| Resumo: | External thermal insulation composite systems (ETICS) for walls - expanded polystyrene insulation faced with a thin rendering - have been used in various countries since the mid twentieth century. In Portugal, these systems were first applied in the nineties. Unfortunately, the results werent always as expected. In recent years, stains have frequently appeared on façades covered with ETICS as a result of algae and mildew growth. These stains compromise the façades aspect and have been greatly contested by property owners. The thermal advantages of ETICS are, therefore, undervalued by owners due to the conspicuous degradation. This problem is intensified by poor building maintenance habits in Portugal. It is essential to study the causes of algae and mildew growth in order to understand the hygrothermal behaviour of façades covered with ETICS. Dynamic heat exchanges between the environment and building components and temperature fluctuations of walls surfaces caused by radiation are two important aspects to be considered. During the night, energy exchanges occur between the ETICS exterior layer and the atmosphere by long-wave emission. This causes surface cooling, condensation and higher surface moisture, therefore promoting the development of algae and mildew. Infrared thermography can be used to determine the superficial temperature of objects. Detectors collect infrared radiation, transform it into electrical signals and create a thermal image based on the superficial temperature distribution. In this process, each colour represents a certain temperature range. Therefore, thermography may be a useful tool to evaluate surface condensation on ETICS. To assess the use of thermography, some simple experiments were carried out at the Building Physics Laboratory (LFC) of the Engineering Faculty of Porto University (FEUP). A sensibility study was performed with LFCs equipment to evaluate the influence of emissivity on the measurements. By using this technology, it was also possible to study the wetting and drying process of building materials, since water evaporation is an endothermic reaction inducing local surface cooling. Theses experimental results are presented in this paper.
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