Energy efficiency is an essential element of server design for high performance computers. Traditional HPC servers or nodes that are air cooled enable efficiency by using optimized system design elements that include efficient heat sink design for critical components such as CPUs, Memory, Networking and Disk Subsystems. In addition, airflow optimization is enabled via critical component placement decisions as well as fan and cooling algorithms that have an objective to optimize airflow and maximize system performance. Critical elements that cannot be avoided in traditional air cooled servers are computer center level management of both the airflow requirements and the exhaust heat flux of the servers. An alternative approach shown in this paper uses a novel water cooled design that enables both extreme energy efficiency for heat extraction of the server heat load and allows for lower device operating temperatures for the critical components. Experimental data documented in this paper illustrates the advantages of using non-chilled water to cool the server, allowing 85 to 90 percent of the server heat load to be extracted by water while allowing inlet water temperatures up to 45 degrees Celsius. A comparison is made of the energy consumption needed to cool the server components for both the air cooled and water cooled systems. The base system used for the comparison uses identical system electronics and firmware. The server thermal data shown in the paper include thermal behavior at idle, typical and maximum power consumption states for the server. The data documents the range of boundary conditions that can be tolerated for water cooled server solutions and the comparative advantages of using this technology.
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