Tips to Improve PUE through Cable Management

It’s important for your data center to perform at optimum levels and to avoid downtime, and there are plenty of ways to improve its PUE. One way is through proper cable management:

Cable management can have a significant impact on a data center’s PUE. If cables are improperly placed and block airflow, your cooling units are forced to work harder (albeit inefficiently), which negatively impacts your PUE. How you manage your cables is an important part of your overall airflow management strategy, but one easily overlooked as the two are not often associated with each other.

Cable openings become a problem if anything more than cables pass through them. Poor management of raised floor openings accounts for nearly half of conditioned air in data centers escaping through unsealed cable openings and misplaced perforated tiles. When a data center has common openings like these, it obviously requires running more fans to provide vital conditioned air to the heat load. This state of cooling inefficiency is a prime example of bypass airflow, which is any conditioned air supplied by a cooling unit that does not pass through (bypasses) IT equipment before returning to a cooling unit. Cable openings in a raised floor and excessive volumes of cold air delivered in to a cold aisle are two principal sources of bypass airflow. So cable openings, as well as those areas noted below, are obvious locations where cable management intersects airflow management (AFM).

Let’s examine a few common trouble areas and some best practices to help deal with them.

Cable Management in the Raised-Floor

Cables under the floor create obstructions that affect the airflow volume and static pressure under the floor, and cable obstructions create friction. If the cooling unit fans cannot overcome the friction, then the static pressure of the raised floor drops. Therefore, they affect the amount of air that exits through perforated tiles on the far side of obstructions, and ultimately how much IT equipment can effectively be cooled.

Do place cable trays under cabinets or hot aisles. This allows the raised floor space under the perforated tiles in the cold aisle to remain free.
Do place cable management trays as high as possible, allowing air to flow underneath them. This is particularly important when running cable trays close to or in front of cooling units where most of the airflow movement is close to the floor. If done incorrectly, the distance the conditioned air can travel will be impacted.
Do place cable trays at a consistent height as much as possible. This allows conditioned air to flow in a straight path.
Don’t place cable management trays under the cold aisle. They may end up under perforated tiles.
Cable Management in the Rack

With increasing densities comes an increase in the individual component count (i.e. the number of components in the cabinet), which increases the number of power and data cords. The more cords you have, the more likely you are to block the airflow or exhaust from IT equipment.

Do use wider cabinets with cable management built into the side and not right behind the exhaust ports.
Do use deeper cabinets that allow the air more room to escape vertically.
Do use blanking panels. When cables increase the pressure within the cabinet, blanking panels become especially important.
Don’t block the exhaust from servers, particularly ones with high volume and velocity fans.

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