Hot/Cold Aisle Containment: Is It the Right Choice for You?
  • There are many options available to one searching for the appropriate method of cooling a data centre, but the most common is probably hot-air and cold-air aisle containment. The efficiency and reliability of an IT network can generally be increased through the use of containment as a method of temperature control. This is generally done by separating the hot air from the cold air in the room through the proper arrangement of heat vents and cooling systems to prevent the mixing of the two. Alternating aisles of cold and hot air will be created by setting up IT racks in a formation that faces the rack fronts toward one another, limiting hot air’s mobility. 

    There are, of course, differences between the two and when it comes to energy costs, for instance, hot-air aisle containment tends to be the better option –saving 40% of the other method’s total expense. The money saved on energy in hot-air aisle containment is mostly the result of increased economizer hours. Economizer hours occur when the rack system’s chiller can be turned off because the temperature of the racks has not reached a raised temperature setting (remained cool). Cooling systems may rack up large energy costs because they are often required to be set at a lower temperature threshold in order to keep hotspots from occurring. Hotspots are made as hot air is pushed upward from the cold air passing from the cooling unit to the front of the rack and concentrating there. 

    In a cold-air containment system (CACS), the CACS encircles the cold aisle to limit the blending of warm and cool air, creating a hot-air return plenum (an enclosed space for airflow) in the data center. Better heat exchange and an increased cooling capacity are the result of using containment in this way, where hot air is returned to the cooling unit and the cold air supply can be raised in temperature. The cold-air aisles are created through the operation of a chiller, which compresses and expands a refrigerant to reach the desired temperature, in most cases set around 45°F/7°C. Economizer hours can be increased by raising the chiller water supply temperature so that it more closely matches the outside air temperature. The setup also allows the cooled air from the cooling unit to reach the front of the racks without mixing with the hot air, reaching uniform IT inlet air temperatures. The supply air temperature can be increased then, along with the number of economizer hours, without the two air flows mixing. 

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    Dehumidification and humidification are additional areas through which costs can be reduced by the effort of separating the cool air from the warm air. Energy and water can be saved when the air being supplied to the racks is kept above the dew point, as humidity will not be removed and the addition of humidity is not necessary. 

    Also, physical infrastructure is a valid consideration, especially in the case of traditional cooling, where equipment my be required to be oversized to complete the task of cooling effectively. Finding the right size for each of the system’s components is critical in raising efficiency and ceasing the waste of energy to cool the area. Physical materials can also be effective in separating the air temperature, such as erecting physical barriers at the ends of the cold-aisle racks including plastic curtains, panel walls, blanking panels and containment strips. Another physical modifier is raised floors, which is the result of adding perforated floor tiles which will allow cool air to be more evenly distributed in determined areas that need cooling. Of course, this can work against the idea of containment, even though the method will cool the hot-air aisle. 

    With a hot-aisle containment system (HACS), however, the opposite occurs: the hot aisle is enclosed to contain the hot exhaust air from the IT machines and creates a cold-air return plenum. Through a consistent row-oriented (hot-air/cold-air) pattern, the HACS will, similarly to the CACS, keep the warm

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