The Compost Heat Exchanger Project

Our project is the design and construction of a compost heat exchanger that will heat a rainwater storage tank within the greenhouse at the Radix Center in Albany.  At the most basic form, the heat exchanger is a compost pile built from bark mulch, wood chips, and manure that has a polyethylene hose transporting water throughout.  Cold water is pumped into the pile and the effluent water is hot due to heat exchange between the compost pile and the water within the hose.  The heat is the result of bacteria aerobically breaking down the carbon and the nitrogen in the compost pile.  This is a sustainable way to heat water, as it has minimal energy inputs and the only waste product is fresh, usable soil.

Video of Heated Water Flowing from the Outlet Tubing

Water leaving the system was found to be reaching temperatures over 120 degrees Fahrenheit; this alone proved the system to be functional and effective for heating water in a sustainable manner.

Testing and Tube Connection Photos

Visual of the temperature prob used take measurements of the system. The hottest areas of the pile were found to be reaching temperatures of over 130 degrees Fahrenheit

Measurements of temperature through ought the system were taken. The data shows that outsides of the pile were warmer than the middle, while vertical location showed now correlations. We believe the outside was warmer due to easier access to oxygen through convective forces. 

Brad taking temperature measurements on different locations of the compost pile. 

Laying the insulted tubing into the trench that leads to the greenhouse.Insulation from the tubing as well as the Earth will stop the water from losing heat on its way back to the greenhouse. 

The compost pile next to the shed where the tubing will go to and from. You can see the unconnected tube on the top of the pile.

Some of the guys hard at work digging the trench. This trench will provide more insulation to the already insulated tubing carrying the water to and from the greenhouse.

Pumping Systems

Pump to move water through the compost and water storage tank system. 

Pump that will be able to measure temperature of water going into the fish tank.

More Construction Pictures

Laying the preliminary tubing that will allow oxygen to enter the system, then rise. Heat producing bacterial processes use oxygen as an electron acceptor.

Layering the bottom of the compost pile

 Inserting water tubing to the system. 3 100ft coils were placed 18'' apart for a total of 300ft. This would allow for plenty of time for the water to become heated. Hay can also be observed on the outside to help preserve the overall shape and insulatioTubing was spaced 6in apart with the use of stakes. This separation would allow for better insulation and a more successful heating process. 

ompleted pile. The system was hosed the entire time to provide an ideal moisture content. Moisture is ideal for living organisms...too dry of a system would slow or stop the composting process.