Estimation of Air Leakage Sizes in Building Envelope using High-Frequency Acoustic Impulse Response Technique

Heating energy in buildings represents a significant proportion of the total global energy consumption. Uncontrolled airflow through the building envelope contributes significantly to its energy losses.  
Existing methods, like the fan pressurisation technique, which measure the air infiltration rate and quantify individual leakage sizes in buildings, are expensive and time-consuming. Additionally, the accurate detection of the leak location with these methods depends strongly on the experience of the respective building inspector. Moreover, it is hardly possible to identify the size of each leakage accurately and quantify their contributions to the entire building air change rate. Thus, the development of a new measurement method is a vital step.  
In this paper, a high-frequency acoustic method is proposed to identify leakage sizes. Using an impulse response technique with multiple microphones and a high-frequency broad-band excitation signal enables the identification of frequency components which are predominantly attenuated inside walls. In a laboratory test chamber, different interchangeable walls have been used. Therefore, it was possible to investigate different leakage sizes and compare them directly in a controlled environment. As an excitation signal, an exponential sine sweep is used, which is able to cover a broad frequency range and simultaneously only excites the desired frequencies.  By analysing the spectra, it is possible to differentiate between different cracks and leak sizes. Therefore, this technique has the potential to concentrate only on significant leaks during a building renovation and save building owners time and costs.