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Hello Crispin,<br>
<br>
The bleed is at top bypassing the need for gases to go down past the
heat exchanger.<br>
<br>
Secondary air is flowing in through some 20mm x 20mm internal
diameter square section tubing. Is this enough or do I need more?
Another 20mm x 20mm square section tube? More?<br>
<br>
I've attached another diagram which shows things as they are
currently planned/progressing.<br>
<br>
Looking at this diagram. Are you saying to have some of the grate
to the left of the red line I've drawn on the diagram?<br>
<br>
Currently this is the thinnest point (or bottle neck, or throat) and
has a vertical ceramic slab either side so that this 'throat' is not
the full width of the hopper. Extending the grate further to the
left will, in effect, increase the area of the thinnest point. I
currently plan to have the lowest part of the grate level with the
bottom of the ceramic block (that is the floor of the combustion
chamber) so it is away from the thinnest/hottest area.<br>
<br>
Is it best to shift the grate to the left? <br>
If so what % of the grate left of the red line?<br>
Should I also raise the grate so that the its level with the top of
the ceramic block that is the floor of the combustion chamber?<br>
<br>
I'm working on the stove today and tomorrow. Going to build the air
tight doors today.<br>
<br>
Best<br>
<br>
Darren<br>
<br>
<br>
<br>
On 08/02/2011 21:13, Crispin Pemberton-Pigott wrote:
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<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">Dear Darren<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">First the cast iron grate is about right for the
4 kW (average, not peak) power you want. I have been trying
to make a 4 kW stove that burned clean and the whole grate
area is about 155 x 220 after discounting the parts that are
hiding under shields. What matters is the volume of coal or
wood burning at once. That sets the power level.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">I just want to confirm that the bleed hole takes
hot fire gases from the top of the combustion area into the
flue before they go down into the heat exchange, in other
words like a GTZ 7.5 (now to be called a GIZ 7.5 after their
name change).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><br>
***** Do people think this should this provide sufficient
secondary air or should I put another similar secondary inlet
in the front of the burner??? *****<br>
<br>
<span style="color: rgb(31, 73, 125);"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">Actually I can’t see it clearly. How big is it?<o:p></o:p></span></p>
<p class="MsoNormal"><br>
<span style="color: rgb(31, 73, 125);">></span>With this
'door' wide open the bleed hole is 5cm x 10cm<br>
<br>
<span style="color: rgb(31, 73, 125);"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">That is easily large enough.<o:p></o:p></span></p>
<p class="MsoNormal"><br>
<span style="color: rgb(31, 73, 125);">></span>My friend
had a grate from an old coal stove that appeared to be a
suitable size and we intend to use - from memory this grate is
approx 15cm x 20cm. Thinking of having the 15cm side in front
of the 10cm throat through into the combustion area.<br>
<br>
<span style="color: rgb(31, 73, 125);"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">The whole grate does not need to be under the
combusting zone. About ½ is correct to give a crossdraft
through the bottom of the fuel in the hopper.<o:p></o:p></span></p>
<p class="MsoNormal"><br>
<br>
<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">>></span><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);">Based on the hopper size, and
presuming you have about 4 metres of chimney, </span><o:p></o:p></p>
<p class="MsoNormal"><br>
<span style="color: rgb(31, 73, 125);">></span>If the
chimney was shorter what would be the effect? <span
style="color: rgb(31, 73, 125);"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">Power is related to the draft, taller chimney
means more draft means more power. You can choke it of
course with a damper.<o:p></o:p></span></p>
<p class="MsoNormal"><br>
<span style="color: rgb(31, 73, 125);">></span>The primary
air hole should be 30x120mm? With a valve so its adjustable?<br>
<br>
<span style="color: rgb(31, 73, 125);"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">Yes. If you are quite short, it will be obvious
in the thermal efficiency number because too much excess air
(secondary air oversupplied) will give a cool burn and a
high Stack EA (= low efficiency).<o:p></o:p></span></p>
<p class="MsoNormal"><br>
<span style="color: rgb(31, 73, 125);">></span>Shes got
plenty experience making air tight doors<br>
<br>
<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"> </span><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
color: rgb(31, 73, 125);">Good!</span><span
style="font-size: 11pt; font-family:
"Calibri","sans-serif";"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">The
Hopper size:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">></span>Am
I better reducing dimensions more than we are talking here?<br>
<span style="color: rgb(31, 73, 125);">></span>Throat?<br>
<span style="color: rgb(31, 73, 125);">></span>Hopper area?
<span style="color: rgb(31, 73, 125);"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">You can easily slim the hopper by dropping clay
slabs inside it to narrow it. Ditto with the grate actually.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">></span>-
or do I not want the entire floor of the hopper to also be a
grate?<br>
<br>
<span style="color: rgb(31, 73, 125);"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">Yes, almost. As the air is not rising into the
hopper other than enough to get over to the combustion area,
making it too small or too much tucked under the combustion
area will limit the power, maybe to the point of it not
working well. In your drawing you have the grate nicely
angled but stopping before it got under the combustion area.
With the angled grate extending from under the hopper
(except perhaps the bit at the very front) to the back of
the combustion area (the flame runs vertically from there)
you can make a crossdraft fire that is adjustable across a
pretty good heat range.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><br>
Perhaps you can make a good drawing in cross section of what
you have now.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">Regards<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">Crispin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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