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Concentration of CO2 in the Atmosphere

Compost Power Combustion

FREE HEAT for Homes, Greenhouses…

Mound - Beginning

Editor’s note: this article is a follow up to one that ran in G.E.T. in 2010 while this concept was in an earlier stage of “experimental.” As Gaelan Brown stated, “G.E.T. is carrying the torch that Mother Earth News first lit on this topic in their article about Jean Pain in 1980.”

Cecil Smith of Haverhill, NH plans to use a different form of solar energy to heat his home this winter. He is capturing the solar energy stored in wood, by composting it, instead of burning it, to generate a 24/7 supply of hot water for his radiant-floor heating system. After heating his home this winter the by-product will be a large pile of high-value organic compost.

“It’s just one of those ideas that makes so much sense that I decided to just give it a try,” said Smith, who operates the solar-power installation company Polar Solar. “I know it’s experimental and I’m not 100% sure it’s going to work through the whole winter. But the input from Compost Power and Vermont Compost gave me the support I needed to go for it.”

Mound - Half done

Smith is one of about a dozen people in the Northeast and Midwest US, and Quebec, who will be attempting to heat homes, domestic water and greenhouses with water heated by a compost-mound this winter. French farmer Jean Pain first pioneered the promising but still experimental concept in the 1970s, but he died young and the idea fell by the wayside in the 1980s. Since 2009 a group of tinkerers, plumbers, compost-experts and engineers in Vermont have been experimenting to adapt the concept to the local climate through the non-profit Compost Power Network at www.CompostPower.org.

“Cecil has what might be the first compost-heated home in North America,” said Jason McCune-Sanders, an engineer who is active with several Compost Power projects. “We still have a lot to learn in order to maximize the output of these systems but we’re seeing promising results.”

Mound in Action - Internal Temp: 160º

This past summer Smith took a “how to” course at Yestermorrow Design Build school in Waistfield, Vermont, with a curriculum put together by members of the Compost Power team. Smith then got design-build guidance for his project from Compost Power and Vermont Compost supplied the fresh bark-mulch blended with some partially mature compost referred to as “hot mix.

In October Smith built a Compost Power mound in his backyard in one day by himself with the help of a small tractor. A small circulation pump moves water from his house through pipes buried in the ground, through the mound-loop returning 120-140-degree water to a storage-tank in his basement, which feeds his radiant-floor heating system.

Inside, including tie-in to Solar Hot Water and the Boiler, Tanks, Gauges, Valves and the plumber: Dan Boutin

According to Smith’s measurements, (temp-gauges on the water-lines/tank, and a flow-meter on the circulation) Smith is collecting approximately 15,000 btu/hour with 120-140 degree water coming from his system, which is like having a small wood-stove burning at full-bore 24/7.

Since the value of the compost 12 months later should be higher than the cost of building the system, any amount of energy collected can be seen as “gravy.”

Cecil & Suzette Smith, owners - alongside the Stiebel Circulating Storage Tank

Smith’s 40 cubic-yard compost power mound of shredded bark-mulch is about 22’ in diameter and eight’ tall, and contains 1200’ of 1” tubing coiled in layers distributed throughout the mound.

A critical factor to ensure success is that aeration has to be “engineered” into the foundation-layer of the mound, to ensure that air can get underneath the material and passively aerate the system to eliminate the need for “turning” to keep the compost process active. Aeration can be achieved by installing perforated pipes or by layer of pallets wrapped in fabric in the foundation to pull in outside air, before spreading the compost and heat-exchanging water-lines.

Jean Pain’s documented work and Compost Power’s experiments have shown that a properly-built system can generate steady heat for 12-18 months. There are many different types of “feedstocks” that can work, including bark-mulch, fine-grain wood-chips, or a mixture of sawdust and wood-chips or manure.

A do-it-yourself Design Guide can be found on www.CompostPower.org, and reports on the performance of previous projects will be updated regularly. The contributors to the Compost Power Network, including Cecil Smith, welcome anyone who is interested in getting help or advice on a project to contact them. Smith’s website is www.polarsolarnh.com and his email address is polarsolar1@yahoo.com.

4 comments to Compost Power Combustion

  • Thanks for the information on compost furnaces to heat a radiant system. One is being planned for the Strawbale Studio, a structure in Michigan 1 hr north of Detroit.

    The design ideas are being put together, and lots of resources are at hand. The Enbridge Pipeline (from the Alberta Tar Sands) has a new line coming through the land here to take the place of the old line put in during the 1960’s. As a result several acres of trees were taken down and there are mountains of rough woodchips on the land, as well as horse farms right next door.

    Questions: Ok to start in mid November? Can the pile be uphill from the building it is heating? What are the options for getting the pipe with hot water to the building? Does it have to go underground and be insulated? Does it have to have an expansion tank? Currently the pipes are installed in the Strawbale Studio and have pressure valves at the manifold on the lower level. There are two loops: a 190 ft loop that is in the lower floor level and a 2nd 300 feet loop that goes through a cob bench and into the “upper” floor, 14″ above the lower level. The hot water would enter the system at the lower level manifold. It would be about 75 feet from the pile to the manifold, and uphill several feet as well. the system would use glycol antifreeze.

    Any concerns or suggestions for this plan?
    Thanks.

  • Hi Deanne, yes it’s ok to start in November as long as it’s not below freezing when you build it, because you need to add many hundreds of gallons of water to the wood chips to activate the microbes and you don’t want that water to freeze before the process kicks in (within a day or two usually). It doesn’t matter if the pile is uphill or downhill from where you are using hot water, but you’ll need a good plumber’s input to help you get the right circulation pump based on your specifics. We usually run the cold supply and hot return pipes from the mound to the point of use in a below-grade trench with pipe insulation and an outer conduit to prevent groundwater from getting near the pipes. You can also just run the pipes on top of a 3ft thick layer of compost feedstock, and cover with another 3-4 feet, to insulate the pipes without at trench but that’s not recommended. You don’t need an expansion tank. Your radiant floor loops sound kind of long but you’ll be able to add significant heat to your floors from the compost hot water. The circulation of water through your compost heat exchange loops needs to be kept very slow, usually 1 gallon per minute or perhaps 2 depending on the size of your system. It’s important to use fine texture wood chips, vs large diameter chips, and it’s best to mix in a large percentage of saw dust (30-40%) if possible, and maybe 10% manure, all thoroughly mixed together.

    Email me Gaelan@compostpower.org if you’d like more focused help on your project. We can do a customized design guide walking you through all the details or I can share more info from previous projects.

  • Anyone out there to advise further? (see the previous post for other details on the proposed Compost Furnace in Michigan. We have had an exploration meeting on the design, and have located a closer location for the pile, just about 30 ft to the West of the Strawbale Studio, on the side that has an access pipe into the building.
    We are looking at the advantages of laying the pipes in horizontal spirals vs, a vertical spiral (for easier extraction of finished compost). I am very interested in having a simple and aesthetic system, preferably without plastic tarping.

  • Hi Deanne, there are a few ways we’ve approached embedding heat exchange loops in the material. A vertical spiral doesn’t really make sense in my opinion, I think that would be more work than horizontal. A year later it takes one person about a day to rake the material off each layer and re-coil the pipe, it’s pretty simple really. But in some projects, especially larger systems, we’ve created modular heat exchange loops on metal frames such as sections of chain link fence, or what is referred to as “cattle panels” (heavy gauge wire fencing. Each layer can then be plumbed together via a manifold along the side. This makes it quicker to build and tear down, just disconnect the manifold and drag each section of pipe out. Email me gaelan@compostpower.org if you’d like more specific help on your project.
    Cheers
    GB

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