A comparative exergy and exergoeconomic analysis of a residential heat supply system paradigm of Japan and local source based district heating system using SPECO (specific exergy cost) method

• Space heating and hot water supply analysis of a small city in Japan is conducted.
• Geothermal and waste source based district heating system is modelled.
• LowEx and SPECO methods are combined for analysis from single user perspective.
• District heating system has lower exergy efficiency of 4.2% against 5.4%.
• Due to thermo-economic synergy district heating system has lower unit exergy cost.

In this study an exergy and exergoeconomic evaluation of a heat supply system paradigm of Japan and a district heating system (DHS) is conducted from a single user perspective, providing cost-based information on the systems inefficiencies and improvement potential. A heat supply system of a case city is used as a paradigm for Japan and a DHS is modelled according to standard practice for the same city, integrating geothermal heat and local waste sources. The local resources can supply 21% of the design load and natural gas is used for supplying the rest. For the analysis a pre-design exergy analysis tool combined with the specific exergy cost method is applied. The DHS and Japanese paradigm system have exergy efficiency of 4.2% and 5.4% respectively. Due to thermo-economic synergy effect however, the DHS has lower unit exergy cost of space heating and domestic hot water of 508 $/GJ and 273 $/GJ compared to 686 $/GJ and 726 $/GJ of the Japanese paradigm system. The DHS has considerable performance improvement potential through reduced operation temperatures and effective use of combustion sources through co-generation. The unit exergy cost difference leaves margin for capital investment cost increase for decreasing exergy consumption of the DHS.