Laboratory assessment of thermal transmittance of homogeneous building elements using infrared thermography

Due to a growing concern with the assessment of the thermal performance of building envelopes, in particular during energy audits and energy certification processes, it has become increasingly important to use inspection techniques to determine the thermal transmittance values (U-value) of building elements. One of the techniques that may be explored to evaluate the thermal behaviour of the envelope is Infrared thermography (IRT). As the accuracy of the thermal transmittance estimation is dependent on the state of the heat transfer, having steady-state or near steady-state conditions is crucial to get reliable measurements and a stable temperature difference between inside and outside is mandatory. With this in mind the authors intend to evaluate the application of IRT to U-value determination studies. For this reason, a set of laboratory measurements were performed. A steady temperature difference was imposed in 4 different homogeneous materials used to build a box that is heated using a thermal resistance. IRT temperatures were measured on the outside surfaces of the box, and are then used to estimate the U-value. Those results are compared with the U-value calculated using the thermal conductivity obtained by means of the guarded hot plate method.