Cold Aisle Containment Systems

Cold aisle containment (CAC) isolates the cooled supply air from the CRAC units within direct proximity of the air intake of critical equipment. In addition, sealing this aisle prevents hot server exhaust air from coming in contact with the server intake. This combination effect allows for a highly controllable and consistent air temperature for critical equipment. This increased control allows the data center manager to accurately choose the temperature supplied to the servers.

ASHRAE 9.9 recommends a maximum supply air temperature of 80.6 F for mission critical applications. Most CRAC units are set to deliver 55 degree air. By the time this air reaches the cold aisle, the temperature will still only be around 60 degrees. This over-cooling is necessary to help mitigate the effect of the hot exhaust air spilling into the cold air’s aisle. By implementing a containment solution, it is possible to adjust the CRAC set points much higher. A rule of thumb is that for every 1 degree increase in set point there will be a 3-4% decrease in cooling costs. Based on that, here is an example of cost savings based on conservative results.

Annual Cooling Costs:  $350,000

10 Degree Increase in Set Point = 30% Savings

Annual Savings = $105,000

With huge savings like this, it is easy to see why containment has become a best practice in data centers. To maximize results it is important to also seal in and under the server cabinets to prevent exhaust air from getting to the server intake. Low cost items such as blanking panels and under-cabinet panels are essential accessories to ensure your containment yields the results you expect.

Choosing the Right Cold Aisle Solution

Cold aisle containment is generally easier to implement than hot aisle in retrofit sites. As long as there is either underfloor or overhead supply air, it is possible to contain the aisle. One common approach is using horizontal ceiling panels across the tops of the cabinets. Clear panels are used to allow for high light transmission. Melt away panels are commonly used to allow panels to fall prior to fire suppression release.

Another common approach is vertical panels. These panels typically extend from the top of server cabinets to the ceiling. This works very well if the ceilings are not too high and there is fire suppression in both the hot and cold aisles. If the ceilings are high, self-supported containment with partial height panels can be very effective. These panels do not go all the way to the ceiling but are high enough to prevent most re-circulation over the top of server cabinets.

Flexible strips are still used at many sites as a cost-effective solution for containment purposes. Air pressure in the aisles can cause gaps and flapping of strips which can cause air leakage. Cool Shield has many solutions to minimize separation including weights, clips and magnetic strips. Fusible links can be used with strips to allow for release prior to fire suppression activation.

 

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Before and After Cold Aisle Containment:

Before and After Cold Aisle Containment Chart

32 10kW racs with no containment VS 32 10kW racs with CAC