High temperature coolant demonstrated for a computational cluster

Energy efficiency is an important aspect of high performance computing systems design, as the power consumption grows. Free cooling is a widespread technique to lower energy consumption of the cooling subsystem, usually requires expensive equipment to be installed. The standard chilled water temperature is 7 °C may be attained large part of the year in the Europe, and in North America, when atmosphere air temperature is low enough. In case the air temperature is higher, freon compressors should be used to cool down the liquid. In the presented work we report about blade server design and computational cluster installation with direct liquid cooling, that operate at coolant temperatures above 50 °C, which enables 24 hour, year-round free cooling with atmosphere air at the most locations on Earth. The server design is based on an approach to utilize coldplates with channel structure and liquid circulation for heat removal from semiconductor components. We have designed a coldplate with low heat-resistance that ensures effective cooling with only 20-30° temperature difference between coolant and electronic parts of a server. Under stress-test conditions the coolant temperature was up to 65 °C while server operation was undisturbed on the individual server level (based on Intel Grantley platform with dual Intel Xeon E5-2697 v3 processors). We also report first stress test results for the 24-node computational cluster on the same platform, when coolant liquid temperature is set to 50 °C and more.