Quantitative internal infrared thermography for determining in-situ thermal behaviour of façades

Abstract

The thermal behaviour of a building is often underestimated or neglected during its construction and operation stages. In recent years, the heat flux meter (HFM) method has been commonly used to determine the U-value, a key parameter for assessing the thermal quality of the building envelope in steady-state conditions. However, this non-invasive test takes at least 72 h to execute, the accuracy is\ud 14–28%, and it is not reliable for non-homogeneous building elements. An alternative technique is based on infrared thermography (IRT). Although it is generally used for qualitative analysis, quantitative internal IRT methods may also be adopted for in-situ measurement of the U-value. This research presents\ud a method for determining in-situ U-values using quantitative internal IRT with a deviation of 1–2% for single-leaf walls and 3–4% for multi-leaf walls. It takes 2–3 h and can be used to provide information about the building envelope for the future refurbishment of existing buildings or to check the thermal behaviour of new building façades according to their design parameters.Peer ReviewedPostprint (author's final draft

Determining the U-Value of Façades Using the Thermometric Method: Potentials and Limitations

“…In addition, the ideal test conditions will be those with no rainfall and a wind speed lower than 1 m/s. In this respect, the effects of these climatological variables can last from 2 to 6 h after these climate events disappear [23].…”

“…The use of a data logger that records data for a period between 1 and 900 s will allow the variation of the frequency of data acquisition used in each test. By analysing the literature, the use of different sampling periods for the heat flow meter method and the quantitative methods of infrared thermography were detected: 2 min [41], 5 min [23,24,33], 15 min [19,25], 30 min [25], 60 min [25], or 90 min [25]. In this regard, we propose the use of sampling times of 15 min, which make the subsequent data analysis easier.…”

“…A fixed mastic can also be used to achieve good contact with the wall [31]. In addition, it is important to avoid mounting the sensors in the corners, since the temperature is usually higher there than in the rest of the wall [23].…”

“…This property can traditionally be determined by means of different procedures such as estimated methods [17] or in situ tests (the heat flow meter method) [18], or quantitative methods such as infrared thermography [19][20][21][22][23]). These methods have been widely studied in the literature and there are several studies in which the validity of their use is compared [24][25][26][27].…”

“…However, these specifications are limited to ensure that the test is performed under correct metrological guidelines. Furthermore, the internal convective coefficient is utilised during the building design process to determine the energy behaviour, which overestimates the thermal transmittance [21,23], so the results obtained may not correspond to the actual values.…”