Hot Aisle vs Cold Aisle

There are a number of arguments for and against each of the two traditional approaches to aisle containment systems. There are benefits of the hot aisle system i.e. improved performance and a more comfortable general room working temperatures compared to a cold aisle system. The reality is that each system is aligned to support a particular cooling technology. Hot Aisle Containment is specific to aisle based In Row cooling and the Cold Aisle Corridor configuration is ideal for perimeter cooling when combined with raised access floors.

Room Characteristic Hot Aisle Return Plenum (HARP) Cold Aisle Corridor (CAC) Hot Aisle Containment (HAC)
Raised Access Floor Required Required Will work with or without floor
General Room Temperature Cold Warm Cold
Room Neutral Yes No Yes
Ceiling Plenum Required This will work with or with a ceiling plenum This will work with or with a ceiling plenum
Reduced Dehumidification Yes Yes Yes
Even Inlet Temperatures Yes Yes Yes
Improved Delta T Yes Yes Yes
Will work with none racked equipment Yes No (unless seperate screening) Yes
Ability to Scale to High Density Yes Up to 7.5Kw without at fan units Yes
Supports Multiple Cooling Technologies Yes No No

Many medium and large Data Centres have downflow perimeter cooling which is ideally suited to cold aisle corridor configuration. However the implementation of Cold Aisle Corridor /Cold Aisle Containment based systems can make it difficult to introduce high density cooling technologies such as APC’s, HACs, rear rack cooling or fresh air cooling systems without complicated screening arrangements.

The use of Hot Aisle Return Plenum based systems overcome the flexibility issues of hot and cold aisle solutions by:

  • Support for multiple cooling technologies and airflow arrangements.
  • Allows the deployment of self contained HAC’s systems to reside alongside traditional downflow perimeter cooling.
  • Simple to retrofit into existing DC’s with return air ceiling plenums.
  • HARP provides a comfortable working temperature for general room access.
  • Increased system cooling capacity through increased Delta temperature and inlet temperature control.
  • Flexibility to positional additional floor grille tiles anywhere out side of the hot aisle.

Traditional Inlet Temperature vs Aisle Contained Inlet Temperature

Download – Data Centre Airflow Containment Strategies Technology Paper