Selecting the Right Airflow Containment Solution

Carl Cottuli is a recognized air flow management expert. He is vice president of products and services at Eaton Wright Line, an American manufacturer of green, state-of-the-art containment systems and data center enclosures.

Carl Cottuli

Reports indicate that in 2011 a full two percent (2%) of the nation's energy supply will be used by data centers. The EPA and electric utilities will be offering financial rebates to data centers that deliver significant energy savings. In order to take advantage of the rebates, data centers will need to implement containment strategies that will keep data center temperatures and energy levels under better, more accurate control.

This article discusses three types of data center containment. It also explores a number of site based constraints that drive the best selection of equipment for a given site.

Containment strategies manage cold air supply streams and hot exhausted air streams in the data center. These strategies, which isolate the air streams, eliminate the waste of legacy chaos cooling (an open supply of cold air and return of hot air that drives an increase in mixing of airstreams in the data center).

These strategies help to maintain consistent room temperatures, manage recommended hardware operating conditions, drive a more predictable work environment, preserve a livable climate for IT personnel and control/lower operating costs.

Selecting the Best Containment Solution

Data center aisle containment strategies provide a proven means of saving energy and optimizing data center equipment. There are three types of data center containment options: hot aisle, cold aisle and rack-based chimney containment.

Hot Aisle Containment: This method isolates the hot aisle with end of row doors and a ceiling structure that encloses the top of the entire row. Hot aisle containment can be integrated with existing server racks in the row or it can be achieved with the use of an free standing Independent Containment System (ICS), which allows racks to be easily added or removed from a row.

Cold Aisle Containment: This method isolates the cold aisle with end of row doors and an aisle ceiling that covers the entire cold row. Cold aisle containment can also be integrated with server racks in the row or spaced separately with the use of an ICS.

End of Row Doors and Aisle Ceilings create more efficient cold or hot aisles and reduce air recirculation and air mixing by blocking obvious air escape/entry routes. This allows for the setting of a higher overall temperature within the data center and also enables air-side economization to be used a greater percentage of the time.

End of Row Doors and Aisle Ceilings can also be a simple, cost-effective solution to improve efficiency while lowering overall operating costs. The elimination of wasted cool air can either reduce the cold air needed for the data center or enable an increase in the IT load.

These solutions offer complete control of data center airflow dynamics at the aisle level producing increased efficiency and equipment performance while reducing overall energy consumption.

Rack-based Chimney Containment: This method involves a chimney structure that mounts directly to the top rear of the IT racks. The heat exhausted from rack-mounted equipment is captured and directed through the chimney where it is then ducted directly back to the data center’s CRAC units. If a ceiling plenum is not available, the hot air can simply rise to a high air return or stratification layer.

Rack-based chimney systems can be passive (without fans) or active (with fans). Active systems allow the fans, installed at the base of the chimney, to respond based on temperature or pressure.

There is additional efficiency in this type of air flow solution because it allows hot exhaust air to return directly to the CRACs. This process increases CRAC efficiency by operating at a higher Delta T (ΔT). (Delta T is defined as the difference in temperature in degrees Fahrenheit between the server exhaust and supply air entering the server intake). It also extends existing cooling capacity throughout the data center, liberating stranded assets and lowering operational costs.

Finally, rack-based heat containment is extremely flexible because it does not require alteration of existing enclosure locations. Taken altogether this solution is highly compatible with many data center needs.

Rack Hygiene

In addition to any containment strategy, a focused effort on managing air at the rack level is recommended. A rack hygiene strategy addresses air leakage in and around equipment that is rack-mounted in each server or network rack. Containment at the rack level can be addressed at five leak or airflow fault areas. These five areas include:

1.Under the rack
2.Left side of left 19” rail
3.Right side of right 19” rail
4.Above top U rack-mount space
5.Below bottom U rack-mount space

Typically, addressing airflow management at the rack level can account for approximately 60% of any containment strategy given the amount of real estate that server and network racks occupy in the white space. Simple solutions such as blanking panels, air seal kits and cable & floor grommets can alleviate the five fault areas and provide sufficient solutions to rack-based airflow management.

All three containment systems are scalable and can be adapted to existing infrastructures to increase rack utilization as capacity demands grow. They are also predictable because they separate hot exhaust air from the cold supply air, increasing the reliability of the data center operating environment. Moreover, these containment options are flexible because they do not require the alteration of existing enclosure locations. Taken altogether, containment is highly compatible with managing the rising energy demands in today’s critical data centers.

Additionally, aisle containment systems are scalable and can be adapted to existing infrastructures to increase rack utilization as capacity demands grow. They also create a more reliable data center operating environment

What’s Best for Your Data Center?

To determine which containment choice is best, it’s important to understand the specific needs of the data center in question.

There’s no “easy button” to determine the best solution. A variety of site based constraints and consumer preferences drive the best selection of equipment for a given site. Once these issues are addressed, the decisions that optimize the data center have a better chance of succeeding. It’s also important to note that trade-offs exist for each type of constraint selection made.

Among the many questions that are important to consider before implementing containment are:

1.Is this a new or existing build-out (aka “Greenfield” or “Brownfield”)
2.What is the current data center cooling system design?
3.What is the evolution cycle of the IT equipment? (How long is the equipment being used? Where is it in this intended lifecycle span?
4.How often does your evolution of equipment occur?
5.Is there a need or desire for uniformity of the equipment rows?
6.What is the mix of rack-based vs. free-standing equipment in your data center?
7.What obstructions are present in the environment – columns, lighting, cabling, etc.?
8.How does your data center handle lighting, cabling, power and fire suppression/detection
9.What are the human behavior patterns in the data center?
10.What’s the corporate philosophy surrounding physical comfort of the IT staff working in the data center?

Other trade-offs to address include:

1.What amount of cool air is desired in the data center?
2.What about IT Staff comfort in the working environment?
3.Is the IT staff adhering to a best practices process?
4.What are the efficiency differences

Post Deployment: Adhering to a Best Practices Process

Once a containment strategy is decided, it’s not enough just to implement it. In order to maintain and even improve upon the optimizing conditions implemented, data center management must drive the ongoing process of monitoring air flow patterns and temperatures to maintain containment integrity. For any containment strategy, IT staff must take responsibility and ownership of the process.

With cold aisle containment there is a tendency to over-drive air supply volume as a means to manage the room temperature. In order to control this tendency, IT staff needs to set an absolute temperature range and stay within it.

Within the hot aisle, when IT personnel are working there, often perforated tiles are placed in the aisle and raised floor cable grommets and blanking panels are removed to provide cool air. Also, ceiling tiles are often removed to access wire trays.

To realize the operational efficiencies that the contained aisle provides, the IT staff must always be diligent in replacing the blanking panels, cable grommets and ceiling tiles that have been removed after working on equipment in the racks.

Balance the Trade-offs

Though each containment solution is beneficial to the data center environment, each has trade offs; and one may be more valuable to a data center with unique constraints than another. Therefore, it is very important to consider all topics discussed above before making a containment decision.

Additionally after the containment implementation has been completed, it is of equal importance for data center personnel to institute an ongoing process of evaluation, test and measurement as a method of process management. This process management will ensure server optimization. The best containment implementation decisions require due diligence both before and after a course of action is selected.

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