Managing Heat and Airflow within Cabinets – Blanking Panels and Recirculation

CRG-West Colocation Toolkit

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Managing Heat and Airflow within Cabinets – Blanking Panels and Recirculation

As cabinets support more and more density with each new generation of server, the requirement to provide power and cooling to racks of blade and 1U server stacks becomes more challenging.

The fundamental requirement for cooling equipment is to keep cold air flowing into the intake side of a switch or server, and then providing unrestricted exhaust of heated air. This article will describe the requirements for airflow within a server or switch environment, and present techniques used to optimize cooling.

A major factor in cabinet or rack design is the idea of “recirculation.” Recirculation occurs when exhaust from a server is recirculated into the intake of the same server or adjacent servers, eliminating much of the benefit of delivering cooling to the cabinet. Figure 1 shows a high level view of a cabinet at risk of significant exhaust recirculation.

If your cabinet is stacked from bottom to top with servers – recirculation can be a real problem. This applies to both open racks, as well as enclosed cabinets without blanking panels between servers. The dynamic of airflow, combined with the strength of suction pulling air into the intake can have the reverse effect of introducing heated air directly into the intake side of a server.

Recirculation can increase the intake temperature of a server by as much as 15 degrees (according to APC), increasing the chance of equipment failure due to overheating.

Fans on the top of cabinets appear to have little effect on relieving recirculation.

A blanking panel is a solid panel used to block recirculation of heated air within a cabinet. The panel is affixed in the blank space, on the server intake side. When a blanking panel is installed, suction on the intake side of a server will have no effect on the flow of heated air from the exhaust side of the server, eliminating recirculation of heated air. Figure 2 shows how a blanking panel will eliminate recirculation within the cabinet:

Hints for cabinet design:

Use open or meshed doors when possible for both intake and exhaust sides of cabinets
Ensure your cabinets are adjacent to each other, further eliminating the potential for recirculation outside of the cabinets
Lay your cabinets out in HOT/COLD row configurations (next article will discuss this concept in more detail)
Use blanking panels on all cabinets where your servers or switches do not fill the entire cabinet

Give us your feedback on this article by sending a note to sales@onewilshire.com You can also request additional assistance on designing your cabinets, cages, and rack layouts through CRG-West's engineering and operations group. Contact John Savageau at +1-213-327-1200 for more details.