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It's Flue Season
Eric De Place, 8 Jan 09

Economic stimulus through energy efficiency.

flue.htmHere's your economic stimulus idea for today: condensing flue gas waste heat recovery.

With a name like that, it has to be good. And it is. It's precisely the sort of off-the-shelf technology that's ripe for stimulus investment. The investments could yield near-term jobs, as well as savings that would begin immediately and compound into the future.

But what is it? Good question. The folks at Sidel Systems are in the waste heat recovery business, and they've peppered me with fun facts. So while I don't fully understand the technology -- and I don't really know anything about engineering -- I'm going to write about it anyway!

(That means, for the rest of this post, caveat lector.)

Here's the low-down. It's not uncommon for large institutions -- universities, hospitals, schools, prisons, hotels, and certain manufacturers -- to use big and fairly inefficient natural gas-fired boilers. These are boilers that are rated at maybe 80 percent efficiency, but that probably don't hit even that modest mark on most days. And these are boilers that are consuming a huge amount of fuel.

The result of inefficiency is that these huge boilers are expelling hot exhaust tbetween 300 and 700 degrees, a gigantic waste of energy. Now back in the day, when natural gas was cheap and climate change was just a twinkle in Roger Revelle's eye, no one really cared much. But now that gas can be expensive, money is tight, and emissions matter, it's starting to seem like a pretty stupid idea to vent off 700 degree waste heat.

That's where the condensing flue business comes in.

The older and inefficient boilers can be retrofitted with stainless steel and aluminum systems that can capture most of the waste heat, boosting the system efficiency to as much as 97 percent. Basically, the system works by transferring the waste energy into water, which can then be used for hot water (duh), space heating, or manufacturing processes. That means, for example, that a public school might be able to heat its swimming pool with the energy currently being wasted and still have energy left over for other purposes. Or a beverage manufacturer -- a common home for huge boilers -- might find all kinds of big monetary savings by employing what amounts to free hot water.

As with most efficiency investments, there's an upfront capital cost that's paid back over time. A government stimulus investment could front the initial money for building and installing the condensing flues. Right away, that would put technicians, engineers, and installers to work. (And, of course, that there would upstream benefits to the supply chain and downstream benefits when the workers spend money.)

If the condensing flue systems went into public institutions -- schools, universities, and so on -- the increased energy efficiency would save money right away, a big boon during a time of constricted budgets. If the flues were installed in private businesses, they would cut operating costs during a rocky time, and might even help keep struggling companies afloat. In either case, the systems would mean more than monetary relief: they would mean significant environmental benefit too. We're talking about real emissions reductions.

Roughly speaking, for every 17,000 cubic feet of natural gas saved, the climate will be spared one ton of carbon-dioxide. (One ton of CO-2 is roughly the emissions of that an average American car produces over a two month period.) Since it's common for institutions to burn through that much natural gas every hour, boosting the efficiency of just a single boiler from 10 percent -- say from 80 to 90 percent -- would be on the order of taking 100 cars off the road every year. And since some installations burn through 10 times that much natural gas, upgrading one of those big boilers could be the climate equivalent of getting 1,000 or more cars off the road.

Ballpark figures here, but you get my drift. We're talking about a real climate benefit -- and we're talking about doing it by saving money and creating jobs now. In my book, that's a great buy for an economic stimulus investment.

Now that's condensing flue gas waste heat recovery we can believe in.

Read more about waste heat in our archives:
Clean Energy's Best-Kept Secret: Waste Heat Recovery
We've Got SSSSSSSSSteam Heat
Hot Idea: Recycling Wasted Energy

This piece originally appeared on The Sightline Institute's blog, The Daily Score.

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Condensing boilers have been compulsory in the UK for about five years now and work well provided the rest of the heating system is set up so that the boiler runs in condensing mode. A low return temperature is required to condense the flue gases.

Perhaps the US may now catch up with Europe and Asia by moving to cars with one or two litre engines, giving 40 to 80 miles per gallon, instead of five or seven litre engines. Then you would really see some fuel savings.

Posted by: Ken Neal on 16 Jan 09

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