Measurement Method of Thermal Diffusivity of the Building Wall for Summer and Winter Seasons in Poland

Abstract

The thermal diffusivity of building materials is an extremely important parameter influencing the subsequent thermal comfort of building users. By definition, thermal diffusivity describes how quickly heat from a hot source can flow through a material. Therefore, this parameter includes both the thermal conductivity and the heat capacity of the material. This parameter is often neglected in heat-related calculations which, in the case of dynamic problems, leads to unreliable results. It should be taken into account that heat flows through all materials at a finite speed. On the other hand, knowing the correct thermal diffusivity value of building materials, it is possible to accurately determine the internal parameters in rooms over time. There are several methods for determining thermal diffusivity, most of which are destined to determine this property in laboratories. The aim of the present research is to show how the thermal diffusivity of materials can be determined in existing buildings. The presented method can be used to determine more real thermal parameters used for thermal calculations in buildings, for example, during energy audits or when calculating the demand for cooling for air conditioning or heat for space heating. This research presents the results for a 60 cm brick wall. Thermal diffusivity was determined for specific summer and winter days—most representative of the whole year. This research has shown that the applied method should be used in the summer period, due to the fact that the wall has greater temperature fluctuations. The obtained results are comparable with the previously mentioned laboratory methods. However, due to the fact that the materials analyzed on the spot, the results are more reliable, and also take into account changes in the value of thermal diffusivity resulting from the use of binders, inaccuracies in joining and external layers made of other materials.

Keywords

• thermal diffusivity measurements
• temperature distribution in building element
• two dimensional approximation
• Ångström method