hot water from a compost pile

We want to do something a bit like this:



We have lots of woody bits and sawdust. We have been feeding our kitchen scraps to the critters, and the critters do the paddock shift thing, so there is not much in the way of piles of manure to grab.

Maddy Harland (the editor of Permaculture Magazine) suggests that we pee on it! I think that will help, but I suspect that if 100% of our N comes from pee that that might not work. Or there could be issues. Does anyone have experience with this?

I'm thinking 40% pee would be optimal and 70% would be pushing the limits - but this is entirely speculation.

This would be for the upcoming workshops. For showers, laundry and handwashing.

(I'm repeating myself as this thread is more specific to this topic. I did add a bit.)

For heat in your sawdust pile, could you not gather some of the surely copious pig manure? I know they're doing paddock shift, but they also tend to hang out where a person might show up with goodies, plus there's the natural piggy tendency to pick a spot. Also, what happened to the cattle non-cleaned out innards? None of this is fun, but persistent herbicides could be present in most manures you get from outside sources (who weren't as strict about hay).

Perhaps a combination of gathered onsite manure, animal innards, and urine. Install 5 gallon buckets with sawdust in all flush-toilet equipped bathrooms, and put a bucket at the end of the urine diversion system at the pooper. With enough sawdust (and mixing), none of this should stink.

This wouldn't be a bad use for human food waste from say, the Riverside Cafe. I've learned from Walter Jeffries that you don't want to give post-consumer food waste to pigs because they can catch colds and flu from it, but you could compost it. . .

I suppose we could pop out and see what we could find.

Another thing I want to point out is that i think we should put a few posts in the ground in a circle about three feet in diameter, and then attach the poly pipe to the posts so that the pipe stays in a fixed position. I think this setup will cause air pockets which will help with hot composting.

http://www.compostpower.org is an excellent resource for this endeavor. They are working with the Jean Pain method in Vermont. From their "Design and Installation Guide" page:

Feedstocks: Bark Mulch, Wood Chips, Sawdust,

We believe a variety of feedstock-materials can be used to generate significant heat. Controlled tests are being conducted through UVM and other demonstration-sites to document the temperature and longevity of various combinations of mulch, chips, sawdust, manure and other compost-process materials. Some materials or mixtures may run hotter but for shorter periods of time. Hard wood materials may provide more heat than soft materials but soft woods may heat for longer periods.

It’s important for at least some of the material to be shredded or small-diameter wood-chips to provide enough surface area for the bacteria and air to reach the material and build critical mass of activity (heat).

A mound made of wood-chips alone will produce 95 to 110 degree water for in the spring/summer/fall but will cool off in the winter. Shredded bark-mulch works very well and should provide 110 to 140 degree water as long as it’s fresh and has not been contaminated with industrial lubricants. Rot-resistant feeds-stocks like cedar, hemlock or black locust will not produce heat and are to be absolutely avoided. Pine is ok in small proportions but not recommended as the primary feedstock. Fresh double ground barks will provide about the right particle size for most projects but wood-chips mixed with sawdust and/or manure will also work. The quality of the feedstock and the aeration of the system are the main factors determining the amount of heat produced and the value of the compost after you stop collecting heat from it.

So, it looks like nitrogen will be needed to battle the cold weather, but maybe not as much as you might think.

Poultry manure makes the hottest compost. Using only that and maple leaves, I've produced scalding conditions. I suspect that the rock dust from a bird's gizzard, adds extra nutrient for decay organisms. I used rock dust in my mix to add thermal mass and to hold things in place. A thick layer of dry leaves or sawdust, works as insulation. Incoming water should circle the outer material first so as to gain benefit from the lower temperate there and then, the preheated water should loop through the hottest area and exit.

Heat that has migrated to near the surface, is in danger of being lost. A system that uses several pre heat loops in this zone, will be more efficient. We want the core to always remain hot, so it is never exposed to cold well water.

Under construction:





It took about two days for the compost to heat up to be used. But then we seemed to run out of hot water quickly. We think that when the pile gets hotter, the heat will last longer. More news as events warrant!

I'm curious what your recipe was for the compost pile on this attempt. How many bales of hay went in, about how much sawdust, how many barrels and how much poly pipe did you bury with it? I'm very interested in this method so any details would be appreciated.

J

I would guess about six bales of hay. And then there was that much plus another 50% or so of sawdust. A few shovelfuls of soil here and there. And then we added some compost activator - just to be sure. We added water once in a while. Then a bunch of water at the end. And then lots and lots of people peed on it.

I think there is a hundred feet of pex wrapped around six t-posts.

I'm keen to hear how it progresses.

Thanks for the update.

J

I think you need more tubing, i.e. more surface area. What I see is that the pile is probably hot, but the material can only transfer heat at a certain rate and your tubing can only conduct that heat at a certain rate.

According to the handy-dandy chart on page 7 of http://www.heatlink.com/sites/default/files/Info%20Sheet/L2305-PEX-Tubing-Technical-Information-2012-10-29.pdf, for 1/2" PEX (not sure what you're using), your tubing:
- hold about .00921 gallons per foot (about 1 gallon across your 100' pipe)
- conducts heat at about 5 BTU/h/Ft (about 500 BTUs/hr in your 100' pipe)

If I did my math correctly and read the chart correctly (that's a big if), then your 1 gallon (8.3 pounds) static in the pipe can be heated about 60 degrees in one hour...I think. And once you use that water in a minute or two of showering, your tubing will lose all its heat and you'll quickly move to source temp.

So... I'd say there are a couple of options:
- increase to about 500' of tubing as explained in your video and maybe use a larger diameter tubing (1" tubing will give you more than 3X the volume and act as a larger holding tank - i.e. 15 gallons)
- slowly recirculate water through an insulated storage tank and the pile loop and just tap showers off the storage

J

I'm very interested to see how this turns out, keep us updated Paul! The showers look great! I bet the pile is still getting warmed up.

One thing to consider is that while pex is a great product and relatively inexpensive it has a lower heat conductivity factor. Copper is a much better conductor than pex. I've read as little as 12% in some places, other places say 60% more. I guess you could do a cost analysis if you wanted. You could also do a retro fit to the pile, add another new pile next to the first one, use cooper in that one or a ton more pex.

I picked up some pex off Amazon for $28 for 100 feet. Copper pipe on there is running about $110 for 100 feet.

If it were me, but of course its not, the nerd in me would do two similar piles one with pex the other with cooper and compare in an experiment.

you would need a lot of pee to be able to add enough nitrogen to get the process going.....Humanure get a pile super hot but I know your not a fan....alternatives to this include spent grains from a brewery and coffee grounds. If you can find a few hundred pounds of each then mix in with some straw and or wood chips you will have a super hot compost that will last for a while.

Oh right! We do have about a bunch of spent grain from a brewery at the bottom of the pile. From a permaculture-savvy brewery in the bitterroot: Wildwood Brewery.

paul wheaton wrote:Oh right! We do have about a bunch of spent grain from a brewery at the bottom of the pile. From a permaculture-savvy brewery in the bitterroot: Wildwood Brewery.

My experience in composting spent grain is it get anaerobic quickly. I think the anaerobic processes don't get nearly as hot as the aerobic; however, the moisture might help keep the upper portion of the compost nice and hot. I get a dump trailer of the stuff nearly every day of the week. I've tried it as a mulch, incorporating it in with other manures to compost, and feeding to animals. Warning: it will probably be stinkier than the rest of the compost pile!

Is the hot water lasting longer yet? I'm really curious about other designs for capturing heat from compost.

I made a pile last year using mostly goat bedding/manure and some beer grain. It was about 8' wide, 6' high and 70' long (I have a shitload of goat bedding available.) I made layers a couple feet thick and ran 1" black tubing through each layer. I think I must've had at least 500' of the 1" tubing. At first I pumped cold well water through and it'd stay hot for a few minutes until the water in the tube had been flushed (about 5 gal per minute for maybe 4 or 5 min.) This could be a good 20 min shower if I used a 1 gallon/min shower head. I then used a pump to recirculate water through the system. I just had a stock tank with about 75 gallons in it. That was up to hot tub temperature and would stay there. Eventually the cheap pump I was using blew out and the thing froze up...afterall, the thing was running in mid-June in Maine with the pie outdoors and the tank in an unheated greenhouse. I wasn't paying enough attention to it to know if the pump died first or if the water cooled enough to freeze and the pumped failed pushing against ice.

My thoughts:
- how to build the pile with the tubing so it can be deconstructed easily for rebuild - rather than build layers upwards, how about horizontally with a manifold at the end so a new pile can built and added on
- move minimal amount of water through the system to keep the bacteria immediately around the tubing from chilling so much that the composting process slows
- recirculating water can make a stockpiled water supply pretty hot

So, I'm curious to see how this works for you and your gang, Paul.

Justin

From my experience as a plumber and a lot of study of domestic how water systems; also various ideas:

1) When the water warms in the tube the compost around it cools somewhat. How fast does heat move through the compost to keep the area near the tube hot? Probably not very fast; the wetter the compost the faster the heat transfer.

2) Assuming some sort of adequate heat transfer, what BTU's can you get from 1 cubic foot of compost (or yard or whatever)? How does that square with your needs for heating water from, say 50F?

3) What is your freeze depth in your location? Plumbing installed above the level s/b well insulated.

4) A "closed" system will be more reliably sanitary.

5) Keeping a tank over 140F will discourage legionaire's disease (bacteria borne); 160F is better in that regard. 85F to 120F is the favored range for bacteria growth. The more change-over in the tank water (from usage) the less chance of disease from bacteria.

Moving water through the tube at higher velocity reduces the amount of heat pickup but requires a more powerful pump. This may be desirable because of the slow heat movement in a compost pile. Many smaller tubes have more surface area per unit fluid (more heat pickup) than a few larger tubes. Slow heat gain probably means you need large insulated water storage. Insulating the plumbing anywhere it isn't actively picking up heat _will_ make a noticeable difference in the amount of useable heat you harvest and deliver. If you want the system workable any time soon you probably need to use pumps, not try to rely on thermal siphons; siphons are temperamental phenomena, very picky about everything and good for a hobby but not a production system. (Based on trying to get half dozen or so siphons to work under close to ideal conditions on hot water tanks. Siphons _will_ go gang buster when you don't want them to though... <g>) Large storage tanks w/minimal flow relative to tank size (when not in use) will stratify - that is there will a about 1/2 to 2/3 tank of hot water over the remaining noticeably cooler water. This implies delivering water from the top of the tank; also the quantity of hot water actually available is less than the full tank size. But this is a good thing because when delivering hot water at full demand incoming water will _not_ get heated enough for use and you don't want the cooler water to dilute the good stuff. So run new water into the bottom of the tank. The larger the tank relative to the demand/inflow the less disturbance of the thermocline and the more hot water you can get off the top before you hit the cool stuff. You can tell how much heat you're taking from the pile by comparing in/out temperatures, but it might be easier to understand a temp probe in the pile. If the theoretical pile temps go over about 200F, install a Pressure/Temperature relief valve on the tank.

3) If mining and rebuilding the pile quickly matter you might consider _straight_ tubes run through the pile only once, connected to a manifold at both ends. Disconnect the tubes at one end, cap or plug, and pull them all straight out of the pile using the other manifold. Lay the tubes in 10-20 tube wide layers using multiple manifolds to add more tubes to make handling easier. Demolish the pile as you please. But disconnecting 50+ tubes might be pretty time consuming itself; using a _long_ compost pile might improve that efficiency, though. Don't know how it all might balance out.

I'm tempted to build one of these. Where I live, a lot of people have horses, but they also don't really want the horse manure. It's pretty easy to pick up two truckloads of manure in less than an hour. Anyone see a problem in using horse manure for this setup?

Thanks,
Daniel

Daniel Weeber wrote:I'm tempted to build one of these. Where I live, a lot of people have horses, but they also don't really want the horse manure. It's pretty easy to pick up two truckloads of manure in less than an hour. Anyone see a problem in using horse manure for this setup?

I think it's fine. Higher C:N ratio because of horse poo being high in carbon and usually comes with a good amount of bedding and old hay. Only potential problem is it could contain persistent herbicides in the final end compost, but that just depends on the source of the hay.

Justin

OK how do I jump in here. There are many things that can be said in order to really address the solution to this task.

Problem: Heat water for a bunch of dirty permi folk all year long without enough harvestable nitrogen throughout the year.

1- In order to heat enough hot water for 4 shower stalls you will need 4 well built compost heaters but you will get 4 good piles of compost and you could stager them so that as one is cooling down the other is heating up.
2- In my humble opinion it looks like your compost pile is really lacking in nitrogen. What you need is a lot more manure and lush freshly scythed green material, grass, nettles, comfy etc. The pile you built may heat up but it won't sustain the heat very long without the food for the microbes. Fungus likes carbon, bacteria likes nitrogen and minerals. Look at carbon to nitrogen ratios: sawdust 500-1, straw 130-1, cow manure 18-1, fresh lawn clippings 12-1 you are shooting for 30-1 or higher for a compost pile to heat water for long period of time. Building a good compost pile is truly an art form it takes years to perfect for this kind of desired results. If you want to just make compost for the sake of compost it is not as hard. As they say "COMPOST HAPPENS". More on composts and carbon to Nitrogen ratios can be found here, http://www.oregonbd.org/Class/Mod4.htm and here, http://www.oregonbd.org/Class/CtoN.htm
3- The water coil must be long (at least 150' for poly) and conduct heat (better then pex). For best results it must be evenly distributed throughout the pile ( see photos for my method). Heat rises if you stack the tube on top of its self as in a vertical coil you will only be able to harvest the heat from one vertical area within the pile. If the tube is evenly distributed willy nilly throughout the pile you disperse your collection points evenly through the horizontal and vertical space within the pile
4- The pile needs to be much larger like 5'-6' wide by 10'-12' long by 5'-6' tall for one shower stall. Also the water pipe that runs through the pile must be at least 1' from the outside of the pile. lots of straw insulation covering the whole pile from the top all the way down the sides to the bottom.
5- If the pile is built right... and the coil is properly installed... and the pile is big enough one should be able to expect 2-3 months of hot water, hotter at first tapering off towards the end. However if there is an excessive demand there is the potential to kill the pile by freezing the horny little microbes that are franticly procreating to create the heat. So a regulated use should be observed for the longest run of the pile. Read- low flow shower heads and staggered use. Don't overly chill your microorganisms!
6- It strikes me that compost piles are not the best solution in your climate and situation for a year round bath house in Montana. Not enough green material not enough manure, not enough permi power to build and harvest and rebuild the compost. What about a rocket hot water heater? You have lots of wood all year round! Build it once and stoke it up for all four shower stalls any time of year! In the summer when you have an abundance of green biomass and manure then build a compost hot water heater for diversity and education to run one shower stall. What about this as a solution?

7- You need to ask yourselves what are your goals for using compost to heat water? Is it for the compost? Is it for the novelty? Do you have too much biomass? Do you want to use this as an avenue to do experiments? Or do you want to clean up the stinky permis? All of the answers to these questions will lead you to the right approaches to take.

Hope this helps.

I would be happy to answer specific questions about what I have learned after doing 5 Summers of showers here with my compost heated [youtube][/youtube]shower system.
P.S. I'm not sure how this is going to post as I am still getting used to this site

Brian,
Thanks for your post. Great stuff! I like the pictures illustrating the spirograph style. I think my biggest difficulty in the whole system is the deconstructing the pile if it's any larger than your size. I still like the idea of building it such that the spirograph hoops are turned on the side and building the pile sideways. Maybe if I get a chance this fall, I'll try it again.

One thing I am curious about (read: disagree with you slightly) is the C:N ratio. Ideally a compost pile is 30:1, but that is to reach the pathogenic microbe and weed seed killing temperatures (135-175 degrees F.) So the N is chewed up quickly and you get a hot pile fast, but it also cools quickly. Take a look at the chart at http://whatcom.wsu.edu/ag/compost/fundamentals/needs_carbon_nitrogen.htm. That is why I'd suggest a higher C:N, which is a bit closer to the Jean Pain method of chipped wood. And I almost wonder if the pile could be aerated in a simple way, it'd stay hotter for a much longer time.

Also, from my experience here in Maine, I don't think it would be hard to keep a good compost pile warm through winter. It may not make it through the whole winter, but there isn't any reason you couldn't build another pile later. It might be a little slower to come up to temperature, but it'll heat up.

Justin

I would also suggest taking a look at this design and build by Rob Frost from One Straw Rob. He does a good job of explaining the setup and has done multiple attempts. His also includes a methane collector.

http://onestrawrob.com/?p=1308

Milkwood Farm in Australia built a rocket stove water heater for their PDCs:

During our twice-yearly on-farm PDCs we have over 30 people at our farm for 2 weeks straight, all using this system exclusively for their showers. While I’m not sure everyone chooses to shower every day, many do and the system holds up under the enthusiastic strain. A pretty good recommendation, i think.

http://milkwood.net/2011/08/03/our-rocket-stove-water-heater-2-5-years-on/

Re: Rob Frosts' epic Midden Methane build, here is a current assessment. Some major learning happened... new ideas

http://onestrawrob.com/?p=2662

My acquaintances (profiled in my book, The Composting Toilet System Book) tell me this works as a preheater but not as a heater. Unless you don't mind lukewarm versus hot water.

Carol

There is a pretty good website that can tell you exactly how much of what you need to put in. We just built one of these to heat up a building for the next 18 months, we oversized it a bit due to the building being horribly bad in terms of insulation. We used about 100 cubic meters of fairly rough woodchips and about 40 cubic meters of sliced corn greens. It has been running for about a month and keeps the water at a comfortable 40 degrees Celsius (104 Fahrenheit), and climbing every day.

Here is the website: http://www.native-power.de/en

Brian Kerkvliet wrote:
7- You need to ask yourselves what are your goals for using compost to heat water? Is it for the compost? Is it for the novelty? Do you have too much biomass? Do you want to use this as an avenue to do experiments? Or do you want to clean up the stinky permis? All of the answers to these questions will lead you to the right approaches to take.

Pretty much anything Paul is doing right now seems to be for the sake of experimentation. I would suspect that the reason he hasn't decided to go RMH on this project is primarily because he wants to mimic the other people who are doing the compost heated design. I'm still kind of new to the Wheaton/permies world, but Paul seems like the type to constantly be trying and improving methods within the permaculture realm.

I have to thank you for posting that video, though. I love watching Geoff Lawton lecture.

How about a 2 or even 3 phase approach?

1. I'd suggest burying coils of poly a trench below frostline. This should give you 50 degree water.

2. The next piece is poly coils under compost. Even better if the compost is under a cold frame of some sort. Trenching with compost might be a good idea.

3. Then the poly connects to a passive solar water heater. This could be bypassed if weather isn't "happy"

I'm also working with evacuated solar tubes but haven't gotten far.

Fascinating. I'm not thinking shower, but I AM thinking about a recirculating warm water drinking trough for my sheep, with a small solar pond pump maybe... I wonder what temps this could combat and how big a compost pile outside the fence would need to be. The sheep provide the manure, the manure warms their water, the sun keeps it running. Hmm. More research needed.. off to follow the links and websites in this thread...

Heather Staas wrote:
Fascinating. More research needed.. off to follow the links and websites in this thread...

Same here.
I know compost has been successfully used to heat a green house in Canada and a compost pile successfully used for human showers in the PNW.
I would think the optimal solution would be to use the compost derived heat to generate electricity and then simply use as on-demand water heater when the showers were wanted. Most showers would be in the early morning and the afternoon at the end of a work day. Why heat an outside watertank at other times.

I think a trickle pump on the water trough drain would keep ice from forming at the critical point so between a bit of hot water pipes near the drain end of the trough should do it. Keep the compost pile as far away from the trough as you can and have a heat exchanger run from the compost interior to the drain end of the trough.

Critical in all systems would be to bury a thermosensor and a transmitting device so you know the temperature of the compost and the temperature of the heat exchanger water.

I'm not sure how I missed this first time round, but i suspect I know why your water is running out quickly.

Cold water is sitting in the pipes in your heap. It heats up slowly over the day drawing heat from the surrounding compost and eventually reaching and equilibrium. 4 stinky permies turn up at once and try to shower and use up all the stored hot water in the pipes. How cold water is flowing through the system and only has a few minute to warm up, compared to the hours that the water had been sitting for before.

Basically you need a lot more pipe in there - try to estimate what volume your largest batch of water need will be and make sure you have that much volume of water in the pipes in the heap (crossectional area of pipe multiplied by length).

This design uses a wheelie bin for hot water that might be useful for skidable structures and hotwater on diffrent parts of the laboritory.

Regarding copper pipes in the compost pile...

There is a podcast called This Week in Microbiology Episode #55 "In The Copper Room". One of the podcast's normal hosts talks about the study he did to prevent hospital acquired infections by using copper on bed rails, grips, and plumbing fixtures. Copper is anti-microbial. It stops electron transfer in organisms by providing an easier pathway for the electrons. Eventually microbes die if in prolonged contact with copper by having all their energy leeched away. Which makes it ideal if you are trying to sterilize water.(i.e. a basin to store filtered water in) It is as effective as bleach(though slower acting) in killing bacteria, but does so continuously and non-toxicly. This effect is strong enough to be FDA approved as anti-bacterial for alloys with 60% copper or more.

This is one of their more accessible episodes to laypeople. It is normally a show for microbiologists, by microbiologists. This episode is worth a listen for anyone who is looking for non-toxic ways to prevent bacterial growth.

That's why copper flashing is put on the peaks of roofs to prevent green growth just by having rain water wash across it and grab enough copper ions from the peak and wash down across the rest of the roof to kill whatever is on there (algae). I imagine putting copper in a compost pile will kill all kinds of stuff nearby and degrade the pile. Thermal conductivity probably isn't the problem (what's the conductivity of compost?). To have more hot water, you need more energy (temp * volume) so the pile just needs to be hotter or use a larger volume of water to store the temperature that is there. I think PEX is a good choice for tubing.

I just build a compost hot water heater using polyethylene tubing for domestic hot water. I plumbed the system out of our town supplied cold water and into intake of the water heater. My thinking was that the compost pile would preheat the water for the electric water heater. So far so good. The water flowing from the compost system is about 120 degrees F.

The problem is that two days into use there is a very strong plastic smell in the hot water. Bummer. Will this smell go away, and will this water be safe to wash dishes with and bathe in? All I have to do to revert to town water is turn a couple of valves and drain the system, but it was a lot of work for nothing in that case.

In my research of compost water heaters nothing was said about this issue, but most applications of the system are for heating greenhouses...

Those more knowledgable can correct me, but plastic hot water pipe is meant for flowing hot water. Normally, the hot water is kept in a metal tank, and only flows to its final destination through the pipe. It isn't heated through the plastic. In a compost hot water system, your transit mechanism is the same as your storage and heating. I don't know how acutely toxic the plastic taste is, stagnant water can pick up all sorts of unpleasant, but non-harmful tastes.

With standing water that is < 140F you run the risk of legionella. Copper negates the risk, since it is intrinsically anti-bacterial. Copper is a relatively expensive pipe material, but hot water applications are one place where it is worth it.

The largest and most elaborate urinal in Montana

That ladder cracks me up!

The ladder/stair thing works far better than I expected!

I have been told that two women have contributed to this pile, although I cannot imagine how.

The plan is to set up a bit of a privacy screen at some point.