Energetic and exergetic analysis of alternative low-temperature based district heating substations arrangements

Abstract

District Heating (DH) technology is an efficient and cost-effective solution to provide heating services to the built environment. However, the existing DH technology may not be technically and economically effective to service buildings with low energy demands. Here, low-temperature based district heating (LTDH) can provide a better match between supply and demand in terms of energy quality and quantity. This paper deals with the energy and exergy analyses of a LTDH substation supplying a secondary LTDH network as a subnet of the existing DH system. In order to improve the temperature match, a mix of supply and return streams from the main DH network are used to supply the substation. Based on modelling and simulation, an energy and exergy analysis is employed to compare the performance of two proposed substation configurations to that of a conventional DH substation operating at low temperatures. The results of this analysis show that the proposed LTDH substation reduced the share of energy demand covered by the main DH supply by 20% to 25%. Likewise, by using the flow from the main DH return pipe, the final exergy efficiency of the overall system increased by 5% on average. The exergy destruction occurring at the system components was also identified and compared: during high heat demands the substation heat exchanger is responsible for the largest share of exergy destruction, whereas for low heat demands, it is due to the pumping effort. Based on these results, the proposed system is seen as an effective approach to increase the quality and quantity match between the low-temperature network and the conventional supply.