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For an existing traditional data center, hot air and cold air mixing can lead to more than 25% waste of the cooling capacity. As a result, the cooling system is normally oversized in order to make up for this waste, which results in much higher energy costs. And what is worse, hot spots can be caused by hot air recirculation at the top of the racks or at the end of the rack rows, which may lead IT equipment downtime.
High energy costs and accelerated energy consumption rates have forced data center professionals to consider containment strategies for their existing data centers. There are six potential air containment solutions you can choose between to save energy. These solutions are done by either containing the hot or containing the cold, and are described as follows:
1. Cold aisle containment system (CACS): this method applies to a raised floor (room-cooled downflow units) cooling distribution system. It encloses the cold aisle, allowing the rest of the room to become a large hot-air return plenum.
2. Ducted hot aisle containment system (Ducted HACS): this method can be used with either a raised floor or a hard floor-based (room- cooled) air distribution system. It encloses the hot aisle, allowing the rest of the data center to become a large cold-air plenum.
3. Ducted rack: this method best applies to environments with scattered high density racks with a front-to-back airflow pattern. With this method, a duct is mounted to the back of the rack to contain the hot exhaust air, which is then ducted into the drop ceiling.
4. Row-cooled hot aisle containment system (Row-cooled HACS): this method applies to data centers with existing row-based cooling units but could also serve as a solution for data centers with perimeter cooling units.
5. Rack air containment system (RACS): this method is an ideal solution for use with very high density racks by integrating rack-based cooling units with the racks, forcing the air to circulate only inside of the containment.
6. Row-cooled cold aisle containment system (Row-cooled CACS): this method should be used in data centers with perimeter cooling units and when all racks are in some form of cold aisle containment. This solution adds row-based cooling units in between racks. The cold aisle is enclosed and the containment system is deployed as a pod.
All of these containment solutions will allow for higher rack power densities, increased cooling system energy savings, elimination of hot spots, and increased cooling unit capacity.
But, each air containment solution has its unique application conditions, and existing facilities also have various constraints that are dictated by circumstances which are typically out of your control. These constraints may restrict the selection of these solutions. Therefore, an assessment of the existing conditions of the facility is essential to choosing the right containment solution for a given data center.
For more information on this topic see White Paper 153, “Implementing Hot and Cold Air Containment in Existing Data Centers.” This paper shows some likely assessments and solutions, and provides guidance on when each solution is recommended, when it is less than optimal, and describes important considerations for deploying it including payback periods.