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Energy performance of earthen wall office buildings in equatorial and tropical climates is investigated using a Simulink model and EnergyPlus software. The main aim of this numerical simulation study is to quantify the magnitude of the effect of adding a fibrous material or a stabiliser in the compressed earth block on the energy requirement or thermal comfort of a building taking into account different operating modes of the cooling system (continuous, intermittent and no cooling) in some climatic conditions in Cameroon. For continuous air-conditioned space and intermittent air-conditioned space, the assessment parameters are cooling load and its peak, while it is thermal comfort index for no air-conditioned space. Thermophysical properties of the used earthen materials were previously measured. The results show that the mixing of sawdust or pozzolan with earth material improves its performances for continuously and intermittent cooling space case, and degrades it for non-air-conditioning space case. It can provide a reduction in peak sensible cooling rate by up to 6.3%, 7% and 10% in Yaounde, Douala and Garoua, respectively. The thermal comfort index obtained with earth block wall can be smaller than that of earth block with 8% of sawdust wall by up to 10.41% and 13.03% (in August) in Yaounde and Douala, respectively.

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.

This study aims to describe the onsite sanitation and the quantification of faecal sludge in the city of Yaoundé. The city of Yaoundé, The population of Yaoundé City is about 3.1 million inhabitants in 2018 , will reach 4.7 million in 2030 with an average annual growth rate of 3.5%. The city of Yaoundé is dominated by an autonomous sanitation system which is used by 99% of households. Domestic wastewater of the city is mainly dealt through on-site sanitation systems represented by septic tanks, traditional pit latrines, ventilated improved pit latrines, etc A survey was carried out among 1100 households in the city of Yaoundé. The choice of household to be surveyed was made according to the stratified sample method. It is reviewed, the methods of quantification of existing used sludge, in order to choose a method adapted to the context of the city of Yaoundé. Several criteria are analyzed to access to the sludge produced by households: the existence or not of roads, their state of deterioration, the types of sanitation structure, the position of the structure in relation to the waterways, etc. Among the methods for quantifying the sludge explored, we found that "the specific production method" is more adapted in the context. But this method has been revised in order to integrate the analyzing elements on the accessibility of the facilities. The application of the method used has been done on 120 pit emptying during two months (june and july 2018). The choice of these pits as been done hazardly on the potential of 600 pit emptying in the city of Yaoundé during this period. The accumulation rate of faecal sludge in the city of Yaoundé is of 0.356 l/hab/jour for septic tanks and of 0.21 l/hab/jour for pit latrines. It equally varies according to the luxury of the habitat. At the scale of the city, in 2018, 41% of single pits and 84% of septic tanks can be drained by trucks. The interval between two emptying is of 7 years for septic tanks and 10 years for pit latrines. Finally, the city of Yaoundé produces 2018, 283 175 m3 of faecal sludge per year, thus 51.7% can be drained by truck (146 514 m3), either 401 m3/jour. Only 52.4% are collected and (210 m3/jour) and sent-on the site of unloading of NOMAYOS., La présente étude porte sur le traitement sur l’assainissement dans la parcelle et la quantification des boues de vidange dans la ville de Yaoundé. La population de la ville de Yaoundé 3,1 millions d’habitants en 2018, atteindra 4,7 millions en 2030 avec un taux de croissance moyen annuel de 3,5%. La ville de Yaoundé est dominée par un système d’assainissement autonome qui est utilisé par 99% des ménages. Les eaux usées domestiques de la ville sont principalement traitées par des systèmes d'assainissement autonomes représentés par des fosses septiques, des latrines à fosse traditionnelles, des latrines à fosse améliorée ventilées, etc. Une enquête a été effectuée auprès de 1100 ménages de la ville de Yaoundé. Le choix de ménage à enquêter a été faite selon la méthode stratifiée. Il est passé en revue, les méthodes de quantification des boues de vidange utilisées existantes, afin de choisir une méthode adaptée au contexte de la ville de Yaoundé. Plusieurs critères sont analysés pour évaluer l’accès aux boues produites par les ménages : l’existence ou non de voirie, leur état de dégradation, les types de l’ouvrage d’assainissement, la position de l’ouvrage par rapport aux voies d’accès etc. pour la quantification des boues de vidange. Parmi les méthodes de quantification des boues de vidanges explorées, nous avons trouvé que « la méthode production spécifique » est plus adaptée au contexte. Mais cette méthode a été revue afin d’intégrer les éléments d’analyse sur l’accessibilité des ouvrages d’assainissement. L’application de la méthode retenue a été faite sur 120 ouvrages d’assainissement vidangés entre Juin et juillet 2018, choisis au hasard sur le potentiel de 600 ouvrages vidangés dans la ville de Yaoundé pendant cette période. Le taux d’accumulation des boues de vidange dans la ville de Yaoundé est de 0,356 l/hab/jour pour les fosses septiques et 0.21 l/hab/jour pour les latrines. Il varie également en fonction de standing de l’habitat. A l’échelle de la ville, 41% des fosses uniques et 84% des fosses septiques peuvent être vidangées par camion. L’intervalle entre deux vidanges est de 7 ans en moyenne pour les fosses septiques et 10 ans pour les latrines. Au final, la ville de Yaoundé produit en 2018, 283 175 m3 de boues de vidange par an, dont 51,7% peuvent être vidangés par camion (146 514 m3), soit 401 m3/jour. Seuls 52,4% de la quantité vidangeable, sont collectés en 2018 (210 m3/jour) et acheminés sur le site de dépotage de NOMAYOS.

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.

This paper aims to study the mechanical behavior and surface chemistry in relationship with moisture content of Iroko (Milicia excelsa), Bilinga (Nauclea diderrichii), and Tali (Erythrophleum suaveolens). Mechanical characterization was done experimentally using tensile and bending tests. Chemical semi quantitative analysis of the wood at 10%, 15%, 20% and 30% of moisture content was investigated using attenuated total reflectance Fourier transform infrared spectroscopy. The main chemical functions involved by the presence of water were identified as well as the other functional groups. The ratio between lignin and carbohydrates was estimated for all the wood species. The results indicated a negative correlation in the relation between moisture content and mechanical properties. Tali had the higher bending strength while Iroko had the lowest value. The average percentage change rate of the Young’s moduli induced by 1% of moisture content changes, especially between 10% and 20%, varied with the wood species: 1.69% in Tali, 1.65% in Bilinga and 2.54% in Iroko approximately. The infrared spectra obtained differed among species. The results also showed that Iroko contained higher lignin and were the least sustainable according to mechanical properties. The bands at 3340 cm−1 and 1635 cm−1 were more impacted by moisture content. Keywords: Tropical wood, Chemical component, Strength, Moisture content, ATR-FTIR

Cameroon's economic growth demands an increase in energy-services. These, in turn, increase demand for energy carriers, such as electricity. However, electricity generation based on fossil fuels emits greenhouse gases (GHGs). In this paper, three scenarios of electricity demand in Cameroon are presented, assuming different economic growth levels. The corresponding expansion of the electricity generation system (and its emissions) was then analyzed. The MAED model is used for energy demand assessment. While, the MESSAGE model is used to optimize the supply system and quantify GHGs emitted. 2012 was chosen as the base year, with an overall electricity consumption of 5 TWh. Results shows that in 2035, electricity demand could reach 35 TWh, 19 TWh and 17 TWh for High, Intermediate and Low scenario respectively. Hydro, Thermal (GAS, HFO, LFO), Biomass, Solar and Wind power plant projects have been considered in the study, with different implications based on countrypolicy. Results show that GHG emissions constraints can be met if appropriate investments are made. Keywords: Electricity production in Cameroon, Energy planning, Renewable energies, Greenhouse gas

Most of the composite materials are manufactured by mixing several aggregates such as sand, cement, gravel and others. The aim of this paper was to present a method dedicated to the determination of the thermal effusivity and porosity for building material that is in aggregates granular form. A transient asymmetrical hot plate device was constructed to characterize the thermal effusivity. Experimental measurement of the specific heat capacity using the Differential Scanning Calorimeter (DSC) and measurement of apparent density enabled the estimation of the volumetric heat capacity of the aggregates. With these values and that of the thermal effusivity pre-estimated using the simplified 1D model, the study of the reduced sensitivity of the experimental temperature to parameter E ag and ρ C ag and ρ C h is carried out. The thermal effusivity is then estimated from a complete 1D model by minimization of the quadratics errors between the experimental temperature curve and simulated one. Experimental results applied on clusters with maximum diameter aggregates 1.6 mm; 1 mm; 0.8 mm, 0.4 mm and 0.2 mm show that for the same diameter, the black pouzzolan have higher thermal effusivity and thermal conductivity than the red pouzzolan (e.g. for D = 1 mm, E BPZ = 418 J m - 2 K - 1 s - 1 / 2 , λ BPZ = 0.166 W m - 1 K - 1 , E RPZ = 418 J m - 2 K - 1 s - 1 / 2 , λ RPZ = 0.135 W m - 1 K - 1 ). Pouzzolan has the smaller value of porosity and lateritic the greater one.

The prediction of the air temperature (IT) and relative humidity (IH) in a building can help to reduce energy consumption for air conditioning. The purpose of this work was to apply the artificial neural network (ANNs) for an hourly prediction, 24–672 h in advance of (IT) and (IH) in buildings found in hot-humid region. The inputs used in the model are 12 last values of indoor and outdoor air temperature and relative humidity. The experimental building is built with cement hallow block in Douala-Cameroon. IT and IH were collected for 24 months. The experimental data were used to determine the optimal ANN structure with levenberg-marquardt algorithm using Matlab software. The optimal structure was the multilayer perceptron (MLP) with 36 input variables, 10 hidden neurons and two neurons in the output layer. The activation functions were respectively the hyperbolic tangent in the hidden layer and the linear function in the output layer. Moreover, the IT and IH results simulated by using the ANN model were strongly correlated with the experimental data, with the coefficient of correlation of 0.9850 for IT and 0.9853 for IH. These results testified that ANN can be used for hourly IT and IH prediction.

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.

The mechanical and thermal behaviour of traditional clay bricks were investigated after one hour exposure at three different temperatures (200, 400, 600 °C). Specimens collected from small-scale production units in Cameroon were used. It has been shown that the mechanical behaviour of traditional clay bricks after exposure depends on their quality of firing, which is most of the time affected by the limits of the traditional technologies used for their production. Among the samples collected, bricks of good quality and low quality of firing were identified. Bricks of good quality of firing have shown a progressive decay of mechanical strength from 200 °C after an increase from the room temperature to 200 °C. Those of low quality have shown an increase in mechanical strength from 400 °C after a stability observed between the room temperature and 400 °C. Both bricks have shown a phenomenon of embrittlement with the increase of the exposure temperature, which was much accentuated in the case of less fired bricks. Thermal conductivity of both bricks has shown a quasi-stability with exposure temperature due to their high porosity from the beginning.

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.

In Cameroon, these last centuries, an increase in energy demand for cooling and heating in buildings has been witnessed all over the world. Solutions must be proposed by researchers and specialists of buildings to remedy this situation. In this study, a literature review on the thermal insulation applications to external walls of buildings was presented, and a case was investigated in a tropical wet and hot climate. The economic model including the cost of insulation material and the present value of energy consumption and the cost over a lifetime of 22 years of the building, were used to find the optimum insulation thickness, energy saving, and payback period, for buildings in Cameroon. Materials that extruded polystyrene were chosen and used for two typical wall structures (Concrete block (HCB) and compressed stabilized earth block wall (CSEB)). The yearly cooling transmission loads, according to wall orientations and percentage of radiation blocked were calculated using the explicit finite-difference method under steady periodic conditions. As a result, it was found that the lowest value of optimum insulation thickness (0.09 m) and energy savings (79.80%) were obtained for the south-oriented wall, while the payback period (4.73years) was the highest on the same face compared to all wall orientations. Insulation optimum thickness was higher in the HCB wall (0.0983 m) than in CSEB wall (0.0958 m), however, the payback period was the weakest for the HCB wall compared to the other wall type.

In order to reduce the heat and mass transfers in buildings, which increase energy bills, the development of composites materials such as earth bricks stabilized with thatch fibers is important for their construction. This paper aims to study a one-dimensional model of heat and moisture transfer through porous building materials. The coupled phenomena of heat and mass transfer are described by the Luikov model. Equations and boundary conditions are discretized using the finite difference method. The results obtained illustrate the temporal evolutions of the temperature and the moisture content, as well as the distributions of the temperature and moisture content inside the wall. The profile of the temperature and water content that are obtained are compared with the other numerical solutions that are available in the literature.

The aim of the present work is to investigate the behavior of building envelopes made of local lateritic soil bricks subjected to different climatic conditions. The building envelopes studied in this work consist of lateritic soil bricks with incorporation of natural pozzolan or sawdust in order to obtain small thermal conductivity and low-density materials. In order to describe coupled heat and moisture transfer in wet porous materials, the coupled equations were solved by the introduction of diffusion coefficients. A numerical model HMtrans, developed for prediction of heat and moisture transfer in multi-layered building components, was used to simulate the temperature, water content and relative humidity profiles within the building envelopes. The results allow the prediction of the duration of the exposed building walls to the local weather conditions. They show that the durability of building envelopes made of lateritic soil bricks with incorporation of natural pozzolan or sawdust is not strongly affected by the climatic conditions in tropical and equatorial areas.

This paper presents an experimental study of two solar stills, a single-compartment model and a two compartment type. The single compartment still is optimized under local climatic conditions. An experimental study of the cover slope shows that a cover angle of 16° ensures a very good transmission of solar radiation within the still while preventing the drops of the distillate to fall into the basin. In the prototype using two compartments, the glass of the illuminated compartment is a transparent cover with a part of the condensation happening on it, while the other compartment, also made of glass, is covered with a non-transparent material, which shades the sun; it is used only as a condenser. It has been observed that the distillation of a 38% alcohol initial solution yields a product containing 48% of alcohol when using the single-cover model, while under the same climatic conditions the two compartments still gives a 71% alcohol distillate.

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.

Throught this work, a theoritical and experimental study of a small solar still of a domestic type with two distinct compartments has been lead. It is shown in this study that the Dunkle's relation about the productivity of a classical still can be applied to our system in order to predict reasonably the production of our still. We have then put the stress on alcohol distillation for this model in order to adapt solar distillation to alcohol distillation. On this field, the results show well that solar energy can perfectly be used to produce alcohol with our prototype.

A solar distillation in a single basin is studied theoretically and experimentally. We present a mathematical model to describe the energy balances for the glass cover, water in the basin and base plate. The model neglects the thermal capacity of the base plate and the temperature gradient through the width of the glass. The energy equations for the glass, water and absorber are simultaneously solved. The effects of water depth, wind speed and glass cover thickness on still productivity are evaluated. The daily total production increases with decreasing water depth. A small increasing of productivity occurs with the increase of wind speed. The thickness of the glass cover has no effect on the production. An experiment has been conducted to validate the mathematical model. The relative difference between experiment and theory is 5% for temperatures, and 15% for productivity.

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.