Speaker
Description
An airtight building envelope is necessary to achieve a high thermal efficiency of the building, to prevent mold, for sound proofing and to meet fire safety standards. The total leakage rate of a building is measured with the fan pressurization method described in ISO 9972 or the pulse air permeability test. When airtightness found to be inadequate, leaks are often localized using a combination of previous knowledge of weaknesses of the envelope, fog generators or anemometers. Infrared images taken with a building set under pressure with a blower door can also emphasize leaks. More advanced thermographic methods for leak detection, like differential images or Lock-In Thermography, have been reported, but have found little adoption by the energy consulting community.
Lock-In Thermography has proven to be a reliable method of non-destructive testing in controlled environments. When this method is used in building inspections, it poses particular challenges, as it must deliver clear and unambiguous results in constantly changing environmental conditions. Goal of the presented research is to improve the usability of Lock-In Thermography for leakage detection at buildings by improving the robustness of the detection with respect to changing environment, like changing wind or solar irradiation, or moving objects visible in reflected surfaces. This would enable measurement of the outward-facing side of the facade allowing quick screenings of large facades. This is achieved by two methods: increasing the temperature-signal by inversion of pressure and application of additional digital filters.
Pressure inversion has been investigated using a laboratory test bench with a sample of medium density fiber board, square channels with two 90°-angles from 3 mm to 8 mm characteristic width and length from 32 mm to 512 mm. Changing the pressure signal from 0 Pa/ +50 Pa to -50 Pa/ +50 Pa resulted in a mean increase of the temperature amplitude by a factor of 2.4. Digital filters tested are phase filters and a novel local maximum filter.
In field campaigns both methods have been tested at several buildings. These measurements show the benefits compared to standard techniques and demonstrate the robustness of Lock-In Thermography for leak detection at buildings und challenging environmental conditions.
