Thermo-economic optimization of an ORC driven heat pump based on small scale turbomachinery and comparison with absorption heat pumps

The current paper presents the thermo-economic optimization and comparison, through a multi-objective algorithm, between HP-ORC and the competing single effect absorption heat pump (SEAHP), with the aim to find the best trade-off between investment cost and exergetic efficiency. Heat exchanger (HX) cost, which is the dominant cost driver, is predicted on catalogue-based correlations as a function of heat exchanger areas. The dominating HP-ORC working fluid is R-245fa for all operating conditions, except for hot source temperatures of 180 °C, where R-600a is a better candidate. The resulting Pareto frontiers suggest that, for hot source temperatures up to 120 °C the SEAHP and HP-ORC are highly competitive by yielding similar thermo-economic tradeoffs. For higher hot source temperatures, however, the HP-ORC outperforms the SEAHP both in terms of performance and cost while providing a significantly wider performance range (0.3 < ηexe < 0.55) with respect to the SEAHP (0.4 < ηexe < 0.49).