Thermodynamic Analysis of Full Liquid-Cooled Data Centers

Abstract

One way to model the thermodynamic efficiency of a data center is to perform a second-law analysis using exergy calculations of the individual components. The in-house data center modeling tool Villanova Thermodynamic Analysis of Systems (VTAS) was applied to determine the effect of direct liquid cooling with cold plates on data center efficiency. The effectiveness of the cold plate as a function of the heat output of the servers was also examined. VTAS was used to study a configuration of two rows with eight racks each. Each rack was assumed to have twelve servers, each producing 200 W of heat. In addition to the cold plates and servers, this configuration also included a computer room air handling (CRAH) unit, a chiller, and a cooling tower. Preliminary results show that data center second-law efficiency increases as the cold plate removes more heat than the CRAH unit. Specifically, when using cold plates to remove all of the heat from the servers, the overall data center exergy destruction was reduced by over 30% compared to a configuration with only a CRAH unit and between 12–18% compared to a configuration with hybrid liquid-air technologies, thus showing that configurations with direct liquid cooling are thermodynamically more favorable. Furthermore, the effectiveness of the cold plate increases as the heat output of each server increases, suggesting that cold plates are most effective when removing a greater amount of heat.