Cold / Hot Aisle Containment Solutions


Cold Aisle Containment

The Cold Aisle Containment (CAC) approach encloses the cold aisle with ceiling panels above the aisle between adjoining racks and with doors at the end of the aisle. This allows the cold air from the perforated floor tiles in front of the cabinets to be contained and delivered to the server equipment air inlets. The CAC prevents cold air from mixing with warm air or being obstructed by surrounding equipment/sources before it reaches the servers. Because CAC possesses this ability, it is called focused cooling.

  • Provides focused cooling at the rack
  • Can cool higher heat loads typically up to 10-15kW (raised floor)
  • Minimizes cold and hot air mixing so the return temperature to the cooling unit is higher
  • Cold aisle containment combined with Inrow cooling can cool more than 30kW heat load per rack

Hot Aisle Containment

In its simplest form, Hot Aisle Containment (HAC) consists of a barrier that guides hot aisle exhaust airflow upward back to the CRAC (computer room air conditioner) return. This method keeps hot exhaust air emitted from server racks separated. Keep in mind though, while HAC improves energy efficiency compared to no HAC; it can add cooling (and power) load because of larger fans to overcome additional pressure drops.

  • One redundant cooling unit can serve several aisle containments.
  • HAC with Inrow cooling improves energy efficiency compared to traditional raised floor cooling with HAC.
  • Typically a rack hat style containment with end row doors.
  • Minimizes cold and hot air mixing so the return temperature to the CRAC is higher.
  • HAC with Inrow cooling can cool more than 30kW heat load per rack.

According to a study done by Intel and some of their partners, the point of it all is this:

One thing to keep in mind, the goal of both hot and cold aisle containment is the same: to improve IT equipment intake air temperatures and create an environment where changes can be made to reduce operating cost and increase cooling capacity.

However, that doesn’t really answer the question. Which leads us to the nitty-gritty.

Cold aisle containment is comprised of doors on the ends of the cold aisles as well as some type of roof or partition over the cold aisle.

Hot aisle containment has those same doors on the ends of the hot aisle and some type of ductwork from the hot aisle to the AC return vents.

For the purpose of discussion, let’s assume that our made-up data center is built so that either hot aisle or cold aisle containment is an option. In this instance hot aisle could be the better option because of efficiency and something called ride-through advantages.

But since our made-up data center is perfect, it might not be the best for all. Because of this we need to know the difference between hot and cold aisle containments.

Let’s take a look at the pros and cons of each (detailed more at Upsite Technologies) before we make our decision:

Pros of Cold Aisle Containment:
  • Much easier to implement as it does not require additional build to contain exhaust air and return it to the AC units
  • Only requires doors at the ends and a partition or roof at the top
  • Usually less expensive
  • Easier to retrofit into an older data center
  • Enables more surface area for “cold sinks” in the event of a power & generator failure
Cons of Cold Aisle Containment:
  • The overall data center becomes the hot aisle which makes the space extremely hot, which could result in higher extreme exhaust temperatures.
  • Increases mixing of return air which lowers the delta T
  • Conditioned air could leak from the raised floor and openings under the equipment which reduces the efficiency of the system as a whole.
  • Could obstruct fire detection for the overall data center space
Pros of Hot Aisle Containment:
  • The open area of the room is a cold environment
  • Leakage from the conditioned air goes into the cold space
  • Generally more effective at cooling
  • Can perform well in most data center environments
  • Standard fire detection systems can still be used
Cons of Hot Aisle Containment:
  • Generally more expensive
  • Requires a contained path (the ductwork mentioned earlier) to get air back to the AC units
  • Higher temperatures in the hot aisle can create uncomfortable temperatures for IT technicians.

Based on the lists above, one could conclude that a Hot Aisle containment would be much more beneficial. And they would be correct. Just like in our made-up “perfect” data center, most data centers would benefit from hot aisle containment.

However, not all data centers are the same and considerations must be taken to ensure you’re making the correct choice. Cold aisle containment very well could be better for your particular data center based on some of the pros-parameters listed above. So just make sure you know what kind of data center you’re dealing with before making the decision, but do also keep in mind that even though hot aisle has more upfront cost, it’s a much more efficient system—which is better for the long run, of course.