DIY Water Heating with Compost
(Page 2 of 3)
July/August 1981
By the Mother Earth News Editors
To make the heat-producing mound, our intrepid composter first put down a base layer consisting of about two and one-half feet of "the recipe" mix of three parts wood chips to one part manure. Unlike the previous mounds we've erected, this one makes use of dehydrated cow manure . . . simply because the nearby dairy where we've obtained fresh droppings in the past now processes the material before passing it on to us. (MOM'S researcher suggests that a potential compost-heap builder use whatever form of manure is most readily available in his or her area . . . and then water the structure thoroughly—at one-foot intervals—as the layers are piled up.)
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On top of this foundation, Larry placed two flat coils of one-inch black polyethylene tubing. (Each ring is composed of 100 feet of hose piled in four-foot-diameter loops.) The coils were then connected to separate lengths of half-inch tubing, which carry water into and out of the pile's interior. In addition, three thermocouples were attached to the assembly: One of the heat-sensing devices was placed inside each tubing coil, to measure the temperature of both the incoming and outgoing water . . . while the third heat detector was positioned between the coils, to record the interior temperature of the compost pile itself.
Finally, another full layer of the woodchip/manure mixture was placed on top of the tubing coils . . . and a sheet of black plastic was fitted over the whole structure, to trap moisture and increase heat absorption. The entire construction process—which took Larry just over 12 hours to complete single-handed—produced a neat compost stack measuring approximately 5 feet high, 10 feet wide, and 12 feet long. The compact mound, although smaller than the previous ones we've built (and much less massive than the 50- to 100-ton heaps made by Jean Pain), still weighs a solid six tons.
DIY WATER HEATING
The circulation system that connects MOM's compost-fed "heat generator" to the yurt's water supply is a simple closed-loop arrangement. Approximately 80 feet of half-inch-thick tubing—wrapped in homemade polyurethane-foam pipe insulation—emerges from the pile's interior and travels underground to a water tank located beneath the main floor of the house. (To remodel the receptacle for its new "bacteria-powered" function, MOTHER's research staff completely gutted a used, 40-gallon gas water heater and refitted it with an inner heat exchanger.) Water from a nearby spring is gravity-fed into the tank, where it circulates around a center column full of the hot liquid that's pumped in from the compost pile. Thus, the running water that emerges from the yurt's tap is always fresh—and warm! —while that circulating between the pile and the water tank is simply used over and over.
