LAUSR

Abstract The use of Organic Rankine Cycles (ORCs) for waste heat recovery can reduce energy consumption in data centers, which in turn benefits the environment through the reduction of carbon-based fuels. However, data center applications exist in the ultra-low temperature range (40 − 80℃), making efficient and economical operation challenging. The operating fluids that are viable in this temperature range are limited, so it can be a challenge to identify a suitable drop-in replacement for a proven fluid. In this study, the use of HCFO-1233zd(E) is explored to determine its suitability as a low Global Warming Potential and zero Ozone Depletion Potential alternative to the more common HFC-245fa in ultra-low temperature data center applications. This study features the first known comprehensive comparison between the alternative working fluid HCFO-1233zd(E) and HFC-245fa in a lab-scale experimental ORC under ultra-low-grade waste heat temperatures. The results of this study show that the lower HFCO-1233zd(E) saturated pressures impact the ORC operation by reducing the mass flow rate by 3–21%, thereby reducing the heat transfer across the evaporator and condenser. However, the peak thermal efficiency of the lab-scale system is seen to increase with the use of HCFO-1233zd(E) to a high of 5.0% from 4.6% with HFC-245fa. This work also identifies the minimum feasible waste heat temperature as 55 °C for a successful ORC application with both working fluids.