Exploring Perimeter Cooling

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Exploring Perimeter Cooling
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• Computer room air conditioning (CRAC) has been
  the subject of extensive research conducted to
  get optimum cooling within a datacenter.
• The complexity and intensity of processing has
  increased in the recent years, and this has put a
  tremendous strain on the equipment. This
  increases the importance of cooling techniques in
  the datacenter.
• Currently, the best practice used for cooling the
  datacenter is the hot aisle-cold aisle rack
  containment.

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• In a hot aisle/cold aisle arrangement, the racks
  are arranged in a series of rows. Every cold
  aisle consists of perforated raised floor tiles.
  The server should be mounted on the racks such
  that the front faces the cold and the back is
  towards the hot air.
• The cold air enters the front of the servers and
  is heated as it passes through the servers. The
  hot exhaust air is directed to the cooling units.
  
• CRAC units placed around the perimeter of the
  room or at the end of hot aisle to push the cold
  air under the raised floor through the cold
  aisle.

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• The entire concept behind using various
  techniques to cool the data center is to prevent
  the heated IT exhaust from mixing with the cold
  air.
• The hot aisle and cold aisle containment is a
  step above the perimeter cooling method. The
  perimeter cooling method distributes cold air
  under the raised floor tile with no form of
  containment.
• Here large air conditioners work in parallel
  pushing in the cold air and drawing out the hot
  air.
• In such a situation, there is a chance of hot air
  and cold air mixing to get bring the temperature
  of the room to an average temperature. This
  prevents the formation of hot spots.

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• On the flipside, this method of cooling is
  effective only if the power needed to maintain
  the temperature in the datacenter is not more
  than 2 kW/rack.
• Thats why this traditional method of cooling is
  applicable only for a small premise. When it
  comes to larger datacenters, it becomes even more
  vital to maintain lower temperatures to avoid
  damage to the equipment.
• In such huge setups, the power density of racks
  goes up to 20kW per rack or more. For such heavy
  equipment, a traditional method of perimeter
  cooling is not effective anymore.

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• To combat such issues, there are now alternative
  cooling technologies such as Row- and Rack-based
  cooling.
• They work with the concept that the closer the
  cooling source is to the equipment, the lesser
  there is loss of energy, and the more effective
  is the cooling.
• These new approaches of cooling use the same
  principle as the air conditioner, when it comes
  to cooling.
• However, each of these new approaches use a
  different method of distributing air flow to
  minimise heating and maintaining efficiency of
  the cooling system.

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• Row-based cooling provides cooling to each row of
  the equipment placed in the room. Instead of
  cooling the entire room, this approach directs
  the cool air only where the cooling is needed.
  This makes the air flow more predictable as it
  reduces the load on the CRAC unit, thus
  increasing its efficiency. This can prove to be a
  major benefit as it provides scope for better
  design when deploying high density loads.
• Rack-based cooling is more molecular approach of
  cooling the equipment. It brings the cooling down
  to the rack level. The source of cooling is as
  close to the equipment as it can be. This makes
  for more predictable air flow because the paths
  are more clearly defined. This also promotes
  better utilisation of the CRAC unit used for
  cooling the equipment. Rack-based cooling is
  recommended for server racks consisting of high
  density racks. The only problem with this
  approach is that it needs a lot of cooling
  equipment based on the servers used in the room.

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• However, recent studies have shown that a
  combination of perimeter cooling and the newer
  technologies proves to be an even more effective
  method of cooling, economy-wise and
  efficiency-wise. This combined approach is called
  Hybrid Cooling.
• In this approach, it is possible to combine
  perimeter cooling with rack- and row-based
  cooling approaches.
• While the perimeter cooling ensures optimum
  cooling for the equipment at low density and the
  rack and row based cooling approaches ensure
  cooling for the high-density load.
• This makes it easy to high-density racks, and the
  rack cooling approach tend to isolate the racks
  from the room cooling system making them neutral.
  
• Perimeter cooling has a traditional approach of
  cooling the room but when it is combined with the
  modern approaches, it yields better results than
  only using the approaches singly.