Published: Jan 1997
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The thermal properties of building materials are of great importance for many technical questions. The thermal insulation characteristics of external wall constructions decisively determine the utility value and the running costs in housing and public buildings. In this paper possibilities are represented to record such values by means of in-situ-measurement. A measurement arrangement is introduced to determine the thermal resistance of external wall structures and/or the thermal conductivity of material layers. This method works with a heating system transmitting a definite steady heat flux through the objects. The generated temperatures determine the thermal resistance and the thermal conductivity. When a periodical intermittent heat flux is generated, the storage capacity or the specific heat can also be determined. To measure the thermal properties of each layer of multilayered constructions, like thermal conductivity, thermal diffusivity or specific heat, it is advantageous to use temperature and flux gradients existing there in according to the prevailing initial- and boundary-conditions. To gain knowledge of mentioned gradients, temperature sensors are being placed among all layers of different depths. Additionally the heat exchange occurring across the surface has to be measured by means of heat flux transducers. Temperature measurements are taken at certain points in the space-time-grid underlying the given construction to enable the description of the thermal development. By making use of mathematical approaches the course of temperature is described in the form of space-time-functions of polynomial character. The application of fundamental laws allows the user to gain exact knowledge of thermal material properties. This method has been applied to numerous practical cases and it was found to satisfy our expectations, finally enabling the user to investigate deeper into the complexity of building materials and constructions.
in-situ-testing, thermal conductivity, thermal resistance, specific heat, building materials, building constructions, multi-layered constructions
O. Univ.-Prof.Dipl.Phys.DDr., Technische Universität Wien, Wien,