Hot or Cold Air Containment? Examine Your Constraints to Decide

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It’s well known by now that air containment systems can eliminate hot spots and provide energy savings over traditional, uncontained data center designs. But which is best for an existing facility – hot air or cold air containment?

This question has raised a lot of discussions among manufacturers, consultants and end users. To get to the bottom of it, a trio of Schneider Electric experts looked at all sides of the question and report their results in a new white paper, “Implementing Hot and Cold Air Containment in Existing Data Centers.”

The answer, as is so often the case, is “it depends.” But in this white paper the authors detail what the answer depends on, helping you make an informed decision for your own data center.

The first step is to examine your data center for any constraints, which are obstacles that cannot be overcome, or at least not without great expense. Many such constraints will effectively make the decision for you as to whether to use hot or cold air containment, if indeed either will work.

Following we’ll look at a few examples of such constraints.

IT equipment arrangement: Having a hot aisle/cold aisle arrangement is pretty much a prerequisite for a containment solution (as is proper aisle width). But this is a well-known data center best practice that you will want to eventually tackle anyway, so this is one constraint that is worth fixing if it applies to you.

Ceiling height: If you don’t have enough ceiling height above your racks, you won’t be able to install a drop ceiling for use as an air return plenum, which is a requirement for some types of hot aisle containment solutions.

Raised floor depth: On the other hand, if the plenum depth underneath your raised floor is too small, you may not be able to adopt a cold aisle containment solution because the plenum is used to deliver cool air to your racks. Similarly, cabling, conduit, and piping located under the raised floor may cause resistance to cold air flow, limiting the effectiveness of a cold aisle containment solution.

Column location: A support column is often located within a row of racks or aligning with a rack aisle in a data center, either of which may cause interference between the columns and aisle containment panels.

Cabling: Overhead cabling can interfere with ducted containment panels, which may eliminate ducted hot aisle containment or ducted racks as possible options. If cabling is routed across the aisle in a single location, the ducted solutions may still be possible.

Air distribution type: It’s normally difficult to change the type of air distribution in an existing data center, and that’s a critical factor in determining the level of investment and complexity involved in deploying a particular containment method. For example, hot air containment is well-suited for data centers with targeted return and flooded supply, while cold air containment makes more sense for data centers with targeted supply and flooded return.

Lighting considerations: Creating a containment space in an existing data center can lead to poor lighting inside of the space. Although some containment solutions use transparent or translucent ceiling panels to let existing light in, it will reduce the amount of light, especially if the panels get dirty.

Fire detection and suppression: Once you put in a containment system, you’ll have high volumes of air flowing to your IT equipment and back to your cooling units. These airflow patterns can dilute smoke, which is not a good thing from a fire detection and suppression perspective.

Working conditions: If you go with cold air containment, the rest of the room effectively becomes a large hot-air return plenum, with the same temperature as the hot aisle. That may be a problem if you’ve got IT personnel who work in the data center, or if you’ve got IT equipment located at the perimeter of the data center, outside the contained aisles.

Examining all of your constraints is just one step in choosing the best containment system for your data center. To learn more, read white paper no. 153, “Implementing Hot and Cold Air Containment in Existing Data Centers.”

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