Parametric study of the method for determining the thermal diffusivity of building walls by measuring the temperature profile

•Thermal diffusivity is needed to determine the dynamic thermal characteristics of a wall.•Masonry walls have a heterogeneous structure.•The local measurement of thermal properties of large building components may be inaccurate.•It is possible to measure thermal diffusivity by measuring the temperat...

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Bibliographic Details
Published in:Energy and buildings 2019-11, Vol.203, p.109426, Article 109426
Main Author: Owczarek, Mariusz
Format: Article
Language:English
Subjects:
Approximation
Buildings
Dependence
Diffusivity
Fourier's equation
Heat flux
Heat transfer
Laboratory methods
Measurement methods
Parametric statistics
Polynomials
Temperature distribution
Temperature distribution in building element
Temperature profiles
Thermal diffusivity
Thermal diffusivity measurements
Two dimensional approximation
Walls
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Summary:•Thermal diffusivity is needed to determine the dynamic thermal characteristics of a wall.•Masonry walls have a heterogeneous structure.•The local measurement of thermal properties of large building components may be inaccurate.•It is possible to measure thermal diffusivity by measuring the temperature profile in the wall.•The time of measurement of thermal diffusivity by the method is about 90 min. For a better understanding of the energy characteristics of a building, it is useful to find heat fluxes and a temperature field in a transient state. To obtain the temperature in a solid using the Fourier equation a thermal diffusivity is needed. For thermal characteristics of existing buildings, measurement can provide data on this property for a specific case. Laboratory methods of diffusivity measurement encountered in the literature take into account the layers of material close to the surface. A measurement method dedicated to large elements, for example parts of buildings, has been proposed. It is based on temperature survey in the element's volume and assumption that the obtained results meet the Fourier equation. The temperature is approximated by a polynomial and then this function is substituted to the heat transfer equation and diffusivity is determined. In order to validate the method, the temperature measurements for the actual wall were made, the discrete values were approximated by a polynomial of various degrees with respect to the spatial coordinate and time. On the basis of obtained function, the inverse task was solved and thermal diffusivity was determined. The dependence of the results on the length of time in which the values of temperature were approximated and polynomial degree was analysed. A preliminary analysis of errors was made. The obtained values were compared with the results of other authors' research.
ISSN:0378-7788
1872-6178
DOI:10.1016/j.enbuild.2019.109426