Thermal Design and Performance Modeling of A High Compute Density Liquid Cooled Chiller Less Modular Edge Data Center

Abstract Holistic design of a modular energy-efficient edge datacenter with compute densities of 20 kW/m3 is presented. The datacenter uses a single chiller-less liquid loop to extract heat from server components and reject it to the ambient using a mixture of 25% propylene glycol and water. Heat is extracted from the chips using a micro-pin array cold plate and rejected to the ambient air is achieved using a counter-flow microchannel polymer heat exchanger (MPHX) dry cooler. Experiments on performance of the cold plate and MPHX components are presented, and a validated system model of the cooling loop is developed. Baseline performance results at an outdoor temperature of 40 C for a maximum GPU case temperature of 75 C reveals an optimum setting of liquid flow rate and dry cooler fan flow rate to minimize the system cooling power to under 4 percent of the compute power. Sensitivity studies are performed to assess the impact of improvements in thermal interface material, cold plate convective resistance, and dry cooler air-side heat transfer coefficient on system performance. Results show that a combination of improvements to the cold plate and dry cooler, or a significant reduction in TIM resistance can decrease the cooling power ratio. Annual simulations in Portland, Sacramento, and Phoenix show that the edge datacenter uses 1.34, 1.32 and 1.7% of the compute electrical energy for cooling, respectively, with peak ratio under 5 percent for 98.42% of the hours in the hottest location.