Submittal

WW-CPWP-09, Rev.0, 09/2009

Deploying a Vertical Exhaust System

to Achieve Energy Efficiency and Support Sustainability Goals

To realize the full potential of a Vertical Exhaust System and for effective separation of cabinet exhaust air from

the room ambient air, use blanking panels in empty cabinet spaces and properly seal all cable pass-through

openings. These best practices eliminate the bypass of cold air, recirculation of hot exhaust air, and unwanted

airflow leakage. This also enables server inlets to draw uniformly cool air at the front of the cabinet, eliminating

the need to oversupply cool air to achieve desired thermal performance.

Keep the Exhaust Area Open

The VES functions by containing and channeling hot exhaust air. A

slightly lower pressure in the ceiling return plenum than in the room

helps draw hot exhaust air from the cabinet and into the plenum. The

VES should be properly sized, sealed, and free from obstructions to

avoid introducing choke points that impede the continuous flow of

exhaust air and limit system effectiveness.

The impact of chimney size on system performance is fairly

straightforward-- the larger the channel and less obstruction, the less

impedance to server fan airflow and hence the greater the volumetric

airflow through the vertical duct. The more critical limiting factor for

VES effectiveness is the size of the space behind servers, as the

back pressure on the exhaust side of the cabinet may adversely

affect the cooling of IT equipment. To minimize the back pressure

effect on server fans and to optimize VES effectiveness, the space

behind the servers should be free from obstructions and sized to

avoid any substantial back pressure.

The free space behind servers is also a critical parameter to control,

as server cabling density can have a significant impact on the ability

of hot exhaust air to exit the cabinet. For example, in a standard

24-inch-wide server cabinet, the effective open space behind

servers is often reduced by improper cabling and horizontal cable

management (see Figure 4).

As shown in Figure 5, data cables behind servers in a 24-inch-wide cabinet are forced to occupy valuable

exhaust area space, with data cables positioned to one side of the rear of the enclosure and power cables on

the other. Cable management arms also extend approximately four inches into the exhaust area, blocking that

space with cables and reducing the effective size of the exhaust area by 33%. (Loose or poorly managed

cabling can add clutter to this area, reducing cooling system effectiveness even further.)

In contrast, a 32-inch-wide cabinet adds 8 inches of width to the exhaust area without sacrificing depth: cables

are routed into vertical spaces to the sides of the servers to keep the entire exhaust area clear. Data and power

cabling can be managed outside the exhaust area to maximize the airflow channel and maintain optimal cooling

system performance. The result is an effective doubling of the open exhaust area (see Figure 5), dramatically

increasing airflow capacity while observing best cable management practices to ensure system performance.

Figure 4. Poor in-cabinet cable manage-

ment practices introduce clutter and choke

points in the exhaust area that limit cooling

system effectiveness.