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The best containment solution for an existing facility will depend on the constraints of the facility. While ducted hot aisle containment is preferred for highest efficiency, cold aisle containment tends to be easier and more cost effective for facilities with existing raised floor air distribution.

A new paper from Schneider Electric, 'Implementing Hot and Cold Air Containment in Existing Data Centers ' - written by Paul Lin, Victor Avelar and John Niemann - investigates the constraints, reviews all available containment methods and provides recommendations for determining the best containment approach.

According to the authors of the paper, containment in general provides some important benefits for an existing data centre: Reliability will be increased by preventing hot spots. Containment can prevent the mixing between hot air and cold air, which can provide a lower uniform IT inlet air temperature for IT equipment to reduce hot spots. Rack power density can be increased by eliminating hot air recirculation.

For a traditional, uncontained raised-floor data centre, they state, rack power densities are typically kept below 6kW/rack average to help prevent hot IT exhaust air from re-circulating back into the front of the IT equipment. After containing and sealing the holes to eliminate hot air recirculation paths, rack power densities can increase without the threat of hotspots. Cooling capacity will be increased by increasing the deltaT’ (ie, the difference in temperature between the cold supply air and the hot return air) across cooling units. For a traditional, uncontained raised-floor data centre, more than 50% of the cold air supplied from the cooling units will bypass back to these units directly as a result of any leakage paths that exist.

“After contained, supply air will instead go through IT equipment where it will absorb heat energy and transport it back to the cooling units,” they point out. “The higher exhaust air temperatures will lead to a bigger deltaT across cooling units, which can increase the cooling capacity about 20% or more. Cooling system energy savings will be increased by being able to shut down cooling units that become redundant as the result of effectively separating hot and cold air streams through the use of an air containment system. Additionally, economiser mode hours are increased.

“When the outdoor temperature is lower than the indoor temperature, the cooling system compressors don’t need to work to reject heat to the outdoors.”

The paper goes on to describe containment methods available today, investigates constraints and user’s preferences, provides guidelines for determining the appropriate containment approach and emphasises the importance of on-going air management maintenance.

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