Dynamic thermal characteristics of opaque building components. A proposal for the extension of EN ISO 13786

In order to dynamically characterise the opaque components of a building envelope subject to sinusoidal loadings in steady periodic regime conditions, the use of nondimensional periodic thermal transmittance is proposed. Such a parameter allows for the evaluation of the decrement factor and time lag that the heat flux undergoes while crossing the wall and the efficiency of the heat storage. For non-sinusoidal loadings, dynamic characterisation is obtained by the decrement factor, defined as the ratio between energy in a semi period entering the indoor environment and entering the wall and as the ratio between maximum heat fluxes entering the environment and the wall, and as the ratio between the minimum heat fluxes. These parameters allow to determine the heat storage capacity of the component, the maximum heat flux in summer and winter conditions and their time lags. The defined dynamic properties were calculated considering two commonly used walls and surrounding conditions that are representative of the effective operative conditions.