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Getting wood chip compost to heat up

 
steward
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Sorry for the lack of updates, deer season got in the way.  Today it was up to 131.  The smell keeps getting less bad.  The test depression where I have the thermometer buried is sinking so the thermometer dial is getting harder to see over time as it sinks into the developing crater.

Pretty soon I'll think about if I want to mix up more liquid fertilizer and spread it more broadly on the pile and down in the pvc pipes.  

 
Mike Haasl
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I think it's plateaued at 133.  So I poked the thermometer around in a number of places and it was generally around 130 in much of the pile.  The only place that was more generally colder was the perimeter on the side with the extra green material (right side) where it was closer to 115-120.

So, what to do now?  I could mix up more fertilizer with water and pump it onto the pile more broadly (instead of in the 5 test spots like last time).  Still letting it sink in in a number of spots.  I could play with the aeration fan and try running it more.  It's a rather powerful radon fan and currently it's on for 15 min daily.

The pile is definitely cooking at the level needed to compost effectively.  Now I just need more heat from it and/or to have the heat radiate out to the perimeter of the bin to provide heat to the greenhouse.

The smell is not noticeable except when I open the hatch.
 
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Exciting! Are winter temps about where they tend to be at this point?

I am thinking you have big factors: temp humidity oxygen nitrogen. The minerals I see like hand grnades just have to be closish, I might throw some azomite  in there to add some micros. Now that the temp is self catalizing you can modify one variable at a time to see if you can get to the point where it is almost too hot and you can bleed heat out of the pile.

I’m excited for you this seems like all that work is paying off.
 
Mike Haasl
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Thanks TJ!  Winter temps outside are normal to a bit warm (upper 20s for the highs, teens for the lows).

The fertilizer has some micro nutrients in it (I believe), plus I've been urigating it as well.  How would you apply azomite?  Looks like it's a powder...  I can mix things with water and pour them on the pile or into the PVC pipes.  But I don't want to plug the pipes up, they only have 1/8" holes (give or take).
 
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It seems to me you’ve done a lot of things right, and many of my first ideas have been mentioned already. The only things I can think of as possible problems in your system
- are contamination from biocides in the chips or other additives (a risk I also accept when taking arborist chips)
- the metal container itself possibly being coated in a biocide
- a non permeable container restricting air flow

Someone called the fire department on my woodchips pile last month after I had been taking from it for mulch and left it steaming. Nothing had been added to this pile of pine and fir. Everyone in California is terrified about fires with all those going on in southern and central CA.

I have had good results from putting duck pond water over woodchips and seeing it heat up to the point of feeling hazardous to climb, and then it developed nice fungal hyphae.
 
Tj Jefferson
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I have a bag of powder I mix in a slurry for my new plantings. It’s fine enough to get down into the pile.

 
Mike Haasl
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Thanks team!  Ben, I doubt there are biocides in the chips since they're just prunings and cut trees in the city that were reduced to chips.  There could very well be some cedar or other rot resistant species in the mix.  The metal container is 20 year old galvanized steel roofing so maybe the galvanized coating could be a problem.  The container is not permeable so I have to give it air with the fan.  I can play with the amount of air I supply at will so if that should be my next experiment, I'm cool with that.

Thank TJ, I'll see if I can get a bag of the stuff.
 
Ben Zumeta
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I may have missed it posted already, but have you tried using a black “chimney”, with perforations in the section in the pile? The black heats up in the sun, when ventilation is most beneficial, and a thermosyphon passively ventilates the pile. This is just an adaptation off the classic design for ventilating a house passively, and since any heat loss is escaping within your greenhouse (ideally into a thermal mass like you are doing in your soil), it would seem to be worthwhile to me.
 
Mike Haasl
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Yeah Ben, that chimney thing won't work for my pile.  It's in an enclosed chamber inside my greenhouse.  So the only way I get air to the microbes is via a perforated drain tile under the pile that is fed from a radon fan.  After pushing air into the pile from underneath, the air exhausts from the chamber in non-perforated tile and runs 50' underground and through a planting bed before returning to the greenhouse interior.  So as long as the air is actually moving through the pile, which I think it is, I'm in relatively good control of aeration.

Currently I'm running the fan for 15 min every day at 4pm.
 
Ben Zumeta
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I think you would have better efficiency pulling the air than pushing it. I’d also consider drilling numerous holes in your container. I would also wet the whole batch down to the point where it runs off slightly at the beginning, then adding moisture only as needed thereafter.
 
Mike Haasl
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Thanks Ben, I think I'll change the fan around later this winter once I finish tinkering with other variables.

I haven't rounded up any azomite yet so I'm failing on that account.

The majority of the pile is cruising along at 135F but it isn't really making the sides of the chamber warm to the touch.  So this heater isn't doing much heating.  The spot I urigated really well warmed up from 130 to 136 and plateaued there.

So this evening I mixed up much more of the liquid fertilizer (3/8 gallon) into about 25 gallons of water and pumped it all over the pile.  I pumped it onto about 16 spots and gave each one at least 3/4 gallon.  It was at least as strong a stream as my house spigot and the pile sucked it in without pooling or running off.  I poured extra in the center and ran some down the upper PVC pipes.  That was trickier since the pump moved more water than the perforated PVC could accept so I'm a bit wet right now.

It's supposed to be -14F on Tuesday night so hopefully this starts doing something extra awesome.....  I'm a bit dubious
 
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Mike Haasl wrote:I'm attempting to get heat from wood chip compost.  I did a modest amount of homework first but my pile isn't really cooking.  Please let me know if I'm doing anything clearly wrong.

First off, I should have temperature and moisture sensors buried in the pile for data analysis.  As it was I was lucky to get the pile built before the snow prevented me from accessing the location.

The bin is inside a large greenhouse.  It's sheet metal roofing in a 8' diameter circle and the bin is 8' tall.  I was able to fill it about 6' high with mostly fresh wood chips from the city.  At the bottom of the pile I coiled a perforated drain pipe with an inlet from the room to let air in under the pile.  At the top I capped the bin so it is moderately air tight.  I also have a 4" duct exiting the top and connected to a radon fan (relatively strong fan).  

The wood chips were mainly fall clean up branches.  There was a decent proportion of pine and minimal cedar/arborvitae.  Lots of the branches were pinkie diameter and had green bark on them.  The chips were generally the size of a pinkie finger chopped into thirds (sorry for that visual).  Of the 6 trailer loads we collected, 4.5 of them were fresh, 1.5 of them were springtime chips that were partially broken down.  Sometimes the pile we collected from was starting to warm up from being chipped recently.

The chips were a bit damp.  If you buried a paper towel in the pile it would become damp but probably not wringable.  As we added the 10 cubic yards of chips to the bin I added about 120 gallons of water.  I have no idea if that was the right amount.

4 days after building the pile, steam started rising from it and spots were heating up.  I finished the cap on the bin about that time.  Since then it's been a week and the pile hasn't gotten any warmer.  In fact, it seems to be cooling down based on the temperature of the side of the bin.  Today I opened up the door and looked inside.  Everything is damp and it's warm inside but not hot.  Probably in the 70s.  The greenhouse is around freezing inside in the morning and warms up tremendously on sunny days.  I want the compost to start providing heat before it freezes itself.

I have the radon fan drawing air through the pile for an hour a day.  It pushes a fair bit of air out of the bin but most is from leaks.  A small to modest amount of air is entering the drain tile under the pile so some air is drawing through the pile.  The hot/steamy exhaust travels through a grow bed and likely condenses out a modest amount of water.  This is water I'll need to replace into the pile so it doesn't dry out.

My main variables are how often and how long the fan operates and how much more water I add to the pile.  Today I changed the fan to stay on for 3 hours a day.

Hopefully I explained my situation, does anyone have any ideas?


Thats a really gorgeous looking greenhouse.Looks like a boat hull upside down.
Your verry skilled if you build that and i wonder what do you plan to grow in it.
As for the heating with wood chips i think its better to burn them in a stove like a rocket mass heater then to wait for the bacteria to burn it ( ie oxidise it through their metabolism).
Burned by bacteria or by a stove you consume the same ammount of wood chips for the same ammount of heat.
Wood has 4 kw of power per kilo but to wait until bacteria reduces a kilo of wood it takes too long and the 4 kw of heat its too little to heat the greenhouse efficiently on such a long time.
There is an advantage that you dont have to supervise the fire going much if you use compost heating but its weak heat and i wouldnt use conpost heating in such a beautifull greenhouse.
 
Mike Haasl
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Thanks Mahai, here's a thread about the greenhouse itself: Mike's Passive Solar Greenhouse Build.  My goal is to grow tropical perennials.  I have bananas, lemon, lime, mandarin, dragonfruit, papaya, turmeric, miraclefruit, ginger, mango and avocados in there now.  Most are in pots and I've moved them up on top of the compost bin where I can nurse them through winter if (when) this compost system doesn't work well enough.

If I can't do tropical plants, I'll back down and do Mediterranean or Florida plants.

I chose compost so that I could hopefully have heat for months without having to tend a fire.  Many people have theorized that it could be done so I'm testing it (imperfectly).

I also like that the waste at the end is many cubic yards of compost.  And the feedstock is considered waste by my city so I get it for free.

But if it doesn't work, I'll either give up on heat all together or put in a wood burner of some kind.
 
Mihai Ilie
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This stove for 7 kw costs just 250 dollars new at this manufacturer.
I recommend it,its efficient with gasification.

Il have a good time reading your greenhouse blog.Tryed to post a comment there but for somme reason it didnt worked.
 
Mike Haasl
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Well, I don't have the best news.  I accidentally ran an experiment and it didn't work.  I attempted to program the timer to have the aeration fan come on twice a day for 15 minutes.  In reality, I set it to come on and never turn off.  So from the morning of the 12th through the morning or afternoon of the 13th it ran constantly.  The pile temp dropped from 136 to 110.  Shit.

Ok, well that simulated turning the pile really well and adding a lot of oxygen, we'll see how that does.  So I unplugged the fan for a few days and the temperature continued to drop.  102 yesterday and 97 today.  Shit.

So I plugged the fan back in and triple checked the program was set correctly this time for two rounds of 15 minutes per day.

I'm definitely getting the inkling that this system is a bit too challenging to get correct.  If a day of extra aeration crashes the system, that's a bad sign (in my mind).  And when it is cruising at 135 I can barely feel any heat on the surface of the metal hopper.  I'm glad it has been mostly working this winter so that I could make the right decision this spring on it I leave it in or change paths.  Right now it's looking like I'll change paths in the spring.
 
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