Development of a hybrid electric organic Rankine vapor compression cooling system for energy system resiliency

Abstract

Thermally activated chillers, like absorption and organic Rankine vapor compression (ORVC) systems, are solutions to improve efficiency, reduce costs, 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 conditions. This work presents an extensive investigation of a novel, electrified ORVC system, an innovative approach designed to combine the efficiency and emissions benefits of thermally driven cooling with the on-demand reliability of conventional electric systems. By utilizing both electric and thermally driven compressors in an integrated system, this research addresses the fundamental limitations of purely thermal cooling systems while maximizing the benefits of thermal energy utilization. A thermodynamic and turbomachinery model was developed to evaluate three distinct compressor configurations across diverse operating scenarios. Simulation results revealed that positioning the thermal compressor before the electric compressor (TC1 configuration) provided optimal performance by mitigating the choking limitations of the electric compressor. This configuration demonstrated exceptional performance flexibility, operating effectively across heat inputs from 100 kW to 327 kW while achieving thermal coefficient of performance (COP) values up to 1.6 and electric COP values reaching 18.2—significantly outperforming both purely thermal (COPth = 0.44) and purely electric (COPe = 5.86) baseline operations. To validate the simulation findings, a large-scale prototype test facility was constructed and subjected to extensive experimental evaluation. The experiments confirmed the simulation predictions regarding compressor configuration performance, with only the TC1 arrangement successfully achieving the target 175 kW cooling capacity. Under design conditions, the prototype delivered 176 kW of cooling utilizing 257 kW of thermal input and 20.1 kW of electric input. Parametric studies examined system response to variations in heat supply (85-110°C), cooling delivery temperature (2-14°C), heat rejection temperature (25-39°C), and electric compressor power (19.2-33.9 kW). These investigations revealed substantial operating flexibility but also identified critical limitations, particularly regarding compressor isentropic efficiency and operating map constraints. Part-load performance evaluation yielded integrated part-load values of 7.40 and 0.56 for electric and thermal COP, respectively, though performance at lower capacities was constrained by electric compressor lift limitations. This research demonstrates that hybrid ORVC technology can successfully expand the operational flexibility of cooling systems while maintaining high efficiency across diverse conditions. The findings highlight the critical importance of properly matched compression equipment and identify compressor efficiency as a fundamental determinant of both system performance and operational range. These insights provide a foundation for further research and development surrounding hybrid ORVC technology that can contribute to more cost-effective and sustainable cooling solutions.