Composter heating

What about putting together a "Biomeiler " or compost heater?  These can be built relatively inexpensively and quickly and will produce useful heat for several months.  Just about any organic material can be used including wood chips, tree leaves, manure, tree trimmings, and yard waste.  Unlike burning wood products, the fuel doesn't need to be dry.  In fact, it needs to be wet!  Also, relative to combustion devices, there is much less or even zero concern about permitting, insurance, certifications, and environmental regulation.  I suspect usable fire wood might be in short supply as everyone looks to it as an alternative fuel.  Far fewer people will be competing for organic waste products.  Even if you can't produce all the heat you need it might significantly reduce the amount of additional heat needed from conventional sources.

jack vegas wrote:What about putting together a "Biomeiler" or compost heater?  These can be built relatively inexpensively and quickly and will produce useful heat for several months.  Just about any organic material can be used including wood chips, tree leaves, manure, tree trimmings, and yard waste.  Unlike burning wood products, the fuel doesn't need to be dry.  In fact, it needs to be wet!  Also, relative to combustion devices, there is much less or even zero concern about permitting, insurance, certifications, and environmental regulation.  I suspect usable fire wood might be in short supply as everyone looks to it as an alternative fuel.  Far fewer people will be competing for organic waste products.  Even if you can't produce all the heat you need it might significantly reduce the amount of additional heat needed from conventional sources.

That is a fascinating idea.  Nobody had yet thought about this option, including me, but compost heaters are indeed cheap and effective.  You can learn more about building a Jean-Pain-style compost heater here:

https://www.youtube.com/watch?v=-Jm-c9B2_ew
https://www.youtube.com/watch?v=kXvKcvrvqPE
https://permies.com/t/43035/composting/Heat-house-Compost

But my thoughts immediately run to the Cons:

- If you live in anything like an urban or suburban environment, it might not work.  You need a little bit of yard space adjacent to a window.  Compost heaters for high rise apartments are not an option.  And even if you have the space at ground level, do you have the privacy?  This is not a concept that your close neighbors will likely endorse, unless they're free thinkers or you live in a run-down area where nobody gives a shit.  A Home-Owner's Association will never let a compost heater fly.
- You would have to improvise a pass-through built into a window to pipe the hot water from the compost heater inside the house, where it could be circulated through radiators.  See photos I posted above showing a window pass-through stove pipe; something similar could easily be built.  Or you might just slip a small-diameter PEX pipe through a cracked double-hung window and stuff the rest of the crack with a towel.
- The whole system - compost pile and window pass-through - will be highly visible.  There is no way to escape the notice of neighbors/landlords/local authorities.  Jack Vegas proposes that a compost heater would not draw the ire of local code enforcement.  Perhaps, but my guess is exactly the opposite.  Bureaucrats do not encourage individual initiative, innovation, or just about anything that does not fit into one of their pre-approved check boxes.  Hell, I wouldn't even try to get a compost heater past the code officials here, and I live in a US state more laissez-faire than most.  If they don't understand it, they won't go for it.  The difference is that I could hide mine, if I were to go down that route, and no inspector will come randomly snooping to discover it so long as neighbors don't complain.  It has already been noted, above, that German inspectors do exactly that!

Matthew - you make some excellent points!  Thanks for the thoughtful comments.  Though I'm certainly not an expert, I will try to address your "cons" with thoughts on how some of them  might be overcome.

First, my frame of reference - I live on a remote part of the Washington coast in a poorly insulated 750 sqft cottage on 1/4 acres in a small community of maybe 30 other houses.  Outside city limits but within county jurisdiction where building and health codes are enforced.  Winter temperatures are generally between 20 and 40 deg-F.  Certainly not as cold as Germany (spent 3 wonderful years there when I was a kid) but cold enough.

Several years ago I built a very small indoor "pile" in a 55 gallon steel drum.  It had a small computer fan to circulate fresh air and the exhaust was dumped through the kitchen ceiling fan vent.  An automotive electric window motor was used to rotate the drum periodically to keep all material inside uniformly damp and break up any clumps.  All this was enclosed in a box made of 2" foam insulation that allowed heat to build as the bacteria did its work.  The heat produced soaked through the steel drum and heated the air inside the box.  Once the temperature inside the box exceeded 130 deg-F a fan pulled air through the box and dumped the heated air into the room.  If the box exhaust temperature dropped below 120 deg-F, the fan cut off.  I kept it running continuously by feeding organic material daily.  It actually worked relatively well and kept the house temperature between 55-60 deg-F.  During the day I augment with electric heat.

I mention this as an illustration of how compost heat might be generated in a small apartment.  I doubt if anyone would notice or care if one or two of these were installed in an apartment and the vented air really has little odor if the unit is working properly.  There is a slight earthy smell, similar to fresh potting soil and it really doesn't even need to be vented.  I vented mine to avoid humidity build-up since that is a problem in my location.  The downside of this unit was its mechanical complexity (I'm a machine nut) and its need to be fed often due to its small size and high rate of bacterial activity.  Also, it was relatively small so it had a limited heat output.

A more powerful "pile" that I'm considering building this winter would be contained in an insulated box 4 ft x 4 ft x 8 ft long that will sit in my backyard. No mechanical devices this time, just an insulted box filled with organic material.  It will have two rods running through it with paddles welded along their length that I can hand crank periodically to stir the contents.  This will be a closed box, painted to match my house and I doubt if anyone will notice or complain.  Local regulation allow an un-permitted shed up to 120 sqft so I don't think this will break any codes and certainly no HOA regs (we have a few but sheds and even compost piles are allowed).  I really think this is an approach that could work for just about any suburban house without raising many eyebrows.  I'm hoping it will produce enough heat over 4 months to keep the house interior above 60 deg-F.  If it does, sun on the house should raise daytime temperatures well above 65 deg-F.

As might be noted, I'm not a fan  of the Jean-Pain-style "pile".  I like the idea of containing the organic material in an insulated structure that allow heat to build rapidly and evenly giving better control of heat production.  Insulated piles can have very high rates of bacterial activity.  The end goal is not compost but complete digestion of the organic material for maximum heat production.

It's a neat idea, but I don't think it would realistically produce enough heat to help the OP in a country with genuine winter.

This would make a great stand-alone thread though.

jack vegas wrote:Several years ago I built a very small indoor "pile" in a 55 gallon steel drum.  It had a small computer fan to circulate fresh air and the exhaust was dumped through the kitchen ceiling fan vent.  An automotive electric window motor was used to rotate the drum periodically to keep all material inside uniformly damp and break up any clumps.  All this was enclosed in a box made of 2" foam insulation that allowed heat to build as the bacteria did its work.  The heat produced soaked through the steel drum and heated the air inside the box.  Once the temperature inside the box exceeded 130 deg-F a fan pulled air through the box and dumped the heated air into the room.  If the box exhaust temperature dropped below 120 deg-F, the fan cut off.  I kept it running continuously by feeding organic material daily.  It actually worked relatively well and kept the house temperature between 55-60 deg-F.  During the day I augment with electric heat.

Wow!  I've never heard of an interior compost heater before.  That is way cool.  I can definitely see that you are a machine nut, but I still think that your design could be achievable by most people with a little bit of work.  My first thought is that you don't need a motor to turn the compost drum; that could easily be achieved manually.  Clearly it's already mounted on bearings, so just remember to give it a couple spins whenever you open up to add your scraps.  And you said yourself that your whole venting system was mostly optional, as the compost smell wasn't offensive.  If that part was skipped, then we've really just got a steel barrel on bearings with some sort of sealable access hatch, a wooden box with sheet foam insulation, and an electric fan on a very simple thermistor control circuit.  I could build that, no problem.

The upfront cost would be nominal; not non-existent, but still a tiny investment.  And the fuel would be super cheap, if not free.  Yard waste and food scraps would go a long way if you could gather from all your neighbors.  I'm imagining several of these set up and running at once, one in each room perhaps, and I'll bet you'd need no other heat source in any decently-insulated, weather-proofed home.  The only downside is the amount of square footage sacrificed.  There is also some minimal daily maintenance (feeding more organic matter to the digester), though that would certainly be equal or less than the time needed to tend a woodstove.

jack vegas wrote:A more powerful "pile" that I'm considering building this winter would be contained in an insulated box 4 ft x 4 ft x 8 ft long that will sit in my backyard. No mechanical devices this time, just an insulted box filled with organic material.  It will have two rods running through it with paddles welded along their length that I can hand crank periodically to stir the contents.  This will be a closed box, painted to match my house and I doubt if anyone will notice or complain.  Local regulation allow an un-permitted shed up to 120 sqft so I don't think this will break any codes and certainly no HOA regs (we have a few but sheds and even compost piles are allowed).  I really think this is an approach that could work for just about any suburban house without raising many eyebrows.  I'm hoping it will produce enough heat over 4 months to keep the house interior above 60 deg-F.  If it does, sun on the house should raise daytime temperatures well above 65 deg-F.

Also a good design.  And again, something I'd not considered.  You didn't specify: will the heat transference from this outdoor box composter be via air or water?  What do you imagine you will rig up for the penetration into the interior of your building envelope?  Do you envision this being a one-pile-one-season device, or do you plan to regularly feed it?  You could fit over 4 cubic yards of fuel inside your box, which I'm going to guestimate is comparable to a classic Jean Pain pile.  And those have been proven to generate heat for several months, depending on composition of the compostable fuel.  I understand that you can coax a longer heating season out of a compost pile heater by making the mix more carbon-heavy, at the expense of lower continuous thermal output.

jack vegas wrote:As might be noted, I'm not a fan of the Jean-Pain-style "pile."

Yeah, I gathered that.  But I'd say your designs are taking his concept to the next level.  The basic Jean Pain approach is simple, easy, and cheap.  Whereas, with a little added complexity and investment, you have achieved greater versatility (indoor or outdoor options), greater efficiency, and greater aesthetic appeal.  I think this last attribute is perhaps the most important, for reasons you already pointed out: it opens up the utility of compost heaters beyond the rural venue into the suburban.  Perhaps even into the urban, though then you'd certainly be dependent on importing all of your fuel.  Aesthetically "clean" compost box heaters could become widespread.  Perhaps one day even mainstream.  And they have great potential for "below the radar" installations.  For the OP of this thread, that might prove critical.

Douglas Alpenstock wrote:This would make a great stand-alone thread though.

Yes, it really would!  Hint, hint, Jack Vegas ; )

Matthew Nistico wrote:

jack vegas wrote:First, my frame of reference - I live on a remote part of the Washington coast in a poorly insulated 750 sqft cottage on 1/4 acres in a small community of maybe 30 other houses.  Outside city limits but within county jurisdiction where building and health codes are enforced.  Winter temperatures are generally between 20 and 40 deg-F.  Certainly not as cold as Germany (spent 3 wonderful years there when I was a kid) but cold enough.

I'm imagining several of these set up and running at once, one in each room perhaps, and I'll bet you'd need no other heat source in any decently-insulated, weather-proofed home.  The only downside is the amount of square footage sacrificed.  There is also some minimal daily maintenance (feeding more organic matter to the digester), though that would certainly be equal or less than the time needed to tend a woodstove.

Ah man, now you've got me intrigued with the idea of interior compost heaters for my own property!

My winters are mild, I'd say very comparable to yours: 20-40 degrees F.  The house I'm building is much larger than your little cottage (about 2000sq ft), but also super-insulated and efficiently designed (passive solar straw bale).  It will use a single modern woodstove, which on paper should be more than adequate to heat the structure.

Once building inspectors are gone and never to return, I'm currently planning two modifications relative to heating.  First, installing a DIY solar air heater.  Second, removing the woodstove and installing a rocket mass heater in its place.  I should have more than enough fuel production off of my own small property (1 acre, heavily wooded) to run the RMH.

But now I'm thinking that I could chip all of that same wood, mix it with some nitrogen-rich inputs, and use it to fuel multiple indoor compost heaters based on your 55gal steel-drum-in-a-box model.  There are nearby farms from which semi-composted manure can be purchased cheap by the truck-load; I've done it before.  I could probably fit two drums in the space I've set aside in my Great Room for the RMH.  Perhaps combined with my solar air heater that would suffice?  If not, I could find places to stash an extra few drums elsewhere in the same Great Room and/or in various bedrooms.

PROS:

- I could likely set up these compost heaters for even less than I'd planned to spend on building the RMH.
- They represent a modular investment: start with a couple the first winter, and add more if needed.
- They need not be permanently installed.  I could move them to somewhere less in the way during the warm seasons.
- If I were willing to forgo recovering the capital investment from my woodstove, I could leave it in place and unused next to the compost heaters.  If my life plan were to change someday, this would greatly facilitate selling my home, compared with having an illegal and difficult to remove RMH.
- Most importantly... a well-built RMH is much safer than a woodstove, which is in turn much safer than a fireplace.  But an RMH still involves combustion, which is inherently dangerous.  Whereas the probability of burning down my house with a compost barrel is 0.00%.

CONS:

- If I ended up using 3 or 4 or 5 composters, I would be loath to give up all of that additional floor space, particularly in bedrooms.
- Fire is pretty and fun to play with!  Though I say this as someone who has never before depended on wood heat throughout a winter.  Still, I can imagine no social value from sitting around watching the compost digest.

Matthew Nistico wrote:Still, I can imagine no social value from sitting around watching the compost digest.

Hahaha!

Douglas Alpenstock wrote:

Matthew Nistico wrote:Still, I can imagine no social value from sitting around watching the compost digest.

Hahaha!

On the other hand, if Dr. Doolittle could 'talk to the animals', perhaps this would be that golden opportunity to learn how to 'converse with the microbes'!

John Weiland wrote:

Douglas Alpenstock wrote:

Matthew Nistico wrote:Still, I can imagine no social value from sitting around watching the compost digest.

Hahaha!

On the other hand, if Dr. Doolittle could 'talk to the animals', perhaps this would be that golden opportunity to learn how to 'converse with the microbes'!

In a clear container with coloured lighting and a little heat at the bottom for convection, it could be like a lava lamp.

Everything above here was copied from the thread What heat to use when supply chains break down?
It is a fascinating idea, I'm looking forward to seeing what y'all come up with on it!

Really love the creative thinking here!
Come to think of it, the need for warmth in the high-altitude mountain winters could have been the reason ancient communities in the Southwest built new homes on top of older homes. The lower natural building was filled with decomposing organic material (often called "trash middens" by archeologists) that could have conceivably produced the heat for the new upper home.

One of my issues on the Pacific Wet Coast, is that we're so wet in winter, and too cold and dark to grow stuff, that I don't like adding urine to plants then. (I'm worried about it running into the high water table and becoming a pollutant.)  I've been trying to come up with a urine system that will work - sawdust barrel with mostly urine added? I'm not sure compost really works when it's just wood carbon and nitrogen and little else.

So the question becomes, would the barrel idea work with just sawdust and some urine added on a daily basis? Would enough composting happen to create warmth? Would it just turn into a stinky mess? Is my thinking right that it would work better if the compost was damp to begin with? Might I need to add other things to help - coir comes to mind, although it's an import. I do have plenty of moss growing around here - would it help with moisture control and absorption? (I recall the Indigenous People used some sort of moss as their version of diapers.)

I definitely would love to see more people experimenting with this concept. Even if one's climate is too cold for this to provide all of one's winter heat, houses often don't heat evenly - our two west-most bedrooms can get *really* cold under certain weather conditions, so a barrel system in each could make the difference - we wouldn't have to over-heat our east rooms with wood heat, just to keep the bedrooms from going moldy!

Jay Angler wrote:I've been trying to come up with a urine system that will work - sawdust barrel with mostly urine added? I'm not sure compost really works when it's just wood carbon and nitrogen and little else.

Sure it will.  Compost is very forgiving.  Ideally, you want the perfect mix of carbon and nitrogen content.  But if you don't have that, it doesn't mean your compost pile is a total loss.  If you have nothing but "carbons," say a pile of woodchips and nothing else, and you leave it outside long enough, it will compost.  It will take forever and might not get that hot, but it will compost.  Same same if you have nothing but "nitrogens," say a pile of pure kitchen scraps.  It will get all stinky and slimy, but it will compost.  Neither of these situations is ideal.  In the ideal situation, with a balanced mix, your pile composts in a nominal timeframe at a high temperature with minimal smell.  But the fact remains: provide organic matter with adequate moisture and adequate time, and decomposition will occur.

If anything, I might worry that compost produced from organic matter lacking in diversity - just sawdust and urine, for example - won't provide maximum fertilizer value compared to a more mixed pile.  Different organic feedstocks provide different micronutrients and trace minerals, for instance, though I really don't know how big a deal that is.  Any compost is still better than no compost.

But that isn't even a concern in this case, since the primary objective is heat rather than fertilizer.

Jay Angler wrote:So the question becomes, would the barrel idea work with just sawdust and some urine added on a daily basis? Would enough composting happen to create warmth? Would it just turn into a stinky mess? Is my thinking right that it would work better if the compost was damp to begin with?

Of course I cannot yet say from experience, but my educated guess is yes, it would work.  If you get the C:N ratio right, your compost pile should decompose at a good temperature.  I don't think the bacteria care from where the carbon and nitrogen are coming.  And again, assuming an ideal ratio, I see no reason to think that it would generate more stink than any other compost pile.  Even the urine by itself doesn't really smell too bad if you handle it while still fresh.  And if you avoid eating asparagus ; )

Yes, the composting process does require moisture.  Too dry, and organic waste mummifies rather than decomposes.  I would guess that a good mix of compostable ingredients would provide adequate moisture on their own, particularly if your N source is a pure liquid, as in urine.  But in any case, with trial and error you would quickly learn whether an additional sprinkle of water is required, and how much, and how often.

Another consideration is air flow.  I imagine that your indoor compost barrel needs to be sealed up tightly, since you are spinning it to mix the contents and you don't want leachate to drip out.  Deprived of fresh air, the culture of decomposing microbes will eventually go anaerobic.  That, I do believe, would create a stinky mess!

In Jack's prototype system, he reported implementing a small, forced-air ventilator.  He said it was intended primarily to vent excess moisture outside of his house.  I would like to avoid that feature, if possible, to simplify the system.  A composting barrel without such a ventilator could be positioned anywhere in the house, whereas his was positioned where it could connect to an existing exhaust vent.  Lacking a mechanical ventilator, would opening up the barrel once a day to add fuel provide enough air exchange to keep the compost oxygenated?

I don't know, and I don't know how to calculate the answer, either.  Perhaps someone else knows?  Sufficient trial and error would also provide the answer.  But a ventilation fan should not be necessary.  If opening the barrel daily proved insufficient, then opening it X times per day would certainly suffice; you just need to determine how often.  If too often, then the maintenance/hassle factor might detract from the value of the whole system, and might suggest that adding a fan is worthwhile, after all.

Also, I wouldn't want to worry about going away for a long weekend and my compost heater "dies" in the meantime.  You are maintaining a living culture, and so it will require care.  This also argues for a ventilation fan.  Perhaps leaving the feed door cracked open when away could be a workable alternative?

@Jack Vegas - Could you please post photos of your existing barrel heater and its various features?  That would be excellent!

Yikes!  This really took off!  First, my sincere thanks to Pearl for making this a thread!  I probably would never have done it on my own and I really appreciate having a place that this can be discussed.  I'll try to catch up with some random responses, but let me reiterate, I'm no expert.  Just a curious experimenter so I'm looking for input just like everyone else.

1) Yes, Jay Angler, sawdust and urine works!  My original intent for the barrel in a box was to make a pellet stove without combustion to circumvent code and insurance problems.  I thought it would be cool if a renter or apartment dwellers could use one as a portable appliance that wouldn't jeopardize their lease.  Wood pellets are basically sawdust and once you get them wet so bacteria can digest them, they revert to wet sawdust.  I used urine as a handy source of nitrogen to get things going... so to speak.  The smaller the particle size the faster it digests, so sawdust gets things hot quickly (like hours not days) and require feeding the unit more frequently.  The result is a lot of heat quickly from a small unit.  For this reason I figured wood pellets would be an ideal material for a small high performance unit.

2) Matthew - to clarify, I used a small fan to circulate air through the barrel to both to introduce oxygen and to exhaust CO2 and water vapor.  The flow rate is low and there is no reason it can't be dumped into the room if things are running properly.  If things don't run right and the little critters don't get enough oxygen, things can become anaerobic and smelly.  I vented outdoors primarily because I have a humidity problem.  The bacteria doesn't need trace elements to survive.  They eat glucose from the organic matter and water and poop out CO2 and heat.  Most trace elements in organic matter are fine, but some of course are toxic.  Most common yard and forest materials are fine.  Sorry, sadly no pictures.  Victims of the great back-up drive crash in 2018.

Some general notes:

Bacteria are tough little critters but they are living creatures and need care and feeding to prosper.  Too hot, too cold, not enough oxygen or water, and they die.  If we make sure these factors stay within proper bounds, they live and make heat.  Stray outside the limits because they are suddenly chilled because a lot of cold fresh material is dumped into their cozy little lair too quickly, and they die... quickly.

Digesting one pound of material releases about 8,000-9,000 Btu.  To digest 1 lb of material per hour, air flow should be about 7 CFM.  Only about 1.2 CFM in needed to provide adequate O2, but exhausting CO2 and water vapor required the full 7 CFM.  Hence, by making sure that adequate flow is available to exhaust byproducts, plenty of O2 is available.

If fresh wet material is used very little water needs to be added.  If dry material is used, about 1/2 lb of water needs to be added to every pound of dry matter.

Mesophilic bacteria will bring temperatures up to about 120 deg-F.  After that they begin to die and thermophilic bacteria take over and generate heat at a much higher rate.  Somewhere beyond 150 deg-F they die and if they get colder than about 120 deg-F they also die.  Its important to keep them in the sweet zone of about 125 to 150 deg-F.

Such devices are nearly 100% efficient.  A couple percent is lost in the biological processes, and a couple percent is lost if it is vented outside.  If it is located indoors, all the rest goes into the space being heated.

Digesters aren't easily throttled.  The oxygen supply can be restricted somehat to slow things down, but generally they are either on or off, and if they are off, they usually need a couple days to get back up to temperature.

These things are basically wood stoves that use biological decomposition to make heat and CO2.  This means lugging many pounds of material into the house to keep it warm, be it fire wood, wood pellets, or yard waste.  Plan accordingly.

For a given volume, would an anaerobic system produce more heat?

Can't say with certainty, but two things make me think that pound for pound, aerobic digestion will produce more heat.  First, a large portion of the elements in the feed material remain as methane after anaerobic digestion, so what ever energy value it has is still locked up and has not yet been released.  Second, after anaerobic digestion is complete there is a relatively large fraction of the original material remaining as sludge that can be further broken down by aerobic digestion.

jack vegas wrote:Digesters aren't easily throttled.  The oxygen supply can be restricted somehat to slow things down, but generally they are either on or off, and if they are off, they usually need a couple days to get back up to temperature.

Yes, that had occurred to me.  I imagine the easiest thing to do on an unusually warm winter day, rather than attempting to fiddle with the airflow or refueling rate of the composter, would be just to open a window as necessary.  Once you've got a good daily rhythm going that you know will keep your compost culture happily humming along, I would be hesitant to break that routine.

I put together a more complete description of my "Barrel in Box" compost reactor to help people understand how it was built and how it worked.

Physical description with reference to the attached drawing:
The core of the unit is a 55 gallon steel drum with a removable head to facilitate loading and clean out.  A steel drum is used to maximize heat transfer and the inside and outside are epoxy coated to prevent rust.  The drum is mounted horizontally on four rollers allowing it to rotate rotisserie style.  The rotisserie motion is driven by a 12 volt automotive electric window motor (not shown).  Since I doubt the motor is rated for continuous operation it is controlled using an interval timer so that it runs for 1 minute every 30 minutes.  Periodic rotation is desired to keep the compost material evenly moist (a small water puddle is always present in the bottom of the drum) and also to break up any clumps so anaerobic regions don't form.

The drum assembly is enclosed in a removable box made of rigid 2" foam insulation with a 6 inch air gap between the drum and box walls.  The box limits heat loss from the system so that the compost can come up to and maintain operating temperature.  During operation a 12 volt 6 inch boat bilge duct fan pushes air into the box where it is heated and then exits the other side of the box through an 8 inch duct.  Not shown are thin plastic film flaps over the downstream side of the inlet and outlet ducts to minimize air entry into the box when the duct fan is not operating.  These flaps are lightly weighted with wood strips (tongue depressors) to minimize air entry into the box when the fan is off, but also allow the flaps to open when the fan is on.

A PVC pipe is rigidly mounted to one end of the box and penetrates a hole in the drum head.  The hole is slightly larger than the PVC pipe creating a small air gap so the drum can rotate without the pipe rotating and also to facilitate air flow into the drum to feed oxygen to the compost.  On the exterior end of this pipe a 2 inch 12 volt computer fan is mounted to pull fresh air through the drum head gap and then exhaust CO2 and water vapor laden gas overboard.  The PVC pipe also provides a convenient place to attach a thermocouple for remote monitoring of compost temperature.

Finally a small 12 volt 200 watt hair dryer is included to feed warm air into the box during startup and to help maintain temperature if the compost inadvertently chills too quickly during operation.

Operation:
Operation begins by turning on the rotisserie and hair dryer circuits.  The fan circuits are off during startup.  The hair dryer heats the air inside the box to about 125 deg-F.  Without the hair dryer the compost will slowly self-heat but the warm hair dryer air really kick starts the process and the compost is up to temperature in a matter of hours, not days.  There is enough oxygen in the air inside the system to allow the compost to reach about 100 deg-F at which point the fan circuits are turned on manually.  After that the computer fan stays on continuously.  There is little risk of it pulling cold air into the reactor since it draws from the larger heated box surrounding the drum. The computer fan is on a rheostat which provides some degree of throttling.  The main duct fan uses a thermal switch that turns the fan on whenever the temperature at the box exit exceeds 135 deg-F.  At first it cycles fairly often but as the compost heating builds it runs for longer and longer periods.  I adjusted the fan discharge using a rheostat so that even when fully operational the fan cycles off briefly after 15-20 minutes.  This is to ensure that it will still cycle for even longer periods if heat output increases unexpectedly.  Eventually I planned to insert a rheostat override circuit if temperature exceeded 150 deg-F so the fan would throttle up to maximum speed to cool runaway heating which could kill the bacteria.  The hair dryer circuit uses a thermal switch to turn it off whenever temperature exceeds 125 deg-F.  Once this temperature is reached during startup the pile continues self-heating rapidly.   Should the pile cool unexpectedly, the hair dryer will cycle on at 125 deg-F to prevent excessive cooling that might also kill the thermophilic bacteria.

I tried to make the system as bulletproof as possible so that it would be hard to inadvertently kill the bacteria.  It could be simplified considerably but that would require more attention and careful monitoring.  With the exception of the rotisserie interval timer, everything ran on 12 volts DC so that it could be battery powered during a power outage.  I never found a 12 volt interval timer I liked.

jack vegas wrote:I put together a more complete description of my "Barrel in Box" compost reactor to help people understand how it was built and how it worked.

Physical description with reference to the attached drawing:
The core of the unit is a 55 gallon steel drum with a removable head to facilitate loading and clean out.

Thank you!  A trove of useful info.  I was surprised, though, to learn that you feed the drum through a removable barrel head.  I assume that would be the "lid" of the barrel on the right-hand side, as it appears in your diagram.  How do you keep compost and leachate from spilling out into the box when you remove the head?  I would have guessed that you cut an access port into the side of the drum, with a screw-down cover over a water-tight gasket.  That way, you can rotate the cover to face up when you want to open it, and the compost would settle on the bottom of the drum, safely below the opening.

And you said that you open the barrel to feed more organic matter once daily, yes?  How much fuel do you have to add daily to maintain a constant compostable mass?

Matthew - You managed to identify one of the big problems with this design on the first pass.  Congratulations!  The illustration didn't allow for describing the feed approach I used.  As previously mentioned I did the initial loading and final clean-out through the removable drum head.  For loading during operation I had a small hatch in the box with a matching resealable port in the drum that allowed feeding the drum without removing the box.  If you face the left hand side on the drawing, the ports were at the 9 o'clock position.  I'd stop the rotisserie and fans, open the ports and pass fresh material into the drum.  It was tedious and it meant leaking warm air from the foam cocoon and feeding a lot of fresh cold material into the drum all at once which was definitely not good for the bacteria.  To make feeding a bit easier and faster I made a long tool from a piece of 6" PVC that was split in two to make a long trough-like scoop.  I'd fill the scoop, stick it through the ports, then rotate the scoop so it dumped it contents into the drum.

I'm pretty proud of the design from the standpoint of automating temperature maintenance for continuous high performance digestion, but from an operability standpoint it was disappointing.

Some problems and thoughts on possible solutions:
Rotating drum - many desirable mechanical adaptations were not possible due to the drum rotation and particularly due to the PVC pipe "wand" down its core.  At first I thought the wand was a pretty clever way of solving the rotational seal problem, but it prevented filling the drum more than about 40 % full due to leakage through the gap between the drum and pipe.  I'm fixed on the rotisserie approach because I think it does the best job of maintaining moist material and breaking clumps.  I've considered internal paddles but power requirements to push material with paddles could be excessive.  In my ideal design I'd use a stationary vertical drum, but I've never been able to adequately address all the issues to my satisfaction with that configuration.

Feeding - As described above, it was tedious, required breaching the thermal cocoon, and it meant dumping a lot of cold material into the drum all at once.  Ideally there should be a way of feeding small quantities of fresh material frequently or even continuously without breaching the thermal cocoon.  Since a lot of my experimentation used wood pellets I considered a pellet feed setup similar to a pellet stove.  That could probably be achieved but it would preclude using wood chips or yard waste.  Wood chips are very inexpensive where I live and I can get large quantities free in the fall from tree trimming services.  I also have a surprisingly large amount of yard waste on my property that I'd really like to use since I put so much effort into cutting it back in the fall.  A note of feed material.  Early on I scored an 800 lb load of wood pellets that had gotten wet because the owner had stored it outside.  Entirely useless to him but perfect for me and free for the taking!  Also, we use wood pellets for cat litter.  Urine soaked pellets... the perfect feed material and a great way of disposing of them!

Clean out - Clean-out at the end of a run was a pain.  I'd remove the box, withdraw the wand, then tilt the drum up onto its sealed end.  After that it was a simple job of rolling the drum outside on a hand truck, dumping the residue in the garden and hosing it out.  The pain was disassembling the unit to get to the drum.  I'm older now (72) and it would be neat to find a way of only handling the residue and not the whole drum.  I keep noodling on ways of cleaning it out like a wood stove... except in this case the ashes would be moist soil that doesn't blow around!

Heat transfer - though I've never run calculations, I think the drum could be a limiting factor.  Its volume is such that if full and running at high digestion rates, more heat might be created than can be transferred through the drum's steel walls.  I need to look into this.  It turns out that with continuous feed of small particles like sawdust or grass clippings, a small volume can generate a lot of heat when running in high performance thermophilic mode.  It would be nice to make sure adequate heat transfer is available to be able to use that capability.

Regarding your question about feed rate - Using wood pellets I could load 40-50 lb of pellets and once running well they were consumed at a rate of about 1 lb/hour.  This works out to an equivalent of about 8,000-9,000 Btu/hr depending on fuel quality.  If I could have filled it more than 40% full I feel I could have pushed output to 15,000 Btu/hr.

(I haven't read this entire thread, just saw urine and sawdust in a barrel and remembered seeing this video not too long ago.)  

In case it helps:  

Fascinating thread!
I think we can simplify the delivery of oxygen to the compost by using an aquarium air pump.
I think this would also eliminate the need for turning the compost.

I can think of a couple of ways it might work.

In a barrel or defunct water heater, we could use window screen to separate the solids from the liquids.
We place our air pump in the bottom reservoir of fluids and use it to power a lift pump, which will deliver escaped solids and oxygenated air to the top of the barrel.

Alternatively we build a basic compost tea aerating system with a bubble spewing manifold at the bottom and add our pee and sawdust to that.

We could shrink the foot print by using a defunct water heater, peeling off the sheet metal but leaving it insulated and adding more, and plumbing in a set of heat exchanging coils, one inside the tank, the other in front of a fan in the space to be heated.
Even if you cut the top entirely off, there will be multiple threaded openings available.

Another very available container option is a defunct fridge or freezer.

One nice thing about these "wet" designs is ways the results can be dispensed.
The liquid can be used for fertigation.

As to the anaerobic digester, my reading indicates that they need a heat input, if anything, to do the thing they do.

One year, while my husband and I were living in our 17' camper during the day and sleeping in the uninsulated living quarters of our aluminum horse trailer at night, I decided to seal the gap between the bottom of the trailer and the ground with a long pile of horse manure.  I decided fresh manure would compost and make the aluminum trailer warmer.  Not heated, but not freezing cold.  It actually helped a little, though the acid in the fresh manure etched the aluminum, and of course it was rather inefficient since I didn't turn the pile.

This spring I bought myself one of those plastic garden tumblers to compost my house scraps.  It's pretty extraordinary how quickly everything breaks down into beautiful crumbly dark compost (except for the pistachio shells).  There's no smell to it that I notice, and my nose is pretty sensitive to that.  I've been wondering what to do in the winter -- maybe I should just bring it inside, put it into a sunny spot, and keep composting!  

I do love the notion of a larger composter specifically for heat, though.  Even if it only warmed a little it would be that much less wood burned to keep the place warm in the winter.  Please forgive my ignorance, but why is the metal barrel in an insulated box with a fan sucking hot air out?  Why the insulated box at all?

Still, I can imagine no social value from sitting around watching the compost digest....
Mathew, you should at least try to watch some compost digest...It's faster than watching paint dry and smells waaay better ;

Good question Lif Strand, and boy do I admire you for sleeping in an un-insulated horse trailer sealed with manure!  I started with the insulated box because I wasn't using the hair dryer to preheat the system and needed to hold the heat till the system came up to a reasonable operating temperature.  With the hair dryer one could probably dispense with the insulation.  I'd still use the box though since it contains the heat to a large extent which results in more uniform heating overall.  It also serves as a heat exchange duct to guide the air flow over the drum.  What I describe is a high performance system that generates uniform heat throughout the compost so it all decomposes uniformly at high temperature.  It also digests nearly everything loaded.  There is little compost left once it is finished running.  Just a bit along with what looks like (and probably is) undigested mineral waste.  Very much like ash in a stove once all the wood and coals have been consumed.

William Bronson - I've played a lot with concepts for vertical barrels but have never built one.  I've always focused on how to provide the absolute optimum conditions for the bacteria so  I could maintain continuous high operating temperature.  That said I remain curious about systems that might be less than optimum.  How bad do they have to be before they don't work?  Everything is worth a try as long as the conditions needed for the bacteria to thrive are delivered.

Let me suggest a slight variation to your bottom water sump concept.  Inject air into the gap between the compost and water surface using a hair dryer like blower.  Initially the heat element would be on, heating the bed rapidly to operating temperature.  It would cycle on and off to maintain optimum bed temperature.  Once the bed generates enough of its own heat the heating element would no longer come on and just the fan component of the hair dryer would continue operation feeding fresh oxygen to the bed.  The computer fan from the horizontal concept would no longer be needed.  I think mixing would still be needed, but perhaps a simple paddle system could be used that is hand cranked periodically.

Combine this with Lif Strand's question regarding the need for the insulated box.  Don't use one.  The hair dryer will certainly allow the compost to reach optimum temperature.  The question is can it remain there once the heater is turned off.  If it does, then the insulation is not needed.  To prevent the compost from getting too hot, a simple box fan might be aimed at the outside of the reactor.  It would cycle on, or speed up, whenever the compost starts getting too hot.  The only missing element I see in this is a way to preheat hair dryer air when the heater is off so cold air is not introduced into the compost.  It might look something like the attached image.

A lot of the complexity is unnecessary if it is to heat a greenhouse.  I see using one of my old barrels that is solid on the sides but the bottom is rusted out.   What water that comes out the bottom screen goes into a planting bed soil.   It will replace one of the water filled barrels used for passive heat storage.  The lid will  be the top of a plastic barrel which I use for seed starting so the soil needs to be kept warm.   I will screw in plastic pipes in the bung holes to let the air exit the top of the barrel.  I will be using my riding lawn mower to gather leaves as they fall and dry grass from the field for fuel and add urine for nitrogen along with the wood based cat litter.  Probably will put it between 2 water filled barrels and log the temperature of the 3 barrels while I am logging the high/low thermometer each day.

I found this same time ago, hope it is of some help:

The Victorian method of growing pineapples had been lost but thanks to the restoration of the gardens on the Heligan estate near St Austell in Cornwall we know a lot more. The art of pit management was lost and in the absence of any written instructions, the staff had to learn through trial and error.

They found that temperature control and humidity are all important and the plants must not be over watered. Frequent changes of fresh horse manure are essential to keep up the temperature during cold periods and emptying and re-filling the trenches, either side of the pit, are tough and unpleasant manual tasks.

These trenches are covered with boarding to maximise the delivery of heat into the pit itself, through holes in their double-skinned walls. They have also realised that as the days of horse-power have long passed it’s increasingly difficult to source the quality, and expensive to transport the amount needed of freshly rotting horse manure required for a whole winter’s heating.

It has been quite a learning curve for the staff at Heligan. The current variegated variety when ready to harvest took five years before it even began to fruit, then another two to grow the fruit. With the hours it has taken to look after the pineapple, transport costs of manure, maintenance of the pineapple pits and other tasks, each pineapple would probably cost more than £1,000 to grow.

Although pineapple pits are heated by fresh horse manure but the pineapples themselves do not come into contact with any manure or urine at any stage. Manure is loaded into manure trenches behind and in front of the pit itself. The heat generated from the manure travels through the hollow walls and through the bark beneath the potted plants to recreate a tropical environment for them to grow in.

So this is a valuable exercise in learning just how the Victorians grew the exotic fruit and after restoring the pits at Heligan, keeping them in use is rewarding for the staff and for the visitors. Any pineapples that grow are given to members of staff as a thank you for their hard work.

https://www.countrygardener.co.uk/2020/01/08/how-gardeners-managed-to-grow-pineapples-in-england/

jack vegas wrote:Rotating drum - many desirable mechanical adaptations were not possible due to the drum rotation and particularly due to the PVC pipe "wand" down its core.  At first I thought the wand was a pretty clever way of solving the rotational seal problem, but it prevented filling the drum more than about 40 % full due to leakage through the gap between the drum and pipe.  I'm fixed on the rotisserie approach because I think it does the best job of maintaining moist material and breaking clumps.  I've considered internal paddles but power requirements to push material with paddles could be excessive.  In my ideal design I'd use a stationary vertical drum, but I've never been able to adequately address all the issues to my satisfaction with that configuration.

I can appreciate your position, Jack.  The alternate sketch, above, portraying a vertical drum system is intriguing.  But in the end, I agree that a horizontal rotating drum is preferable.  The convenience of setting it up for automatic intermittent rotation is just too irresistible.  Depending on manual activation of mixing paddles is not something I would want to introduce into the design.  For one, who mixes it at night?  Or when I am gone for the weekend?  For another, there is definitely a break-even point beyond which the hours of maintenance required for any heating system become too many hours.  Exceed that point, and it is simply not worth it.  Not when I could theoretically work an extra week, or less, earning enough money to buy electricity sufficient to heat my home all winter with zero maintenance required.  I'm just ball-park-estimating the expense involved in doing that, but you will take my point, I'm sure.  Of course, I'm not actually installing an electric heat system, but portable oil-filled electric radiators are cheap and surprisingly effective.

I've been thinking, and I can't arrive at a better solution for aerating the barrel than the central "wand" you originally used.  I can certainly see the limitations it imposes, particularly on your ability to fill the tank with fuel beyond 40%.  But so long as the tank rotates, any aeration solution simply must run down the central axis of the barrel.  Any off-center air ports would inevitably leak leachate or become clogged with compost.  The best I can come up with is this...



...but I don't think it's very good.  The idea is that the U-shaped PVC wand would be braced to the inside of the insulated box and remain stationary while the barrel rotates.  Only the length of the PVC inside the barrel would be perforated with many small holes, using a power drill.  I imagine these holes penetrating all portions of the pipe: top, bottom, and sides.  The upward bend of the two "U" ends are intended to keep any leachate that might settle inside the pipe from overflowing into the box.  I don't imagine too much should settle, though, as it would drain out the bottom holes about as quickly as it dripped in from the top.

The two problems I see are, first, that I have no idea if you would actually achieve enough air exchange between inside and outside of the barrel this way.  Second, I have a hard time imagining that you could really achieve a firm enough seal between the stationary pipe and the surrounding, circular lengths of rubber gasket affixed to the rotating barrel at the two penetration points.  I suspect it could leak if you fill the barrel with compost higher than "wand level."  It wouldn't leak compost, but it might leak leachate.  Perhaps it would leak only a very little, and be acceptable?  You could avoid this risk by filling only to below wand level, but then you might as well use the original, Jack-Vegas-proven design.

jack vegas wrote:Feeding - As described above, it was tedious, required breaching the thermal cocoon, and it meant dumping a lot of cold material into the drum all at once.  Ideally there should be a way of feeding small quantities of fresh material frequently or even continuously without breaching the thermal cocoon.  Since a lot of my experimentation used wood pellets I considered a pellet feed setup similar to a pellet stove.  That could probably be achieved but it would preclude using wood chips or yard waste.  Wood chips are very inexpensive where I live and I can get large quantities free in the fall from tree trimming services.  I also have a surprisingly large amount of yard waste on my property that I'd really like to use since I put so much effort into cutting it back in the fall.

Agreed: I wouldn't want to be limited to using pellets, either.  Assorted yard waste is too convenient, and wood chips can be had for next-to-free, as you say.  I currently have a giant pile on the side of my driveway, delivered by a trimming service.  Plus, my city collects and chips trimmings at a central municipal yard for use as mulch, which you can pick up for free.  Those two sources represent a limitless supply.  Though I would likely produce enough wood just on my own property.  Any way you look at it, pellets are pricey in comparison.

I have a proposal for more convenient feeding.  Not an ideal one, perhaps, but I think a workable one.  Step one, as I wrote previously, is to keep both ends of the barrel permanently in place and instead cut an access port into the side of the drum along its circumference - which would be on the "top" or "bottom" as depicted horizontally in our diagrams - with a screw-down cover over a water-tight gasket.  The cover would be cut from the side of another steel barrel.  Use stainless steel screws and wingnuts, and make the access port plenty large for ease of use: big enough to quickly stuff a large scoop into the barrel.  Featuring all flat pieces of metal and no moving parts, I'm sure that this gasket arrangement could be made to seal well.

Step two, mount the entire top of the insulated box on a hinge, so you can open it up entirely for quick and easy access to the barrel.  This will of course disgorge all heated air inside the box at once.  So you will be required to...

Step three, replace the 200W DC hairdryer in the original design with an AC hairdryer.  1.9kW AC hairdryers can be had from Walmart for $10.  With this extra electric horsepower, the initial "pre-heat" cycle when starting a new batch would go much, much faster.  So then, every day when you open the box to feed, the hairdryer would run again automatically in what we will now call its "re-heat" cycle, quickly returning the box interior to minimum operating temperature.  At my residential electric rate, if the hairdryer ran for a full hour to reheat the box, it would cost 17 cents.  Over a 3-month heating season, that is $15, which I can cope with.  And I could run the hairdryer for 1.5 hours off of my Jackery, if needed.

The rapid cooling won't be easy on our bacteria, but I suspect enough will survive for the culture to recover.  The problem of adding cold fuel remains, but that could be mitigated using hot water from the kitchen.  You reported previously that you add 50% of your dry fuel's weight in water.  Assuming 24lbs fuel, that's 12lbs water, equal to about 1.5 gallons.  1.5 gallons of water pre-heated to 140 degrees is a lot of extra energy to help the system recover.

jack vegas wrote:Clean-out at the end of a run was a pain.  I'd remove the box, withdraw the wand, then tilt the drum up onto its sealed end.  After that it was a simple job of rolling the drum outside on a hand truck, dumping the residue in the garden and hosing it out.  The pain was disassembling the unit to get to the drum.  I'm older now (72) and it would be neat to find a way of only handling the residue and not the whole drum.  I keep noodling on ways of cleaning it out like a wood stove... except in this case the ashes would be moist soil that doesn't blow around!

Clean out doesn't seem so daunting to me, but then I'm not 72 yet : )  Even though I am in a wheelchair.  One thing to clarify, though: you said that your system digests fuel to a very high percentage of totality.  So I am assuming you clean it out as described only at season's end?  If I had to disassemble, clean out, and reassemble multiple times throughout the winter, then yeah, I might be a little more daunted.

jack vegas wrote:Using wood pellets I could load 40-50 lb of pellets and once running well they were consumed at a rate of about 1 lb/hour.  This works out to an equivalent of about 8,000-9,000 Btu/hr depending on fuel quality.  If I could have filled it more than 40% full I feel I could have pushed output to 15,000 Btu/hr.

I am very curious to learn how you measured or calculated your output of 8-9K BTU/hr?  I am also wondering how that would compare with using wood chips instead of wood pellets?  Pellets are smaller and less dense, so more surface area per weight of fuel.  I'm guessing that this gives pellets a faster "burn rate," and thus a higher output per hour.  I think you said as much previously.  Do you yet have any experience composting chips?

I am assuming that you do not wait for your 40-50lb full fuel load to compost completely and then start a new load.  Clearly your system is designed for continual, steady output.  So, you refuel with about 24lbs every 24 hours?  Also, when describing your fuel load in pounds, is that total weight of carbons and nitrogens - in your case, the weight of your pellets pre-soaked in urine?  I would likely be using wood chips, or maybe wood chips mixed with some shredded leaves if I'm getting free mulch from the city, mixed with manure.  I seem to recall from somewhere else the recommendation of a 70:30 to 80:20 ratio of wood chips to manure for building a Jean Pain-style pile.  How do you react to that when thinking about your steel barrel digester?

Thank you again, Jack, for sharing about your amazing (unique?) experiment.  I remain optimistic!  Considering that my house's "design heat loss" is only about 20-24K BTU/hr, which of course describes the predicted coldest day of winter, and you can see my reason to be excited.  If I were to replicate your original design exactly, filled to 40% capacity, only substituting wood chips for wood pellets, I am still guestimating that I might fulfill nearly my total heating needs using only two barrels.  Recall that two barrels (probably inside a single insulated box) is the number I could install in my own house "cost free," which is to say they would occupy only the floorspace I had otherwise allocated for an RMH.  Recall too that I don't actually need them to meet 100% of my needs, as I also plan to use a solar air heater.

Hans Quistorff wrote:A lot of the complexity is unnecessary if it is to heat a greenhouse.  I see using one of my old barrels that is solid on the sides but the bottom is rusted out.   What water that comes out the bottom screen goes into a planting bed soil.   It will replace one of the water filled barrels used for passive heat storage.  The lid will  be the top of a plastic barrel which I use for seed starting so the soil needs to be kept warm.   I will screw in plastic pipes in the bung holes to let the air exit the top of the barrel.  I will be using my riding lawn mower to gather leaves as they fall and dry grass from the field for fuel and add urine for nitrogen along with the wood based cat litter.  Probably will put it between 2 water filled barrels and log the temperature of the 3 barrels while I am logging the high/low thermometer each day.

I'm super interested in providing some supplemental heat to my greenhouse (the one that's not yet constructed) this winter.  I hope you report how your system works as you develop it!  Photos, please!

Joe Grand wrote:I found this same time ago, hope it is of some help:
The Victorian method of growing pineapples...

I found a webpage with a cross-section diagram for a pineapple pit at the Lost Gardens of Heligan https://www.heligan.com/news/the-story-of-the-10000-pineapple  The equivalent of the $10,000 tomato that I'm so familiar with!  Actually, that design looks basically like what I tried with my "bedroom" horse trailer.  For it to work, though, there has to be lots of hot (freshly pooped) horse manure, and that means replacing cooked-out manure with freshly pooped, which would be a tough job if done by hand.  I suppose the troughs for the manure could be constructed just wide enough to get a garden tractor with a blade in it.  



Pineapple pit cross-section


Brick pineapple pit[/url]

I'm now musing on the idea of a long "pineapple pit heater" trough that butts up against my house, which is on short piers.  I'm a low-tech kind of person due to my low skill-levels, and I'm also always looking for solutions that don't require additional power (I'm totally off-grid), so the pineapple pit idea seems like a real possibility to me.

Hey Jack,

Gotta question for you. I have threatened myself to do an indoor 55 gallon drum pile this winter. I have been thinking of the idea for several weeks now. I had already started to prep a drum, last year(while living away from the house, caretaking a friend). I drilled the holes in it for standard outdoor compost tumbler idea. How did you handle any liquid removal from the drum when you did the indoor drum idea? I do have two other identical drums which I haven't did anything with as of yet, they are just sitting there waiting to be used. Granted I don't know if they are food grade or not. I got them for free a couple of years ago from the guy I was caretaking, they were at one of his rental properties and a former tenant left them behind when they moved out.

This thread is once again making me think more about the idea and think more about, since I think the drums don't have removal tops, about just how I would go about getting the compost out of the drum and more importantly, out of the house. I am starting to think of making the hole smaller(maybe already small enough) and instead of using a cart for hauling the compost, just use a 5  gallon bucket. You got the ideas flowing right now. Thanks.

Lif Strand wrote:

Joe Grand wrote:I found this same time ago, hope it is of some help:
The Victorian method of growing pineapples...

I found a webpage with a cross-section diagram for a pineapple pit at the Lost Gardens of Heligan https://www.heligan.com/news/the-story-of-the-10000-pineapple  The equivalent of the $10,000 tomato that I'm so familiar with!  Actually, that design looks basically like what I tried with my "bedroom" horse trailer.  For it to work, though, there has to be lots of hot (freshly pooped) horse manure, and that means replacing cooked-out manure with freshly pooped, which would be a tough job if done by hand.  I suppose the troughs for the manure could be constructed just wide enough to get a garden tractor with a blade in it.  

Pineapple pit cross-section


Brick pineapple pit[/url]

I'm now musing on the idea of a long "pineapple pit heater" trough that butts up against my house, which is on short piers.  I'm a low-tech kind of person due to my low skill-levels, and I'm also always looking for solutions that don't require additional power (I'm totally off-grid), so the pineapple pit idea seems like a real possibility to me.

That the article I read many months ago, I lost it, then googled the one I posted here.
Thank you for posting it!
It is amazing how much you can do off grid, when you have unlimited resources.
The Queen had tons of horse manure & many gardeners.
Once the system was complete & work ever farmer could do it on a smaller scale.
The really great thing is it did not waste or use up the manure, only finished it.
When it was removed & replace, the compost could be applied to the garden.

Hi, maybe you already know this guy's work, but I put a link anyway.

I am willing to build one for my 100% off-grid hut in the Alps, 1100 mt altitude, probably this autumn.

https://mb-soft.com/public3/globalzl.html

Sorry for yesterday’s post, I finally read the full thread this morning. I copied the thread into a document file yesterday so I could read it this morning, no internet access at home.

Matt has given me an idea that might help solve several key component details of this design idea.

First, a few things need to be made clear. How big of a pile do you really need? Obviously if Jack was only filling the bucket 40% full, then he was only using around 20 gallons. Yes, the bigger the pile the higher the output and vice versa. I guess it all depends on how much output you need, aka how much BTUs you need to heat the room/house in question.

Second, is there a way of turning the pile, without actually turning the pile? Don’t jump to conclusions, follow along down to points 3&4.

Third, what does turning the pile actually do for the pile? Does it keep it from clumping up? Does it matter if it clumps up or not? Does turning the pile aerate the pile? Is it the aeration that matters or what matters most in turning the pile in keeping the pile working and keeping it producing the temperature output?

Fourth, is there a way to get the aeration in the pile without turning it? Yes, this sounds stupid, but my ideal answer, is stupider than anything I read thus far.

Take a vertical drum, or back up to the first point, a 5 gallon bucket(sorry I’m not an artist, especially not on a computer), remove the lid and keep it off. Sit it upright, not laid over. Put a window screen down in the bottom of the bucket set up on a couple pieces of angle iron/copper piper(something that won’t compost) to keep it up off the bottom of the bucket. Maybe use some welded wire mesh right below the screen to help give some rigidity to the screen, so it doesn’t want to slump down to the bottom of the bucket/drum. This is how any liquid will leak down and not be kept in the pile to help keep the pile from clumping???(please clarify on this point, I’m not really sure what causes the clumping). You can put in a drain off valve, so you can easily drain off the moisture any time it becomes necessary.

Put in the wood pellets/chips/leaves/yard waster, etc.

Make up a simple PVC manifold. A 1.5-2 inch PVC pipe with ‘t’’s stuck on it, with the side arms sticking out of it, making it look like a paddle wheel. Drill holes in both the down tube and the side tubes, aka to provide the aeration from the computer fan or better yet, hair dryer. Using a 1-2 liter pop bottle top, depending on whether you are using a computer fan or a hair dryer, aka the size of the opening from the blower device in question, take a clothes iron and melt the plastic around the fan/dryer to give it a fairly airtight seal. Put the other end down into the PVC pipe, aka forced air injection. Turn on the fan/dryer and let it blow air throughout the pile on set intervals.

Using a dryer will be blowing in warm air, which could be controlled through a thermostat. When the pile gets to cold it turns on the dryer, otherwise it stays off. Not only is this helping to push air through the pile to keep it aerated and working, but now it is also making sure the pile stays warm to keep the pile working. It is also keeping the excess liquid nice and available to be drained off in a friendly manner versus leaking out any standard compost tumbler holes onto the floor in the house. It also provides for no need for rotation because of the way the manifold is set up it provides the oxygen to the pile when you turn on the fan/dryer.

Think something like this, no drawing programs so I’m doing it crudely.

                 Hair dryer or computer fan to inject the heat down the PVC pipe
                     | |
                     | |
|---------------------------------------| screen to keep leaves/chip/pellets from blowing out when air is applied
|                    | |   perforated |
|                    | |       1/2-2”     |
|                    | |       PVC         |
|                    | |                      |
|                    | |                      |
|        ==============         | perforated PVC running sideway through the pile
|                    | |                      |
|                    | |                      |
|                    | |                      |
|        ==============         | perforated PVC running sideway through the pile
|                    | |                      |
|                    | |                      |
|                    | |                      |
|        ==============         | perforated PVC running sideway through the pile
|                    | |                      |
|                    | |                      |
|                    | |                      |
|        ==============         | perforated PVC running sideway through the pile
|                                               |
|--------------------------------------| screen to allow the liquid to run down to the bottom of the bucket/drum
|                                               |
|                                               |\
|______________________________|\ \
                                                   \ \ drain plug to drain off the liquids

The drain plug could also be something as ease a hole in the bottom of the bucket which could drop right down into a container on the floor. This would eliminate any need for any kind of plumbing valve. Also as I mention, in questioning down below(rereading and editing this as I go) you could drill several holes in the sides of the bucket, down below the screen mesh to get rid of the CO2, or is it heavier than air, at which it would be gotten rid because you no have lid on top of the bucket/drum.

A very simple system and can be used in any sized bucket. I say any sized bucket because the post I made in the original thread on ‘Try to say your butt in Europe this winter’ quote/unquote, I don’t have any indoor plumbing. I just crap into a 5 gallon bucket and throw in food scraps as well. I never use any sawdust or anything else to cover it up. I just keep a five gallon bucket lid on top and let it go. Yes, I must fess, I have no sense of taste or smell, and I live by myself, so I would never notice any smell if there were to be any. I do piss in a completely separate container so no liquid goes into the crap bin other than through food scraps. I typically have to take it outside and dump the bucket once every couple of weeks, mostly because of the food scraps, not much crap in it, typically.

The strange thing I have noticed is when the bucket is only a couple of days old, not much food or crap in the bucket, whenever I open the lid I do notice a fair amount of heat coming off the pile, even if it has been 6-12 hours after I last took a dump. By the time the bucket is getting full I don’t notice any heat, even immediately after taking a dump. The real question comes, what am I noticing, the lack of aeration or what? Even a five gallon bucket can provide the heat. Given what I think I may looking at for heat needs within the part of the house I keep heated during the winter I may not be needing much extra heat, using a 5 gallon bucket compost pile, built the way I layout above may provide all the extra heat I need. Again, it all depends on why I am losing the heat in the crap bucket in the first place.

If using a 5 gallon bucket probably you would want to drop down to 1/2-3/4” PVC/copper pipe instead of using 1.5-2” PVC, otherwise the PVC would be taking up too much space. In a 55 gallon drum 1.5-2” PVC would be okay.

Jack please explain a little further your big issue, CO2 and water vapor. Would both of these conditions be eliminated with what I suggest? The water vapor would be turning to liquid and dropping down to be drained off, or would that not happen? I can see both sides of the equation on this matter. I’m not sure about the CO2 though. By keeping the lid off, since you can, since it is a vertical bucket, the CO2 should be able to escape, or is CO2 heavier than standard air, need to remember my old science classes from 30+ years ago, darn it. As I mention above you could put holes between the lower screen and the bottom of the bucket to let any CO2 out that way if it is heavier than air. Heck put some plants down by the bottom of the bucket, they will soak up the CO2.

This idea would completely eliminate the need for rotating the pile, keeping it warm and keeping it aerated. All you have to do is feed it and clean it out.

I will ask for the same information asked for above. How often were you having to clean it out, Jack? Also, I will ask the question, how much fuel were you putting in each day, roughly by weight?

I am writing this on Monday September 12, while at home, so I haven’t read any post beyond Lil’s post about liking the Pineapple pile, which included the photo. If you have answered the question since then I will read when I get online later on today and make this posting.

Thanks for the ideas. It’s opening up a lot of new interesting concepts which I like better than anything else I have been thinking of doing heading into this winter.

PS. Thought an idea while out running, err biking errands a little bit ago. Instead of using PVC I think I will try repurposing all the aluminum cans I have been picking up along the road I’ll make the air duct out of them instead of out of PVC. I don’t have any PVC laying around, but a lot of collected pop/beer cans, actually just picked up another 10 or so while on the ride into the library to get online. I thought I was only going to be grabbing two of them I had seen earlier...boy was I in for a surprise on the ride into town.

Hank Fletcher wrote:Third, what does turning the pile actually do for the pile? Does it keep it from clumping up? Does it matter if it clumps up or not? Does turning the pile aerate the pile? Is it the aeration that matters or what matters most in turning the pile in keeping the pile working and keeping it producing the temperature output?

As I understand it, the answer is "yes to all," because all of your questions here are interrelated, even though you phrased some of them as "either/or" propositions.  Turning it does keep it from clumping.  It also aerates the material.  But the clumping issue and aeration issue are actually one and the same; the problem with clumped material is that it doesn't aerate as well, and thus could go anaerobic more quickly.  And it IS the aeration of the pile that DOES keep it working and providing thermal output.

Hank Fletcher wrote:Think something like this, no drawing programs so I’m doing it crudely.

                 Hair dryer or computer fan to inject the heat down the PVC pipe
                     | |
                     | |
|---------------------------------------| screen to keep leaves/chip/pellets from blowing out when air is applied
|                    | |   perforated |
|                    | |       1/2-2”     |
|                    | |       PVC         |
|                    | |                      |
|                    | |                      |
|        ==============         | perforated PVC running sideway through the pile
|                    | |                      |
|                    | |                      |
|                    | |                      |
|        ==============         | perforated PVC running sideway through the pile
|                    | |                      |
|                    | |                      |
|                    | |                      |
|        ==============         | perforated PVC running sideway through the pile
|                    | |                      |
|                    | |                      |
|                    | |                      |
|        ==============         | perforated PVC running sideway through the pile
|                                               |
|--------------------------------------| screen to allow the liquid to run down to the bottom of the bucket/drum
|                                               |
|                                               |\
|______________________________|\ \
                                                   \ \ drain plug to drain off the liquids

The drain plug could also be something as ease a hole in the bottom of the bucket which could drop right down into a container on the floor. This would eliminate any need for any kind of plumbing valve. Also as I mention, in questioning down below(rereading and editing this as I go) you could drill several holes in the sides of the bucket, down below the screen mesh to get rid of the CO2, or is it heavier than air, at which it would be gotten rid because you no have lid on top of the bucket/drum.

Thank you for providing a graphic, because frankly I was not following your narrative description at all.  And I must congratulate you on how effectively you do convey the info with your diagram, even without benefit of a drawing program.  Well done.

I think your idea has potential!  This could be a good fusion of some of the concepts both Jack and I introduced.  It reminds me of a Johnson-Su style compost system, only you would leave your aeration pipes in permanently, whereas they are removable in the J-S bioreactor.  That work gives us some useful guidelines from a proven design.  For instance, they determined that all organic matter in such an un-turned/un-mixed system will sufficiently aerate if it is within 12" of ambient air, which informs our design of our forced-air piping.  Though now I wonder if introducing forced air into the system, as opposed to passive aeration, might alter their guideline, increasing the minimum safe spacing to 18", say, or 24"?  In any case, if 12" works for passive air, it will absolutely work for forced air.

The most obvious difference between the two concepts is of course that the J-S bioreactor is designed to make compost over an extended period, rather than to make heat over a short period.  In the J-S design, you are waiting to get past the initial thermophilic stage, so that you can add your worms and settle in for the long haul.  In our heater design, we would want to keep adding more fuel and maintain the thermophilic stage indefinitely.  However, this comparison/contrast gives me pause.  The archetypal J-S bioreactor is much larger than a 55-gallon drum, granted, but the very fact that one is designed to digest for 12 months or longer and still have copious volumes of compost left over - compared to Jack's results with his original rotating design, in which the fuel was nearly completely consumed within a couple days - makes me wonder if we would achieve the desired results with our modified vertical system?

I don't know, but I do think your design proposal is worth more thought, more design tweakage, and some experimentation.  The promise of achieving results similar to Jack's while simultaneously being able to hold a much larger working volume and avoid the need for turning it, either via rotating drum motors or manual paddle mixers, is very enticing!

You would not want to drain away the leachate at the bottom, as indicated in your diagram.  The biomatter needs to remain at a high moisture content in order to decompose effectively.  In our case, "effective" decomposition means "quick" and "hot."  You would want to irrigate from the top down, as done in a J-S bioreactor, and as Jack achieved with a recirculating pump in his theoretical vertical drum concept (see diagram "biothermolator-2.jpg" from Jack's post of September 10th).  And you would likely want to incorporate some other features of Jack's from that diagram, like a way to selectively turn the heating element inside the forced-air-hair-drier on or off as necessary, based on a thermostat reading of the barrel's internal working temperature.  Same same for adding an external floor fan, also automated on a thermostat, to cool the whole system if it overheats.

To answer your question, CO2 is heavier than air.  So in theory it would settle in the drainage area at the bottom of the vertical barrel.  You could let it vent itself through small holes down there, as you proposed, but I think I might want to avoid drilling holes at the bottom of the barrel so to avoid any chance of leaking leachate.  I strongly suspect that using a hair drier to forcefully circulate air throughout the barrel will adequately mix the gases so that plenty of CO2 vents among the hot air rising out of the screened top of the barrel, and we wouldn't need to worry about excess CO2 accumulation.  

Matthew Nistico wrote:...And you would likely want to incorporate some other features of Jack's from that diagram, like a way to selectively turn the heating element inside the forced-air-hair-drier on or off as necessary, based on a thermostat reading of the barrel's internal working temperature.

That reminds me: Jack originally proposed the problem with this binary design for a forced-air-hair-drier aerator.  When using it to pre-heat a pile of all fresh, new biomatter during the system start-up phase, you want the hair drier pumping out full heat.  But when using it to aerate the pile in the midst of operation, when the biomatter is already at optimal temperature, the addition of more heat becomes undesirable, as it could push the culture close to the upper danger threshold temp.  But nor do you want to turn off the heat entirely, as introducing lots of room temperature air is counterproductive, and could even push the culture too close to the lower danger threshold temp.

Seems to me the answer is to bifurcate the aerator, splitting it into two devices on two different circuits.  One device would be a hair drier with the heating element permanently disconnected.  The second device would be a direct-resistance electrical heating coil, through which the hair drier would blow.  So it would be mounted in line between the hair drier exhaust and the mouth of the forced air pipe.  This might literally be the heating element ripped from a second hair drier.  It would have some sort of rheostat in its circuit, like a dimmer for a light switch.  A timer would turn on both circuits, triggering the hair drier to blow and the heater to start heating.  But the rheostat would vary the amount of current flowing to the heater, either on a continual scale or according to several pre-set gradations, based on the temperature read by a thermostat inside the barrel.

I wouldn't know which type of rheostat circuit would be easier to set up.  Hell, I wouldn't know how to set up such a circuit at all.  But I do know that it can be done, and that it shouldn't be prohibitively complicated or expensive.  Certainly nothing that a few hours of research on YouTube couldn't teach one how to build.

Matthew - I like your central wand.  One reason is that it would allow the fan to blow air rather than suck.  My sucking fan had to work in a humid vapor saturated environment which is not great for an electrical device.  There should probably be a dam in the the middle of the wand however to divert all flow through the drum.  Without it, air could preferentially just travel in one end and out the other, without much flow through the perforations.  Need to think about how to handle the rubbing seal.

Bigger hair dryer - A bigger hair dryer may not help much since its important not to overheat the bed beyond about 140 deg-F, otherwise it kills rather than nurtures the bacteria.  I picked the one I did since it was powerful enough and also it was DC.  Another option might be to use an infrared "reptile heater" bulb installed inside the box.  These can be had for about $25 including a a remote thermostat.  In this case the computer fan would still be needed to push or pull air through the drum.

Clean-out residue and estimating heat rate - Since I was mostly experimenting, I never ran the thing more than 4-5 days without shutting it down.  I cleaned it out every time, though I'm guessing it could easily have run a month before clean-out would be needed.  I estimated heat by taking the total dry material added over a run and dividing by the hours that were run, estimating 8,000-9,000 Btu/lb of dry material.

I think your two barrel approach is a good one since if actually used to heat a space, it would be nice to keep one running while the other is down for clean-out.  Also, since these things can't be easily throttled its probably a good idea just to run them full blast for base heat load and have another source (I used my electric heat) on a thermostat to trim the final few degrees of heat desired.

Your last post came through just before posted this so I'll need to think it through before responding.

Corrado de Cesare - Wow!  I love northern Italy!  Wish I could spend every summer there.  Unfortunately it has been maybe 20 years since I was there last.  Yes I have seen this site and it has a wealth of info for anyone interested in generating heat from compost.  The site is a little hard to navigate since a lot of the links seem corrupted.  I've learned these can generally be fixed by eliminating one of the "public3" parts from the web addresses.  For some reason they are duplicated which makes the links fail.  He started his experimenting with a "giant bag" approach that I still find intriguing.  Perhaps difficult to manage but a great SHTF idea.

Hank Fletcher - I think your concept has some merit.  First, I think reactor volumes can be fairly small if they are well insulated.  The key to how small is the size of the particles being digested and the ability to add more.  The smaller the particle (thinking saw dust or lawn clippings) the more surface area and the faster the digestion.  The other key to small volumes is how to draw the heat crated out effectively.  Small volumes have small surface areas.  From a practical standpoint, I suspect 20-30 gallons volume is about the minimum.  Below that and the power output is probably too small to be useful for anything more than heating a single room or very small cabin.  I've thought of using 5 gallon stainless steel soup pots for reactors but never pursued them.  Also, more in keeping with your concept, I thought of a rectangular reactor enclosing a stack of large baking sheets, each filled with a few inches of fuel.  A problem I see with your concept is how to reload it.  My baking sheet concept allowed removal of each layer for refill while the others continued to "bake".

As long as digestion is strictly aerobic there is little problem with dumping the CO2 and water vapor directly into a living space assuming normal ventilation.  However, the humidity could be a problem for you.  It is for me, so I dumped the gasses to outside the house.  I love the idea of using aluminum cans for ducting!

To all - I finally broke down and calculated heat soak through the barrel.  Can't believe I never did before.  Perhaps I did and promptly forgot about it.  Anyway, a 55 gallon drum has about 21.6 sqft of surface area.  The maximum surface temperature I can imagine is about 140 deg-F and at that point the steel can only radiate about 145 Btu/hr-sqft.  So without convection, pure radiation can only dump about 3,130 Btu/hr.  Convection with air (or water) is needed to draw more heat out of the system.  This is both good and bad.  The good news is an un-insulated drum could reach full operating temperature so insulation isn't needed.  On the other hand, a fan is needed to be to push enough air over the drum to draw heat away through convection.  Both to prevent over-heating and to draw more heat out of the system.  It seems my insulated box served as a duct to channel that air.  I may have been operating very close to the limits of my system and not have known it!  So a good design would probably use the hair dryer to start the system and to protect against sudden cooling and the "box" should be configured to provide a good air cooling jacket to maximize convective heat transfer.  Just about any material could be used for this air cooling jacket since it doesn't need to provide insulation.  Cardboard and duct tape might be used to build a well formed cooling jacket and a relatively quiet and inexpensive box fan might be used as the convective air source!

Matthew - the way the original system was set up the hair dryer was used primarily as a heat source to heat the box and its contents to 140F while the computer fan was used to draw warm oxygen rich box air through the drum continuously.  Maybe a reptile bulb suggested in the last post could be used in place of the hair dryer.  This should work as well and emulate your bifurcated system I think.   It would also eliminate the noisy fan from the hair dryer which probably has a poor service life over the long run.  BTW - I used Chinese temperature controllers that are (were) prolifically available on ebay for $15-$20.  They come with instructions that, even in fractured English translation, allow simple setup of temperature controlled systems.  Just search ebay for "temperature controller".  I use panel mount types that look similar to this.

Matthew - Oh boy does your last response to Hank Fletcher have my head reeling.  Lots of new stuff to think about!  The Johnson Su Bioreactor paper is a real find.  I haven't read it in depth yet but its bound to keep me awake tonight.  Its particularly interesting to me because after getting into this conversation I'm thinking more and more about how to build a larger scale system needed to accommodate larger chunk material like yard waste and wood chips.