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By only relying on building characteristics, one could get a wrong understanding of the thermal performance of a building

explanation could be that some mistakes had been made in the initial installation of the insulation. Lastly, the data used in the calculations was based on hand-drawings from the facility manager of Technopark. The material mentioned by the facility manager had to be matched to the materials listed in the u-wert.net database. Also, during these processes errors or inaccuracies might have occurred. A thorough analysis was required to find out what the exact reason was for the higher-than-estimated U-Value.

Conclusion

In summary, it can be stated that a successful measurement was conducted in line with the ISO 9869. The outcome of the measurement can, therefore, be

Case study

Inaccurate U-Values – in situ assessment identifies differences in calculations The background

A case study was conducted to find out to what extent the U-Value calculated with the construction data deviates from today’s measured value. greenTEG, Switzerland, which has developed a U-Value measurement tool to assess the quality of building insulation, was called in to ascertain the U-Value of an office wall at Technopark, a business and meeting centre in Zürich. The building was built in 1990 according to the highest energy standards and, therefore, reached excellent thermal characteristics for that time.

Method used and findings

A measurement with the U-Value measurement Kit from greenTEG was taken and

compared to the theoretical U-Value calculated through the online model of u-wert. net, using the materials and thicknesses of the wall. The building had not been renovated since its erection. The wall was a multi-layered structure (figure 1) built of concrete (180 mm; 1), mineral wool insulation (100 mm; 2), a vented cavity (40 mm; 3) and a gypsum fibreboard (10 mm; 4). The calculated value was 0.31 W/m²K and the measured U-Value was 0.63 W/m²K. The in-situ measured U-Value was more than twice as high as the calculated U-Value. The insulation of the wall was much worse than would be expected from the construction data. It was hard to determine why the U-Value was so much higher than expected. The insulation quality of mineral glass wool had hardly been influenced by ageing effects. However, an increase in the moisture content could have led to a significant deterioration of the thermal performance. Another

considered reliable. Although the material characteristics of the wall were available, the measured in-situ value appeared to be twice as high as the calculated value, indicating that by only relying on building characteristics, one could get a wrong understanding of the thermal performance of a building and the heating costs the office tenant was facing. Further investigations are required to review if refurbishment could be an interesting option for Technopark. CPI Industry accepts no liability for the views or opinions expressed in this column, or for the consequences of any actions taken on the basis of the information provided here.

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December 2015

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49

CCME Jan 2016  

January 2016 Issue of Climate Control Middle East

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