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The compost heater (also Biomeiler) it a setup for utilization of the heat dissipation of a composting process. The thermal effect is well known from a compost heap, where the biomass is decayed by the digestion and metabolism of many different microbes and invertebrates. The heat is used, for instance, for a dwelling house. In contrast to the production of biogas, the composting process requires enough oxygen, resulting in an aerobic decay.
The french agronomist Jean Pain is held responsible for the invention of the Biomeiler. His system was a combination of a sealed biogas reactor in the center of a big compost heap, producing both biogas and heat. He also worked on agricultural principles in harmony with nature.
Three basic types
Compost Heap in the Garden with Water Circulation System
The traditional compost heater exploits the heat of a big compost heap in the garden to warm up a house. This type requires a big compost heap in the Garden, interveined with a spirally water hose. The water circulation conducts the heat to the building, where it can be fed to a heating circuit.
The compost heap must contain at least 8000 liters biomass to be able of holding a temperature during the freezing winter, allowing the thermophilic microbes to continue their work.
Combination of Hot Water and Biogas
The 'Biomeiler' has been invented by Jean Pain. While the idea of using the aerobic process for heating purpose is used in several locations, mostly on demonstration facilities, the combination with biogas, like the original setup of Jean Pain, has not spread much.
Compost Heater Silo inside a Building
The composting process is running in an airtight container inside a house. The produced heat can be distributed by a heating circuit, whereas a simple model of such a compost heater silo does not require a water circulation, radiating the heat directly to the interiors of the house.
In a 1000 square meter garden a considerable amount of biomasse (chipped wood, foliage, chopped bush) can be harvested. This amount holds an annual energy of about 4000 kWh. The following data are from energy forestry.
|Harvest per hectare||8 to 12 tons|
|Energy contents of biomass||3,86 kWh per kg wood (at 20% residual moisture)|
While the heating of older dwelling houses require more than 20,000 kWh per year, the recently developed well insulated houses require less than 10000 kWh. For example, the House-in-a-House can be easily served by a compost heater silo of the size 2000 l, making the interior of the house comfortably warm throughout the year.
Further Information on the Internet
- European bioconversion projects and realizations for macroalgal biomass: Saint-Cast-Le-Guildo (France) experiment, reference to Pain method of breaking down wood chips in relation to the composting of macroalgal biomass
- DIY Water Heating with Compost, article in Mother Earth News (July/August 1981)