Cable Management Vs Aisle Containment

Isn’t it typical? You think you’ve solved one problem only to find that, in doing so, you’ve created another one!

Trying to optimise aisle containment for cooling alongside cable management is a great example; cooling and cable management each have their own, contrasting needs.  While aisle containment needs an airtight environment to keep the cold air where it is needed, cable management needs gaps to be left for cable entry paths.

This is a common problem and does mean making a few compromises with your aisle containment in order to route cables without affecting the airflow efficiency through a rack.

Keeping IT Equipment at Optimal Temperatures

Ensuring that IT equipment is kept within its optimal temperature range is a constant challenge, so choosing the best solution for your data centre requires careful consideration.

In a traditional data centre, built-in cooling systems will lower the air temperature across the entire space.  But this type of scheme doesn’t direct the cool airflow across the IT racks, and the cooled air will mix with the hot exhausted air.  So, as a system, it’s not very efficient.

To combat this, racks can be arranged into hot and cold areas. The front of the racks then draw in cool air, before exhausting the warmed air through the rear of the cabinets into the hot aisle. This type of containment helps create separate cool and hot air zones, which means they don’t mix.  It also means that air is returned to the cooling units at a higher temperature, which in turn, makes the data centre more energy efficient.

Cold Aisle Containment

Cold aisle containment (CAC) confines the cold supply air within the aisle so the only route it can take is through the IT equipment;  it can’t escape above or below the server cabinets.

CAC can be created by installing roof panels and sliding doors at each end of the rows over a raised floor. Computer Room Air Conditioning (CRAC) units, positioned at either end, then fill the plenum (space) below a raised floor with cold air.  The cold air is then directed up through perforated floor tiles in front of the racks and pulled across, rather than around the side of, their internal electrical components.

Alternatively, CAC systems can work equally well with inline cooling units, which are placed within the rows of racks.

A CAC system is easily retrofitted and can accommodate existing fire suppression systems with the use of drop-down roof panels.  It can also be installed below existing cable trays and other cable management systems.

Hot Aisle Containment

Hot aisle containment (HAC), by contrast, focuses on isolating hot exhaust air on its return to the CRAC units, while cold air is typically generated by inline cooling units.  It works on the same principle as CAC by separating the hot and cold air paths, although it has its downsides. 

Retrofitting these systems in legacy sites can be challenging because the hot air must be routed back to the CRAC units through a hot air plenum (i.e. in the raised ceiling void), which may not be feasible. 

Furthermore, because the hot air is being confined, engineers working in the back of the racks may be subjected to extremely hot conditions.

Cable Management

The effectiveness of aisle containment can easily be compromised if the hot and cold air zones are not fully sealed.  Small gaps, perhaps above a rack or cable entry points, can easily be missed, and these can lead to serious leaks, meaning the cooled air can then mix with the hot air.

So, as well as the aisle containment, it is important to effectively manage the airflow.  Air baffle kits can be fitted at the front of cabinets to force the cooled air through the servers. Ideally, these should include brush strips to allow cables to pass from the front to the rear of the cabinets, while not compromising the airflow.  If there are any spaces between the installed equipment, these should be blocked by blanking panels for maximum cooling efficiency.

Cable management accessories such as cable trays and cable management rings can be installed inside the cabinets to help route the structured cabling to the outside, either from above or below the rack.

It’s also important for both hot and cold aisle systems, that they are modular and easily integrated with existing cable management solutions such as high-level basket and ladder work to support the structured cabling above. You can use overhead containment fixed to the top of a cabinet to support cable management at high-level but, if you do, you will need to consider how much loading your cabinets can support.  This loading includes the installed equipment, the roof panels, and the containment structure itself.

Challenges Associated With Increasing Rack Size

Bear in mind, of course, that any increase in the size of your racks to accommodate more servers will mean finding room for more cables. You will need to fasten the cables neatly and securely to the cable trays inside the enclosure – so your system’s specification must ensure there will still be sufficient room for the hot air from the servers to freely leave the cabinet.  If not, the lack of airflow can lead to overheating and ultimately equipment failure.

Replacing your existing enclosures with deeper cabinets may enable you to accommodate more cables or, alternatively, you might add extension frames to be bayed at the front or rear of the existing cabinet to increase their size.  These extension frames typically come in sizes of 200 mm in-depth. They accommodate deeper equipment and give you an effective retrofitted solution without having to swap-out the original cabinet. 

Typically, where third-party racks are installed within a row, cabinets are simply added as the number of racks increases.  The cabinets can vary in size, creating a 'skyline' effect.  This creates challenges for containment systems, but they can be easily addressed through the use of freestanding containment.

Freestanding CAC can offer a flexible solution, making it easy for you to regularly remove, or replace cabinets.  The system includes all the components needed to construct a self-supported structure to capture the airflow in the contained aisle, while accommodating a mix of cabinet sizes and allowing IT racks to be changed when required.


The ever-increasing demand for more space to mount IT equipment continues to grow. Although this growing trend often allows for better space utilization, it doesn't come without its challenges.

Ensuring the effectiveness and efficiency of your data centre requires a rigorous and detailed approach to cabinet layouts, cable and airflow management.

To find out more, please contact Rittal today.

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