Sandia National Laboratories researchers designed a cooling system for supercomputer centers that is expected to save four to five million gallons of water annually in New Mexico if installed at Sandia's computing center, and hundreds of millions of gallons nationally if the method is widely adopted. It is being tested at the National Renewable Energy Laboratory (NREL), which expects to save a million gallons annually. The system, built by Johnson Controls and called the Thermosyphon Cooler Hybrid System, cools like a refrigerator without the expense and energy needs of a compressor.

The cooling system at Sandia's supercomputing center. (Photo by Randy Montoya)

Currently, many data centers use water to remove waste heat from servers. The warmed water is piped to cooling towers, where a separate stream of water is turned to mist and evaporates into the atmosphere. Like sweat evaporating from the body, the process removes heat from the piped water, which returns to chill the installation. But large-scale replenishment of the evaporated water is needed to continue the process. Thus, an increasing amount of water will be needed worldwide to evaporate heat from the growing number of data centers, which themselves are increasing in size as more users put information into the cloud.

The prototype method uses a liquid refrigerant instead of water to carry away heat. Water heated by the computing center is pumped within a closed system into proximity with another system containing refrigerant. The refrigerant absorbs heat from the water so that the cooled water can circulate to cool again. Meanwhile, the heated refrigerant vaporizes and rises in its closed system to exchange heat with the atmosphere. As heat is removed from the refrigerant, it condenses and sinks to absorb more heat, and the cycle repeats. There is no water loss, as there is in a cooling tower that relies on evaporation. Also, chemicals such as biocides are not required, and the system does not utilize a compressor, which would incur more costs. The system utilizes phase-changing refrigerant, and only requires outside air that's cool enough to absorb the heat.

In the summer in New Mexico, the state's ambient temperature is high enough that a cooling tower or some method of evaporation could be used. But more efficient computer architectures can raise the acceptable temperature for servers to operate, and make the occasional use of cooling towers even less frequent. If a data center does not need to be cooled to 45 °F, but only to 65 to 80 °F, a warmer outside temperature that is slightly cooler than the necessary temperature in the data center could be sufficient.

For indirect air cooling in a facility, better design brings the correct amount of cooling to the right location, allowing operating temperatures to be raised, and allowing the refrigerant cycle to be used more during the year.

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NASA Tech Briefs Magazine

This article first appeared in the March, 2017 issue of NASA Tech Briefs Magazine.

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