Data servers take a mineral bath to stay cool

Data servers take a mineral bath to stay cool

Here's an idea for saving energy: Stick all the servers in a server farm in a bath tub of liquid coolant.

That is exactly what the four-year-old company Green Revolution Cooling does to reduce cooling energy use by 90 to 95% while also cutting server power by 10 to 20%. The coolant is basically a special grade of nonconductive white mineral oil. The mineral oil has 1,200x more heat capacity by volume than air. That means servers placed vertically in tanks of the mineral oil can be cooled by convection as the oil circulates through the system. The oil is then cooled by a variety of means, such as an evaporative cooler or a radiator.

The scheme is more energy efficient than air cooling because it works at lower differential temperature. Mineral oil at 40°C (104°F) cools about as well as air at around 24°C (75°F). Of course, significantly less energy goes into maintaining a coolant temperature of 40°C than at 24°C.

The servers themselves also dissipate less energy because they don't need cooling fans. In fact, servers setup for air cooling can be reconfigured for submersion cooling in about 20 minutes, says GRC CEO and Technical Founder Christiaan Best. The reconfiguration process usually involves removing the fans and replacing a thermal interfacing compound on a couple power components. The compound is generally aluminum oxide slurry and petroleum. Left submerged in mineral oil, the petroleum would eventually dissipate. So it gets replaced with an indium foil. Any hard drives also must be sealed using a technique proprietary to GRC.

It doesn't make sense to go through this process for perhaps 40 servers or less, says Best. But the bigger the server farm, the better the economics. "Our technique is much cheaper than the ordinary approach once you hit 500 to 1,000 servers. The traditional data center takes a year to build, involves CFD analysis for the air conditioning, chillers, water towers, and lots of redundancy. Our equipment comes in a box that can be installed in a couple days," Best says.

Servers sitting in mineral oil bath tubs also take up less floor space than air cooled versions, Best says. "You don't need air space around the rack so you can run them back-to-back. A lot of people run double or four times the power density compared to the air cooled versions. When that is the case, the number of servers per square foot goes up," he explains.

The net power savings per server is on the order of $170 per year for this scheme, Best says. Efficiency wise, it looks impressive. Best says its Coefficient of Performance (COP) is high, somewhere between 30 and 50. For comparison, a typical heat pump for a residential air conditioning system might have a COP of about 3.5. The COP of the typical data center cooling system is only around one or two, Best says. "If you bought the cheapest window air conditioning unit you could find and cooled a data center with truck load of them, it would still be more efficient than what they do now," he says.

GRC doesn't release sales figures but says its system is installed in six countries and on three continents.

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