Microsoft researchers have proposed that "servers can be sent to homes and office buildings and used as a primary heat source. We call this approach the Data Furnace or DF. Data Furnaces have three advantages over traditional data centers: 1) a smaller carbon footprint 2) reduced total cost of ownership per server 3) closer proximity to the users." Data centers are already being used as heating sources in Europe, 'data furnaces' takes the concept to the distributed residential level.

Liquid cooling was once a staple of large-scale computing, but has increasingly been replaced by air cooling. Now, several companies are applying liquid cooling to standard servers to reduce energy. One, through a Swedish research initiative, is also seeking to recapture heat.

The Green Grid released a survey of data centers' use of economizers, cooling technologies that take advantage of favorable outdoor conditions (air and/or water) to provide partial or full cooling without using a refrigeration cycle. Fifty percent reported that they were already using economizers, but it is not clear that economizer use translates into overall data center energy efficiency.

The ars technica folks published this informative breakdown of server power consumption in 2007, credited to "Intel and EXP Critical Facilities":

We've been tracking the growth in mega-datacenters since 2009. These faculties feature technical and operational innovation that has overturned previous notions of limits on energy efficiency. But does the focus on efficiency obscure an acceleration in ICT energy and water consumption and in CO2e production? While mega-data center operators are claiming exceptional power usage effectiveness (PUE) ratios, we're still talking about facilities that consume 20-200 MW apiece and emit a considerable carbon footprint unless powered by renewable energy. Here's our most recent look at their reported PUE and the technology behind them.

We've always taken a broad view of the definition of an ICT facility. More than just data centers, ICT facilities include everything from broadcast studios to telecom network operating centers. Hospitals' network closets, an instance of decentralized ICT, are the focus of an informative white paper from Emerson Power Networks.

Green ICT is concerned with all the resource consumption involved with creating and operation ICT gear. Significant amounts of water are used in everything from chip fabrication to PC manufacture to data center operation.

The Green Grid paper on data center power efficiency metrics covers two key measures of data center infrastructure efficiency: PUE and DCiE (formerly DCE). The basic notion is that the most efficient facility is one in which most of the power goes directly to power the IT equipment, rather than to cooling, etc. But there are complexities.

A lot has changed since we wrote three years ago: "Yahoo plans to go carbon neutral by the end of 2007. Part of this will be achieved through carbon offsets, including hydroelectric and sustainable agriculture projects in Brazil." Co-founder and Chief Yahoo David Filo now says, "Reducing our carbon footprint has always been a priority and we’ve decided to focus all our energy and investment on that philosophy. We will no longer purchase carbon offsets as announced in 2007. Instead, we’ll focus our resources on reducing our carbon impact while helping the rest of the industry do the same. We believe creating highly-efficient data centers will have a greater long-term, direct impact on the environment and gives us the best opportunity to play a leadership role in addressing climate change."

Another focus appears to be reducing the amount of water typically consumed by a data center. Here is Yahoo's report about its newest data center, the Lockport, NY "Chicken Coop":

Google's Bill Weihl gave an update on ICT sustainability at Green:Net 2010 iin April. Livestream has posted the video; here the items I found useful. (Time location in video for each item is in parentheses in mm:ss format.)