Cooling Solutions

Cold aisle containment (CAC) is a cooling method that increases cooling efficiency and reduces energy costs in data centers.

This cooling method relies on the fact that most network equipment and servers are designed to cool themselves by drawing air in through the front and exhausting it out the rear. To implement cold aisle containment, rows of cabinets or racks are arranged facing each other to form aisles, and cool air is routed between the rows. Equipment takes the cool air in at the front of the cabinet and exhausts it out the back into the room.

To keep cool air from mixing with warm air, row ends are closed off with an air-flow barrier. This barrier can range from makeshift arrangements of plastic strips to doors made expressly for this purpose.

Because cold aisle containment concentrates cool air at the front of equipment where it’s most needed, it’s an exceptionally effective cooling method. Cold aisle containment significantly reduces energy costs, lowering power bills as well as reducing data centers’ carbon footprints.

The trend toward high-density installations with higher-powered CPUs has made heat a critical issue in data centers. Blade servers present a special challenge—a rack of blade servers can dissipate more than 25 kW, generating more heat than an electric oven.

Heat-generated problems
The heat generated in today’s high-density data centers can shorten equipment lifespan, negatively affect equipment performance, and cause downtime. Traditional air-cooling methods such as hot/cold aisle arrangements simply can’t keep up with these heat-generating installations. Data center managers often try to compensate for the inefficiency of air cooling by under-populating racks, but this wastes space—an often scarce commodity in modern data centers.

Why liquid
Because of the inherent inefficiencies of air cooling, many data centers have turned to liquid cooling through water or other refrigerants. Liquids have far greater heat transfer properties than air—water is 3400 times more efficient than air—and can cool far greater equipment densities.

Liquid cooling is usually done at the rack level using the airflow from the servers to move the heat to a cooling unit where it’s removed by liquid, neutralizing heat at the source before it enters the room. Liquid cooling may also be done at the component level, where cooling liquid is delivered directly to individual components. Liquid cooling may also arrive in the form of portable units for cooling hot spots.

Liquid cooling options
Types of liquid cooling commonly used in data centers include:

• Cabinet-door liquid cooling: With this method, cooling units are special cabinet doors that contain sealed tubes filled with chilled liquid. The liquid is circulated through the door to remove heat vented by equipment fans. Because liquid-cooled doors can replace standard cabinet doors, they’re the favored method for retrofitting liquid cooling into existing data centers.
• Integrated liquid cooling: This consists of a specialized sealed cabinet that has channels for liquid cooling built into it to act as heat exchangers. Fans move hot air past the heat exchangers before sending the cooled air back to the servers. These cabinets are closed systems that release very little heat into the room.
• Component-based liquid cooling: Some servers are preconfigured with integrated liquid-based cooling modules. After the servers are installed, liquid is circulated through the cooling modules.
• Immersion cooling: This rather counterintuitive cooling method immerses servers in a non-conductive liquid, which is circulated to cool the servers.
• Portable liquid cooling: These are small units that operate by blowing air across water-cooled coils. They can usually accept water from any source—including a nearby faucet. They’re generally plumbed with ordinary garden hoses and require no special skills to use. Portable cooling units are intended for emergency cooling rather than as a permanent solution.

Liquid cooling requires a shift in the way you think about cooling. Installation may require that you acquire a new skill set or hire a professional installer. However, the space savings and cost savings gained through liquid cooling more than make up for the inconvenience of installing a new cooling technology.

Not only does liquid cooling enable data centers to operate at far greater densities than conventional air cooling does, it gets rid of the infrastructure associated with air cooling, enabling you to eliminate hot/cold aisles and raised floors. Liquid cooling can support from 25 to 80% more equipment in the same footprint, resulting in significantly lower infrastructure costs.

Add to this the fact that cooling is often the majority of a data center’s operating cost, and it’s plain to see why an investment in the efficiency of liquid cooling goes right to the bottom line.

The National Electrical Manufacturers’ Association (NEMA) issues guidelines and ratings for an enclosure’s level of protection against contaminants that might come in contact with its enclosed equipment.

There are many numerical NEMA designations; we’ll discuss NEMA enclosures relevant to our on-line catalog: NEMA 3, NEMA 3R, NEMA 4, NEMA 4X, and NEMA 12.

NEMA 3 enclosures, designed for both indoor and outdoor use, provide protection against falling dirt, windblown dust, rain, sleet, and snow, as well as ice formation.

The NEMA 3R rating is identical to NEMA 3 except that it doesn’t specify protection against windblown dust.

NEMA 4 and 4X enclosures, also designed for indoor and outdoor use, protect against windblown dust and rain, splashing and hose-directed water, and ice formation. NEMA 4X goes further than NEMA 4, specifying that the enclosure will also protect against corrosion caused by the elements.

NEMA 12 enclosures are constructed for indoor use only and are designed to provide protection against falling dirt, circulating dust, lint, fibers, and dripping or splashing noncorrosive liquids. Protection against oil and coolant seepage is also a prerequisite for NEMA 12 designation.

Understanding cabinet and rack measurements.
The main component of a cabinet is a set of vertical rails with mounting holes to which you attach your equipment or shelves. When you consider the width or height of a cabinet, clarify whether the dimensions are inside or outside.

The first measurement you need to know is the width of the rails. The most common size is 19 inches with hole-to-hole centers measuring 18.3 inches. There are also 23-inch and 24-inch cabinets and racks. Most rackmount equipment is made to fit 19-inch rails but can be adapted for wider rails.

After width, the most important specification is the number of rack units, abbreviated as “U.” It’s a measurement of space available to mount equipment. Because cabinet width is standard, the amount of space is what determines how much equipment you can actually install. Remember, this is an internal measurement of usable space and is smaller than an external measure of the cabinet or rack.

One rack unit (1U) is 1.75 inches of usable space and is usually, but not always, measured vertically. So, for example, a rackmount device that’s 2U high takes up 3.5 inches of rack space. A rack that’s 20U high has 35 inches of usable space.

Choosing the right cabinet.
Here’s a quick checklist of features to keep in mind before you choose a cabinet for servers or other network devices:
• High-volume airflow.
• Adjustable rails.
• Rails with M6 square holes.
• Moisture and dust resistance.
• Air filters.
• Front and/or rear accessibility.
• Locking doors.
• Left- or right-hinging doors.
• Power strips and cable organizers.
• Interior lighting.
• Preassembly.
• Availability of optional shelves, fans, and casters.
• Cable management rails, space, and knockouts.
• Extra depth to accommodate newer, deeper servers.

Don’t forget to accessorize.
Even if your cabinet is in a climate-controlled room, you may need to add a fan panel to help keep your equipment from overheating. It’s especially important to have ventilation in an enclosed cabinet.

Rackmount power strips mount either vertically or horizontally. Some have widely spaced outlets to accommodate transformer blocks. Some power strips include surge protection.

Mission-critical equipment should be connected to an uninterruptible power supply (UPS). A UPS keeps your equipment from crashing during a brief blackout or brownout and provides you with enough time to shut down everything properly in a more extended power outage.

For accessories that make cabling easier, just take a look at our many cable management products. We have cable management guides, rackmount raceways, horizontal and vertical organizers, cable managers, cable hangers, and much more.