Hakan İbRahim Tol

This paper presents a techno-economic optimisation of supply-side transition pathways for the district heating system of Stadtwärme Kapfenberg GmbH (Austria), aiming at full decarbonisation by 2040. Conducted within the SUPPORT DHC project, the study assesses how industrial waste heat, renewable heat options, and Power-to-Heat (P2H) can be combined to provide cost-efficient and reliable heat supply under evolving boundary conditions. A detailed energy system model was implemented in energyPRO and optimised at hourly resolution over a full year using validated demand profiles and operator-specific constraints, including source availability, maintenance schedules, technology priority constraints, operational cost parameters, and fixed installed capacities for existing assets. The analysis pursues two objectives: one with identifying cost-optimal supply portfolios for the current and planned expanded system, and the other with sizing P2H under two operational modalities (PV-only and PV plus grid electricity – grid import is permitted only when day-ahead prices are at or below a threshold; proxying hours with high renewable availability and/or low marginal emissions) within predefined capacity ranges. Across the analysed scenarios, industrial waste heat remains the dominant component of the cost-optimal portfolio. For the PV capacities considered, PV-only P2H exhibits a limited system-wide impact, indicating that achievable benefits depend strongly on local generation scale. In contrast, grid-enabled P2H improves economic performance and operational flexibility under the applied electricity price threshold formulation. Minimum levelized cost of heat occurs at approximately 2 MW P2H capacity with a grid price threshold of around 40 €/MWh; beyond this point, marginal benefits diminish as low-price operating hours saturate. The paper provides decision support for municipal utilities by demonstrating an optimisation-based heat production planning workflow that informs EED-aligned transformation and investment planning for accelerated integration of industrial waste heat and low-grade renewable heat, with sector-coupling options assessed to strengthen operational feasibility.

This review paper provides a comprehensive examination of current strategies and technical considerations for reducing return temperatures in district heating (DH) systems, aiming to enhance the utilization of available thermal energy. Return temperature, a parameter indirectly influenced by various system-level factors, cannot be adjusted directly but requires careful management throughout the design, commissioning, operation, and control phases. This paper explores several key factors affecting return temperature, including DH network, heat storage, and control strategies as well as the return temperature effect on the heat source. This paper also considers the influence of non-technical aspects, such as pricing strategies and maintenance practices, on system performance. The discussion extends to the complex interplay between low return temperatures and temperature differences, and between operational temperature schemes and economic considerations. Concluding remarks emphasize the importance of adopting a holistic approach that integrates technical, operational, and economic factors to improve DH system efficiency. This review highlights the need for comprehensive system-level optimization, effective management of system components, and consideration of unique heat production characteristics. By addressing these aspects, this study provides a framework for advancing DH system performance through optimized return temperature management.

This review presents a comprehensive examination of recent advancements and findings related to return-temperature reduction in District Heating (DH) systems, with a focus on enhancing overall system efficiency at end-user sites. The review categorizes and clarifies various return-temperature reduction techniques, emphasizing aspects such as building energy performance, heat emitters, thermostatic radiator valves, and substation units. One shall note that return temperature is not a parameter that can be directly controlled within a DH system; instead, it is influenced indirectly by adjusting various system parameters throughout the design, commissioning, operation, and control phases. Key insights include the direct impact of heat demand on return temperatures; the pivotal role of indoor heating systems in optimizing thermal energy use in relation to heat demand; the significance of thermostatic radiator valves in regulating heat output and maintaining low return temperatures; the advantages of ventilation radiators and add-on fans in enhancing radiator efficiency; the necessity for effective substation operation to improve system cooling capacity; and the critical role of operational control strategies in achieving optimal system performance. These findings underscore the need for integrated approaches in DH system design and operation to achieve lower return temperatures and improve overall system efficiency.