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Compost heater silo

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Revision as of 21:32, 13 July 2019 by Carlosia (talk | Contributions) (re-arranging the pictures)
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Compost silo inside a dwelling house

The Compost Heater Silo is the central part of an inhouse compost heater. The composting process is run in an airtight silo, placed in an appropriate part of the building. 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 autumn the silo is filled up with fresh biomass, after which the silo delivers comfortable heat all winter long.


Construction of the silo

Inlet air and outlet air provide the necessary oxygen supply for the microbes and invertebrates in the silo. To avoid a bad smell, the outlet air must go out to the open, and it must be protected against incoming animals (mice).

The moisture in the silo must be high enough to support the composting process, providing optimal conditions for microbes and fungi. After successful start the decay process produces additional water, which is drained at the bottom of the silo. This water can be put in to the top of the silo for better distribution of the microbes in the whole processing volume. If pumped periodically or continuously to the top and let it rinse through the silo the whole system becomes similar to the wet composting (C.R.O.P. Project of the DLR[1][2]).

Optionally, the composting process in the silo can be used to heat up water, which requires the additional installation of a vertical water pipe in the silo, maybe in combination with a hot water storage tank.

Pre-Heating of the Inlet Air

Using a heat exchanger for the inlet air
Using an existing waste water canal for the inlet air

The outlet air is leaking part of the heat. There are a few solutions to reduce this:

  • An optional heat exchanger can be built in, which withdraws heat from the outlet air and increases the incoming air temperature.
  • Connecting the air inlet to a waste water canal. The construction utilizes the venting of the canal while adequately prevents influx of waste water into the silo. Usually, there is warm air rising from a waste water canal. Although foul-smelling the air contains enough oxygen for the well-being of the microbes and invertebrates.

Conditions of Usage

The amount of produced heat is limited. The size of the compost heater silo must be adapted to the actual heat energy demands of the building. For example, the House-in-a-House concept is suitable for it due to the very low heating requirements. For calculations refer to the respective paragraph in compost heater.

Existing Systems

Prototype of size 300 liter for feasibility study. It serves for research on the features and their optimization. The system has been working since September 2017 and is doing very well.

Planned Extensions

Doppelwandige Ausführung zur gerichteten Abführung der Wärme über Warmluftschächte
Weiterleitung der Wärme mit einem Wasserkleislauf
Mit Vorratsbehälter für Warmwasser im Inneren des Silos

Concret and Tiles

The final setup for heating a dwelling house will be made from thin layered concret, encased with tiles. It will resemble a tiled stove.


The silo will be double-walled, which allows better channeling of the warm air. If less heat is wanted, say on a warm spring day, the excess heat can be lead away into the open.

Water Heating

A heat storage tank for warm water will be placed in the center of the silo. The tank absorbs thermal energy from the surrounding decay process. The warm water can be used for domestic usage. The best performance is achieved if constructed as layered or stratified charge storage.

Combination with a Toilet Function

When combined with a composting toilet, the system will serve as a heater and a toilet at the same time. For convenience the toilet input is located on the upstairs floor, where the biomass inlet is combined with a toilet seat. In contrast to a dry toilet the excreta are processed in a wet environment and therefore much faster decomposed.

Information on the Internet