practice

DoI: 10.1145/1666420.1666438

Article development led by queue.acm.org

What will it take to make server-side computing more energy efficient?

BY DAVID J. BRo Wn AnD ChARLeS ReAmS toward energy-efficient Computing

by no W, most everyone is aware of the energy problem at its highest level—our primary sources of energy are running out, while the demand for energy in both commercial and domestic environments is increasing. Moreover, the side effects of energy use have important global environmental considerations. The emission of greenhouse gases such as Co2, now seen by most climatologists to be linked to global warming, is only one issue.

The world’s preeminent scientists and thought leaders are perhaps most focused on a strategic solution: the need to develop new sources of clean and renewable energy if we are ultimately to overcome the energy problem. Lord Rees, president of the Royal Society, emphasized its urgency in an annual address delivered in 2008.13

The practical expectation of new sources of sustainable energy is at least three decades away, however. Steve Chu, who was the director of the Lawrence Berkeley National Laboratory prior to his recent appointment as U.S. Secretary of Energy, placed this situation in context: 3

“A dual strategy is needed to solve
the energy problem: ( 1) maximize en-
ergy efficiency and decrease energy
use; ( 2) develop new sources of clean
energy. No. 1 will remain the lowest-
hanging fruit for the next few de-
cades.”
What part does computer equip-
ment play in the demand for energy,
and where must we focus to reduce
consumption and improve energy ef-
ficiency?

In August 2007, the Environmental
Protection Agency (EPA) issued a re-
port to Congress on energy efficiency
of servers and data centers. 5 Some key
findings from the report include:
Servers and data centers con- ˲
sumed 61 billion kWh (kilowatt
hours) in 2006. This was 1.5% of total
U.S. electricity consumption that year,
amounting to $4.5 billion in electric-
ity costs—equivalent to 5. 8 million av-
erage U.S. households.

Electricity use in this sector dou- ˲ bled between 2000 and 2006, a trend that is expected to continue.

Infrastructure systems necessary ˲ to support the operation of IT equipment (for example, power delivery and cooling systems) also consumed a significant amount of energy, comprising 50% of annual electricity use.

Excerpts from the EPA report are shown in the accompanying figure and table. There are two particularly notable points in the data. The first is that as much energy is being consumed by site infrastructure as by the computing equipment itself. This infrastructure primarily represents heating, ventilation, and air-conditioning (HVAC) equipment, as well as that used to convert and transmit power and to maintain its continuity (the latter includes transformers