Data Centers With Direct Liquid-Cooled Servers: Experimental Analysis and Modeling

Data centers worldwide face rising electricity consumption, with a substantial portion used for cooling IT components. Traditional air-cooling methods have become increasingly inefficient as server power densities rise, causing a transition towards liquid-cooling technologies. Direct liquid-cooled servers operate at higher coolant temperatures than air-cooled systems, significantly reducing cooling demands and improving the potential for waste heat reuse. However, elevated coolant temperatures may increase server power consumption, reduce heat transfer to the coolant, and potentially affect IT equipment performance. To systematically quantify these effects, a comprehensive analysis based on benchmark tests was conducted on ten liquid-cooled servers under varying coolant inlet temperatures (25 degrees C-50 degrees C) and IT loads. Results demonstrated that server performance remained unaffected within this temperature range. Nonetheless, raising the average cooling temperature from 30 degrees C to 50 degrees C increased server power consumption by 8.5% and reduced heat transfer to the coolant by 14.6% due to thermal losses. Based on these experimental results, a simulation model was developed and implemented in TRNSYS. This model enables the prediction of the behavior of direct liquid-cooled servers and the assessment of practical applications for waste heat utilization.