Exergetic and sustainability performance assessment of geothermal (ground source) ejector heat pumps

Abstract

Although ejectors have been used in cooling/refrigeration and Heat Pumps (HP) applications for a long time, utilisation of Geothermal Ejector Heat Pump (GEHP) with Ground–Heat Exchanger (GHE) is a new idea, which has recently appeared in the literature. In this study, we model a GEHP system with a GHE in terms of exergetic aspects and apply our model to this system in the heating mode. The system consists of mainly three parts, namely a GEHP unit, a GHE, and a heat distribution system. We determine the exergy transports between the components and the consumptions in each of the components of the whole system and we also calculate exergy efficiency and Sustainability Index (SI) values for the system components to evaluate its performance. In this regard, exergy efficiency values for the GEHP unit and whole system are calculated to be 85.3% and 84.6% on the product/fuel basis at dead (reference) state values for 19°C and 101.325 kPa, respectively. An improvement of about 16.17% in the energetic and exergetic coefficient of performance value of the GEHP unit is obtained by adding an ejector to the HP system. SI values for some system components such as ejector, compressor, condenser and evaporator are also obtained to be 1.82, 2.79, 3.22 and 3.94, respectively.