Low-Grade heat utilization: Techno-Economic assessment of a hybrid CO2 heat pump and Organic Rankine Cycle system integrated with photovoltaics and thermal storage

The shift toward sustainability requires comprehensive strategies that include the utilization of low-grade waste heat. To address this gap in integrating combined heat and power (CHP) systems, we introduce a novel hybrid CHP system that integrates a CO2 heat pump (HP) with an organic Rankine cycle (ORC) for low-grade heat utilization. Firstly, it replaces a conventional refrigerant-based HP with a transcritical CO2 HP, assisted by photovoltaics (PV). Secondly, it introduces a model predictive control optimization strategy that enhances the system's self-sufficiency. Lastly, the CHP system is integrated with thermal energy storage (TES) for demand management. The integration of multiple components enables the efficient utilization of various low-grade heat sources sustainably, with adaptability to different operational strategies based on demand and supply dynamics. We conduct techno-economic and parametric analyses focusing on component and system-level performance through detailed seasonal case studies for Miami, FL, and Chicago, IL. Our findings show that the COP in Chicago decreased by 11.1% (without ORC) and 8.2% (with ORC). However, the annual efficiency of the ORC in Chicago increases by 4.3%. The total cost of the CHP is similar for both locations. The system self-sufficiency is higher in Miami, while the system COP is better in Chicago.