New supercomputer cooling method could save water

US scientists have developed a prototype cooling system for supercomputer data centres which they claim could save hundreds of millions of gallons of water if widely adopted.

The system, developed by researchers at Sandia National Laboratories in the US, called the Thermosyphon Cooler Hybrid System cools like a refrigerator without the expense and energy needs of a compressor. The prototype method uses a liquid refrigerant instead of water to carry away heat. The water heated by the computing centre is pumped within a closed system into proximity with another system containing refrigerant.

The refrigerant absorbs heat from the water so that the water, now cooled, can circulate to cool again. Meanwhile the heated refrigerant vaporises 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.

Currently, many data centres 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. An increasing amount of water will be needed worldwide to evaporate heat from the growing number of data centres, which themselves are increasing in size as more users put information into the cloud.

"There is no water loss like there is in a cooling tower that relies on evaporation," said David J Martinez, researcher at Sandia National Laboratories. "We also do not have to add chemicals such as biocides, another expense. This system does not utilise a compressor, which would incur more costs. The system utilises phase-changing refrigerant and only requires outside air that's cool enough to absorb the heat."

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. "We arranged for air to flow more smoothly instead of ignoring whorls as it cycled in open spaces. We did that by working with supercomputer architects and manufacturers of cooling units so they designed more efficient air-flow arrangements," Martinez said. "We installed fans sensitive to room temperature, so they slow down as the room cools from decreased computer usage and go faster as computer demand increases. This results in a more efficient and economical way to circulate air in a data centre."

"Improving efficiencies inside a system raises efficiencies in the overall system. That saves still more water by allowing more use of the water-saving refrigerant system," he added.