Multi-mode and exergoeconomic analysis of a novel combined cooling, heating, and power system applied in the geothermal field

Abstract

The exploitation and utilization of geothermal resources contribute to alleviating energy crisis and reducing environmental pollution caused by the use of fossil fuels. The energy systems driven by low-grade geothermal heat sources also have the potential for energy-saving and emission reduction. Among all kinds of energy systems, multi-mode systems with characteristics of various operation modes and flexible energy output have been widely concerned. In this work, a multi-mode CCHP system with a novel structure is proposed and driven by a closed type of geothermal heat source. The proposed parallel system is composed of a vapor compression heat pump cycle, an organic Rankine cycle, and a vapor compression refrigeration cycle. The exergy efficiency and total product unit cost are selected as objective functions in multi-objective optimization processes to characterize system thermodynamic and exergoeconomic performances, respectively. The proposed system can operate in seven different modes to realize the conversion of power, heating, and cooling capacity output. The effects of main parameters, including evaporation pressure, condensing temperature, split ratio, etc, on system performances were studied. Results found that the coupling evaporator had the highest exergy destruction rate while the component turbine showed the largest capital cost. From the viewpoint of exergoeconomic performance, the turbine and coupling condenser were the most two important components. After that, the multi-objective optimization results revealed the limits of comprehensive system performance under such closed heat source conditions. Finally, the adjustable analysis found the performance range of the proposed system regulating the seven different operation modes. The exergy efficiency and total product unit cost fluctuated in the ranges of 18.68–52.64 % and 9.56–14.93 $/GJ, respectively.