Back in the fall of 2010, my son Russell was looking for a science fair project. He wanted to enter the regional HS science fair competition. After discussing several ideas, he remembered a web page we discussed about getting heat from decomposing material.

I first learned of the idea from one of my solar customers. She was a long time reader of MotherEarth News and sent me this link right after we installed her solar electric system. (FYI, this customer has a 1,500-watt solar electric array which zeros out here electric bill each month and she grows about 50% of her food on an 8,000 square foot lot (including the house) in Jamaica Plain (Boston).

The link takes you to an article about Jean Pain. In the 1980s Pain built piles of compost and threaded them with piping to capture the heat of decomposition and the methane. It was an early example of someone attempting to live sustainably off renewable energy. Pain’s heat capture method was based on water, and, in effect, worked the same as a solar hot water (solar thermal) system.

After getting approval from his Science teacher, Russell began his plans. The key difference between his system and Pain’s system was that he wanted to heat air rather than water. He felt that an air system would be easier to build, less costly, and less complicated. I agreed.

NOTE: This was a purely empirical experiment. Russell does not yet have the background to go deeply into the thermodynamics of a system like this and determine beforehand what to expect. Instead he relied on common sense and a bit of  input from me (Dad, a recovering nuclear engineer). I did play a relatively small roll – as the rules of the science fair dictate. (Though after going to the science fair, I’m doubtful that everyone followed that rule.) I also had to play “reminder of the budget limitations” and reminder of the stated objective – “To learn if useful heat could be captured from decomposing material using an compost-to-air-based heat exchanger.”