In situ measurement method for the quantification of the thermal transmittance of a non-homogeneous wall or a thermal bridge using an inverse technique and active infrared thermography

Abstract

Thermal bridges tend to increase overall buildings energy demand and might cause water condensation problems. They are thermally characterized by a linear transmission coefficient ψ or a point transmission coefficient χ. Today, most studies of thermal bridges are based on theoretical or numerical calculations. Standardized methods define default values and assumptions to make in simple or detailed simulations. The few existing in situ characterization methods of thermal bridges are based on steady-state assumptions. This makes them highly sensitive to weather conditions and often requires very long measurements. The present paper proposes a novel active method for the in situ characterization of a thermal bridge. It generalizes a measurement of a homogeneous wall thermal resistance. The indoor air is rapidly heated for a few hours (typically 6) and the wall thermal response is analyzed with an inverse technique based on a white-box model. Surface temperatures and heat fluxes are measured with contact sensors on a sound area and these quantities are then extrapolated to nearby thermal bridges using infrared thermography. The total heat transfer coefficient, required in the heat flux extrapolation process, is monitored with a specific device. The method is validated on a full-size loadbearing wall built inside a climate chamber. The mechanical supports, holding the internal insulation system implemented on the wall, generate several thermal bridges. The ψ-values estimated by the active method are less than 20% away from steady-state measurements taken as reference. Many configurations were tested with constant and varying external temperature and the method proved its robustness to these unsteady conditions.

A State of the Art of the Overall Energy Efficiency of Wood Buildings—An Overview and Future Possibilities

“…Thermal bridges affect the energy performance of buildings due to an increase in heat loss in winter and heat gain in summer [ 122 ]. Moreover, according to François et al [ 123 ], two main types of thermal bridges can be found in buildings. The first is geometrical or structural, which occurs due to the shape of the building (e.g., wall/floor junctions, corners).…”

Surface heat transfer coefficients in building envelopes: Uncertainty levels in experimental methods

“…IRT methods have been commonly used in qualitative assessments over several decades (Lucchi, 2018), as well as for the assessment of heat transfer in uneven areas. Some methods (Franc xois et al, 2021;Marshall et al, 2018) have proven useful in combination with point heat flux measurements to perform qualitative assessments of overall U-value of walls considering thermal bridges and heterogeneous heat transfer patterns.…”

Remote sensing of indoor thermal environment from outside the building through window opening gap by using infrared camera

“…Infrared thermography, a nonintrusive technique for measuring temperature, might be a breakthrough for large-scale indoor temperature investigation. As a prominent tool for detecting infrared energy emitted by object surfaces, infrared thermography has been widely applied in building diagnostics, such as determination of the overall thermal conductivity (U-value) of exterior walls [ 19 – 21 ] and windows [ 22 – 24 ] and the detection of heat loss points [ 25 – 27 ], air leakages [ 28 – 30 ], and moisture [ 31 – 33 ] of the building envelope. Several attempts have been made to employ infrared thermography to measure indoor temperature.…”