On the applicability of quantitative infrared thermography on window glazing

Energy efficient buildings are an essential factor to reduce the energy consumption by 2020. New buildings have to meet severe requirements, whereas older buildings need renovation to reduce the heat losses through the building envelope. Infrared thermography (IRT) might be an improvement over existing methods to assess the thermal performance of an existing wall in a non-destructive way, or to check upon the as-built quality, specifically in the case of window glazing. The technique instantly visualises the surface temperature of a whole building part, and in turn might allow to deduce the thermal transmittance accordingly. However, many parameters can influence the surface temperature and lead to distorted conclusions. This paper reports on the impact of different indoor and outdoor boundary conditions for the assessment of the U-value of glazing, using the results from a numerical simulation model. After an analysis of 6 types of windows, it is concluded that for specific conditions, IRT might allow to estimate the U-value with an acceptable accuracy, based upon the instantaneous indoor surface temperature. In future research, experiments will be performed to validate this conclusion and the assessment methodology will be improved.