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A review of the influence of the convective coefficient in the assessment of the U-value of façades with the infrared thermography method

In recent years, increasing concerns about the high building energy consumption have been focused on the energy rehabilitation to reduce this consumption. In this regard, the thermal transmittance (U-value) of walls determines this energy consumption to a great extent, so there is a considerable interest in using methods assessing it accurately [1, 2]. Such property could be determined by various procedures, both theoretical and experimental, and all these methods are subject to a series of factors that could result in obtaining atypical values [3]. One of the thermal transmittance evaluation methods most studied in recent years is that of quantitative infrared thermography method [4]. This is because the method allows both a qualitative and quantitative analysis of the building envelope. However, the main limitation of this approach is the great variety of different approaches. In total, there are up to 5 different approaches in the scientific literature [5–9]. The biggest difference between these approaches is due to the convective heat transfer coefficient used and the place from where the measurement is made (indoor or outdoor). For this reason, this research reviews the results obtained from the optimization of the infrared thermography method in two publications made by the authors [10, 11]. This analysis was performed based on the different existing approaches and using a wide variety of equations for the convective heat transfer coefficient. The results showed that the use of experimental correlations of dimensionless numbers for the internal quantitative infrared thermography method constitutes the most appropriate application for this method. The analysis of the data obtained for this aspect reflected that the number of valid results obtained with this configuration was higher than that of other experimental correlations from the interior and exterior. Likewise, performing tests from the interior ensures the decrease of the influence of environmental conditions.

Thermal transmittance (U-value), infrared thermography, convective heat transfer coefficient, walls

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