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Author Topic: Compost Heating - Anybody tried it?  (Read 2291 times)

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Offline btulloh

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Compost Heating - Anybody tried it?
« on: November 07, 2016, 09:24:11 pm »
I've been looking into heating a small cabin using heat from a compost pile.  There's quite a bit of info around and it looks like it might  work for a small cabin.

So far in the early stages, I think I can use several hundred feet of pipe in a 20 cu yd compost pile to get the job done.  Thinking about using a car radiator for heat exchange and circulate the water by thermosiphon.

Does anyone have any opinions or experience or advice?
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Offline thecfarm

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Re: Compost Heating - Anybody tried it?
« Reply #1 on: November 08, 2016, 06:29:28 am »
I have not done any research but I would think it would have to be a BIG one to make it work.
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Offline btulloh

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Re: Compost Heating - Anybody tried it?
« Reply #2 on: November 08, 2016, 07:17:26 pm »
Not as big as you might think.  Check this out:  http://compostpower.org/node/24

That one produces 20-40k btu/hr.

Here's some more interesting info:

http://smallfarms.cornell.edu/2012/10/01/compost-power/

I only need about 4-6000 btu/hr for what I want to heat.  I produce a lot of compostable material every year.  Not counting sawdust and slabs. I have a pile of various organic debris right now that's probably 100 cu yds just from the past 6 months.  It would be nice to use the heat that's already generating.  Details are important though.

Do a search on "Jean Pain" who did a lot with this back in the 70's in France.

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Offline LittleJohn

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Re: Compost Heating - Anybody tried it?
« Reply #3 on: November 09, 2016, 12:41:16 pm »
There would only be 2 main issues that I see, other than the pile not generating enough heat:
  • You pull too much heat out, and your compost heap begins to slow down
  • There is too much heat, and the pipes/tubes that are "In the pile" can not take it and fail

**Please note I am neither an Expert or Scholar, just guessing at potential failure points - I tend to do that as an Engineer

Offline btulloh

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Re: Compost Heating - Anybody tried it?
« Reply #4 on: November 09, 2016, 11:40:01 pm »
Taking out too much heat is an important consideration.  That is something that has to be managed.  Most of the articles discuss this aspect of operation.  I think using thermosiphon circulation would take care of that as long as the pile is constructed properly. 

The piles generally don't get hotter than 160 degrees (f) so I don't think getting too hot is a problem.

These and other details need to be accounted for.  Taking this from a general concept to a viable design that's matches the requirements requires some additional info that I haven't been able to dig up yet. I'm hoping more people will chime in.

 
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Offline Kbeitz

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Re: Compost Heating - Anybody tried it?
« Reply #5 on: November 19, 2016, 06:20:22 pm »
If the piles don't get hotter than 160 degrees why do you
here about some catching fire ?
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Offline r.man

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Re: Compost Heating - Anybody tried it?
« Reply #6 on: December 02, 2016, 05:22:15 pm »
There was a pile near here, acres big, that used to catch fire occasionally, not sure why. I have heard that compost piles, or biomass piles can have a heat problem if they are over a certain height/mass and dissipating heat is one of the reasons commercial operations turn their piles. Great problem to have for a heating source.
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Offline ScottCC

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Re: Compost Heating - Anybody tried it?
« Reply #7 on: January 21, 2017, 09:21:12 pm »
Just wondering if running tubes through the cover of your septic tank sounds like a compost pile, gross or already been done?  That system never needs working unless we stop eating.  Maybe this is a way to bring up the temperature of water entering the hot water heater?
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Online Don P

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Re: Compost Heating - Anybody tried it?
« Reply #8 on: January 22, 2017, 09:41:06 am »
Interesting, does a septic tank run a temperature? It would be easy to make them insulated with radiant tubing in the walls. Not sure I'd want the potential for cross contamination with domestic water.

Offline LittleJohn

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Re: Compost Heating - Anybody tried it?
« Reply #9 on: January 23, 2017, 08:57:45 am »
Interesting, does a septic tank run a temperature? It would be easy to make them insulated with radiant tubing in the walls. Not sure I'd want the potential for cross contamination with domestic water.

Since your drinking water is pressurized and you septic tank isn't, if a leak did occur water would go from the house into the septic.  I would however, at least have a heat exchanger in between the two system - don't want foul smelling water, or whatever else you could get.

You have the same issue if you are running a closed loop or glycol system for radiant and using it to heat hot water.  Typical closed loop radiant system aren't above 15psi, with Pressure relief valves (PRV) set at 35psi, so any leak from drinking water to radiant would immediately increase the pressure in the radiant system and the PRV would pop releasing excess water and pressure

Offline r.man

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Re: Compost Heating - Anybody tried it?
« Reply #10 on: January 23, 2017, 07:49:21 pm »
I have an outdoor wood burner which uses water to store and transfer heat into the house at atmospheric pressure and it occasionally needs additional water. Even though the house system is pressurized I use two separate valves to isolate the two systems. Some things should have a redundancy when a failure has serious effects. A septic system produces some heat but not enough to warrant harvesting in the average household.  One energy saver that most homeowner DIYs would be capable of is reclaiming shower water heat. The incoming cold water to the shower is piped through a long run of the shower drain so that the outgoing waste water heats the incoming cold water so less hot water is used in the mix. The longer the run, the more heat is recovered.  Ideally all waste water should leave the house at no more than room temperature and could conceivably leave at a lower temp if it was used to warm up enough incoming cold water.  I do like the idea of the compost heating system, heat with the compost and then use the leftover for soil amendment.
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Online Don P

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Re: Compost Heating - Anybody tried it?
« Reply #11 on: January 24, 2017, 12:22:29 am »
I doubt a septic could run at more than body temperature, with 1500 or so gallons and a slow heat recovery, then line loss from tank to house. I think you're right, just not enough there.

Offline Ron Wenrich

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Re: Compost Heating - Anybody tried it?
« Reply #12 on: January 27, 2017, 12:50:49 pm »
I think there is too much water to compost so that the heat is dissipated over a larger area.  The breakdown is a lot more drawn out.

The compost heating unit that I saw years back in Mother Earth News was wood chips.  If I recall, it was a pile that was about 8' high, and it had a wire wrap around it.  There were layers of black tubing through it.  I forget how long there would be heat coming from it.  I imagine you can do that with sawdust.  Maybe use a bin with pipe running through it.  Insulate it and have a way to clean from the bottom and add to the top.  An even better compost to use is particle board dust.  The urea used to hold it together will give off lots of heat.  I know that sawdust will give off a bunch of heat until it is dry.

The reason you hear of wood piles catching fire is due to compaction.  The mills that I worked at had the occasional bark pile fire.  It was always in the winter, where you had accelerated drafting of heat to cold, and it was where it was stacked high and run down by truck or loader.   

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Offline florida

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Re: Compost Heating - Anybody tried it?
« Reply #13 on: February 07, 2017, 10:02:41 am »
There was an article in Mother Earth News 30 years ago about a guy in France who heated his home using poly tube in a compost pile. All the material from the pile came from his property which was fairly small. There has to be an archive of their articles somewhere on line.

Well here! I found it for you.

http://www.motherearthnews.com/diy/compost-heater-zmaz80sozraw
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Offline wesdor

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Re: Compost Heating - Anybody tried it?
« Reply #14 on: February 07, 2017, 03:42:20 pm »
Interesting discussion. I found a PDF translation of the work of Frenchman Jean Pain. Downloaded it but haven't looked closely. I hope this adds the the body of knowledge.

https://ia800202.us.archive.org/8/items/Another_Kind_of_Garden-The_Methods_of_Jean_Pain/Another_Kind_of_Garden-The_Methods_of_Jean_Pain.pdf

Offline HousewrightVA

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Re: Compost Heating - Anybody tried it?
« Reply #15 on: February 10, 2017, 05:58:29 pm »
I have always wanted to be able to use the sawdust and shavings we produce to heat the shop.A biofueled boiler is a huge monetary stretch but when I ran across this idea last year it was a perfect fit. I had put radiant tubing in the floor and a salvaged fuel oil boiler to connect to it. But here is this new idea, I have a manure pit that is 60' from the boiler room, just fire up the backhoe and trench from one to the other. So armed with a book or two and the internet.to guide us my helpers and I put this together in about a day.

 
There is 900' of 100PSI poly pipe coiled in layers in the pile.

 
We used a mixture of sawdust, planer shavings, and horse manure.

 
The base is about 20' in diameter and 8" between layers of pipe.

 
Lesson learned take some care and pressure test as you go. We had to tear it back down after everything including interior plumbing was complete to repair a hole caused by a manure fork.

Well, it does work. And I still have some learning to do.
Output has been very consistent in the 85-95 degree range.This is not enough to really heat the shop but it does help even things out and hold through the night with the woodstoves still providing the bulk of the btus.
Next year (this fall) I am going to try to have fresher shavings and perhaps some chicken litter to get it a bit hotter. Also going to set up the tubing in a modular fashion to make teardown and assembly easier.

It has been a lot of fun messing with this thing.
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Offline Ron Wenrich

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Re: Compost Heating - Anybody tried it?
« Reply #16 on: February 10, 2017, 07:17:16 pm »
I did some work with a sawdust dealer a good number of years ago.  He was interested in making mulch with the sawdust he was getting in.  He was getting more sawdust than he could market at the time.  I did some research and I knew we needed to get the pile heat up in order to get the decomposition needed.  There was also an upside limit. 

So, I went up one day and we took some temperatures on the pile.  We put in a soil thermometer and got a reading of 140.  He told me it was a delivery from the night before.  He got the dust from a cabinet shop that was using particle board.   The urea binder in particle board caused the dust to heat up quickly. 

I also worked at a mill that had a sawdust bin that they built so they could open some doors and it would load up a dump truck.  But, it was poorly planned, and you had to go and shovel dust every couple of hours so it would fill up.  I remember it was always hot and humid. 

The problem with the open pile is you probably lose a lot of heat to the outside air.  I have to wonder how long you can suck heat out without stopping the decomposition process.  The addition of manure should certainly help.   
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Re: Compost Heating - Anybody tried it?
« Reply #17 on: February 11, 2017, 07:35:27 am »
When we lived in a duplex in town I brought home a couple of truckloads of dry planer shavings to help with a garden my wife was putting in. I had bought some fertilizer and lime and left instructions to layer it in the pile and water it down, we had done that with large leaf piles in a nursery I had worked at. When I rounded the corner with the next load there was a steamy fog coming down the street. I hadn't explained the layering well enough and the pile was very hot. Not sure how expensive that is but it sure kicked off the pile.

Offline btulloh

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Re: Compost Heating - Anybody tried it?
« Reply #18 on: February 12, 2017, 08:49:52 pm »
it's all about getting the C to N ratio right to produce enough heat but not work so fast that you use up your ingredients too fast. A ratio of 1to1 will finish composting in about six weeks I think. I've read somewhere that 20 to 1 has produce internal temps of 130-140f for 16 months. 

I plan to put something together this summer. But I have a lot of plans and time seems to go faster than projects.

Good stuff. Thanks for all the feedback.
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Offline gimpy

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Re: Compost Heating - Anybody tried it?
« Reply #19 on: February 21, 2017, 03:39:41 pm »
Just gotta say, WOW. And to think I was about to spend a few hundred dollars for a woodstove to keep me warm all Winter.

However, a similar ideas have been used successfully to heat the greenhouse beds during growing season.

With the ease of heating with wood this type system would require more close scrutiny.
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