Of all the factors that can impact the energy efficiency cooling represents the majority of facility related energy usage in the data center, outside of the actual IT load itself. This article is an part of the DCK Executive Guide to Energy Efficiency and the fifth article in a 5-part executive education series on Energy Efficiency.
While there are several variations on cooling systems, they generally fall into two categories, the Computer Room Air Conditioner “CRAC” wherein each unit has its own internal compressor, and Computer Room Air Handler “CRAH” which is primarily a coil and a fan which requires externally supplied chilled water. From an energy efficiency viewpoint, the CRAH which is usually supplied by a water cooled central chilled water plant, is more efficient than an air-cooled CRAC units. However, the air-cooled CRAC unit has one advantage over a centralized chiller system; they are all autonomous and therefore offer inherent redundancy and fault tolerance, in that there is no single point of failure (other than power failure).
Regardless of the type of cooling system, the amount of cooling required and therefore the energy required is reduced if the data center temperatures can be increased. Moreover, tightly controlled humidity is another area where a lot of energy is used, in many cases quite needlessly.
So what does this mean to the data center facility and its cooling system design and operation? Data centers have historically kept very tight environmental conditions to help ensure the reliability of the IT equipment. This was originally driven by older equipments susceptibility to temperature and humidity changes as well as a very narrow range of “recommended” environmental condi¬tions mandated by the equipment manufacturers them¬selves. (Download the complete DCK Executive Guide to Energy Efficiency for more details on the ASHRAE Expanded Thermal Guidelines).
In 2011 ASHRAE in conjunction with the consensus of major IT equipment manufacturers radically hoped to change the direction of the data center industry’s view toward cooling requirements by openly stating that: “A roadmap has been outlined to facilitate a significant increase in the operational hours during which economizer systems are able to be used, and to increase the opportunity for data centers to become “chillerless,” eliminating mechanical cooling systems entirely, in order to realize improved Power Usage Effectiveness (PUE).”
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