Measured vs. Calculated U-Values: New Publication

Researchers at the University of Applied Sciences and Arts Northwestern Switzerland compared measured U-values and calculated U-values of unheated basements in typical Swiss houses. They conclude that the calculated U-values are often higher (i.e. worse) than actually measured U-values. Therefore, U-values should be measured when assessing the thermal behavior of buildings for energy demand calculations.

Caroline Hoffmann and Achim Geissler (2017): The prebound-effect in detail: real indoor temperatures in basements and measured versus calculated U-values. Energy Procedia 122, 32–37.

Why is this finding important?

The authors of this paper asked 10 energy consultants (experts for Swiss cantons’ building energy label GEAK) to calculate the U-values. They were given detailed descriptions of the constructions but the consultants needed to make their own assumptions in regard to thermal conductivity values of the materials involved. This is the typical situation for energy consultants. Usually they then take conductivity values listed for the different materials. This approach does not take into consideration that these values usually are derived from measurements in controlled environments. In real situations however, the actual values may be quite different due to the aging of materials and other influences of the environment. It is therefore advisable to actually measure the U-value in order to get a solid understanding of a building’s thermal behavior.

The results of this research are consistent with the findings of a similar study commissioned by the Swiss Federal Office of Energy.

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