How To Improve Raised Floor Airflow Management

Raised Floor Airflow Management is part of a strategy that follows Data Centre best practices known as The 4Rs of Airflow Management.

Data Centres consume vast amounts of energy, with approximately 40% of the total usage dedicated to cooling. Optimising cooling systems can lead to significant energy efficiency gains. Unfortunately, many Data Centres are overcooled, often to compensate for poor layout or failure to follow best practices. Furthermore, Data Centres with a poor airflow management strategy suffer from a variety of issues including:

• Bypass Airflow – Any conditioned cold air that fails to go through IT equipment constitutes Bypass Airflow. Typical causes for this can include misplaced floor grilles, unsealed cable openings, or gaps in and around the racks. Consequently, this mismanagement results in the loss of cooling efficiency.
• Latent Cooling – This issue occurs when hot exhaust air mixes with cold cooling air on its return path to the cooling units. When this mixing happens, it reduces the cooling capacity of these units. As a result, this, can lead to a decrease in humidity levels. If humidity drops too low, additional humidification of the Data Centre may be required, incurring extra costs.
• Short Cycling – Another form of bypass airflow, short cycling occurs when air fails to be delivered via floor grilles. This typically happens when the speed of airflow beneath the floor grilles creates a negative pressure, preventing air from flowing out of the grille. In severe cases, it can even suck air back into the plenum. This phenomenon is referred to as the Venturi effect.
• Hot Spots – Hot spots especially arise in areas where hot air mixes with cold conditioned air or where there is insufficient cooling. For example, they commonly occur at the top of racks due to hot exhaust air wrapping over the top of racks. Similarly, they can occur because cold air fails to reach the area. As a result temperatures exceed their target levels, which can compromise the reliability and longevity of equipment.

The 4Rs of Data Centre Airflow Management represent a strategy that follows best practices across three distinct levels: Raised Floor, Rack, and Row. Actions taken at these three levels affect the fourth level – the Room. At the Room level, operators can optimise cooling systems by increasing cooling unit air temperature set points, reducing fan speeds, and improving relative humidity control. Consequently and in some cases, operators can switch off excess cooling units.

As a result of this optimisation, it allows energy efficiency gains to be achieved.

Operators should conduct the first stage of improving Data Centre airflow management at the Raised Floor level. At this level, they can implement several steps to enhance airflow management.

Considerations

• Firstly, it is important to layout the data hall properly. Place rows of racks in a hot-aisle-cold-aisle configuration. Position the front of the 19” cabinets to face into the cold aisle, while the rear should face into the hot aisle. Good airflow management fundamentals focus on preventing hot and cold air-streams from mixing. By configuring the racks this way, you simplify the process of improving airflow management.
• Secondly, position cold air supply grilles only in the cold aisles. Furthermore, if you place grilles in cold aisles where racks contain no equipment, you should fit them with a floor grille cover. Once you populate the racks, you can then remove the cover.

Solutions

• Using advanced airflow grilles like Triad grilles can improve air delivery. The unique hole pattern and specially designed under-grille fins of the Triad grille disrupt the air under the floor, causing it to bend outwardly through the grille. Consequently, resulting in better stratification.
• Seal any openings in the raised floor with Floor Grommets or Air Barriers. KoldLok raised floor grommets provide the leading solution for sealing cable openings in raised floors.
• Segregate the areas under the raised floor where the floor above is not in use. Doing so prevents the supply of cold air to those areas. You can achieve this by using PlenaForm Air Baffles, which attach to pedestals and create a barrier to stop air from flowing into that section.

KoldLok raised floor grommets, from Upsite Technologies, provide the leading solution for sealing cable openings in Data Centre raised floors.

Infrastructure services or connectivity cabling pass through these openings. If unmanaged, these openings create a source for cold air leakage. This air leakage can lead to bypass airflow, latent cooling, and hotspots. For example, 200 cable openings, each 12cm x 15cm, in a Data Centre raised floor are equivalent to having 10 missing floor tiles.

KoldLok offers a range of floor grommets that effectively seal openings while still allowing infrastructure and cabling to pass through. The original KoldLok grommets feature two layers of brush; the lower-level brush is slightly thicker to provide greater support to the finer top layer. The deep frame protects cables from snagging on any rough edges of the cutout. The KoldLok Integral seals new cable openings in raised floors, while KoldLok Surface can be retrofitted around existing cable openings and fits on top of the floor tile. The KoldLok Surface L and Surface XL use additional plates fitted to the Surface grommet, enabling them to be used on larger openings. The 3” Extended and 6” Extended grommets can seal larger perimeter openings. Extended grommets also allow for customisation, making them suitable for various openings in the raised floor.

For ease of installation, KoldLok offers the KoldLok Round. This features a single brush supported by a membrane beneath. Installation is quick and easy, as the 4” or 6” opening can be cut with a core drill.

Once openings are sealed, it is important to optimise cooling at the room level.

Conduct Raised Floor airflow management as part of an overall airflow management strategy that also focuses on rack airflow management and row airflow management. Only by managing airflow at all three levels can you realise full cooling optimisation at the room level. Each step complements the others. Therefore, to achieve maximum energy efficiency gains, it is important to implement improvements at each level.

Finally, to learn more about airflow management, review other Airflow & Cooling blogs or contact us to discuss your requirement for one of our airflow management solutions.