Conference Agenda

Airtight building envelopes are essential for energy efficiency. Fast and reliable leak detection is crucial, especially when retrofiting large buildings. In previous research, feasibility studies in the field and small-scale laboratory tests have demonstrated the potential of the acoustic beamforming method as a tool for rapid and large-scale leak detection. To systematically investigate leaks and analyze the measurement system's behavior, an airtight test facility (ATLAS), as introduced in earlier studies, has been cosonstructed. Building on foundational investigations from that research, this study presents findings from complex test specimens designed to simulate more realistic leakage scenarios. A sandwich system is used to model leaks with cavities (e.g. roof-wall transition) and a labyrinth system is used to simulate twisted leakages (e.g. window seals). The laboratory work is supplemented by an accompanying measurement campaign on a building in need of retrofit in order to ensure practical suitability. This investigation particularly focuses on the effects of the angle of incidence and the output signal from loudspeakers, using a leaky window as a case study. In the two measurement scenarios, leakages were located with success; notably, one leak featuring two consecutive cavities was detected by the measurement technology at the test facility. In addition, two real leakages were found at the analyzed window, whereby a newly developed evaluation algorithm was able to greatly improve simultaneous detectability. The findings indicate that acoustic beamforming is capable of detecting complex leaks in both laboratory and field settings. However, further experimentation is necessary to accurately classify measured noises and facilitate automated analysis.

Infiltration through the building’s envelope is a significant heat loss mechanism. Total leakage rates for buildings can be measured, for example, with the fan pressurization method (ISO 9972). Localization of leakages, however, is often a manual process where previous knowledge of weaknesses of the building is combined with fan pressurization and methods like smoke generators, anemometers, or infrared images. Lock-in thermography advances this by using a periodic cycle of pressurized/unpressurized interior combined with numerical analysis with Fourier transform. This paper presents laboratory measurements in which periodic inversion was used with cyclically pressurized/depressurized interior using Lock-In thermography. Goal of the inversion is to improve the temperature amplitude in Lock-In thermography. This increases sensitivity and decrease susceptibility to disturbances due to environmental changes of the method. Measurements were performed on a sample from MDF with Z-channels of diameters from 3 mm (0.12 in) to 8 mm (0.31 in) and channel lengths from 32 mm (1.3 in) to 512 mm (20.2 in). By application of pressure inversion the average temperature amplitude could be increased by +138%. Additionally, the temperature saturation – the reduction of amplitude with increasing number of measured periods – could be significantly reduced.

Retrofit air sealing methods are manual and achieved air-tightness levels are highly variable based on the time allotted and the vigilance and experience of the contractor who performs the work. A review of Weatherization Assistant Programs showed that air sealing work resulted in an average air leakage reduction of 27% in single family homes and 18-20% in multifamily units. Automated aerosol sealing has been deployed in new residential construction to achieve tighter envelope assemblies. The process pressurizes the residence while injecting an aerosol sealant fog to the inside. As air escapes through leaks in the envelope, the sealant is transported with the air to the leak where it sticks and forms a seal. This can be applied to existing residences, but requires significant effort to cover finished, horizontal surfaces.

A new method has been developed that releases the sealant in adjoining areas (e.g., attics, crawlspaces, and attached garages) while the residence is depressurized. This method can be performed in occupied residences without disrupting occupants. Since the bulk of the particles are isolated to unfinished zones, minimal particles ultimately enter the occupied residence reducing the preparation time. Furthermore, the fan used for de-pressurizing the home allows the particles that enter through leaks to be exhausted outside.

Demonstrations of attic and crawlspace sealing were performed on seven single-family homes and twelve multifamily units. Half of the homes had a leakage reduction greater than 35%. All 12 multifamily units had a leakage reduction greater than 30% with a median reduction of 40%. This is significantly better average air leakage reductions for manual sealing methods, especially considering that only the leakage to the attic and/or crawlspace was sealed. Commercialization of the attic and crawlspace aerosol sealing method would provide a new tool for addressing air leakage in our existing building stock.