Gaining Data Center Efficiency Through Containment - Part 2

July 15, 2015 / by Dave Meadows

In our last post, we talked about the TC 9.9 thermal guidelines for data processing equipment and how they are providing an opportunity to use new, highly energy efficient technologies. In this post we will examine how we can achieve higher return air temperatures in your data center.

The enemy of high return air temperature is air mixing. So how do we prevent air mixing? There are several strategies that we will review but first, let’s talk a little bit about containment. At STULZ, we are staunch proponents of containment because we recognize that this allows our equipment to operate in its most efficient manner.

The first type of containment we will look at utilizes a raised floor with containment.  (Keep in mind that all the solutions shown below can be used with both indoor perimeter cooling solutions as well as outdoor mounted solutions like the Indirect Evaporative Cooling solution: STULZ IeCE.  


In raised floor containment systems, we have two options, hot aisle containment or cold aisle containment. In hot aisle containment, we’re basically capturing the hot air that is being discharged off of the servers into a central area, where it can be ducted to the return plenum back to the cooling equipment. What this does is separate the cold air stream from the hot air stream, allowing us to achieve those high return air temperatures we were discussing in Part 1.

In cold aisle containment, we’re still basically doing the same thing, except this time our goal is to confine the cold supply air. Our goal is still to separate the cold and hot air streams but what we’re doing differently is that we’re capturing the cold aisle and allowing the room itself to be the hot aisle.


What are the advantages? As far as a CRAC/CRAH unit goes, it doesn’t care as long as it gets the higher return air temperature but what about the facility itself? With hot aisle containment, there are some minor advantages in the facility. IT Managers and their personnel are able to do much of their work in the more comfortable cold aisle environment. There is also much more thermal mass available in the “cooled room”, giving us a little longer ride through time should the data center experience a loss of cooling casualty.    

Now let’s examine a data center that has a slab floor instead of a raised floor. In this situation, we can also utilize hot aisle containment. In our indoor mounted CRAC/CRAH, we are utilizing chimney style racks that separate the cold air stream from the hot air stream. By doing this, we effectively duct the hot air directly back into the cooling equipment, reaping all the benefits of air stream separation.


Using cold aisle containment on a slab floor is just as effective. In this particular case, we’ve provided a plenum to direct the air to the enclosed cold aisle and we’ve used the data center space as the hot return. If we used this strategy with our outdoor mounted IeCE unit, these air streams would be ducted into the space from the IeCE unit.


Using best practices in establishing rack hygiene is important to realizing all the benefits of containment. Installing blank off plates, door sweeps, and plugging holes around cables with grommets will all help in limiting air mixing.  

All the strategies discussed here are effective and will provide the benefit of increased efficiency, lower PUEs, reduced capital investment, and reduced operating costs.  In addition, all the solutions shown can be used with both indoor perimeter cooling solutions as well as outdoor mounted solutions, such as STULZ IeCE: Indirect Evaporative Cooling Equipment.  

Indirect Evaporative Cooling Solutions    Perimeter Cooling Solutions

Do you use containment in your data center? Tell us how it’s worked for you in the comments below. 

Topics: Data Center Design, Energy Efficiency

Dave Meadows

Written by Dave Meadows

Dave Meadows is the Director of Industry, Standards and Technology at STULZ USA. He has a BS in Mechanical Engineering from the University of Maryland, Baltimore County, and is an active participant on ASHRAE committees.

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