Study of a Lab-Scale Organic Rankine Cycle for the Ultra-Low-Temperature Waste Heat Recovery Associated With Data Centers

The ongoing growth in data center rack power density leads to an increased capability for waste heat recovery. Recent studies revealed the organic Rankine cycle (ORC) as a viable means for data center waste heat recovery since the ORC uses waste heat to generate on-site, low-cost electricity, which can produce economic benefits by reducing the overall data center power consumption. This paper describes the first experimental and theoretical study of a lab-scale ORC designed for ultralow grade (40–85 °C) waste heat conditions typical of a data center server rack, and it outlines the implementation of a similar ORC system for a data center. The experimental results show thermal efficiencies ranging from 1.9% at 43 °C to 4.6% at 81 °C. The largest contributors to ORC exergy destruction are the evaporator and condenser due to large fluid temperature differences in the heat exchangers. The average isentropic efficiency of the expander is 70%. A second-law analysis estimates a reduction of 4–8% in data center power requirements when ORC power is fed back into the servers at a waste heat temperature of 90 °C. The data from the lab-scale experiment, when complemented by the thermodynamic model, provide the necessary first step toward advancing this type of waste heat recovery for data centers (DCs).