Lowering the exergy content of heat required for heating purposes decreases the primary energy consumption. District heating systems are often an important link between facilities that generate heat with low exergy content and consumers. Exergetic efficiency of heat distribution is an important performance criterion in heat supply to consumers. It can serve as a criterion for optimization, towards a more sustainable distribution-network design and operation. This paper presents a methodology for an exergy-based distribution-network analysis in a district heating system. Criteria for performance evaluations are defined. They can be used to evaluate heat supply to different points in the network, or individual system components. A case study is performed on an existing district heating system. Energetic and exergetic efficiencies of supply lines are analyzed. Exergy destructions and exergy losses are studied. Large differences in efficiency of heat supply to different points in the network are discovered. Over-dimensioned parameters of the distribution network are investigated.Keywords: district heating system; distribution network; energy; exergy; efficiency

In this paper the attention is on the heat losses of a main, aboveground supply, hot-water pipeline, whose length is 5430 m. It is situated between the Šoštanj Thermal Power Plant (TEŠ) and the Central Energy Station (CES) Velenje as part of the district heating system in the Šaleška Valley. It was renovated because major heat losses were identified. A numerical analysis and a comparison between the temperature fields of the pipe's insulation before and after the renovation was performed to discover the main causes for the high heat losses before renovation. An integral measuring method for determining the heat losses was adapted and used to determine the pipeline's heat losses after the renovation. Taking into consideration the real operating parameters, the annual energy savings and the consequent operational cost reduction, due to the lower heat losses, resulting from the pipeline renovations, are presented. The calculation is made with measured heat-loss coefficients and is therefore based on the real state of the pipeline. The aim is to show the necessity to investigate the heat losses of a hot-water pipeline whose design or state of insulation is questionable.