Now I have done lots of thinking like many of you on the subject of heating greenhouses during the winter. I have pretty much have come to a conclusion and summarized my favorite aspects of compost heating compared to rocket heaters.
Safety - there is no danger of carbon monoxide buildup.
Thermal Utilization - closed loop systems can be employed due to non-toxicity so there is no need to exhaust heat (wasted energy).
Carbon Dioxide - a known problem in wintered greenhouses, the compost pile produces enough to feed the plants and sustain growth rates.
Upkeep - compost piles can last months and when timed correctly can match the demand of the weather requirements in many temperate regions.
Byproduct Utilization - what farm or homestead does not need compost?
Simple Design - simple systems reduce the occurrence of failure.
Cheap - less to spend.
The above is an entertaining video and example of the potential heat. Unfortunately, there is no efficient usage. Most of the heat generated escapes into the atmosphere. In a closed loop system the compost pile can be applied in a system where heated air travels into the greenhouse creating a siphon effect circulating air between the enclosed compost pile and the greenhouse. This can be integrated into one enclosed building but the pile would consume a lot of space. The added benefit is a steady and abundant source of carbon dioxide to the plants. My proposed system would be similar to this.
The following video series was conducted with the concept of a rocket mass heating system.
To the benefit of us all, Bigelow Brook Farms http://www.bigelowbrook.com has invested in a very well designed burn fuel system which heats a beautiful geodesic style greenhouse. However, if you follow the series you can see the design challenges that can occur. Burning fuel does have distinct advantages where large quantities of heat can be produced will relatively smaller spacing but this does come at an expense of efficiency in energy. This does little to say regarding the added complexity of its designs which produces more potential for failure.
My closing remarks on the matter, if you are looking to design with minimal maintenance issues than I would choose a compost heating solution. You can support the producers of these videos by watching them so they can collect advertising royalties, thank you.
Those who hammer their swords into plows will plow for those who don't!
There was a French guy called Jean Pain who successfully channelled compost heat into his garden. Apparently a Canadian guy was able to use this technique to successfully grow tomatoes in Winter with outside temperatures of -35°.
link to article (in French)
I read years ago, in a wine making book, that many Austrian farmers used wine pomace (marc) to heat their barns in winter time. The pomace is the residue left after pressing the grapes and fermentation - a waste product.
It was stated that 2 cubic metres of pomace would keep their livestock cozy warm all winter.
In the spring, the pomace would be spread on the fields as an organic fertilizer.
Double use from a readily available waste product.
I looked into compost heat extensively because I had the ideal conditions for it, or at least I thought. I am not saying it would not work; it surely would and obviously does, it just comes down to that nagging issue of return on investment. This is where a person's individual farm changes everything.
I never went with compost heat despite having a host of already-in-place ideals for this type of heat because:
1) I live on a hill and to get sufficient long term heat I would need 9000 gallons of water I do not have that much water available here
2) This area has 10% field and 90% forest, and dedicating fields to produce the compost would reduce my open land to feed/graze sheep (my main income source)
3) With 90% forest, it is simply easier and faster for me to gather and burn firewood then it would be to make the equivalent compost pile.
I am not saying it won't work, and I thought of doing it just to prove that it could work in Maine, but the issue is why bother to go through that effort when I can cut and harvest firewood with less expense and ease? But again this is my farm, others are vastly different. This is not even a regional, state, or micro-climate thing, it is an individual farm type thing.
The one time I made a compost pile in a greenhouse, the air-quality inside the greenhouse became so poor that it was uninhabitable. If I were to attempt heating a greenhouse with compost, there would be no air exchange between the greenhouse and the compost pile. In other-words, if air from the greenhouse circulated into the compost pile, it would do so through a closed-loop system, and not by direct-exchange.
There are a lot of problems with most all of the designs suggested above, unfortunately. The direction you want to go if you want compost heat cogeneration for a greenhouse is detailed in the following book, which is especially useful if you have an unlimited supply of woodchips or a large, concentrated amount of manure. It is based on the work of Jean Pain (video above), but utilizes the heat in a much different way. Also look at the New Alchemists of the early 1980s (covered in this book). I have researched all the literature and this book is the best approach available, providing you have the massive amount of inputs required-- "The Compost-Powered Water Heater" by Gaelan Brown (the title is a little misleading since it primarily focuses on greenhouse heat cogeneration!) Bruce (of the New Alchemists) is currently testing a new version in Boston, which is the culmination of all his research of the last 30 years. I went to look at it last summer and it is pretty exciting. The other major best greenhouse design innovation is the Chinese solar greenhouse. Millions of acres of greenhouse have been feeding northern China for decades, now, without fossil fuels. There is very little awareness of this but you can find a couple decent blog posts covering it. Another interesting variation is Anna Edey's newest book "Green Light at the End of the Tunnel" which has an "earth lung" design (her name for it, but also originally developed by Bruce). She is on Martha's Vineyard and I have also visited and inspected her various projects. The most promising to me is actually the flush toilet to worm bin composting setup, which we are now using. But her chicken coop to greenhouse "earth lung" is also interesting if you don't know an arborist who can give you a large supply of freewood chips or have a dairy barn full of manured bedding.
Sorry for my short reply this morning, I was headed to church and had no amount of time for a proper reply. Now I can explain better...
One of the reasons I say I have ideal conditions for compost heat is because my house has 100% radiant floor heat. That is huge in this case because with PEX tubing, I could capture the heat within the compost pile and transfer it efficiently to the floor of my home to heat it. Water is 600 times more dense then air so it makes an excellent way to transfer it, and radiant heat especially so since I am using the mass of my concrete floor as a radiator. Because it is so big (and I have geothermal heating as well), it only requires 80-100 degree water instead of the typical 180 degree water baseboard heating systems use. My heating system is designed to control low temp waters precisely already, and compost heat is a low temperature heat, but long in duration, whereas wood is intense, but short in duration.
Also my manure pad is located just off from my barn which is a scant 100 feet away from my home. With modern pex plumbing systems, this is within efficient reach and move heated water.
And finally as a farmer all my life I am well acquainted with how hot a compost pile can get, though our experience is in putting up silage piles where we do NOT want it to heat, but to that end I have the utmost respect for the heat possible to be generated from compost and for incredibly long lengths of time.
It is tough enough to put up silage piles as is; to put up silage piles that you want to heat up would be even harder. You would have to include air in the pile and a heavy dose of water to keep things cranking during the long winter months. The biggest challenge for me was the amount of water. To get 9000 gallons atop this hill I would have to pay my local fire dept to deliver it. My drilled well just won't cut it at its 2 GMP recovery rate. Paying for heat slowly eats into the efficiency. Then there is all the pex it would take to run through the pile. It could be reused, but inevitably lengths of it would be destroyed when the compost heat was hauled off and renewed. This would be another annual cost. Then there is the fact that to get the hottest, longest temperatures you need both green and brown. This is wood and grass if you will. For my situation I had an issue with both components:
Grass: As stated before, I use every acre I can to graze sheep and for their winter fodder. Dedicating what I calculated out to be 2 acres in order to heat my house seemed rather wasteful per year. If I was going to do that then I might as well just take the 10 sheep I could raise with those 2 acres and sell them and just buy propane/coal or firewood. This is what I mean as it becomes an issue of return on investment. Buying silage would cost me about $48 a ton which is rather expensive for the tonnage needed.
Wood: I ran into the same problem here. I have plenty of forest and biomass I could chip and put into the compost pile, but that takes time and money. I could buy my chips, but that is a $1600 fee. I can heat my home for $1100 burning straight propane.
Then there is the issue of firewood. Yes it takes 35 years for a decent hardwood tree to grow, but here we can harvest 1 cord per acre per year sustainably. In three days time I could get enough firewood to heat my home without all the fuss of compost heat. That is ultimately why I never did it. Could I do it...YES! Should I do it when I can get firewood so much easier, cheaper, less labor and a lot less fuel...I don't think so, not for my particular farm anyway. As for anyone else...I don't have a rocket stove, but even with limited acreage, from what little I know of them, they glean the most BTU's out of a cord of wood simply because unlike a typical stove where 50% goes up the chimney (an outside wood boiler sends 70% up the stove pipe). In my way of thinking, you would have to be hard pressed to beat a rocket stove.
You ought to ventilate your mind and let the cobwebs out of it. Use this cup to catch the tiny ads:
Better Wood Heat: DIY Rocket Mass Heaters (8-Movie Set) by Paul Wheaton