[HN Gopher] Masonry Heaters: 18-24 hours of heat output from a s...
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Masonry Heaters: 18-24 hours of heat output from a single wood fire
Author : gjsman-1000
Score : 26 points
Date : 2023-02-25 18:57 UTC (4 hours ago)
(HTM) web link (www.mha-net.org)
(TXT) w3m dump (www.mha-net.org)
| macmac wrote:
| Malwarebytes flags this site as having a Trojan.
| gjsman-1000 wrote:
| Well, then it's wrong.
|
| https://www.virustotal.com/gui/url/3d43fe6f2a5b96525b5b76817...
| sp332 wrote:
| It's also blocked by Plume routers, but it's not categorized as
| anything specific.
| devwastaken wrote:
| 3rd party AV is useless in modern computing. Ublock origin and
| knowing your file extensions is a significantly better
| solution.
| skybrian wrote:
| The electric version of this is called "electric thermal storage"
| where the electric heater is used off-peak to heat up ceramic
| bricks. It seems unlikely to beat a heat pump, though. Could they
| be combined?
| world2vec wrote:
| My parents have a fire stove like those ones in their house,
| built almost 30 years ago. Not a common design in the country
| they live but apparently it is in Switzerland where they worked
| for many years before. Very efficient indeed.
| Dma54rhs wrote:
| This is also common and very old tech in all the colder
| countries in Eastern Europe but obviously electricity has taken
| over. I'm even a bit surprised because I'm having a hard time
| thinking how else would you hear your house but probably it's
| enough in milder climates to not store the energy like that.
| thriftwy wrote:
| Did they just invent a Russian stove?
|
| https://en.m.wikipedia.org/wiki/Russian_stove
|
| Now when the end game is known, perhaps it is better to just
| adopt the existing designs instead of trying to perfect the
| current product.
| twawaaay wrote:
| I built one with my father when I was a kid.
|
| It was dual purpose cooking range and a huge mass of bricks for
| heat capacity. It was built at the spot where multiple walls met
| in the centre of the house to increase mass of bricks in contact
| and to heat multiple adjacent rooms. The walls in those rooms
| would typically be too hot to touch.
|
| One weakness of our setup was that it would suck the air out of
| the house through the night. Another was that complex internal
| tunnels made the maintenance difficult.
|
| If I built one today I would make sure to fix it and create a
| sort of heat exchanger for coming air.
| ghaff wrote:
| It's an interesting idea although I assume it has to be somewhat
| baked into new house/addition construction.
|
| A big downside of conventional wood stoves I find is that, if I'm
| not going to be hanging out at home--mostly around where the fire
| is--for the day it's not really worth it a lot of the time. I
| fire up my wood stove mostly when it's especially cold and I'm
| not primarily working in my office.
| pjkundert wrote:
| If you want a lot of background on designing and building an
| effective "rocket stove" (the core of a masonry heater), you'll
| enjoy this:
|
| https://batchrocket.eu/en/building
| mmastrac wrote:
| I vaguely recall seeing a YouTube video about some folks living
| in Siberia and using these to keep their homes warm.
| fwlr wrote:
| You have to follow a few links to get to a definition of what
| masonry heaters actually are, but it ends up at https://www.mha-
| net.org/docs/def-mha.htm
|
| Specifically the important parts: "a mass of at least 800 kg.
| (1760 lbs.)", "an overall average wall thickness not exceeding
| 250 mm (10 in.)", "external surface of the masonry heater ...
| does not exceed 110 C. (230 F.)", "at least one 180 degree change
| in flow direction" of the released gas.
|
| Essentially, it's a rocket stove and a large thermal mass of
| masonry, and the masonry has a few design restrictions to meet
| certain performance characteristics (i.e. it should absorb most
| of the heat released by the stove and it shouldn't release that
| heat too quickly from any particular point on the mass). Mostly
| I'm surprised it's that easy; I would have thought anything that
| can radiate heat slowly and consistently would by necessity also
| absorb heat slowly and consistently, making it difficult to
| capture most of the heat from a fast-burning stove.
| a9h74j wrote:
| > I would have thought anything that can radiate heat slowly
| and consistently would by necessity also absorb heat slowly and
| consistently
|
| Something like a ratio of flame-side heat absorption at flame
| temperatures, to room-side emissivity at room-side
| temperatures(wavelengths)?? This could fall out from material
| properties without appearing as an explicit design detail (e.g.
| a surface treatment).
| bcbrown wrote:
| > Mostly I'm surprised it's that easy; I would have thought
| anything that can radiate heat slowly and consistently would by
| necessity also absorb heat slowly and consistently, making it
| difficult to capture most of the heat from a fast-burning
| stove.
|
| My understanding is that this is the motivating principle for
| the "bell" part of the stove. The hot exhaust from the
| combustion chamber is piped into a massively larger enclosed
| airspace, which has an exhaust port at the very bottom. Since
| hot air rises and cool air falls, most of the heat in the
| exhaust will be absorbed by the bell enclosure before finally
| being vented through the exhaust port. By enclosing the bell in
| masonry, it meets the design restrictions you mention.
|
| I think it's also possible to build a masonry heater without
| using rocket stove principles, just a fireplace with a huge
| mass of masonry surrounding it. In that case, you'd want
| cladding with somewhat high thermal conductivity to capture the
| exhaust heat, but it's thick enough that the solution to the
| Fourier heat equation [0] is low enough to meet the design
| restrictions.
|
| https://en.wikipedia.org/wiki/Heat_equation#Heat_flow_in_a_u...
| Tcepsa wrote:
| TL;DR different modes of thermal transfer can transfer heat at
| different rates.
|
| There are a couple factors at play that help it absorb heat
| faster: 1) Convection rather than radiation. As the hot gasses
| travel through they stove they are in contact with the mass and
| can transfer heat more directly to it, which then spreads
| through the mass via conduction. This is aided by... 2)
| Newton's Law of Heating and Cooling, which basically says "the
| greater the temperature difference, the faster the heat
| transfer". Since the gasses from the combustion are around 1000
| degrees or higher (at least initially) they transfer heat much
| faster to the mass (several hundred degrees delta) than the
| mass transfers it to the room temperature air (one or two
| hundred degrees delta).
|
| Similarly, much of the radiation of the hot inner mass is
| absorbed by other parts of the hot inner mass; only the parts
| near the outside actually radiate heat away from the mass.
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(page generated 2023-02-25 23:00 UTC)