Analysis of the measurements reliability in dynamic test of the opaque envelope
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The characterization of opaque building components’ thermal behavior is essential in early design stages to compare different design and refurbishment alternatives. Evaluating the dynamic thermal response to an external solicitation is necessary for an effective design especially for the climates with important annual cooling demand. According to EN ISO 13786:2007, opaque elements can be characterized through some dynamic parameters (i.e., periodic thermal transmittance, decrement factor and time shift), which can be calculated starting from the wall materials’ thermal properties. However, when either the material thermo-physical properties are unknown (e.g., in existing buildings) or the assumptions about 1-dimensional heat flux on which the method is based are not met (e.g., in platform-frame structures), proper accuracy of results is not ensured. Hence, for these cases and components, a direct measurement of dynamic parameters would be extremely useful. Differently from the procedure to determine the steady-state thermal transmission properties, which is well established, there are no technical standards defined for the experimental measurement of dynamic thermal parameters so far. Since these experimental procedures are still under development, the extent to which several aspects limit accuracy and precision of the measurements are not yet cleared. In this framework, this paper presents both experimental and numerical tests, which have been performed in order to assess the impact of different sources of uncertainty on the estimation of EN ISO 13786 dynamic parameters by means of heat flux meter measurements on a timber wall specimen.