Exergoeconomic and exergoenvironmental based multi-criteria optimization of a new geothermal district heating system integrated with thermal energy storage driven heat pump

Abstract

In this study, a new geothermal district heating system, which includes a heat pump (HP) system driven by thermal energy storage (TES) unit, was optimized throughout the multi-criteria decision making analysis named efficiency analysis technique with output satisficing (EATWOS). In this regard, the objective functions were chosen as exergoeconomic and exergoenvironmental indicators varying with the handled designs. 111 different designs formed considering different working parameters and fluids in this aim. Three environment-friendly refrigerants according to their thermal behaviour (wet, dry, and isentropic types) and suitable phase change materials (PCM) according to the design conditions were evaluated. The designed system was evaluated by energy, exergy, exergoeconomic, and exergoenvironmental tools to determine the objective functions. As conclusion, Case 108 with the refrigerant of R1234ze and PCM of RT70HC was determined as the best design. The sustainability index, exergoeconomic factor, exergoenvironmental factor, relative cost, and relative exergoenvironmental impact of this optimal case were determined as 1.24, 0.002583%, 0.0540%, 460.85%, and 649.50%, respectively. For this case, the energy and exergy efficiencies of the system were determined as 74.56% and 19.17%, respectively. In comparison to conventional system, a decrease of 38.86% in relative exergoeconomic cost (r) and a decrease of 19.21% in the relative exergoenvironmental impact (rb) were achieved.