This paper presents the lessons learnt during the development of a library for the modelling of district heating systems (DH systems), especially focusing on the distribution network. The library was built based on elements from the Modelica Standard Library (Modelica Association, 2012) and the NewThermal library (Lopez, del Hoyo, 2014). The modelling strategy chosen is described. Furthermore, the requirements established by the DH networks are set out as well as the models created in response to these demands. Finally, the artificial diffusion phenomenon, present in the simulation of this kind of thermo-fluid systems, is described.

This article presents the NewThermal library that extends the capacities of Thermal library from the Modelica Standard Library (MSL) including a proposal for standardizing the use of Material models. The new library is intended to decouple the models that collect the equations of heat transfer phenomena from the thermo-physical properties of the matters (fluids and solids). The NewThermal library, in the same way that the current Thermal library from MSL, is composed of thermal system components to model heat transfer and simple thermo-fluid pipe flow. Nevertheless, the models from the package proposed inherit the thermal properties from Media and Material models of the fluids and solids involved (either temperature dependent or constant). In this way, the user has three aspects to define; the heat transfer phenomena to be modelled, the geometrical characteristics of the bodies, and the matters involved. Components inside HeatTransfer package are implemented such they can be used for any material model in Materials package, in the same way that components from Modelica.Fluid were carried out for their use with media models from Modelica.Media. The NewThermal library, in addition, provides some general base models for the modelling of 2D and 3D heat conduction in basic solid geometries. Two examples of use for different domains are presented to illustrate the features of the new libraries.

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