For the past decade, we have been working to make our data centers as efficient as possible; we now use less than half the energy to run Google's data centers than the industry average. In the open letter below, I am very happy to welcome a group of industry leaders who collectively represent most of the world's most advanced data center operators. -Urs Hoelzle

Recently, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) added data centers to their building efficiency standard, ASHRAE Standard 90.1. This standard defines the energy efficiency for most types of buildings in America and is often incorporated into building codes across the country.

Data centers are among the fastest-growing users of energy, according to an EPA report, and most data centers have historically been designed and operated without regard to energy efficiency (for details, see this 2009 EPA Energy Star survey). Thus, setting efficiency standards for data centers is important, and we welcome this step.

We believe that for data centers, where the energy used to perform a function (e.g., cooling) is easily measured, efficiency standards should be performance-based, not prescriptive. In other words, the standard should set the required efficiency without prescribing the specific technologies to accomplish that goal. That’s how many efficiency standards work; for example, fuel efficiency standards for cars specify how much gas a car can consume per mile of driving but not what engine to use. 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.

Unfortunately, the proposed ASHRAE standard is far too prescriptive. Instead of setting a required level of efficiency for the cooling system as a whole, the standard dictates which types of cooling methods must be used. For example, the standard requires data centers to use economizers — systems that use ambient air for cooling. In many cases, economizers are a great way to cool a data center (in fact, many of our companies' data centers use them extensively), but simply requiring their use doesn’t guarantee an efficient system, and they may not be the best choice. Future cooling methods may achieve the same or better results without the use of economizers altogether. An efficiency standard should not prohibit such innovation.

Thus, we believe that an overall data center-level cooling system efficiency standard needs to replace the proposed prescriptive approach to allow data center innovation to continue. The standard should set an aggressive target for the maximum amount of energy used by a data center for overhead functions like cooling. In fact, a similar approach is already being adopted in the industry. In a recent statement, data center industry leaders agreed that Power Usage Effectiveness (PUE) is the preferred metric for measuring data center efficiency. And the EPA Energy Star program already uses this method for data centers. As leaders in the data center industry, we are committed to aggressive energy efficiency improvements, but we need standards that let us continue to innovate while meeting (and, hopefully, exceeding) a baseline efficiency requirement set by the ASHRAE standard.

Chris Crosby, Senior Vice President, Digital Realty Trust
Hossein Fateh, President and Chief Executive Officer, Dupont Fabros Technology
James Hamilton, Vice President and Distinguished Engineer, Amazon
Urs Hoelzle, Senior Vice President, Operations and Google Fellow, Google
Mike Manos, Vice President, Service Operations, Nokia
Kevin Timmons, General Manager, Datacenter Services, Microsoft
Joseph F. Dzaluk, VP, Global Infrastructure and Resource Management, ITDelivery, IBM

Update (4/20/10): Added Joseph F. Dzaluk (IBM) as a signer.