This paper describes the development of an optimization-friendly thermodynamic property model of water and steam that covers liquid, vapor, 2-phase as well as the super-critical region. All equations are at least twice continuously differentiable with respect to all model variables and can be used in dynamic optimization problems solved by efficient derivativebased algorithms. The accuracy has been verified against the industry standard IAPWS IF97 and performance and robustness have been tested by solving a trajectory optimization problem where the start-up time of a gas power plant has been minimized while satisfying constraints on temperature gradients, pressure and flows. Simulations of various plant models have also been performed to verify and benchmark the implementation. The results show that the new media can be used in both solving dynamic optimization and simulation problems yielding reliable results. The new media has been integrated into Modelon's Thermal Power library 1.13. This article is built upon the work in (Åberg, 2016).

Recent studies show that district heating infrastructures should play an important role in future sustainable energy systems. Tools for dynamic optimization are required to increase the efficiency of existing systems and design new ones. This paper presents a novel framework to represent, simplify, simulate and optimize district heating systems. The framework is implemented in Python and is based on Optimica Compiler Toolkit as well as Modelon's Thermal Power Library. The high-level description of optimization problems using Optimica allows flexible optimization formulations including constraints on physically relevant variables such as supply temperature, flow rate and pressures. The benefit of new algorithms for symbolic elimination in Optimica Compiler Toolkit is also investigated. The framework is applied on a test case, which is based on a planned city district located in Graz, Austria. The results demonstrate the generality of the representation as well as the accuracy of the simplification for dynamic optimization of temperature supply and pressure control.

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This paper describes the development and requirement specification of a platform for design and operation of microgrids. The goal is to have a flexible platform based on open standards that can be used to efficiently solve current and future engineering problems for distributed energy sources and storage systems. By basing it on a unified architecture, collaboration and efficient work flows are enabled. In this work we investigate the requirements on the model and on the tool side. We also demonstrate how an energy storage system can be designed to reduce the maximum peak power and how it can be operated in the most economic efficient way, taking into consideration constraints and limitations of the system. This work is based on Modelon's web-based modeling and simulation platform and its Modelica library Microgrid.