In this master thesis a dynamic simulation of the heating and cooling system of a stirred tank reactor is developed. The foundation for this simulation is an Excel spreadsheet, which is used at the company of Bilfinger Life Science for the dimensioning of such heating and cooling systems. The simulation is created in the open-source flowsheet simulator DWSIM, using a custom python unit operation. One of the goals of this work is to investigate the potentiality of using open-source software for complex dynamic simulations, by expanding it with custom unit operations. Using the previously mentioned Excel tool as a foundation, a lumped parameter model of the system is developed. The model acts as a black box with the half-pipe coil of the tank and the heat exchanger packaged together into one unit. Input parameters have to be entered, then the model calculates the output values. This lumped parameter model can already be described as a dynamic model, since the time component is already included. The problem is that while this approach is very effective, it is not possible to change any parameters during the simulation. Therefore, the lumped parameter model is expanded by splitting up the heat exchanger unit and the half-pipe coil. Both units are then connected so that the data of one unit can be accessed by the other, making the simulation truly dynamic. This has multiple advantages. On the one hand, it leads to a more realistic model and the program better resembles the real-life process. On the other hand, by dividing the model into two separate units, direct intervention in the process, during simulation is possible. Using this dynamic, split unit model a PID controller can be simulated. The simulation can then be used to determine the parameters of the PID controller. The simulation and virtual tuning of the PID controller has multiple advantages. Different configurations can be tested, that would otherwise have to be tested on the real plant. The parameters that are determined using the simulation, can then be used as a starting point for the actual tuning. First attempts of virtual tuning look promising.