Thermodynamic and turbomachinery analysis of a hybrid electric organic Rankine vapor compression system

Thermally activated chillers, like absorption and organic Rankine vapor compression (ORVC) systems, are solutions to improve efficiency and meet decarbonization goals in the heating, ventilation, and air-conditioning (HVAC) industry. However, technical limitations prevent these chillers from providing steady cooling power under variable operating parameters. This work evaluated an electrified ORVC system that can address the limitations of thermally activated chillers, by utilizing both thermal and electric input. Three different configurations (one with parallel compressors and two with series compressors) were evaluated using coupled thermodynamic and turbomachinery analysis. The highest performing configuration (series with the thermal compressor first) was simulated at 175 kW scale under industry standard operating conditions, and across a range of parameter studies to characterize off design performance. Simulation results indicated efficient performance, with compression load being shifted between the thermally and electrically driven compressors. With the compression load balanced, the thermal COP was 0.69 and the electric COP was 10.1 at design conditions. Simulations showed a wide operating range, with acceptable heat input ranging from 100 kW – 327 kW in hybrid operation, in addition to purely electric or thermal operation. Parametric results also indicated large operating ranges for heat supply inlet temperature (85 °C – 117 °C), chilled water delivery temperature (2.1 °C – 10.7 °C), and heat rejection inlet temperature (26.6 °C – 30.9 °C). Turbomachinery analysis indicated a mismatch between the thermal and electric devices, which impacted the performance of the system. Simulations with a properly sized electric device increased the capacity to 268.3 kW, highlighting the importance of turbomachinery analysis for this technology.