Modelica Copyright: © EBC

Simulation with Modelica/Dymola

Modelica is an object-oriented modeling language. It enables the direct usage of "text book- equations" for modeling systems from an engineering point of view. Furthermore it allows for an “acausal” modeling style, meaning the direction of energy flows in the system depends on the current state and does not need to be predefined. These properties make Modelica ideal for the modeling of hybrid systems: mechanical, hydraulic and electrical systems.

On top of all this, it is just exciting to work with Modelica. While not being a dedicated language for building energy simulations, it is a modeling language for any type of describable physical phenomenon. Only two conditions must be fulfilled: the equation systems must be solvable and the developer must always strive to improve his/her models.

  Modelica Copyright: © EBC

In order to have a simulation, a simulation environment is needed that will solve the equation system and run the dynamic simulation. At EBC we use mainly the commercial software Dymola, which in a way grew up alongside the Modelica language and currently offers the best solver capabilities for our applications. We also use Dymola as part of our teaching activities, and we have recently started working with the open source tool JModelica.


Open Source Library AixLib

Our focus at EBC lies in dynamic simulations of buildings and their energy systems. The interactions between buildings, technical equipment and control are diverse. The main function of the energy system is to ensure adequate indoor conditions while being as energy-efficient as possible. On top of this comes the human component, with the user setting set values for the indoor conditions according to personal preferences, but also acting as a source of energy (heat, humidity) in the building itself.

Our extensive Know-How in working with Modelica under Dymola in the field of dynamic building energy simulation produced the open source library AixLib. It contains Modelica models for the building envelope and HVAC equipment such as boiler, radiator, heat pump and CHP. Emerging from the institute’s needs in research and teaching, AixLib contains models at different levels-of-detail. In particular for building envelopes, it contains models focusing on individual buildings (High Order Models) as well as on neighborhood or urban scale applications (Reduced Order Models). The library extends the collaboratively developed Modelica IBPSA Library, which focuses on basic models. AixLib is available under the Modelica license 2.0.

As the library is developed at RWTH Aachen University's EBC, the library's name AixLib is derived from the city's French name Aix-la-Chapelle, which the people of Aachen are very fond of and use a lot. With the name AixLib we follow this local tradition.

  Modelica Copyright: © EBC

Our Know-How covers the analysis of single components, through energy systems for whole single family dwellings up to entire city districts simulations. Considering the constant trade-off between model resolution and computational time, while considering the available data for describing complex systems, we developed models with different degrees of detail for relevant components, be it technical equipment or building elements.

  Modelica Copyright: © EBC

Simulation coupling with further programs

Furthermore, Modelica/Dymola can be used as part of co-simulations, by coupling with other Software, e.g. Matlab/Simulink, Java, or Python, also to implement new types of control algorithms. The coupling is done via functional mock-up units (FMUs), dedicated software or specially developed solutions. Coupling with real hardware is also possible, via the Hardware-in-the-Loop method.


Vapor-Compression Modeling using TIL Suite

In addition to the development of the AixLib library for dynamic building and energy system simulation, we work in close cooperation with TLK Energy GmbH , which distributes the commercial model library TIL Suite . With the help of TIL Suite, detailed thermodynamic cycles (e.g. vapor-compression cycles) can be simulated and investigated dynamically. On the one hand, this promotes system understanding. On the other hand, our test benches can be simulated, which allows us to develop innovative control concepts, among other things. Furthermore, buildings (AixLib), heat distribution system (AixLib) and detailed energy conversion systems (TIL Suite) can be coupled, enabling a complete consideration of the building energy system.