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Could a compost pile generate a little heat for months at a time?

 
pollinator
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Location: Colville, WA Zone 5b
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I'm a lazy composter - I don't worry about ratios, because I generally just let it take it's time.

BUT - I'm wondering if it would be possible to build a compost pile that wouldn't be too massive and would generate a little heat over months?

Here's why I ask - I'm about to begin a root cellar build. Here in the north, I am going to expect my root cellar temps won't exceed 35-40 degrees in the winter.

BUT I also want to use it as a cheese cave & wine cave. Those things prefer temps closer to 50-60 degrees.

So I'm trying to figure out a way to passively heat a small section (I may make it a 2-room deal) just a little bit so it doesn't get quite so cold in the winter. I'd like it to be as passive as I can. I've been racking my brain but then I remembered how sometimes people make a "hot bed" with manure in the spring to keep seedlings warm in cold temps.

But I think the big issue is that unless I can keep it generating a little heat consistently, I'd end up with a pile that would generate a lot of heat and then stop. Unless I could make a relatively brown-heavy pile that might be slower decomposing? Anybody know?
 
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Would it make sense to build a Compost water heater then just use an old cast iron radiator powered by a solar circletory pump to heat caller. Then you can control the temperature and generate heat for months.
 
steward
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Is it possible?  Yes.  Is it probably?  Not in my opinion.  It's hard enough to keep a pile running hottish for an extended period of time but then to couple it to something that wants that heat to be consistent would be a real challenge.

In the interest of coming up with some ideas though...  What temperature is your soil at the depth where you'll put this root cellar?  I'm in zone 4a and the soil 4' deep is something like 42 degrees in the winter.  So for me to get a root cellar in the 30s I'm counting on some cooling from the winter air above the cellar to fight off the "warmth" of the earth around the cellar.  (This is based more on my thinking process than on actual experience-my root cellar is in my basement)

I'm assuming your soil is warmer in Washington.  Who knows, maybe it's closer to 52 degrees?  So maybe you'd have a perfect cheese cave if you insulated it well from the winter cold above?  A bigger issue is that you may have trouble getting your root cellar cold enough.

If it was too cold for cheese, adding a tiny electric heater may solve all your problems for a few bucks a week in electricity.
 
master gardener
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Location: southern Illinois.
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Interesting.  I can't give hard figures, but I do use composting straw to assist in heating my high tunnel.  The high  tunnel stayed above freezing in 2018 until around Christmas.  I did put an LP heater in it for a couple of nights when the temps plunged, and I do have about 200 gallons of water in there as well. This year I have bought a small wood heater to help it through the winter.  But there is no doubt the composting straw did give off a significant amount of heat judging by the heating felt when I put my hand into the compost.
 
pollinator
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Location: North Idaho
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I have been studying this idea for years.  I knew a guy that tried to heat his house with a gigantic mountain of mulch, he thought it out well and laid it out well even putting in a concrete pad for it all but he used PVC pipe to flow water through to conduct the heat.  He ended up melting the pipe down...   I have been thinking of this ever since and am resetting up my 20 x 60 greenhouse this year and thought I might incorporate this into the design.  It really tough to find good information this.  Lots of conjecture and thought experiments but very little actual numerical results to be found.

I finally found the following video where the guy actually gives some numbers and results, he was also kind enough to answer some of my questions in the comments.  I asked him how long he managed to get heat from this setup and he stated it petered out after three months.  He managed to run at about 120 F to 130 F for three months adding material about every three weeks.  I also suggested in the comments the potential of having more direct control over the reaction rate of the bacteria by having pipes going through the pile allowing one to control the level of oxygen reaching the bacteria within the pile.

This video is posted by "From Concept to Creation"...  The video name is .. Heating your greenhouse with compost: How to, posted feb 14 2018.



I have had issues with posting a link to a Youtube video on other sites in the past, if I am messing up with this please remove the link.  I have added enough info that anyone should be able to easily look it up if need be.

From what I could gather from what this video shows and the results this guy got is that for "me" I would need about 80 cubic feet of mulch for every 1,000 cubic feet of greenhouse, this 80 cubic feet is the reaction area not the total amount of mulch.  The total amount of mulch would likely be around 120 to 140 cubic feet or 4 1/2 to 5 yards of mulch per every 1,00 cubic feet of greenhouse space to keep me 25 F to 35 F above ambient air temperature.  With the caveat that I would using dual plastic which is far more efficient at holding in heat, I also would have a better sealed greenhouse than he has.

To heat any sizable greenhouse would require a great deal of mulch, one would likely need to look at supplies.  Me I have a farm and it wouldn't be a big issue but for others it would not be so easy. Some potential ideas for cheap sources of mulch...

I used to work at a cedar mill and we would chip all of the garbage wood, most of it sold to the University of Idaho as hog fuel for their electrical generation, some higher quality chips would go to the paper mills in Lewiston or Walla Walla.  Anyone could come in with a truck and or trailer and buy chips as well, we were charging $10 a ton for the wood chips.

Tree trimming companies often have to pay to get rid of wood chips, contacting them could get you some cheap wood chips in mass quantity.

One may call the county landfill and see if they have wood chips to offer, sometimes you can pick them up for free.

Waste hay is a common thing in rural areas, I often drive around and watch in the fields and whatnot and often see entire piles of hay that are slowly rotting away and unusable for feed. My neighbor commonly has several tons of ruined hay each year and I often go over with my boys and clean it all up for him, it is a great supply of waste hay for mulch.  My last round we hauled 15 trailer loads home somewhere around 15 tons of wetted down half rotted hay. Not an easy job dealing with wet rotting hay but boy it worth the effort if you have a lot of gardening to do need large quantities of mulch material.

One could also contact local mills and see if they have any free sawdust.  There is a mill 20 miles from here that gives away truckloads of sawdust for free, you just pull up and they dump a bucket load in your truck or on your trailer and off you go.

Trying to keep up with that level of mulch would be challenging to say the least. I am in north Idaho and we see temps as low as -30F to -50F here in January and the guy in the video is also in a very cold climate.  If one lived in a less severe climate this idea would be easier and more effective.  Here just to grow cold tolerant plants in January I would need to produce a "lot" of heat.  But I could grow pretty from October -December with this kind of system.  Shut the greenhouse down for January and February and then start up again each March.

Hope maybe something here is useful to you.  Good luck on your study...

P.S...  I understand that my post is geared toward greenhouse heating and yours is about root cellar heating, but I figured the basic information and ideas would be close enough to give a potential idea of what it might take.  I figured you might be able to take the much smaller temperature requirement and maybe get a rough guestimate from that.
 
gardener
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Edible Acres posted a video or two about heating a high tunnel with an attached compost pile and it kept the temps noticeably warmer. Getting a pile of sawdust or finer ground browns, that you could say add urine to regularly to keep it cooking, might work well. As long as it's ventilated it should work, but will certainly be variable in heat output.
 
John F Dean
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My high tunnel is 12 x 24 with a curved roof 8ft at max.  As a rough guess, I have around the equivalent of 11 bales of composting straw in it.  They come out of the stalls and are packed into 2 ft high raised beds.  I soak the well with water. And, of course, they have goat manure from the stalls mixed in.
 
pollinator
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Location: Lake Geneva, Switzerland, Europe
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I have come across two designs on the Internet.
One is the Jean pain method or Biomeiler in German. 5m3 min of green wood chipped with the branches and soaked will heat for up to a year. In one case a huge pile generated hot water for a hotel.
A couple in the UK generate heat for 4 showers a day in a pile of half cow manure, half bark shreddings.
In both  cases coils of pvc pipe are run through the heap.
The trick is to not extract too much heat so that the composting continues.
 
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