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Old 01-31-21, 06:42 AM   #2
IamIan
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Compost pile heating.

A fairly good book is "The Compost Powered Water Heater" .. not perfect , but a good place to start.

There is roughly the same wh of energy weather the material is burned or composted .. A well made compost pile has a potential for a small thermodynamic efficiency benefit because burning usually leaves allot of heat energy in exhaust gasses going out a hot chimney .. a compost pile can have much less heat 'going up the chimney' .. colder temperature exhaust gases .. but if the compost pile is outside and uninsulated , than allot of the pile's wh of heat it produces / converts .. will get used / lost just to heat the pile itself from those colder outside ambient conditions (lower net efficiency) .. and if you insulate it , you add cost , complexity , etc.

It does vary .. leaves vs paper , type of wood , etc .. but a basic average for common composted hydrocarbons is around ~5kwh per kg .. although not all compost kg are those wh containing hydrocarbons .. for example water content is needed for the biology of the compost pile to function , but the kg of water does not bring with it kg of hydrocarbon wh fuel chemical energy.

Compost pile is vastly slower than burning (stove or such) .. slower to get up to temperature .. hours to days instead of minutes .. and slower to process the same kg of fuel .. the easiest hydrocarbons break down over days to weeks instead of minutes to hours .. the most resistant hydrocarbons break down over months to years instead of minutes to hours.

Condition Complexity .. A stove burn style is fairly simple (in comparison) operating conditions .. fuel that isn't too wet (the drier the better can't be too dry) .. enough oxygen for combustion (if damper turned down it goes slower but doesn't stop entirely) .. start slow (kindling) and build up to a hot fire .. Composting can be either .. less complex , when years are available to process the kg of fuel , or for very large piles .. it will basically happen all by itself (actually difficult to prevent) if given a big enough material in a pile and enough time .. the smaller the pile and the faster one wants the kg to be used the more complex / details kreep in .. what is the moisture content (not too wet, not to dry) , what is the the O2 ratio content , trace nutrients (available nitrogen , etc) , operating temperature (not to hot , not to cold) , etc , etc.

I have leaves , junk mail , etc .. every year .. and if needed (free to me) where I work has a hundreds of tons of wood waste they dispose of every year .. about a dozen or so people take some home for their wood stoves , fire pits , etc.

Both have a start up cost .. cost to buy and install a wood or pellet stove .. or a cost to buy and install compost pile heating .. it is easier legally to do the compost pile heater .. Here in RI (legally) I would have to pay a licensed pro to install a fire place / wood stove / pellet stove / etc .. and the stove itself has to have been EPA approved .. soo, no DIY home made , or some of the old versions .. etc .. but compost piles do not have such restrictions .. DIY is encouraged .. it can't smoke or catch fire .. but both of those is a failure case to be avoided in design anyway.

The time investment for a compost heater is more concentrated .. subjective if that's good or bad .. you spend ~98% of your invested time at the ends .. beginning and end .. A wood stove / pellet stove / etc .. unless you your entire winter heating fuel in some type of automated fuel delivery to stove heating system , you spend __ of your time every day feeding the stove .. the compost pile heater concentrates all that time .. setup time and then end tear down time , but (ideally) doesn't require your time day to day , week to week , etc.

Space investment .. The wood / pellet stove itself as a reaction space is compact .. but the chimney also uses space .. __ tons of pellets ... or __ cords of wood also eats space .. total combined space is roughly about the same either way .. compost pile or stove .. but .. the orientation and type of the space is a different mix between them.
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