. The results showed that the only the percentage of incorporatedEPS beads impacted the thermal performance of the concrete mixtureswhile the EPS diameters have a negligible effect on the thermal propertiesof the concrete samples

Analysis of Heat Transfer Phenomena inside Concrete Hollow Blocks

During both hot and cold seasons, masonry walls play an important role in the thermal performance between the interior and the exterior of occupied spaces. It is thus essential to analyze the thermal behavior at the hollow block’s level in order to better understand the temperature and heat flux distribution in its structure and potentially limit as much as possible the heat transfer through the block. In this scope, this paper offers an experimental and numerical in-depth analysis of heat transfer phenomena inside a hollow block using a dedicated experimental setup including a well-insulated reference box and several thermocouples and fluxmeters distributed at the boundaries and inside the hollow block. The block was then numerically 3D modelled and simulated using COMSOL Multiphysics under the same conditions, properties, and dimensions as the experimentally tested block. The comparison between the numerical and experimental results provides very satisfactory results with relative difference of less than 4% for the computed thermal resistance

Thermal analysis of Lille's old houses and assessment of different configurations of thermal insulation of their walls

Le secteur des logements présente un potentiel non négligeable d'économies d'énergie surtout au niveau du chauffage qui constitue une part importante des factures énergétiques en France. Notre travail s'inscrit dans l'optique de réduction des consommations énergétiques des logements en étudiant le transfert thermique dans les parois opaques du bâti ancien et en étudiant différentes configurations et différents types d'isolants thermiques. Après une analyse du contexte et des enjeux de la problématique énergétique des bâtiments anciens, nous avons abordé une analyse typologique des maisons anciennes lilloises en identifiant les quatre familles principales de typologies : la maison de courée, la maison ouvrière, la maison de ville et la maison bourgeoise ; en identifiant ainsi leurs ressemblances et leur variantes. Ensuite, nous avons étudié en détails le transfert thermique dans un mur en brique caractéristique de la région Nord-Pas-de-Calais; une étude expérimentale a été comparée à diverses approches théoriques en divers régimes (régime permanent, régime harmonique et régime quelconque). Après l'étude du mur dans son état initial (avant isolation), nous avons caractérisé expérimentalement cinq matériaux isolants (polystyrène, laine de bois, laine de mouton, lin et métisse) pour étudier ensuite leur apport en termes de réduction de déperditions thermiques pour le mur étudié. Nous avons appliqué expérimentalement 3 cm de polystyrène pour l'isolation du mur afin de valider la méthode théorique. Une fois cette dernière validée, une comparaison de différents matériaux isolants et différentes configurations (isolation par l'intérieur et isolation par l'extérieur) a été établie afin d'identifier la configuration et le(s) matériau(x) le(s) plus intéressant(s). Enfin, des simulations thermiques dynamiques à l'échelle du bâtiment ont été réalisées pour les différentes typologies dans le but de valider les résultats obtenus à l'échelle du mur, de comparer les performances énergétiques des différentes typologies et de quantifier les économies d'énergie possibles pour différents bouquets de travaux d'isolation.The housing sector has a significant energy saving potential especially in terms of heating which constitutes an important part of energy bills in France. Our work joins the optics of reducing energy consumption of housing by studying heat transfer in the opaque walls of old buildings and studying different configurations and types of thermal insulation materials. After an analysis of the context and the energy’s problematic of old buildings, we discussed a typological analysis of Lille’s old houses by identifying four main families of typologies: the “courée” house, the worker’s house, the town house and the mansion, thereby identifying their similarities and variations. Then, we thoroughly studied the heat transfer in a brick wall characteristic of the Nord-Pas-de-Calais region; an experimental study was compared to various theoretical approaches in various regimes (steady state, harmonic, and random regime). After the study of the wall in its initial state (before insulation), we experimentally characterized five insulating materials (polystyrene, wood wool, sheep wool, linen and recycled textile) in order to study then their contribution in terms of heat losses’ reduction through the studied wall. We experimentally applied 3 cm of polystyrene wall insulation to validate the theoretical method. Once it was validated, a comparison of different insulating materials and configurations (interior insulation and external insulation) was established to identify the most interesting configuration and insulation material(s). Finally, dynamic thermal simulations on the building scale were carried out for the different buildings typologies in order to validate the results obtained on the wall scale, to compare the energy performance of the different building typologies, and quantify the energy savings potential for thermal insulation scenarios

Identification paramétrique des propriétés thermophysiques d’un mur en brique ancienne : Approches expérimentale et numérique

International audienc

Parametric identification of thermophysical properties in masonry walls of buildings

ACLInternational audienceThe objective of this work is to improve the knowledge on the thermophysical characterization of opaque walls by determining the thermophysical properties of an experimental massive brick wall identical to old buildings walls in the North of Europe. This method allows the determination of equivalent dynamic thermal properties of existing building walls λ and ρCp by simple measurement records of the inner (Twi) and outer (Two) wall temperatures as well as heat flux at the inner (or outer) face of the wall Fi. The approach developed here consists in carrying out a parametric identification of the thermophysical properties of the wall in question (namely the thermal conductivity λ and the heat capacity ρCp), by comparing and minimizing the difference between the results resulting from the experimental tests and those resulting from the numerical model. The optimization of the identified parameters is based on the Levenberg-Marquardt algorithm via the Comsol tool. The validation of the algorithm was carried out as well as its use in different ambient conditions (harmonic and random temperature profiles). The investigated method shows satisfactory results for both λ (0.877, 0.880, and 0.935 W/(m.K)) and ρCp (1,012,400, 944,710, and 1,057,100 J/(m3.K)). The inner heat exchange coefficient hi was also successfully determined for the three tests with similar values (6.13, 6.53, and 6.03 W/m2.K). The results were also confirmed by comparing measured and numerical outer heat fluxes for the optimized values. The second part of this article is devoted to the study of the sensitivity of the results with respect to various parameters: the optimization algorithm, the total simulation time, the simulation time step, and the meshing element size

Experimental and Numerical Thermal Assessment of EPS Concrete Hollow Blocks in Lebanon

International audienceHollow concrete blocks can be thermally improved either by modifying their cavities shapes or by adding insulation materials into these cavities. It is also possible to improve the thermal conductivity of solid concrete matrix by incorporating some materials to its composition like recycled solid wastes for example. This paper offers a solid and comprehensive study for thermally improved hollow blocks through a case study from the Lebanese context and provides a scientific basis for improving the thermal performance of these blocks. The effect of adding expanded polystyrene (EPS) beads to the concrete solid mixture was investigated in this study through numerical and experimental approaches. The experimental and numerical results were in good agreement and the potential thermal improvement by adding EPS beads to concrete mixture was examined on both numerical and experimental levels. The numerical results for the three-dimensional (3D) model allow the visualization of the heat flux and temperature distribution in the block as well as the air velocity and convective heat exchanges inside the cavities of the block. The results showed that the block thermal resistance can almost double by adding 18 g of polystyrene beads to the concrete mixture

Thermal performance evaluation of a massive brick wall under real weather conditions via the Conduction Transfer function method

The reliable estimation of buildings energy needs for cooling and heating is essential for any eventual thermal improvement of the envelope or the HVAC equipment. This paper presents an interesting method to evaluate the thermal performance of a massive wall by using the frequency-domain regression (FDR) method to calculate CTF coefficients by means of the Fourier transform. The method is based on the EN ISO 13786 (2007) procedure by using the Taylor expansion for the elements of the heat matrix. Numerical results were validated through an experimental heating box with stochastic boundary conditions on one side of the wall representing real weather conditions and constant temperature profile on the other side representing the inside ambiance in real cases. Finally, a frequency analysis was performed in order to assess the validity and accuracy of the method used. The results show that development to the second order is sufficient to predict the thermal behavior of the studied massive wall in the range of frequencies encountered in the building applications (one hour time step). This method is useful for thermal transfer analysis in real weather conditions where the outside temperature is stochastic; it also allows the evaluation of the thermal performance of a wall through a frequency analysis

Hygrothermal behavior of wood fiber insulation, numerical and experimental approach

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