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Effect of Warm Water Cooling for an Isolated Hybrid Liquid Cooled Server
Keywords: Warm water cooling, Liquid cooled server, cooling power consumption
Data center cooling strategies have changed overtime due to increase in power densities and ever increasing server power requirement. The most common server cooling technique adopted is air cooling where the CRAC units pump volumes of chilled air to cool IT equipment and dispose the heat from the servers to the ambient. With demand for energy-efficient and cost-effective data centers growing, alternative methods to both provide electrical power and cooling systems are the subject of active investigation. As data centers increase in size and current air-cooling systems reach their limitations, cooling technology will inevitably evolve towards air-liquid or liquid cooling systems. Server level cooling is achieved through a combination of warm water cooling and recirculated air (hybrid cooling) in a 2OU (OpenU) web server. The work presented highlights the impact of various inlet supply water temperatures within the ASHRAE TC 9.9 liquid cooling classes (W4) ranging from 27.5C to 45C in terms of server power consumption, component temperatures and cooling power consumption. The liquid cooled server was equipped with thermocouples for Radiator, DIMMs, Hard disk drives and water inlet to provide representative temperatures during operation. The server is completely isolated from ambient air to accommodate for hybrid cooling solution. An experimental run for 18 hours is performed with different inlet water temperatures varying from 27.5C to 45C in increments of 2.5C. The server is exercised computationally using a script with CPU power levels at 40%, 60%, 80% and 100% to provide continuous and steady heat dissipation from the processors and DIMMs and to characterize the system performance. Hence for every test, the operation temperatures, data on power consumption can be made available at different power levels. The test results show that IT power consumption increases linearly with rising water inlet temperature. In order to compare the results of cooling power consumption, a similar server outfitted for air cooling is tested in a thermal test chamber for inlet temperatures varying from 25C to 45C.
Alekhya Addagatla, Graduate Student Assistant
University of Texas at Arlington
Arlington, Texas

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