Thierry Langlet

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.

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.

A multi-scale homogenization approach for the effective thermal conductivity of dry lime–hemp concrete

Lime–hemp concrete is an environmentally friendly material that is used more and more in building construction. This study develops a multi-scale homogenization approach to model the effective thermal conductivity of this bio-based material. The developed model dedicated to non-compacted and compacted hemp concrete takes into account the shape and the orientations of pores of hemp particles as well as imperfect particle-binding interfaces. Unknown properties of the solid phase of hemp particles and binding, and that of the particle-binding interface are calibrated by inverse analysis using available experimental data. The model is then used to carry out a sensitivity analysis to study the effect of the porosities of hemp particles and binding, the volume fraction of hemp particles, density and temperature on the overall thermal conductivity of hemp concrete. Analytical solution proposed can be used for a fast estimation and optimization of the thermal conductivity of hemp concrete, which is very useful for the building design.

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.