FREE HEAT for Homes, Greenhouses…
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.”
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.”
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.
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.”
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 firstname.lastname@example.org.