*Article* **Non-Destructive Possibilities of Thermal Performance Evaluation of the External Walls**

**Henryk Nowak and Łukasz Nowak \***

Faculty of Civil Engineering, Wroclaw University of Science and Technology, Wybrzeze Wyspia ´ ˙ nskiego 27, 50-370 Wrocław, Poland; henryk.nowak@pwr.edu.pl

**\*** Correspondence: lukasz.nowak@pwr.edu.pl

**Abstract:** Identification of the actual thermal properties of the partitions of building enclosures has a significant meaning in determining the actual energy consumption in buildings and in their thermal comfort parameters. In this context, the total thermal resistance of the exterior walls (and therefore their thermal transmittance) in the building is a major factor which influences its heat losses. There are many methods to determine the total thermal resistance of existing walls, including the quantitative thermography method (also used in this study). This paper presents a comparison of the calculated total thermal resistance values and the measured ones for three kinds of masonry walls without thermal insulation and the same walls insulated with expanded polystyrene boards. The measurements were carried out in quasi-stationary conditions in climate chambers. The following three test methods were used: the temperature-based method (TBM), the heat flow meter method (HFM) and the infrared thermography method (ITM). The measurement results have been found to be in good agreement with the theoretically calculated values: 61% of the measured values were within 10% difference from the mean value of total thermal resistance for a given external wall and 79% of the results were within 20% difference. All of the used measuring methods (TBM, HFM and ITM) have proven to be similarly approximate in obtained total thermal resistances, on average between 6% and 11% difference from the mean values. It has also been noted that, while performing measurements, close attention should be paid to certain aspects, because they can have a major influence on the quality of the result.

**Keywords:** external walls; thermal measurements; R-value; thermal resistance; temperature-based method; heat flow meter method; infrared thermography method
