[Stoves] Oversized stoves / thermal insulation

Boll, Martin Dr. boll.bn at t-online.de
Wed Nov 3 05:41:18 CDT 2010


Dear Crispin and Andrew,

 

The problem of "oversized" stoves is rising in Germany. The new houses are
built regarding low-energy standards, made by the government to bring down
CO2 emission.( German key-words for different grades of energy-saving
houses: Niedrigenergiehaus, Passivhaus, Nullenergiehaus). Their main
problems/difficulties/not-low-tech-solutions are condensing-water and the
need of forced change of air with its heat-recuperation.

 

In that houses, the old "Kachelofen" with its high mass and slow radiation
of heat does not fit, even it is worse, because of its good heat-radiation,
which helps better in bad insulated old houses to keep down
heating-energy-needs.

   

Many people like to have a stove apart from their central-heating. But the
current commercial stoves, which are used in normal thermal-insulated houses
have a normal working output ( Nennleistung ) of at least 4kw. Naturally
they can be choked, mostly with less efficiency and less cleanliness. The
only commercial solutions for those new houses seem to be pellet-stoves.

I did not check how low they can be run, because pellets are not my favour,
but I saw a pellet stove in working, burning only about some 5 or 10 pellets
at once.

 

Crispin, possibly you are interested to know. There is an Canadian
wood-stove for boats with an thermal output of  only 2kW, which runs on wood
or charcoal ( http://www.dickinsonmarine.com/solid.html )

 

I ask myself: How far wood-stoves can be downsized?

 

>From my opinion, real small wood-stoves, working properly on _wood_ , differ
a lot from normal sized stoves.

 

-By the way, Crispin, there are projects in Austria building well-insulated
gers as well ( ger in German mostly called: Jurte ). 

 

Regards

Martin

 

Referring to:

Message: 3

Date: Sat, 30 Oct 2010 07:36:43 -0400

From: "Crispin Pemberton-Pigott" <crispinpigott at gmail.com>

To: "'Discussion of biomass cooking stoves'"

      <stoves at lists.bioenergylists.org>

 

Dear Andrew

 

Do you refer to cooking stoves? I was actually referring to the air quality
problem in UB.

 

I agree there are different perspectives on stove problems.

 

In Africa for a long time it was a fuel saving problem and stoves were
developed to have a higher heat transfer efficiency.

 

Later emissions were a larger issue with indoor air quality being the main
point. Fuel saving is not as important save from the (incorrect) point of
view that if one reduces fuel consumption exposure to emissions is
automatically reduced.

 

The situation in Ulaanbaatar is one of outdoor air quality. In fact indoor
air quality is pretty good compared with outdoors. As the place is so cold
that one has to heat the home to live more than a few days, everyone needs
to generate heat somehow. The best answer is thermal insulation and this is
definitely being addressed, however upgrading the entire housing stock is a
formidable challenge. GTZ is working on demonstrating super-insulated
retro-fitting to old Soviet era precast concrete buildings (basically 6"

slabs of concrete as walls). Millennium Challenge Corp is demonstrating
super insulated ger blankets (yurt covers). They cut heat demand in half.

 

The problem is there are no stoves that match the lower heat demand of the
highly insulated buildings. The emissions from the stoves are produced in
the first 40 minutes of burning - almost all of it. If the home is insulated
well, it means less heat is required and people light the stove more often,
which increases total emissions. That was not the plan, eh?

 

So the lighting emissions have to be modelled into the stove use equation.

If we want to clean up the air, we have to either limit the number of
ignitions, modify the ignition sequence to reduce emissions, keep the home
fires burning all the time at a low level (not good with existing hardware)
or increase the amount of fuel burned so the fire is running at a normal
power level and not being re-started several times a day.

 

The increasing popularity if mass walls for storing heat is likely to
increase emissions even though at least in theory they save fuel (because
they are condensing heat exchangers).

 

Interesting problem. We need a 2 kW stove for heating an super insulated
ger. There is no such  thing at the moment as a clean burning 2 kW coal
stove. I am thinking of trying a fan stove.

 

Regards

Crispin

 

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