In this paper a simulation tool is presented which can be used for the modeling of air and water distribution networks. Based on basic approaches for network resistances and topology a model for the calculation of the pressure and flow distribution in any kind of network is developed. Further on it is described how the model can be used as a standalone tool or as an integrated module within the simulation program TRNSYS. With the presented tool it is possible to simulated meshed networks with an arbitrary number of pumps or fans. The applicability of the tool is shown with two examples. In a first example the simulation of a chilled water distribution network within an industrial plant is described . The second example shows the integrated network simulation within TRNSYS for a HVAC system.