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 Post subject: Compost heat
PostPosted: Tue Apr 20, 2010 3:57 pm 
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Location: Minneapolis, MN
In an effort to make the greenhouse self sustainable, I have a flurry of things flying through my head for heating the greenhouse in the winter. One of these things is using a compost bin and put a coiled pipe inside filled with water, then do in-floor heat.

The only thing that I'm wondering is how often I would need to turn the compost over. I've been doing some reading, and some people are saying that the only reason you need to turn your pile is to get oxygen in the middle so that it starts the process over, and to get around this, some people have drilled holes in a pvc pipe to get oxygen to the center without the need to turn it over.

How feasible does all this sound? The greenhouse will be roughly 1000 cubic feet on the inside, with limited insulation (obviously). Any other ideas for heating the greenhouse without spending a fortune?


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 Post subject: Re: Compost heat
PostPosted: Tue Apr 20, 2010 4:49 pm 
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If you got any real heat from it, I think it would stop the composting. The bacteria that make it work need pretty high temperatures to really do anything. Any heat you pull out would just kill the process. The other thing is the gasses given off by the compost. In a close environment like a winter greenhouse, it could be deadly.

That being said, there is no reason to put pipes in it. All the energy released by the compost will leave the pile and go into the air. No reason to put plumbing into it. Energy can't be destroyed, so it will come out of the pile at the same rate it is being released over time. Putting PVC pipes in the middle to prevent turning soulds like a good idea.

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 Post subject: Re: Compost heat
PostPosted: Wed Apr 21, 2010 8:49 am 
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I do realize that the greenhouse is a closed system. I should have put in the original post, that this would be designed so that the compost is attached to the outside of the greenhouse, and not internal. There are quite a few case studies on using compost heat to run a radiant heat system, but it also makes sense that if you pull too much heat out of the pile, it will stop generating heat because the cycle will have been killed off.

Maybe I'm trying to find the easy way out, but I figured since I have an abundance of cow manure available to me, I could leverage that for some heat.


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 Post subject: Re: Compost heat
PostPosted: Wed Apr 21, 2010 10:03 am 
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If you have fresh cow manure, you should consider making a methane generator and heating with the gas.

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 Post subject: Re: Compost heat
PostPosted: Wed Apr 21, 2010 8:31 pm 
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dwaller I like the idea of heating with the compost pile .... I've never heard anyone even speculate on this before! It has definitely given me some ideas ;). I've been wondering how I'm going to heat a system of about 800 gallons, 140F sounds like a good heat source! I've got to figure out some heat-conducting "pipe" or "non-toxic hose" (maybe PEX?) to run inside the pile ......... now if I could just collect enough compost .........

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 Post subject: Re: Compost heat
PostPosted: Thu Apr 22, 2010 6:28 am 
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Getting enought compost is a problem. And keeping it hot is a bit of an art form. There is a lot of heat in the attic space in houses. Running your air pumps from inside the roof may transfer a little heat if the FT are close. Or move the hot water system into the green house. I wanted a hot house next to the house for heating the house of a day and sharing a little extra heat of a night.


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 Post subject: Re: Compost heat
PostPosted: Thu Apr 22, 2010 10:33 am 
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I'm pretty excited about the methane generator idea. The most exciting part is that my wife is fully on board with it (to be honest, she actually suggested that we look into a methane generator originally, since the greenhouse will be located on a farm with 400 head of cattle...).

I'll probably focus on building the greenhouse first, but I do need to figure out what type of heat I'll be utilizing. Forced air would be easy, but I'm guessing it would not be good for the plants, especially in the winter. In-floor is the other option, but I need to figure out what type of water heater to use, and if using methane is acceptable.

The other big one with the methane generator is the storage of the methane. I wonder if it is possible to pressurize it in tanks similar to propane, so that I can store large amounts of it over the summer to be prepared for winter. Lots of stuff to look into.


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 Post subject: Re: Compost heat
PostPosted: Thu Apr 22, 2010 11:05 am 
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Forced air is the way to go. In a greenhouse with fish you won't have dry-out issues.

Loads of publications on methane. One source of reprints from the 50's and 60's is here:
http://www.ush2.com/978-1-60322-031-6_detail_page.htm

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 Post subject: Re: Compost heat
PostPosted: Fri Jul 02, 2010 6:58 am 
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Hi floridamary4....welcome... :D

Going by your name....would you be one of my fellow (or lady) Floridians ? There are several of us signed up here... :)

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 Post subject: Re: Compost heat
PostPosted: Wed Nov 03, 2010 6:48 pm 
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Sorry to bump an old thread, but this subject is one that I have a strong interest in and would possibly like to incorporate into my own AP system.

The idea of using compost for GH heating was well tested back in the 1970's and 80's, and has been used in Europe for decades. The Mother Earth News, Rhodale, and others, ran various types of projects with compost heating, but probably the most successful and extensive GH testing was done by a group calling itself the New Alchemy Institute in Woods Hole Massachusetts. They were able to maintain constant winter growing temps with the use of enclosed and insulated compost chambers along the north wall of their greenhouses as the only source of heat aside from solar gain. Greenhouse air was forced into the center of each of 10 compost bins through perforated pipes, thus avoiding the need for any manual or mechanical mixing. Exhaust from the top of the compost bins was drawn off and forced through perforated pipes laid beneath the compost-rich soil of the grow beds. Soil bacteria then converted ammonia, produced by reaction of nitrogen with water vapor during decomposition, into the usual nitrites and nitrates. Compost heat was thus transfered directly into the soil, maintaining bed temperatures in the 70's F on the coldest winter days, while filtered CO2 was passed up through the soil and made directly available to the plants.

Interestingly, these folks were also early pioneers of greenhouse aquaponics.

Aside from generating heat, compost produces lots of CO2 which increases plant productivity significantly (25% or more.) As I recall, it was found that when unventilated, as is often the case during cold cloudy weather, a lush greenhouse can consume virtually all the available CO2 in an hour or two, thus bringing photosynthesis to a complete halt until more is made available. Many commercial greenhouses heat with natural gas to maintain high CO2 levels and increase crop yields, and some even use compressed CO2 in the summer months. AP and hydroponic systems are especially prone to CO2 loss since there is little or no decomposing organic material in the otherwise soil-less grow beds.

Aside from compost, experiments were also done using chickens housed at one end of a hoop greenhouse and separated from the food growing area by a wall that incorporated straw and sawdust filters to get rid of "chicken dust" which would otherwise settle on the plants. A solar powered forced air system circulated the filtered air from one side to the other. The seasonally enclosed chickens added both heat and CO2 to the system, and their waste was incorporated back into the compost system to apparently accelerate the thermal output. The chickens and eggs also provided an additional food stream, along with the produce and fish.

Manure from cows, rabbits, and goats was also composted using red worms. While not generating much heat, vermacomposting does boost the CO2 levels, and the worms provided a supplemental food source for the fish.

Much of the New Alchemy Institute research was adopted and expanded upon by folks like Anna Eddy who built quite a successful business for herself providing AP salad greens to restaurants in the Cape Cod area. She went on to write a classic book on the subject called "Solviva: How to Grow $500,000 on One Acre and Peace on Earth." (Gotta love that 70's title!) The New Alchemy Institute is now defunct, but some of their scanned original research papers and other publications can still be found online with a little effort and patience.

Gary


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