Termographic testing on buildings using a simplified heat transfer model

Thermographic testing is widely used to analyze inner wall structures. Many variables, including nonhomogeneous optical and thermal characteristics, still make these applications difficult. The materials inside the investigated walls are unknown and the nonhomogeneous optical and thermal characteristics change in every small surface. Plaster delaminations can also stop heating propagation through the wall. These typical difficulties in thermographic applications can be overcome by selecting the appropriate heating method. One requirement is that the mathematical heating model, even if approximated, must take into account thermal and optical characteristics of the materials that determine the surface temperature and the actual environmental conditions. The heat transfer equations can be analytically solved by simplifying boundary conditions on superficial temperature and incoming heat flux. The approximate solutions allow the testing of the necessary heating in order to obtain thermal images from the inner parts of the wall. Special attention has to be paid to the heating system. It is not easy to obtain a uniform heating condition through masonry thickness. Heat propagation must reach the inner part of the wall without significant variation due to lateral diffusion. Different kinds of models are discussed in the present work. The models supply effective heating processes (by convection or radiation) in field conditions. The setup carried out in actual field conditions at an ancient church in northern Italy and the results of the mathematical model are presented.