Cascade utilization of organic Rankine cycle and absorption chiller assisted phosphoric acid fuel cell waste heat for dynamic building demands

The interest in fuel cells is rapidly increasing owing to the development of distributed power generation systems, and various attempts have been made to recover waste heat from fuel cells. This has led to the emergence of cascade heat utilization systems that integrate thermally driven equipment and fuel cells. However, the performance of these hybrid systems has been evaluated under steady-state conditions without considering energy demands, limiting the prediction of their effectiveness and feasibility in practical applications. To address this, a cascade system utilizing fuel cell waste heat is developed to investigate system performance and viability when applied to building energy demands under dynamic conditions. Annual profiles of energy sources and demands are collected to configure a holistic energy system and perform transient analysis. Numerical models of various components are developed and experimentally validated to reflect the actual performance. The cascade system is constructed by integrating the components based on their operating temperature and purpose. A novel dual cascading strategy is adopted using tap water as the heat sink medium to recover the low-temperature waste heat dissipated from the bottoming cycles. In addition, the overall equipment effectiveness of the main components is evaluated to verify accurate determination of operation time and capacity. The proposed system reduces the primary energy consumption and carbon dioxide emissions by 15.8% and 15.4%, respectively, compared to the conventional system. The best-case scenario results in an internal rate of return and payback period of 21.74% and 4.77 years, respectively, indicating the economic feasibility of the proposed system.