Dear Crispin and all,
I have added Chas Hinckley's address so that he receives Crispin's
message as well as my reply. (if responding to this message, please
klick "Reply All" to include Chas.)
Relating to Crispin's comments:
1. I had forgotten about the condensation. A difficulty to solve,
but an advantage of gaining back all that latent heat.
2. BECAUSE the TLUD is a batch operation, (and can even be rigged to
have a small alarm that says when the batch is about over), therefore
the total fire is removed and the dampers and doors on the high mass
heater can be tightly closed without any fears of further emissions
from lingering regular fires.
3. Thanks for the target numbers of 12 to 25 kW.
Is this the energy content of the fuel? or is it the amount of
thermal energy that is captured and is useful in the household?
What does this translate into as kg of common wood (or Mongolian dung
or other fuels)?
Paul
--
Paul S. Anderson, PhD
Known to some as: Dr. TLUD Doc Professor
Phone (USA): 309-452-7072 SKYPE: paultlud Email: [email protected]
www.gtz.de/de/dokumente/giz2011-en-micro-gasification.pdf (Best ref.)
Quoting Crispin Pemberton-Pigott <[email protected]>:
Dear Massive Friends
There is a strong preference to put mass walls into homes in
Mongolia as spare income becomes available. Something like 60% of
people who used to live in a ger (yurt) have built permanent
structures and many of the small homes have a mass wall in them.
There is a significant risk with these devices and that is the
problem of controlling the air flow through them once the fire dies
down. The amount of heat lost up the chimney can be very significant
when the wall is hot and there are open holes. It is not possible to
close the chimney completely because it is never certain that a fire
is completely out so CO would get into the home if the ventilation
of the wall is blocked.
When checking the excess air ratio of a couple of these ?wall
stoves? as they call them, I found a lot of air is being pulled
through, driven by the retained heat. It is not only possible, but a
surety that the thermal efficiency drops below 0% under late-fire
and fire-out conditions. There are a few things one can do with the
design, but keep in mind that having an episodic fire instead of a
continuous one exacerbates the problem. A continuous fire for a long
time is inevitably going to have different firepower at different
stages so it is not a complete cure either.
The big advantage of a mass wall is not that it smooths the heat
delivery (which is does) but that it will deliver heat throughout
the night. That is the biggest issue. 10 hours of heating. No one
wants to get up on the night and tend a stove.
There is a lot of work needing to be done on this to get systems
that drain water effectively (there is a huge amount of condensation
inside such devices) and to work out the best mass. I did a little
work with (then) GTZ modelling this and we arrived at a number of
500 bricks as being the minimum number to be effective in that
climate. Maybe 1-2 tons.
The brick layout determines the effectiveness at picking up heat so
possibilities abound. It is expected that these devices will
approach the efficiency of a high efficiency condensing natural gas
furnace (92%). At present there are huge issues with the
condensation because it appears not to have been seriously
considered when building them. The amount of water to be handled is
large: perhaps 450 litres per month. Only some of it passes through
as water vapour.
I look forward to seeing this application applied with rigour.
We tested a double TLUD stove in Ulaanbaatar made by a local
artisan. It worked in sequence so there was always a fire going.
Whether the fire is continuous or episodic, there is still a large
advantage to a well-build mass wall: it turns the stove into a
condensing heat exchanger! That is a gain of at least 15% in
efficiency, more likely 60% compared with the baseline devices. The
downside risk is that the chimney will run all the heat out of the
system by pulling cold air into the home and shoving it up the
chimney when the fire is out, or nearly out, at a (negative)
efficiency of -250% or even more. What we know for sure is that
people who have a heating wall use about 1.5 times as much fuel as
those who do not (for a complex of reasons).
If you want to build suitable ones in which we would be interested,
go for 12 and 25 kW sizes.
It may surprise you to know that the major application of new stoves
this year (season starting Aug 2011) is TLUD stoves from ?Silver?
being installed on heating walls. The market is sometimes ahead of
the stovers! They are installing a couple of thousand a week, many
connected to heating walls.
Regards
Crispin
+++++++++
Alex: I believe the most appropriate answer to your final question
below ("What do you see as the advantages of combining these two
approaches?") is one you gave yourself: ("...a desire for char ...").
The beauty of high mass heaters is that they mesh well with a
batch process - the main (only?) drawback of char-making stoves.
Ron
++++++
Paul,
The TLUD configuration has it's advantages and disadvantages, like
any system. One advantage is it's steady state energy release. High
mass heaters strive for a similar result. It seems a bit redundant
to pair the two. Perhaps it depends on other considerations like a
desire for char or an available particulate fuel supply.
There are some folks doing fine work at the Masonry Heater Association.
http://mha-net.org/
They have done a lot on emissions, efficiency and durability. They
have looked into Down feed rocket configurations.
I'm not sure if they have quantified losses between firings, or
seasonal efficiency.
Its a simple concept with lots of technical details.
What do you see as the advantages of combining these two approaches?
Alex
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