Performance investigation of a new geothermal combined cooling, heating and power system

In this paper, a new geothermal combined cooling, heating and power system that integrates flash power cycle and ammonia-water absorption refrigeration cycle, is proposed to supply electricity, refrigerant water and domestic hot water simultaneously to users. In the system, the refrigeration cycle serves as the bottom cycle of the power cycle by further utilizing the exhausted geothermal water from the flasher of the power cycle, meanwhile all waste heat of the power and refrigeration cycles is recovered for supplying heat, thus effectively improving the energy conversion efficiency of whole system. This paper establishes detailed mathematical models of the proposed system and conducts a valid model validation. Then a preliminary design condition of the system is given and the results show that the exergy efficiency of system could reach 43.69% under the condition of 170 degrees C geothermal water. An exergy loss analysis is carried out based on the design condition, demonstrating that the maximal exergy destruction exists in the condenser of flash cycle, accounting for 48.53% of the total exergy destruction of the system; the components used for separating or mixing fluids including rectification column, absorber and flasher, occupying 17.68%, 9.02% and 9.30% respectively, are prone to generate exergy destructions. Finally a thermodynamic parameter analysis, in order to assess the effects of seven key parameters on the system performance, is performed. The results show that there are an optimal flash pressure (about 300 kPa) and an optimal generator temperature (about 120 degrees C) respectively that could make the exergy efficiency of system maximal. Within some scopes, lower turbine back pressure and rectification column pressure, higher ammonia concentration of ammonia-strong solution, bring about higher exergy efficiency of system. Additionally the evaporation pressure and the reflux ratio of rectifier just make little difference on the exergy efficiency of system.