What is it about?
In recent years, District Heating (DH) systems have become significantly more efficient. However, ongoing investigations reveal that there is still untapped potential for even greater benefits and efficiencies. An intriguing direction for exploration involves considering the adjustment of operational temperatures, transitioning from high levels to lower ones. This study delves into the impact of different operational temperature levels on DH systems. To ensure precise evaluations, the focus is given on a specific DH network case study, with a Combined Heat and Power (CHP) plant serving as the primary energy source. Three distinct design scenarios were evaluated for the system, analysing the energy, exergy, and economic implications for both individual components and the entire heat grid. The findings demonstrated that reducing operational temperature levels led to notable improvements in both the energetic and exergetic efficiencies of the CHP-supplied DH system. Additionally, this adjustment resulted in decreased costs per unit of exergy associated with meeting the demands for space heating and domestic hot water.
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Why is it important?
The significance of DH systems in future sustainable energy frameworks is undeniable. Lowering the temperature of supply and return in hot water pipelines holds promise for enhancing both technical and economic efficiency. Thus, this article seeks to evaluate the potential benefits of such heat distribution grids across various operational temperature levels. Consequently, emphasis is placed on heat networks supplied by a Combined Heat and Power (CHP) plant across various design scenarios, encompassing high-, medium-, and low-temperature supply levels adhering to intentional standards. The investigations encompass energy, exergy, and economic analyses of the entire DH system, as well as individual subcomponents including pipelines, substations, and the heat supply plant. The conversion of a coal-fired thermal power plant, originally dedicated to electricity production, into a CHP plant to fulfil space heating and domestic hot water heating demands underscores the adaptation to DH operational temperatures. In this conversion process, the lowest pressure stage of the LPT where steam can be extracted was determined to minimize electricity loss generation in the power plant. The analysis unequivocally demonstrates that lowering operational temperature levels in a CHP-based DH system enhances the energy, exergy, and thermoeconomic performances of the overall system.
Perspectives
The investigation of the impact of operational temperature levels on combined heat and power systems, particularly concerning energy, exergy, and economic aspects, is imperative within the field. This study endeavours to bridge a notable gap in the existing literature by delving into this crucial area. Thermoeconomic analyses, encompassing both energy and exergy assessments alongside economic principles, are indispensable for comprehensively evaluating the costs associated with thermodynamic inefficiencies within district heating systems. Given that previous research predominantly focuses on low-temperature district heating systems, primarily grounded in the first law of thermodynamics, this exergoeconomic inquiry holds significant merit. By juxtaposing low-temperature operations with high and medium-temperature district heating systems, and meticulously considering all subsystems within the DH system along with the exergetic efficiency of the CHP plant, this study offers valuable insights and a comprehensive perspective on the subject matter.
Dr. Hakan İbrahim Tol
Eindhoven University of Technology
Read the Original
This page is a summary of: Energy, exergy and economic investigation of operating temperature impacts on district heating systems: Transition from high to low-temperature networks, Energy, July 2022, Elsevier,
DOI: 10.1016/j.energy.2022.123845.
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