500 hot showers from one, small compost pile

My new youtube video

http://www.youtube.com/watch?v=-Jm-c9B2_ew

I really like the concept, i wonder about using the water to heat a green house or hypothetically attaching it to piping in the ground or in flooring for heating a home. hmmm. my understanding is with using compost to heat a solar greenhouse is it produces harmful levels(to plants) of c02 and ammonia,but by running piping it might solve this issue.hard to say how efficient it would be but i love creative innovations.

awesome video paul.

billy that's a great idea, i just might have to try that this winter as im almost already set up for it, compost piles next to the greenhouse and all, and lots of extra tubing. better start saving material now though.

By heating the water, aren't you also cooling the compost pile?  Is there a noticeable change to the decomposition process?

I think if you try to heat a greenhouse with the compost pile inside, I would worry about offgassing.  And if you have the compost pile outside - it would need to be super duper big to keep from freezing.

Having a compost pile in a greenhouse has been discussed somewhere in these forums previously.

If you want to do it outside, you might look for "jean pain" in this forum.

By heating the water, aren't you also cooling the compost pile?  Is there a noticeable change to the decomposition process?

Without measuring, I would have to say "yes".  But the pile appears to have still shrunk, so I think it didn't really hurt the composting.

john jeavons mentions compost/greenhouse heating in How to Grow More vegetables, said that french farmers do/did this on a huge scale in biointensive farming there.  I think the idea of running this through a in-floor heating system is a wonderful idea, perhaps even in a closed loop system hooked into an existing in-floor heating system to boost water temps before the boiler kicked in. 

I know that pot growers add CO2 to the growing environment to speed growth...I think you'd have to have a very well sealed greenhouse to have an atmosphere that had co2 levels too high for growing, I think too the size of your compost pile inside the greenhouse would limit that accumulation. 

Can anybody tell me how long it takes before a new compost pile generates enough heat to get the water warm enough for a shower? Thanks.

Another great video Paul. Thank you.

Last winter I used a compost pile to keep my horses water tank from freezing. I partially buried two empty & upside down 100 gallon tanks (with straw bales in them) in a compost pile. I made sure the exposed portion of the tanks was on the east side of this "compost berm." I covered the compost with worn, hole-ridden tarps held down by old tires. Then I placed a 25 gallon tank on top of the exposed portion of the 100 gallon tanks. I filled the trough daily for my three horses and never saw more than 1/2 inch of ice on the surface. Toward the end of February I though I might have to use a tank heater because the compost pile had begun to freeze. But, the freeze did not penetrate deep enough to kill heat-source and I squeaked by.

My compost pile was maybe 8-10 yards of material in a mounded, kidney bean shaped pile.

Carola, it normally takes a few days, maybe a week for a compost heap to heat up (maximum is around 70 degrees C, don't know what that is in F, sorry, I'm from Europe, 50 or less is more usual, due to poor mixing of air and materials).
You need a "reasonable" volume of material for good composting, probably at least 100 litres, more is better, all placed together pretty much in one go.
The number of showers you could power then depends on the mass of material in the compost heap and how quickly the heat transfers to the water pipe running through the compost pile.
You would want a reasonable length of pipe, so as to amass a “sensible” volume of water for each shower.
I had this discussion with a friend recently and calculated from Paul's video:
The coiled pipe is given as 100' long x 0.5” diameter. Assuming my maths is ok (a significant assumption!) = just under 4 litres, say 4l.
Assuming a toasty compost pile, 60C, = 4l of water at 60C.
He said he also had a cold feed to the shower. In summer, the temp of the “cold” would probably be well over 10C (assume 10).
Diluting the hot and cold together say gives 8l of 35C water; you could have more cooler water, or less hotter.
This is adequate for a short warm shower (i.e. ok for many “green” folk, but probably not for “normals”).

(You might get more hot water per shower: the compost heap has a large mass, which would be transferring its heat to the new, now cooler water in the coiled pipe in it, as the initially hot water is drawn off. I have no idea how to calculate this though. I think that in reality, the shower would cool quickly and dramatically. The system would then need to be left to re-heat the now ambient temperature water in the coiled pipe.)

He ways it delivered about 500 showers. Assuming these are all short (i.e. only use the 4 l of hot water, the compost pile has heated around 2000l of water over 2 months, an output of around 2000l x 1000g x 60C = 120,000,000 J*, around 33kW.
*(It takes 4.186 Joules to heat one gram of water by 1-degree Celsius).


Note that as available oxygen in the heap is used up, composting will slow, so it would be sensible to include some means of aerating the pile (though this could also promote heat loss).

Bill, if a “compost” heap is generating ammonia, then the composting process is turning anaerobic – it needs more oxygen (air) for "proper" composting to continue.
“True” composting is aerobic (i.e. with oxygen), which generates mostly heat (484 to 674 kcal per gram of glucose) and CO2.
Anaerobic decomposition generates far less heat (about 26 kcal of potential energy per gram), methane and CO2 (in varying proportions, but typically more methane than CO2).

CO2 concentration is generally a limiting factor for plants, so elevated concentrations in a greenhouse would be beneficial (to the plants).
You might want to air the greenhouse before entering, or monitor concentrations though!

Don, thank you very much for your extensive and very useful reply! Being in Ireland myself I'm very happy with the centigrade!

Have you - or has anybody else - any experiences with heating up a hot tub this way?

Hi Carola, no, no experience of heating a hot tub this way.
I guess if you set a bath in (or built a large compost heap around) a tub of some sort, & heavily insulated the top of the tub (to prevent heat loss), water in the tub would heat up over time, ultimately to whatever the temperature of the compost heap was.
A typical bath is aroudn 100 litres or so of water, a significant volume to heat, i.e. it would heat relatively slowly. The original show compst heap appears to have heated much more than this over its 2 month life though, so it should be possible. I guess you may need something in the water to prevent hot-water loving things growing in the lush-temperature water as it heated up. Epsom Salts maybe???
I've friends who removed the spiral copper heat exchanger from inside a typical (UK) copper hot water cylinder, and cobbled this (somehow; I can ask them if you are interested) to a tub of some description to make a hot tub. They just filled the empty centre of the copper coil with wood, lit it and the hot water naturally gravity circulated (thermosyphoned) to the top of the tub; with a lower, return water connection in the tub (possibly via the plg hole) for the (cooler) water to circulate back to the coil to be re-heated by the fire. Appropriate relative levels are ctircal for an efficient thermosyphoning system.
The simpler solution is a (heavy guage) tin bath directly over a fire. There was an article about this type somewhere on the Permaculture UK site recently (2011, via a Facebook notification), though all I could see just now was: http://www.permaculture.co.uk/issue/summer-2006.
Cheers, Don

The video!

Hi
We're about to try out the compost hot water approach and was wondering if anyone has any advice on the balance of green and brown that's optimal for us.

We've got a good pile of woodchips which have been sitting a few months. There's heat in places in the wood chip pile but not very much - I reckon this is because we haven't added any nitrogen material (green or urine). This is good for us because we didn't want the woodchip to start decomposing before we set it all up. We're probably going to have a pile of 3 or 4 cubic metres with a pipe coiled in the middle. From research it looks like if we mix about half green (grass cuttings or similar) with brown (woodchips or maybe straw or old leaves) this is about the best mix if you want to get it really hot (about 55 degrees C). But since we're wanting it to stay hot/warm (about 45 degrees) for longer then what sort of mix should we use?
Any ideas on whether we're better off using grass cuttings or cow manure as the green (nitrogen) element?

We've also got easy access to lots of urine for starting the process off!

Also has anyone done this and knows more or less how long we'd be able to get heat from it?

We're in Wales where it's really wet at the moment, so we shouldn't have any problems making sure the material is damp, but maybe it could be too damp - we'll cover it if it looks like it's heading that way. (But we're also going to make sure it has air going in by putting the pile on a pallet with air flow at the bottom.)
Thanks very much.

Hi Don,

I'm so sorry I never replied to this last post of yours - this is really bad and I do apologize. It must have slipped my mind at the time, and then other things took over and I forgot all about it.
I thank you very much for your detailed reply to my question, and although we haven't started yet we're still wanting to get both going - a shower and a hot tub; the shower probably soon.
Your friends' bath ideas seem great, and I'm sure we'll use them to work something out for ourselves.

Thanks again,
Carola

Don McLean wrote:Hi Carola, no, no experience of heating a hot tub this way.
I guess if you set a bath in (or built a large compost heap around) a tub of some sort, & heavily insulated the top of the tub (to prevent heat loss), water in the tub would heat up over time, ultimately to whatever the temperature of the compost heap was.
A typical bath is aroudn 100 litres or so of water, a significant volume to heat, i.e. it would heat relatively slowly. The original show compst heap appears to have heated much more than this over its 2 month life though, so it should be possible. I guess you may need something in the water to prevent hot-water loving things growing in the lush-temperature water as it heated up. Epsom Salts maybe???
I've friends who removed the spiral copper heat exchanger from inside a typical (UK) copper hot water cylinder, and cobbled this (somehow; I can ask them if you are interested) to a tub of some description to make a hot tub. They just filled the empty centre of the copper coil with wood, lit it and the hot water naturally gravity circulated (thermosyphoned) to the top of the tub; with a lower, return water connection in the tub (possibly via the plg hole) for the (cooler) water to circulate back to the coil to be re-heated by the fire. Appropriate relative levels are ctircal for an efficient thermosyphoning system.
The simpler solution is a (heavy guage) tin bath directly over a fire. There was an article about this type somewhere on the Permaculture UK site recently (2011, via a Facebook notification), though all I could see just now was: http://www.permaculture.co.uk/issue/summer-2006.
Cheers, Don

Interesting video. I think that guy should have the interns relocate such fine compost to a growing area and start over on the same spot. Otherwise, I am in the city and showering outside would create some police visits. How does one get interns hooked in to help out anyway!?!

How did Paul Wheaton pump water through his pile? Also, what was his water flowrate?

Tyler Reed wrote:How did Paul Wheaton pump water through his pile? Also, what was his water flowrate?

This is actually Brian Kervliet's contraption - I'm just the doofus with the camera.

But! My impression is that there was just a standard water hose with house pressure going up to the poly pipe.

Although half inch poly pipe is kinda small - so I suspect that the pressure coming out of the shower was not huge.

Thanks, this helps. I am an engineering student working on a team project that involves extracting energy from compost to heat water.