Guide To Airflow Management In Data Centres
Discover more about Data Centre Airflow Management
EDP Europe is a leading provider of Airflow Management Solutions that are designed to improve the effectiveness and efficiency of data centre cooling systems. In this Guide to Airflow Management we look at what Airflow Management is, why it is important, and how it can be improved.
What is data centre airflow management?
Data centre airflow management is the process of managing the airflow paths of cold air and hot air within the data centre.
Cold air is delivered by CRAC units or air handlers; in raised floor environments via a plenum under the floor tiles. This cold air is delivered via perforated floor grilles to the racks housing the IT equipment and is used to cool the equipment. The running IT equipment generates hot exhaust air which needs to be returned back to the CRAC units so that it can be re-cooled. Efficient data centre airflow management is all about controlling these air paths and preventing, as much as possible, them from mixing, conditioned air being stranded or bypassing the active IT equipment.
Why is management of airflow an important part of data centre management?
Efficient management of airflow plays an important part in overall data centre management. Producing the cold air requires vast amounts of energy so managing airflow as efficiently as possible is critical to optimising power-hungry cooling systems to enable energy cost savings to be made. Many data centres are overcooled for a number of reasons, these include poor design, poor room layout and poor airflow management. Poor airflow management can lead to a number of issues these include bypass airflow, latent cooling, short cycling and hot spots.
- Bypass Airflow – Bypass airflow is deemed as any conditioned air that fails to pass through the IT equipment that it is supposed to be cooling. Common issues that result in bypass airflow include: misplaced floor grilles or unsealed gaps within the raised floor which allow cold air leakage, or gaps within or around the racks where cold air can mix with hot exhaust air. Reducing the amount of bypass airflow and preventing the mixing of hot and cold airflow patterns helps enable changes to be made to the CRAC units that can lead to reductions in energy costs.
- Latent Cooling – If hot exhaust air mixes with cold conditioned air on its return to the cooling units it can reduce the cooling capacity of the cooling units and can cause latent cooling. Latent cooling results in a reduction of humidity within the data centre, which in turn can affect the performance of your servers. Latent cooling can also result in cooling coil condensation, which consumes cooling capacity. The resulting moisture collects in drain pans and exits the data centre further drying out the room. If the room ends up requiring humidification it further increases costs to both power usage and water usage.
- Short Cycling – Short cycling is another form of bypass airflow that results in floor grilles failing to deliver cold air to the location intended. Short cycling, occurs where the speed of the cold air moving beneath the grille produces negative pressure which hinders the air flowing out of the tile, and in some cases, it can even lead to air being sucked back into the plenum, this is known as the Venturi effect.
- Hot Spots – Hot spots within server racks result from areas that fail to be cooled effectively. These can occur anywhere in a rack but are predominantly found in the top third of the rack. Hot spots if left uncorrected can result in poor equipment performance and in severe cases equipment failure.
This image shows hot spots caused through inadequate floor tiles. The left image shows the heat build up from traditional floor panels while the image on the right shows the cooling supplied by Triad floor grilles.
Use of environmental monitoring equipment can help identify some of these issues, which can then be eliminated by following airflow management best practices. These best practices can help improve equipment cooling and performance, as well as enabling adjustments to cooling units that result in energy cost savings.
How does data centre design play an important role in data centre cooling?
Data centre design plays a very important role in data centre cooling. Poorly designed or managed data centres often end up with the airflow management issues discussed above.
The layout of the room should be in the cold aisle / hot aisle formation, where the front of the racks containing the equipment air intakes form the cold aisle, and the rear of the racks venting hot exhaust air form the hot aisles. The cold aisles are then supplied with cold air, in raised floor environments via grilles placed only in the cold aisle. Where the racks are positioned within the room is also important, placed too close to the air handlers can result in short cycling. The height of the plenum within the data centre floor design plays a significant role in data centre cooling. A low height floor plenum often suffers from reduced cooling capacity. Obstructions in the plenum such as pipework and cabling can restrict airflow and affect how the data centre is cooled. The use of underfloor barriers can help direct air to the areas where it is required and block areas where it isn’t.
How managing data centre airflow at raised floor, rack and row level helps CRAC unit efficiency?
Managing data centre airflow efficiently so that cooling costs can be reduced whilst maximising cooling performance can only be achieved by segmenting the data centre into four main sectors. The 4R’s of airflow management splits the data centre or IT room into four segments and advises the best practices required to make each segment as efficient as possible. The 4R’s are:
- Raised Floor – At raised floor level the room should be configured in the cold aisle / hot aisle formation discussed above. Floor grilles should only be positioned in the cold aisle. Openings within the raised floor for cables or pipework to pass through should be sealed with raised floor grommets or foam sheets. Doing so ensures that the cold air only comes out of the floor where it’s suppose to through the floor grilles.
- Rack – At rack level it is vital to prevent the mixing of hot air from the rear of the racks and allowing it to migrate to the front of rack where it can affect the cold air cooling the equipment. This can happen in various places within the rack: unused rack space should be blanked off with blanking panels, gaps between or beneath racks, or between mounting angles and side panels, as well as gaps at the top and bottom should be sealed with expanding foam tape or other air barriers such as the HotLok RAM Kit or AisleLok Under Rack Panels. Where cables pass from front to back through the middle of the rack the use of brushed blanking panels allows the cables to pass through whilst sealing the rest of the opening.
- Row – At row level airflow management can be greatly improved by the addition of an aisle containment solution. Aisle containment falls into two main categories; cold aisle containment or hot aisle containment. As the names suggest, aisle containment solutions either fully or partially enclose either the cold aisle or hot aisle to further reduce the mixing of hot and cold air patterns.
- Room – The room level provides the central checking point and is where changes made to the cooling systems can be seen. These changes enable the PUE to be lowered and energy cost savings to be made.
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