As global demand for data centers grows, so does the size and load placed on data centers, leading constraints on power and space available to the operator. Cooling power consumption is a major part of the data center energy usage. Liquid cooling technology has emerged as a viable solution in the process of optimization of the energy consumed per performance unit. In this data center rack level evaluation, 2OU (Open U) hybrid (liquid+air) cooled web servers are tested to observe the effects of warm water cooling on the server component temperatures, IT power and cooling power. The study discusses the importance of variable speed pumping in a centralized coolant configuration system.

The cooling setup includes a mini rack capable of housing up to eleven hybrid cooled web servers and two heat exchangers that exhaust the heat dissipated from the servers to the environment (the test rig data center room). The centralized configuration has two redundant pumps placed in series with heat exchanger at the rack. Each server is equipped with two passive (i.e. no active pump) cold plates for cooling the CPUs while rests of the components are air cooled. Synthetic stress load has been generated on each server using stress-testing tools. Pumps in the servers are separately powered using an external power supply. The pump speed is proportional to the voltage across the armature [1]. The pump rpm has been recorded with input voltages ranging from 11V to 17V. The servers are tested for higher inlet temperatures ranging from 25°C to 45°C which falls within the ASHRAE liquid cooled envelope W4 [2]. Variable pumping has been achieved by using different input voltages at respective inlet temperatures.

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