Hot-Aisle Containment Systems (HAC)

The Cool Shield hot aisle containment systems (HAC) channel the heat from the server exhaust directly back to the returns on the cooling units. This results in two instances of containment, both of which can significantly improve cooling efficiency. First and foremost, containing the hot exhaust air prevents it from re-circulating over the top of server cabinets to mix with the supply air. In addition, returning warmer air to the cooling units will improve the performance of those units. This double benefit generally makes hot aisle containment preferable to cold-aisle containment. However, many existing sites are not set up to take advantage of a system like this.

Depending on your circumstance, a cold aisle containment system (CAC) may be a better option. For information on CAC systems, click here: cold aisle containment

HAC Systems: How They Work

Typically, the perimeter of the hot aisle is enclosed with a vertical partition from the top of the server cabinets to the drop ceiling return. An aisle containment door is installed at both ends to facilitate access into the aisle. If there is no ceiling return, a duct system can be used to channel the exhaust air to one or more CRAC units directly. Since the hot exhaust air is removed from the room, the cooling units can be set to deliver supply air at a comfortable temperature for servers without the need to over-cool.

Returning warmer air to the CRAC/CRAH units actually increases their capacity. A 20-ton cooling unit may be able to deliver 25 or even 30-tons if the return air temperature is high enough. Besides increasing capacity, this will also improve efficiency, especially if the cooling units have variable speed fans. The increased capacity reduces wear on compressor and allows fans to operate on a more efficient spot on the energy curve.

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Hot Aisle Containment (HAC) Systems: Conditions Needed For Implementation

As effective as hot aisle containment is, it can be difficult to implement unless the site conditions are well-suited. The following conditions are ideal for this system:

  1. Unobstructed drop ceiling return plenum at least 24″ high.
  2. Top return CRAC/CRAH units with vertical extensions to drop ceiling.
  3. Variable speed fans on cooling units.
  4. Fully sealed cabinets with blanking panels, floor covers and no gaps between cabinets.

These conditions can allow for huge efficiency gains and energy savings. It is not unrealistic to reduce cooling costs by as much as 40%. If your site does not have these ideal conditions, it will not prevent you from implementing an effective containment solution. Contact one of our experienced Project Managers for a free site assessment, and to discuss our installation process.

Benefits of using a HAC System:

  • ✓ A single, redundant cooling unit can be applied to multiple aisle containments.
  • ✓ HAC with in-row cooling can improve overall efficiency versus traditional, raised-floor cooling with HAC.
  • ✓ Minimizes cold air from mixing with the hot, expelled air, returning warmer air to the CRAC, making the system more efficient.
  • ✓ HAC systems with in-row cooling are able to cool more than 30kW heat load per rack.


Hot Aisle Containment - Hot Aisle Containment