A modelica based computational model for evaluating a renewable district heating system

Name of student: ir. F.F.M. (Frank) Soons
Supervisors: J.L.M. (Jan) Hensen, I. (Ignacio) Torrens, MSc
Chair research belongs to: Building Performance
Strategic area: Energy
Project year: 2014

District heating (DH) systems are considered a viable method for mitigating long-term climate change effects, through their ability to reduce CO2 emissions, their high conversion efficiencies and their ability to be integrated with renewable energy sources (RES). The current evolution towards sustainable DH, e.g. integration of RES, results in increased complexity and diversity during the early-design phase.

In the early-design phase of DH systems a feasibility study is conducted to assess if the economic feasibility and environmental impact meet the given requirements. The assessment is currently conducted with a traditional district heating computational model (DHCM) utilizing a simulation language which limits the evaluation of sustainable DH systems in terms of flexibility and comprehensibility. Therefore, the need for an alternative language capable of effectively modeling a DH system with integrated RES led to the use of Modelica which offers improved flexibility, reusability as well as hierarchical and multi-domain modeling. In this work, a case study is presented to evaluate this new DHCM considering its modeling capabilities and system performance. For an optimum utilization of the biomass gasifier, two power plant configurations are assessed:  a biomass gasifier system with and without thermal energy storage (TES).

The system performance evaluation indicates a significant increase in the utilization of the biomass gasifier with 8.2% (353 hours) compared to results obtained from the traditional DHCM. This deviation is due to a more accurate consideration of the DH thermal capacity and the space heating demand. Furthermore, the models in this DHCM enable assessment of the impact of building retrofits or climate change scenarios. Thus, the increased modeling capabilities and system performance demonstrate that this new DHCM is suitable and beneficial for early-design feasibility studies of innovative RES integrated DH systems.