Application of fluorometric and numerical analysis for assessing the algal resistance of external thermal insulation composite systems

Abstract

The problem of algal growth on external thermal insulation composite systems (ETICS) due to the continually raised insulation standard has not yet been satisfactorily solved until today. Adopted strategies for improving the algal resistance can be divided into chemical or hygrothermal approaches, which can be assessed either directly in laboratory and weathering tests or indirectly by quantifying the growth conditions with numerical simulation tools.The thesis starts with a comprehensive review on the state of the scientific and technological knowledge and examines the application of fluorometric and numerical analysis for evaluating the algal resistance of ETICS.The efficiency of Pulse Amplitude Modulation (PAM) fluorometry for directly quantifying the algal biomass on the facade surface was analysed within three weathering tests which comprised 33 different ETICS specimens. The fluorescence measurements were performed using the IMAGING PAM of the company Walz, which features a large examination area and an image analysis. The results of the fluorometric analysis confirm the effectiveness of biocides and indicate a higher algal resistance of the mineral rendering systems compared to the organic systems.The options and limitations of using numerical simulation for the assessment of the algal resistance of ETICS were evaluated using the software WUFIR Pro 5.0 developed by the Fraunhofer Institute of Building Physics. Within selected parameter studies an appropriate evaluation criterion was identified and the impact of varying material data and exterior boundary conditions was assessed.The results illustrate the added value of combining experimental and numerical analysis. The numerical simulation shows that a high liquid moisture diffusivity theoretically improves the algal resistance of ETICS. If the algal resistance of rendering systems can be actually reduced by an adjusted liquid moisture diffusivity or is dominated by phenomena not included into the numerical study (e. g. weathering, soiling and leaching) can only be validated experimentally.The experimental results demonstrate that the actual algal resistance of ETICS specimens in the course of the weathering process can be measured objectively and efficiently using fluorescence measurements. The missing correspondence between the calculated and measured algal resistance is attributed to the simplifications inherent to the approximation of the hygric material functions and therefore emphasizes the need for further research.

The problem of algal growth on external thermal insulation composite systems (ETICS) due to the continually raised insulation standard has not yet been satisfactorily solved until today. Adopted strategies for improving the algal resistance can be divided into chemical or hygrothermal approaches, which can be assessed either directly in laboratory and weathering tests or indirectly by quantifying the growth conditions with numerical simulation tools.The thesis starts with a comprehensive review on the state of the scientific and technological knowledge and examines the application of fluorometric and numerical analysis for evaluating the algal resistance of ETICS.The efficiency of Pulse Amplitude Modulation (PAM) fluorometry for directly quantifying the algal biomass on the facade surface was analysed within three weathering tests which comprised 33 different ETICS specimens. The fluorescence measurements were performed using the IMAGING PAM of the company Walz, which features a large examination area and an image analysis. The results of the fluorometric analysis confirm the effectiveness of biocides and indicate a higher algal resistance of the mineral rendering systems compared to the organic systems.The options and limitations of using numerical simulation for the assessment of the algal resistance of ETICS were evaluated using the software WUFIR Pro 5.0 developed by the Fraunhofer Institute of Building Physics. Within selected parameter studies an appropriate evaluation criterion was identified and the impact of varying material data and exterior boundary conditions was assessed.The results illustrate the added value of combining experimental and numerical analysis. The numerical simulation shows that a high liquid moisture diffusivity theoretically improves the algal resistance of ETICS. If the algal resistance of rendering systems can be actually reduced by an adjusted liquid moisture diffusivity or is dominated by phenomena not included into the numerical study (e. g. weathering, soiling and leaching) can only be validated experimentally.The experimental results demonstrate that the actual algal resistance of ETICS specimens in the course of the weathering process can be measured objectively and efficiently using fluorescence measurements. The missing correspondence between the calculated and measured algal resistance is attributed to the simplifications inherent to the approximation of the hygric material functions and therefore emphasizes the need for further research.