Compost heating

[Kimberly Irene Lewis]

Hi I am new and just researching my systems before I put them in. I plan on eventually having at least one large greenhouse full of aquaponics. I Live in Virginia and where as it doesn’t get too cold for too long there is half the year where I would have to heat my tank if I uses tilapia. I have been watching video’s where people used compost to heat their greenhouses when it is cold. I saw one video where a off the grid researcher used a hose coiled up in his mulch to create hot water for his shower.  He changed the mulch out whenever is cooled down.  Since I also plan on vermiculture this is an intriguing idea to me.  You could heat  you r green house and have a hot water source for your tanks at the same time.  Save a lot on power.  Does anyone have any input?

[Jim Fisk]

Hi Kimberly and welcome to the addiction

I am a bit S of you but high in the Smokys of NE TN so it may be a bit colder here. I have been composting in all sorts of ways for a lot of years including my 22 foot automated composter that I have mentioned here before that was featured in Yankee Mag some years ago. It would take a lot of compost here as a sole source of heat. The best way to look at heat is multi-source in my experience. Just to be sure I can get through a cold Winter spell I use a wood stove of my own efficient design suited for heating the GH air as well as the AP water using a ss 3/4" pipe looped inside the stove. Our GH is in it's temporary stages of build and we skated thru our first pretty cold and loooong Winter in style thanks to our own wood sources. When the Sun is out you have no problem staying toasty of course but given a week or so of no Sun and averaging in the 20's with no double glazing takes some steady btus and wood is a great, and at least for us, cheap way to go. I also use a kero space heater on a thermostat in case I get stupid and miss the forecast for a colder than expected night. (it came on so seldom my biggest challenge was to make sure I NEVER left anything in front of it! Melted a trash can on one drain bamaged night) Once I had the stove installed I doubt we used 2 cups of kero all Winter. That was the goal.

Back to compost. A well ground mix with lots of chicken manure or other high nitrogen source batch of fresh organics will reach 160F within 24 hrs and peak at about 170F but then starts to fade after a couple days. So if you have a large source of compostable material in the order of tons, in other words a pretty darn big mound, you won't get more than a supplement of heat. You may have access to that much waste but I really don't. Like anything it would take a system and a source. Of course it also depends upon how well your GH is insulated. Next Winter ours will be well insulated in the fish room (2" foam and wood walls and insulated roof) and double glazed in the Sun room side. That will make a huge difference I am sure. At that point more passive heat sources like solar storage in water filled barrels on top of the system's 2000 gal capacity, compost and wood heat should be more in balance with less reliance on any one source.

If you haven't started your build yet and can afford to dig down an extra 2-3 feet and bury 3 layers of 4" drain pipe along with gravel and blowers, you may be able to get by on very little outside heat sources. There is a whole discussion here under our GH group I believe.

There are so many ways to skin this heating cat that you must in the end consider all your options and do what works for you. We heat everything with wood here and are already well equipped to do so so that was a no brainer main heat source for us not to mention a great means of exercise as well but we have been heating with wood since the 70's when I first started designing and building my own stoves.

This is my perspective on heat, hope it helps.

[Linda Logan]

In my experience with composting and vermiculture.  You'd have to have a lot of compost to keep a pile active enough to heat a large body of water.  The heat from my worm bin is just enough to keep the composting happening.  But here in Oregon I put a heat coil on top of the compost in the winter to keep the worms warm enough.

I'm interested to hear if others have been successful.

[Kimberly Irene Lewis]

I would think that heat tape under the pile would work better for that. I have been here for two years they say the winters have been exceptionally mild. When I grew up living in Illinois we would put heat tape on the water pump.

Kim

[Linda Logan]

The way my bin works is the compost is raked from the bottom by a manual crank and falls through to a storage space below.  the worms are mostly working the top 10" so heat from the top works.

The idea that Jim presented is a very successful method.  There is work upfront but then it takes care of itself.  I wish I had known of it before I built my greenhouse.

Kimberly Irene Lewis said:

I would think that heat tape under the pile would work better for that. I have been here for two years they say the winters have been exceptionally mild. When I grew up living in Illinois we would put heat tape on the water pump.

Kim

[Jim Fisk]

Dido Linda, BUT if I had done all that I might never have started. Now if $ is no object for sure but we, like most folks, do everything hand to mouth. That floor plan would double the cost of the GH I bet especially if you hire it out. Having our own loader I would have been VERY tempted had I seen that sooner.

Linda Logan said:

The way my bin works is the compost is raked from the bottom by a manual crank and falls through to a storage space below.  the worms are mostly working the top 10" so heat from the top works.

The idea that Jim presented is a very successful method.  There is work upfront but then it takes care of itself.  I wish I had known of it before I built my greenhouse.

Kimberly Irene Lewis said:

I would think that heat tape under the pile would work better for that. I have been here for two years they say the winters have been exceptionally mild. When I grew up living in Illinois we would put heat tape on the water pump.

Kim

[TCLynx]

I know people who have tried to heat with compost.  The coil of tube in the pile works for one off shower heaters for short events sometimes (like an outdoor camping festival) when you have a big pile of stuff and the extra labor to build it.

Or if you have lots of space and composting material you could do like growing power does and build big piles against the long sides of the greenhouse (on the outside) which gives them insulation and a small amount of heat from the compost.  But this is definitely not something to keep the water at 74 degrees while the air is below freezing sort of thing.  This kind of heating is to just take the edge off the freeze and help keep the snow melted off the greenhouse.

Oh, FYI worms don't like to live in the hot hot compost and if you try to do compost heating with your worm bin you will be cooking or causing your worms to flee.

[Jim Fisk]

So true. I still have my bin in the GH and I had to insulate it and I put box cardboard panels on top to keep it cool (works great btw) and it is still pretty cold around here so soon the 55gal bin will go outside under shade. It will take the loader to move it I'm sure. That one bin is keeping 40 trout very happy so I will take good care of it and I monitor the temps constantly. I water the bin every few days and catch the tea that drains out and use it on the GBs.

But do not expect any heat from a cool loving worm bin. Compost heat depends upon a very well mixed ratio of carbon to nitrogen that is well ground to small particle size or you won't get enough heat to talk about. When done right it will reach 170F but yikes it would take a mountain to heat a GH around here. It will help to compost in there in the Winter but a real heat source like wood is essential especially in light of the temp swings we are experiencing these days.

TCLynx said:

Oh, FYI worms don't like to live in the hot hot compost and if you try to do compost heating with your worm bin you will be cooking or causing your worms to flee.

[TCLynx]

One should also take into account "how much heat" you are really trying to get.  Some greenhouses really only need just a little heat to take the edge off.  Like if you are growing kale through a Wisconsin winter in a hoop house.  Truth is you probably need more light than you need actual heat since kale likes it chilly.  But if you are trying to heat a norther single layer hoophouse greenhouse to tomato and tilapia temperatures year round, well that is going to require serious BTUs.

Careful greenhouse design to work with your location and provide the most solar heating and insulation possible for the cold season is important but be sure to design in proper ventilation and means to control over heating come the hot season.  Proper greenhouse design is a huge subject and what will work well in one location could be worse than pointless (read detrimental to growing anything) in another location.  (my plants have done far better since I gave up the greenhouse in my location, growing climate and season appropriate stuff, but I'm lucky with a year round outdoor growing climate.)

[Converse]

Good sources to get volume matter for large a composting effort:

  Breweries:  Spent grain is a year-round source.  Some places give the spent grain away...some sell it.  It is great livestock feed too (and tilapia will eat it).It is U-Haul.

Spent grain is a "green" for hot composting....the following is from Univ. of Alaska Extension....

 "Carbon-to-Nitrogen (C:N) Ratio: With C:N ratios ranging from 17:1 to 12:1, spent grain clearly is considered a source of nitrogen to the compost pile. Many people mistakenly believe that it is a source of carbon, a "brown" material. Because the carbohydrates in the grain are removed for use in the brewing process, the spent grain has a higher concentration of nitrogen (proteins) than does unprocessed grain ."

     Another source for a thermophilic compost pile is to contact your local tree trimming service or local PUD.  They chip tree limbs, etc., and have to empty their chippers somewhere.  Some places develop a list of those who want the chips.  You could request to have your name on one of those lists.

Garden Care Businesses - Most mulch their own clippings on the sites they manage. But some transport and dump them...You can get on those lists too.

Wood chips are the "Brown" component needed for a thermophilic compost pile.

 

French innovator Jean Pain has lots of things on the internet about his large compost heating projects.  You need lots of teenagers with shovels, or  heavy equipment to keep up with his scale of  operation....But on a smaller scale it is possible.  One thing to keep in mind is that mid winter, when the snow is several feet deep and the compost pile is at the end of its heating cycle, do you have the ability/access/materials to re-work the pile or build a new one?  The tilapia will care.

     Worms do not like hot compost though.  The two are distinctly separate operations.

 

  We live at the crest of the Cascade Mtns. and have a very large redworm farm.  We do not baby our redworms.  They live outdoors year round.  No heat coils...never even considered it. We do prepare the wormbeds for winter with a deep layer of bedding matter (Leaves, etc.) on top.  We harvest redworms year-round (yup, we dig them up by hand from under feet deep blanket of snow) and they are thriving in the winter here too. 

 

  Look at Pop Can Heaters for your greenhouse.  Simple and inexpensive to make.  They WORK!  Of course you need sun.  But it is another inexpensive heat source for those cold days with sun.  You can find instructions to build pop can heaters if you do a Google search. Some are simple some are more complex. I was just at a school garden workshop with a bunch of Jr. High Students.  They built these one their own in 1/2 an hour - a simple version- and were getting heat for the school greenhouse within one hour!

 

Best to you in your effort to find the best way to use compost heating for your greenhouse.

 

- Converse