Test facility for building envelope leakage type analysis and improvement of acoustic and thermographic airtightness measurement methods

Ensuring the airtightness of building envelopes is crucial for enhancing the energy efficiency of buildings. The prompt detection of leaks is essential, particularly when undertaking building renovations. Consequently, efforts have been made in recent years to implement new measurement techniques that facilitate the rapid, straightforward, and wide-scale identification of leaks in building envelopes. Two notable methods are the use of acoustic and thermographic technologies. In the acoustic beamforming method, a microphone array technology is employed, whereby sound propagation is assumed to occur in a manner similar to that of airflow through the building envelope. The infrared camera, however, is capable of rapidly identifying problem areas through the use of intelligent experimental setups. 
Although both methodologies have undergone preliminary evaluation on smaller façade elements and in field trials, this paper presents the initial findings of the first large-scale laboratory testing of these methodologies in the context of leak detection on building envelopes. To facilitate the investigation on such a comprehensive level, a new airtightness test facility was constructed. This test facility has a volume of approx. 11.4 m3, has an n50 value of 0.0088 and can hold test specimens of various sizes up to 3 m2. 
Initial investigations utilising an acoustic camera revealed that a simple leakage in the form of a 3.3 mm hole could be precisely localised at different measurement distances. Furthermore, it was demonstrated that the spectra of different hole sizes exhibited a similar curve shape, and that there was a correlation between the maximum sound pressure level and the hole size. 
Thermographic measurements with 6-7 K temperature difference, 50 Pa pressure were performed with camera distances between 1.5 m and 5.0 m at normal and 45° angle. Individual leaks of 3.3 mm diameter could be detected at all distances. With lager distance and shallower incidence angle, the signal reduced, but localization was possible with objects smaller than the pixel-resolution. 
The outcomes of the tests conducted at the test facility confirmed the assumption that comprehensive laboratory testing is essential for a more accurate evaluation of both methods in the context of leak detection on building envelopes, and thus for subsequent field use. Further measurement campaigns are already underway and will continue to investigate the methods themselves, as well as more complex and therefore more realistic leakages.