DIY Water Heating with Compost

Enlarge Image Image Gallery Simple DIY Water Heating with Compost. [1] MOTHER's newest compost mound shown here partially completed Is a low, rectangular heap with sloping sides (a shape that eliminates the need for a cage) and two flat coils of polyethylene tubing buried inside it. [2] The rings are connected to insulated hoses which will carry water in and out of the pile. [3] The warmed water travels 80 feet (see the diagram at left) and then is circulated through a heat exchanger inside this converted water heater. [4] MOM's second Jean Pain-style compost heater will be a hard act to follow! Supported by a wire frame and sheathed in black plastic, the circular mound maintained for almost teal months its highest temperature of 140?F, as registered on . . . [5] this thermometer.

All systems are "go" with Mother’s latest innovation in the field of "bacteria—fueled" home energy: a decomposing compost heap that will produce hot water.

It's been a while—almost a year, in fact—since we last reported on the progress of Mother's ongoing experiments in obtaining usable heat from compost. (Our efforts, as most of you probably recall, were initially inspired by the pioneering work of the French organic gardener and biotechnologist, Jean Pain.) However, our recent silence on the subject doesn't mean that MOM's research staffers have been idle. On the contrary, they've been hard at work over the past months . . . measuring the heat-generating capacity of our second "Pain-style powerplant" (for details of that mound's design and construction, see "Update II: Mother’s Compost Heater"), as well as testing various other modifications on the design of M. Pain's original shredded-brush piles.

Mother’s second compost heap—as recorded on the performance chart which accompanies this article—surpassed its predecessor by registering an inner temperature of 140°F for two months . . . and then leveling off again at a plateau of 130°F, which it sustained for another two months before dropping any further. The success of that particular heatmaking cylinder convinced us that we could produce temperatures as high as those claimed by M. Pain for his experimental mounds. Later, when the next pile we built actually registered a high of 155°F for a good portion of its 4-1/2-month life span, we knew we were onto something that was potentially very important!

So, Larry Hollar—one of Mother’s horticulturists and our staff compost-heating expert—decided to undertake an even more ambitious project. In order to tap the heat produced in compost piles for home use, Larry decided to hook up our newest heap to a closed-loop circulation system . . . and provide hot water for one of the yurts at MOM's Eco-Village. His goal is to demonstrate that a decaying compost pile can indeed be a practical source of abundant energy for individuals.

SIMPLER CONSTRUCTION

In order to avoid the effort that was spent in building chicken-wire-and-bamboo enclosures to support the earlier piles (which were all cylindrical), Larry settled on a lower, rectangular-shaped heap with sloping sides. Such a configuration, he reasoned, would have the advantage of not requiring a wire-and-wood cage to hold it together . . . and could be constructed quite easily with common garden hand tools. (While preparing all his previous humus-heating experiments, Larry had needed to use a cumbersome tractor-mounted loader to shape the tall, cylindrical piles.)