The Ashburn Corporate Campus ACC7 data center will use an evaporative chilled water plant with plate and frame heat exchangers for water side economization and centrifugal chillers to assist during the summer months. Bob Rosenberger, vice president of data center mechanical operations at Dupont Fabros, calls the chillers "among the most efficient ... on the planet."
The plant will produce 70° F chilled water to cool the data center. The temperature of the chilled supply water marks a sharp departure from conventional chillers that historically cool water to 45° F, Rosenberger notes. Once the water absorbs the heat from the equipment in the data center, it will reach a temperature of 95° F in the return flow. Normally, return water temperatures have been around 55 to 65 degrees.
The higher design temperatures of the supply and return water, made possible by ASHRAE's revised temperature guidance for data centers, will let ACC7 use "free cooling" 70 percent of the year. That's because wet-bulb temperatures in Virginia are low enough for 70 percent of the hours in a year to let the cooling towers and the heat exchangers produce 70° F chilled water.
"It's a radically different design, and it's all about efficiency," Rosenberger say.
Syracuse's Green Data Center, meanwhile, pursues a different take on chillers, using waste heat from its onsite power generation capability, natural gas-fired microturbines. The 585° F turbine exhaust is routed to absorption chillers. The exhaust re-concentrates a lithium bromide solution and releases water vapor, which is re-condensed in a cooling tower, according to Syracuse.
A stream of cooled water — which is kept above the dew point, typically 60° F -—is directed to the data center, where it's piped to heat exchangers located in the server racks. The Coolcentric rear door heat exchanger model SU uses has a cooling capacity of 18 to 24 kilowatts, while the prototype sidecar model is rated at 30 kW. The Green Data Center uses 56 rear door and 5 sidecar heat exchangers, Sedore notes.
Sedore says the cooling process means the data center doesn't rely strictly on moving air around with computer room air handlers. He notes that air handlers are still used for humidity control and comfort control for people working in the data center.
Syracuse partnered on its Green Data Center with IBM and the New York State Energy Research and Development Authority.
Efficient Data Centre Cooling Means Multiple Methodologies
Companies working toward more efficient cooling employ multiple methods. At REI, for example, the evaporative cooling system is the most visible physical attribute of the company's cooling approach, but it works in combination with more prosaic efficiency measures.
For one, REI replaced belt-driven fans with more efficient Electrically Commutated (EC) plug fans to circulate the air in its data center, Stachowiak says. The belt-driven fans are typical of air conditioning systems used in data centers. At REI, the EC plug fans were placed below the raised floor to move cool air to the data center equipment, he says.
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