Cooling Data Centers

April 18, 2010

The enormous growth of the Internet, and particularly the growth of large Web-based services, such as Yahoo!, YouTube, Facebook, and Google, has meant a corresponding increase in the number and size of data centers to sustain an adequate level of service.  Computers, of course, run on electricity; and although your individual PC doesn’t use all that much, when you start putting many thousands of machines, together with other devices like routers, in a single data center, it starts to add up.  (It has been estimated that data centers consume 2% of all electricity used on a global basis.)  What people sometimes forget is that all those machines also generate a lot of heat, and more energy has to be expended to remove it, lest the whole thing end up as a very expensive puddle of silicon.  This means that availability and cost of electric power have become important factors in siting data centers.  Google, for example, has constructed a large new facility in The Dalles, Oregon, because of its abundant and relatively cheap hydroelectric power.

As energy becomes more expensive, and as environmental concerns like global warming increase, there is naturally an interest in improving the energy efficiency of data centers.  As reported in an article at Ars Technica, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers [ASHRAE] has issued a new Standard 90.1, which specifies how data center  cooling is to be done.  The ASHRAE standards are significant, because they are frequently incorporated into local building codes in the US.

Google has sensibly objected to the proposed standard, on the grounds that it specifies how efficiency is to be achieved, rather than setting efficiency standards.  It has been joined in its objection by several other large data center users.  (The posted objection is one of the few documents you are likely to see signed by both Google and Microsoft.)

A performance-based standard for data centers can achieve the desired energy saving results while still enabling our industry to innovate and find new ways to improve our products.

The note goes on to point out that an agreed-upon method [PDF] for measuring data center energy efficiency, Power Usage Effectiveness [PUE] already exists, and has been adopted by the US government’s EnergyStar program.

The statement’s point is a very good one.  If one is devising a set of rules or standards, one should be careful that they are actually directed at the desired objective.   (A very similar problem and potential pitfall exists in the design of incentive compensation systems.)  If the goal is energy efficiency, then that should be the metric used by the standard.

Fortunately, it appears that ASHRAE is open to suggestions for improvement; so, with a bit of sense all around, the final standard might look much better.

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