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?