Cold Aisle Containment versus Hot Aisle Containment

In the constant pursuit for the energy efficiency, cost savings and reduction of the carbon footprint, it can be difficult to decide on the product most suitable to your needs. A common dilemma facing modern Data Centres is how best to combat the ever-present problem of DC cooling. The two most widely recognised and effective solutions to this problem come in the form of Cold Aisle Containment Systems (CACS), and Hot Aisle Containment Systems (HACS) – but the question is: which one is right for you?
Here at Cross-Guard, we’re committed to making sure every customer has the product that will perform best for them, so we’ve compiled a basic, yet comprehensive rundown of the strengths and weaknesses of both CACS and HACS so that you might see which of these two best fits your business.

Cold Aisle Containment (CACS)


  • Improves energy efficiency up to 30% relative to no CACS
  • Functions best in raised floor environments with raised floors and room-level cooling with flooded return, not requiring the special return ductwork a HACS would need in this situation
  • Easier to retrofit than HACS, reducing cost and difficulty of adding system to pre-existing infrastructures
  • Ability to direct contained cold air to specific equipment based on the power being consumed through adjustment of floor vents manually or through automated, motorised vented tiles, giving greater overall control to data centre managers


  • High temperature for staff working within data hall, outside containment unit due to purged hot air
  • High temperature for perimeter IT equipment, which must be evaluated for suitability, due to risk of overheating, for reason above
  • Room acts as the Hot Aisle, contradicting the general perception that data centres should be cold, meaning that the customer’s expectations need to be adjusted on first viewing

Hot Aisle Containment (HACS)


  • Ability to set working temperature to 24°C. The cooling set points can be set higher whilst maintaining a desirable work environment temperature promoting a positive perception upon walking into a data centre
  • In-Row Cooling is Closed Couple Cooling – short air paths and low air pressure resistance – uses a lower power consumption by fans
  • Higher ride through during cooling failure – significantly larger cold aisle air volume – decreasing risk of damage to the stored data
  • Methodology allows for channelling of hottest air directly into coolers for most efficient cooling speed
  • More free cooling days available with HACS leading to significant saving in electrical cost


  • Inside of data containment is the Hot Aisle, creating a high temperature for staff working inside the containment
  • HACS improves energy efficiency compared to no HACS; however, it can add cooling (and a power) load because of larger fans to overcome additional pressure drop
  • Cold air distribution is open and exposed to surrounding disturbances


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