Energy Star for the cloud

The move toward cloud computing has brought data centers into the headlines. Pundits claim the primary rationale for companies to go into the cloud is to cut IT support costs. But cloud computing has an energy efficiency angle as well: At least in theory, concentrating enterprise data in a few heavily used data centers makes operations more energy efficient.

It is easy to see why this is so from the fact that power consumption in a data center doesn't scale linearly with its computing load. A server operating at 100% capacity consumes 100% of its maximum rated power, but an idle server does not consume 0% of its total potential power consumption. In fact, most modern servers consume about 60% of their total potential power consumption when they are simply idling. So it makes sense from the standpoint of energy efficiency to collect operations into a minimum number of servers, then run the servers flat out.

Still, even server farms with optimized resources consume a lot of energy. No wonder, then, that server farm operators are taking steps to curb their appetite for electrical power. Industry experts, for example, estimate that a 100-rack server farm could save $270,000 to $570,000 annually and cut its square footage simply by using the most efficient power supplies available today, which run at about 95% efficiency. They also estimate that use of more efficient supplies could reduce cooling loads by up to 20% and allow a downsizing of mechanical cooling equipment in new structures.

Though it has long been known that server farms are power hogs, the most recent statistics are still eye opening. A typical data center can use 30 times more energy per square foot of space than an ordinary office area. Power usage by these facilities is still growing at an alarming rate of more than 20% annually and is on a pace to double within the next few years. The most recent statistics from EPA show that data centers consumed about 60 billion kWh of electricity in 2006, roughly 1.5% of total U.S. electricity consumption.

You might think that with this sort of energy use, data centers would be low-hanging fruit for energy efficiency initiatives. But though the Environmental Protection Agency (EPA) in 2007 took the first steps toward the Energy Star Label program for data centers, that effort is off to what seems like a slow start. Few data centers have applied for the Energy Star designation. EPA insiders say interest in the program is growing, however. To get an Energy Star label, a data center facility must be in the top 25% of its peers in energy efficiency, as measured by an energy performance scale devised by EPA called the Power Usage Effectiveness (PUE) metric.

Much of the cost of operating a data center goes into managing the generated heat. Even within well-designed data centers, the cooling and managing of air flow with equipment like chillers and heating, ventilating and air-conditioning (HVAC) systems can account for more than a third of data center electricity costs.

EPA took these factors into consideration when it developed an interactive energy management on-line tool called the Portfolio Manager. The Manager program helps collect data on data centers (as well as on other kinds of buildings) applying for Energy Star label certification. The Portfolio Manager, for example, lets a data center operator track and assess energy and water consumption across an entire portfolio of buildings. It can help set investment priorities, identify under-performing buildings, verify efficiency improvements, and receive EPA recognition for superior energy performance.

To rate data centers, the EPA assigns a numerical rating between 1 to 100 for label applicants. Data centers need a rating of 75 or greater to qualify for the Energy Star label. And this system works great, in theory.