Modelling thermal processes in buildings using an object-oriented approach and Modelica

Most of today’s modelling and simulation concepts originate from the times and methods of analog computers. Usually, it is assumed that the model must be expressed in an explicit state-space form. Consequently, the topology of the system gets lost and any future extension and reuse of the model is tedious and error-prone. In other words, it is the modeller’s task to consider the computational order of the operations during a simulation.In this paper we discuss the re-implementation of a passive-solar- building simulator in an object-oriented environment; it was originally built in the non-object-oriented simulation environment of Matlab–Simulink. The former simulator was designed to resemble a real physical test chamber with regard to the thermal and solar radiation flows. However, due to the lack of object orientation in Matlab–Simulink it was very difficult to apply any configuration modifications and extensions.We start with a brief description of the mathematical modelling which includes thermal dynamics and solar radiation. Then the implementation in Modelica is presented. So, a much superior environment in comparison with Matlab-Simulink was obtained, giving us the possibility of high-level modular and object-oriented modelling. The model is also extremely efficient in multidisciplinary projects in which control-engineering specialists (our group) cooperate with specialists from civil engineering, because civil engineers can more easily understand graphical and textual models in Modelica than schemes in Simulink.We expect that such a model will fulfil and significantly improve several model properties in comparison to the Matlab–Simulink implementation, i.e., a better understanding of the influences of thermal and radiation flows on comfortable living conditions, a model-based control-system design, which will enable the harmonization of active and passive energy resources, important energy savings, and a very suitable environment for education in modelling, simulation and control.