Heat is a by-product of biodegradation, the natural process which occurs within a compost pile, and it is possible to use compost to heat water, providing the pile is big and healthy enough.
Maintaining an equal balance of carbon and nitrogen in a compost pile produces free garden fertiliser and can reduce the amount of waste sent to landfills. Energy usage can be cut too, just by using the heat from a compost pile to warm water.
How using compost to heat water works:
A successful compost pile comes about by creating the right conditions for the right microorganisms needed to carry out biodegradation. Biodegredation, or compost, happens at the highest rates when a pile is looked after with balanced ingredients, aeration, and moisture. These three elements regulate the compost’s environmental conditions and the nutrients needed to encourage microorganisms like bacteria and fungi to thrive and reproduce, decomposing material as they do. Microorganisms take the organic waste matter found in compost piles and turn it into carbon dioxide, water, and humus – the material left after decomposition. Heat is a byproduct of this process of conversion, and it can be used efficiently with just a few bits of equipment and a little bit of care for the environment.
When biodegradation occurs, the more heat that’s produced the faster the composting happens. The greatest heats, and the fastest rates of composting, are achieved in larger piles. Compost heaps of more than 3 cubic feet can generate heats of over 60 degrees Celsius. Heat production is best at the centre of a pile of 4 to 5 feet squared. Hot compost heats can reach even greater heats of over 70 degrees Celsius.
Anyone using compost to heat water will probably follow a variant of the Jean Pain method from the 1970s. Water gets pumped through coils of plastic pipes laid centrally through compost heaps. Jean Pain estimated that a large heap could heat a small structure for six months of the year in France. That’s around 50 tons of compost heating 1,000 square feet. The potential greatness of the heat to be extracted is relative to location and the process. Compost season is generally in alignment with, or longer than, the local growing season. Water conducts heat well, so simple piping systems can be used to transfer heat short distances.
If you use compost to heat water, it is ordinarily done within a closed-loop system. It is possible to heat a small space using compost-heated water by using fans to blow air across the pipes. In such a system, the water (once cooled) is pumped back to the heap to be reheated. These systems are perfect for heating greenhouses, for example, especially due to their being in closer proximity to the compost heap. To extend a system’s capacity, a circuitous system can be linked to a secondary heat source such as a regular water heater, using a heat exchanger. In a similar way to passive solar heating, the water inside the tank is preheated by tubes of hot water which are fed from the compost heap. Therefore less electric energy is required for household hot water during composting season. Water will generally account for 14%-25% of household energy consumption, so this sort of system may effectively bring down your electricity bills.
Image: Alan LevinetagscompostDIYwater