Performance Assessment of Model-Based Controlled Organic Rankine Cycle System for Waste Heat Recovery

Abstract

Abstract. Within the current global effort toward decarbonization, improving energy efficiency across industrial, residential, and transportation sectors represents a critical priority. Waste heat recovery (WHR) technologies, particularly the organic Rankine cycle (ORC), offer a versatile and effective solution for reclaiming low-to-medium grade thermal energy that would otherwise be lost. This work provides a comprehensive performance assessment of a small-scale ORC system designed to operate efficiently under variable and off-design conditions, making it suitable for a wide range of thermal waste streams. The research methodology centers on the development of a detailed 0D/1D computational fluid dynamics (CFD) mathematical model, which was rigorously validated against experimental data obtained from a dedicated test bench at the University of L’Aquila. A core contribution of this study is the implementation of an advanced model-based control strategy. By employing a physics-based feedback-feedforward architecture, the controller regulates pump speed to maintain a target superheating degree between 15 °C and 20 °C, ensuring system stability and protecting components from fluid degradation. The system was evaluated across several operating points, demonstrating its capability to recover over 40 kW of heat. The results show a net electrical power output generally between 0.5 kW and 1.5 kW, reaching a peak of approximately 2 kW. The thermodynamic cycle efficiency ranged from 5% to 12%, while the maximum net overall system efficiency was recorded at 5.5%. These findings confirm that integrating advanced control strategies allows small-scale ORC units to maximize energy recovery and maintain optimal performance across diverse and fluctuating thermal sources.