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The aim of this work was to investigate the thermal behavior of solid wood used as building materials. Three tropical wood species namely Iroko (Milicia excelsa), Bilinga (Nauclea diderrichii), and Tali (Erythrophleum suaveolens) were chosen. The thermophysical properties in the longitudinal, radial and tangential directions were determined experimentally for different moisture contents. Asymmetrical hot plate method was used to measure the thermal conductivity and volumetric heat capacity. The influence of water content and the direction of the fibers on thermophysical properties of the species studied were investigated. The results show that thermal conductivity and volumetric heat capacity increase with moisture content, while the diffusivity decreases. In the wide range of moisture content considered, thermal conductivities varied between 0.1 and 0.6 Wm−1 K−1. The increase of moisture content by 1% induces a 0.2% increase in thermal conductivity for Bilinga, 0.4% for Tali and 0.3% for Iroko. Tali, whose density is the highest, presented high values of thermal conductivity in longitudinal direction but lowest values in radial and tangential directions compared to other species. Thermal conductivity is 2 to 3 times higher in the longitudinal direction than in the radial and tangential directions. The volumetric heat capacity was not influenced by the direction of the heat flow.

Thatch fibres grow in large quantity in the Adamawa region of Cameroon. During the long dry season, these fibres cause numerous fire incidents, which not only devastate large areas of cash crops, but also contribute to increase emissions of greenhouse gases into the atmosphere. This article aims to show how fibres could be used with compressed clay bricks to manufacture an insulating material used in building. Four fibre contents 1%, 2%, 3% and 4% made up the sample studied. The asymmetric hot plate methodology was used to determine the thermophysical properties of these composite materials. The volumetric heat capacity and the thermal effusivity of these materials were estimated. These two parametres were used to determine their apparent thermal conductivities. The results obtained show that the thermal conductivity decreases as the volume of fibres in the mixture increases. It is 0.689 W·m-1·K-1 for simple compressed clay bricks and 0.510 W·m-1·K-1 for a dosage at 3% of thatch fibres. In a bit to validate the results of the pilot study of the apparent thermal conductivity, the heat mass capacity of this composite material was achieved through the use of the dehydration method. The relative difference obtained with the results of the volumetric heat capacity carried out with these two methods was good. All results showed that the use of fibres in compressed laterite brick gives a more insulating composite material that respects Civil Engineering Norms.

Uninsulated concrete block walls commonly found in tropical region have to be retrofitted to save energy. The thickness of insulation layer used can be reduced with the help of modified laterite based bricks layer (with the considerably lower thermal conductivity than that of concrete block layer) during the retrofit building fabrics. The aim of this study is to determine the optimum location and distribution of different materials. The investigation is carried out under steady periodic conditions under the climatic conditions of Garoua in Cameroon using a Simulink model constructed from H-Tools (the library of Simulink models). Results showed that for the continuous air-conditioned space, the best wall configuration from the maximum time lag, minimum decrement factor and peak cooling transmission load perspective, is dividing the insulation layer into two layers and placing one at the exterior surface and the other layer between the two different massive layers with the modified laterite based bricks layer at the interior surface. For intermittent cooling space, the best wall configuration from the minimum energy consumption depends on total insulation thickness. For the total insulation thickness less than 8 cm approximately, the best wall configuration is placing the half layer of insulation material at the interior surface and the other half between the two different massive layers with the modified earthen material at the exterior surface. Results also showed that, the optimum insulation thickness calculated from the yearly cooling transmission (estimated only during the occupied period) and some economic considerations slightly depends on the location of that insulation.

One of the greatest challenges in the construction sector throughout the world is the development of appropriate building materials that can reduce energy consumption. In this work, an investigation on the thermophysical properties of three wet composite building materials was carried out: the black pouzzolan, the red pouzzolan and sand cinder blocks. Experimental measurements were carried out on these three materials each with a water contentranging between 0 and 5%.Using an asymmetrical hot plate device, a transient method, the thermal effusivity and volumetric heat capacity were estimated experimentally with respect to water content. With the values of the mass specific heat capacity of pouzzolans, sand and cement separately measured by the Differential Scanning Calorimeter (DSC) method, the values of the volumetric heat capacity of these composite materials were evaluated according to their water content calculated from the theoretical developed model. The results obtained are in good agreement with those determined experimentally with the asymmetrical hot plate method (maximum standard deviations 5%). Results reveal that the thermal conductivity of red pouzzolan cinder blocks (e.g. λ = 0.503 W m−1K−1 at 0% water content) and of black pouzzolan cinder blocks (e.g. λ = 0.549 W m−1K−1 at 0% water content) are lower than that of sand cinder blocks (e.g. λ = 0.875 W m−1K−1 at 0% water content). Results also show that pouzzolans cinder blocks have higher volumetric heat capacity than sand cinder blocks. These results further confirm that blocks based on pouzzolans are better insulator materials than sand blocks (usually uses) and can contribute significantly to the energy saving and thus reduce the GHG emission in the air-conditioning building.

International audience; This article presents two methods dedicated to the determination of the thermophysical properties of natural fibers grown in almost all countries of the world. Experimental measurements were carried out on four dry natural plant fibers of low density: kapok fibers; groundnut shell fibers; rattan fiber and coconut fibers. The thermal effusivity has been estimated by a transient method (the asymmetrical hot plate method). With experimental measurement of the specific heat capacity by Differential Scanning Calorimeter (DCS) which made it possible to deduce the thermal conductivity of such fibers. The thermal properties estimated by this method are then compared to the results obtained by radial flux flow method, a steady state method that directly measures the thermal conductivity. The experimental results compared by these two methods are in good agreement (relative error < 5%). The thermal conductivities of kapok fibers (λ = 0.045 W m−1 K−1) and coconut fibers (λ = 0.055 W m−1 K−1) obtained all showing that they can be used as substitutes for synthetic insulating materials such as polyester fibers (λ = 0.045 W m−1 K−1) or glass wool (λ = 0.04 W m−1 K−1). Also the thermal conductivities of kapok and coconut fiber measured correspond with the results obtained by other measuring methods in the literature. This can then help us infer that the quadrupole 1D model developed to estimate the thermal properties of bulk fiber is valid and can allow a good estimation of thermo-physical properties. Therefore, the thermal conductivity of groundnut shell fibers and cane fibers is estimated in the order of λ = 0.093 W m−1 K−1 and λ = 0.072 W m−1 K−1 respectively.

This study aims to optimize the thicknesses of insulation layers in external walls of continuously used building in a tropical region according to shade level. The investigation is carried out under steady periodic conditions for various wall orientations using a Simulink model constructed from H-Tools (the library of Simulink models). Walls are assumed to be insulated using expanded polystyrene material. The shade level of the building site is assumed to be varying from 0 to 97% with an increment of 25% or 22%. Yearly cooling load is calculated and used as input to an economic model for the determination of the optimum insulation thickness. It is seen that as shade level increases, optimum insulation thickness decreases at an average rate of 0.035 cm, 0.029 cm and 0.036 cm per percentage of solar radiation blocked for south, north and east/west oriented wall, respectively. Results also show that energy savings vary between 46.89 $ m−2 and 101.29 $ m−2 and payback periods vary between 3.56 years and 4.97 years depending on shade level and wall orientation.

This paper presents the study of a hot strip made of thin rectangular electrical resistance with a thermocouple placed on its centre. The purpose was to simultaneously estimate thermal effusivity and conductivity in a limited time (t2 20 s) and that has higher sensitivity to the thermal conductivity between t1 and t2 (2D transfer). The thermal effusivity is estimated between 0 and t1 by minimization of the quadratic errors between the experimental curve and the curve calculated by the classical hot plate model. The thermal conductivity is estimated between t1 and t2 but using the complete 2D model. To validate the model and the estimation process, experimental tests were realized on three materials with low diffusivities (a < 2 × 10−7 m2 s−1) and having typical area of 6 cm × 4 cm and typical thickness of 1.5 cm.

d ´´ ´ Abstract An experimental study was carried out in order to determine the properties of local materials used as construction materials. Cement stabilized compressed bricks were tested. The thermal properties of lateritic soil based materials were determined. The objectives of work reported in this paper are to determine the effect of addition of pozzolan or sawdust in lateritic soil brick on the thermal properties. It was shown that the effect of incorporation of pozzolan or sawdust is the decreasing of the thermal conductivity and density. The moisture content of these materials can modify their thermal performance. Thus a study of the influence of the water content on the thermal conductivity k and the thermal diffusivity a is presented. The thermal conductivity as a function of water content increases rapidly between 0 and 12% for lateritic soil. The thermal diffusivity curve presents a maximum for values of water content of 15% for lateritic soil and 8% for lateritic soil-pozzolan or lateritic soil-sawdust. However, the composite materials used for building shielding must present sufficient mechanical strength to be suitable for constructions. According to the experimental results the effect of adding cement or pozzolanic stabiliser is expressed in increase of strength of samples studied. � 2004 Elsevier Ltd. All rights reserved.

An experimental study has been carried out to determine thermophysical properties of tropical wood. Five species, covering a wide range of densities of most of the wood used in Central Africa, has been chosen. These properties which characterise the thermally insulating materials, are related to basal density in order to help predict the thermophysical properties of any tropical wood as soon as its basal density is known. Steady-state and unsteady state methods were used to measure thermal conductivity and thermal diffusivity, respectively. Specific heat and thermal effusivity were then calculated. The influences of moisture content and the principal cutting plan on the thermophysical properties of tropical wood were examined. Higher conductivity, diffusivity and effusivity in the axial direction were observed, as well as the non-directional dependence character of the specific heat. It was also observed that thermal conductivity of tropical wood increases with infradensity both in the axial and the transverse directions. Finally, it was shown that conductivity and effusivity increase and thermal diffusivity decreases with the increase of moisture content. © 2005 Elsevier Ltd. All rights reserved.