In different parts of the U.S., gray-water recycling and rainwater capture are discussed as options to minimize the millions of gallons of groundwater required to cool large data centers, but the simple answer in many climates is to use liquid refrigerant.

Sandia National Laboratories researcher David Martinez, engineering project lead for Sandia’s infrastructure computing services, is helping design and monitor a cooling system expected to save up to 5 million gallons annually if installed at Sandia’s computing center in New Mexico. The system, which cools like a refrigerator without the expense and energy needs of a compressor, is now being tested at the National Renewable Energy Laboratory, in Colorado.

Sandia National Laboratories engineer David Martinez examines the cooling system at Sandia’s supercomputing center. Image credit: 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.

“My job is to eventually put cooling towers out of business,” Martinez says.

The prototype 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 water, now cooled, 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’s no water loss like there is in a cooling tower that relies on evaporation,” Martinez says. “We also don’t have to add chemicals such as biocides, another expense. This 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 New Mexico, that would occur in spring, fall and winter, saving millions of gallons of water.

In summer, 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.