We have seen multiple ways to distribute the cold/hot air within the white space area. According to  TIA 942-B, the “Cabinets and racks shall be arranged in an alternating pattern, with fronts of cabinets/racks facing each other in a row to create “hot” and “cold” aisles.”. In the previous article, we have seen different ways to distribute/return the air from CRAH/CRAC unit to the racks using Hot aisle/cold aisle strategy. What if we can save more of this by implementing some more techniques? Prevent hot and cold air leakage?

Hot and cold air leakage

Most hot exhaust air from IT equipment goes back to the CRAH where it is cooled. Hot-air leakage occurs when the IT exhaust air makes its way back to the IT equipment inlets and mixes with the cold inlet air. Cold-air leakage occurs when the cold supply air from the CRAH mixes with the CRAH’s hot return air without ever getting to the IT equipment inlets.

While looking at the containment systems strategy in white space, there are mainly four types to understand and namely as below,

• Aisle containment
• Curtain System/Soft Containment
• Modular systems containment
• Rack-based containment/Chimney systems

Aisle containment

The separation of hot and cold air is one of the most promising energy-efficiency measures available to new and legacy data centers today. When we consider the air distribution through hot/cold air aisles there is a much efficient way to achieve this by using different Aisle containments. High energy costs and accelerated energy consumption rates have forced data center professionals to consider hot-air and cold-air containment strategies. Even though these are optional approaches this can really improve the cooling efficiency with the below advantages,

• Reduced Energy Consumption
• Increased Cooling Capacity
• Increased Rack Population
• More Power Available for IT Equipment
• Increased Equipment Up-time
• Longer Hardware Life
• Provides focused cooling at the rack.
• Minimizes cold and hot air mixing so the return temperature to the cooling unit is higher.

There are two terminologies you need to understand when considering the aisle containment systems, namely as below,

• Cold Aisle Containment(CAC)
• Hot Aisle Containment(HAC)

Cold Aisle Containment (CAC)

When using a cold aisle containment method, containment is used to surround the cold aisle, allowing the rest of the white space area to become a large hot-air return plenum. By containing the cold aisle, the hot and cold airstreams are separated. This method encloses the cold aisle with ceiling panels above the aisle between adjoining racks and with doors at the end of the aisle. This allows the cold air from the perforated floor tiles in front of the cabinets to be contained and delivered to the server equipment air inlets.

This method prevents cold air from mixing with warm air or being obstructed by surrounding equipment/sources before it reaches the servers. Because CAC possesses this ability, it is called focused cooling. Note that this containment method requires that the rows of racks be set up in a consistent hot-aisle / cold-aisle arrangement. Racks inside the aisle containment must be expanded in even numbers. Additional expandable aisle panels must be installed for odd gap openings in the row between racks.

Hot Aisle Containment(HAC)

A hot-aisle containment system (HACS) encloses the hot aisle to collect the IT equipment’s hot exhaust air, allowing the rest of the data center to become a large cold-air return plenum. By containing the hot aisle, the hot and cold airstreams are separated. Hot Aisle Containment immediately captures server exhaust air and restricts its entry to the rest of the data center.

Generally, there are two types of containment designs in hot aisle containment system.

The Room: One version of hot aisle containment turns the hot aisle into its own room. Once cabinets are aligned in the traditional hot aisle/cold aisle layout, the hot aisle is sealed with doors, sidewalls, and roofs. From there, an In-Row air conditioner takes over. This unit, more compact, is embedded within a row of enclosures. It captures the exhaust air of the equipment, conditions it, and returns it to the cold aisle.

The Chimney: This approach involves a specialized cabinet with a solid rear door and attachments for ductwork (also called a chimney) and a false ceiling. Attached to the rear of the server cabinets, these ducts catch the exhaust air of the servers and channel it into a false ceiling. The false ceiling serves as a plenum, delivering the hot exhaust air to a perimeter-mounted air conditioner, which may also extend, via ducts, to the ceiling level.

The exhaust air’s destination depends on the containment configuration.

Both hot-aisle and cold-aisle containment provide significant energy savings over traditional uncontained configurations. While hot-aisle containment is the preferred solution in all new installations and many retrofit installations, it may be difficult or expensive to implement in retrofit applications that have a raised floor, but low headroom or no accessible dropped ceiling plenum. Cold-aisle containment, although not optimal, may be the best feasible option in these cases.

While both hot-aisle and cold-aisle containment strategies offer energy savings, studies show that hot-aisle containment can provide 40% cooling system energy savings over cold-aisle containment due mainly to increased economizer hours. It also concludes that hot-aisle containment should always be used for new data centers.

Curtain System/Soft Containment

The functionality and design of this system look almost similar to CAC/HAC and the major change is the materials used in this model are Clear View Vinyl Curtain(often a higher grade than the materials you are familiar with in the grocery store walk-in refrigerators) to form the containment. Soft containment systems are a cost-efficient way to isolate conditioned air and control airflow between data center racks, while still providing access to the IT equipment. Soft containment is made up of two parts; thermal doors and thermal walls. Combine the two for effective airflow management. Each containment solution is custom-built to the needs of the customer. Most products can be customized with the finish, material, and upgrades.

By using clear view vinyl curtains and combine those with an aluminum track system and fuse Links allowing you to attach the data center curtains to the drop ceiling and to the tops of the racks. More intelligently designed aisle containment curtains utilize UL-listed fuse-links that melt at a temperature that is below the temperature at which your fire suppression system would be activated thus, allowing the curtains to drop to the floor before the temperature would be sufficient to trigger a data center fire suppression system. This is the most user-friendly, versatile, and clean attachment system available for Cold Aisle / Hot Aisle containment. To address fire safety concerns, UL listed fuse-links with 135F temperature ratings are available for situations where modification of the existing fire suppression system is not feasible.

Modular Systems Containment

This is one of the methods developed by Upsite Technologies and these are known as AisleLok Modular Containment. This model is one of the easiest to install and maintenance-free among all other methods that we have seen so far. The unique design of the AisleLok modular aisle containment system attaches to the racks magnetically, creating a truly tool-less design that can be moved, reconfigured, and reused as many times as needed.

The two main components of the AisleLok Modular Containment are the Rack Top Baffle and the Bi-Directional Doors, with an optional row gap filler. The Rack Top Baffle can be purchased in either a 30° angle from the horizontal position (best for cold aisle containment) or in a vertical 90° angle from the horizontal position (best for hot aisle containment). Both components attach directly to the racks. The open-sealing design ensures fire safety with an elegant appearance that brings professional aesthetics to your server room. Have a look at this video and you will be amazed.

Rack based Containment/Chimney System

A chimney system consists of a solid metal chimney that extends from the top rear of the IT racks. The hot air is pushed through the chimney up to the ceiling return air plenum. Chimneys can be installed on individual cabinets or as a system, which spans several cabinets. Fans within the chimneys can be provided, which assist airflow and help minimize pressure buildup at the rear of any high-density cabinets. Please note that this method is mainly used only when the consideration is to remove the hot air. There is nothing to do with cold air aisle on this method. It has to be supplied through the cold aisle as usual.

There are several advantages to this with increased flexibility and modularity, since the chimney cabinets can be more easily added, moved, and reconfigured. The chimney fan option can also be added later as the cabinet load grows over time. Also, the containment system can be purchased only when the cabinet itself is purchased, instead of having to install a full aisle-containment system prior to installing the cabinets in that aisle.

Disadvantages also exist. Because many chimneys have a relatively small cross-sectional area, and total cabinet airflow can be large, there is a potential for excess pressure buildup at the IT server discharge, restricting proper airflow through the servers and causing massive internal cabinet recirculation if the cabinets do not have a proper separation between the front and back. The cabinet and chimney design must be carefully chosen, since gasketing, leakage, and airflow performance vary greatly between manufacturers. 

Now the question would be which containment solution is better?

The answer is ‘ it’s up to your environment’. Look out for your data center design and modeling, choose as per that. If your data center is hosted in a colocation the best solution would be cold aisle containment, a modular system since you don’t want to make any changes to your building infrastructure. If you are concerned more about the expenses the cheapest would be soft containments. Hot aisle containment would be the better solution if you are having an enterprise data center.

Knowledge Credits: www.42u.com and www.apc.com

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