[Stoves] Servals natural draft wood stove

Crispin Pemberton-Pigott crispinpigott at gmail.com
Fri Jul 20 09:43:01 CDT 2012


Dear Rajan

>> I recognise a couple of parts from other devices in there. 

>They are standard items from the market. Easy to replace if and when
required.

Good idea. Many of the best innovations go to great lengths to use standard
components!

>The grate greatly helps.

What is it made of?

>The fuel-wood stand is height-adjustable. One of the purposes here is to
reduce/regulate the excess air  -  also encouraging air-flow at the bottom
of the stand. 

It is very likely, looking at het stove, that the excess air is surprisingly
high. I understand your point that the primary/secondary air split can be
modified by the fuel shelf level (I am glad to see that it is a sheet of
steel, not a ladder-type support). However if you were to put a combustion
analyser on the gases coming out, I am really sure you would find that the
quantity of unneeded air passing through is much more than you need. If you
use a couple of damp rags you can experiment with limiting the air entering
above and below. At some point, even without instrumentation, it becomes
obvious that there is more smoke, not less. That is too little air. A little
bit more and you will notice no smoke (or very little) and a much improved
time-to-boil.

>The opening at the "flame concentrator" ( just below the vessel support )
is also tuned for 2 KW fire-power.

It is an off-the-shelf part?

>I have been toying with the idea of a drop plate also. But I am worried
whether the user will find it convenient.

Toy with it and watch the performance. There are various ways to make it
convenient.

>The pot-skirt is height adjustable ( 20 mm to 90 mm ) for various cooking
appliances. Ten different heights are possible  -  5 in one direction and
another 5 by reversing the pot-skirt.

It is a good and simple idea. If it seals at the bottom, it increases draft
which can be used to make the air perform tricks.

>The stove boils 3 kgs water in 18 minutes using around 200 grams of
firewood ( ambient temperature around 33 C ).

That is roughly a 25% efficiency. Now I am really sure you have too much
air. Try blocking the lower air perhaps 80-90% and the upper air perhaps 75%
(air going in with the fuel). Check the temperature of the gases as they
emerge between the pot and the stove body. Do not be surprised if the
temperature goes up. That does not mean the efficiency went down, not at
all. If the airflow is less, the temperature may go up and the efficiency
too because the volume of gases at that temp is much lower. Losses are a
combination of the two + unburned CO.

>The dry weight of the stove is around 7 kgs.

That is surprisingly high. What is inside that it weighs so much?

>> How much does it cost, say per 100?

>This of course, Servals has to say. I feel pricing is moderate.

Understood.

Thanks
Crispin






More information about the Stoves mailing list