Maintain appropriate temperature, humidity and air flow by containing data center hot and cold aisles. Admins must monitor these factors to ensure server efficiency and keep a data center running using the least amount of energy.
In 1993, Dr. Robert Sullivan developed the standard hot aisle/cold aisle cabinet layout for data centers. However, this particular layout degraded a data center’s cooling as warm exhaust air from one row blew into the intakes of the next row. Introducing hot and cold aisle containment to this layout can decrease degradation by enabling more control over the data center’s environment.
The practice of containment means placing a door at the end of each aisle and barrier panels from the tops of cabinets to the ceiling, creating sealed enclosures around cabinets to increase the efficacy of cooling. The tighter the enclosure, the better the air management becomes.
Temperature control
ASHRAE bases its thermal guidelines on IT equipment inlet temperature as opposed to return air temperature, which ignores air distribution differences within aisles. Organizations can integrate hundreds of sensors affixed to cabinet fronts and automatically control air conditioner discharge temperature. In-row and overhead coolers come with their own sensors to deliver the highest acceptable inlet temperature at each device while maintaining uniform cooling.
Organizations can mount temperature indicating blanking panels to check inlet temperature quickly. For the best setup, they should install three such panels in each cabinet at the top, middle and bottom. Admins can then check on inlet temperatures at a glance.
Hot aisle vs. cold aisle containment
Hot aisle containment is easier to manage and puts the rest of the room at a more comfortable cold aisle temperature. Cold aisle containment, by contrast, is often easier to retrofit to existing data centers, and delivers the most uniform air to servers when properly managed.
Containing the cold aisles puts the rest of the room at hot aisle temperature, and can make it challenging to deliver the right quantity of air to cabinets because providing more air than necessary wastes expensive-to-produce cool air. When central air conditioners, under-floor or overhead ducts serve cold aisle systems, the data center requires expensive pressure differential sensors to monitor and regulate air delivery.
A data center can also partially contain aisles by hanging special plastic strips — similar to those used on loading docks and in grocery store warehouses — at the ends of aisles and above racks. Partial containment is easier and cheaper to implement and control, and can be up to 75% as effective as full containment. Partial containment eases cold aisle air control because fans can pull air through the curtains if necessary.
Humidity control
Recent ASHRAE research shows that data centers no longer require 45%-55% relative humidity (RH) to avoid static discharge damage to IT hardware. With a good grounding system, organizations can lower RH to 8%, as long as technicians use wrist straps when working on opened equipment.
The best way to monitor and control humidity is by dew point (DP), also referred to as absolute humidity. DP represents the actual amount of moisture in the air, which is essentially uniform everywhere in a given space. Ideally, data centers should keep humidity below 60% RH DP so that gaseous contaminants from vehicles or industrial plants don’t form acids that damage circuit boards and connector contacts, a concern with air-side free cooling.
Fire protection
A data center should place fire protection heads in every aisle, although many organizations put them in every other aisle. This practice often occurs in retrofitted data centers as well as new ones.
In terms of fire protection, organizations should avoid fusible links because fire must grow hot enough to melt them before the links drop air barriers. Magnetic barriers work well as long as they don’t drop into aisles and impede escape. False ceilings that open automatically are probably the best fire protection option, but are more expensive than other methods.
