Compost heat pump?

[Mart]

If you ever get to Madrid, visit the Botanical Gardens. There is a tropical/palm house that has a central trough with cast iron grating.
This was used to heat the place over winter after it was filled with manure/compost in the autumn.
I think there’s also a thread either on here (or the other place) of using very large compost heaps to provide heating to dwellings.

I suppose it’s feasible, just depends how practical.

I'm sure the Victorians had "Melon beds" which were big cold frames installed on a manure pile - or one with deep foundations filled with the stuff - for the heat.
I was surprised that there wasn't a problem from either ammonia given off or excess humidity.
A

That rings a bell, possibly 35+ years ago, watching something (Blue Peter springs to mind) about 'Victorian forcing houses'? A room filled with manure to grow plants out of season, or something like that?

[AE-NMidlands]

That rings a bell, possibly 35+ years ago, watching something (Blue Peter springs to mind) about 'Victorian forcing houses'? A room filled with manure to grow plants out of season, or something like that?

I found this https://www.richardjacksonsgarden.co.uk/growing-melons/ which explains it. I hadn't heard of the hurdle/wattle sides though, just big brick enclosures with a cold frame above.

[richbee]

There was a fella that did this in forests. Made monster compost piles and heated everything he needed.

Worth a read.
https://www.permaculturenews.org/2011/1 ... -pain-way/

It would be easy enough to run a gravity fed system ending in a tap for outdoor hand-wash testing. If it works upgrade to a 2nd hand mixer tap and run the cold water feed from the top tank.

Or an outside hot tub or paddling pool, take advantage of the spring / summer high temperatures.....
https://www.cotswoldkoi.co.uk/product/s ... mkQAvD_BwE

OK, maybe slightly beyond my compost bins - see link below - 6ft high, 12ft diameter pile to power a hot tub for 18 months!
https://www.foodgardenlife.com/show/compost-heater

[sharpener]

How many watts of heat do you think a typical compost heap gives off? Should you maybe insulate the heap?

With a very rough calculation - If the compost heap is approx 1 cubic metre, and the temperature is roughly 50 degrees above ambient, and the compost is largely water, or at least has the same specific heat capacity as water (4200j/kg/°C) - and assuming the whole heap is the same temeprature - which it won't be:
1000 x 50 x 4200 = 210MJ of energy - that sounds like a huge amount - but equivalent to 58kWh if my calculations are correct!

Yes. Reckoning that it takes 9kWh to heat a typical 210 l HW tank to 60C, that's pretty consistent.

But what we need to know is the rate at which the heat is replaced if you draw it off. Losses from a HW tank are of the order of 2kWh in 24h so about 167W. If the compost heap is comparable then 5x that, maybe 1kW, though my feeling is that is on the high side. Although the "insulation" is not the same I suspect the thermal conductivity is poor owing to its fibrous nature and this may therefore be an over-estimate of how much heat is needed to keep the centre hot.

AFAIR there is a Pineapple House at Wimpole Hall which works along these lines.

[richbee]

That rings a bell, possibly 35+ years ago, watching something (Blue Peter springs to mind) about 'Victorian forcing houses'? A room filled with manure to grow plants out of season, or something like that?

I found this https://www.richardjacksonsgarden.co.uk/growing-melons/ which explains it. I hadn't heard of the hurdle/wattle sides though, just big brick enclosures with a cold frame above.

Brilliant! I will construct some wattle sides over the weekend & collect some manure

[richbee]

How many watts of heat do you think a typical compost heap gives off? Should you maybe insulate the heap?

With a very rough calculation - If the compost heap is approx 1 cubic metre, and the temperature is roughly 50 degrees above ambient, and the compost is largely water, or at least has the same specific heat capacity as water (4200j/kg/°C) - and assuming the whole heap is the same temeprature - which it won't be:
1000 x 50 x 4200 = 210MJ of energy - that sounds like a huge amount - but equivalent to 58kWh if my calculations are correct!

Yes. Reckoning that it takes 9kWh to heat a typical 210 l HW tank to 60C, that's pretty consistent.

But what we need to know is the rate at which the heat is replaced if you draw it off. Losses from a HW tank are of the order of 2kWh in 24h so about 167W. If the compost heap is comparable then 5x that, maybe 1kW, though my feeling is that is on the high side. Although the "insulation" is not the same I suspect the thermal conductivity is poor owing to its fibrous nature and this may therefore be an over-estimate of how much heat is needed to keep the centre hot.

That may be a fair estimate about heat loss - and would explain why the hot tub guy needed such a huge pile to generate enough heat over a long time. If you take too much heat out, it will slow down the composting & heat generation

[Mr Gus]

My colleges swiss garden semi sunken grotto was manure heated (you can pay to visit it, ..sadly now I have to as well) our old BIG walled garden is no longer sided .."progress" ..(lack of investment by the council who took it over in the 1960's) but visible at many Nat trust homes (wimpole hall local home for instance is a good example of a walled garden which would have contained a lot of manure banked not only to fertilise soil, to satisfy cropping demands of the kitchen but to bank heat into sun exposed walls inside the garden as part of the overall scheme to grow wall trained fruits etc & attempt to keep a wind free micro climate.

Our hothouse / glasshouse beds were deep troughs packed with manure & a smell sealing top soil (because it was a designed for visitors & dignitaries as entertainment, it was "beautiful" to show off & entertain as per disney world today, solid floors in the hothouse, tiled, drainage to water tanks for recirculation, a lake made/ linked in for use as required as well as fishing swimming boating etc, tea taken at the central piece the "swiss" (not swiss) tea house built through a banked mound central to the garden, dog cart track to take ladies / children round the perimeter to the various gazebo's & plantings.
The grotto really gets the heat despite it's mature woodland location stained glass, dapples light, rock for heat & release capture.. all from the past.

Note some north american indian reservations are sub ground greenhousing nowadays in an attempt to feed themselves & limit climate craziness. a good move. (I think i linked to it previouly)

With that degree of engineering capability, I wonder where we'd be if they'd had solar thermal back then?

[robl]

There's a guy in the states who claims to heat his house with a "gently rocking" insulated composter, which has water pipes in it, and airflow through it. I found it very interesting, but it was just a thought exercise, would love to see one in action! Caution - I think there's a lot of work involved, a lot of "double mowing" of yards, collecting dry clippings, storage, etc.

https://mb-soft.com/public3/globalzl.html

[sharpener]

My colleges swiss garden semi sunken grotto was manure heated (you can pay to visit it, ..sadly now I have to as well) our old BIG walled garden is no longer sided .."progress" ..(lack of investment by the council who took it over in the 1960's) but visible at many Nat trust homes (wimpole hall local home for instance is a good example of a walled garden which would have contained a lot of manure banked not only to fertilise soil, to satisfy cropping demands of the kitchen but to bank heat into sun exposed walls inside the garden as part of the overall scheme to grow wall trained fruits etc & attempt to keep a wind free micro climate.

I imagine this is the one you mean @Mr Gus https://www.gardenstovisit.net/the-swiss-garden. Looks fascinating, thanks for drawing my attention to it! We visited Wimpole Hall walled garden on Sunday, the flower beds round the outside are looking good but the veg plots inside are a bit threadbare atm.

[Mr Gus]

If you go, bear in mind the village is an extension of the once grand country estate, plenty of model village type architecture there if you poke around.
When I was therr, it was nigh on derelict (swiss garden) one gardener to keep the very worst at bay) happily the council applied more people to it but latterly (by 2008) had partitioned areas for a payg birds of prey "experience" cutting a third off the immediate area & locking off good specemin tree's ...I was very disappointed.

even back in the late 80's the charge was a bit crazy as it was so overgrown & dilapidated.
We got in free being Shuttleworth estate agri college students.

If you go plan carefully around / for the shutts airshows, as those days can limit access to a day, do try to envisage cardington hangar minus the houses around it ( 20 yrs past) & the hydrogen dirgibles /r101 ..try & stop off at the nearby monument to the airmen if the airships history is of interest, shutts collection has a few r101 bits in its colllection (wooden propellors & the like)

Cardington hangar was till recently Bruce dickinsons usaf prototype i.p. brought slowly to commercial scale project, they are now yorkshire based for some unknown reason ..after all the money sunk in locally

If the doors are open to the tea house , go in, its a lovely little place.