 20, we came up with the idea of testing a modular composting system that would capture the CO2, moisture, heat, and nutrients that are usually lost from a compost pile and drive those under a grow bed to help plants grow during the fall, winter, and spring here in Wisconsin. We'll get into the background of this idea in a minute, but what follows is the run of this test over the next two years. We started out calling this hot box composting, but as you'll see, we ran into some pitfalls and some successes and then some more pitfalls as the system was being tested, rebuilt, and tested again. I hope that the information here will be helpful to somebody who wants to use a compost system to its fullest potential in terms of energy in and energy out. This is Low Tech Video Number 26, I'm Scott Johnson, and I run the Low Technology Institute where we research ways in which we can live in a future less dependent or not dependent at all on fossil fuels. You can hear more about what we do in our podcast, that's the Low Tech Podcast, also found on YouTube or wherever you find your podcast. Or you can go directly to our website, lowtechinstitute.org for more. But to start talking about our composting study, we need to have a little bit of a story time first. So once upon a time, eight or so years ago, when I was thinking about creating the Low Tech Institute, I was looking around to find similar organizations that combined research and hands-on experimental learning and testing. And I found something called the New Alchemy Institute, which was founded in 1969 by John Todd, Nancy Jack Todd, and William McLarney to research human-scaled systems of food, water, and shelter. They were ahead of their time and tested a lot of great ideas on their 12-acre research farm out on Cape Cod. They were doing aquaculture in the 1970s, something that didn't really catch on elsewhere until recently. What you're seeing behind me here is a clip from a documentary film from the Film Board of Canada called The New Alchemists, which I'll link to in the show notes. It provides a postcard from this research outpost in the 1970. It's really cool. One of the things that they studied at the New Alchemy Institute was a composting greenhouse. Now, compost has been used to heat greenhouses for as long as there have been greenhouses. It's long been understood that composting manure is a ready source of free heat and moisture. And before the advent of fossil fuels, there was a lot more horse and cow manure available for growers to use as compost. What the New Alchemist greenhouse did was create 12 large composting bays on the north side of a greenhouse, which ran east to west. Every few days, they would empty and refill two bays with fresh manure or compost feedstock. Instead of turning the compost piles by hand with a pitchfork, like most of us do or at least try to do, they used what is called an aerated static pile, which is essentially perforated pipes underneath the compost bin that pushes fresh air into the pile. The reason we need to turn compost is to put fresh oxygen into the system so that the thermophilic or heat-producing bacteria can continue to go to work. If we don't turn our piles, they start to stink because anaerobic decomposition has set in, creating methane and ammonia. As the blower motor pushes fresh air through the aerated static pile on top of the compost systems, heat, moisture, and carbon dioxide are pushed out of it. And these are exactly the things that plants need to grow, especially in the winter up here in Wisconsin. What New Alchemy did was seal the bays off with custom-built grow beds that absorb the heat, moisture, and carbon dioxide through a bit of wood chips and then soil, releasing all of that beneficial materials directly into the plant's roots and underside of the leaves where the CO2 can be absorbed. To do this, though, they had to build a large custom-built greenhouse with a permanently installed set of bays, blower motors, and other infrastructure. What I wanted to do was create a modular version of this that market gardeners could bring into their greenhouses in the fall, grow greens all winter, and then remove again in the spring to open up more space for their usual growing activities. My first idea was what I called the hot box. So I imagine a cube measuring four feet on each side. On top of the cube is a rich bed in which greens are growing. The soil is watered and fertilized from below. Plus, carbon dioxide would seep up in the soil. The soil is warm, even though this box would have been in an uninsulated greenhouse. Inside the box is a yard of compost waiting for use in the spring. This was my central idea for hot box composting. We wanted to run a series of control tests to determine the best practices with the system, including determining the optimum aeration of the compost, ideal carbon to nitrogen ratios, moisture content, and other variables related to the system. So in the spring of 2021, this project got underway with funding from USDA's Sustainable Agriculture Research and Education Grant Program. I did take a lot of footage of how the boxes were put together, and I'm playing those now. And I could go into great detail showing how they were built. But with a little bit of hindsight, I don't think this is necessary because although the idea was great on paper, I ran into a number of problems with this setup that make it essentially not worth trying. If anyone out there wants to build some for themselves and test them out, I'm glad to give you more information about how they were built. But just get in touch with me. My email is scott at lowtechinstitute.org. But essentially, these were boxes that were calculated to hold about one cubic yard of compost. We had two versions, one with an insulated stud wall, skinned with double wall corrugated poly and plywood exterior. The other was a tongue and groove single wall construction. Both were mounted on pallets so they could be picked up by a forklift or tractor and moved in and out of greenhouses, barn sheds, whatever easily. Both had a hinge mounted door on the front that I thought would allow for easy filling of compost feedstock and emptying finished manure. At the bottom of each compost bay was a four inch perforated PVC pipe to introduce air from the blower motor. Also jabbed into the compost feedstock were perforated one inch PVC pipes to allow offgassing of CO2 moisture and heat. The boxes were topped with a grow bed consisting of a half inch hardware cloth, floor supported by compost rafters, which I used because wooden rafters would have been composted in a season and rotted away. The lower portion of the grow bed was filled with wood chips, which would hold ammonia and methane friendly bacteria that would break it down into nitrates, which are more usable for plants. On top of the wood chip bed was a soil which would hold the plants. I built six each of each version of the box, which was a challenge because if you remember back to the spring of 2021, two by four prices, for example, had risen to over $12 a piece, which was not really priced into my initial budget. But I was able to build all the boxes on budget and on time, which was a shock to me, especially the on time part. If I had to modify, I had to modify the design to use less two by fours and other materials to stay on target. I spent the summer filling the boxes with various feedstocks from grass clippings and leaves to metagrass mowed down in a neighboring field. I experimented with various blower settings, which moved air through the piles anywhere from every 15 minutes to every hour, depending on the settings. Over the summer, I learned that smaller, fairly densely packed compost feedstock was performing best. With a nitrogen carbon ratio somewhere between 1 to 20 or 25 or 30, which is pretty typical of most composting systems, I did find that I had to add about five gallons of water per week to keep each box hydrated. Otherwise, the moisture was lost due to evaporation from the heat and constant movement of air. The plants growing on top didn't know better or worse for all this work, but it was summer and I really didn't expect the plants to need extra heat or moisture. And then came the fall and the real beginning of the test. The summer was mostly used just to get me used to the system and how it functioned. So I built a greenhouse and moved six of the hot boxes into it. I was expecting to move six hot boxes to the Parisi family farm later in the fall for a field test, but in short order, it became apparent that these were not functioning very well. First of all, getting enough compost feedstock was very difficult in the winter until we found that the three gates stable had a plentiful horse manure and bedding that they need to get rid of regularly. So even with the weekly influx of a yard of manure, we could not get the composting cycle started in cold weather. Because the boxes were only able to hold the yard at a time, a critical threshold of volume was difficult to meet. I tried pouring hot water into the compost to get started, but the manure just froze solid and refused to compost. Additionally, the boxes proved more difficult to load and unload than expected. I had forgotten to consider how much weight the grow bed would have had when propping open the lid to allow easier access. Because of these two reasons, this size of a hot box does not seem to be a viable way forward. Perhaps one could work that holds two yards, but such a large box would be difficult to move around without a forklift. And these boxes alone required a reasonable amount of resources to build a lot of labor. They were just more trouble than they're worth just to have a mobile unit. One might as well build a custom greenhouse like the new alchemist had instead. So as I struggled through this first winter, I had plenty of time to think of a better way. And instead of trying to downsize what the new alchemist had done into a modular unit, why not take the concept and build up from a more user-friendly design? So I started thinking about how I would design an aerated static pile to run without consideration of capturing the off gases for future use in a bed. And the idea of using simple composting bays like a typical medium scale composting setup came to mind. This is the beginning of a system that I've redesigned to try out this winter where it's built into the ground but it can be taken up into the summer and stored away with not a lot of space. All of these parts come apart. They can just be tucked together in a corner, in a barn or another outbuilding. And then in the winter, you could build them again very quickly in an afternoon. So basically what I'm doing right now today is putting together the plenum that distributes the air from the pump and then I'm going to put wood chips. And then on top of that bed of wood chips, I will put a pallet and that pallet is then gonna get wire on it to help keep everything above it. And then basically we'll have four bins because it takes about four weeks to work through the compost. And then each bin will be covered with compost and then air will be pumped up underneath. Now to catch that air, it's going to have a bladder or a tarp over it with a perforated flexible pipe that will then be directed into a grow bed. So we'll still have the grow bed but the grow bed will be in the ground. And so in a greenhouse where this is a modular seasonal thing, you could keep that pipe in the ground all summer and then in the winter, when you're ready to set this back up, you can reuse that pipe system. So it would take a very minimal install in your greenhouse. Okay, so I've filled this thing up with four yards of horse manure on some of the hottest days of the year. So that's been super fun. What I have here is a pile with, these are PVC pipes with sluts drilled in them and they are to help increase the airflow out of the center of the pile. These can get kind of dense and heavy. And so I've taken these PVC pipes and cut them, they're two feet long, and I put them down when it's halfway filled and then fill it up the rest of the way. And this allows moisture to escape in this morning. We saw all the moisture coming out of them in the sunlight. And then up top this, this is the intake for the pipe that will go under the grow bed. So this is corrugated and punctured drain tile pipe that's attached to the top here. Not only will this intake the moisture, ammonia, nitrogen, CO2 and heat coming out of this pile, but it also, being up top here, will help protect the tarp from resting on this wood that may have sharp edges. All right, so this is what drives this system. This is a Bair, B-A-I-R blower, Kodiak power KP1. It's a one horsepower 3250 RPM inflatable bouncy castle blower. And what this does is it cycles on, well, it cycles on every half an hour for a minute, although you can vary that and really depending on how much and what stage of compost you have, you need to vary it more. The more oxygen you put in, the faster that reaction in your compost is. The more oxygen the microbes have, the faster they turn it to compost. But the more air you put in, the more you cool it down. So those thermophilic or those heat-loving bacteria get chilled every time that you pump cold air in there. So this is especially true in the winter. In the winter, you might wanna use some preheated air from somewhere, if possible. But basically there's a balance and you have to find that balance and you have to experiment with that balance with your own setup. So right now what I'm gonna do is turn this on and it's going to blow air, I'll follow it with the camera through the plenum into the compost pile and then up. Right now I don't have the tarp over it so it's gonna gas into the atmosphere, but let's see. I can actually feel hot air coming out of this port. So it's definitely pushing air through the pile which is a good sign, I want that to be happening. And here I have, and here I've got what regulates this one, tells you how long it's on, so that's just one minute. And this says how often, this is every 30 minutes. You can also set it just to work at night or day, whatever, I have it on during 24 hours. When I plug this in, it should kick on and then I'm gonna cover it and this will be protected from the rain. You can use a five gallon bucket or whatever you want. That should keep out pretty much all the rain. So every half hour, this comes on, puts fresh air in there. This traps all the nitrogen, the CO2, the heat, the moisture all in this and then around the back it comes out of this port. So let's take a look. And then right here you can't feel it, but I can, here comes a good amount of air out. Nice, warm, moist air. Smells like compost. Around the bottom, I've put weight with logs and then I've covered it with soil to help seal this all in. That goes all the way around. So now I'm gonna attach this pipe, force all this air to go into the grow bed. Now that all that heat and moisture and nitrogen well it's done here, I'm gonna get a longer extension pipe so it doesn't have to go over the top like that. Comes down under this mulch. And so if we excavate out down to the pipe, we should be feeling and smelling a little bit of, oh yeah, I can feel the air coming in and push through. So that's exactly what we want. Wood chips, compost. Now this bed is getting all that moisture and nitrogen. So it was modular and it was more user-friendly since the tarp simply could just be pulled back. I didn't have to lift those heavy grow beds. I could just lift the tarp back and pull a trailer right up to the bays. It would also solve the problem of a critical mass of heat to get the compost system started since the bays shared walls and covered space with one another, the already running compost heaps could bring the temperature of the new feedstock up really, really efficiently. So I built and tested this new system thanks to a no-cost extension from the SAIR grant agency staff, so thank you them for that. I ran the system using manure all through the summer of 22. That system was very consistent and I was able to get measurements of heat, moisture, carbon dioxide, and other gases throughout the summer. So each week I come out here and I test. This is the old configuration. I'll show you the new configuration in a minute. But I popped the vent off and I put in two testers. This is a methane tester, which is currently showing zero parts per million. Today is August 28th. So I test this twice. Right now I call it passive. The bladder isn't full. When the motor runs and it puffs with air, I'll test it again just to see if I get a different reading. But right now I have zero parts per million methane. And you can hear the beeping and the crowing. The beeping is my CO2, which has maxed out. I've maxed out my CO2 parts per million. The temperature is 27, 5, and 99% humidity. So it's a little warmer than it has been and we've maxed out the CO2. So if you think about this, your compost pile is putting out large amounts of CO2, which is a greenhouse gas. Composting is actually adding to global warming. Any breaking down of carbon will add to global warming. But so what I'm doing is capturing that CO2 and pushing it under a garden bed where hopefully it's a little bit more used by the plants and things before it gets put into the atmosphere. I don't really know how much that's happening. I'd have to do a CO2 test. Anyway, beep, beep, beep, sorry about that. All right, so now we're gonna puff this and let it run through the, oh, perfect timing. Usually I have to cycle it myself. Temperature has heated up because it's pushed some of the heat out. I've lost, I've let in my pencil. All right, so I'll write that down here in a minute. Yeah, so each week I do this, as well as take internal temperatures. So I'll show you how I do that now. And now I'm gonna come through and measure directly the temperature of each pile. These were put in, that was put in two weeks ago, one week ago, four weeks ago, three weeks ago. So I just keep moving through and cycling these out with my new horse manure. So in theory, that should be the lowest temperature. I take both a compost thermometer, pH, almost a PhD, a pH tester and I'm hoping for something under 120. But I also have digital, if I can find it. So this is the digital thermometer saying 139. This is saying 112. So this I need to put into a, this I need to put into a Ziploc bag because it is, I've lost some due to water. All right, now to close this thing up. I have a trench, a trench here in front, that's full of manure on the sides. Just clean out this trench a little bit. The trick is to get this bladder airtight and you need a certain critical mass of compost to do it. So the way I found to do it that works best for me is to bring this corner around and lay it down. So now that's down in there. Same thing on this side. So I leave kind of like a U-shaped trough. Now, pull down the front and I continue to keep that trough shape so I can seal this all in. Otherwise the air escapes and you have blowouts and you lose all your precious carbon dioxide and nitrogen and heat and moisture. So, okay, and now I put these heavy pieces of wood down in there and help kind of hold it. All right, and now to seal this in, I liberally apply compost to fill in that trench. All right, let's give it a run and see if it holds. This is gonna stay inflated as it pushes all this CO2, nitrogen, heat, moisture through that pipe that comes out the back that I just reinstalled and into this grow bed. And that, just over here. So this garden bed is unplanted. But for the winter, what I'm gonna do is cover this over with a small greenhouse enclosure and then plant this. And then the heat from this compost will be blown in here constantly throughout the winter to hopefully keep the temperature up a little above ambient. I'm also gonna have to put in an intake pipe for my blower that runs through the compost because I found last winter, if I just sucked in ice cold air and it's 20 below, you're putting minus 20 degree Fahrenheit air into a compost pile, it drops that microbial activity and it drops the composting activity significantly. So you gotta preheat your air. So yeah, like I said, what I'm gonna do is run a pipe just right through that bladder and the intake then will take in warmer air to pass into the compost. So it won't cool down quite so much. I might also have to vary my blower motor speed. I found that in hot weather, I have to run the blower a little more often to maintain optimum's heat in the piles. Otherwise it can run away and get too hot and kills off microbes. In the winter, I might have to run it less often because that microbial activity needs time to get its heat back up. So it's a little bit of an interplay and takes a little bit of finicky fiddling for wherever you are in your low local conditions. Right now this meter's running at 30 seconds every 30 minutes. I found when I ran it for a full minute, it was too much pressure and I got a lot of blowouts. So right now, like I said, I'm running it for a maximum of 30 seconds. If I need to vary the amount of air that's coming in there, I will put it on a faster periodicity so it will run every 15 minutes, 10 minutes, whatever, rather than a longer run because the longer run blows out this bladder. In the fall, I was able to install a new version at the Parisi family farm for testing in the winter of 22-23. The only changes I made between my first version of the system and the new one was that I did not try and put the corrugated off-gassing pipe through the tarp because that created a point of failure that I had to try and attach the tarp to the corrugated pipe. It made a mess. Instead, I just routed the pipe underground into the grow beds adjacent to the composting system. And here's a perforated pipe 16 feet long with a T in the middle that will come out of the off gases from the compost pile here, letting all the nitrogen, carbon dioxide, heat and moisture into a grow bed. I'm gonna cover this up with wood chips now. Now the wood chips cover up the pipe so that when the nitrogen and other gas-containing gases come out, they go through this wood chip pile which will become inoculated with good microbes that help convert things into plant-usable nutrients. And now I've used some scrap timber to spike down the tarp. It's gonna cover this whole thing. The new configuration, the grow beds were built right next to the ground, or next to the bladder on the ground with perforated drain tile covered by wood chips used to diffuse the gas and absorb any nitrates and convert them into nitrates. This whole thing was covered by six inches of soil for holding the plants, of course. So let's talk a little bit about what we found out. We were excited to have temperature monitors, taking readings every 15 minutes inside these boxes and we were excited to see what was going to happen. So we were excited to see what was going to happen taking readings every 15 minutes inside these boxes and inside the later system. But as you can imagine, little electronic devices being kept at 150 degrees, 99% humidity for months on, and really just meant we had little plastic electronic bricks. Before long, even buying new ones and sealing them in bags didn't help. Luckily, we had been monitoring our data with other means and can certainly report some of our findings here. Let's start with temperature. Even though the digital thermometers eventually failed due to heat and moisture, I had been comparing the monitor's temperature to an analog compost thermometer inserted into the piles each week when we were emptying and filling. And I found that the inserted thermometer was within a degree or two of the digital ones. So luckily, I had been recording the temperature of each pile each week manually as a backup because I used to work field projects and don't trust electronic systems. Instead of having just data recorded every 15 minutes, we only had data recorded every week. But the temperature rise and fall were slow and steady and therefore we can still create trend lines and talk about compost heat profiles. The system produced textbook compost pile temperature curves. As you can see here in the figure, each well-documented temperature curve is shown in gray and is partially transparent. So where the curve is darker, that means multiple curves are overlapping, meaning it's in a more common occurrence. Essentially, the darker the area in the graph, the more common the reading. We can see that the manure was emptied into the bins more or less at ambient temperature between 60 and 80 degrees Fahrenheit. And within a week or two, the pile would hit its maximum of about 160 degrees. And this is where the bacteria and microorganisms responsible for composting begin to shut down at that high temperature. It would hold at this temperature for at least a week or two before a slow fall off over the next three weeks. And by the time we're emptying the bins four to six weeks later, it's down to about 120 degrees. We also measured the temperature of the air inside the bladder, which was also warm as the piles breathed out into this confined space. And although the air being blown out of the piles would have been over 120 degrees, it was moderated by the ambient temperature of the outdoors. The bladder skin, which was really just an impermeable tarp, was only insulated by the addition of a second tarp on top, creating a bit of an airspace. So the warm, moist air coming out of the piles quickly condensed on the inside surface and cooled. The air being blown out of the bladder into the grow beds, averaged between 60 and 70 degrees Fahrenheit, compared to the ambient temperature that was down often in the mid-30s or 20s. So unlike the new alchemy setups, we lost a lot of heat through the bladder. The new alchemy setup had grow beds on top of the bins, collecting that heat passively. And this is one downside that could be potentially attenuated by a better insulating blanket over the bladder perhaps. We also measured humidity. And there isn't much to say about humidity since it was basically 99% pretty much all the time. As long as I was keeping the piles wet and as long as the compost was active, humidity hit 99%. Water was one of our limiting factors and we had to pour five to 10 gallons of water each week into each bay to avoid stalling the composting process. And once we figured this out, composting functioned very smoothly. In the hot boxes, the moisture did rise up and collect on the grow beds, but in the tarp covered model, the moisture often collected on the tarp and then dropped back onto the compost, which actually allowed us to put in slightly less water into the bays as compared to the boxes since the microorganisms that drive composting had as much oxygen as they needed. Water was our limiting factor. Also in the bladder, moisture getting up into the air could then be more distributed between the four adjacent bays rather than in the individual boxes where it was they only had to depend on them or could only depend on themselves. Now I say that the microorganisms had enough oxygen and I know that because we never found much for methane or ammonia present. We used a combustible gas sniffing detector and never found anything over one part per million. Actually, we never found anything. So this suggests that our composting system was functioning completely aerobically. And although this is good as methane is 25 times more potent than other carbon dioxide for global warming, it does not transmit much in the way of nitrogen to the plants through the air. And that nitrogen was going somewhere though and it was into the compost itself. We sent off a sample of our manure to the University of Wisconsin, soil and forage analysis lab in Madison. And we learned that our composted horse manure had about 8.32 pounds of total nitrogen per ton. That amount didn't change after 72 hours of further composting suggested that we had completely composted our feedstock. In that same time, we would get 6.35 pounds of phosphorus, 1.85 pounds of potassium plus 1.15 pounds of sulfur. It also had a whole bunch of minerals. And in the end, we could consider this compost to be a one to 0.76 to one compost as far as those composting ratios go. Now, each week, we also measured the carbon dioxide levels in the air within the bladder. And again, it maxed out the sensor at 10,000 parts per million, which is twice as high as OSHA's exposure limit. So as long as the compost piles were fully functioning, the carbon dioxide production was more than plentiful. And actually I made the joke, and obviously this is a joke, that I said, you know, don't mess with me. In my backyard, I have a composting system that will asphyxiate you, right? Like if I put you, knocked you out and put you in this bladder, you would quickly die because it's all carbon dioxide, no oxygen. And then what would happen, the compost would break down your body and in a month, you'll have completely ceased to exist. A little bit of an exaggeration. And obviously I was joking, I would never do that. But it's a fairly, it could be a lethal system is what I'm saying. So it's a little bit of care is needed. You don't want it to go into the bladder and be closed up in there. You would asphyxiate pretty quickly. So when we were just getting the system online during the first week or two and we just had a couple of bays working, we would see carbon dioxide levels in the four, between four and 7,000 parts per million. But quickly it went over 10,000. We also did test our grow beds but because of the difficulty we had in getting the systems up and running smoothly, we were far behind in the season to effectively test this component of our study. We did anecdotally transplant some bok choy into our grow beds at the Parisa Family Farm but these died and it's unclear if it was due to transplant shock, winter exposure or overexposure to carbon dioxide because we didn't have a huge amount of growing beds to absorb the amount of carbon dioxide being produced. And that will actually, too much carbon dioxide will burn and kill plants. And that may have been what happened that we don't know without further testing. We did end up with what worked out to be best practices for our system in our location but keep in mind that these may be different for you and warmer, colder locations or different amounts or types of feedstock. So for us, we found a blower which is a bee air, one horsepower, a 1,170 cubic foot per minute inflatable castle blower. Could be run for 30 seconds every 20 minutes in the summer, 25 seconds every 25 minutes in the fall and spring and then 20 seconds every 30 minutes in the winter. If we blew any more in the winter, it would introduce too much cold air. If, however, your recycling air already warmed from a greenhouse, you could probably blow at a higher level. We had to add at least five gallons per week to each pile, especially in the summer as things ran a little hotter. We found that horse manure with straw and sawdust bedding was already the perfect mixture of nitrogen and carbon for our needs, since horses really don't digest their food as thoroughly as cows. There's quite a lot of carbon in their manure. But if one were using cow manure, for example, you'd have to throw a lot more carbon in on top, I suggest, I suspect. So we found that manure needed about four weeks in the composting bin to be largely spent and then another month outside in the pile with other manure with previous weeks to cool off or to finish itself off before putting on crops to avoid burning them with excess nitrogen. So if we are going forward and wanted to continue to use the modular type of composting system to capture the heat and moisture and carbon dioxide from the compost for winter growing, we do have some recommendations. The first is install an automatic watering system. Maybe even a moisture sensor at the bottom of each pile, which is where they dry out first because the dryer is coming in. Maybe a drip hose or something at the bottom of each pile to provide moisture on an automatic basis would help further stabilize these systems and make them less to do each week. Second, with more time to experiment with the amount of air being blown in, we could probably throttle it down until we start to see the production of a methane or ammonia, meaning that we're starting to get some anaerobic digestion, meaning we're getting, we're a little short on oxygen. And then turn the blower up just a little bit so that you're getting just enough air. Just enough air is absolutely necessary to keep the system aerobic. This would help increase the heat and efficiency of the composting because every time the blower turns on in excess of what it needs, it cools down the compost pile, which then has to regenerate the heat. It's inefficient, plus it's an extra waste of energy. Third, we did experiment with using a temperature sensor to turn on and off the blower, but we found that the sensor was not consistent enough due to difficulty in placing it. We tried putting it in the air inside the bladder, but that was too variable. We tried putting it inside the compost pile, but the internal variability of the pile itself and the small sensor could not capture what was really going on. And then we would go for long periods of the blower off or on and it would just bring the system out of whack. So it was better just to adjust the blower seasonally like I described before. Fourth, we determined that the carbon dioxide levels on the bladder was the best indicator of the system's health. And if one wanted to put an alarm on the system that indicated CO2 levels below 10,000 parts per million, you could be alerted to a system that wasn't functioning properly and needed probably more water, more airflow or more feedstock. But really, after testing the system out, I think the real solution is to just build a permanently installed composting system within the north side of a greenhouse. By building permanently, you can have a lot more control over how the system works and pushing air right into the grow beds with less wasted heat. So I wanna thank Earl Bernhard at the Green Center, which succeeded the New Alchemy Institute and Peter Moon of O2 Compost for both their technical advice during this project. And of course, none of this would have been possible without USDA's sustainable agricultural research and education grant funding. So thank you to the reviewers and the staff of that program. Thanks so much for watching and listening. Please feel free to ask questions in the comments. Reach out to me again. I'm Scott at lowtechinstitute.org. Find out more about what we're doing at our website, lowtechinstitute.org, or through our social media channels. We're on Instagram, Facebook, YouTube, as you can tell. So anyway, thanks a lot for watching. Take care.