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Old 04-23-11, 09:29 PM   #10
Lurking Renovator
Join Date: Apr 2011
Location: USA, FL
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Default An elegant solution

I like the way you are thinking skyl4rk! The nice thing about fall leaves is they usually are dried up and store pretty well. You might benefit from shredding the leaves so they take up less space. But you can store them dry for a long time without fear they will compost on their own. You might even try posting flyers around your neighborhood requesting bagged leaves. Or you might use craigslist to request people who live near a part of your town contact you if they want leaves picked up. You would need lots of bags of leaves but they are easy to get and easy to store dry. Neighbors wont complain about bags of leaves piling up if you teach them about your system. They will probably want to contribute. Every one wants to be green these days. I will be talking about collecting and storing fuel for compost really soon.
Computer control is great. A far less complicated set up is more in line with most peoples needs. The least complicated compost heat generator is a large compost pile like the one in the video above. It consists of alternate layers of compost and plastic tubing to capture the heat. But this will not suffice for extreme climates in the dead of winter. An insulated box must be constructed to prevent freezing and control airflow and heat exchange. In its simplest form one must create a box with an insulated floor, walls, and ceiling with provisions for air tubes water tubes, and electrical connections. Your bioshed can be placed indoors or outdoors because the air will come from outside and be expelled outside. However indoor designs must be built "air tight" because if your box is relying on fans to circulate air and you should experience a power outage your compost will begin to decompose anaerobically. Methane gas is produced anaerobically and the process smells bad. If your box is well sealed any gas pressure will exit through the vents rather than into your living space.
So let me start describing the process from the ground up. Insulate the floor. How much insulation will depend on your climate but more is always better. The insulation must be capable of maintaining a temperature between 125 degrees Fahrenheit and 180 degrees Fahrenheit. This heat will be generated by the compost itself. Actually less than 180 degrees is probably better. I read a book which described the " U.C. Berkeley Method" of soil sterilization for commercial growers. It describes 180 degrees as the temp to sterilize most pathogens. I am hoping to find this book or any source that can give me better information on temperature ranges for composting bacteria. So lets set the upper limit at 170 degrees Fahrenheit for now.
It occurs to me people want specifics and pictures for any DIY project. I will be outlining my plans for this fall's compost project. The process of composting is as much an art as it is a science. So if you need a quick proven answer too bad for you. But you can join with me as I plan and build my system and watch as I share my results. So how big to build the floor? Well I have a space on the side of my house near my electric water heater ( in Florida an outdoor water heater is not uncommon) and near an outdoor electrical receptacle. That seems good. Also that wall butts up to the bathroom which is always cold anyhow in winter. So I intend to measure this space and begin designing from there.
Some key points of my design will be a system of perforated tubes to allow for ventilation of the compost, a tube in tube heat exchanger that allows for water to distill back into the compost instead of just spewing out warm moist air, hydronic heat coils, various temp sensors, and monitoring plus motor controls located centrally inside for my own comfort.
There is only one problem with this line of thinking. Perhaps you have already spotted it. A design like this one High-Performance HeatGreen Home Heating System Version 3a is already very simple and effective. The fact that it can aerate the compost and turn it makes it far superior to any design that simply insulates a mound. Insulating a mound requires a far larger working mass of compost, requires more insulation, requires more pipes, etc. There is no good middle ground that I can think of. You must either have a giant mound big enough to insulate itself from the cold and steep enough (or covered) to slough off snow and ice or you need an elegant digestion box. I have few concerns with the design I see here. It may actually be too big and produce more heat than is needed depending on what is being composted. It needs a heat exchanger for the incoming and exhaust air. Also it could benefit from buffer tanks to even out the heat exchange instead of increasing airflow.
I can't think of a more elegant solution than a good digester box. Can you? SO I will focus on adapting a digester to fit my needs for this fall. I had to point this out because I fear too many people will try to make compost mounds heat their homes and give up after achieving less than spectacular results, if any. I have shown you my thought process in its naked form. I hope I have not bored you away from this forum topic. My next blog will be about parameters to measure and control in a digeter box system.
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