The development of sustainable manufacturing systems necessitates the knowledge of the thermal loading conditions of the manufacturing equipment in interaction with the manufacturing building. Especially for the early planning phases a dynamic evaluation of different concepts is advantageous and leads to an acceleration of the overall planning procedure. This article introduces an approach for the development of simulation models for the assessment of thermal loading conditions in brownfield manufacturing applications by dynamic simulation. The approach makes use of the novel Modelica Thermal Integration Library, which provides basic models for representative manufacturing equipment in the metal working industry. It enables an efficient simulation of manufacturing equipment with the related manufacturing building to analyse the overall thermal loading conditions. The approach is applied to a machine tool in the manufacturing line at the ETA Research Factory of the Technical University of Darmstadt.