Wood chip Compost Water Heater

[gds]

Here's some photos of my initial trials with wood chip compost water heater. I thought I'd give it a go after hearing about what Jean Pain started off in France in the early 80s.

Basically its a pile of wood chips with a coil of pipe in the middle... heat is generated from the composting process and transferred through the pipe to the water. Jean Pain had piles (wood chip variety!) 6m in diameter and 3m high. These lasted for 18 months, after which they were dismantled and the compost used in his garden.

This was last October (2009)
I started with enough chips to fill a bulkbag... these had been chipped earlier that morning  



and about 25m of 10mm irrigation pipe...
ignore the insulation :-)



a bulk bag...



starting with 75mm of chips in the bottom of the bag, the irrigation is coiled round, compressing it and also spraying it with water to help the composting process



eventually the bag was full, so I connected a butterfly valves to the top...



and another to the bottom. I connected a standard hose adapter and filled the pipe and left it overnight



Reconnected hose the following morning and voila... hot water flowed through. I inserted a silometer into the woodchip and this was reading 50 deg C.

So it worked... now I wanted to build a bigger better pile :-)

Unfortunately I didn't take any photos of work in progress for the next stage... so you'll have to make do with a written summary. I'll know next time!

Firstly, I needed some wood chips. Fortunately, a friend had managed to source a huge amount of wood chips from local contractors cutting down trees for the electricity board. We cleared a space in the garden, erected a framework of 8x4 chipboard. This was lined with 50mm Kingspan on the sidewalls and floor to insulate it. He kindly delivered them and tipped them over the wall. For the water pipe I used 150m of 25mm black MDPE pipe - I calculated (correctly?) there would be approx 40 litres of water in the pipe. We coiled the pipe in a spiral fashionwith approx 30cm between each layer.

We did all this during the cold weather in January - it took 8 days for the core temperature to rise. I was beginning to think I had a 6m³ white elephant :-(  but eventually nature kicked in and over 3 days the temperature rose from 10°C to 51°C.

I wanted to monitor the temperature so I buried an iButton temperature logger 45cm into the centre of the pile and hung a second one from the chipboard frame.

Results so far have been excellent. Max temp recorded was 61.5°C. This has now steadied out to 54°C. I haven't connected it to a pump or tank yet - that is the next stage. However as it is, there is enough water for 5 (outdoor) showers with a reheat time of approx 1 to 2 hours.

The water heater today...

[martin]

Excellent stuff!

[MR GUS]

Great 1st post!

 ..good experimentation (or frottering as it's known here) 

[dhaslam]

Well done.   There should be  some  methane gas produced as well but not so easy to collect or use. 

[gds]

Well done.   There should be  some  methane gas produced as well but not so easy to collect or use. 

Thanks for the comments 

You're right - Jean Pain ran his 2CV, generator and kitchen gas rings from the methane he produced. I was going to try the same but had limited space as the gas needs cleaning and storing.

Here's a link with more info http://www.electricitybook.com/composting-for-heat/

[KenB]

gds,

Excellent small scale experimentation.  I did some temperature monitoring of my lawn cuttings compost heap and it is amazing how quickly they can take off.

I was very keen on the Jean Pain work, and it is great to see that someone has been brave enough to try it.

Having watched the JP videos,  I cannot quite understand the methane collection system.  He seems to put an empty drum at the centre of the pile as a collection vessel - but it would apprear that this only collects methane from a very small section of the overall pile.  Is the pile kept gas tight with a tarpaulin so the methane is forced to exit through the central collection drum. Can you shed any light on this?

Having had to barrow 4m3 of woodchips to the end of a neighbour's garden, I understand fully the convenience of having the tree surgeon dump them over the wall.  A very full builder's barrow is 100 litres - so at least 40 trips per tonne.

It might be possible to use surplus 1.8m3 cylindrical "roto" orange juice concentrate containers to make a black plastic, gas tight compost heap.  The action of the sun on the black plastic roto would soon get the bugs working.  Water cooling is needed so you don't cook the methanogenic bugs (or is that methanophillic?)

Keep up the good work.



Ken  - still in China - hence the odd timekeeping

[gds]

Having watched the JP videos,  I cannot quite understand the methane collection system.  He seems to put an empty drum at the centre of the pile as a collection vessel - but it would apprear that this only collects methane from a very small section of the overall pile.  Is the pile kept gas tight with a tarpaulin so the methane is forced to exit through the central collection drum. Can you shed any light on this?

Hi Ken,

My understanding is that the steel tank (fermentation chamber) in the centre is filled with compost that is already a few months old - see video 1 at 6:23. This presumably has a head start methane production wise. Only the methane produced from the fermentation chamber is used.

Maybe I should cut a hole in the top of the tarpaulin to vent any methane.

I had a visit from a local solar installer who suggested hooking up a ground source heat pump to the heap. He also gave some tips on the size of the pipe - large diameter is not necessarily the best as proportionally more water is in contact with the pipe wall on a smaller diameter pipe thus improving efficiency of the heat transfer - and also mentioned about legionella if the water temperature is below 60°C.

Andy

[Ivan]

Aerobic decomposition is responsible for the heat. The limiting rate of oxygen entering the stack slows the heat production so it's released over months (rather than hours - eg if you set fire to the stack).  JP used an anaerobic digester to produce methane. He sited this inside his pile so that it would be optimally heated by the decomposing wood chips (anaerobic decomposition doesn't produce much heat).

Don't bother with a heatpump. Heatpumps aren't magic technology - they don't generate heat from nothing - they're good at pumping from low grade heat sources. So a heatpump won't generate any more heat from your pile than using the hot water directly.

What would be really interesting would be to see what flow of heat you can sustain from the pile - eg pumping the water continuously around a radiator