U-value assessment by infrared thermography: A comparison of different calculation methods in a Guarded Hot Box

The thermal transmittance (U-value) of the vertical opaque building envelope plays a key role for the evaluation of the thermal performance of a structure. In order to speed up the assessment procedure and to investigate wider portions of buildings directly in situ, new methods based on the use of quantitative infrared thermography have been proposed during the last years. Although the studies agree about the influence of the operative conditions, a detailed report, based on measurements effected on a large wall in a controlled environment and at different boundary conditions, is still missing in literature. The aim of this work is to assess the validity of thermographic methods by using different operative conditions in a controlled environment. The results obtained by different IR methods in a Guarded Hot Box have been compared with heat flow meter measurements and theoretical values.