[Stoves] Heat / cook stove

Crispin Pemberton-Pigott crispinpigott at gmail.com
Fri Jan 7 07:58:04 CST 2011


Dear Darren

 

The link
<http://www.hearth.com/econtent/index.php/wiki/Downdraft_Stove_Operation/>
http://www.hearth.com/econtent/index.php/wiki/Downdraft_Stove_Operation/ has
an explanation of how one of the Crossdraft stoves works. There is quite a
lot of confusion about what is a downdraft and crossdraft and the
instructions are so complicated one is forgiven by not working out what is
going on.

 

Part of the operating instructions are related to the fact he is using a
large masonry chimney and the compensations needed have nothing to do with
the way the stove works, in principle.

 

Many downdraft and crossdraft stoves have a bypass to get the chimney
started. A lot of work has been done in the past two years at the SeTAR
Centre in Johannesburg on how to avoid the need for this, in order to make
the device and operation simpler. 

 

The layout of the Resolute Acclaim 1988 stove (above link) is nearly
identical to the GTZ-7 series stoves being made in Ulaanbaatar for burning
coal. The main difference can't be seen in the cross-section: the combustion
chamber in the Resolute (and many similar coal and wood burners made in
Europe) is much wider than the front-to-back depth. It is the dramatic
narrowing of the combustion chamber from the wide fuel hopper that is
responsible for the very low PM emissions of the GTZ-7 series stoves.  The
width is 80mm whereas it is common for the Resolute style stove to have a
combustion zone that is the same width as the fuel hopper.

 

The wide burning zone allows what Tom Miles calls 'sneakage' of CO and smoke
into the chimney when not operating at full power. You can see there is a
small amount of secondary air provided by the Resolute at the bottom right
of the picture. That is essential as well because of changing hopper
conditions.

 

The SEET lab in UB has developed very low emission ignition methods which
are much easier (and better) than the one described for the Resolute. The
stove is made to optimise the methods. I described it earlier as basically a
TLUD start.

 

Attached are two stove tests showing the PM 2.5 and mass of fuel burned. The
first is pretty much like a typical 'grandma's cast iron cook stove' and the
second is the TLUD lit crossdraft GTZ-7.5 showing what is technically
possible with a change in the lighting method and the hardware. In both
cases the stoves were new and operated well.

 

If you want to build something, go with the Resolute layout but if you like
I can send you something about the better placement of the heat exchanger
and how to avoid the need for a 'bypass' and complicated lighting. 

 

Regards

Crispin digging snow in Waterloo

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