Omar Douzane

Transport of fluids in cement–rubber composites

Abstract The transport properties of building materials exposed to an aggressive environment represent the essential parameters affecting their durability. Furthermore, the deterioration process of materials is highly related to the movement of water contained in a porous volume, whether in liquid or vapour form, and to the air permeability. The present study has been undertaken to examine the influence of rubber aggregates on the durability factors of cement–rubber composites. Results reveal the importance of the cellular character of rubber aggregates with respect to the composite’s behaviour in contact with fluids.

Incorporation of thermal inertia in the aim of installing a natural nighttime ventilation system in buildings

The objective of this study is to propose a simplified characterization of thermal inertia, as part of the installation of a system of summer refreshment by means of nighttime cooling ventilation. On the basis of a previous study, conducted by relying upon a modal analysis, the interactions between the thermal inertia of a building and the variation of the air exchange rate have been explained. It can then be shown that the notion of useful thermal mass has herein been altered in order to take the thermal inertia of the building into account; it would then be suitable to substitute this notion for an approximated calculation of the buildings main time constant. Moreover, the necessity of adding a parameter that characterizes the rapid dynamics of a particular zones air temperature can be justified. Lastly, a characterization of the thermal inertia based upon the three-criteria calculation is proposed. An approximated value of the time constant both during the period of nighttime cooling and beyond this period, as well as an approximated value of the height of the line associated with the rapid dynamics, can be computed.

Use of a cellular clayey concrete for a wall specially fitted with water pipes

A vertical wall made of cellular clayey concrete, which has been fitted with water pipes, is the subject of the study carried out herein under a heating mode of operations. The monitoring of this prototypes behaviour has been performed over 24-h cycles which include an 8-h period of water circulation. With both the material and the geometry of the prototype being held constant, the influence of energy-related parameters affected by water circulation, flow and temperature upon the amount of stored energy can be evaluated. It has been shown that within the particular domain of investigation, a variation in the flow does not engender significant fluctuations in the prototypes thermal performances. As the temperature of the intake water increases, the amount of energy stored in the wall also increases. Moreover, for a water intake temperature of 42°C, the surfacic heat flow remains less than the maximal threshold imposed for floor-heating installations. A model, which has already been validated for other types of materials, is applied herein in order to simulate the prototypes behaviour. The comparison with an experimental series, which includes both a storage and a depletion phase, has shown a good level of agreement.

Impact of combined moisture buffering capacity of a hemp concrete building envelope and interior objects on the hygrothermal performance in a room

In this article, a hygrothermal building model, taking into account the building envelope, indoor heat and moisture sources, indoor environment and moisture buffering capacity of interior objects, is presented and validated with the test cases found in the literature. The model is used to study the impact of hemp concrete and the moisture buffer capacity of the interior elements on the prediction of the hygrothermal comfort in the building. The numerical results show that the use of hemp concrete in buildings can ensure good hygrothermal comfort. Besides, taking into account the effect of moisture buffering of indoor objects increases the building performance. Our results also suggest that neglecting moisture transfer through the envelope increases significantly the predicted percentage of dissatisfied indices and reduces the acceptability of indoor air quality during the occupied period. This study also confirmed that the combined relative humidity-sensitive ventilation system and moisture buffering capacity of building envelope and of interior objects is a very efficient way to reduce the heating energy consumption.

Thermophysical property measurements of building materials in a periodic state

Abstract A simplified experimental device and a theoretical model used for measurement of thermal diffusivity and effusivity of building materials are presented. This study is an extension of methods which employ a periodic signal, performed in our laboratory. The impact of contact thermal resistances between the device’s different components and the role played by the presence of the heat flowmeter have been studied. Experimental results obtained for two materials with different thermal properties are finally presented.

SENSITIVE ANALYSIS OF HARMONICS ON THE ASSESSMENT OF THERMAL DIFFUSIVITY OF BUILDING MATERIALS OF A PERIODIC STATE

Thermal efficiency of buildings requires a perfect knowledge of the thermal properties of materials which compose building envelope. To this end, the use of reliable testing methods for thermal diffusivity measurements of buildings materials is fundamental. Currently, periodic methods are based on the exploitation of fundamental harmonic, resulting from Fourier series decomposition. The objective of this paper is to demonstrate that fundamental is necessary and sufficient in order to characterize the thermal diffusivity. For those purposes, a sensitive analysis of harmonic contributions from Fourier series is supported by a substantial experimental campaign. Moreover, some dissymmetrical tests were carried out in order to highlight the preponderant influence of fundamental, compared to other harmonics. The analysis of contributions of harmonics shows that the evolution of thermal diffusivity is very slightly dependent on the number of harmonics. Then, the exploitation of fundamental is necessary and sufficient, and the characterization test protocol is validated by experimental results and by the comparison with commonly accepted values for these kinds of materials.