But since desperate times call for desperate measures, it seems that water cooling is getting a second look. A number of systems designers are starting to argue that air-based systems have just about reached their maximum effectiveness in an age of super-dense, highly consolidated server racks.
One firm touting the effectiveness of liquid-cooling is Panduit. The company claims that liquid designs can shave some 20 percent off of energy costs compared to air-cooled systems and can continue consolidation drives within the data center by doing away with hot-aisle/cold-aisle designs. And with new approaches like the rear door heat exchanger that can be fitted onto standard enclosures, start-up costs are coming down as well.
Enterprises with significant server infrastructure are also taking a second look at liquid. Google, which has long used a proprietary server of its own design, just patented a new machine described by some as a "server sandwich" due to its central aluminum heat sink bound by motherboards above and below. The design is similar to a standard cold plate, except that the plate would contain water or some other liquid coolant. Fans along the outside of the device would still be used to cool low-heat components like memory chips. At this point, it's hard to tell whether Google is actually planning to deploy such a device or is simply looking to claim it as a concept.
About the only area where liquid cooling has gained a foothold is in the high-performance sphere. Facilities like Switzerland's Federal Institute of Technology say they gain maximum cooling efficiency through systems like Aquasar, developed jointly with IBM. The system delivers cool water to two-thirds of its BladeCenter H and QS22 servers, with traditional air-cooling serving the rest. Not only does the system produce about 450 megaflops per watt in performance, but its higher output temperature is used to heat other university buildings during the winter.
And it seems liquid cooling is starting to encroach on the PC realm as well. A company called Asetek has devised a liquid-cooled all-in-one PC that the company says matches the price/performance of top-tier models on the market today without the annoying hum of a standard air fan. The prototype features a 130W Intel Core i7-920 processor, a 75W nVidia GTX280M graphics card and a 22-inch monitor. Heat is captured from the main enclosure and is expelled through a small radiator in the base.
Liquid cooling does have a lot to offer in terms of efficiency and effectiveness, but let's face it: Those efficiencies can only be realized after the retrofit is made. And most facilities have yet to reach the upper limits of the heat load currently available under air-cooled designs.
For the common data center then, liquid cooling may be an idea whose time is yet to come.