Pressure Inversion for Leakage Detection at Building Envelopes with Lock-In Thermography

Abstract

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 leaks, 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 decreases 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.