Water cooling for enterprise servers is slowly creeping in from the fringes to the mainstream of data center use as vendors and end users alike realize the limitations of air cooling. With increased compute density, fans just don\u2019t cut it anymore, and water cooling is far more efficient.\nSeveral vendors have adapted their cabinets to accommodate water-cooling systems, and now Lenovo is the latest to get religion on the subject with Neptune, a series of technologies for the data center. The company announced the new system at the International Supercomputing Conference (ISC) in Frankfurt, Germany.\n\nNeptune is a three-pronged approach, borrowed from the legend of the Roman god of the seas Neptune, who wields a three-pointed spear. It offers direct-to-node liquid cooling, rear door heat exchangers, and hybrid cooling that mixes air and liquid, all of which is documented in a lighthearted blog post by the company.\nAll of these are managed by Lenovo\u2019s Energy Aware Runtime (EAR) software, which optimizes systems for energy efficiency and performance from the component level to the chassis.\nLenovo has a history with water-cooled systems\nThis isn\u2019t new territory for Lenovo. Back in 2012 when it was still IBM\u2019s System x server division, it installed the first water-cooled x86 cluster at Leibniz-Rechenzentrum (LRZ), a supercomputer facility in Munich, Germany. That system helped LRZ reduce electrical consumption by up to 40 percent. Since then, Lenovo has installed over 24,000 liquid-cooled nodes at customer sites.\nLenovo is making the case that enterprises can cut their electric bills by shifting from air to much cheaper water cooling and that the initial investment isn\u2019t pricey at all. Water cooling has something of a myth that it is much more expensive than air cooling, but Lenovo says that in most cases, liquid cooling is only 2 percent more expensive than air cooling.\nOne reason is that water-cooling systems have cut out an expensive element. Earlier water-cooling systems would route hot water away from the server to a chiller, which cooled the water down considerably. The chiller, though, was the expensive part and used a lot of power.\nNow, many water cooling systems use what is called warm water cooling, meaning they simply let physics do the job of thermal dissipation rather than spending the money and power on a chiller. As the water runs through the pipes, it naturally cools \u2014 just not as much as a chiller would do. But it\u2019s still more than enough.\nThe direct to node component is what it sounds like: a heat sink attached to the CPU that brings in cool water, absorbs the heat, and routes the warm water away. The rear door heat exchanger is the second part, a big car radiator for the cabinet. It serves to cool the back of the system and thus avoids the hot air ventilation out of the back of a cabinet in the hot aisle\/cold aisle configuration. The hybrid solution is said to be coming in the near future.