Performance evaluation and multi-criteria decision analysis of thermal energy storage integrated geothermal district heating system

Abstract

Geothermal energy use in district heating systems has been prevalent and familiar in areas with rich sources for many years. In conventional geothermal district heating systems (GDHS), the geothermal fluid is transported to a heat center to give its heat energy to the secondary fluid. Then, this secondary fluid is circulated in the city network to give its heat energy to the heating circuit by the heat exchangers in the substations. Finally, the geothermal fluid is re-injected to handle the continuity of the resources. This current system works under the designed conditions of a heating system with significant electricity consumption and enormous heat waste. In this study, a thermal energy storage (TES) system was integrated into substations instead of heat exchangers to prevent the waste of heat and overconsumption of electricity by obtaining just-in-time working conditions. In this regard, a shell and tube latent heat TES system was designed for residential use for peak loads and integrated into the heating circuit of GDHS, preserving the current main structure. A number of 37 available cases were formed parametrically to evaluate the system's performance. These cases were analyzed thermodynamically by energy and exergy methods. The net present value (NPV) method was used to evaluate the cases' economics. Finally, an efficiency analysis technique with output satisficing (EATWOS) was conducted to determine the most efficient design from the viewpoints of exergy efficiency, NPV, and CO2 emissions.