Mike Haasl wrote:As long as the compost gasses can't get into the system, it seems like it should work. Maybe have the fan pushing the air towards the compost so that the pipe is positively pressured when going through the compost to avoid any chance of gasses getting into the room.
Mike Haasl wrote:I'm glad you said 80-90 feet, that suggests to me that you have a decent feel for the amount of surface area of pipe that needs to be touching the compost. Would the black corrugated drain tile (non perforated) be an option? I think you want a lot of turbulence in the air stream to increase heat transfer.
There are some calculators that have been used to calculate GHAT systems for geothermal air transfer for greenhouses. I think SunnyJohn was one that isn't available anymore but searching for that and GHAT could get you connected up to a calculator.
Mike Haas wrote: I think you want a lot of turbulence in the air stream to increase heat transfer...
Directly heating air with a compost pile is also possible as Jean Pain shows. By burying a 125mm [5"] air duct in a 50 ton pile, a 12m3, uninsulated forest shed can maintain a constant temperature of 52°C for 8 months. This system used a thermo siphon effect, the hot air coming in at the ceiling of the shed, and the cool air falling to the floor and exiting through a pipe there.