In a recent ICT Today magazine article David Knapp, Chatsworth Products (CPI) Product Marketing Manager, examines and compares three containment systems, breaking down the differences, the challenges and the advantages that distinguish one system over the other. By understanding the differences, you can determine the best containment option for your data center's specific requirements.

Ducted Exhaust Cabinets (CPI Vertical Exhaust Ducts)

Ducted exhaust cabinets are enclosed server rack cabinets with an attached vertical exhaust duct. The hot exhaust air given off by servers is enclosed within the cabinet, completely isolating the air from the room. The hot air exits the cabinet through the overhead vertical exhaust duct, which directs the hot air into a plenum above the drop ceiling and back to the cooling units or to outside vents. See the figure below.

Benefits

• They are the simplest and most cost-effective method to deploy and change 
• Cabinets can be placed anywhere in the room and in any orientation
• No additional aisle clearances are required to deploy a DEC; the locations of building columns and support structures do not impact deployment
• Eliminates the need for a raised floor
• Cold supply air can be delivered from anywhere in the room; strict front of cabinet delivery is not required

Challenges

• The system requires an overhead plenum and the addition of collars on air handler units to create a complete closed return, and ducts to be placed above each cabinet; the ducts must be able to extend to the overhead plenum
• Fan speeds on the air handlers should be adjusted to closely match equipment requirements; this may require some units to be shut off or upgraded with variable speed fans
• Optimizing operation conditions may require the addition of some instrumentation or heating, ventilation, and air-conditioning (HVAC) controls

Hot Aisle Containment (HAC) 

Hot Aisle Containment (HAC) is the most popular type of containment solution used today. In this method, a configuration of duct work with baffles is set up over the hot aisle, with doors blocking the aisle entrances at either end. The HAC solution contains and isolates the hot exhaust air from the room, preventing it from reaching the adjacent cold aisles and mixing with the cold air. The hot exhaust air in the hot aisles is then returned to the cooling units, usually through drop ceiling plenums. See the figure below.

Benefits

• Contained aisles are the hot aisles and the entire room (except the contained hot aisle) is the cold aisle, and provides supply air.
• HAC eliminates the need for a raised floor
• Cold air can be delivered from anywhere in the room; strict front of cabinet delivery is not required
• Auxiliary equipment can be placed anywhere and still be sufficiently cooled, because the room is cool
• Minimal or no changes are required to the fire suppression system

Challenges

• HAC is more complicated and more expensive to deploy and change than the DEC system
• Cabinets must be placed in adjacent hot aisle / cold aisle rows and deployed in pairs to create hot aisles
• The system may require row lengths to be evenly sized, parallel and aligned
• This system requires an overhead plenum and the addition of collars on the air handler units to create a closed return, and also that a duct be constructed over the hot aisle
• Optimizing operating conditions may require the addition of some instrumentation or HVAC controls

Cold Aisle Containment (CAC) 

Cold Aisle Containment (CAC) configurations are typically used to retrofit data center environments where a raised floor cooling system already exists. A roof or partitions are set up over the cold aisle, with doors at either end. This isolates the cold intake air within the cold aisle, keeping it separate from the hot air in the neighboring hot aisles. The hot exhaust air rises up freely in the hot aisles, and returns through the room to the air handlers. See the figure below.

Benefits

• CAC is an easy retrofit for existing hot aisle / cold aisle environments, especially over a raised floor supply air plenum
• The contained aisle is the cold aisle and provides supply air
• Some solutions can be deployed over uneven aisles
• Sliding doors require no additional clearance for door swing

Challenges

• It is more complicated and more expensive to deploy and change than a DEC
• The system may require row lengths to be evenly sized, parallel and aligned
• Additional aisle clearances may be required for the doors at the ends of each aisle
• The containment ceiling structure over the contained cold aisle must be constructed around building columns and other support structures
• Auxilary equipment will be in a hot aisle space, which may reduce performance

Choosing the Right Containment System

The type of containment system selected for your data center should be based on specific business requirements and architectural limitations. Whichever method is chosen, it must isolate hot from cold air within the data center.

Knapp goes on to discuss why an effective seal is critical and how to prevent interior recirculation and bypass airflow in his article. Click here to view the full article, or to further evaluate CPI containment systems, click here.

Brittany Mangan, Digital Content Specialist