Radical energy savings method 7: Bury heat in the earth
In warmer regions, free cooling may not be practical all year long. Iowa, for example, has moderate winters but blistering summers, with air temperatures in the 90- and 100-degree range, which is unsuitable for air-side economization.
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But the ground often has steady, relatively low temperatures, once you dig down a few feet. The subsurface earth is also less affected by outdoor weather conditions such as rain or heat that can overload traditional equipment. By sending pipes into the earth, hot water carrying server-generated heat can be circulated to depths where the surrounding ground will usher the heat away by conduction.
Again, the technology is not rocket science, but geothermal cooling does require a fair amount of pipe. A successful geothermal installation also requires careful advance analysis. Because a data center generates heat continuously, pumping that heat into a single earth sink could lead to local saturation and a loss of cooling. An analysis of ground capabilities near the data center will determine how much a given area can absorb, whether heat-transfer assistance from underground aquifers will improve heat dissipation, and what, if any, environmental impacts might ensue.
Speaking of Iowa, the ACT college testing nonprofit deployed a geothermal heat sink for its Iowa City data center. Another Midwestern company, Prairie Bunkers near Hastings, Neb., is pursuing geothermal cooling for its Data Center Park facility, converting several 5,000-square-foot ammo bunkers into self-contained data centers.
Radical energy savings method 8: Move heat to the sea via pipes
Unlike geothermal heat sinks, the ocean is effectively an infinite heat sink for data center purposes. The trick is being near one, but that is more likely than you might think: Any sufficiently large body of water, such as the Great Lakes between the United States and Canada, can serve as a coolant reservoir.
The ultimate seawater cooling scenario is a data center island, which could use the ocean in the immediate area to cool the data center using sea-to-freshwater heat exchangers. The idea is so good that Google patented it back in 2007. Google’s approach falls far afield of the objectives in this article, however, since the first step is to either acquire or construct an island.
But the idea isn’t so farfetched if you’re already located reasonably close to an ocean shore, large lake, or inland waterway. Nuclear plants have used sea and lake water cooling for decades. As reported in Computer Sweden (Google’s English translation) last fall, Google took this approach for its Hamina, Finland, data center, a converted paper pulp mill. Using chilly Baltic Sea water as the sole means to cool its new mega data center, as well as to supply water for emergency fire protection, demonstrates a high degree of trust in the reliability of the approach. The pulp mill has an existing water inlet from the Baltic, with two-foot-diameter piping, reducing the project’s implementation costs.
Freshwater lakes have been used successfully to cool data centers. Cornell University’s Ithaca, N.Y., campus uses water from nearby 2.5-trillion-gallon Cayuga Lake to cool not just its data centers but the entire campus. The first-of-its-kind cooling facility, called Lake Source Cooling and built in 2000, pumps 35,000 gallons per hour, distributing water at 39 degrees Fahrenheit to campus buildings located 2.5 miles away.
Both salt- and freshwater cooling systems require one somewhat expensive component: a heat exchanger to isolate natural water from the water used to directly chill the data center. This isolation is necessary to protect both the environment and sensitive server gear, should a leak occur in the system. Beyond this one expensive component, however, sea (and lake) water cooling requires nothing more complex than ordinary water pipe.
How much money do you want to save?
The value of these techniques is that none are mutually exclusive: You can mix and match cost saving measures to meet your short-term budget and long-term objectives. You can start with the simple expedient of raising the data center temperatures, then assess the value of other techniques in light of the savings you achieve with that first step.