NCAR Uses MeeFog System to Prevent Electrostatic Damage to its New Supercomputer

Opening in 2012, the NCAR Wyoming Supercomputing Center (NWSC) is a 170,000 square foot data center with two 12,000 square foot raised floor spaces. The site will house the IBM Yellowstone 1.6 Petaflop supercomputer in one of those modules, with the other set aside for future expansion. “We have pursued ‘right-sized’ construction in order to limit capital construction costs while ensuring that we have the needed infrastructure to meet scientific community computing needs now and for the next 20-30 years,” says NWSC Project Director Krista Laursen. “We have built infrastructure that will support computing and data archival needs for at least the next decade, and should facility expansion be necessary down the road it can be accomplished in a straightforward fashion.” In addition to the computing space, the NWSC has 6,000 square feet of data storage and archival space, a 2,500 square foot network operations center, administrative offices and a visitor center, with 100,000 square feet devoted to mechanical and electrical equipment.

NCAR chose the Wyoming site, in part, because the climate would allow it to maximize the use of outside air and minimize the use of chillers. “The high and dry climate in Wyoming is ideally suited for the ‘free cooling’ design used in the NWSC,” says Laursen. “Such a design option might not make sense in other geographic regions.” Average summer afternoon temperatures in Cheyenne only reach the lower 80s, dropping into the 50s at night. From October to April, nighttime lows drop below freezing. With such a temperature range, all the air handlers are designed to use 100% outside air economization when appropriate. Because NCAR doesn’t want to take the chance of temperature excursions on its high-end equipment, the data center also includes two evaporative towers sending chilled water to heat exchangers at the fan wall. To ensure that the inlet temperature stays at the desired 75°F, the NWSC also has one 1000 ton chiller and two 100 ton chillers to further cool the water as needed, but it is not anticipated that these will be needed more than a few hundred hours per year.
Using outside air in a dry climate, however risks electrostatic discharge damage to the equipment. In Cheyenne, the relative humidity drops below 40% on summer afternoons, outside the ASHRAE recommended operating range. The bigger issue is on the winter days. Although the relative humidity tends to stay above 50% at the outside temperatures, it plummets when heating the air up in the data center: That missing moisture needs to be added to the incoming air to prevent electrostatic damage to the equipment.