This is an important consideration in building construction because heat energy arrives in different forms and proportions. The contribution of radiative and conductive heat sources also varies throughout the year and both are important contributors to thermal comfort
The deterioration of R-values is especially a problem when defining the energy efficiency of an existing building. Especially in older or historic buildings the R-values defined before construction might be very different than the actual values. This greatly affects energy efficiency analysis. To obtain reliable data, R-values are therefore often determined via U-value measurements at the specific location (in situ). There are several potential methods to this, each with their specific trade-offs: thermography, multiple temperature measurements, and the heat flux method.[40]
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