Exergoeconomic analysis of heat supply by a district heating system

摘要

Results of the exergy analyses and optimizations of heat supply by a district heating system help us to investigate the distribution network design and operation parameters that enable improved utilization of primary energy sources.The optimal distribution network pipe diameters depend on the demanded amounts of heat transportation,pipe's isolative properties and the temperature area in which they operate.Furthermore,the supply and return temperatures have a high impact on the overall exergetic efficiency of heat supply with a district heating system.In addition,the daily heat demands change continuously through the year.Accordingly the search for the thermodynamically optimal design of a district heating system is complex.However,the sensitivity of exergetic efficiency of heat supply on some design parameters such as pipe diameters is relatively low.Therefore,an additional economic criterion to the dimensioning procedure reduces the optimum pipe diameters with relatively low reduction in efficiency of heat supply.By attributing the fuel,capital investment and operating and maintenance costs to exergy streams in a district heating system,the cost optimum system design can be investigated.In this paper the impacts of the distribution network's design and operation parameters on the exergoeconomic performance of heat supply are investigated.Doing this,the cost of heat supplied by a district heating system as a function of various parameters is studied.The supply of heat through a supply line operating in low and moderate temperature regimes is studied and compared,and the optimum diameters and supply temperatures are determined.The results of an iterative dimensioning procedure for a simple distribution network are shown.A comparison is made between the exergy-based optimum distribution network design and the cost optimum distribution network design.The first one represents the best thermodynamic solution while and in the second case also costs are considered.