Raised access flooring systems have become a staple in modern commercial and office environments across the UK, providing a versatile and adaptable infrastructure for power, data, and HVAC distribution. However, the efficient management of airflow dynamics within these raised floor plenums is crucial for ensuring optimal thermal regulation and energy efficiency.
The Importance of Airflow Dynamics
The challenge of effective airflow management in raised flooring systems is two-fold: first, ensuring that the cold “supply” air from cooling equipment reaches the IT equipment inlets without mixing with hot exhaust (“return”) air; and second, ensuring that the hot exhaust air returning to the cooling equipment intake does not mix with the cold supply air.
This task has become increasingly critical as data centres and commercial spaces incorporate high-density server racks and equipment with ever-increasing power demands. Today’s racks can require up to 60 kW of power per unit, generating ten times the heat per square foot compared to just a few years ago.
In an ideal scenario, the cold supply air would be directly ducted to the IT equipment intakes, and the hot return air would be ducted directly back to the cooling unit(s). However, in the real world, even simple measures such as clearing clutter from the airflow path and installing physical devices to direct and separate hot and cold air can significantly improve overall cooling efficiency.
Airflow Management Strategies
Three highly effective airflow management strategies commonly employed in raised flooring systems are:
- Hot Aisle/Cold Aisle Layout: Arranging server racks in alternating hot and cold aisles to create distinct air circulation patterns.
- Containment: Physically isolating the hot and cold air streams using barriers, curtains, or doors.
- In-Rack/In-Row Cooling: Placing cooling units directly within or between server racks to target high-density loads.
While these larger-scale strategies are crucial, this article will focus on the smaller devices and modifications that can optimise airflow dynamics and enhance energy efficiency in almost any raised flooring environment.
Airflow Management Devices
Blanking Panels
Blanking panels are essential for covering unused areas of server racks, ensuring that the cold supply air passes through the IT equipment rather than over or under it. By reducing bypass airflow, blanking panels can decrease server inlet air temperatures and increase the temperature of air returning to the cooling units, both of which improve operational efficiency. A single 12-inch blanking panel can reduce rack temperatures by as much as 20°F.
Structured Cabling
Proper cable management is key to maintaining optimal airflow. Tangled, unstructured cabling can constrain the exhaust airflow from rack-mounted equipment. By cutting cables and power cords to the correct length and using cable management systems, you can create more room for hot air to flow away from the back of the racks, improving overall circulation.
Floor Grommets
Air restrictors or floor grommets are an effective way to seal around cables where they enter and exit the raised floor plenum. Reducing air leaks from around cabling helps direct more cold air to the IT equipment, rather than allowing it to escape through unintended openings.
CRAC “Chimneys”
CRAC “chimneys” are simple sheet metal extensions that raise the return air intakes of computer room air conditioning (CRAC) units closer to the ceiling of the server room. This maximises the temperature of the return (exhaust) air at the cooling units, improving overall efficiency. While chimneys can sometimes impede maintenance access, the filters can be relocated to the top of the chimney or access panels can be provided in the sides.
Vented Tiles
Most raised flooring systems utilise vented (or “perforated”) tiles to deliver the cold “supply” air from the CRAC units below the floor, allowing it to rise through the vents and into the server racks. However, the placement and type of these tiles is crucial to ensuring effective airflow.
It’s not uncommon to find “hot spots” in data centres caused by inadequate cold air distribution or dense heat loads. This is often due to suboptimal airflow patterns below the floor, improper tile placement, or the wrong tile type. Determining the optimal number, type, and location of vented tiles requires technical expertise, but simple fixes like removing stray tiles in hot aisles can make a significant difference.
Visualising Airflow with CFD and Thermal Imaging
Two key technologies allow data centre and facility managers to identify and address airflow issues in raised flooring systems:
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Computational Fluid Dynamics (CFD) Modelling: CFD uses computer simulations to model a data centre’s airflow patterns, providing a detailed 3D thermal map that can inform the placement of vented tiles and other airflow management devices for optimal cooling and energy efficiency.
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Thermal Imaging: Infrared cameras can capture the temperature gradients across server racks, making it possible to identify hot and cold spots that may be caused by airflow problems. This technology can also help locate overloaded circuits and loose connections before they result in unplanned outages.
By utilising these tools, data centre and facility managers can make informed decisions about adjusting airflow management devices and cooling equipment to reduce hot and cold spots, ultimately reducing the runtime of cooling units and saving valuable energy.
Optimising Airflow for Energy Efficiency
The cumulative impact of properly managing airflow in raised flooring systems can be substantial. Adding a single 12-inch blanking panel to the middle of a server rack, for example, can yield 1-2% energy savings per rack. Sealing open spaces around cable feeds in the floor plenum can reduce energy expenses by 1-6%.
One case study from Kaiser Permanente’s ENERGY STAR certified data centre illustrates the potential savings. By using blanking panels and other airflow management strategies, the facility was able to eliminate nearly 70,000 cubic feet per minute (CFM) of bypass air, resulting in significant energy and cost savings.
Similarly, a small data centre profiled in Google’s Green Data Centers: Network POP Case Study demonstrated a return on investment in less than a year after implementing CRAC air return extensions, vented tile optimisation, cold aisle containment, and temperature/humidity adjustments.
Maintaining Optimal Airflow
Due to the complexity of airflow in raised flooring systems, the proper use of airflow management devices is not always obvious. A professional airflow assessment can help identify ways to further optimise cooling efficiency by better deploying these technologies.
Such an assessment should examine:
- The placement and type of vented tiles
- Potential air leaks around cabling and other penetrations
- Opportunities for CRAC unit location optimisation
- The effectiveness of blanking panels, cable management, and other airflow devices
By addressing these factors, facility managers can ensure that their raised flooring systems are operating at peak efficiency, delivering optimal thermal regulation and energy savings for years to come.
To learn more about optimising your raised flooring system, visit raised-flooring.co.uk or contact our team of experienced consultants.
