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Compost Heat Exchanger

17 posts & 8 voices | Started 1 year ago by ditch_jockey | Latest reply from coffeeking

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ditch_jockey - Member

Anyone know anything about the possibilities of using a large compost heap to provide hot water for a heating system?

We're in the process of refurbing an old bothy, and it would be possible for us to make use of a large amount of garden waste that is currently burned on an open fire to create a fairly large compost heap, to which could be added kitchen waste and so on.

I've seen very simple designs involving tubing buried in the pile, but I wondered if there was any way to store the hot water as it was produced, or use it to power some radiators in the building

Any info would be much appreciated

Posted 1 year ago #
Nick - Member

bury a coil in the heap, hot water will rise, drawing cold water in at the bottom, this will get some kind of flow going which could be used to fill a rad, as for storing and using the water for other purposes that sounds a little more complex

maybe give CAT a call?

Posted 1 year ago #
genesis - Member

give these a calleco heat pumps we have ground source at work and its suprising how good it is.

Posted 1 year ago #
tankslapper - Member

+1 CAT

Works well in any compostable material including woodwaste (I guess at least until the composting process / neighbours become exhausted....

Posted 1 year ago #
skiprat - Member

Do you intend to harvest the compost? Putting pipes through it will make it hard to get the compost out. We're doing it on a large scale at work - just the composting part so know how hard that bit is.

What waste you putting in and will you be keeping tabs on it? Ours is fed and monitored each day to make sure its hitting 70 deg C. We are animal by products approved so can put all sorts of stuff in it. We are tested on a regular basis to make sure we're hitting standards.

Posted 1 year ago #
coffeeking - Member

I've been looking at turning this into a proper research project for students, but my initial conclusions have put me off - difficulty using the compost and very minimal power output, removal of excess heat = non-worky-composty.

Posted 1 year ago #
tankslapper - Member

Without volunteering him, Zokes is the *ahem! Compost King *ahem!

Compost is all about getting the mix right, the right amount of food for the micro organisms that generate the heat, the right amount of air to stop the heap going anearobic, the right balance of carbon and greens. TBH its not that difficult.

Minimal power outputs Coffeeking? The compost we deal with regularly achieves 60deg c + !

Posted 1 year ago #
ditch_jockey - Member

"what waste you putting in"

realistically, mostly garden waste - chipped wood and cuttings. Some kitchen waste, although with a variety of groups using the bothy, I can't see any obvious way of ensuring people only put appropriate stuff on.

If the whole thing turns out to be very high-maintenance in terms of monitoring and regulation, then it's a non-starter as far as I'm concerned. We already have enough **** about with water, electrics and fire regs.

Posted 1 year ago #
thisisnotaspoon - Member

60degC is the temp, not the power, you've achieved 60degC in a very well insulated system over a period of months, I'd suspect the average heap produces less heat than a lightbulb (an energy saving one at that).

Composting is essentialy just partialy burning it very very very slowly to leave the nutrients behind (i.e. you lose some energy but not all of it). If you want heat just dry it and burn it in a open fire and/or solid fuel central heating.

Posted 1 year ago #
genesis - Member

used to work as a stable hand, it amazed me the amount of heat manure mounds seemed to produce.

Posted 1 year ago #
ditch_jockey - Member

Running a wood burner that takes woodchips is one of the alternatives. I came up with a number of alternatives during my marathon burning session yesterday, some of which may have the taint of madness - I'm blaming those on mild smoke inhalation.

The clear priority for this is 'low maintenance' - the less faff the better, so the possibility of a pile of rotting vegetation providing some warmth for the building was/is an attractive one.

Posted 1 year ago #
rootes1 - Member

skiprat,

where is your site? In-vessel? What system? TEG, VCU, Tunnel?

just interested as I'm in the waste industry myself.

Si

Posted 1 year ago #
skiprat - Member

Si

We're based just outside Leeds. We have a VCU that is ABP approved by DEFRA and we are currently manufacturing one that is a VCU, just on a much bigger scale. This is housed inside a building so it will be easier to monitor and control.

We're making compost to Pass 100 standard and diverting a hell of alot of waste away from landfill.

Are you local or far away?

Posted 1 year ago #
rootes1 - Member

Hi Skiprat,

no not nr leeds, but do round the UK a bit visiting waste plants. Not been to leeds for a while - last time to look are recycled aggregate processing.

Si

Posted 1 year ago #
coffeeking - Member

Minimal power outputs Coffeeking? The compost we deal with regularly achieves 60deg c + !

Yup, as TINAS says, you're thinking temp, not heat - there's a difference. A spark from grinding metal is at 700+ degrees C, but you can sit your arm under a shower of them and not have it hurt because they carry sod all mass and so sod all heat energy to impart to your arm. What I suspect is that you'll rapidly over-cool the organisms and they'll just work slower. I've finally got my heat exchanger sorted and I@m awaiting a compost bin to carry out the tests on this.

On top of the above, multiple things strike me:
1) It takes a LOT of waste to be composted down to virtually nothing, bothys see very few (relative) visitors with very little waste.
2) It needs management to maintain the composting process, who is going to do it?
3) They're fairly easily "poisoned" - who polices it?
4) Who removes the compost when it's done, and where does it go?
5) Compost and waste will be wrapped around the heat exchanger if it is optimally designed for heat transport, which will make operation a bit 'mareish

Posted 1 year ago #
rootes1 - Member

I've finally got my heat exchanger sorted and I@m awaiting a compost bin to carry out the tests on this.

if you are making this, the cooling grid off the back of a fridge makes for a good exhanger element i built one in an isulated box as a solar collector..

fridge element might be useful for putting in your heap.

Posted 1 year ago #
coffeeking - Member

rootes, interesting point, though I don't have one spare, I do have stacks of microbore. I'll keep my eye out for a scrap fridge, but I'd need to a) roll it to a cyl and b) hope it was pre-vented, or I'd be being a nasty person venting the refridge.

In your solar collector, did you bond it to a backing plate or just use the light that hit the mesh?

Posted 1 year ago #

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