What You Need to Know About Rack Airflow Management

Sealing the open gaps in server racks is a well-known best practice when implementing airflow management improvements in a data center. After all, sealing these gaps (both within and along the sides of cabinets) often provides the greatest return on investment of any airflow management effort, both in the ability to reduce hot spots and the ability to reduce energy consumption. However, like any other airflow management initiative, how you implement this step is crucial to effectively achieving and maximizing these benefits.

Before we jump into the specifics, one thing to point out is that the goal of all airflow management initiatives is to improve the intake air temperatures to IT equipment. More specifically, to reduce the highest intake air temperatures so that all intake temperatures are as low and even as possible (try not to get tongue-tied saying that). This, in return, enables you to make changes to the controls of the cooling infrastructure, such as increasing temperature set points or lowering fan speeds. Making these changes is the key to achieving many of the benefits of airflow management, like improved efficiency, increased capacity, and reduced operating costs. To maximize these benefits, managing the airflow at all levels in the data center is very important. Upsite Technologies' 4 R’s of Airflow Management™ methodology provides a protocol to do this. Just as a reference, the 4 R’s are: Raised Floor, Rack, Row, and Room.

Managing Airflow at the Rack Level

Managing airflow at the rack level refers to properly sealing, well, the server rack. This means sealing off every open space along the vertical plane of IT equipment intakes. There are two primary locations you need to seal in order to do this:

1. Open U spaces. Sealing open U spaces by installing blanking panels is a well-known best practice throughout the industry, however it’s surprising how many sites still have not achieved 100% blanking panel use. Remember, every U space that is not occupied by IT equipment should be sealed with blanking panels. This is particularly important in cases where full racks have not been populated with any IT equipment at all (which is surprisingly common, especially in new data center builds). For these cases, there are full rack blanking solutions available to do this efficiently. Also, make sure your blanking panels are creating a complete seal. This might sound like a no-brainer, but you’d be surprised at how many blanking panels do not seal effectively. Many leave a 1/16” to 1/8” gap between adjacent panels. Even at just a 1/16” gap between panels in a 42U cabinet filled with blanking panels there will be 45.5 in² area left open (41 spaces x 17.75” between rails x 0.0625” gap = 45.5 in2). This is equivalent to the open area of 1.5 missing blanking panels.
2. Rails to the sides of the cabinets. Also very important is sealing the open space between the rails and the sides of cabinets/racks. In some racks this space is sealed by design, however in many it is left open. When blanking panels have been installed but this space remains open, this becomes a primary location of both exhaust air recirculation to the front of the cabinet or loss of conditioned airflow that doesn’t pass through IT equipment (bypass airflow). Retrofit solutions to seal these areas are available for various rack sizes and configurations. In cabinets where this space has not been sealed there is often a 1.5” to 2” wide space the height of the cabinet. For a 42U cabinet there will be 220.5 in² area left open (42 spaces x 1.75” x 1.5” between rails and side of cabinet x 2 sides = 189 in2). This is equivalent to the open area of 6.1 missing blanking panels.

The Importance of Rack Airflow Management

Sealing the vertical plane at the face of IT equipment intakes in the rack is important for two main reasons:

1. To prevent exhaust air from the backs of cabinets flowing into the cold aisle and raising equipment intake temps. This condition often limits how high conditioned air supply temps can be raised and how much fan speeds can be reduced or cooling units turned off. These conditions limit the efficiency gains and release of stranded capacity that could otherwise be achieved.
2. To prevent the loss of conditioned air from the cold aisle. By holding the conditioned air in the cold aisle it is made available to cool IT equipment. This prevents bypass airflow through the cabinets, maximizing the IT load that can be effectively cooled or maximizing the reduction of cooling unit fans speeds to reduce operating cost.

Conclusion

As densities and the pressure to reduce operating costs increase, it becomes more and more important to improve both the effectiveness and the efficiency of the cooling infrastructure in data centers. Airflow management, and particularly sealing the open area in server racks, is an important way to support these goals and maximize the benefits.

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