A detailed simulation model for fifth generation district heating and cooling networks with seasonal latent storage evaluated on field data

TL;DR

This work introduces a physics-based, ODE‑driven simulation framework for fifth generation district heating and cooling networks (5GDHC) with seasonal latent storage, explicitly modeling the interaction between uninsulated pipes and surrounding ground, a central ice storage, and building transfer stations. The approach is software-agnostic and implemented in Modelica, validated against field data from Gutach-Bleibach, achieving $NMBE = 4.5\%$ and $CVRMSE = 15.9\%$, demonstrating accurate replication of network temperatures and storage dynamics. Key contributions include detailed ground-heat exchange modeling, a latent-heat ice storage module, and an open-source implementation that supports optimization and scenario testing for 5GDHC infrastructures. The results underscore the practical relevance of ground and ice-storage interactions for planning and operating low-temperature networks, with potential extensions to soil variability and precipitation inputs.

Abstract

Fifth generation district heating and cooling (5GDHC) networks accelerate the use of renewable energies in the heating sector and enable flexible, efficient and future-proof heating and cooling supply via a single network. Due to their low temperature level and high integration of renewables, 5GDHC systems pose new challenges for the modeling of these networks in order to simulate and test operational strategies. A particular feature is the use of uninsulated pipes, which allow energy exchange with the surrounding ground. Accurate modeling of this interaction is essential for reliable simulation and optimization. This paper presents a thermp-physical model of the pip connections, the surrounding soil, a latent heat storage in the form of an ice storage as a seasonal heat storage and the house transfer stations. The model is derived from mass and energy balances leading to ordinary differential equations (ODEs). Validation is performed using field date from the 5GDHC network in Gutach-Bleibach, Germany, which supplies heating and cooling to 30 modern buildings. With an average model deviation of 4.5 % in the normalized mean bias error (NMBE) and 15.9 % in the coefficient of the variation of the root mean square error (CVRMSE), the model's accuracy is validated against the available temperature measurements. The realistic representation of the thermal-hydraulic interactions between soil and pipes, as well as the heat flow within the network, confirms the accuracy of the model and its applicability for the simulation of 5GDHC systems. The model is made openly accessible under an open-source license.

Figures (13)

• Figure 1: Illustration of the 5GDHC network in Gutach-Bleibach, Germany. The ice storage (blue circle) is operated as a seasonal storage to provide heat during the heating period and cooling during the summer to 30 buildings (red circles). Map based on OpenStreetMap data © OpenStreetMap contributors, modified by the authors. Used under the Open Database License https://www.openstreetmap.org/copyright
• Figure 2: The ice storage is filled with water and exchanges heat with the brine flowing through the pipes. If the temperatures inside the storage reach 0 the storage eventually starts to freeze leveraging the effect of crystallization heat. During summer the frozen storage is used to cool buildings. For the sake of simplicity, only one heat exchanger coil is shown.
• Figure 3: View of the inside of the ice store at Gutach-Bleibach during the heating season. Ice forms around the extraction heat exchanger.
• Figure 4: Schematic depiction of the pipe routing at the ice storage. The position $y$ of the mixing valve is manipulated using a PI controller with seasonal reference temperatures for the supply temperature of the network $T_{\mathrm{n},\sup}$.
• Figure 5: Sketch of the pipe geometry.