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Buy Some Compost and get Free Hot Water?

Here’s a very cool system that I’m currently considering as part of my home’s resilient make-over.  You might be interested in this too.

What is it?  It’s a system that uses a compost pile to produce hot water.

Specifically, this system turns the waste heat of the compost pile you need for your gardening, into something you can use to wash the dishes or heat an ad hoc greenhouse.

I like it because it allows me to take something I’m already doing (making compost for my garden) and do something else productive with it at the same time.

Compost piles as hot water heaters

How does it work?  Well, we all know that compost piles generate heat as part of the decomposition process.  How much heat?  A large, well balanced (nitrogen/carbon), and aerate compost pile can get up to 120-140 degrees for as long as six months, depending on the size of the pile.

It’s certainly not a new technique, it’s been used for thousands of years by farmers to keep livestock warm during the winter.  However, in the last century, the resilient tinkerer Jean Pain resurrected it as a way to generate a) methane for cooking/driving and b) hot water heat for his home/barn.

In the process, he developed some pretty interesting designs (see right) and reignited interest in it as a way to locally produce energy.

For my purposes, and perhaps yours, the system I’m considering would be much more modest.  The reason?  While I have a need for garden compost, I don’t have the need, space, or time required for a huge pile of loose compost.

Instead, I do have space for a less ambitious small system that can a) pre-heat hot water for home use or b) heat a greenhouse.

The resilient home compost heating system?

What would a system like that look like?  Of course, in today’s world, systems that are this innovative aren’t available.  You are going to need to build it as a do-it-yourself project to take advantage of it.

Here are two examples for how to do that.

The pictured system uses hay bales as the walls of the container, garden hose for the piping, and 55 gallon drums as a reservoir.  Pretty slick.

A second approach is to lay out the compost and the piping horizontally, so it can act as the floor of a greenhouse as this family in Oregon did.  They were able to generate at least 90 degree water for 18 months from their system and grow plants outdoors during the winter.

Where do we go from here?

I’d like to see this become a resilient business opportunity.

What do I mean?

Composting is already a big part of the resilient lifestyle (people that don’t compost are throwing wealth away) and efforts to permanently integrate it into a home’s design are already underway.

So, the idea that local professionals will install and maintain permanent composting systems that allow both fast and efficient composting as well as heat isn’t that much of a leap.

It even open ups the potential for deliveries of the composting material you need in bulk (as a supplement to what you already produce), on an annual basis.   For example: a delivery of pulped wood/sawdust or shredded leaves to beef up your home’s supply, in a fashion similar to how a septic tank gets emptied or an oil tank filled, isn’t really that strange of an idea.

Finally, it gets even more interesting when you think about the productive impact of a home scale greenhouses that incorporate composting as a heat source — see picture and click for more info.

 

Hope this gets you thinking,

 

JOHN ROBB

 

 

 

 

 

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  • Tom

    Source of last image: “The Composting Greenhouse at New Alchemy Institute”, http://www.builditsolar.com/Projects/Sunspace/NewAlchemycompost.pdf

    • John Robb

      Thanks. I had the link to the report they posted, not sure why it was dropped from the final copy I published. Putting it back into it. JR

  • I tried a very small prototype of this to heat a small hoop house. It worked well. However, I worried that if I got it much bigger, I’d have to increase my compost pile size to make sure I didn’t cool the pile so much that the composting took longer. I need that compost to put organic matter and nutrients back into my soil’s bank account, so I can make withdrawals later.

    One thing I thought that would help would be to have some chickens and add their manure, which is very “hot” as it decomposes, to the pile.

    • John Robb

      Scott,

      The chicken idea is pretty great. Also, if you can grind down brush/leaves in abundance, it would help with the volume of material you need.

      JR

      • Grass clippings are great, but you can only rob so much of them without starving the lawn. Local horse stalls and cow barns are great sources of “hot” manure, if you’re up to hauling it or paying someone to. Some local logging companies let me grab their sawdust, but you have to mix it with manure or grass clippings, because it consumes nitrogen in the decomposition, and you don’t want a bunch of compost with very little nitrogen in it.

        Also, a problem with using garden hose is that chipmunks, squirrels, and other non-tasty will chew it. This has become a whole big deal for me, as I found some hose that is chew proof (braided steel), but it’s over $3 a foot, and I’m not sure of it’s heat conductive capabilities. A copper coil would be ideal, of course, but again, expensive.

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