The use of multiphysics to solve hygro thermal building physical problems related to insulating high rise building facades

In The Netherlands high rise buildings from 1960 and before hardly were insulated. To improve the thermal performance of the buildings the facades may be insulated afterwards. The energy loss will be reduced and thermal comfort will be improved by higher indoor surface temperatures. Problems however may be introduced by thermal bridge effects of anchors, floors and indoor walls. Further more the outer facade surface will be colder during winter time. Frost damage and internal condensation may be the deleterious building physical effects. The purpose of the work is to prevent damages which may result from insulating retrofitting of building facades. For this kind of building physical problems specific software has been developed and is in use all over the world. The coupling of thermal, hygric and air flow effects, however, has not been solved most of the times. An attempt has been made to solve this kind of coupled problems by the use of COMSOL. As an example of this kind of coupled problems the thermal bridge effect of an anchor in an uninsulated and afterwards insulated facade of a high rise building has been examined. The air flow calculation in the cavity was coupled to the thermal and hygric diffusion process. The results of the separately uncoupled COMSOL simulations (like thermal bridge calculations) were compared with results from third party software and the coupled simulation results were compared with infrared thermographs. The conclusion of the paper is that the use of COMSOL in this kind of problems may solve the problem of coupled building physical effects in building constructions.