Posted by & filed under Compost, Energy Systems.

by Frank Gapinski, from Ecofilms

Here’s a great tip given by a member of the Aquaponics Made Easy Forum on a cheap easy-to-build hot water system using compost.

The original question posted to the forum was "how to heat a fish tank over winter without any extra energy costs?" A hard thing to do. Thermal Mass heating was one answer but a crafty member posted a very interesting solution and swears that it works a treat. We’ve illustrated his simple design. It’s so simple you will think “Ah-ha! Why didn’t I think of that?”

Daryl from Windsor in NSW came up with an innovative solution using two ordinary wheelie bins that are filled with compost and a wound central pipe arrangement to turn cold water hot very quickly. How does it work?

“What I have made is a compost heater, inside a wheelie bin with 20 mm poly pipe coiled around the outside wall of a pipe – about 8 metres in each bin.” he says.

Compost can reach a core temperature of 70 degrees Centigrade. Conventional Hot Water systems are thermostatically set to heat the water to around 65 – 70 degrees centigrade. So at its peak this system will create very hot water for free.

“Then I load the first wheelie bin with grass clippings and horse manure and after two weeks load the second wheelie bin with the same stuff. After four weeks I empty and reload the first bin. You can leave the system running longer but the main heat production is in the first four weeks.” says Daryl.

Sourcing a wheelie bin in the city is quite easy. The main ingredients are Nitrogen and Carbon. Any green leafy material like fresh grass clippings is suitable as a nitrogen source. When mixed with an alternating layer of carbon such as dry leaves, shredded newspapers or cardboard the end result is ignited by micro organisms to create compost.

Make sure the mixture is well watered as a dry mix will not work so well. But harnessing the heat given off in the core of the wheelie bin is where this idea really shines.

The central vertical pipe could also benefit with a number of large size holes drilled into it to assist oxygenation of the compost heap core without turning the heap over as is the case with most conventional compost systems.

Daryl says you can enjoy quite a number of free hot showers before the system will eventually cool down and he advocates a rich grass mixture.

"If the grass is packed in tight it should hit peak temp in about a week and hold for about 3 weeks then start tapering off.

“It’s best if you can have a second bin started and just swap from one to the other. You can use other stuff in the bin like a normal compost heap but because the grass has so much nitrogen in it its start up time is much faster.

“A few years ago I helped build a large compost heap that had about 300 meters of 25mm rural pipe going through it. After 4 weeks this system was providing enough hot water for 35 people to wash up and shower with. I was there for 3 months and we kept adding compost onto the heap and it worked the whole time I was there, eventually you would have to dig out the pipe, use the compost, and start all over again. That’s why I used the wheelie bins”, said Daryl.

The end result is an endless supply of rich garden compost and lots of free hot water!

16 Responses to “Free Hot Water from Compost Wheelie Bin”

  1. Darren J. Doherty

    G’day, Nice work on this one….would be interested to see how long the pipe can survive this environment….we have been playing with this one for a while now both on a small scale (compost shower see: http://www.youtube.com/watch?v=ILzxOH6n7-c) and larger scale (home scale hydronic heating systems – see: http://picasaweb.google.com/permaculture.biz/CompostHouseHeating) and have found that LDPE & HDPE pipe degrades in the heated environment of a compost pile…Coated aluminium, copper or Stainless/Inox pipe doesn’t suffer over the journey, though of course have both a higher emergy and dollar cost: however have a longer life span than the plastic….Another interesting fact is that you can smell the plastic in the water heated in these systems which obviously can’t be good as it must be decomposing in enough for the outgas to cause the odour in the water…No such issue with the non-ferrous metal pipes…

    Anyways its great to see that this kind of innovation is out there and serves to show good Permaculture thinking in action….

    All the best,

    Darren J. Doherty

    Reply
  2. leigh blackall

    I have also discovered that the HDPE is giving off a smell, so I would second the idea of using an alternative to poly pipe. Also, I’d like to know how you wrapped a 20mm polypipe so tightly.. and how many metres it was. I need 100metres of 30mm pipe to heat about 90L. Does yours feed into an insulated storage tank perhaps?

    Reply
  3. Kat

    Heya

    Fabulous find, great technology!

    I’m keen to give this a go at my local community garden, particularly since our local council are incentivising people to switch to the small wheelie bins. I love the Jean Pain method, and enjoyed the hot showers powered this way up at Zaytuna last year. But, big pile composting can a bit confronting for some people with small back yards! So, this seems like a really nice compact (and tidy) suburban solution. I would be delighted to hear more from anyone who has tried this out at wheelie bin scale.

    Kat

    Reply
  4. peter furze

    trying your system now, but using 200 litre drums, so far so good but i think i will need 4 drums to keep up a consistant supply of hot water.
    pete

    Reply
  5. InBox485

    I’d be leery about really getting much heat off that unless it is one of the full sized totes that municipal trash systems use. I’ve tried unshredded compost in a 32 gallon tote, and got no noticeable heat, and while the shredded one got at least warm, it was too heavy to even wheel around. I don’t plan on messing with a full sized one any time soon. Also, I’ve been experimenting with different mixing techniques, and nothing has compared to finely shredding and mixing everything together. I haven’t gotten into the whole balancing ratios of carbon to nitrogen, but just in terms of getting the hot pile so that you can stop worrying about various toxins, or so you can make use of the heat, shredding it all together has worked by far the best. I’ve had very little luck with layering.

    I could see some use for patching in a system like this into a hot water line right at the point where the shower head is. That could reduce the amount of time it take to warm up a shower. For that, I would have the water line, but instead of a coil, I’d have something like one or more 4″ pipes where the water came in the bottom, the pipe was filled with lava stone, and water came out the top. That way you would get immediate hot water, and the cold water between the system and the water tank would get the extra heat from the stones so that you wouldn’t have the sudden dip and rise from the cold water that would rush through and the hot water behind it.

    Another thought is to have the water passively rise into an insulated storage tank in a semi closed loop where check valves allow new water to flow in and only the hot water to flow out when used.

    To me the best use for stuff like that is for passive area warming. For beds or ponds you have the pile at a lower elevation with a closed loop of water that rises once heated to the bed or pond and then returns once cooled back down from the bed or pond. For home or green house (or tent) heat, you run an air conduit so that hot air rises to one side of the structure and cold air sinks from the opposite side. Gravity will do all the pumping here. No fans, radiators, pumps etc. needed.

    Reply
  6. Jessie - Rabid Little Hippy

    Our hot water is heated by solar or wood fire but this gives me the perfect idea for helping keep my greenhouse warm over the winter months AND fill up a garden bed in the meantime. Thank you!!!

    Reply
  7. Gordon

    I’m surprised no one has suggested insulating the wheelie bin. It could be as simple as wrapping it in aircell (a building insulation material like big people’s bubble wrap)or, possibly better, a layer of rockwool or similar then the aircell. If there is enough heat in the mass to heat the water, then there must be a lot of heat escaping through the plastic sides of the bin.

    Reply
  8. tony callaghan

    I’d love to see a time-temperature graph over 3-6 months use.
    The laws of physics do not offer much hope. You have an non insulated container (it will lose heat via surface area bin), and the pipe is cooling the inner waste. The speed of composting is based on temperature (Q10 equation). The speed of composting will be determined by the cold water temp (lets say 5-10C). The composting is going to be very, very slow and if you add any food waste it high risk it will go anaerobic.
    A typical home produces about 2-5Kgs of food waste a week, the calorific value is about 30 watts (J/s). Compare this to the BTU/power of a central heating system….
    Look forward to time temp and waste loading (Kgs) added profile

    Reply
  9. mountaingran

    Would like the plans ie: drawing, to build this…
    Looks easy, but need plans….
    Thank you…

    Reply
  10. Robin

    Thinking this would be great in a hen house, lots of nitrogen in hen poo, and would be warm enough for the compost to work through the winter, but would there be a methane problem? Would not want to poison air the hens!

    Reply
  11. Odile Siro

    I am new but very interested in permaculture. I would really much like to try this in my home. Learning a lot from new experiences through this site.

    Reply
  12. David

    I’ve seen quite a few of these illustrations but not one that’s actually been built and in service.
    I highly doubt the throughput would be enough to be useable as a supply to shower with, there’s not enough surface area contact and plastic is a poor conductor. Also, the introduction of cold water will slow down the process of the compost. None of the illustrations I’ve seen show any type of aeration for the compost bins and without oxygen, the process will stop.
    Good idea, poor execution.

    Reply

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