Implementing Hot and Cold Air Containment in Existing Data Centers


Containment solutions can eliminate hot spots and provide energy savings over traditional uncontained
data center designs. 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. This paper investigates the constraints, reviews all available containment methods, and provides recommendations for determining the best containment approach.


Data center containment strategies can greatly improve the predictability and efficiency of traditional data center cooling systems. In fact, The Green Grid views an air management strategy as “the starting point when implementing a data center energy savings program”1. However, most existing data centers are constrained to certain types of containment strategies. Note that this paper is for existing data centers. For information on containment for new data centers, see White Paper 135, Impact of Hot and Cold Aisle Containment on Data Center Temperature and Efficiency.
Containment, in general, provides some important benefits for an existing data center:
  • 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 center, 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” (i.e. the difference in temperature between the cold supply air and the hot return air) across cooling units. For a traditional, uncontained raised-floor data center, 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. 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, economizer 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. 

This paper describes containment methods available today, investigates constraints and user’s preferences, provides guidelines for determining the appropriate containment approach, and emphasizes the importance of...