Google & Amazon Propose Metric-Based Efficiency

A group of data center operators and technology providers is asking the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to reconsider recommendations for cooling data centers that could become part of ASHRAE Standard 90.1 as an addendum. Standard 90.1 is a building efficiency standard that is often incorporated into building codes across the country.

The group published an open letter expressing its concerns about the addendum, saying that "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." The letter is signed by executives from Digital Realty Trust, Dupont Fabros Technology, Amazon, Google, Nokia and Microsoft.

The addendum recommends data centers use economizers to reduce energy consumption. Economizers are relatively new and provide data center cooling using less power than standard chiller systems. Air-side, also known as dry-side, economizers rely on outside air to cool the hot return air and reuse it to cool IT equipment. Wet-side economizers rely on a thermodynamic effect called "evaporative cooling." As hot water leaves the data center, it is directed to a cooling tower then sprayed into the air, over the tower. As the water evaporates, that process removes the heat and the cool water is then returned to the data center for cooling purposes.

Google uses wet-side economizers and has found the technology to be very efficient, says Chris Malone, a member of Google's operations team. Thanks to the wet-side economizers, Google's data centers can operate much of the time in "free cooling" mode, which means the chillers are off. Since installing the economizers and other green technologies, Google says it has reduced its energy overhead across all Google-built data centers to 19 percent, versus the average of 96 percent reported by the U.S. Environmental Protection Agency.

But while the Google and the others agree economizers are excellent options to help reduce energy consumption, the group contends that by prescribing their use in a standard used by building engineers across the country might preclude the use of other technologies, especially technologies that have yet to be developed."Data center and infrastructure efficiency systems, like cooling, have rapidly evolved. But we really don't know how things might change," Malone says. "Ten years ago, the notion of using economizers was very foreign to data centers, particularly air-side economizers. But economizers may not be the solution of the future. It is more important to set the goal, set an aggressive standard, and let companies innovate toward that goal."

One consideration the group recommends is to include an efficiency metric in the standard, perhaps something similar to the power usage effectiveness (PUE), a ratio that expresses the total amount of power used by a data center, including overhead power such as lighting and even cooling, to the power consumed by the computing equipment. "Going down that route would allow innovators to create solutions that we haven't even thought of," Malone says.

For its part, ASHRAE issued a statement saying that the addendum proposes "cost-effective measures in the prescriptive path of Standard 90.1 to save energy in data centers. The addendum includes eight exceptions to requirements for the use of economizers in data centers.  The addendum does not change the portion of the standard that already allows, through the Energy Cost Budget method (an alternate method of compliance), for data centers to be designed without economizers if other energy saving methodologies, including power usage effectiveness (PUE), are employed."

The addendum is currently moving through the public review process, and ASHRAE says it encourages anyone with comments regarding the proposed addendum to participate.  Comments are due to ASHRAE by April 19. Malone says Google will submit its comments about the addendum through ASHRAE's official public review process.