Is a Liquid-Cooled Data Center in Your Future?
by: Herb Zien – CEO of LiquidCool Solutions
Most data centers in operation today defy logic. They are cooled by circulating conditioned air around the data processing room and through the racks. Separate hot and cold aisles are maintained in an attempt to conserve energy. In most installations, cold air is forced up through holes in the floor. And humidity control is necessary to avoid condensation on IT equipment if too high or electrostatic discharge if too low.
Air-cooled data centers are expensive to build and operate. Up to 15% of the total power supplied to a data center can be used to circulate air, and another 15% is used by rack and blade fans. Not only are fans inefficient, they fail. Fan cooling also limits power density, which is critical to reducing the white-space footprint as well as maintenance and infrastructure costs.
Cooling with air creates problems beyond wasting energy and space. Contact between air and electronics leads to oxidation and tin whiskers. Pollutants in the air cause additional damage. Filters clog, resulting in overheating. Fans transmit vibrations that loosen solder joints, and they generate heat that must be dissipated. Many data centers operate at excessive noise levels from the fans, and OSHA regulations require earplugs.
It gets even worse. Raising the temperature in a data center to reduce the need for mechanical refrigeration causes fans in the central air-handling system, CRAC units and device chassis to spin faster to move more air. Fan energy increases as the cube of the volume of air circulated, which means doubling the airflow requires eight times more energy.
All of these problems can be avoided through liquid-cooled data centers. It’s simple physics. Liquids cool electronics 1,000 times more effectively than air. Air is an insulator with negligible heat capacity or thermal mass. Warm air rises and cold air sinks, so if a data center has a raised floor and cold air is blown uphill, energy is unnecessarily being wasted to fight gravity.
Ironically some of the earliest computer installations were liquid cooled, but the technology available then was expensive, messy, difficult to maintain and inconvenient, and water leaks had the potential to be catastrophic. Air conditioning for employee comfort was already installed in the building, so the simplest thing to do was expand the AC system to pick up the additional cooling load of the server rooms. Rather than isolating and solving the data center cooling problem, a bandage was applied—an easy fix.
A lot has changed in the past few years. Energy waste and carbon footprints have become high-visibility issues. Rack power densities have increased, in some cases to the point where air cooling is bumping against thermodynamic limits. The bandage is becoming unstuck.
Importantly, some liquid cooling technologies available now overcome the perceptions that carried over from the old days. Liquid-cooled IT devices can be neat, easy to maintain, scalable and inexpensive. In some cases it is possible to commercially recycle much of the input energy to heat buildings or domestic hot water, cutting the carbon footprint even further.
Three technologies have emerged to cool electronic equipment with liquids: cold plates, in-row cooling and immersion in a dielectric fluid.
Cold plates, originally designed to enable gamers to overclock their machines, target the hottest or highest-power-density components in servers, namely the processors. Device fans, facility fans and other infrastructure are still required to cool other components that are not covered by cold plates. Additionally, cold plates are an ineffective way to cool switches, which lack point sources of heat. Cooling efficiency for cold-plate systems can be 50% better than air.
In-row cooling is essentially an attempt to make the room around the IT equipment smaller. This technology can reduce cooling energy by 60% compared with air, but it still requires all the elements of a complete data center air-conditioning system.
Immersive cooling means that electronics are totally immersed in a nonconducting dielectric fluid, thereby decoupling electronics from the room and eliminating fans. A closed cycle dissipates heat. Some direct-contact systems are single phase, where the dielectric fluid remains a liquid throughout the heat-dissipation cycle. Others use a two-phase system in which the fluid boils and then condenses. Cooling efficiency for an immersive system can be more than 90% better than air.
If an organization is considering liquid cooling to address capital cost, operating cost, space, reliability, noise or carbon-footprint problems, immersive-cooling systems are a logical choice. A number of technologies are commercially available, and the devil is in the details, but immersing electronics in a dielectric fluid instead of an air bath offers significant benefits:
?- The highest possible thermal efficiency
– No rack or chassis fans to fail
– No oxidation or corrosion of electrical contacts
– Reduction in the thermal fluctuations that drive solder-joint failures
– Much lower operating temperatures for the board and components
– No fretting corrosion of electrical contacts induced by structural vibration caused by chassis fans
– No exposure to electrostatic-discharge events
– No sensitivity to ambient particulate, humidity or temperature conditions
– Waste energy can be recaptured in a form convenient for recycling
In addition to the obvious space and power benefits, immersive cooling eliminates the need to purchase, install and maintain chillers, room air handlers, humidity-control systems, water-treatment equipment and air-filtration equipment.
It is curious that, considering its obvious advantages, immersive cooling is only now beginning to get market traction. The status quo has a lot of inertia, but it’s not just about power density. Steve Jobs summed it up best: “It takes a lot of hard work to make something simple, to truly understand the underlying challenges and come up with elegant solutions.” Liquid cooling, cleverly executed, can be an elegant solution to reducing data center energy waste, water usage, carbon footprint and cost.
The brass-era generation did not trade up from a horse and carriage to a horseless carriage to go 30 miles per hour; they did it to get rid of the horse! The horse used far too much energy, took far more space and polluted the environment. Fans are the horses of the digital age, and immersive cooling is the only certain way to completely eliminate fans.