Dear Reader,

For the 56th issue of our heatbeat Research Newsletter, we take a look into the latest research based on thermal-hydraulic modelling of district heating networks.

The first paper "Thermal-hydraulic modelling of a flexible substation layout for low-temperature waste heat recovery into district heating" from Anania et al. covers the modelling and detailed analyzation of a bidirectional substation connected to a district heating grid for space heating and domestic hot water supply of a steel mill.The second paper this month gives an overview of the impact and feasibility of supply temperature reduction in district heating networks. The title is "Determining economic feasibility of supply temperature reduction in existing district heating system through thermohydraulic modelling" from Kotilainenet al.

The paper titled "Thermal-hydraulic modelling of a flexible substation layout for low-temperature waste heat recovery into district heating" explores the design and simulation of a bidirectional thermal substation that enables efficient integration of industrial waste heat into district heating (DH) systems. The study focuses on a real-world application at a steel mill in Ospitaletto, Italy, where waste heat from cooling processes is recovered to meet internal heating demands and, when in surplus, is fed into the DH network. The substation includes heat pumps (HPs), thermal energy storage (TES), and a detailed hydraulic system, allowing it to function both as a heat consumer and producer — embodying the concept of a “thermal prosumer.”

A dynamic model of the substation was developed using TRNSYS and validated against real operational data. The model incorporates detailed representations of hydraulic components, dynamic heat pump behavior, and control logic based on temperature sensors. It supports multiple operating modes and configurations, making it adaptable to various network conditions and user demands. Validation results showed high accuracy, with performance estimation errors under 5%. The model was used to simulate two scenarios: a conservative “upgrade” scenario reflecting current network conditions, and an “optimal upgrade” scenario assuming expanded network capacity to utilize all available waste heat.

Simulation results demonstrated that the system could reduce non-renewable primary energy consumption and CO₂ emissions by up to 75 % compared to conventional gas boilers. Additionally, about 90% of the available waste heat could be recovered and reused, especially in summer when internal demand is low. The study highlights the importance of bidirectional substations in enhancing energy efficiency, decarbonizing heating systems, and supporting the transition to sustainable energy networks. The flexible model developed can be applied to various industrial and geographical contexts, offering a valuable tool for optimizing waste heat recovery in district heating systems.

The study titled "Determining economic feasibility of supply temperature reduction in existing district heating system through thermohydraulic modelling" investigates the potential cost savings and operational impacts of lowering supply temperatures in district heating (DH) systems. Using the Kangasala DH network in Finland as a case study, the authors employed the Fluidit Heat simulation tool to model various supply temperature scenarios, ranging from 115°C to 90°C. The goal was to assess whether reducing supply temperatures could yield significant economic benefits by lowering heat losses, despite the potential increase in pumping energy and infrastructure strain. The model incorporated detailed hourly data from 314 customer substations and considered both existing and upgraded substation configurations.

The results revealed that with existing infrastructure, the economic benefits of reducing supply temperatures are minimal. The best-case scenario showed only a 0.5 ‰ reduction in total production costs, primarily due to increased pumping energy offsetting the savings from reduced heat losses. A sensitivity analysis further demonstrated that the economic viability of temperature reduction is highly dependent on the ratio between electricity and fuel prices. When substations were upgraded to modern standards (90/33°C), the savings increased to 2.37% of total production costs. However, the high investment costs associated with upgrading substations make this approach economically unfeasible unless paired with broader system changes, such as integrating low-temperature heat sources like waste heat.

The review covers 3 LT-ATES, 8 HT-ATES, and 2 MTES research sites across Germany. Although these studies span diverse locations and methods, most are still in early-stage development with low technology readiness levels (TRL 2-4). Notably, HT-ATES projects are more prevalent, indicating growing interest in high-temperature storage integration with district heating networks. However, few initiatives aim for real-world implementation. Key barriers include complex regulatory frameworks, permitting challenges, and site-specific constraints, especially in urban areas.

The study concludes that supply temperature reduction alone is not a cost-effective strategy in systems already using outdoor temperature compensation, such as in Finland. The real economic potential lies in combining temperature reduction with a transformation of the heat production portfolio. This includes incorporating low-cost, low-temperature heat sources and optimizing plant operations. The findings challenge the common assumption that lower supply temperatures inherently lead to significant cost savings and highlight the importance of system-specific modelling in DH planning.

Further Information

As always, we recommend reading the article in full. In addition to this research newsletter and various blog posts, we have added a monthly feature update to our blog, summarizing important developments and new features in our heatbeat Digital Twin. You can find the latest entry at "https://heatbeat.de/en/blog/64/" Whenever you need to use thermohydraulic modelling approach in district heating applications, reach out to us and we can discuss how we can help.

The next issue of our newsletter will be published on July 2, 2025.