Sustainable Immersion Cooling of Servers

Current developments in IT lead to an exponential growth in energy usage in data centers, with a foreseen use of 4-5% of global energy by 2030. Air cooling is no longer feasible, and immersion is a liquid cooling alternative. The choice of coolant today has considerable effect on the environment in the future. Three dielectric fluids for immersion cooling are investigated: FC (fluorocarbon), HC (hydrocarbon) synthetic oil, and plant-based oil. These fluids differ significantly in physical and environmental sustainability properties. FC is the poorest choice for environmental sustainability but has a low viscosity, plant oil is the best for environmental sustainability but has the highest viscosity and hence less flow. A realistic case is considered consisting of a 2000W IT board in the Open Compute Project (OCP) Accelerator Module (OAM) form factor, cooled in forced convection immersion cooling using viscosity derated pump curves of existing water pumps. The design target is to have the component case temperatures below 85 degrees C with 40 degrees C coolant approach temperature. A copper heatsink with characteristics inside existing heatsink technology is used, optimized for low pressure. CFD simulations show that all three immersion fluids can meet the target. Thermally, HC synthetic oil and plant oil perform similarly, and FC performs slightly worse. Based on combined thermal and environmental sustainability characteristics, plant oil comes out as the best choice with HC a close second, FC as by far the worst choice.