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Hot Idea: Recycling Wasted Energy
Adam Stein, 30 Sep 08
Article Photo

Computers and cacti go together like chocolate and peanut butter.

Bill McKibben once lamented the unsexiness of waste heat recovery, an energy efficiency technique that languishes in obscurity despite its potentially huge environmental benefits. Perhaps this story will capture the public imagination: in a move that will save money and cut carbon emissions, the University of Notre Dame in Indiana has begun housing some of its computer servers in the nearby "Arizona Desert Dome," a conservatory for cacti and other desert plants.

Computer servers create a lot of waste heat -- so much so that keeping them cool is a major cost driver and engineering challenge for data centers. Particularly in coal-fired Indiana, air conditioning for data centers equates to a lot of carbon emissions.

Cacti, on the other hand, need a lot of heat, particularly in the winter, when South Bend is blanketed in snow.

You can see where this is going. Housing servers in the desert dome, where air currents can carry away their waste heat, is expected to save the university about $100,000 in cooling costs. Meanwhile, the city will save some of the $70,000 it spends each year to keep the conservatory warm. Given that the conservatory was cut out of the city's 2010 budget altogether, such steps toward self-sufficiency are necessary to ensure its continued existence.

And here's some recycled energy news with perhaps wider impact: Vinod Khosla is backing a company that creates solar energy systems designed to harness the waste heat from traditional solar photovoltaic panels.

Details on the technology are scarce. It sounds a bit like a solar panel smooshed together with a solar hot water heater -- presumably alongside some clever engineering to make the smooshing as efficient as possible. The company claims to be able to double the energy capture of today's solar photovoltaics, which, if true, would represent an an enormous leap forward for rooftop systems.

Recycled waste heat presents one of the biggest, cheapest opportunities for slashing our carbon budget. It looks like the idea is starting to get its day in the sun.

Adam Stein is a co-founder of TerraPass, where this post originally appeared. He writes on issues related to carbon, climate change, policy, and conservation.

Photo credit: University of Notre Dame.

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Nice post! I'm associated with Recycled Energy Development, the company featured in the Orion article to which you link. The Notre Dame effort on computer servers sounds like a great idea. And you're right that energy recycling (particularly recycling waste heat) has an awful lot of untapped potential. Actually, according to DoE and EPA estimates, energy recycling could slash greenhouse emissions by 20% in the U.S. That's as much as if we pulled every passenger vehicle off the road. And as far as I know, that doesn't even count waste heat from computers.

So why isn't more being done? The problem is regulations that protect monopoly utilities from competition. If everyone buys less power, utilities lose money -- so the regulations make it hard for more efficient competitors to emerge. Crazy, isn't it?

Posted by: miggs on 30 Sep 08

OK this is a pet peeve of mine,
I HATE, HATE, Hate the term "recycled" energy. It grates on my nerves and misstates basic thermodynamics. You can't recycle energy, what you are doing is using energy more efficiently not recycling it.

Posted by: jim moore on 30 Sep 08

Energy can't be recycled according to the laws of thermodynamics but the laws of thermodynamics don't work in PR and marketing. I tend not to use "energy conservation" either, preferring energy efficiency instead.

"Recycled energy" is not a technical term. It is an advertising term.

My report on Tom Casten's recent talk at MIT is at

Posted by: gmoke on 30 Sep 08

It would be great to see more posts like this on WorldChanging: about mundane-but-effective, roll-up-your-sleeves topics. There is so much more to be done in the short term increasing energy efficiency than there is in the "sexier" realms of PV, wind, hydrogen, etc. When people's eyes light up as much over greywater heat recovery as they do over wind turbines, that will be a good thing.

Posted by: David Foley on 1 Oct 08

This is a really interesting innovation, but what is more interesting is that the concept is not new. Only the application of the concept is innovative.

As an example, Permaculture design, pioneered by Bill Mollison and David Holmgren, advocates siting two or more things that complement each other to make the best use of resources, especially energy. For example piping and storing waste water from a home's showers and baths in a conservatory in order to utilise the heat stored in the water for warming the plants in the conservatory (i.e. what David Foley mentioned above re: greywater heat recovery).

Or allowing a passionfruit vine to grow over a chicken house to help moderate the sun's heat and thus the temperature within.

But it is interesting to see intelligent initiatives like this being taken up by large institutions, on a larger scale, and not just in homes. David Foley is right - we need to get more excited about the methods and concepts that we know already work, and expand their application. Not just the sexy stuff.

What's this post also reminds us is that this kind of efficient, intelligent thinking and design can save money, as well as energy.

Posted by: Mark L on 2 Oct 08



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